JP2007177078A - Fluorophor for display device and field emission-type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorophor for display device, with high emission luminance on being excited by electron beams lower than 15 kV in accelerating voltage. <P>SOLUTION: The fluorophor for display device is a blue fluorophor based on a thiogallate fluorophor activated with cerium(Ce) and sodium(Na) substantially represented by the chemical formula: SrGa<SB>2</SB>S<SB>4</SB>: Ce, Na and emits on being excited by electron beams lower than 15 kV in accelerating voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a phosphor for a display device and a field emission display device using the same.

  With the advent of the multimedia era, display devices, which are core devices of digital networks, are required to have large screens, high definition, and compatibility with various sources such as computers.

  Among display devices, field emission display devices (field emission display; FED) using electron emission elements such as field emission cold cathode elements are large screens capable of displaying various information in a precise and high definition. As a thin and thin digital device, research and development have been actively conducted in recent years.

The FED has the same basic display principle as a cathode ray tube (CRT) and excites a phosphor with an electron beam to emit light. However, the acceleration voltage (excitation voltage) of the electron beam is lower than that of a CRT. In addition, the current density per unit time by the electron beam is also low. Therefore, in order to obtain sufficient luminance, a very long excitation time is required as compared with CRT. This means that the input charge amount per unit area for obtaining a predetermined luminance has to be increased, which promotes the deterioration of the life. For this reason, if a phosphor based on zinc sulfide, which has been used for CRTs, is used as a base material, sufficient light emission luminance and lifetime cannot be obtained. (For example, see Patent Document 1)
JP 2002-226847 A

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a phosphor for a display device having high emission luminance. Another object of the present invention is to provide a field emission display device (FED) having high luminance and excellent display characteristics such as color reproducibility by using such a phosphor.

The phosphor for a display device of the present invention is mainly composed of a thiogallate phosphor activated by cerium (Ce) and sodium (Na) substantially represented by the chemical formula: SrGa ₂ S ₄ : Ce, Na, and an acceleration voltage. Is a blue phosphor that emits light when excited by an electron beam of 15 kV or less.

  The field emission display device according to the present invention includes a phosphor layer including a blue-emitting phosphor layer, a green-emitting phosphor layer, and a red-emitting phosphor layer, and an electron beam having an acceleration voltage of 15 kV or less. A field emission display device comprising: an electron source that emits light; and an envelope that vacuum-seals the electron source and the phosphor layer, wherein the blue light-emitting phosphor layer is the display of the present invention described above. It contains the fluorescent substance for apparatuses.

The phosphor for a display device of the present invention is based on strontium thiogallate (SrGa ₂ S ₄ ), which is a ternary compound combining strontium (Sr), gallium (Ga) and sulfur (S), as an activator, Since it contains cerium (Ce), which has a high probability that the electronic state transitions from the ground level to the excited level, an excellent luminous efficiency is realized by irradiating with a pulsed electron beam at an acceleration voltage of 15 kV or less. Luminance can be obtained. In addition, a longer life is achieved as compared with zinc sulfide phosphors and oxysulfide phosphors conventionally used as CRT phosphors. Therefore, by using this phosphor for a display device, it is possible to realize a thin flat display device such as an FED having high brightness, good display characteristics, and long life.

  Hereinafter, modes for carrying out the present invention will be described.

  Embodiments of the present invention include strontium (Sr) belonging to Group II of the periodic table, gallium (Ga) belonging to Group III, and sulfur belonging to Group VI using cerium (Ce) and sodium (Na) as activators, respectively. It is a phosphor mainly composed of a ternary compound combined with (S), and is excited by a pulsed electron beam having an acceleration voltage of 15 kV or less, more preferably 5 to 15 kV, and emits blue light.

More specifically, it is a blue light-emitting phosphor mainly composed of cerium and sodium-activated strontium thiogallate having a composition substantially represented by the chemical formula: SrGa ₂ S ₄ : Ce, Na.

In the phosphor of the embodiment, Ce is a first activator (main activator) that forms a light emission center, and has a high transition probability, so that the light emission efficiency is high. Ce, which is the main activator, is preferably contained in a range of 0.1 to 5.0 mol% with respect to strontium thiogallate (SrGa ₂ S ₄ ) that is the base material of the phosphor. A more preferable Ce content is 0.5 to 1.0 mol%. When the content ratio of Ce is out of this range, the light emission luminance and the light emission chromaticity are lowered, which is not preferable.

Na is called a coactivator and compensates the charge of Ce activated to strontium thiogallate (SrGa ₂ S ₄ ). The content ratio of Na is preferably in the range of 0.1 to 20.0 mol% with respect to strontium thiogallate which is a phosphor matrix.

  The cerium- and sodium-activated strontium thiogallate phosphor that is an embodiment of the present invention can be produced, for example, by the following method.

That is, a phosphor raw material containing an element constituting a phosphor matrix and an activator (a main activator and a coactivator) or a compound containing the element is obtained with a desired composition (SrGa ₂ S ₄ : Ce, Na) is weighed, and sodium carbonate is added as a flux if necessary, and these are mixed in a dry process. Specifically, a predetermined amount of strontium sulfide and gallium sulfide are mixed, and an appropriate amount of activator and flux are added to obtain a raw material for the phosphor. Alternatively, an acidic strontium raw material such as strontium sulfate may be used instead of strontium sulfide. As the activator, cerium sulfide or cerium oxalate can be used, and as the coactivator, sodium carbonate, sodium chloride or the like can be used.

  Subsequently, such a phosphor raw material is filled in a heat-resistant container such as an alumina crucible together with appropriate amounts of sulfur and activated carbon. In addition and mixing of sulfur, it is preferable to mix a slightly larger amount than the phosphor raw material using a blender or the like, fill the mixed material in a heat-resistant container, and then cover the surface with sulfur. This is fired in a sulfide atmosphere such as a hydrogen sulfide atmosphere, a sulfur vapor atmosphere, or a reducing atmosphere (for example, an atmosphere of 3 to 5% hydrogen-remaining nitrogen).

Firing conditions are important in controlling the crystal structure of the phosphor matrix (SrGa ₂ S ₄ ). The firing temperature is preferably in the range of 700 to 1100 ° C. Although the firing time depends on the set firing temperature, it is preferably 60 to 180 minutes, and after firing, it is preferably cooled in the same atmosphere as firing. Thereafter, the obtained fired product is washed with ion-exchanged water and dried, followed by sieving to remove coarse particles as necessary, thereby activating cerium and sodium activated strontium thiogallate phosphor (SrGa). ₂ S ₄ : Ce, Na) can be obtained.

  The cerium- and sodium-activated strontium thiogallate phosphor according to the embodiment can be synthesized using gallium metal and strontium sulfide or strontium sulfate as starting materials. Firing can be performed under the firing conditions (temperature and time) described above.

  Further, the phosphor raw material can be fired using a rotary heating furnace as shown below. That is, the above-described phosphor raw material is put into a rotating tubular heating furnace that is arranged so as to be inclined with respect to the horizontal direction, and continuously passed. Then, the phosphor material is rapidly heated to a predetermined firing temperature in the heating furnace, and the furnace is moved from the upper side to the lower side while rolling according to the rotation of the heating furnace. In this way, the phosphor material is heated and fired for a necessary and sufficient time. Thereafter, the fired product is continuously discharged from the heating furnace, and the discharged fired product is rapidly cooled.

  In such a firing step, the inside of the tubular heating furnace and the cooling part of the fired product discharged from the heating furnace are preferably maintained in an oxygen-free state from which oxygen has been removed. It is desirable to maintain in an inert gas atmosphere such as argon or nitrogen, a reducing gas atmosphere containing hydrogen, or a hydrogen sulfide atmosphere.

  According to such a firing method, since the phosphor material is rapidly heated while rolling in the process of moving in the heating furnace, uniform heat is applied to the phosphor material in an oxygen-free state and in a hydrogen sulfide atmosphere. As a result of energy being added, firing can be completed in a shorter time compared to a conventional firing method using a crucible. Therefore, a phosphor having a small particle diameter can be obtained without causing a decrease in luminance. Further, since aggregation of the phosphor particles can be suppressed, there is no need to further pulverize after firing. Therefore, phosphor deterioration due to repeated pulverization steps can be suppressed. Furthermore, since the phosphor material is heated and fired while rolling in the heating furnace, phosphor particles having a uniform particle size and a shape close to a sphere can be obtained.

  The cerium- and sodium-activated strontium thiogallate phosphor of the embodiment thus obtained is a phosphor that emits blue light when irradiated with a pulsed electron beam having an acceleration voltage of 5 to 15 kV, and has high luminous efficiency, and thus has high Luminance can be obtained. In addition, although the color purity is slightly inferior to that of a zinc sulfide phosphor that has been conventionally used as a blue phosphor for CRT, it has a high luminance among known cerium-activated phosphors. This point sufficiently compensates for the demerit of the color purity, so that a high-intensity FED can be realized by using this blue phosphor.

  Using the blue phosphor of the embodiment, the blue phosphor layer can be formed by a known printing method or slurry method. In order to form a phosphor layer by a printing method, the phosphor of the embodiment is mixed with a binder solution made of, for example, polyvinyl alcohol, n-butyl alcohol, ethylene glycol, water, and the like to prepare a phosphor paste. The body paste is applied on the substrate by a method such as screen printing. Next, for example, baking is performed to decompose and remove the binder component by heating at a temperature of 500 ° C. for 1 hour.

  In the slurry method, the blue phosphor according to the embodiment is mixed with a photosensitive material such as pure water, polyvinyl alcohol, and ammonium dichromate, a surfactant, and the like to prepare a phosphor slurry. After applying and drying on a substrate using a spin coater or the like, exposure and development are performed by irradiating ultraviolet rays or the like, followed by drying. Thus, a blue phosphor layer having a predetermined pattern can be formed.

  Next, a field emission display device (FED) in which a blue light emitting phosphor layer is formed using the blue phosphor of the embodiment will be described.

  FIG. 1 is a cross-sectional view showing a main configuration of an embodiment of an FED. In FIG. 1, reference numeral 1 denotes a face plate, which has a phosphor layer 3 formed on a transparent substrate such as a glass substrate 2. The phosphor layer 3 has a blue light-emitting phosphor layer, a green light-emitting phosphor layer, and a red light-emitting phosphor layer that are formed corresponding to the pixels, and the light-absorbing layer 4 made of a black conductive material is separated between these layers. It has a structure. The blue light emitting phosphor layer is formed using the blue phosphor of the above-described embodiment. The green light-emitting phosphor layer and the red light-emitting phosphor layer are formed using a known green light-emitting zinc sulfide phosphor and red light-emitting oxysulfide phosphor, respectively.

  The thickness of the blue light emitting phosphor layer formed of the blue phosphor of the embodiment is desirably 1 to 10 μm, and more preferably 6 to 10 μm. The reason why the thickness of the blue light emitting phosphor layer is limited to 1 μm or more is that it is difficult to form a phosphor layer in which the phosphor particles are uniformly arranged with a thickness of less than 1 μm. On the other hand, if the thickness of the blue light-emitting phosphor layer exceeds 10 μm, the light emission luminance is lowered and cannot be put to practical use. It is desirable that the green light emitting phosphor layer and the red light emitting phosphor layer have the same thickness as that of the blue light emitting phosphor layer so that no step is generated between the phosphor layers 3 of the respective colors.

  The blue light-emitting phosphor layer, the green light-emitting phosphor layer, the red light-emitting phosphor layer, and the light absorption layer 4 that separates them are sequentially and repeatedly formed in the horizontal direction, and these phosphor layers 3 And the part in which the light absorption layer 4 exists becomes an image display area. Various patterns such as a dot shape or a stripe shape can be applied to the arrangement pattern of the phosphor layer 3 and the light absorption layer 4.

  A metal back layer 5 is formed on the phosphor layer 3. The metal back layer 5 is made of a metal film such as an Al film, and improves the luminance by reflecting light traveling in the rear plate direction, which will be described later, out of the light generated in the phosphor layer 3.

  The metal back layer 5 has a function of imparting conductivity to the image display area of the face plate 1 to prevent electric charges from accumulating, and serves as an anode electrode for the electron source of the rear plate. Further, the metal back layer 5 has a function of preventing the phosphor layer 3 from being damaged by ions generated by ionizing the gas remaining in the face plate 1 or the vacuum container (envelope) with an electron beam. Furthermore, the gas generated from the phosphor layer 3 during use is prevented from being released into the vacuum container (envelope), and the vacuum degree is prevented from being lowered.

  On the metal back layer 5, a getter film 6 formed of an evaporation type getter material made of Ba or the like is formed. The getter film 6 efficiently adsorbs the gas generated during use. The face plate 1 and the rear plate 7 are arranged to face each other, and the space between them is hermetically sealed via the support frame 8. The support frame 8 is bonded to the face plate 1 and the rear plate 7 by a frit glass or a bonding material 9 made of In or an alloy thereof, and is surrounded by the face plate 1, the rear plate 7, and the support frame 8. A vacuum vessel as a container is configured.

  The rear plate 7 includes a substrate 10 made of an insulating substrate such as a glass substrate or a ceramic substrate, or a Si substrate, and a large number of electron-emitting devices 11 formed on the substrate 10. These electron-emitting devices 11 include, for example, a field-emission cold cathode, a surface conduction electron-emitting device, and the like. That is, a large number of electron-emitting devices 11 are formed in a matrix according to the phosphors of each pixel, and wirings (XY wirings) crossing each other that drive the matrix-shaped electron-emitting devices 11 row by row. have. The support frame 8 is provided with a signal input terminal and a row selection terminal (not shown). These terminals correspond to the cross wiring (XY wiring) of the rear plate 7 described above. Further, when a flat plate-type FED is enlarged, there is a possibility that bending or the like may occur due to the thin flat plate shape. An atmospheric pressure support member (spacer) 12 may be appropriately disposed between the face plate 1 and the rear plate 7 in order to prevent such deflection and to provide strength against atmospheric pressure.

  In the FED of this embodiment, since the blue light emitting phosphor layer is formed of the blue phosphor of the embodiment, the luminance and color purity of light emission by irradiation with an electron beam with an acceleration voltage of 15 kV or less are high, and a good display Characteristics are obtained. Next, specific examples of the present invention will be described.

Example A raw material containing an element constituting a phosphor base material and an activator or a compound containing the element is represented by the composition shown in Table 1 (SrGa ₂ S ₄ : Ce content ratio 0.6 mol%, Na content ratio 4 0.8 mol%), and excess sodium carbonate was added as a flux and mixed well. Appropriate amounts of sulfur and activated carbon were added to the obtained phosphor material, filled in a quartz crucible, and fired in a hydrogen sulfide atmosphere. The firing conditions were 850 ° C. × 60 minutes.

Thereafter, the fired product obtained was washed with water, dried, and further sieved to obtain cerium- and sodium-activated strontium thiogallate phosphor (SrGa ₂ S ₄ : Ce, Na).

Subsequently, using the phosphor thus obtained, a phosphor layer having a thickness of 10 μm was formed by screen printing, and an aluminum metal back layer was further formed thereon by a lacquer method. Further, as a comparative example, silver and aluminum-activated zinc sulfide phosphor (ZnS: Ag, Al) (Ag content: 50 × 10 ⁻³ mol%, Al content: 70 × 10 ⁻³ mol%) were similarly used. A blue phosphor layer was formed, and an aluminum metal back layer was further formed thereon by a lacquer method.

Next, the light emission luminance and light emission chromaticity of the phosphor layers obtained in Examples and Comparative Examples were examined. The light emission luminance was measured by irradiating each phosphor layer with an electron beam having an acceleration voltage of 10 kV and a current density of 40 mA / cm ² . And the light emission brightness | luminance was calculated | required as a relative value when the brightness | luminance of the fluorescent substance layer of a comparative example was set to 100. FIG.

The emission chromaticity was measured using SR-3 manufactured by Topcon as a chromaticity measuring instrument. The emission chromaticity was measured in a dark room where the chromaticity at the time of light emission was not affected from the outside. Table 1 shows the measurement results of emission luminance and emission chromaticity.

  As is apparent from Table 1, the cerium- and sodium-activated strontium thiogallate phosphors obtained in the examples have lower acceleration voltages (15 kV or less) than the silver and aluminum-activated zinc sulfide phosphors of the comparative examples. The emission brightness when irradiated with an electron beam with a high current density is greatly improved. In addition, it can be seen that it has sufficiently good emission chromaticity.

Example 2
Cerium- and sodium-activated strontium thiogallate phosphors (SrGa ₂ S ₄ : Ce, Na) obtained in the examples, known green-emitting phosphors (ZnS: Cu, Al), and red-emitting phosphors (Y ₂ O) ₂ S: Eu) was used, and a phosphor layer was formed on a glass substrate to form a face plate. The face plate and the rear plate having a large number of electron-emitting devices were assembled through a support frame, and the gap between them was hermetically sealed while evacuating. It was confirmed that the FED produced in this way was excellent in color reproducibility including light emission luminance, and showed good luminance characteristics even after being driven at room temperature and rated operation for 1000 hours.

  According to the phosphor for a display device of the present invention, it is possible to obtain blue light emission with high luminance and good color purity when irradiated with an electron beam having a low voltage and a high current density. Therefore, by using such a phosphor, a thin flat display device having high luminance and excellent display characteristics such as color reproducibility can be realized.

It is sectional drawing which shows schematically FED which is embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Face plate, 2 ... Glass substrate, 3 ... Phosphor layer, 4 ... Light absorption layer, 5 ... Metal back layer, 6 ... Getter film, 7 ... Rear plate, 8 ... Support frame, 11 ... Electron emission element.

Claims (2)

Chemical formula: SrGa ₂ S ₄ : Ce, Na
A blue phosphor that emits light when excited by an electron beam having an acceleration voltage of 15 kV or less, mainly composed of a thiogallate phosphor activated by cerium (Ce) and sodium (Na) substantially represented by A phosphor for a display device. A phosphor layer including a blue-emitting phosphor layer, a green-emitting phosphor layer, and a red-emitting phosphor layer; an electron source that emits light by irradiating the phosphor layer with an electron beam having an acceleration voltage of 15 kV or less; A field emission display device comprising a source and an envelope for vacuum-sealing the phosphor layer;
The field emission display device, wherein the blue light emitting phosphor layer includes the phosphor for display device according to claim 1.

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