JP2008140617A - Red light-emitting element and field emission display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a red light-emitting element with high luminance emitting light excited by pulsated electron beams with an accelerating voltage of 5 to 15 kV. <P>SOLUTION: The red light-emitting element consists of alkaline earth complex sulfide ((Mg, Ca)S:Eu) phosphor activated by bivalent Eu, emitting red light excited by pulsated electron beams with an accelerating voltage of 5 to 15 kV. The light-emitting element in question, when an energy density per pulse is 10 mJ/cm<SP>2</SP>, has a luminous efficiency higher than one with an Eu-activated Y-acid sulfide phosphor, and at excitation by electron beams with an energy density lower than 1 mJ/cm<SP>2</SP>per pulse, has a light-emitting efficiency lower than that equipped with the Eu-activated Y-acid sulfide phosphor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a red light emitting element and a field emission display device using the red light emitting element.

  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 an yttrium oxysulfide phosphor that 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 red 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 turn red. A light-emitting element that emits light, and has an emission efficiency higher than that of a light-emitting element comprising a europium-activated yttrium oxysulfide phosphor when the energy density per pulse of the pulsed electron beam is 10 mJ / cm ² ; Excitation with an electron beam having an energy density lower than 1 mJ / cm ² per pulse has a light emission efficiency lower than that of a light-emitting element including a europium-activated yttrium oxysulfide 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 red light-emitting phosphor layer is formed according to the present invention. A red light emitting element is included.

The present invention is a red light-emitting element comprising a europium-activated composite sulfide phosphor. When the energy density per pulse is 10 mJ / cm ² in irradiation with a pulsed electron beam having an acceleration voltage of 5 to 15 kV, It has higher luminous efficiency than a light emitting device including a europium activated yttrium oxysulfide phosphor. In addition, excitation with an electron beam having an energy density per pulse lower than 1 mJ / cm ² has lower luminous efficiency than a light emitting device comprising a europium activated yttrium oxysulfide phosphor. Therefore, compared with the conventional red light emitting element provided with the europium activated yttrium oxysulfide phosphor, light emission with a wide luminance from low luminance to high luminance can be realized. By using this red 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 device comprising an alkaline earth composite sulfide phosphor activated with divalent europium (Eu), and more specifically, a chemical formula: (Mg, Ca) S: A red light-emitting element mainly composed of an Eu-activated magnesium / calcium sulfide phosphor having a composition substantially represented by S: Eu. When the ratio of Mg and Ca is (Mg _x , Ca _1-x ) S, it can be synthesized in the range of 0 <x <1, but the range of 0 <x ≦ 0.7 is preferable. A more preferable range in which both chromaticity and chromaticity are satisfied is a range of 0.4 ≦ x ≦ 0.7. 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 red light whose emission spectrum has an intensity peak in a wavelength range of 640 to 680 nm.

  In the Eu-activated magnesium / calcium sulfide phosphor, Eu is an activator having an emission center and has a high transition probability, so that high luminous efficiency can be obtained. The trivalent Eu as the activator is contained in the range of 0.001 to 1.0 mol% with respect to magnesium / calcium sulfide ((Mg, Ca) S) which is the base of the phosphor. Is preferred. A more preferable Eu content is 0.01 to 0.5 mol%. If the Eu content is outside this range, the light emission luminance and light emission chromaticity decrease, which is not preferable.

  The Eu-activated magnesium / calcium sulfide 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 magnesium / calcium sulfide phosphor can be produced, for example, by the following method.

  That is, a phosphor raw material including an element constituting the phosphor base and an activator or a compound containing the element is weighed so as to have a desired composition ((Mg, Ca) S: Eu), and these are measured. Mix dry. Specifically, a predetermined amount of magnesium sulfide (MgS) and calcium sulfide (CaS) are mixed, and an appropriate amount of an activator (compound containing) is added to obtain a raw material for the phosphor. 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).

  The firing temperature is preferably in the range of 1000 to 1250 ° C. Although the firing time depends on the set firing temperature, it is preferably 60 to 600 minutes, and after firing, it is preferably cooled in the same atmosphere as firing. Thereafter, the obtained fired product is washed in a non-aqueous solution such as alcohol and dried, followed by sieving to remove coarse particles, if necessary, to thereby activate Eu-activated magnesium / calcium sulfide phosphor. ((Mg, Ca) S: Eu) can be obtained.

  A red light emitting device can be formed by using the Eu-activated magnesium / calcium sulfide phosphor thus obtained and forming a phosphor layer using a known printing method. In order to form a phosphor layer by a printing method, a phosphor paste is prepared by mixing an Eu-activated magnesium / calcium sulfide phosphor with a binder solution made of, for example, ethyl cellulose, and this phosphor paste is screen-printed or the like. It is applied on the substrate by the method. Since this Eu-activated magnesium / calcium sulfide phosphor is a highly hydrolyzable material, water must not be used in the preparation of the paste. Next, for example, baking is performed to decompose and remove the binder component by heating at a temperature of 500 ° C. for 1 hour.

The red light-emitting element having the Eu-activated magnesium / calcium sulfide phosphor layer thus formed is an element that emits red light when irradiated with a pulsed electron beam having an acceleration voltage of 5 to 15 kV, more preferably 7 to 13 kV. Luminous efficiency higher than that of a light emitting device including a trivalent Eu-activated yttrium oxysulfide (for example, Y ₂ O ₂ S: Eu) phosphor by excitation of an electron beam having an energy density of 10 mJ / cm ² per pulse. On the other hand, when excited by an electron beam whose energy density per pulse is lower than 1 mJ / cm ² , the energy density is lower than that of the light emitting device including the Eu-activated yttrium oxysulfide (Y ₂ O ₂ S: Eu) phosphor. It has luminous efficiency. Therefore, this red light-emitting element can obtain light emission with higher luminance than the red light-emitting element provided with the Eu-activated yttrium oxysulfide (Y ₂ O ₂ S: Eu) phosphor, and also has low luminance. Light emission with a wide range of brightness up to high brightness can be realized. Here, the energy density per pulse is represented by the product of the acceleration voltage and current density of the pulsed electron beam and the pulse width.

  Next, a field emission display device (FED) having the red 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 red light emitting phosphor layer is the red light emitting element of the first embodiment described above. The blue light-emitting phosphor layer and the green light-emitting phosphor layer are formed using a known blue light-emitting zinc sulfide phosphor and green light-emitting sulfide phosphor, respectively.

  The thickness of the red light emitting phosphor layer that is the red 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 red light emitting phosphor layer is limited to 1 μm or more is that it is difficult to form a phosphor layer having a thickness of less than 1 μm and phosphor particles uniformly arranged. On the other hand, if the thickness of the red 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 green light-emitting phosphor layer are preferably the same as the red 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 red light emitting phosphor layer is constituted by the red light emitting element of the first embodiment described above, 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, the red light emitting element has a short afterglow time of less than 100 μs and high activator concentration when excited by a pulsed electron beam having an acceleration voltage of 5 to 15 kV. Even in pulsed electron beam excitation in a high energy density region, there is little loss of photoelectric conversion with respect to input energy. Therefore, particularly excellent display characteristics are exhibited.

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

Example 1
As shown below, an Eu-activated magnesium / calcium sulfide phosphor ((Mg _0.6 , Ca _0.4 ) S: Eu) was produced. That is, a raw material including an element constituting a phosphor base material and an activator or a compound containing the element is converted into a predetermined composition ((Mg _x , Ca _1-x ) S: Eu, x = 0.6, and (Eu content ratio 0.1 mol%) and weighed thoroughly, and after filling the obtained phosphor material with a suitable amount of sulfur and activated carbon into a quartz crucible, Firing was performed in a hydrogen sulfide atmosphere. The firing conditions were 1200 ° C. × 240 minutes.

  Thereafter, the obtained fired product was washed with water, dried, and further sieved to obtain an Eu-activated magnesium / calcium sulfide phosphor ((Mg, Ca) S: E) having an average particle size of 7 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 was 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 A luminescent element was formed in the same manner as in Example 1 using yttrium oxysulfide (Y ₂ O ₂ S: Eu) phosphor instead of Eu-activated magnesium / calcium sulfide phosphor.

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 1 mJ / cm ² per pulse. FIG. 2 shows an emission spectrum of the light emitting element of Example 1, and FIG. 3 shows an emission spectrum of the light emitting element of the comparative example. The emission intensity is expressed by standardizing the maximum value of each emission spectrum as 100%.

  2 and 3, it can be seen that the light-emitting element obtained in Example 1 exhibits red light emission having a light emission peak in the wavelength range of 640 to 680 nm.

  Moreover, when the afterglow time of each light emitting element was measured, the afterglow time of the light emitting element of Example 1 was 8 microseconds, and the afterglow time of the light emitting element of the comparative example was 10 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 element of Example 1 is (0.67, 0.33), and the light emission chromaticity (x, y) of the light emitting element of the comparative example is (0.64, 4). 0.35), and it was found that the light-emitting element of Example 1 exhibited good red 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. 4 shows the relationship between the obtained light emission efficiency and the energy density per pulse obtained from the current value and the pulse width.

From the graph of FIG. 4, in the light emitting device using the Eu-activated magnesium / calcium sulfide phosphor of Example 1, the yttrium acid of the comparative example is in a high energy density region where the energy density per pulse is 10 mJ / cm ^2. Compared with a light emitting device using a sulfide (Y ₂ O ₂ S: Eu) phosphor, it has higher luminous efficiency, and conversely, in a low energy density region where the energy density per pulse is lower than 1 mJ / cm ² , it is yttrium. It can be seen that the phosphor has lower luminous efficiency than the light emitting device using the oxysulfide (Y ₂ O ₂ S: Eu) 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 10 mJ / cm ² , a light emitting device using Eu-activated magnesium / calcium sulfide phosphor is more yttrium oxysulfide. It can be seen that the luminous efficiency of red light emission is superior to the light emitting element using the phosphor (Y ₂ O ₂ S: Eu).

  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
The Eu-activated magnesium / calcium sulfide phosphor ((Mg, Ca) S: Eu) obtained in Example 1, a known blue-emitting phosphor (ZnS: Ag, Al), and a green-emitting phosphor (ZnS: Cu, Al) were 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 of this invention. It is a graph which shows the emission spectrum of the light emitting element obtained by 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 by divalent europium and emits red 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 10 mJ / cm ² , the pulsed electron beam has higher light emission efficiency than the light emitting device including the europium activated yttrium oxysulfide phosphor, and 1 mJ / cm ² per pulse. A red light emitting device having lower luminous efficiency than a light emitting device comprising a europium activated yttrium oxysulfide phosphor when excited by a lower energy density electron beam.   2. The red light emitting device according to claim 1, wherein a peak of an emission spectrum intensity caused by the electron beam irradiation exists in a wavelength range of 640 to 680 nm.   3. The red light emitting device according to claim 1, wherein an afterglow time of light emission by irradiation with the electron beam is less than 100 μs.   4. The red light emitting device according to claim 1, wherein the europium-activated composite sulfide phosphor is an alkaline earth metal composite sulfide phosphor. 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;
A field emission display device, wherein the red light emitting phosphor layer includes the red light emitting element according to any one of claims 1 to 4.

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