Patent Application
20110008584
1. Field of the Invention
The present invention relates to a fluorescent material, a fluorescent substance and a process for preparing the same, and a display using the fluorescent substance.
2. Description of the Related Art
Preparation of a fluorescent layer having a light-emitting function and a process for synthesizing fluorescent substance powder are important technologies for realizing light emitting devices or display devices.
For preparation of a fluorescent layer, a process is employed which is optimum for each device. For example, fluorescent layers for cathode ray tubes (CRTs), plasma display panels (PDPs) or field emission displays (FEDs) are prepared by powder firing method. On the other hand, fluorescent layers for electroluminescence displays (ELDs) are prepared using a physical vapor deposition method such as electron beam deposition resistance heating deposition or sputtering, or a chemical vapor deposition method such as chemical vapor deposition, sol-gel deposition or chemical solution deposition.
To accommodate a variety of display applications, fluorescent substances are required to give full color light, and thus, fluorescent substances of three primary colors—red, green and blue which excel in luminous efficiency, color purity, stability and emission response are being developed energetically. For fluorescent substances for CRTs or FEDs, which are excited by electron beam, sulfides are in use which have undergone surface treatment with a silicate compound to improve their lifetime. However, for fluorescent substances for FEDs, the electron beam irradiation time is longer than that of fluorescent substances for CRTs, whereby their deterioration is accelerated. For fluorescent substances for PDPs, which are excited by UV light, an oxide or an oxysulfide containing sulfur as its part is in use.
A blue fluorescent substance BaMgAl10O17:Eu2+ (BAM) for PDPs presents a problem of deterioration by moisture adsorption etc. at portions where bonding force is weak due to its crystalline structure, that is, at Ba—O layers between spinel layers in β-alumina structure. In more particular, in the β-alumina structure of the BAM fluorescent material, the distance 46 between the spinel layers between which a Ba—O layer 45 comprised of barium 42 and oxygen 43 lies, as shown in
Diopside has a crystal structure where SiO4 tetrahedrons 11 bond with each other at their two corners to form a chain-like shape, as shown in
In the light of the above described technological background, the principal object of the present invention is to provide a novel oxide fluorescent material which has good resistance to external environmental factors such as water and suffers less temperature quenching, and moreover, to provide a display using the fluorescent material.
According to an aspect of the present invention, there is provided a fluorescent material comprising an element selected from the group consisting of Mg, Ca, Sr and Ba; an element selected from the group consisting of Si and Ge; an element selected from the group consisting of rare earth elements; and oxygen and having a pseudowollastonite crystal structure.
The fluorescent material preferably has a composition of (Mgx, Cay, Srz, Euw)(Si1-aGea) oxide, where 0.45≦x, 0.05≦y≦0.5, 0.05≦z≦0.5, 0<w≦0.4 and 0≦a≦1. More preferably, 0.45≦x≦0.55, 0.15≦y≦0.4, 0.05≦z≦0.35, 0.01<w≦0.1 and a=0.
According to another aspect of the present invention, there is provided a fluorescent substance comprising a portion comprised of the above fluorescent material; and an adjacent layer which is comprised of an element selected from the group consisting of Si and Ge and is in contact with the portion. The interface of the portion comprised of the fluorescent material and the adjacent layer preferably has a curved shape on a cycle 0.1 to 1 μm.
According to still another aspect of the present invention, there is provided a fluorescent substance comprising a layer comprised of the above fluorescent material and a layer comprised of an element selected from the group consisting of Si and Ge, the layers stacked on a substrate.
According to a further aspect of the present invention, there is provided a display comprising the above fluorescent substance and a means of exciting the fluorescent substance.
According to a further aspect of the present invention, there is provided a process for preparing a fluorescent substance comprising the steps of preparing a precursor by providing a first member which is comprised of an element selected from the group consisting of Mg, Ca, Sr and Ba, a rare earth element, an element selected from the group consisting of Si and Ge, and oxygen and a second member which is comprised of Si or Ge and arranging the second member adjacent to the first member and heat-treating the precursor in a reduced atmosphere. The precursor preferably comprises a layer comprised of the first member and a layer comprised of the second member, the layers stacked on a substrate.
According to a further aspect of the present invention, there is provided a display, comprising an oxide fluorescent substance that has a crystal structure of pseudowollastonite; and a means of exciting the oxide fluorescent substance.
According to the present invention, it is possible to provide a novel oxide fluorescent material which has good resistance to external environmental factors such as water and suffers less temperature quenching, and moreover, to provide a display using the fluorescent material.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The pseudowollastonite has a crystal structure characterized in that it includes SiO4 tetrahedrons 11 each three of which are linked together to take the form of a three-membered ring 21 and divalent metal ions which bond the SiO4 tetrahedrons 11 in the form of a three-membered ring together, as shown in American Mineralogist, Volume 84, pages 929-932 or in
The fluorescent material of the present invention is a novel fluorescent material prepared by adding an activator of a rare earth element to a base material having a pseudowollastonite crystal structure. Use of a fluorescent material having the crystal structure of the present invention makes it possible to decrease the dependency of luminescence or luminous efficiency on temperature.
Silicate compounds having a pseudowollastonite crystal structure are generally expressed by the chemical formula XYO3 (X, Y each represent an element), as is represented by CaSiO3. However, the composition ratio of X, Y, O in the pseudowollastonite crystal structure that constitutes the fluorescent material of the present invention is not limited to 1:1:3. The composition ratio of X, Y, O in the fluorescent material of the present invention is not specifically limited one as long as the crystal structure that constitutes the fluorescent material is a pseudowollastonite crystal structure. For example, the fluorescent material of the present invention is an oxide of (Mgx, Cay, Srz, Euw)(Si1-aGea), that is, (Mgx, Cay, Srz, Euw)(Si1-aGea)Ov wherein the composition of Mg, Ca and Sr is such that 0.45≦x, 0.05≦y≦0.5 and 0.05≦z≦0.5, as shown by the triangle 101 in the triangular diagram of
The fluorescent material of the present invention exhibits excellent crystallinity when it is formed into a fluorescent thin layer of fluorescent substance on a substrate. A thin layer 54 having a crystal face comprised of two kinds of layers A, B stacked alternately ABABAB—(A=SiO4 or GeO4 tetrahedral layer, B=divalent metal ion layer), as shown in
The fluorescent material of the present invention can be synthesized in powder by using MgCO3, SrCO3, CaCO3, MgCl2, SrCl2, CaCl2, Eu2O3, EuCl3, SiO2 or GeO2 as starting materials and mixing and firing the same.
The fluorescent substance of the present invention can be formed as a thin layer (hereinafter referred to as “fluorescent thin layer”) on a substrate of, for example, Si, Ge, alumina, quartz or SrTiO3.
If an adjacent layer 52, which includes Si and/or Ge, is provided in such a manner as to allow it to come in contact with the fluorescent thin layer 54, as shown in
The term “fluorescent substance” used for the present invention means a fluorescent substance including a fluorescent thin layer and optionally an adjacent layer.
As materials for the adjacent layer, SiO2, GeO2, SiNx or SiOxNy can be used.
Preferably the thickness of the adjacent layer is equal to or larger than the thickness of the portion comprised of a fluorescent material. The thickness is, for example, 10 nm to 1 μm.
To obtain a fluorescent substance having a high external quantum efficiency, preferably the interface of the fluorescent thin layer and the adjacent layer has a curved surface on a cycle 0.1 to 1 μm. The reason is that the interface having a shape that changes on a cycle almost the same as the wavelength of the fluorescence in the visible range, about 0.1 to 1 μm, emitted in the inside of the fluorescent material of the present invention can scatter the emitted fluorescence effectively, whereby the fluorescent substance can emit the fluorescence outside effectively.
The fluorescent material of the present invention can be synthesized in powder by using MgCO3, SrCO3, CaCO3, MgCl2, SrCl2, CaCl2, Eu2O3, EuCl3, SiO2 or GeO2 as starting materials and mixing and firing the same.
Besides, the fluorescent material of the present invention can be formed as a thin layer on a substrate of, for example, Si, Ge, alumina, quartz or SrTiO3. For the formation of a fluorescent thin layer, a various types of layer forming means such as sol-gel deposition, vacuum deposition or chemical vapor deposition can be used; however, preferably sputtering is used which can provide a close and excellently reproductive layer relatively easily.
One example of preferred processes for preparing a fluorescent substance of the present invention is a process that includes: a step of preparing a precursor, which is comprised of a substrate, an adjacent layer and a fluorescent thin layer, by providing a first member that includes, as constituting elements, at least one element selected from the group consisting of Mg, Ca, Sr and Ba, at least one element selected from the group consisting of rare earth elements, at least one element selected from the group consisting of Si and Ge, and oxygen adjacent to a second member that includes Si or Ge as a main component; and a step of heat-treating the precursor in a reduced atmosphere.
The above preparation process will be described with reference to
First, a substrate 51 having a layer 52 which includes Si or Ge, as a second member, is prepared. Any one of various types of substrates comprised of, for example, alumina, quartz or SrTiO3 can be used. The substrate may be a Si substrate with SiO2 obtained by forming a thermal oxide layer in any thickness on a Si substrate or a quartz substrate may be used. A substrate on which a layer of SiO2 or GeO2 is formed can also be used.
On the adjacent layer 52 comprised of the second member and formed on the substrate 51, a thin layer 53 comprised of the first member, which includes, as constituting elements, at least one element selected from the group consisting of Mg, Ca, Sr and Ba, at least one element selected from the group consisting of rare earth elements, at least one element selected from the group consisting of Si and Ge, and oxygen, is formed so that a precursor 71 comprised of the thin layer 53, the adjacent layer 52 and the substrate 51 is formed (
The precursor 71 is subjected to heat treatment in a reduced atmosphere so that its crystallinity is improved and the activator added is activate. Examples of reduced atmospheres include: atmospheres of an inert gas such as N2, Ar or He, hydrogen gas, carbon monoxide gas, or a mixed gas of hydrogen or carbon monoxide with N2, Ar or He; and a vacuum atmosphere. To obtain divalent Eu, preferably a mixed gas of Ar or He that contains several % of H2 is used. The heat treatment temperature is in the range of, for example, 600° C. to 1400° C., though it depends on the composition of the materials used or the atmosphere in which the treatment is conducted.
The heat treatment causes diffusion of substances between the thin layer 53 and the adjacent layer 52, whereby a fluorescent thin layer 54 having excellent crystallinity can be formed. As a result, a fluorescent structure 72 is obtained which includes a fluorescent substance 59 comprised of the fluorescent thin layer 54 and the adjacent layer 52 on the substrate 51. Further, since the adjacent layer 52 contains a Si or Ge composition (e.g. SiO2, GeO2) which is also contained in the fluorescent thin layer 54, the fluorescent thin layer 54 can be preferably prepared by an easy process in a stable manner while avoiding the effect of the composition deviation in the thin layer. To fully obtain the effect of the substance diffusion, preferably the thickness of the thin layer 53 prepared in advance is equal to or larger than the thickness of the fluorescent thin layer 54.
The identification of the material composition and crystal structure can be made by X-ray diffraction analysis, X-ray fluorescence analysis, energy-dispersive spectrometry, inductively coupled plasma emission spectrometry, or transmission electron microscopy.
Combining the above described fluorescent substance with means of exciting the fluorescent substance provides a display. Examples of exciting means include: electron beam, UV light, and X ray. In other words, the fluorescent substance of the present invention is applicable to FEDs using electron beam excitation, PDPs using UV light excitation, light emitting devices such as EL, image displays, lighting systems or printing systems.
In the following the present invention will be further described by examples with reference to
In this example, was prepared on a substrate a silicate fluorescent substance characterized in that it was composed of Mg, Ca, Sr, Si, 0, as constituting elements, it included a rare earth element, as an activator, and its crystal structure was that of pseudowollastonite.
First, a thin layer 53 including Mg, Ca, Sr, Eu, Si and O, as constituting elements, was formed on a Si substrate 51 with a thermal oxide layer 52 about 500 nm thick formed on its surface, as shown in
For the layer formation, a magnetron sputtering system mounted with 3 cathodes was used. The thin layer 53 about 500 nm thick was formed by using 3 targets MgSiO3, CaSiO3 and SrSiO3 each having about 2% of Eu2O3 added and supplying 200 W of RF power to each target so that a precursor 71 was obtained. In this layer forming operation, the temperature of the substrate 51 was 200° C., the pressure in the chamber was kept at about 1 Pa by flowing the mixed gas of argon and oxygen in the chamber, and the deposition rate was about 3 nm/min.
Then, the precursor 71 was heat treated at about 1000° C. in an Ar atmosphere containing 2% of H2 using a vacuum annealing system to obtain a fluorescent structure including a fluorescent substance 59 comprised of a fluorescent thin layer 54 and an adjacent layer 52 on the substrate 51 (
When the resultant fluorescent structure 72 was exposed to 254 nm UV light from a mercury lamp, blue emission with excellent color purity was obtained. When excitation and emission spectra were measured with spectrophotofluorometer, an excitation spectrum 61 having the maximum peak at 245 nm and an emission spectrum 62 having a peak at 447 nm were obtained, as shown in
The examination of the dependency of the fluorescent substance having a pseudowollastonite crystal structure on temperature of the substrate revealed that the change in emission intensity of the fluorescent substance having a pseudowollastonite crystal structure (represented by the curve plotted with ) was smaller than that of the fluorescent substance having a diopside crystal structure (represented by the curve plotted with ▪) as shown in
The X-ray fluorescence analysis using a Rh tube and the inductively coupled plasma emission spectrometry conducted for the fluorescent thin layer 54 of the resultant fluorescent substance 59 showed that in the oxide of (Mgx, Cay, Srz, Euw)Si, x=0.53, y=0.25, z=0.2 and w=0.02.
By the X-ray diffraction analysis using CuKα ray, a peak associated with the pseudowollastonite crystal structure was observed. The evaluation of electron beam diffraction using a transmission electron microscope showed that the fluorescent thin layer 54 had a pseudowollastonite crystal structure where the metal atoms (Mg, Sr, Ca) and the SiO4 three-membered ring were alternately stacked.
Further, the observation of the cross-sectional structure of the fluorescent thin layer using a transmission electron microscope showed that the fluorescent thin layer had a crystal face comprised of two kinds of layers A, B stacked alternately ABABAB—(A=SiO4 or GeO4 tetrahedral layer, B=divalent metal ion layer), as shown in
In the heat treatment step, substance diffusion was caused between the thin layer 53 and the adjacent layer 52, whereby the interface 55 of the fluorescent thin layer and the adjacent layer had a curved surface on a cycle 0.1 to 1 μm. The heat treatment utilizing this substance diffusion made possible the preparation of a fluorescent substance 59 which suffered less composition fluctuation, had fewer grain boundaries or defects, and hence an excellent crystallinity. This improved the luminance, color purity and stability of the fluorescent thin layer. Furthermore, the resultant fluorescent thin layer showed excellent characteristics in dependency of light emission caused by UV light irradiation on temperature.
The fluorescent substance 59 had some other structural characteristics. One of the characteristics was that the angle θ between the stacked crystal face and the substrate surface was fixed, for example, 40°. It was also found that the fluorescent thin layer 54 had vacant spaces (portions having lower density) about 1 μm3 in size in it inside. It is assumed that these characteristic thin layer structure (the curved shape of the interface, the angle between the crystal face and the substrate surface, vacant spaces) makes it possible to effectively take out the light emitted in the inside of the fluorescent material outside. That is, it is assumed that excellent external quantum efficiency can be obtained by such a structure.
If the power supplied to the 3 targets MgSiO3, CaSiO3 and SrSiO3 during the deposition is controlled and fluorescent materials of various compositions are prepared, excellent fluorescent substances can be obtained which have compositions of the oxide of (Mgx, Cay, Srz, Euw)Si, where 0.45≦x, 0.05≦y≦0.5 and 0.05≦z≦0.5 and 0<w≦0.4.
In this example, a fluorescent thin layer 54 including Mg, Ca, Sr, Eu, Si and O as constituting elements was prepared on a single crystal substrate or a ceramic substrate.
As a substrate 51, a sapphire single crystal substrate was used.
First, a SiO2 thin layer about 500 nm thick was formed as an adjacent layer 52 on the substrate 51. Layer formation was performed by magnetron sputtering using a SiO2 target. The substrate temperature was 200° C. or lower, the pressure in the chamber was kept at 0.5 Pa by flowing argon gas in the chamber, and the deposition rate was 6 nm/min.
Then a thin layer 53 was formed which includes Mg, Ca, Sr, Eu, Si and O as constituting elements. For the layer formation, a magnetron sputtering system mounted with 3 cathodes was used. The thin layer 53 about 500 nm thick was formed by using 3 targets MgSiO3, CaSiO3 and SrSiO3 each having about 5% of Eu2O3 added and supplying 180 W, 200 W and 200 W of RF power to the respective targets while keeping the substrate temperature at 100° C., the pressure in the chamber at about 1 Pa by flowing a mixed gas of argon and oxygen, and deposition rate at 3 nm/min so that a precursor 71 was obtained (
Then, the precursor 71 was heat treated at about 1000° C. in a He atmosphere containing 3% of H2 using a vacuum annealing system to obtain a fluorescent structure 72 including a fluorescent substance 59 comprised of a fluorescent thin layer 54 and an adjacent layer 52 on the substrate 51 (
When the resultant fluorescent substance 59 was exposed to UV light, blue emission with excellent color purity was obtained. The X-ray fluorescence analysis using a Rh tube and the inductively coupled plasma emission spectrometry conducted for the resulting fluorescent thin layer 54 showed that in the oxide of (Mgx, Cay, Srz, Euw)Si, x=0.45, y=0.3, z=0.2 and w=0.05.
The process of this example makes possible the preparation of a fluorescent substance on a SrTiO3 single crystal substrate or a fired BaTiO3 ceramic substrate. This allows a fluorescent substance to find wider application.
In this example, a fluorescent thin layer including Mg, Ca, Sr, Eu, Si, Ge and O as constituting elements was prepared.
As a substrate 51, a sapphire single crystal substrate was used.
First, a GeO2 thin layer about 500 nm thick was formed as an adjacent layer 52. Layer formation was performed by magnetron sputtering using a GeO2 target. The substrate temperature was 100° C., the pressure in the chamber was kept at 0.5 Pa by flowing argon gas in the chamber, and the deposition rate was 5 nm/min.
Then a thin layer 53 was formed which includes Mg, Ca, Sr, Eu, Si and O as constituting elements. For the layer formation, a magnetron sputtering system mounted with 3 cathodes was used. The thin layer 53 about 500 nm thick was formed by using 3 targets MgSiO3, CaSiO3 and SrSiO3 each having about 5% of Eu2O3 added and supplying 180 W, 180 W and 200 W of RF power to the respective targets while keeping the substrate temperature at 100° C., the pressure in the chamber at about 1 Pa by flowing a mixed gas of argon and oxygen, and deposition rate at 3 nm/min so that a precursor 71 was obtained (
Then, the precursor 71 was heat treated at about 850° C. in a He atmosphere containing 3% of H2 using a vacuum annealing system to obtain a fluorescent structure 72 including a fluorescent substance 59 comprised of a fluorescent thin layer 54 and an adjacent layer 52 on the substrate 51 (
Then the substrate on which a layer was formed was heat treated at about 850° C. in a He atmosphere containing 2% of H2 using a vacuum annealing system (
When the annealed substrate having a layer formed on it was exposed to UV light, blue emission with excellent color purity was obtained. The X-ray fluorescence analysis using a Rh tube and the inductively coupled plasma emission spectrometry conducted for the resultant fluorescent thin layer showed that in the oxide of (Mgw, Cay, Srz, Euw) (Si1-aGea), x=0.5, y=0.25, z=0.2, w=0.05 and a=0.3.
In this example, a display was produced to which the fluorescent substance of the present invention was applied.
As shown in
A fluorescent layer was comprised of: a fluorescent material including Mg, Ca, Sr, Eu, Si and O as constituting elements and having a crystal structure of pseudowollastonite; and a quartz substrate on which the fluorescent material was arranged. The thickness of the fluorescent layer was about 1100 nm, and an aluminum layer nm thick was formed as a metal back 83 on the fluorescent layer.
The electron-emitting devices 81 were Spindt emitters and the electron beam accelerating voltage was 10 kV.
The display of this example is capable of providing blue display excellent in color purity and displaying images with high visibility and stability.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2005-259213, filed Sep. 7, 2005, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-259213 | Sep 2005 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11469553 | Sep 2006 | US |
| Child | 12886658 | US |
