JP2008130305A - Green light-emitting element, and field emission display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-luminance green light-emitting element that emits light, by being excited by a pulse-shaped electron beam having an acceleration voltage of 5-15 kV. <P>SOLUTION: This green light-emitting element is formed of a phosphor of a composite sulfide (for instance, SrGa<SB>2</SB>S<SB>4</SB>: Eu) activated by bivalent Eu and emits a green light from being excited by a pulse-shaped electron beam, having an acceleration voltage of 5-15 kV. The light-emitting element has luminous efficiency that is not smaller than 1.5 times that of a light-emitting element, having a copper-activated zinc sulfide phosphor, when the energy density per pulse is not smaller than 5 mJ/cm<SP>2</SP>, and has luminous efficiency lower than that of a light-emitting element, having the copper-activated zinc sulfide phosphor in electron beam excitation of energy density lower than 0.1 mJ/cm<SP>2</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a green light emitting element 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 deterioration of the life of the phosphor.

For this reason, if a phosphor based on zinc sulfide, which has been conventionally used for CRT, is used, sufficient light emission luminance and lifetime cannot be obtained. From such a background, there has been a demand for a phosphor for FED with high emission luminance. (For example, see Patent Document 1)
JP 2002-226847 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a light-emitting element 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 light emitting element.

The green light-emitting device of the present invention is composed of a composite sulfide phosphor of two or more elements activated by divalent europium, and is excited by irradiation with a pulsed electron beam having an acceleration voltage of 5 to 15 kV to become green. When the energy density per pulse of the pulsed electron beam is 5 mJ / cm ² or more, the luminous efficiency is 1.5 times or more that of the light emitting element comprising the copper-activated zinc sulfide phosphor. And excitation with an electron beam having an energy density lower than 0.1 mJ / cm ² per pulse has a light emission efficiency lower than that of a light-emitting element including a copper-activated zinc sulfide phosphor.

  The field emission display device of the present invention includes a phosphor layer including a blue light-emitting phosphor layer, a green light-emitting phosphor layer, and a red light-emitting phosphor layer, and an electron beam having an acceleration voltage of 5 to 15 kV applied to the phosphor layer. A field emission display device comprising: an electron source that emits light upon irradiation; and an envelope that vacuum-seals the electron source and the phosphor layer, wherein the green light-emitting phosphor layer is formed according to the present invention. A green light emitting element is included.

The present invention is a green light-emitting element composed of a europium-activated composite sulfide phosphor. When the energy density per pulse is 5 mJ / cm ² or more in irradiation with a pulsed electron beam having an acceleration voltage of 5 to 15 kV, It has a high luminous efficiency of 1.5 times or more that of a light-emitting device including a copper-activated zinc sulfide phosphor. Moreover, excitation with an electron beam having an energy density per pulse lower than 0.1 mJ / cm ² has a lower luminous efficiency than a light emitting device comprising a copper activated zinc sulfide phosphor. Therefore, compared with the green light emitting element provided with the copper activated zinc sulfide phosphor, it is possible to realize light emission with a wide luminance from low luminance to high luminance. By using this green light emitting element as the light emitting layer of the field emission display device, it is possible to realize a good display with high light emission luminance.

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

The first embodiment of the present invention is a light-emitting element composed of a strontium thiogallate phosphor activated with divalent europium (Eu), and more specifically, substantially represented by the chemical formula: SrGa ₂ S ₄ : Eu This is a green light-emitting device mainly composed of Eu-activated strontium thiogallate phosphor having a composition expressed as follows. This light emitting element is excited by a pulsed electron beam having an acceleration voltage of 5 to 15 kV, more preferably 7 to 13 kV, and emits green light whose emission spectrum has an intensity peak in a wavelength range of 525 to 550 nm.

In the Eu-activated strontium thiogallate phosphor, Eu is an activator that forms an emission center, and has a high transition probability, so that high luminous efficiency can be obtained. The divalent Eu that is an 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 a matrix of the phosphor. A more preferable Eu content is 1.5 to 4.0 mol%. If the Eu content is outside this range, the light emission luminance and light emission chromaticity decrease, which is not preferable.

  This Eu-activated strontium thiogallate phosphor has a short afterglow time of less than 100 μs. The afterglow time refers to the time until the emission intensity is reduced to 1/10 (10%) of the emission intensity at the time of excitation after the electron beam irradiation is interrupted.

  This Eu-activated strontium thiogallate phosphor can be produced, for example, by the method described below.

That is, a phosphor raw material including an element constituting the phosphor matrix and an activator or a compound containing the element is weighed so as to have a desired composition (SrGa ₂ S ₄ : Eu), and these are dry-processed. Mix. Specifically, a predetermined amount of strontium sulfide and gallium oxyhydroxide are mixed, and an appropriate amount of activator (compound containing) is added to obtain a phosphor material. Instead of strontium sulfide, an acidic strontium raw material such as strontium sulfate may be used. As an activator, europium sulfide or europium oxalate can be used.

  Next, such a phosphor raw material is filled in a heat-resistant container such as an alumina crucible or a quartz crucible together with appropriate amounts of sulfur and activated carbon. This is fired in a sulfide atmosphere such as a hydrogen sulfide atmosphere or a sulfur vapor atmosphere, or in 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 900 ° 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 or the like, dried, and then subjected to sieving to remove coarse particles as necessary, whereby Eu-activated strontium thiogallate phosphor (SrGa ₂ S). ₄ : Eu) can be obtained.

  By using the Eu-activated strontium thiogallate phosphor thus obtained and forming a phosphor layer using a known printing method or slurry method, a green light emitting device can be formed. In order to form a phosphor layer by a printing method, a phosphor paste is prepared by mixing Eu-activated strontium thiogallate phosphor with a binder solution made of, for example, polyvinyl alcohol, n-butyl alcohol, ethylene glycol, water or the like. The phosphor 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 order to form a phosphor layer by a slurry method, Eu-activated strontium thiogallate phosphor is mixed with a photosensitive material such as pure water, polyvinyl alcohol, and ammonium dichromate, a surfactant, and the like. A slurry is prepared, and this phosphor slurry is applied and dried on a substrate using a spin coater or the like, and then exposed to ultraviolet light or the like, exposed and developed, and dried. Thus, a phosphor layer having a predetermined pattern can be formed.

The green light-emitting element having the Eu-activated strontium thiogallate phosphor layer thus formed is an element that emits green light when irradiated with a pulsed electron beam having an acceleration voltage of 5 to 15 kV, more preferably 7 to 13 kV. Excitation of an electron beam with an energy density of 5 mJ / cm ² or more has a high luminous efficiency of 1.5 times or more that of a copper-activated zinc sulfide phosphor, while an energy density per pulse of 0.1 mJ / cm 2 Excitation with an electron beam lower than ² has lower luminous efficiency than the copper activated zinc sulfide phosphor. Therefore, this green light emitting element can obtain light emission with higher luminance than a green light emitting element using a copper activated zinc sulfide phosphor, and realize light emission with a wide luminance from low luminance to high luminance. be able to. Here, the energy density per pulse is represented by the product of the acceleration voltage, current density and pulse width of the pulsed electron beam.

  Next, a field emission display device (FED) having the green light emitting element of the first embodiment will be described.

  FIG. 1 is a cross-sectional view showing the main configuration of an FED according to the second embodiment of the present invention. 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 formed corresponding to the pixels, and the light-emitting layer 4 made of a black conductive material is separated between these layers. It has a structure. The green light emitting phosphor layer is the green light emitting element of the first embodiment described above. The blue light-emitting phosphor layer and the red light-emitting phosphor layer are formed using a known blue light-emitting zinc sulfide phosphor and red light-emitting oxysulfide phosphor, respectively.

  The thickness of the green light-emitting phosphor layer that is the green light-emitting element of the first embodiment is desirably 1 to 10 μm, and more preferably 6 to 10 μm. The reason why the thickness of the green 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 green light emitting phosphor layer exceeds 10 μm, the light emission luminance is lowered and cannot be put to practical use. The thicknesses of the blue light-emitting phosphor layer and the red light-emitting phosphor layer are preferably the same as those of the green light-emitting phosphor layer so that no step is generated between the phosphor layers 3 of the respective colors.

  The green light-emitting phosphor layer, the blue 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. 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, and the surface of the rear plate 7 on which the electron-emitting devices 11 are formed is provided with wiring (not shown). 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 such an FED of the second embodiment, since the green light emitting phosphor layer is composed of the green light emitting element of the first embodiment, irradiation with a pulsed electron beam having an acceleration voltage of 5 to 15 kV is performed. The luminance and color purity of light emission due to the light is high, and good display characteristics can be obtained.

  In the FED of this embodiment, since the green light emitting element has a short afterglow time of less than 100 μs in excitation with a pulsed electron beam having an acceleration voltage of 5 to 15 kV, and the activator concentration is high, Even in the case of pulsed electron beam excitation in a high energy density region, since there is little loss of photoelectric conversion with respect to input energy, particularly excellent display characteristics are exhibited.

  Next, specific examples of the present invention will be described.

Example 1
As shown below, an Eu-activated strontium thiogallate phosphor (SrGa ₂ S ₄ : Eu) was produced. That is, a raw material containing a phosphor matrix (SrGa ₂ S ₄ ) and an element constituting the activator or a compound containing the element has a predetermined composition (SrGa ₂ S ₄ : Eu content 2 mol%). After weighing and mixing well, a phosphor crucible with an appropriate amount of sulfur and activated carbon added to the obtained phosphor raw material was filled in a quartz crucible and fired in a hydrogen sulfide atmosphere. The firing conditions were 800 ° C. × 60 minutes.

Thereafter, the obtained fired product was washed with water, dried, and further sieved to obtain an Eu-activated strontium thiogallate phosphor (SrGa ₂ S ₄ : Eu) having an average particle size of 3 μm.

  Next, a paste was prepared using the phosphor thus obtained, a coating layer was formed by screen printing, and then the resin in the paste was decomposed by baking to form a phosphor layer having a predetermined thickness. The thickness of the phosphor layer (the thickness of the coating layer before baking) was set to 6 μm, which is about twice the average particle diameter of the phosphor. Thereafter, an aluminum metal back layer was formed on the phosphor layer by a lacquer method to obtain a light emitting device.

Comparative Example Instead of Eu-activated strontium thiogallate phosphor, copper and aluminum-activated zinc sulfide phosphor (ZnS: Cu, Al) were used to form a light emitting device in the same manner as in the example.

Next, emission spectra of the light-emitting elements obtained in Example 1 and the comparative example were measured. The emission spectrum was measured by irradiating each light emitting element with a pulsed electron beam having an acceleration voltage of 10 kV and an energy density of 3 mJ / cm ² per pulse. The obtained emission spectrum is shown in FIG. Note that the emission intensity (standardized emission intensity) is a relative value with the peak intensity of the light emitting element of the comparative example being 100%.

  From the graph of FIG. 2, the light emitting device obtained in Example 1 exhibits green light emission having a light emission peak in the wavelength range of 525 to 550 nm, and the emission intensity at the peak wavelength is as high as that of the light emitting device of the comparative example. You can see that

  Moreover, when the afterglow time of each light emitting element was measured, the afterglow time of the light emitting element of Example 1 was 5 microseconds, and the afterglow time of the light emitting element of the comparative example was 20 microseconds. The afterglow time was defined as the time until the luminance after blocking the electron beam became 1/10 of the luminance immediately before blocking. Furthermore, a pulsed electron beam with an acceleration voltage of 10 kV was irradiated while changing the current value and the pulse width, and the emission luminance and emission chromaticity were examined using SR-3 manufactured by Topcon Corporation. The value of current flowing through the light emitting element was measured using an oscilloscope. The chromaticity of light emission was measured in a dark room where the chromaticity at the time of light emission was not affected from the outside.

  As a result of the measurement, the light emission chromaticity (x, y) of the light emitting device of Example 1 is (0.27, 0.68), and the light emission chromaticity (x, y) of the light emitting device of the comparative example is (0.28, 0.61), and it was found that the light-emitting element of Example 1 exhibited good green light emission.

  Furthermore, the light emission efficiency was calculated from the light emission characteristics (light emission luminance and light emission chromaticity) with respect to each energy density value by changing the current value and the pulse width. FIG. 3 shows the relationship between the obtained luminous efficiency and the energy density per pulse obtained from the current value and the pulse width.

From the graph of FIG. 3, in the light emitting device using the Eu-activated strontium thiogallate phosphor of Example 1, the copper and aluminum of the comparative example are in a high energy density region where the energy density per pulse is 5 mJ / cm ² or more. In a low energy density region having a high luminous efficiency of 1.5 times or more compared to a light emitting device using an activated zinc sulfide phosphor, and conversely, the energy density per pulse is lower than 0.1 mJ / cm ² , It can be seen that the luminous efficiency is lower than that of the copper-activated zinc sulfide phosphor. Therefore, in an FED that emits light by electron beam excitation in a high energy density region where the energy density per pulse is 5 mJ / cm ² or more, a light emitting element using Eu-activated strontium thiogallate phosphor is more activated by copper-activated sulfide. It can be seen that the emission efficiency of green light emission is superior to a light emitting element using a zinc phosphor.

  In addition, it can be seen that the light emitting element of Example 1 can realize light emission with a wide range of luminance from low luminance to high luminance by changing the energy density per pulse.

Example 2
Eu-activated strontium thiogallate phosphor (SrGa ₂ S ₄ : Eu) obtained in Example 1, a known blue light-emitting phosphor (ZnS: Ag, Al), and a red light-emitting phosphor (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 green light emitting device of the present invention, green light emission with high luminance and good color purity can be obtained when a pulsed electron beam with an acceleration voltage of 5 to 15 kV is irradiated. Therefore, by using such a green light emitting element, 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 the 2nd Embodiment of this invention. It is a graph which shows the emission spectrum of the light emitting element obtained in Example 1 and the comparative example of this invention. It is a graph showing the relationship between the luminous efficiency of the light emitting element obtained by Example 1 of this invention, and the comparative example, and the energy density per pulse.

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 (5)

A light-emitting element that is composed of a composite sulfide phosphor of two or more elements activated with divalent europium and emits green light when excited by irradiation with a pulsed electron beam having an acceleration voltage of 5 to 15 kV,
When the energy density per pulse of the pulsed electron beam is 5 mJ / cm ² or more, it has a light emission efficiency 1.5 times or more that of a light emitting device comprising a copper-activated zinc sulfide phosphor, and per pulse A green light-emitting element having lower luminous efficiency than a light-emitting element comprising a copper-activated zinc sulfide phosphor when excited by an electron beam having an energy density lower than 0.1 mJ / cm ² .   The green light-emitting element according to claim 1, wherein a peak of the intensity of an emission spectrum caused by the electron beam irradiation exists in a wavelength range of 525 to 550 nm.   The green light-emitting element according to claim 1, wherein an afterglow time of light emission by irradiation with the electron beam is less than 100 μs. 4. The green light-emitting element according to claim 1, wherein the europium-activated composite sulfide phosphor is a phosphor substantially represented by a chemical formula: SrGa ₂ S ₄ : Eu. 5. . 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 5 to 15 kV; A field emission display device comprising an electron source and an envelope for vacuum-sealing the phosphor layer;
5. A field emission display device, wherein the green light emitting phosphor layer includes the green light emitting element according to any one of claims 1 to 4.

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