Patent Application
20070069235
The present invention relates to a light-emitting element. In particular, the invention relates to a light-emitting element as a constituent of a unit pixel of a large-screen display that is configured and manufactured easily and achieves low power consumption.
In recent years, liquid crystal displays and plasma displays have been used widely as large-screen flat displays, and further development is being carried out for displays with higher image quality and efficiency. Examples of such displays include an electroluminescence display (ELD) and a field emission display (FED). ELDs are described in Non-patent document 1 generally as follows. That is, an ELD has a basic structure in which an electric field is applied to a phosphor serving as a light-emitting layer via an insulating layer, and is classified into a distribution type and a thin film type. The former has a structure in which particles of ZnS to which impurities such as Cu are added are distributed in an organic binder, which is then sandwiched between upper and lower electrodes via an insulating layer. The impurities form a pn junction in the phosphor particles. When an electric field is applied, electrons emitted by a high electric field generated on the junction surface are accelerated, and then are recombined with positive holes, resulting in light emission. The latter has a structure in which an electrode is provided at a phosphor thin film of Mn doped ZnS or the like serving as a light-emitting layer via an insulating layer. The presence of the insulating layer allows a high electric field to be applied to the light-emitting layer, and emitted electrons accelerated by the electric field excite the luminescence center, resulting in light emission. On the other hand, a FED has a structure in which an electron-emitting element and a phosphor opposed thereto are contained in a vacuum vessel. Electrons emitted from the electron-emitting element in vacuum are accelerated and irradiated to the phosphor layer, whereby light is emitted.
In either device, light emission is induced by electron emission, and accordingly a technique for emitting electrons at a low voltage with high efficiency is important. As such a technique, electron emission by polarization reversal of a ferroelectric is receiving attention. For example, Non-patent document 2 proposes the following as shown in
Patent documents 1 and 2 also describe the technique for allowing a light-emitting layer to emit light by accelerating electrons emitted by polarization reversal of a ferroelectric in a vacuum vessel, or a display using this light emission technique. A basic configuration thereof is as follows: an
electrode having a phosphor layer is provided instead of the platinum electrode in Non-patent document 2, thereby allowing the phosphor layer to emit light.
On the other hand, patent document 3 discloses an electric light emitting surface light source element as an example of a light-emitting element achieved by using electrons emitted by polarization reversal of a ferroelectric in non-vacuum. As shown in
Patent document 1: JP 7(1995)-64490A
Patent document 2: U.S. Pat. No. 5,453,661
Patent document 3: JP 6(1994)-283269 A
Patent document 4: JP 8(1996)-083686 A
Non-patent document 1: “Electronic Display” written and edited by Shoichi MATSUMOTO, published by Ohmsha, Dec. 25, 1984, p. 147-151.
Non-patent document 2: Jun-ichi ASANO et al., “Field-Excited Electron Emission from Ferroelectric Ceramic in Vacuum”, Japanese Journal of Applied Physics, Vol. 31, Part 1, p. 3098-3101, September 1992
In the above prior art, the light-emitting elements that need a vacuum state have a complicated structure, and it is rather difficult to achieve a large-screen display therewith. For example, a field emission display (FED), which is expected to achieve high luminous efficiency, needs a vacuum vessel in which a high degree of vacuum is maintained for emission of electron beams. This makes the structure of the display complicated, and it is considered to be difficult to realize a large-screen structure. No FED is yet commercially available.
Plasma displays need no vacuum vessel. A plasma display utilizes light emission caused by converting discharge energy into ultraviolet light energy once, so that the ultraviolet light excites phosphors. In the course of exiting the phosphors, a large amount of the ultraviolet light is absorbed by members other than the phosphors. For this reason, it is difficult to increase the luminous efficiency, and a large amount of power will be consumed by a large-screen plasma display.
Also, EL displays need no vacuum vessel. However, an inorganic EL display has a problem in luminous efficiency and color reproduction, and an organic EL display requires large-scale facilities for a thin film formation process for manufacturing a liquid crystal display and the like. Further, it is difficult to realize a large-screen EL display, and thus no such display is yet commercially available.
A light-emitting element of the present invention includes a light-emitting layer including a phosphor, and at least two electrodes. The light-emitting element includes at least two kinds of electrically insulating layers with different dielectric constants, one of the electrically insulating layers is the light-emitting layer, and one of the two electrodes is formed in contact with one of the insulating layers.
The light emission principle of the present invention is as follows. That is, dielectric breakdown is caused between at least two electrodes to generate primary electrons (e−). The primary electrons (e−) collide with phosphor particles of a light-emitting layer to cause surface discharge, and a large number of secondary electrons (e−) are generated. Electrons and ultraviolet rays generated thereby in an avalanche manner collide with the luminescence center of the phosphor, so that the phosphor particles are excited to emit light.
A light-emitting element of the present invention includes, from a back surface side, at least a first electrode, a dielectric layer, a porous light-emitting layer, and a second electrode, and has a gap between the porous light-emitting layer and the electrode. Therefore, when an AC electric field is applied between the first electrode and the second electrode, gas breakdown is caused in the gap to accelerate the generation of primary electrons. By the primary electrons, surface discharge occurs in the porous light-emitting layer between the electrodes, so that secondary electrons and ultraviolet rays are emitted. The emitted secondary electrons and ultraviolet rays excite the luminescence center of the porous light-emitting layer, so that the porous light-emitting layer emits light.
The gap may be provided to have an arbitrary width, but the width is preferably in a range of not less than 1 μm to not more than 300 μm. When the width is less than 1 μm, it tends to be difficult to control the gap. When the width is more than 300 μm, dielectric breakdown is less likely to occur. In general, it is necessary to apply an electric field of 300 V or more (at intervals of 100 μm) at 3 kV/mm to cause dielectric breakdown of air in the atmosphere. Under a reduced pressure, although dielectric breakdown occurs at 300 V or less, the application of a high voltage causes damage to various parts of a cell structure. On this account, in order to apply a voltage that does not cause damage, the width of the gap is preferably in the above-mentioned range. More preferably, the width of the gap is in a range of not less than 10 μm to not more than 100 μm.
The light-emitting element of the present invention emits light by surface discharge in the porous light-emitting layer. There is no need to use a thin film formation process, a vacuum system, a carrier intensifying layer, and the like for forming the porous light-emitting layer. Therefore, the light-emitting element has a simple structure and is manufactured easily. Further, the light-emitting element exhibits favorable luminous efficiency and is to be driven with relatively low power consumption when being applied to a large-screen display. Further, in the light-emitting element of the present invention, discharge separation means may be provided between the porous light-emitting layers, whereby crosstalk during light emission can be avoided. Crosstalk herein refers to a phenomenon in which light emission from a pixel interacts with that from adjacent pixels to deteriorate the luminous efficiency.
It is preferable that the discharge separation means of the present invention is formed in particular of a partition wall and/or a space or the like. The partition wall for separating the porous light-emitting layers is preferably an electrical insulator with a thickness of 80 to 300 μm.
In the case of a partition wall, it preferably is made of an inorganic material. As an inorganic material, glass, ceramic, a dielectric, or the like can be used. As a dielectric, Y2O3, Li2O, MgO, CaO, BaO, SrO, Al2O3, SiO2, MgTiO3, CaTiO3, BaTiO3, SrTiO3, ZrO2, TiO2, B2O3, PbTiO3, PbZrO3, PbZrTiO3 (PZT), or the like may be used.
In the case where the discharge separation means is formed of a space, the space preferably has a width of 80 to 300 μm.
The gap between the porous light-emitting layer and the second electrode may be partitioned by a rib in a thickness direction. As a result, electrons are generated easily by dielectric breakdown from a wall surface of the rib. A preferable material of the rib may be selected from the materials for the partition wall. It is preferable that the rib and the partition wall have a surface that is as smooth as possible. A smooth surface facilitates hopping of generated electrons on the rib, resulting in increased luminous efficiency of the porous light-emitting layer.
It is preferable that an atmosphere in the light-emitting element is at least one selected from atmospheric air, oxygen, nitrogen, and a rare gas.
It is preferable that the light-emitting element is in an atmosphere under a reduced pressure including at least one selected from the above-mentioned gases.
It is preferable that the porous light-emitting layer emits light of at least red (R), green (G), or blue (B).
It is preferable that the porous light-emitting layer is formed of a phosphor particle with an insulating layer on its surface.
It is preferable that the porous light-emitting layer is formed of a phosphor particle and an insulative fiber.
It is preferable that the porous light-emitting layer is formed of a phosphor particle with an insulating layer on its surface and an insulative fiber.
It is preferable that the porous light-emitting layer has an apparent porosity in a range of not less than 10% to less than 100%. In order to allow hopping of electrons in the porous light-emitting layer (an assembly of phosphor particles and spaces), it is necessary that a space among individual phosphor particles is smaller than a mean free path of electrons. When the apparent porosity is within the above range, hopping of electrons is not inhibited.
It is preferable that the first or second electrode is an address electrode or a display electrode.
It is preferable that the second electrode is a transparent electrode arranged on an observation side.
The light-emitting element of the present invention includes a dielectric layer, a porous light-emitting layer, a pair of electrodes, and another electrode. The porous light-emitting layer includes an inorganic phosphor particle, a pair of the electrodes are arranged so that an electric field is applied to at least a part of the dielectric layer, and the other electrode is arranged so that an electric field is applied to at least a part of the porous light-emitting layer between the other electrode and at least one of a pair of the electrodes. Specifically, this light-emitting element is a multi-terminal light-emitting element such as a three-terminal light-emitting element, for example. With this configuration, when an electric field is applied between a pair of the electrodes so that polarization reversal is performed, primary electrons are emitted initially from the dielectric layer due to polarization reversal. Thereafter, when an alternating electric field is applied between the other electrode and at least one of a pair of the electrodes, the emitted primary electrons cause surface discharge in an avalanche manner in the porous light-emitting layer, and secondary electrons are generated. Finally, a large number of the generated secondary electrons excite the luminescence center, so that the porous light-emitting layer emits light.
A pair of the electrodes may be arranged on the dielectric layer. One of a pair of the electrodes may be arranged at a boundary between the dielectric layer and the porous light-emitting layer, and the other may be arranged on the dielectric layer. Further, the other electrode may be arranged on the porous light-emitting layer. A pair of the electrodes may be formed so as to sandwich the boundary between the dielectric layer and the porous light-emitting layer therebetween. A pair of the electrodes may be both formed at the boundary between the dielectric layer and the porous light-emitting layer. One of a pair of the electrodes may be formed at the boundary between the dielectric layer and the porous light-emitting layer, and the other may be formed on the dielectric layer.
The porous light-emitting layer may be formed of a fine pore connected to a surface of the porous light-emitting layer, a gas filled in the fine pore, and a phosphor particle. The gas filled in the fine pore can be at least one gas selected from at least one of atmospheric air, oxygen, nitrogen, and an inert gas, and a gas under a reduced pressure.
The dielectric layer may be formed of a sintered dielectric. The dielectric layer may be formed of a dielectric particle and a binder. The dielectric layer may be formed of a thin film. Further, the porous light-emitting layer may be formed of a phosphor particle and an insulating layer on a surface of the phosphor particle. The porous light-emitting layer may be formed of a phosphor particle and an insulative fiber. The porous light-emitting layer may be formed of a phosphor particle, an insulating layer on a surface of the phosphor particle, and an insulative fiber.
It is preferable that when an electric field is applied between a pair of the electrodes so that polarization reversal is performed, primary electrons are emitted from the dielectric layer to cause surface discharge in an avalanche manner in the porous light-emitting layer, then secondary electrons are generated, and a large number of the secondary electrons generated due to surface discharge collide with phosphor particles, so that the porous light-emitting layer emits light. The porous light-emitting layer may emit light in at least one gas atmosphere selected from an atmosphere of atmospheric air, oxygen, nitrogen, and an inert gas, and a gas atmosphere under a reduced pressure. It is also preferable that an alternating electric field is applied between the other electrode and at least one electrode of a pair of the electrodes after the application of an electric field between a pair of the electrodes for polarization reversal.
The light-emitting element of the present invention includes a porous light-emitting body. The porous light-emitting body includes an insulative phosphor particle, and a predetermined electric field or higher is applied to the porous light-emitting body, so that electric charge transfer is carried out.
The light-emitting element of the present invention includes an electron-emitting body, a porous light-emitting body, and a pair of electrodes. The porous light-emitting body includes an inorganic phosphor particle and is arranged adjacent to the electron-emitting body so as to be irradiated with electrons generated from the electron-emitting body, and a pair of the electrodes are arranged so that an electric field is applied to at least a part of the porous light-emitting body.
With the above-described configuration, electrons are emitted from the electron-emitting body, and when an alternating electric field is applied between a pair of the electrodes, the emitted electrons cause surface discharge in an avalanche manner in the porous light-emitting layer. As a result, the emitted electrons excite the luminescence center, so that the porous light-emitting body emits light. Further, a direct electric field may be applied instead of the alternating electric field.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The present embodiment will be described with reference to FIGS. 1 to 6. In this example, a light-emitting element is formed of an assembly of a plurality of porous light-emitting layers, each having a dielectric layer and a first electrode on one surface and a second electrode on the other surface where the dielectric layer and the first electrode are not formed, and includes discharge separation means between the plurality of porous light-emitting layers. In particular, the dielectric layer is shared by part of the plurality of porous light-emitting layers, and the discharge separation means is formed of a partition wall.
As shown in
In the present embodiment, BaTiO3 is used as the dielectric. However, SrTiO3, CaTiO3, MgTiO3, PZT(PbZrTiO3), PbTiO3, or the like also may be used as the dielectric to achieve the same effect. Further, Al2O3, MgO, ZrO2, or the like also may be used as the dielectric to achieve the same effect. In this case, however, the luminescence decreases as compared with the above-mentioned dielectrics having a higher relative dielectric constant. This can be improved by reducing the thickness of the dielectric layer.
Further, the dielectric layer may be formed by a molecule deposition method such as sputtering, CVD, and deposition or with a thin film formation process such as a sol-gel process. When the dielectric layer is formed of a sintered body, this can be used also as the substrate 5. The thickness of the dielectric layer varies considerably depending on how the dielectric layer is formed, e.g., the case where a sintered body is used or the case where a thick film process is used. Practically, however, the thickness is adjusted relative to the dielectric constant since a certain capacitance property is required.
Then, as shown in
As shown in
As the phosphor particle 3, an inorganic compound, such as BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), with an average particle diameter of 2 to 3 μm can be used. The insulating layer 4 of MgO is formed on a surface of each phosphor particle in a common manner. Specifically, the phosphor particle 3 is added to an Mg precursor complex solution, stirred for a long time, and then taken out from the solution, followed by drying. After that, the phosphor particle 3 is subjected to heat treatment at 400° C. to 600° C. in the atmosphere, whereby a uniform coating layer of MgO, i.e., the insulating layer 4, is formed on the surface of the phosphor particle 3.
In the present embodiment, a kneaded paste containing 45 mass % of terpineol (α-terpineol) and 5 mass % of ethyl cellulose with respect to 50 mass % of the phosphor particle coated with the insulating layer 4 is prepared for each phosphor. As shown in
As shown in
The substrate 5 on which the porous light-emitting layers are printed as described above is placed finally in an N2 atmosphere, and subjected to heat treatment at 400° C. to 600° C. for 2 to 5 hours, whereby the assembly of the porous light-emitting layers 2 with a thickness of about 50 to 80 μm is formed.
The paste is obtained by adding the organic binder and the organic solvent to the phosphor particle. However, the same effect is achieved by using a paste obtained by adding a colloidal silica solution to the phosphor particle.
In the present embodiment, since the heat treatment temperature is set to be relatively low, the porosity of the porous light-emitting layer is increased. The apparent porosity is in a range of not less than 10% to less than 100%. It is not preferable that the porosity is increased extremely to 100%, so that pores are opened widely, because such a porous light-emitting layer causes a decrease in luminous efficiency and air discharge to occur therein. On the other hand, when the porosity is less than 10%, the generation of surface discharge is inhibited. (Surface discharge occurs at an interface between gas (in this case, an air gap) and an insulator solid (phosphor particle). When the apparent porosity is decreased, the air gaps disappear, resulting in difficulty in generating surface discharge. On the other hand, when the apparent porosity is increased, the air gaps become larger than a mean free path of electrons as mentioned above, resulting in difficulty in generating surface discharge.) When the apparent porosity is in a range of not less than 10% to less than 100%, it is assumed that the phosphor particles are in approximate point contact so as to be adjacent three-dimensionally to each other.
Then, in the assembly of the porous light-emitting layers 2, a glass paste is screen-printed at boundaries between the porous light-emitting layers, followed by drying. This operation is repeated a plurality of times, and the assembly is subjected to heat treatment at 600° C. As a result, the partition wall 11 with a thickness of about 80 to 300 μm is formed as shown in
After the formation of the partition wall 11 in the above-mentioned manner, the assembly of the porous light-emitting layers is covered entirely with the transparent substrate 8 such as a glass plate on which the second electrode 7 made of ITO (indium-tin oxide alloy) is formed beforehand so as to be opposed to the porous light-emitting layer, whereby the light-emitting element 1 of the present embodiment as shown in
Instead of the transparent substrate 8 with the second electrode of ITO, a transparent substrate on which copper wiring is provided can be used. Copper wiring is formed in a microporous mesh shape and has an open area ratio (ratio of a portion where no wiring is provided to the entire substrate) of 90%, and accordingly this substrate allows light to pass therethrough approximately as favorably as the transparent substrate with the ITO film. Further, copper is favorable since it has a much lower resistance than ITO and greatly contributes to increased luminous efficiency. As a metal for the wiring of microporous mesh shape, gold, silver, platinum, or aluminum can be used instead of copper. However, in the case of using copper and aluminum that are likely to be oxidized, a treatment for providing resistance to oxidization is necessary.
As described above, in the present embodiment, it is possible to manufacture the light-emitting element that is formed of an assembly of the plurality of porous light-emitting layers, each having the dielectric layer and the first electrode on one surface and the second electrode on the other surface where the dielectric layer and the first electrode are not formed, and includes the discharge separation means between the plurality of porous light-emitting layers. In particular, the partition wall is formed as the discharge separation means between the plurality of porous light-emitting layers, and the dielectric layer is formed on part of the plurality of porous light-emitting layers so that the dielectric layer is shared by the part of the plurality of porous light-emitting layers.
In the present embodiment, the phosphor particle 3 is coated with the insulating layer 4 of MgO. Since MgO has a high specific resistance (109Ω·cm or more), surface discharge can occur efficiently. An insulating layer with a low specific resistance is not preferable since surface discharge is less likely to occur, and a short circuit may occur in some cases. For these reasons, it is desirable to coat the phosphor particle with an insulating metal oxide with a high specific resistance. It should be appreciated that when the phosphor particle itself to be used has a high specific resistance, surface discharge occurs easily without the coating of an insulating metal oxide. As the insulating layer, at least one selected from Y2O3, Li2O, CaO, BaO, SrO, Al2O3, SiO2, and ZrO2 can be used as well as MgO. These oxides are stable substances with an extremely low standard free energy of formation AGfo (e.g., −100 kcal/mol or less at room temperature). Further, the insulating layer of these substances is favorable since it has a high specific resistance and allows discharge to occur easily, and is less likely to be reduced. Thus, this layer also serves as an excellent protective coating for suppressing reduction and deterioration due to ultraviolet rays of the phosphor particle during discharge, resulting in increased durability of the phosphor.
Further, instead of the above-mentioned sol-gel method, the insulating layer can be formed by chemisorption or physical adsorption using a CVD method, a sputtering method, a deposition method, a laser method, a shearing stress method, and the like. It is desirable for the insulating layer to be homogeneous and uniform so as not to be peeled off. To this end, it is important, in forming the insulating layer, to immerse the phosphor particle in a weak acid solution of acetic acid, oxalic acid, citric acid, or the like so as to wash impurities attached to a surface of the phosphor particle.
Further, it is desirable that the phosphor particle is subjected to a pretreatment in a nitrogen atmosphere at 200° C. to 500° C. for about 1 to 5 hours before the formation of the insulating layer. The reason for this is as follows. A usual phosphor particle contains a large amount of adsorbed water and water of crystallization, and the formation of the insulating layer on the phosphor particle in such a state exerts an undesirable effect on the lifetime property, such as a deterioration in brightness and a shift in emission spectrum. When the phosphor particle is washed with a weak acid solution, it is rinsed thoroughly in water before performing the pretreatment.
The points to note during the heat treatment process for forming the porous light-emitting layer include heat treatment temperature and atmosphere. In the present embodiment, since the heat treatment is performed in a nitrogen atmosphere at a temperature in a range of 450° C. to 1200° C., a valence of the doped rare earth element in the phosphor is not changed. When the treatment is performed at temperatures higher than this temperature range, however, the valence of the doped rare earth element may be changed or a solid solution of the insulating layer and the phosphor may be formed, and therefore care should be taken to avoid this.
Also, care should be given to the phenomenon in which the apparent porosity of the porous light-emitting layer decreases with increasing heat treatment temperature. Considering the facts as above, the optimum heat treatment temperature is preferably in a range of 450° C. to 1200° C. As for the heat treatment atmosphere, it is preferable to perform the heat treatment in a nitrogen atmosphere so as to avoid an effect on the valence of the doped rare earth element in the phosphor particle.
In the present embodiment, the thickness of the insulating layer is set to about 0.1 to 2.0 μm. However, the thickness may be determined in view of an average particle diameter of the phosphor particle and efficiency of surface discharge occurrence. Preferably, the phosphor with an average particle diameter on a submicron order has a relatively thin coating. A large thickness of the insulating layer is not preferable since it may result in a shift in emission spectrum, a deterioration in brightness, and the like. On the contrary, it is assumed that a small thickness of the insulating layer makes it somewhat difficult to cause surface discharge. Therefore, the relationship between the average particle diameter of the phosphor particle and the thickness of the insulating layer is desirably in the proportion of 1 part to 1/10 to 1/500.
Next, the light emitting action of the light-emitting element 1 will be described with reference to
In order to drive the light-emitting element 1 as shown in
When the AC electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, first electrons, secondary electrons, and ultraviolet rays are emitted very vigorously, resulting in increased emission brightness. Further, as the voltage of the AC electric field is increased, a burst wave is generated. A burst wave is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. Once surface discharge is started, ultraviolet rays and visible light also are generated, and it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, an electric field (frequency: 1 kHz) of about 0.72 to 1.5 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field (frequency: 1 kHz) of about 0.5 to 1.0 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. When a higher electric field is applied, the generation of electrons and ultraviolet rays is accelerated, and when a lower electric field is applied, the generation thereof is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of each of the three colors.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
The light-emitting element of the present embodiment emits light by surface discharge in the porous light-emitting layer. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for manufacturing the light-emitting element, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is manufactured and processed easily. Further, it is possible to provide a light-emitting element that exhibits favorable luminous efficiency and is to be driven with relatively low power consumption when being applied to a large-screen display. In the present embodiment, the partition wall is provided as the discharge separation means at a boundary between the porous light-emitting layers, whereby crosstalk during light emission can be avoided in a relatively simple manner.
The present embodiment will be described with reference to
In Embodiment 1, as shown in
The light-emitting element of the present embodiment can be manufactured in the same manner as in Embodiment 1. Practically, an Ag paste is baked initially to form the first electrode 6 at a place where the porous light-emitting layer is to be formed in a predetermined pattern and to be arranged. On the first electrode 6, the dielectric layer is formed by a thick film process or the like, and then the porous light-emitting layer is formed by screen printing. After that, as in Embodiment 1, the partition wall is formed, and finally the transparent substrate 8 with the second electrode is arranged, whereby the light-emitting element of the present embodiment as shown in
Next, the light emitting action of the light-emitting element 1 will be described with reference to
When the AC electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons and ultraviolet rays are emitted very vigorously by surface discharge, resulting in increased emission brightness. Further, as the voltage of the AC electric field is increased, a burst wave is generated. A burst wave is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. Once surface discharge is started, ultraviolet rays and visible light also are generated, and it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, an electric field of about 0.72 to 1.5 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field of about 0.5 to 1.0 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. When a higher electric field is applied, the generation of electrons and ultraviolet rays is accelerated, and when a lower electric field is applied, the generation thereof is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of each of the three colors.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
The light-emitting element of the present embodiment emits light by surface discharge in the porous light-emitting layer. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for manufacturing the light-emitting element, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is manufactured and processed easily. Further, it is possible to provide a light-emitting layer that exhibits favorable luminous efficiency and is to be driven with relatively low power consumption when being applied to a large-screen display. In the present embodiment, the partition wall is provided as the discharge separation means at a boundary between the porous light-emitting layers, whereby crosstalk during light emission can be avoided in a relatively simple manner.
With reference to
As mentioned above, the conductive partition wall 11 that has a static-shielding effect and is effective in extending surface discharge is used as the discharge separation means. Such a conductive partition wall can be formed of a deposited metal of various kinds. A description will be given of a method for forming the conductive partition wall by using electroless nickel plating, for example.
The light-emitting element is manufactured specifically as follows. Initially, on a surface of the substrate 5 made of ceramic, a resist film is screen-printed at places other than a place where the partition wall is to be formed. Then, the substrate 5 is immersed in a solution of tin chloride and palladium chloride. This treatment is referred to as a catalyzing/sensitizing treatment, and the treatment including its pre-treatment and after-treatment can be performed easily with a commercially available treatment agent.
When the resist film is peeled off after the treatment, fine particles of palladium are attached only to the place where the partition wall is to be formed. The ceramic substrate 5 treated in this manner is immersed in a solution (pH 4 to 6) containing nickel sulfite and sodium hypophosphite as main components, and is subjected to a treatment at about 90° C. so that metal nickel is deposited to a thickness of 80 to 300 μm, whereby the partition wall 11 with a predetermined shape can be formed on the surface of the substrate 5. In this manner, the ceramic substrate 5 on which the conductive partition wall 1 is formed can be obtained.
After that, an Ag paste is baked on the substrate 5 to form the first electrode 6. At this time, the first electrode 6 is formed slightly apart from the conductive partition wall 11 so as to be kept from contact therewith. Following the formation of the first electrode 6, the dielectric layer 10 is formed on the first electrode 6 by a thick film process or the like. Then, a paste containing phosphor particles 3, each being coated uniformly with the insulating layer 4, is screen-printed, followed by firing, whereby the porous light-emitting layer 2 is formed in a predetermined pattern. Finally, an assembly of the porous light-emitting layers is covered entirely with the transparent substrate 8 made of glass on which an ITO film is provided as the second electrode 7, resulting in the light-emitting element 1 as shown in
In the present embodiment, in the above-mentioned manner, it is possible to obtain the light-emitting element that is formed of an assembly of the plurality of porous light-emitting layers, each having the dielectric layer and the first electrode on one surface and the second electrode on the other surface where the dielectric layer and the first electrode are not formed, and includes the discharge separation means between the plurality of porous light-emitting layers. In particular, the discharge separation means is formed of the conductive partition wall.
Next, the light emitting action of the light-emitting element 1 will be described with reference to
When the AC electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons and ultraviolet rays are emitted very vigorously by surface discharge, resulting in increased emission brightness. Further, as a voltage value of the AC electric field is increased, a burst wave is generated. A burst wave is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. Once surface discharge is started, ultraviolet rays and visible light also are generated, and it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In particular, when the conductive partition wall is formed as in the present embodiment, surface discharge occurs easily, which contributes to a decrease in the driving voltage. More specifically, an electric field of about 0.58 to 1.2 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field of about 0.4 to 0.8 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. When a higher electric field is applied, the generation of electrons and ultraviolet rays is accelerated, and when a lower electric field is applied, the generation thereof is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of each of the three colors.
The light-emitting layer of the present embodiment emits light by surface discharge in the porous light-emitting layer. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for manufacturing the light-emitting element, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is manufactured and processed easily. Further, it is possible to provide a light-emitting layer that exhibits favorable luminous efficiency and is to be driven with relatively low power consumption when being applied to a large-screen display. In the present embodiment, the partition wall is provided as the discharge separation means at a boundary between the porous light-emitting layers, whereby crosstalk during light emission can be avoided in a relatively simple manner.
With reference to FIGS. 9 to 13, a description will be given of a light-emitting element that is formed of an assembly of a plurality of porous light-emitting layers, each having a dielectric layer and a first electrode on one surface and a second electrode on the other surface where the dielectric layer and the first electrode are not formed, and includes discharge separation means between the plurality of porous light-emitting layers. In particular, the plurality of porous light-emitting layers are arranged so as to share the second electrode, and the discharge separation means is formed of a gap.
As shown in
After that, the porous light-emitting layer 2 is formed into a predetermined shape on the dielectric layer 10. At this time, the phosphor particles 3, each being coated with the insulating layer 4 made of a metal oxide such as MgO, are used as in Embodiment 1. As the phosphor particle 3, an inorganic compound, such as BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), with an average particle diameter of 2 to 3 μm can be used.
In the present embodiment, a kneaded paste containing 45 mass % of α-terpineol and 5 mass % of ethyl cellulose with respect to 50 mass % of the phosphor particle coated with the insulating layer 4 is prepared for each phosphor. This paste is screen-printed on the dielectric layer 10, followed by drying. This operation is repeated a plurality of times, so that the thickness of the printed paste is adjusted to be 80 to 100 μm.
The substrate 5 on which the porous light emitting layer is printed in the above-mentioned manner is subjected to heat treatment at 400° C. to 600° C. for 2 to 5 hours in an N2 atmosphere. As a result, as shown in
Then, in the present embodiment, the space 12 of about 80 to 300 μm is left, instead of providing a partition wall, at a boundary in the assembly of the porous light-emitting layers, and functions as an alternative to the partition wall. In the present embodiment, the side wall 15 is formed so as to surround the entire assembly of the porous light-emitting layers, thereby supporting the transparent substrate 8 as described later. The side wall 15 is formed by screen-printing of a glass paste, followed by drying. This operation is performed a plurality of times, and then the thus-obtained substrate is fired at 600° C. As a result, as shown in
The side wall 15 may be formed of a glass paste or a resin containing ceramic particles. Specifically, in the former case, a kneaded paste containing 50 mass % of α-terpineol with respect to 50 mass % of mixed particles of ceramic and glass (1:1 by weight) is screen-printed, followed by drying. This operation is repeated so that the thickness of the printed paste is adjusted to be about 100 to 350 μm. Then, the thus-obtained substrate is subjected to heat treatment at 400° C. to 600° C. for 2 to 5 hours in an N2 atmosphere, whereby the side wall 15 with a thickness of about 80 to 300 μm can be formed. In the latter case, the side wall is formed of a thermosetting resin, such as an epoxy resin, a phenol resin, and a cyanate resin. One of these resins is selected and printed so as to surround the entire assembly of the porous light-emitting layers.
After the formation of the side wall 15 in the above-mentioned manner, the transparent substrate 8 such as a glass plate on which the second electrode 7 made of ITO (indium-tin oxide alloy) is formed is adhered to the side wall 15 so as to cover the assembly of the porous light-emitting layers entirely, whereby the light-emitting element 1 in the present embodiment as shown in
Instead of the transparent substrate 8 with the second electrode of ITO, a substrate on which mesh-shaped fine wiring made of copper, gold, silver, platinum, aluminum, or the like is patterned can be used.
As described above, it is possible to manufacture the light-emitting element that is formed of an assembly of the plurality of porous light-emitting layers, each having a dielectric layer and the first electrode on one surface and the second electrode on the other surface where the dielectric layer and the first electrode are not formed, and includes the discharge separation means between the plurality of porous light-emitting layers. In particular the second electrode is arranged so as to be shared by the plurality of porous light-emitting layers, and the discharge separation means is formed of the space.
Next, the light emitting action of this light-emitting element 1 will be described with reference to
When the AC electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons and ultraviolet rays are emitted very vigorously by surface discharge, resulting in increased emission brightness. Further, as a voltage value of the AC electric field is increased, a burst wave is generated. A burst wave is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. Once surface discharge is started, ultraviolet rays and visible light also are generated, and it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, an electric field of about 0.85 to 1.8 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field of about 0.6 to 1.2 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. When a higher electric field is applied, the generation of electrons and ultraviolet rays is accelerated, and when a lower electric field is applied, the generation thereof is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of each of the three colors.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
The light-emitting element of the present embodiment emits light by surface discharge in the porous light-emitting layer. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for manufacturing the light-emitting element, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is manufactured and processed easily. Further, it is possible to provide a light-emitting layer that exhibits favorable luminous efficiency and is to be driven with relatively low power consumption when being applied to a large-screen display. In the present embodiment, the space is provided as the discharge separation means at a boundary between the porous light-emitting layers, whereby crosstalk during light emission can be avoided in a relatively simple manner.
With reference to
In the present embodiment, the porous light-emitting layer 2 is formed of the phosphor particles and the insulative fibers 18 of ceramic, glass, or the like, regardless of the presence/absence of the insulating layer on a surface of the phosphor particle.
An example of the insulative fiber 18 includes a SiO2—Al2O3—CaO based fiber, which preferably has a diameter of 0.1 to 5 μm and a length of 0.5 to 20 μm. Preferably, 1 weight part of fiber having dimensions in the above range is used with respect to 2 weight parts of phosphor particle, whereby the porosity is increased relatively, and accordingly surface discharge occurs easily in the porous light-emitting layer. In the present embodiment, for the formation of the porous light-emitting layer, a kneaded paste containing 45 mass % of α-terpineol and 5 mass % of ethyl cellulose with respect to 50 mass % of a mixture of the phosphor particles and the insulative fibers is prepared. The paste is screen-printed in a pattern to form the porous light-emitting layer as in Embodiment 1.
The reason for selecting a SiO2—Al2O3—CaO based fiber as the insulative fiber is as follows. That is, a SiO2—Al2O3—CaO based fiber is thermally and chemically stable, has a specific resistance of 109 Ω·cm or more, achieves easily a high apparent porosity in a range of not less than 10% to less than 100% in the porous light-emitting layer, and allows discharge to occur easily on a surface of the fiber, allowing surface discharge to occur in the entire porous light-emitting layer. Instead of the above-mentioned insulative fiber, an insulative fiber including a fiber of SiC base, ZnO base, TiO2 base, MgO base, BN base, and Si3N4 base may be used to achieve substantially the same effect.
The light emitting action of this light-emitting element is the same as in Embodiment 1. In order to drive the light-emitting element, an AC electric field is applied between the first electrode and the second electrode. By the application of an AC electric field, gas breakdown is caused in the gap 9, and accordingly electrons are generated. As a result of electric charge being injected into the porous light-emitting layer, surface discharge occurs. Surface discharge occurs continuously during the application of an electric field. Electrons and ultraviolet rays generated in an avalanche manner during the application of an electric field collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light.
In the present embodiment, an electric field of about 0.65 to 1.4 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field of about 0.45 to 0.90 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. When a higher electric field is applied, the generation of electrons and ultraviolet rays is accelerated, and when a lower electric field is applied, the generation thereof is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of each of the three colors.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
The light-emitting element of the present embodiment emits light by surface discharge in the porous light-emitting layer. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for manufacturing the light-emitting element, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is manufactured and processed easily. Further, it is possible to provide a light-emitting layer that exhibits favorable luminous efficiency and is to be driven with relatively low power consumption when being applied to a large-screen display. In the present embodiment, the partition wall is provided as the discharge separation means at a boundary between the porous light-emitting layers, whereby crosstalk during light emission can be avoided in a relatively simple manner.
With reference to
As shown in
As described above, it is possible to obtain the light-emitting element that is formed of an assembly of the plurality of porous light-emitting layers, each having the dielectric layer and the address electrode on one surface and the data electrode on the other surface where the dielectric layer and the address electrode are not formed, and includes the discharge separation means between the plurality of porous light-emitting layers. In particular, the discharge separation means is formed of the gap.
In the thus-configured light-emitting layer 1 of the present embodiment, a two-dimensional image can be displayed on the porous light-emitting layer. Specifically, the light-emitting element 1 of the present embodiment can be driven in a so-called simple matrix. A pulse signal is transmitted sequentially to an X electrode, and ON/OFF information is input to a Y electrode at a timing of the signal transmission, whereby a pixel at a place where the address electrode and the display electrode cross each other is allowed to emit light in accordance with the ON/OFF information, so that one line is displayed. A two-dimensional image can be displayed by switching scan pulses sequentially. Further, when a transistor is provided for each pixel arranged in a matrix so as to turn ON/OFF the pixel, the light-emitting element 1 can be driven more actively. In the present embodiment, since the gap 12 is provided between the porous light-emitting layers, little crosstalk occurs during light emission. However, when a partition wall is provided between the unit light-emitting elements as in Embodiment 1, crosstalk during light emission can be avoided almost completely.
In the present embodiment, an electric field (frequency: 1 kHz) of about 0.72 to 1.5 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field (frequency: 1 kHz) of about 0.4 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. When a higher electric field is applied, the generation of electrons and ultraviolet rays is accelerated, and when a lower electric field is applied, the generation thereof is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of each of the three colors.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
In the present embodiment, an electric field (frequency: 1 kHz) of about 0.72 to 1.5 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field (frequency: 1 kHz) of about 0.4 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. When a higher electric field is applied, the generation of electrons and ultraviolet rays is accelerated, and when a lower electric field is applied, the generation thereof is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of each of the three colors.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
As Comparative Example 1, silicone oil was impregnated as in a dielectric breakdown test of a multilayer chip capacitor. Specifically, in a multilayer chip capacitor, a true dielectric breakdown voltage value cannot be measured since surface discharge occurs frequently. To solve this problem, silicone oil was impregnated into fine pore portions of an element, and a true dielectric breakdown voltage value was obtained in a state in which no surface discharge occurred. Based on this method, gas in fine pores in the porous light-emitting layer 2 of the light-emitting element 1 in
It was confirmed that when a higher voltage was applied, a burst wave was generated and primary electrons were emitted from the gap. However, no surface discharge occurred in the porous light-emitting layer 2, or surface discharge, if any, occurred in an uppermost surface portion and not in the light-emitting layer 2, and thus no light emission was confirmed. Further, when a further higher voltage was applied, dielectric breakdown occurred instantly in the porous light-emitting layer 2, and the light-emitting element 1 was cracked and destroyed.
It was confirmed that when the light-emitting element 1 impregnated with the silicone oil was washed with an organic solvent such as acetone, and the fine pore portions were refilled with gas, light emission was recovered easily. Light emission was observed also when the fine pore portions were evacuated.
Further, when the fine pore portions were impregnated with a conductive solution such as an acetic acid aqueous solution, short circuit occurred, and no light emission was observed.
From the above, in order to achieve a light-emitting element with the configuration of the present invention, it is necessary that the light-emitting layer 2 has fine pores connected to its surface, and that the fine pores are filled with gas or evacuated. When externally emitted electrons rush into the light-emitting layer 4, the electrons are accelerated while causing surface discharge repeatedly in an avalanche manner along the fine pore portions. Then, the accelerated electrons collide with the luminescence center of the phosphor particles, so that the phosphor particles are excited to emit light. In a state in which the fine pore portions are filled with silicon oil or a conductive solution, it is difficult for electrons to move, or short circuit occurs, so that no surface discharge occurs, and accordingly no light is emitted.
In the present embodiments, the fine pore portion has a size of several hundreds μm or less. However, care should be taken when the size of the fine pore portion is several mm or more, since air discharge may occur to destroy the element. Empirically, the phosphor particles 3 are packed so as to be in point contact with each other. Ideally, it is desirable that the light-emitting layer is porous with an apparent porosity in a range of not less than 10% to less than 100%.
As in the above embodiments, the insulating layer 4 is provided for the following reasons:
a. To increase the surface resistance of the phosphor particle 3 to cause surface discharge easily;
b. To protect the phosphor particle from dielectric breakdown and ultraviolet rays; and
c. To allow more electrons to be emitted by secondary electron emitting action of MgO or the like so as to cause surface discharge more easily.
The thickness of the porous light-emitting layer 2 is not particularly limited. However, light emission was observed when the thickness was in a range of 10 μm to 3 mm caused. It should be appreciated that without the occurrence of short circuit, light is emitted even when the thickness is as small as several μm.
In Embodiment 9, with reference to
In order to achieve desired light emission, three inorganic compounds of BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), each having an average particle diameter of 2 to 3 μm, can be used as the phosphor particle 3 singly or in a mixture.
In the present embodiment, the blue phosphor particle 3 coated with the insulating layer 4 of an insulative inorganic substance of MgO is used. The phosphor particles are added to an Mg precursor complex solution, stirred, and taken out from the solution, followed by drying. After that, the phosphor particle is subjected to heat treatment at 400° C. to 600° C. in the atmosphere, whereby a uniform coating layer of MgO shown in
First, a method for manufacturing the light-emitting element of the present embodiment as shown in
Next, the light emitting action of the light-emitting element 1 will be described with reference to
When the AC electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons and ultraviolet rays are emitted very vigorously by surface discharge, resulting in increased emission brightness. Further, as the voltage of the AC electric field is increased, a burst wave is generated. A burst wave is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. Once surface discharge is started, ultraviolet rays and visible light also are generated, and it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, when a voltage of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the dielectric layer 10 by using an AC power supply, the primary electrons (e−) 24 are emitted due to polarization reversal and the secondary electrons (e−) 25 are generated due to surface discharge, followed by light emission. A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission. Further, it becomes possible to manufacture a light-emitting device with luminous efficiency of about 2 to 5 lm/w.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
The light-emitting element 1 of the present embodiment has a structure similar to that of an inorganic EL display (ELD), but has a completely different configuration and mechanism. Regarding the configuration, a phosphor used in an inorganic EL display is a light-emitting body formed of a semiconductor such as ZnS:Mn2+ and GaP:N as described in the background art section. On the other hand, the phosphor particle in Embodiment 9 may be either an insulator or a semiconductor. More specifically, even when the phosphor particle is formed of a semiconductor with an extremely low resistance value, surface discharge occurs continuously without the occurrence of short circuit due to the uniform coating of the insulating layer 4 of an insulative inorganic substance, and the phosphor particle is allowed to emit light. In an inorganic EL display, a phosphor layer has a thickness of submicron to several μm. On the other hand, the phosphor layer in Embodiment 9 has a porous structure with a thickness of several μm to several hundreds μm. Further, in Embodiment 9, the light-emitting layer has a porous structure.
Regarding the porous structure, as a result of observation with an SEM (scanning electron microscope), the phosphor particles are packed so as to be in point contact with each other.
As the phosphor particle, powder that emits ultraviolet rays, which is used in current plasma display panels (PDPs), is used. However, it was confirmed that ZnS:Ag (blue), ZnS:Cu, Au,Al (green), and Y2O3 (red), which were used in cathode ray tubes (CRTs), also emitted light similarly. Since the phosphor for use in CRTs has a low resistance value, surface discharge is less likely to occur. However, the coating of the insulating layer 4 allows surface discharge to occur easily, and accordingly light is emitted easily.
The light-emitting element of the present invention emits light by surface discharge that occurs in an avalanche manner due to electrons emitted by polarization reversal in the dielectric. On this account, when a system having a new function, other than polarization reversal, of allowing electrons to collide is added to the porous light-emitting layer 2, the light-emitting element is expected to emit light easily.
In the present embodiment, a colloidal silica solution is used to form the slurry of the phosphor particles 3. However, it was confirmed that the same effect also was achieved by using an organic solvent. A kneaded slurry containing 45 mass % of α-terpineol and 5 mass % of ethyl cellulose with respect to 50 mass % of the phosphor particle is used and screen-printed on a surface of the dielectric layer 10. The thus-obtained substrate is subjected to heat treatment at 400° C. to 600° C. for 10 to 60 minutes in the atmosphere, whereby the porous light-emitting layer 2 with a thickness of several μm to several tens μm can be formed. In this case, controlling temperature and heat treatment atmosphere is important since the phosphor is likely to be deteriorated when the heat treatment temperature is increased excessively. Further, the organic slurry may contain inorganic fibers 18 to achieve the same effect.
In the present embodiment, BaTiO3 is used as the dielectric. However, it was confirmed that the same effect also was achieved by using SrTiO3, CaTiO3, MgTiO3, PZT(PbZrTiO3), PbTiO3, or the like as the dielectric. Further, the dielectric layer may be formed of a sintered body or may be formed by sputtering, CVD, deposition or with a thin film formation process such as a sol-gel process.
In the present embodiment, the dielectric layer is formed of a sintered body. However, light emission is also possible when the dielectric layer is formed of dielectric fine particles and a binder. More specifically, it is possible to use a dielectric layer of dielectric particles and a binder that is formed as follows. A slurry of fine particles in which 15 mass % of glass powder is mixed with respect to 40 mass % of BaTiO3 powder, the fine particles being kneaded with 40 mass % of α-terpineol and 5 mass % of ethyl cellulose, is applied to an Al metal substrate, followed by drying. Then, the thus-obtained substrate is subjected to heat treatment at 400° C. to 600° C. in the atmosphere.
In the present embodiment, the blue phosphor particle is used. However, it was found that the same effect also was achieved by using a red or green phosphor particle. Further, mixed particles of blue, red, and green also achieve the same effect.
The light-emitting element of the present embodiment emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is processed easily.
Further, ITO is used for the electrode 7. However, instead of ITO, copper wiring may be provided on the transparent substrate. Copper wiring is formed in a microporous mesh shape and has an open area ratio (ratio of a portion where no wiring is provided to the entire substrate) of 90%, and accordingly this substrate allows light to pass therethrough approximately as favorably as the transparent substrate with the ITO film. Further, copper is favorable since it has a much lower resistance than ITO and greatly contributes to increased luminous efficiency. As a metal for the wiring of microporous mesh shape, gold, silver, platinum, or aluminum can be used instead of copper.
Next, a manufacturing method and a light emitting action according to Embodiment 10 will be described with reference to
As in
As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the case of
The difference in light emission between
In
In the case of
Next, with reference to
Next, a manufacturing method and a light emitting action of the light-emitting element in
This light-emitting element emits light in the same manner as that in
When the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons are emitted by polarization reversal and surface discharge occurs more vigorously, resulting in increased emission brightness. Further, as a voltage value of the alternating electric field is increased, a burst wave is generated. A burst wave, which is generated when polarization reversal is performed in the dielectric layer 10, is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing peak voltage of the burst wave.
As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, when a voltage of about 0.7 to 1.2 kV/mm is applied in a thickness direction of the dielectric by using an AC power supply, electrons are emitted due to polarization reversal and surface discharge occurs, followed by light emission. Further,
With reference to
In order to achieve desired light emission, three inorganic compounds of BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), each having an average particle diameter of 2 to 3 μm, are used as the phosphor particle 3 singly or in a mixture.
In the present embodiment, the blue phosphor particle 3 coated with the insulating layer 4 of an insulative inorganic substance of MgO is used. The phosphor particles 3 are added to an Mg precursor complex solution, stirred for a long time, and taken out from the solution, followed by drying. After that, the phosphor particle is subjected to heat treatment at 400° C. to 600° C. in the atmosphere, whereby a uniform coating layer of MgO, i.e., the insulating layer 4, is formed on a surface of the phosphor particle 3.
First, a method for manufacturing the light-emitting element of Embodiment 12 as shown in
Next, the light emitting action of the light-emitting element 1 will be described. An AC electric field is applied between the first electrode 6 and the second electrode 7. By the application of a voltage, polarization reversal is performed in the dielectric layer 10, and accordingly primary electrons (e−) 24 as shown in
At this time, when the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons are emitted by polarization reversal and surface discharge occurs more vigorously, resulting in increased emission brightness.
Further, as a voltage value of the alternating electric field is increased, a burst wave is generated. A burst wave, which is generated when polarization reversal is performed in the dielectric layer 10, is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, an electric field of about 0.65 to 1.3 kV/mm is applied in a thickness direction of the dielectric layer 10 for polarization reversal. Thereafter, an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the light-emitting element 1 by using an AC power supply. As a result, primary electrons are emitted and surface discharge occurs, followed by light emission. When a higher electric field is applied for polarization reversal, the generation of electrons is accelerated, and when an excessively low electric field is applied, the emission of electrons is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission. It becomes possible to manufacture a light-emitting device with luminous efficiency of 2 to 5 lm/W with respect to blue light.
In Embodiment 12, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
The light-emitting element 1 of Embodiment 12 has a structure similar to that of an inorganic EL display (ELD), but has a completely different configuration and mechanism. Regarding the configuration, a phosphor used in an inorganic EL display is a light-emitting body formed of a semiconductor such as ZnS:Mn2+ and GaP:N as described in the background art section. On the other hand, the phosphor particle in Embodiment 12 may be either an insulator or a semiconductor. More specifically, even when the phosphor particle is formed of a semiconductor with an extremely low resistance value, surface discharge occurs continuously without the occurrence of short circuit since the phosphor particle 3 is coated uniformly with the insulating layer 4 of an insulative inorganic substance as described above, and the phosphor particle is allowed to emit light. In an inorganic EL display, a phosphor layer has a thickness of submicron to several μm. On the other hand, the phosphor layer in the present embodiment has a porous structure with a thickness of several μm to several hundreds μm. Further, in the present embodiment, the light-emitting layer has a porous structure.
Regarding the porous structure, as a result of observation with an SEM (scanning electron microscope), the phosphor particles are packed so as to be in point contact with each other.
As the phosphor particle, powder that emits ultraviolet rays, which is used in current plasma display panels (PDPs), is used. However, it was confirmed that ZnS:Ag (blue), ZnS:Cu, Au,Al (green), and Y2O3 (red), which were used in cathode ray tubes (CRTs), also emitted light similarly. Since the phosphor for use in CRTs has a low resistance value, surface discharge is less likely to occur. To solve this problem, it is desirable to coat the phosphor with the insulating layer 4 so as to facilitate the occurrence of surface discharge for light emission.
The light-emitting element of the present invention emits light by surface discharge that occurs in an avalanche manner due to primary electrons emitted by polarization reversal in the dielectric, followed by the generation of a large number of secondary electrons. On this account, when a system having a new function, other than polarization reversal, of allowing electrons to collide is added to the porous light-emitting layer 2, the light-emitting element is expected to emit light easily.
In the present embodiment, a colloidal silica solution is used to form the slurry of the phosphor particles 3. However, it was confirmed that the same effect also was achieved by using an organic solvent. A kneaded slurry containing 45 mass % of α-terpineol and 5 mass % of ethyl cellulose with respect to 50 mass % of the phosphor particle is used and screen-printed on a surface of the dielectric layer 10. The thus-obtained substrate is subjected to heat treatment at 400° C. to 600° C. for 10 to 60 minutes in the atmosphere, whereby the porous light-emitting layer 2 with a thickness of several μm to several tens μm can be formed. In this case, controlling temperature and heat treatment atmosphere is important since the phosphor is likely to be deteriorated when the heat treatment temperature is increased excessively. Further, the organic slurry may contain inorganic fibers 18 to achieve the same effect.
In the present embodiment, BaTiO3 is used as the dielectric. However, it was confirmed that the same effect also was achieved by using SrTiO3, CaTiO3, MgTiO3, PZT(PbZrTiO3), PbTiO3, or the like as the dielectric. Further, the dielectric layer may be formed of a sintered body or may be formed by sputtering, CVD, deposition or with a thin film formation process such as a sol-gel process.
In the present embodiment, the dielectric layer is formed of a sintered body. However, light emission is also possible when the dielectric layer is formed of dielectric fine particles and a binder. More specifically, it is possible to use a dielectric layer of dielectric particles and a binder that is formed as follows. A slurry of fine particles in which 15 mass % of glass powder is mixed with respect to 40 mass % of BaTiO3 powder, the fine particles being kneaded with 40 mass % of α-terpineol and 5 mass % of ethyl cellulose, is applied to an Al metal substrate, followed by drying. Then, the thus-obtained substrate is subjected to heat treatment at 400° C. to 600° C. in the atmosphere.
In the present embodiment, the blue phosphor particle is used. However, it was found that the same effect also was achieved by using a red or green phosphor particle. Further, mixed particles of blue, red, and green also achieve the same effect. The light-emitting element of the present embodiment emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is processed easily.
ITO is used for the electrode 70. However, instead of ITO, copper wiring may be provided on the transparent substrate. Copper wiring is formed in a microporous mesh shape and has an open area ratio (ratio of a portion where no wiring is provided to the entire substrate) of 90%, and accordingly this substrate allows light to pass therethrough approximately as favorably as the transparent substrate with the ITO film. Further, copper is favorable since it has a much lower resistance than ITO and greatly contributes to increased luminous efficiency. As a metal for the wiring of microporous mesh shape, gold, silver, platinum, or aluminum can be used instead of copper.
Next, a manufacturing method and a light emitting action according to Embodiment 13 will be described with reference to
In order to drive the light-emitting element 1, an AC electric field is applied between the first electrode 6 and the second electrode 7. By the application of a voltage, polarization reversal is performed in the dielectric layer 10, and accordingly primary electrons (e−) 24 are emitted. At this time, ultraviolet rays and visible light are generated. Thereafter, an alternating electric field is applied between the third electrode 70 and at least one of a pair of the electrodes. As a result, the primary electrons (e−) collide with the phosphor particles 3 and the insulating layers 4 of the porous light-emitting layer 2 to cause surface discharge, and a large number of secondary electrons (e−) 25 are generated. Electrons and ultraviolet rays generated thereby in an avalanche manner collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light. In addition, by the application of an AC electric field, polarization reversal is performed repeatedly in the dielectric layer. Accordingly, electrons are generated, and as a result of electric charge being injected into the porous light-emitting layer, surface discharge occurs. Surface discharge occurs continuously during the application of an electric field. Electrons and ultraviolet rays generated in an avalanche manner during the application of an electric field collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light.
In Embodiment 13, as described in Embodiment 12, when the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons are emitted by polarization reversal and surface discharge occurs more vigorously, resulting in increased emission brightness. Further, as a voltage value of the alternating electric field is increased, a burst wave is generated. A burst wave, which is generated when polarization reversal is performed in the dielectric layer 10, is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing peak voltage of the burst wave.
Once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In Embodiment 13, when a voltage of about 0.84 to 1.4 kV/mm is applied between the first electrode 6 and the second electrode 7 in a thickness direction of the dielectric layer 10, primary electrons are emitted due to polarization reversal. Thereafter, when an alternating electric field of about 0.7 to 1.2 kV/mm is applied between at least one of the first electrode 6 and the second electrode 7 and the electrode 70 in a thickness direction of the light-emitting element 1, surface discharge occurs and a large number of secondary electrons are generated, followed by light emission.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission. It becomes possible to manufacture a light-emitting device with luminous efficiency of 2 to 5 lm/w with respect to blue light.
As shown in
In
Next, Embodiment 14 will be described with reference to
In the present embodiment, as in Embodiment 12, the phosphor particle is coated with the insulating layer 4. In other words, a uniform coating layer of MgO is formed on a surface of the phosphor particle.
A method for manufacturing the light-emitting element of the present embodiment will be described with reference to
Next, the light emitting action of the light-emitting element 1 will be described. An AC electric field is applied between the first electrode 6 and the second electrode 7. By the application of a voltage, polarization reversal is performed in the dielectric layer 10, and accordingly primary electrons (e−) 24 are emitted. At this time, ultraviolet rays and visible light are generated. Thereafter, an alternating electric field is applied between the third electrode 70 and at least one of a pair of the electrodes 6 and 7. As a result, the primary electrons (e−) collide with the phosphor particles 3 and the insulating layers 4 of the porous light-emitting layer 2 to cause surface discharge, and a large number of secondary electrons (e−) 25 are generated. Electrons and ultraviolet rays generated thereby in an avalanche manner collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light. In addition, by the application of an AC electric field, polarization reversal is performed repeatedly in the dielectric layer. Accordingly, electrons are generated, and as a result of electric charge being injected into the porous light-emitting layer, surface discharge occurs. Surface discharge occurs continuously during the application of an electric field. Electrons and ultraviolet rays generated in an avalanche manner during the application of an electric field collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light.
At this time, when the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons are emitted by polarization reversal and surface discharge occurs more vigorously, resulting in increased emission brightness.
Further, as a voltage value of the alternating electric field is increased, a burst wave is generated. A burst wave, which is generated when polarization reversal is performed in the dielectric layer 10, is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave.
As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In Embodiment 14, an electric field of about 0.4 to 0.8 kV/mm is applied in a thickness direction of the dielectric layer 10 for polarization reversal. Thereafter, an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the light-emitting element 1 by using an AC power supply. As a result, primary electrons are emitted and surface discharge occurs, followed by light emission. When a higher electric field is applied for polarization reversal, the generation of electrons is accelerated, and when an excessively low electric field is applied, the emission of electrons is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission. It becomes possible to manufacture a light-emitting device with luminous efficiency of 2 to 5 lm/W with respect to blue light.
Embodiment 15 of the present invention will be described with reference to
In Embodiment 15, as in Embodiment 12, the phosphor particle is coated with the insulating layer 4. In other words, a uniform coating layer of MgO is formed on a surface of a blue phosphor particle in the same manner as in Embodiment 12.
The light-emitting element of Embodiment 15 is manufactured as follows. Initially, 50 mass % of the phosphor particle 3 coated uniformly with the insulating layer 4 and 50 mass % of a colloidal silica solution are mixed to form a slurry. Then, the slurry is applied to a top surface of the dielectric layer 10 (i.e., a plate-shaped sintered body containing BaTiO3 as a main component, on a bottom surface of which an Ag electrode paste is baked to a thickness of 30 μm to form the first electrode 6) with a diameter of 15 mmΦ and a thickness of 1 mm, on which the first electrode 6 is formed, and drying is carried out with a dryer at 100° C. to 150° C. for 10 to 30 minutes. As a result, the porous light-emitting layer 2 with a thickness of about 100 μm is laminated on the dielectric layer 10. Further, on a top surface of the porous light-emitting layer 2, an Ag electrode paste is baked to a thickness of 30 μm to form the second electrode 7 in a portion on the surface of the porous light-emitting layer 2, and then a glass plate (not shown) to which the transparent electrode (indium-tin oxide alloy (ITO), thickness: 0.1 μm) 70 is applied partially is laminated. Consequently, the light-emitting element 1 with a cross-sectional structure as shown in
Next, the light emitting action of the light-emitting element 1 will be described. An AC electric field is applied between the first electrode 6 and the second electrode 7. By the application of a voltage, polarization reversal is performed in the dielectric layer 10, and accordingly primary electrons (e−) 24 are emitted. At this time, ultraviolet rays and visible light are generated. Thereafter, an alternating electric field is applied between the other electrode, i.e., the electrode 70 and at least one of a pair of the electrodes. As a result, the primary electrons (e−) collide with the phosphor particles 3 and the insulating layers 4 of the porous light-emitting layer 2 to cause surface discharge, and a large number of secondary electrons (e−) 25 are generated. Electrons and ultraviolet rays generated thereby in an avalanche manner collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light. In addition, by the application of an AC electric field, polarization reversal is performed repeatedly in the dielectric layer. Accordingly, electrons are generated, and as a result of electric charge being injected into the porous light-emitting layer, surface discharge occurs. Surface discharge occurs continuously during the application of an electric field. Electrons and ultraviolet rays generated in an avalanche manner during the application of an electric field collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light.
At this time, when the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons are emitted by polarization reversal and surface discharge occurs more vigorously, resulting in increased emission brightness.
Further, as a voltage value of the alternating electric field is increased, a burst wave is generated. A burst wave, which is generated when polarization reversal is performed in the dielectric layer 10, is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, an electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the dielectric layer 10 for polarization reversal. Thereafter, an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the light-emitting element 1 by using an AC power supply. As a result, primary electrons are emitted, surface discharge occurs, and a large number of secondary electrons are generated, followed by light emission. When a higher electric field is applied for polarization reversal, the generation of electrons is accelerated, and when an excessively low electric field is applied, the emission of electrons is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission. It becomes possible to manufacture a light-emitting device with luminous efficiency of 2 to 5 lm/W with respect to blue light.
A light-emitting element including an electron-emitting body, a porous light-emitting body, and a pair of electrodes according to the present embodiment will be described with reference to
First, a method for manufacturing the light-emitting element of the present embodiment will be described with reference to the figures.
Then, as shown in
Then, as shown in
Thereafter, as shown in
In the present embodiment, the porous light-emitting body 2 is formed of the phosphor particles 3 or a material containing the phosphor particles 3 as a main component, and the phosphor particle 3 coated with the insulating layer 4 is used.
In order to achieve desired light emission, three inorganic compounds of BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), each having an average particle diameter of 2 to 3 μm, for example, can be used as the phosphor particle 3 singly or in a mixture.
In the present embodiment, the blue phosphor particle 3 is used, and the insulating layer 4 of an insulative inorganic substance of MgO is formed on its surface. Specifically, the phosphor particles 3 are added to an Mg precursor complex solution, stirred for a long time, and taken out from the solution, followed by drying. After that, the phosphor particle is subjected to heat treatment at 400° C. to 600° C. in the atmosphere, whereby a uniform coating layer of MgO, i.e., the insulating layer 4, is formed on the surface of the phosphor particle 3. 50 mass % of the phosphor particle 3 coated with the insulating layer 4 and 50 mass % of a colloidal silica solution are mixed to form a slurry.
Then, a ceramic board formed of inorganic fiber (an Al2O3—CaO—SiO2 based ceramic fiber board with a thickness of about 1 mm and a void ratio of about 45%) is immersed in the slurry, followed by drying at 100° C. to 150° C. for 10 to 30 minutes. As a result, the ceramic board supports phosphor particle powder. Thereafter, on both sides of the ceramic board, an Ag electrode paste is baked to a thickness of 30 μm to form the first electrode 6 and the second electrode 7. As shown in
In order to prevent electrons emitted from the emitter from greatly leaving orbit, an Ag paste may be screen-printed on the gate electrode so as to form a focusing electrode.
Next, the light emitting action of the light-emitting element 1 of the present embodiment will be described.
In order to drive the light-emitting element 1, initially, a direct electric field of 800 V and 80 V is applied between the anode electrode 111 and the cathode electrode 112 and between the gate electrode 113 and the cathode electrode 112, respectively, in
With primary electrons emitted as described above, an alternating electric field is applied between the first electrode 6 and the second electrode 7. Primary electrons emitted due to electric charge transfer are doubled in an avalanche manner, and cause surface discharge in the porous light-emitting body 2. Surface discharge occurs continuously in a chain reaction, so that electric charge transfer is carried out in the vicinity of the phosphor particles. Electrons accelerated further collide with the luminescence center, so that the porous light-emitting body 2 is excited to emit light. At this time, ultraviolet rays and visible light also are generated, and the porous light-emitting body 2 also is excited to emit light by the ultraviolet rays.
When the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave and has its frequency increased by several tens to thousands of Hz, electrons are emitted and surface discharge occurs more vigorously, resulting in increased emission brightness.
Once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
Specifically, when an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the porous light-emitting body 2 by using an AC power supply, electric charge transfer is carried out and surface discharge occurs, followed by light emission. When a higher electric field is applied, the generation of electrons is accelerated, and when an excessively low electric field is applied, the emission of electrons is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission. Consequently, it is possible to manufacture a light-emitting device with luminous efficiency of 2.0 lm/W, a brightness of 200 cd/m2, and a contrast of 500:1 with respect to blue light.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
The light-emitting element 1 of the present embodiment has a structure similar to that of an inorganic EL display (ELD), but has a completely different configuration and mechanism. Regarding the configuration, a phosphor used in an inorganic EL display is a light-emitting body formed of a semiconductor such as ZnS:Mn2+ and GaP:N as described in the background art section. On the other hand, the phosphor particle in the embodiment may be either an insulator or a semiconductor, although an insulative phosphor particle is preferable. More specifically, even when the phosphor particle is formed of a semiconductor with an extremely low resistance value, surface discharge occurs continuously without the occurrence of short circuit since the phosphor particle is coated uniformly with the insulating layer of an insulative inorganic substance as described above, and the phosphor particle is allowed to emit light. In an inorganic EL display, a phosphor layer has a thickness of submicron to several μm. On the other hand, the phosphor layer in the present embodiment has a porous structure with a thickness of several μm to several hundreds μm. Further, in the present embodiment, the light-emitting body has a porous structure.
Regarding the porous structure, as a result of observation with an SEM (scanning electron microscope), the phosphor particles are packed so as to be in point contact with each other.
As the phosphor particle, powder that emits ultraviolet rays, which is used in current plasma display panels (PDPs), is used. However, it was confirmed that ZnS:Ag (blue), ZnS:Cu, Au,Al (green), and Y2O3 (red), which were used in cathode ray tubes (CRTs), also emitted light similarly.
The light-emitting element of the present invention emits light by surface discharge that occurs in an avalanche manner due to electrons emitted from the electron-emitting body 119. When a new electron-emitting body that irradiates electrons is combined with the porous light-emitting body 2 of the present invention, the light-emitting element is expected to emit light easily.
In the present embodiment, a colloidal silica solution is used to form the slurry of the phosphor particles 3. However, it was confirmed that the same effect also was achieved by using an organic solvent. It is possible that a kneaded slurry containing 45 mass % of α-terpineol and 5 mass % of ethyl cellulose with respect to 50 mass % of the phosphor particle is formed, and the above-mentioned ceramic fiber board is immersed in the slurry, followed by heat treatment for degreasing.
In the present embodiment, the blue phosphor particle is used. However, it was found that the same result also was obtained by using a red or green phosphor particle. Further, mixed particles of blue, red, and green also provide the same result. Further, in the present embodiment, although an alternating electric field is applied between the first electrode 6 and the second electrode 7, a direct electric field may be applied.
The light-emitting element of the present embodiment emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is almost no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is processed easily.
A light-emitting element including an electron-emitting body, a porous light-emitting body, and a pair of electrodes according to the present embodiment will be described with reference to
First, a method for manufacturing the light-emitting element of the present embodiment will be described with reference to the figures.
Then, as shown in
It is also possible that the substrate on which the gate electrode is formed is coated with a photosensitive carbon nanotube paste and is exposed to light using a photomask to be developed, whereby the carbon nanotube is patterned. Further, as a process for vertically orienting the carbon nanotube, a laser irradiation method may be used. Specifically, the paste containing carbon nanotube is used to form a carbon nanotube film, and then the film is irradiated with a laser, so that an organic resin contained in the carbon nanotube film is burned out, whereby the carbon nanotube can be exposed and raised on a surface of the film.
Then, as in Embodiment 16, a ceramic board formed of inorganic fiber (an Al2O3—CaO—SiO2 based ceramic fiber board with a thickness of about 1 mm and a void ratio of about 45%) supports phosphor particle powder. On both sides of the ceramic board, an Ag electrode paste is baked to a thickness of 30 μm to form the first electrode 6 and the second electrode 7. As shown in
Next, the light emitting action of the light-emitting element 1 will be described. In order to drive the light-emitting element 1, initially, a direct electric field of 750 V and 80 V is applied between the anode electrode 111 and the cathode electrode 112 and between the gate electrode 113 and the cathode electrode 112, respectively, in
With electrons emitted as described above, an alternating electric field is applied between the first electrode 6 and the second electrode 7. Electrons emitted due to electric charge transfer are doubled in an avalanche manner, and cause surface discharge in the porous light-emitting body 2. Surface discharge occurs continuously in a chain reaction, so that electric charge transfer is carried out in the vicinity of the phosphor particles. Electrons accelerated further collide with the luminescence center, so that the porous light-emitting body 2 is excited to emit light. At this time, ultraviolet rays and visible light also are generated, and the porous light-emitting body 2 also is excited to emit light by the ultraviolet rays.
When the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave and has its frequency increased by several tens to thousands of Hz, electrons are emitted and surface discharge occurs more vigorously, resulting in increased emission brightness.
As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
Specifically, when an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the porous light-emitting body 2 by using an AC power supply, electric charge transfer is carried out and surface discharge occurs, followed by light emission. When a higher electric field is applied, the generation of electrons is accelerated, and when an excessively low electric field is applied, the emission of electrons is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
In the present embodiment, the blue phosphor particle is used. However, it was found that the same result also was obtained by using a red or green phosphor particle. Further, mixed particles of blue, red, and green also provide the same result.
The light-emitting element of the present embodiment emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is almost no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is processed easily.
A light-emitting element including an electron-emitting body, a porous light-emitting body, and a pair of electrodes according to the present embodiment will be described with reference to
First, a method for manufacturing the light-emitting element of the present embodiment will be described with reference to the figures.
Then, as in Embodiment 16, a ceramic board formed of inorganic fiber (an Al2O3—CaO—SiO2 based ceramic fiber board with a thickness of about 1 mm and a void ratio of about 45%) supports phosphor particle powder. On both sides of the ceramic board, an Ag electrode paste is baked to a thickness of 30 μm to form the first electrode 6 and the second electrode 7, respectively. As shown in
Consequently, the light-emitting element 1 of the present embodiment as shown in
Next, the light emitting action of the light-emitting element 1 will be described. In order to drive the light-emitting element 1, initially, a DC voltage of 12 to 16 V is applied between the two Pt electrodes 132 shown in
With electrons emitted as described above, an alternating electric field is applied between the first electrode 6 and the second electrode 7. Electrons emitted due to electric charge transfer are doubled in an avalanche manner, and cause surface discharge in the porous light-emitting body 2. Surface discharge occurs continuously in a chain reaction, so that electric charge transfer is carried out in the vicinity of the phosphor particles. Electrons accelerated further collide with the luminescence center, so that the porous light-emitting body 2 is excited to emit light. At this time, ultraviolet rays and visible light also are generated, and the porous light-emitting body 2 also is excited to emit light by the ultraviolet rays.
When the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave and has its frequency increased by several tens to thousands of Hz, electrons are emitted and surface discharge occurs more vigorously, resulting in increased emission brightness.
As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
Specifically, when an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the porous light-emitting body 2 by using an AC power supply, electric charge transfer is carried out and surface discharge occurs, followed by light emission. When a higher electric field is applied, the generation of electrons is accelerated, and when an excessively low electric field is applied, the emission of electrons is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
As the phosphor particle, powder that emits ultraviolet rays, which is used in current plasma display panels (PDPs), is used. However, it was confirmed that ZnS:Ag (blue), ZnS:Cu, Au,Al (green), and Y2O3 (red), which were used in cathode ray tubes (CRTs), also emitted light similarly.
The light-emitting element of the present invention emits light by surface discharge that occurs in an avalanche manner due to electrons emitted from the electron-emitting body 119. When a device having a new function of irradiating electrons is added to the porous light-emitting body 2, the light-emitting element is expected to emit light easily.
In the present embodiment, the blue phosphor particle is used. However, it was found that the same result also was obtained by using a red or green phosphor particle. Further, mixed particles of blue, red, and green also provide the same result.
The light-emitting element of the present embodiment emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is almost no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is processed easily.
Instead of using the electron-emitting body as described in the present embodiment, it is also possible to use a similar electron-emitting body in which an insulating layer is sandwiched between two electrodes and electrons are emitted by the application of an electric field between the electrodes. Specifically, an upper electrode is formed of an Ir—Pt—Au alloy, a cathode electrode is formed of Al, and the insulating layer is formed of Al2O3. The insulating layer is sandwiched between the two electrodes, and electrons are emitted from the upper electrode when an electric field is applied between the electrodes. Such an electron-emitting body can be used to manufacture the light-emitting element to irradiate the porous light-emitting body with electrons.
A light-emitting element including an electron-emitting body, a porous light-emitting body, and a pair of electrodes according to the present embodiment will be described with reference to
Then, as shown in
After that, the substrate 143 is washed and then is immersed in a sulphuric acid solution. A voltage is applied between the substrate as a positive electrode and Pt as a negative electrode as above, so that surfaces of both the polysilicon 145 and the silicon microcrystal are oxidized. Finally, as shown in
Then, as in Embodiment 11, a ceramic board formed of inorganic fiber (an Al2O3—CaO—SiO2 based ceramic fiber board with a thickness of about 1 mm and a void ratio of about 45%) supports phosphor particle powder. On both sides of the ceramic board, an Ag electrode paste is baked to a thickness of 30 μm to form the first electrode 6 and the second electrode 7, respectively. As shown in
The above-mentioned processes yield the light-emitting element 1 of the present embodiment as shown in
Next, the light emitting action of the light-emitting element 1 will be described. In order to drive the light-emitting element 1, initially, a direct electric field of 15 to 20 V is applied between the metal thin film electrode 141 and the cathode electrode 112 shown in
With electrons emitted as described above, an alternating electric field is applied between the first electrode 6 and the second electrode 7. Electrons emitted due to electric charge transfer are doubled in an avalanche manner, and cause surface discharge in the porous light-emitting body 2. Surface discharge occurs continuously in a chain reaction, so that electric charge transfer is carried out in the vicinity of the phosphor particles. Electrons accelerated further collide with the luminescence center, so that the porous light-emitting body 2 is excited to emit light. At this time, ultraviolet rays and visible light also are generated, and the porous light-emitting body 2 also is excited to emit light by the ultraviolet rays.
When the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave and has its frequency increased by several tens to thousands of Hz, electrons are emitted and surface discharge occurs more vigorously, resulting in increased emission brightness.
As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, when an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the porous light-emitting body 2 by using an AC power supply, electric charge transfer is carried out and surface discharge occurs, followed by light emission. When a higher electric field is applied, the generation of electrons is accelerated, and when an excessively low electric field is applied, the generation of electrons is insufficient.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
In the present embodiment, the blue phosphor particle is used. However, it was found that the same result also was obtained by using a red or green phosphor particle. Further, mixed particles of blue, red, and green also provide the same result.
The light-emitting element of the present embodiment emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is almost no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is processed easily.
An electron-emitting body constituting a part of a light-emitting element of the present embodiment will be described with reference to
Then, as in Embodiment 11, the porous light-emitting body is manufactured by allowing a ceramic board formed of inorganic fiber (an Al2O3—CaO—SiO2 based ceramic fiber board with a thickness of about 1 mm and a void ratio of about 45%) to support phosphor particle powder. Predetermined electrodes are arranged on the porous light-emitting body, and the thus-obtained porous light-emitting body is laminated on the above-mentioned electron-emitting body, whereby the light-emitting element (not shown) is obtained.
Next, the light emitting action of the light-emitting element 1 will be described. In order to drive the light-emitting element, initially, a direct electric field of 850 V and 80 V is applied between an anode electrode and the cathode electrode and between the gate electrode and the cathode electrode, respectively, so that electrons are emitted from the whisker emitter.
With electrons emitted as described above, an alternating electric field is applied between a first electrode and a second electrode. Electrons emitted due to electric charge transfer are doubled in an avalanche manner, and cause surface discharge in the porous light-emitting body. Surface discharge occurs continuously in a chain reaction, so that electric charge transfer is carried out in the vicinity of the phosphor particles. Electrons accelerated further collide with the luminescence center, so that the porous light-emitting body is excited to emit light. At this time, ultraviolet rays and visible light also are generated, and the porous light-emitting body 2 also is excited to emit light by the ultraviolet rays.
When the alternating electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave and has its frequency increased by several tens to thousands of Hz, electrons are emitted and surface discharge occurs more vigorously, resulting in increased emission brightness.
As described above, once surface discharge is started, discharge occurs repeatedly in a chain reaction, and ultraviolet rays and visible light are generated constantly. Thus, it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
Specifically, when an alternating electric field of about 0.5 to 1.0 kV/mm is applied in a thickness direction of the porous light-emitting body by using an AC power supply, electric charge transfer is carried out and surface discharge occurs, followed by light emission. When a higher electric field is applied, the generation of electrons is accelerated, and when an excessively low electric field is applied, the emission of electrons is insufficient. A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to 50% to 80% of the voltage applied initially.
In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of oxygen, nitrogen, and an inert gas or in a gas atmosphere under a reduced pressure, the light-emitting element emitted light similarly.
In the present embodiment, the blue phosphor particle is used. However, it was found that the same result also was obtained by using a red or green phosphor particle. Further, mixed particles of blue, red, and green also provide the same result.
The light-emitting element of the present embodiment emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is almost no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is processed easily.
In the electron-emitting body, silicon carbide or a diamond thin film may be used instead of the whisker emitter. When such a material is used, electrons can be emitted from the material by the application of a gate voltage between the cathode electrode and the gate electrode and irradiated to the porous light-emitting body.
In the present embodiment, a light-emitting element including an electron-emitting body, a porous light-emitting body, and a pair of electrodes will be described with reference to FIGS. 38 to 40. In particular, the description is directed to the pair of electrodes provided to apply an electric field to the porous light-emitting body.
FIGS. 38 to 40 are cross-sectional views of the porous light-emitting body constituting a part of the light-emitting element. Reference numeral 2 denotes a porous light-emitting body, 3 denotes a phosphor particle, 4 denotes an insulating layer, 6 denotes a first electrode, and 7 denotes a second electrode. In the porous light-emitting body shown in
Then, a ceramic board formed of inorganic fiber (an Al2O3—CaO—SiO2 based ceramic fiber board with a thickness of about 1 mm and a void ratio of about 45%) is immersed in the slurry, followed by drying at 120° C. to 150° C. for 10 to 30 minutes. As a result, the ceramic board supports phosphor particle powder. Thereafter, as shown in
In Embodiment 1, as shown in
Next, a description will be given of the case, as shown in
On a surface of the plate-shaped porous light-emitting body 2 thus obtained, an Ag electrode paste is baked to a thickness of 30 μm to form the first electrode 6 and the second electrode 7. Then, 50 mass % of the phosphor particle 3 coated with the insulating layer 4 and 50 mass % of a colloidal silica solution are mixed to form a slurry, and the slurry is applied to the surface of the porous light-emitting body on which the electrodes are formed, followed by drying at 120° C. to 150° C. for 10 to 30 minutes. As a result, as shown in
Further, the insulating layer of MgO may be formed on the surface of the phosphor particle in the following manner. Initially, Mg(OC2H5)2 powder (1 molar ratio) as metal alkoxide is mixed well by stirring in a solution of CH3COOH (10 molar ratio), H2O (50 molar ratio), and C2H5OH (50 molar ratio) at room temperature, whereby a substantially transparent sol/gel solution is prepared. Phosphor particles (2 molar ratio), such as BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), with an average particle diameter of 2 to 3 μm are mixed little by little by stirring into the sol/gel solution. This operation is performed continuously for 1 day, and then the mixed solution undergoes centrifugal separation so as to take powder therefrom to a tray made of ceramic, which is allowed to dry at 150° C. all day and night.
Then, the dried powder is calcined in the air at 400° C. to 600° C. for 2 to 5 hours, so that the uniform insulating layer of MgO is formed on the surface of the phosphor particle.
As a result of observing the phosphor particle with a transmission electron microscope (TEM), the thickness of the insulating layer is 0.1 to 2.0 μm. The coating of the insulating layer can be provided by immersing the phosphor particle in a metal alkoxide solution, by using a metal complex solution as mentioned above, or by deposition, sputtering, CVD, and the like.
As a metal oxide for use as the insulating layer, Y2O3, Li2O, MgO, CaO, BaO, SrO, Al2O3, SiO2, MgTiO3, CaTiO3, BaTiO3, SrTiO3, ZrO2, TiO2, B2O3, and the like are known. It is desirable to use at least one of these materials to form the insulating layer.
In particular, when the insulating layer is formed by a vapor phase method, it is desirable that the phosphor particle is subjected to a pretreatment in a nitrogen atmosphere at 200° C. to 500° C. for about 1 to 5 hours. In general, phosphor particles contain a large amount of absorbed water and water of crystallization, and it is not preferable to form the insulating layer on the phosphor particles in such a state because this has an effect on lifetime properties such as a deterioration of brightness and a shift in emission spectrum.
The thickness of the insulating layer is set to about 0.1 to 2.0 μm. However, the thickness may be determined in view of an average particle diameter of the phosphor particle and the occurrence of surface discharge. In the case of an average particle diameter on a submicron order, it is considered that a very thin coating layer is required to be formed.
A large thickness of the insulating layer is not preferable in terms of a shift in emission spectrum, a deterioration in brightness, and electron shielding. On the contrary, it is expected that a small thickness of the insulating layer makes it somewhat difficult to cause surface discharge continuously. Therefore, the relationship between the average particle diameter of the phosphor particle and the thickness of the insulating layer is preferably in the proportion of 1 part to 1/10 to 1/500.
It is preferable that each phosphor particle is coated with the insulating layer of a metal oxide. Practically, however, 2 or 3 phosphor particles are coated in a flocculated state. Even when the phosphor particles are coated in such a somewhat flocculated state, there is substantially no effect on light emission.
The light-emitting element of the present invention is manufactured by using the porous light-emitting body thus obtained. As a result, it was confirmed that the light-emitting element exhibited a high brightness, a high contrast, a high recognition capability, and a high reliability.
Further, in order to accelerate the occurrence of surface discharge, it is also possible to manufacture the porous light-emitting body 2 by mixing insulative fibers 18 when forming the phosphor particle 3 coated with the insulating layer 4. As the insulative fiber 18 for use in such a case, a SiO2—Al2O3—CaO based electrically insulative fiber or the like is preferable.
In the present embodiment, a general description will be given, with reference to the figures, of a structure of a field emission display (FED) manufactured by combining the porous light-emitting body with the electron-emitting body including the Spindt-type emitter according to the present invention.
As shown in
As described in Embodiment 16, the electron-emitting body 119 using the Spindt-type emitter 100 includes the cone-shaped Spindt-type emitter 100 and the gate electrode 113 formed so as to surround the Spindt-type emitter 100 for the application of a voltage for drawing electrons.
In order to allow electrons to be emitted from the emitter, a positive potential is applied to the gate, and a negative potential is applied to the emitter. A high electric field is concentrated on a front end portion of the cone-shaped emitter, and electrons are emitted therefrom toward the porous light-emitting body 2. In the case of an Mo Spindt-type emitter, the application of a voltage of 15 to 80 V causes electrons to be emitted. In a practical display panel, a plurality of emitters are provided for each pixel, so that a high level of redundancy can be ensured with respect to an operating state of the emitters. Consequently, current fluctuations specific to this type of element are averaged statistically, and thus each pixel is allowed to emit light stably. Further, the field emission display can be driven in a so-called simple matrix. One line is displayed at a time by applying a negative data voltage to the emitter line 172 while applying a positive scan pulse to the gate line 171. By switching scan pulses sequentially, a two-dimensional image can be displayed. Further, when a transistor is provided for each pixel arranged in a matrix so as to turn ON/OFF the pixel, the field emission display can be driven more actively.
The light-emitting element in
Then, as in Embodiment 1, the phosphor particles 3, each being coated with the insulating layer 4 made of a metal oxide such as MgO, are prepared. As the phosphor particle 3, an inorganic compound, such as BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), with an average particle diameter of 2 to 3 μm can be used.
In the present embodiment, the phosphor particle 3 coated with the insulating layer 4 of MgO is mixed with 5 mass % of polyvinyl alcohol to be granulated, and then the granules are molded in a plate shape under a pressure of about 50 MPa by using a molding die. The thus-obtained molded granules are subjected to heat treatment at 450° C. to 1200° C. for 2 to 5 hours in a nitrogen atmosphere, whereby the plate-shaped porous light-emitting body 2 is manufactured.
When the porous light-emitting body has an apparent porosity of less than 10%, the luminous efficiency is decreased for the following reason. That is, when electrons collide with the porous light-emitting layer, although light is emitted on a surface of the porous light-emitting layer, electrons are not injected into the light-emitting layer, and thus substantially no light is emitted inside the layer. To avoid this, in order to allow electrons generated due to discharge to be injected smoothly into the porous light-emitting layer, it is desirable that the porous light-emitting body of the present embodiment has a porous structure with an apparent porosity of not less than 10%. On the other hand, when the porous light-emitting body has an excessively high apparent porosity, the luminous efficiency is decreased or surface discharge is less likely to occur inside the porous light-emitting layer. On this account, the apparent porosity is preferably in a range of not less than 10% to less than 100%, and in particular in a range of 50% to less than 100%.
The plate-shaped porous light-emitting body 2 thus obtained is attached to the dielectric layer 10 by using a glass paste. At this time, the glass paste is screen-printed on the porous light-emitting layer at its both ends, so that the porous light-emitting layer is adhered thereto, followed by heat treatment at 580° C. As a result, the porous light-emitting layer can be adhered to the dielectric layer 10 with the gas layer interposed therebetween.
After that, the porous light-emitting layer is covered with the transparent substrate 8 such as a glass plate on which the second electrode 7 made of ITO (indium-tin oxide alloy) is formed beforehand so as to be opposed to the porous light-emitting layer, whereby the light-emitting element 1 shown in
The gas layers provided both on and under the porous light-emitting layer, i.e., the gas layer interposed between the porous light-emitting layer 2 and the dielectric layer 10 and the gas layer interposed between the porous light-emitting layer and the second electrode, which are a characteristic of the present embodiment, have a thickness preferably in a range of 20 to 250 μm, and most preferably in a range of 30 to 220 μm. When the thickness is larger than this range, a high voltage is required to be applied for the occurrence of discharge, which is not preferable for the reason of economical efficiency. The thickness of the gas layer may be smaller than the above range, and there is no practical problem as long as the thickness is not less than a mean free path of gas. However, when the gas layer has a very small thickness, it may be somewhat difficult to control the thickness in the process of manufacturing the light-emitting element.
It is not necessarily required that the gas layers provided on and under the porous light-emitting layer according to the present embodiment have the same thickness. However, in the case of providing the gas layers at two places on and under the light-emitting layer, it is preferable that the thickness of each of the gas layers is set to be slightly smaller than that of the gas layer provided only on one side of the light-emitting layer as in
As described above, the present embodiment is characterized in that the gas layers are provided on and under the porous light-emitting layer. When an AC electric field is applied between a pair of the first electrode and the second electrode, discharge occurs simultaneously in both the gas layers, so that electrons are emitted from above and below the porous light-emitting layer to be injected into the light-emitting layer efficiently. More specifically, the AC electric field to be applied is increased gradually, and when a voltage not less than the dielectric breakdown voltage is applied to the gas layers, discharge occurs. Accordingly, electrons are doubled in the gas layers and collide with the porous light-emitting body to excite the luminescence center thereof, so that the porous light-emitting layer emits light. In this manner, the gas layers function as an electron supply source, and generated electrons are injected from above and below the porous light-emitting layer and pass through the light-emitting layer in an avalanche manner while causing surface discharge throughout the layer. Surface discharge occurs continuously during the application of an electric field. Electrons generated in an avalanche manner during the application of an electric field collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light. As described above, electrons are injected efficiently from above and below the porous light-emitting layer. Therefore, as compared with the light-emitting element in which electrons are injected from one side of the light-emitting layer as described in Embodiment 1, the light-emitting layer having a porous structure according to the present embodiment wholly emits light thoroughly, uniformly, and efficiently, resulting in a remarkably increased brightness.
As described above, in the present embodiment, it is possible to manufacture the light-emitting element including the gas layers, the porous light-emitting layer in contact with the gas layers, and at least a pair of the electrodes for applying an electric field to the gas layers and the porous light-emitting layer. In particular, the dielectric layer and the first electrode of a pair of the electrodes for applying an electric field are arranged on one surface of the porous light-emitting layer via the gas layer, and the second electrode of a pair of the electrodes is arranged on the other surface of the porous light-emitting layer where the dielectric layer and the first electrode are not arranged, via the gas layer.
In the present embodiment, as shown in
With this configuration, it is possible to allow the porous light-emitting layers 2 to emit light by applying an electric field from a pair of the electrodes 6 and 7 to the gas layers 9 and the porous light-emitting layers 2 in contact therewith.
In the present embodiment, the points to note in particular during the heat treatment process for forming the porous light-emitting layer include heat treatment temperature and atmosphere. In the present embodiment, since the heat treatment is performed in a nitrogen atmosphere at a temperature in a range of 450° C. to 1200° C., a valence of the doped rare earth element in the phosphor is not changed. When the treatment is performed at temperatures higher than this temperature range, however, the valence of the doped rare earth element may be changed or a solid solution of the insulating layer and the phosphor may be formed, and therefore care should be taken to avoid this. As for the heat treatment atmosphere, it is preferable to perform the heat treatment in a nitrogen atmosphere so as to avoid an effect on the valence of the doped rare earth element in the phosphor particle.
In the present embodiment, the thickness of the insulating layer is set to about 0.1 to 2.0 μm. However, the thickness may be determined in view of an average particle diameter of the phosphor particle and efficiency of surface discharge occurrence. Preferably, the phosphor with an average particle diameter on a submicron order has a relatively thin coating. A large thickness of the insulating layer is not preferable since it may result in a shift in emission spectrum, a deterioration in brightness, and the like. On the contrary, it is assumed that a small thickness of the insulating layer makes it somewhat difficult to cause surface discharge. Therefore, the relationship between the average particle diameter of the phosphor particle and the thickness of the insulating layer is desirably in the proportion of 1 part to 1/10 to 1/500.
Next, the light emitting action of the light-emitting element 1 will be described.
In order to drive the light-emitting element 1 as shown in the figure, an AC electric field is applied between the first electrode 6 and the second electrode 7. The AC electric field to be applied is increased gradually, and when a voltage not less than the dielectric breakdown voltage is applied to the gas layers, discharge occurs. Accordingly, electrons are doubled in the gas layers and collide with the porous light-emitting body to excite the luminescence center thereof, so that the light-emitting layer emits light. In this manner, the gas layers function as an electron supply source, and in the present embodiment, generated electrons are injected from above and below the porous light-emitting layer and pass through the light-emitting layer in an avalanche manner while causing surface discharge throughout the porous light-emitting layer. Surface discharge occurs continuously during the application of an electric field. Electrons generated in an avalanche manner during the application of an electric field collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light. As described above, in the present embodiment, electrons are injected from above and below the porous light-emitting layer. Therefore, as compared with the light-emitting element in which electrons are injected from only one side of the light-emitting layer as described in Embodiment 1, the porous light-emitting layer wholly emits light thoroughly, uniformly, and efficiently, resulting in a remarkably increased brightness.
In the present embodiment, the porous light-emitting body having an apparent porosity in a range of not less than 10% to less than 100% is used. In the case of a usual light-emitting layer without a porous structure, light is emitted on its surface but is hardly emitted inside the layer. However, in the case of the porous light-emitting layer of the present embodiment, light is emitted not only on its surface but also inside the light-emitting layer, resulting in considerably favorable luminous efficiency. As described above, in the case of the porous layer, the porous structure allows electrons generated due to discharge to be injected smoothly into the layer, so that surface discharge occurs throughout the layer, and the layer wholly emits light with a high brightness.
It is desirable that the porous light-emitting body used in the present embodiment has a porous structure with an apparent porosity of not less than 10%. On the other hand, when the light-emitting body has an excessively high apparent porosity, the luminous efficiency is decreased, surface discharge is less likely to occur inside the porous light-emitting layer, or the like. On this account, the apparent porosity is desirably in a range of not less than 10% to less than 100%, and most preferably in a range of 50% to less than 100%.
When the AC electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons are emitted very vigorously by surface discharge, resulting in increased emission brightness. Further, as the voltage of the AC electric field is increased, a burst wave is generated. A burst wave is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. Once surface discharge is started, ultraviolet rays and visible light also are generated, and it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the light-emitting element in
A current value during discharge is 0.1 nA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of the phosphor particles of each of the three colors. In the present embodiment, the light-emitting element is driven in the atmosphere. However, it was confirmed that even in an atmosphere of a rare gas or in a gas atmosphere in which pressure is applied or a negative pressure is formed, the light-emitting element emitted light similarly.
According to the light-emitting element of the present embodiment, the porous light-emitting layer is formed by a thick film process or the like. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for manufacturing the light-emitting element, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is manufactured and processed easily. Further, electrons generated due to discharge can collide with the porous light-emitting layer from both sides thereof, and due to the porous structure of the light-emitting body, the colliding electrons are allowed to be injected smoothly into the light-emitting layer while causing surface discharge, resulting in light emission with a very high brightness. In the case of a usual light-emitting body without a porous structure, light is emitted only on its surface. However, as described above, the porous light-emitting layer of the present embodiment wholly emits light thoroughly, resulting in a high brightness. Further, the luminous efficiency is considerably favorable as compared with that achieved by phosphors that emit ultraviolet rays as in plasma display panels. Further, it is possible to provide a light-emitting element that is to be driven with relatively low power consumption when being used in a large-screen display. Since the partition walls are provided as discharge separation means at both ends of the porous light-emitting layer, crosstalk during light emission can be avoided easily.
The light-emitting element in
Then, as in Embodiment 1, the phosphor particles 3, each being coated with the insulating layer 4 made of a metal oxide such as MgO, are prepared. As the phosphor particle 3, an inorganic compound, such as BaMgAl10O17:Eu2+ (blue), Zn2SiO4:Mn2+ (green), and YBO3:Eu3+ (red), with an average particle diameter of 2 to 3 μm can be used.
As in Embodiment 3, in the present embodiment, the phosphor particle 3 coated with the insulating layer 4 of MgO is mixed with 5 mass % of polyvinyl alcohol to be granulated, and then the granules are molded in a plate shape under a pressure of about 50 MPa by using a molding die. The thus-obtained molded granules are subjected to heat treatment at 450° C. to 1200° C. for 2 to 5 hours in a nitrogen atmosphere, whereby the plate-shaped porous light-emitting body 2 is manufactured.
Both ends of the plate-shaped porous light-emitting body 2 thus obtained are attached to an electrode side of the substrate 5 by using a glass paste. Specifically, as shown in
After that, the porous light-emitting layer is covered with the transparent substrate 8 such as a glass plate on which the second electrode 7 made of ITO (indium-tin oxide alloy) is formed beforehand so as to be opposed to the porous light-emitting layer, whereby the light-emitting element 1 of the present embodiment as shown in
As described above, the present embodiment is characterized in that the slight gaps are provided between the porous light-emitting layer and the first and second electrodes, respectively, provided on both sides of the porous light-emitting layer. This configuration allows the gas layers formed of a rare gas, atmospheric air, oxygen, nitrogen, or a mixed gas thereof to be interposed between the porous light-emitting layer and a pair of the electrodes, respectively. An AC electric field is applied between a pair of the electrodes of the light-emitting element, and when a voltage not less than the dielectric breakdown voltage is applied to the gas layers, discharge occurs. Accordingly, electrons are doubled in the gas layers and collide with the porous light-emitting body to excite the luminescence center thereof, so that the light-emitting layer emits light. In this manner, the gas layers function as an electron supply source, and generated electrons collide with the light-emitting layer, are injected into the layer, and pass through the light-emitting layer in an avalanche manner while causing surface discharge throughout the layer. Surface discharge occurs continuously during the application of an electric field. Electrons generated in an avalanche manner collide with the luminescence center of the phosphors, so that the phosphor particles 3 are excited to emit light. As described above, in the present embodiment, electrons are supplied from both sides of the porous light-emitting layer and injected into the light-emitting layer smoothly and thoroughly. Therefore, as compared with the light-emitting element in which electrons are injected from one side of the porous light-emitting body as described in Embodiment 1, the light-emitting layer wholly emits light uniformly and efficiently with an increased brightness.
In the present embodiment, the phosphor particle 3 coated with the insulating layer 4 of MgO is used. This is because MgO has a high specific resistance (109 Ω·cm or more) and surface discharge can occur efficiently. An insulating layer with a low specific resistance is not preferable since surface discharge is less likely to occur, and a short circuit may occur in some cases. For these reasons, it is desirable to coat the phosphor particle with an insulating metal oxide with a high specific resistance. It should be appreciated that when the phosphor particle itself to be used has a high specific resistance, surface discharge occurs easily without the coating of an insulating metal oxide. As the insulating layer, at least one selected from Y2O3, Li2O, CaO, BaO, SrO, A2O3, SiO2, and ZrO2 can be used as well as MgO. These oxides are stable substances with an extremely low standard free energy of formation ΔGf0 (e.g., −100 kcal/mol or less at room temperature). Further, the insulating layer of these substances is favorable since it has a high specific resistance and is less likely to be reduced. Thus, this layer also serves as an excellent protective coating for suppressing reduction and deterioration of the phosphor particle due to electrons, resulting in increased durability of the phosphor.
Further, instead of the above-mentioned sol-gel method, the insulating layer can be formed by chemisorption or physical adsorption using a CVD method, a sputtering method, a deposition method, a laser method, a shearing stress method, and the like. It is desirable for the insulating layer to be homogeneous and uniform so as not to be peeled off. To this end, it is important, in forming the insulating layer, to immerse the phosphor particle in a weak acid solution of acetic acid, oxalic acid, citric acid, or the like so as to wash impurities attached to a surface of the phosphor particle.
Further, it is desirable that the phosphor particle is subjected to a pretreatment in a nitrogen atmosphere at 200° C. to 500° C. for about 1 to 5 hours before the formation of the insulating layer. The reason for this is as follows. A usual phosphor particle contains a large amount of adsorbed water and water of crystallization, and the formation of the insulating layer on the phosphor particle in such a state exerts an undesirable effect on the lifetime property, such as a deterioration in brightness and a shift in emission spectrum. When the phosphor particle is washed with a weak acid solution, it is rinsed thoroughly in water before performing the pretreatment.
Next, the light emitting action of the light-emitting element 1 will be described with reference to
In the present embodiment, the porous light-emitting body having an apparent porosity in a range of not less than 10% to less than 100% is used. In the case of a usual phosphor layer without a porous structure, light is emitted on its surface but is hardly emitted inside the layer. However, in the case of the porous light-emitting layer, light is emitted not only on its surface but also inside the layer, resulting in considerably favorable luminous efficiency. The reason for this is that the porous light-emitting layer allows electrons due to discharge to go into the layer, so that surface discharge occurs throughout the layer, resulting in light emission with a high brightness.
When the AC electric field to be applied has its waveform changed from a sine wave or a sawtooth wave to a rectangular wave or has its frequency increased by several tens to thousands of Hz, electrons are emitted very vigorously by surface discharge, resulting in increased emission brightness. Further, as the voltage of the AC electric field is increased, a burst wave is generated. A burst wave is generated at a frequency immediately before the peak of the frequency in the case of a sine wave, and is generated at the peak of the frequency in the case of a sawtooth wave or a rectangular wave, and the emission brightness increases with increasing voltage of the burst wave. Once surface discharge is started, ultraviolet rays and visible light also are generated, and it is necessary to suppress deterioration of the phosphor particle 3 due to these rays of light. For this reason, it is preferable to decrease the voltage after light emission is started.
In the present embodiment, as in Embodiment 2, an electric field of about 0.57 to 1.2 kV/mm is applied in a thickness direction of the porous light-emitting layer to allow the phosphor particles 3 to emit light. Thereafter, an alternating electric field of about 0.39 to 0.78 kV/mm is applied, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3. As compared with the case where a rare gas is not sealed as in Embodiment 2, light emission is sustained even when the voltage value is decreased to about 60% to 80%. The reason for this is that the sealed rare gas makes an atmosphere in which discharge is more likely to occur. Further, the brightness can be increased remarkably by sealing the rare gas under pressure.
A current value during discharge is 0.1 mA or less. It was confirmed that light emission once started was sustained even when the voltage was decreased to about 50% to 80% of the voltage applied initially, and that a high brightness, a high contrast, a high recognition capability, and a high reliability were ensured in light emission of the phosphor particles of each of the three colors as compared with the light-emitting element of Embodiment 2.
As compared with the above-mentioned case where the rare gas is sealed under pressure, when the light-emitting element without the dielectric layer according to the present embodiment is to be driven to emit light in the atmosphere, it is required that an electric field of about 0.89 to 1.9 kV/mm is applied to allow the phosphor particles 3 to emit light, and that an alternating electric field of about 0.62 to 1.3 kV/mm is applied thereafter, so that surface discharge occurs continuously to sustain the light emission of the phosphor particles 3.
According to the light-emitting element of the present embodiment, the porous light-emitting layer is formed by a thick film process or the like. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for manufacturing the light-emitting element, and neither a vacuum system nor a carrier intensifying layer is necessary. Therefore, the light-emitting element has a simple structure and is manufactured and processed easily. Further, the light-emitting element emits light by surface discharge that occurs due to electrons injected into the porous light-emitting layer, resulting in a high brightness. The present embodiment is characterized in that the porous light-emitting layer wholly emits light thoroughly, unlike a usual phosphor that emits light only on its surface. Further, the luminous efficiency is considerably favorable as compared with that achieved by phosphors that emit ultraviolet rays as in plasma display panels. Further, it is possible to provide a light-emitting element that is to be driven with relatively low power consumption when being used in a large-screen display. Since the partition walls are provided as discharge separation means at both ends of the porous light-emitting layer, crosstalk during light emission can be avoided easily.
The light-emitting element according to the present invention emits light by surface discharge. Thus, unlike a conventional light-emitting element, there is no need to use a thin film formation process for forming the phosphor layer, and neither a vacuum vessel nor a carrier intensifying layer is necessary. Therefore, the light-emitting element can be manufactured easily. Consequently, the light-emitting element of the present invention is useful as a light-emitting body that constitutes a unit pixel of a large-screen display, and also as a light-emitting body to be applied to lighting, a light source, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-366508 | Oct 2003 | JP | national |
| 2003-383907 | Nov 2003 | JP | national |
| 2004-027204 | Feb 2004 | JP | national |
| 2004-181442 | Jun 2004 | JP | national |
| 2004-303178 | Oct 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/15614 | 10/21/2004 | WO | 3/21/2006 |
