Patent Application
20060001353
Priority is claimed to Korean Patent Application No. 10-2004-0051966, filed on Jul. 5, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a fluorescent lamp, and more particularly, to a flat fluorescent lamp.
2. Description of the Related Art
Flat fluorescent lamps are typically employed as backlights of liquid crystal displays (LCDs).
Since LCD panels do not have self-luminance property, LCDs require a separate optical source to display images. In this regard, LCDs generally include a liquid crystal panel, a driving circuit unit, and an optical source.
In early LCDs, a small lamp disposed on a front or lateral side had been used as an optical source. However, as a need for large area LCDs and high quality LCD images increases, there has been widely used a backlight disposed at the back of a liquid crystal panel and uniformly supplying light to the front surface of the liquid crystal panel. Preferably, it is required that a LCD backlight can uniformly supply a white light with high brightness to the front surface of a LCD.
As well known, fluorescent lamps have advantages of an extended life span and a low power consumption. In this respect, flat fluorescent lamps can be very efficiently used as backlights of LCDs. The flat fluorescent lamps can be classified into an opposite discharge type, a surface discharge type, or a combination type according to an electrode configuration.
By the discharge induced in the above-described manner, the discharge gas is excited. The discharge gas thus excited emits a vacuum ultraviolet light. The vacuum ultraviolet light excites the phosphor layer 30, thereby emitting visible light. The visible light is emitted from the transparent front substrate 20. Generally, the phosphor layer 30 is made of a mixture of a phosphor excited by the vacuum ultraviolet light and generating red light, a phosphor excited by the vacuum ultraviolet light and generating green light, and a phosphor excited by the vacuum ultraviolet light and generating blue light. Therefore, the light emitted from the front substrate 20 is white light.
It is noted that the color purity of LCDs is significantly affected by the quality of white light emitted from a backlight. That is, the color purity of light passing through a color filter of a liquid crystal panel is dependent on the color purity of three colors (red, green, blue) constituting white light emitted from a backlight.
In a conventional flat fluorescent lamp, red, green, and blue phosphors contained in the phosphor layer 30 are excited by vacuum ultraviolet light. For example, (Y, Gd)BO3:Eu is used as a red phosphor, LaPO4:(Ce, Tb) is used as a green phosphor, and BaMgAl10O17:Eu is used as a blue phosphor. Generally, it has been evaluated that the purity of red, green, and blue colors of visible light emitted from these phosphors excited by vacuum ultraviolet light is not very good.
In this respect, a flat fluorescent lamp that can emit light composed of color components with improved color purity is still being required.
In the flat fluorescent lamp as shown in
U.S. Pat. No. 6,559,598 B2 discloses a plasma picture screen including an ultraviolet (UV) light emitting layer. According to the plasma picture screen disclosed in the document, a red, green, and blue-emitting phosphor pattern is disposed on an upper surface of a rear substrate. For this reason, vacuum UV (VUV) light heading toward a front substrate cannot contribute to emission of visible light. According to a suggestion in the document, the UV light emitting layer excited by vacuum UV light and generating UV light is disposed on a lower surface of the front substrate. Therefore, vacuum UV light heading toward the front substrate is converted to UV light, which is then emitted toward the rear substrate. The emitted UV light is responsible for exciting the red, green, and blue-emitting phosphor pattern disposed on the upper surface of the rear substrate. As a result, the red, green, and blue-emitting phosphor pattern disposed on the upper surface of the rear substrate is excited by the vacuum UV light heading toward the rear substrate and the UV light emitted from the UV light emitting layer of the front substrate, thereby resulting in enhanced brightness.
However, the plasma picture screen disclosed in U.S. Pat. No. 6,559,598 B2 cannot be applied to a flat fluorescent lamp. This is because in the plasma picture screen disclosed in U.S. Pat. No. 6,559,598 B2, a phosphor layer emitting visible light is disposed on the rear substrate. Application of such a structure to a flat fluorescent lamp can significantly lower brightness.
Therefore, an improved flat fluorescent lamp that can provide visible light with enhanced brightness and brightness uniformity is still being required.
Embodiments of the present invention provides a flat fluorescent lamp that can emit white light composed of color components with enhanced color purity and/or white light having enhanced brightness and enhanced brightness uniformity.
Embodiments of the present invention also provides a novel ultraviolet (UV) light-emitting phosphor that is excited by vacuum UV light and emits UV light.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
Exemplary embodiments of the present invention provide a flat fluorescent lamp, which includes:
a front substrate and a rear substrate separated from each other and defining a discharge space therebetween;
a discharge gas filled in the discharge space and generating a first ultraviolet (UV) light with a wavelength of 260 nm or less by discharge of the discharge gas;
at least a pair of electrodes inducing the discharge of the discharge gas;
a second phosphor layer disposed on an inner surface of the rear substrate and including a phosphor excited by the first UV light and generating a second UV light having a wavelength of 200 to 400 nm which is longer than the wavelength of the first UV light; and
a first phosphor layer disposed on an inner surface of the front substrate and including a phosphor excited by the first UV light and the second UV light and generating a visible light.
Generally, vacuum UV light refers to a light beam with a wavelength of about 200 nm or less and UV light refers to a light beam with a wavelength of about 200 to 380 nm. However, the terms “first UV light” and “second UV light” are used herein. The first UV light has a wavelength of about 260 nm or less (similar to that of vacuum UV light). The second UV light has a wavelength of about 200 to 400 nm (similar to that of UV light). The second UV light as used herein has a longer wavelength than the first UV light.
In exemplary embodiments of the flat fluorescent lamp of the present invention, a portion of the first UV light generated in the discharge space and heading toward the rear substrate is incident in the second phosphor layer and converted to the second UV light. The second UV light thus generated is emitted toward the front substrate and incident in the first phosphor layer. Of course, a portion of the first UV light generated in the discharge space and heading toward the front substrate is directly incident in the first phosphor layer. Therefore, in the flat fluorescent lamp according to this embodiment, visible light is generated only from the first phosphor layer excited by the first UV light and the second UV light.
An advantage of the above-described configuration is that the luminance efficiency of visible light induced by the portion of the first UV light generated in the discharge space and heading toward the rear substrate is higher than that in a conventional flat fluorescent lamp. As described above, in a conventional flat fluorescent lamp, a portion of a first UV light (or vacuum UV light) generated in a discharge space and heading toward a rear substrate excites a visible light-emitting phosphor disposed on the rear substrate, thereby generating visible light from the phosphor of the rear substrate. The visible light thus generated is transmitted through a phosphor layer disposed on a front substrate and then emitted from the fluorescent lamp. It is noted that when the visible light generated from the phosphor of the rear substrate is transmitted through the phosphor layer disposed on the front substrate, it is partially absorbed in the phosphor layer of the front substrate. However, in exemplary embodiments of the flat fluorescent lamp of the present invention, all visible light emitted from the flat fluorescent lamp is generated only from the first phosphor layer disposed on the front substrate. Therefore, the absorption phenomenon of visible light that is generated in a conventional technique is not involved in the flat fluorescent lamp of exemplary embodiments of the present invention. Consequently, the exemplary flat fluorescent lamp has an enhanced luminance efficiency of visible light, thereby ensuring an enhanced brightness.
Another advantage of the exemplary flat fluorescent lamp of the present invention is that the first phosphor layer can be disposed in a thicker thickness on the inner surface of the front substrate, thereby enhancing the thickness uniformity of the first phosphor layer. Consequently, the uniformity of visible light emitted from the flat fluorescent lamp of the present invention over the entire area of the front surface of the flat fluorescent lamp can be remarkably enhanced. In a conventional flat fluorescent lamp, it is common to minimize the thickness of a phosphor layer of a front substrate so that visible light generated from a phosphor of a rear substrate is efficiently transmitted through the phosphor layer of the front substrate. According to a common understanding, there is a trade-off relationship between the minimization of the thickness of a phosphor layer and the thickness uniformity of the phosphor layer due to the limit of the coating technology. When the thickness of the phosphor layer is minimized, the thickness uniformity of the phosphor layer is lowered. Therefore, the uniformity of visible light emitted from the front surface of a flat fluorescent lamp over the entire area of the front surface of the flat fluorescent lamp is lowered. However, in this exemplary flat fluorescent lamp of the present invention, visible light is emitted only from the first phosphor layer of the front substrate, and thus, there is no need to minimize the thickness of the first phosphor layer. In this exemplary flat fluorescent lamp of the present invention, the first phosphor layer having excellent thickness uniformity due to an appropriate thickness can be easily realized.
Still another advantage of this exemplary flat fluorescent lamp of the present invention is that the color purity of red, green, or blue component of visible light generated from the phosphor excited by the first UV light and the second UV light is more excellent, relative to that of visible light generated from a phosphor excited only by vacuum UV light like in a conventional flat fluorescent lamp. Therefore, when this exemplary flat fluorescent lamp of the present invention is used as a LCD backlight, the color purity of light passing through a color filter of a LCD panel can be remarkably enhanced.
Hereinafter, a flat fluorescent lamp according to exemplary embodiments of the present invention will be described in more detail.
Exemplary embodiments of the flat fluorescent lamp of the present invention include:
a front substrate and a rear substrate separated from each other and defining a discharge space therebetween;
a discharge gas filled in the discharge space and generating a first UV light with a wavelength of 260 nm or less by discharge of the discharge gas;
at least a pair of electrodes inducing the discharge of the discharge gas;
a second phosphor layer disposed on an inner surface of the rear substrate and including a phosphor excited by the first UV light and generating a second UV light having a wavelength of 200 to 400 nm which is longer than the wavelength of the first UV light; and
a first phosphor layer disposed on an inner surface of the front substrate and including a phosphor excited by the first UV light and the second UV light and generating a visible light.
The front substrate and the rear substrate are separated from each other by a predetermined distance. Therefore, a space is defined between the front substrate and the rear substrate. The space is filled with the discharge gas. For example, the discharge gas may be He, Ne, Xe, Kr, Hg, or a mixture thereof.
The first UV light generated by the discharge of the discharge gas may have a wavelength of about 260 nm or less. For example, when a mixed gas of Xe and He or Ne (e.g., the content of Xe is about 30% or more) is used as the discharge gas, the first UV light generated by the discharge of the discharge gas has a main wavelength of about 172 nm and a small part of 147 nm. [For example,] [w]When a mixed gas of Hg and an inert gas (He or Ne) (e.g., the content of Hg is several mg in a 4-feet fluorescent lamp) is used as the discharge gas, the first UV light generated by the discharge of the discharge gas has a main wavelength of about 254 nm.
In the flat fluorescent lamp of the present invention, a non-limiting example of the front substrate may be a glass plate. The front substrate has opposite two surfaces. Among the two surfaces, a surface exposed outside is referred to as an outer surface and an opposite surface to the rear substrate is referred to as an inner surface. The first phosphor layer is attached to the inner surface of the front substrate.
The first phosphor layer includes a phosphor which can be excited by the first UV light and the second UV light and generating visible light. The phosphor of the first phosphor layer may be a phosphor excited by the first UV light and the second UV light and generating red light, a phosphor excited by the first UV light and the second UV light and generating green light, a phosphor excited by the first UV light and the second UV light and generating blue light, or a mixture thereof. When the phosphor of the first phosphor layer is a mixture of a phosphor excited by the first UV light and the second UV light and generating red light, a phosphor excited by the first UV light and the second UV light and generating green light, and a phosphor excited by the first UV light and the second UV light and generating blue light, if the mixture ratio is appropriate, light generated from the first phosphor layer may be white light. In particular, when the first phosphor layer generates white light, exemplary embodiments of the flat fluorescent lamp of the present invention can be advantageously applied in the fields requiring white light, like a LCD backlight.
The phosphor excited by the first UV light and the second UV light and generating red light may be Y(P,V)O4:Eu, YVO4:Eu, Y2O2S:Eu, or the like. These phosphors may be used alone or in combination. These phosphors may be those known or commercially available.
The phosphor excited by the first UV light and the second UV light and generating green light may be BaMgAl10O17:(Eu,Mn), BaMgAl14O23:(Eu,Mn), BaMg2Al16O27:(Eu,Mn), (Y,Gd)BO3:(Ce,Tb), SrAl2O4:Eu, or the like. These phosphors may be used alone or in combination. These phosphors may be those known or commercially available.
The phosphor excited by the first UV light and the second UV light and generating blue light may be BaMgAl10O17:Eu, BaMgAl14O23:Eu, BaMg2Al16O27:Eu, or the like. These phosphors may be used alone or in combination. These phosphors may be those known or commercially available.
In the flat fluorescent lamp of the present invention, a non-limiting example of the rear substrate may be a glass plate with a UV reflective layer such as an Al2O3 layer. The rear substrate has opposite two surfaces. Among the two surfaces, a surface exposed outside is referred to as an outer surface and an opposite surface to the front substrate is referred to as an inner surface. The second phosphor layer is attached to the inner surface of the rear substrate.
The second phosphor layer includes the phosphor excited by the first UV light and generating the second UV light. Examples of a phosphor excited by vacuum UV light and generating UV light include YBO3:Bi, YBO3:Gd, YBO3:(Bi,Gd), YAl3(BO3)4:Gd, LaPO4:Pr, LaPO4:(Pr,Gd), SrB4O7:Eu, Y2GeO5:Gd, LaPO4:Ce, LaPO4:(Ce,Gd), GdPO4:Ce, LaMgAl11O19:Ce, SrB4O7:Eu, BaSi2O5:Pb, YMgB5O10:Ce, LaMgAl11O19:Ce, LaB3O6:Ce, and LaPO4:Ce. These phosphors may be used alone or in combination. Among these phosphors, those except YBO3:Bi, YBO3:(Bi,Gd), and LaPO4:(Pr,Gd) are known or commercially available. YBO3:Bi, YBO3:(Bi,Gd), and LaPO4:(Pr,Gd) are new phosphors provided by the present invention and a detailed description thereof will be provided later.
For example, when the first UV light has a wavelength of 200 nm or less, it is more preferable that a phosphor generating the second UV light is YBO3:Bi, YBO3:Gd, YBO3:(Bi,Gd), YAl3(BO3)4:Gd, LaPO4:Pr, LaPO4:(Pr,Gd), SrB4O7:Eu, Y2GeO5:Gd, LaPO4:Ce, LaPO4:(Ce,Gd), GdPO4:Ce, LaMgAl11O19:Ce, or a mixture thereof. For example, when the first UV light has a wavelength of 200 to 260 nm, it is more preferable that a phosphor generating the second UV light is SrB4O7:Eu, BaSi2O5:Pb, YMgB5O10:Ce, LaMgAl11O19:Ce, LaB3O6:Ce, LaPO4:Ce, or a mixture thereof.
The flat fluorescent lamp of the present invention includes at least a pair of electrodes inducing the discharge of the discharge gas. There is no particular limitation to the configuration of the electrodes. For example, the configuration of the electrodes may be a coplanar arrangement (surface discharge type), a matrix arrangement (opposite discharge type), or one of various combinations thereof. The electrodes may be disposed on the inner or outer surface of the front substrate, the inner or outer surface of the rear substrate, or a combination thereof. The electrodes may be covered with a dielectric layer. The dielectric layer covering the electrodes may be covered with a protective layer. The dielectric layer may be made of SiO2, PbO—SiO2—B2O3, or ZnO—PbO—P2O5. The protective layer may be made of MgO.
In the exemplary flat fluorescent lamp, if the thickness of the first phosphor layer including the phosphor excited by the first UV light and the second UV light and generating visible light is too thin, the phosphor may be incompletely excited by the UV light, thereby lowering brightness. On the other hand, if it is too thick, transmission of visible light generated inside the flat fluorescent lamp may be difficult. Typically, the thickness of the first phosphor layer may ranges from about 15 to about 25 μm. It is noted that the first phosphor layer of the present invention can have a thickness appropriate to easily ensure thickness uniformity without lowering of brightness. In this regard, the thickness of the first phosphor layer may be more preferably from about 15 to 20 μm and still more preferably from about 18 to 20 μm.
In the exemplary flat fluorescent lamp of the present invention, if the thickness of the second phosphor layer including the phosphor excited by the first UV light and generating the second UV light is too thin, the phosphor may be incompletely excited by the first UV light, thereby lowering brightness. On the other hand, if it is too thick, the discharge space for the discharge gas may be excessively decreased or a capacitance or a discharge voltage may be increased. Typically, the thickness of the second phosphor layer may ranges from about 50 to 100 μm.
The first phosphor layer and the second phosphor layer may be respectively formed on the inner surfaces of the front substrate and the rear substrate by a dry coating process or a wet coating process. Examples of the dry coating process include electrostatic deposition and electrostatically supported dusting. Examples of the wet coating include dip coating, silk-screen printing, spin coating, meniscus coating, and blade coating. In the case of using a wet coating process, the phosphor is used in a dispersion form. A dispersion medium may be water, one of various organic solvents, or a mixture thereof. A phosphor dispersion may include a dispersant, a surfactant, an antifoaming agent, a binder, or a mixture thereof. The binder may be an organic binder or an inorganic binder. A wet-coated phosphor dispersion is subjected to thermal treatment. At this time, the dispersion medium, the dispersant, the surfactant, the antifoaming agent, and the organic binder are removed. The inorganic binder may also remain in the each phosphor layer after the thermal treatment.
An exemplary method of fabricating the flat fluorescent lamp of the present invention can be performed using any one of commonly known various methods, and thus, a detailed description thereof is omitted.
Hereinafter, several non-limiting embodiments illustrating the structure of the flat fluorescent lamp of the present invention will be described with reference to the accompanying drawings.
It will be understood by those of ordinary skill in the art that various changes in the structures of the flat fluorescent lamps as shown in
The present invention also provides novel UV light-emitting phosphors. The UV light-emitting phosphors of the present invention are YBO3:Bi, YBO3:(Bi,Gd), and LaPO4:(Pr,Gd). These phosphors are efficiently excited by a first UV light and generate a strong second UV light.
15.16 g of Y2O3, 0.175 g of Bi2O3, 2.72 g of Gd2O3, and 10.23 g of H3BO3 were mixed using a ball mill. The reaction mixture was thermally treated in a 500° C. air atmosphere for two hours and then under a 1,100° C. air atmosphere for four hours. A product thus obtained was pulverized to make powders. These powders were five times washed with deionized water and dried at 100° C. for one day.
An X-ray diffraction (XRD) analysis for the resultant powders was performed and the result is shown in
The luminance characteristics of the (Y0.895Gd0.1Bi0.005)BO3 powders were analyzed by a spectrophotometer using an Xe excimer lamp as an optical source and the results are shown in
16.85 g of Y2O3, 0.175 g of Bi2O3, and 10.23 g of H3BO3 were mixed using a ball mill. The reaction mixture was thermally treated in a 500° C. air atmosphere for two hours and then under a 1,100□ air atmosphere for four hours. A product thus obtained was pulverized to make powders. These powders were five times washed with deionized water and dried at 100□ for one day.
An XRD analysis for the resultant powders was performed and the result is shown in
The luminance characteristics of the (Y0.095Bi0.005)BO3 powders were analyzed by a spectrophotometer using an Xe excimer lamp as an optical source and the results are shown in
14.34 g of La2O3, 1.82 g of Gd2O3, 0.87 g of Pr(NO3)3.6H2O, and 11.5 g of NH4H2PO4 were mixed using a ball mill. The reaction mixture was thermally treated in a 500° C. air atmosphere for two hours and then under a 1,100° C. air atmosphere for four hours. A product thus obtained was pulverized to make powders. These powders were five times washed with deionized water and dried at 100° C. for one day.
An XRD analysis for the resultant powders was performed and the result is shown in
The luminance characteristics of the (La0.88Pr0.02Gd0.1)PO4 powders were analyzed by a spectrophotometer using an Xe excimer lamp as an optical source and the results are shown in
In an embodiment of the present invention, a phosphor contained in a first phosphor layer may be a mixture of Y(P,V)O4:Eu (red), BaMgAl14O23:(Eu,Mn) (green), and BaMgAl10O17:Eu (blue). These phosphors can be efficiently excited by first UV light and the second UV light and generate visible light. A mixture ratio of these phosphors can be appropriately selected so that visible light generated from the first phosphor layer is white light.
Therefore, it can be seen that a flat fluorescent lamp including a first phosphor layer efficiently emitting light by first and second UV light according to the present invention can produce an enhanced brightness, relative to a conventional flat fluorescent lamp.
From
A flat fluorescent lamp of the present invention can produce an enhanced brightness since a visible light absorption phenomenon does not occur, unlike a conventional technique.
A first phosphor layer of the exemplary flat fluorescent lamp of the present invention can be a thickness appropriate to easily ensure thickness uniformity without lowering brightness, thereby ensuring the enhanced brightness uniformity of the flat fluorescent lamp.
The exemplary flat fluorescent lamp of the present invention can have more excellent color purity, as compared to a conventional flat fluorescent lamp having a color purity of visible light generated from a phosphor excited only by vacuum UV light.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0051966 | Jul 2004 | KR | national |
