JP2008179748A - Red light emitting device and field emission display device - Google Patents

Abstract

Provided is a red light-emitting element having high luminance that emits light when excited by an electron beam having an acceleration voltage of 15 kV or less and an irradiation time of 0.1 to 20 μs.
A red light emitting device of the present invention is mainly composed of a yttrium oxysulfide phosphor activated with trivalent Eu, and is excited by an electron beam having an acceleration voltage of 15 kV or less and an irradiation time of 0.1 to 20 μs. The light-emitting element emits red light, and is characterized in that the content ratio of elements other than the elements constituting the phosphor matrix and the activator existing on the phosphor surface is less than 1% by weight.
[Selection] Figure 1

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 the CRT, and the electron beam irradiation time is actually as long as several μs. (For example, see Patent Document 1)

  For this reason, the density of energy per unit area irradiated to the phosphor as a whole is increased, and as a result, the temperature of the phosphor layer is increased as compared with the CRT.

In general, it is known that the light emission intensity (light emission efficiency) of a phosphor changes depending on the ambient temperature. In particular, red phosphors whose base crystal is yttrium oxysulfide, which is being studied for use in FEDs, such as europium-activated yttrium oxysulfide (Y ₂ O ₂ S: Eu ⁺³ ), have a luminous efficiency that increases with increasing temperature. The decrease, so-called temperature quenching is large. Therefore, in the FED in which the temperature rise of the phosphor screen is larger than that of the CRT, the red emission luminance tends to be insufficient.

Further, in the phosphor for FED, surface treatment is performed on the phosphor particles in consideration of the process of forming the phosphor screen. In order to prevent luminance degradation, the blue phosphor (for example, ZnS: Ag, Al) and the green phosphor (for example, ZnS: Cu, Al) are surface-treated with phosphate, so that yttrium is a red phosphor. Since oxysulfides have no problem of luminance life, silica-based surface treatment agents are used. Therefore, there has been a problem that under the excitation by a high energy density electron beam, the surface treatment agent is charged up and the temperature rises, and temperature quenching is more likely to occur.
JP 2002-226847 A

  The present invention has been made in order to solve the above-mentioned problems. Charge-up caused by surface treatment (the phosphor surface is negatively charged by an electron beam not involved in light emission to inhibit the entry of the electron beam) or An object of the present invention is to provide a light-emitting element with reduced temperature rise and high luminous efficiency. 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 mainly composed of yttrium oxysulfide phosphor activated with trivalent europium, and is excited by an electron beam with an acceleration voltage of 15 kV or less and an irradiation time of 0.1 to 20 μs to become red. It is a light emitting element which emits light, and is characterized in that the content ratio of elements other than the elements constituting the phosphor matrix and the activator existing on the phosphor surface is less than 1% by weight.

  The field emission display device of 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 acceleration voltage of 15 kV or less and an irradiation time of 0 on the phosphor layer. A field emission display device comprising: an electron source that emits light by irradiating with an electron beam of 1 to 20 μs; and an envelope that vacuum seals the electron source and the phosphor layer, and the red light emitting phosphor The layer includes the above-described red light emitting device of the present invention.

  The present invention is a red light-emitting element mainly composed of europium-activated yttrium oxysulfide phosphor, the phosphor surface is not treated with a treatment agent such as silica, and the element is substantially derived from the surface treatment. Is not present on the phosphor surface. That is, the content ratio of elements other than yttrium (Y), oxygen (O), sulfur (S), and activator element (Eu), which are host constituent elements existing on the phosphor surface, is 1 with respect to the entire phosphor. It is less than wt%. Therefore, the temperature rise of the light emitting element is further reduced, and the decrease in light emission efficiency (temperature quenching) accompanying the temperature rise is suppressed. Therefore, the light emission efficiency when excited by an electron beam with an acceleration voltage of 15 kV or less and an irradiation time of 0.1 to 20 μs is improved as compared with the conventional red light emitting device, and has high luminance, color purity, and long life. Red light emission 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 red light emitting device mainly composed of europium (Eu) activated yttrium oxysulfide phosphor having a composition substantially represented by the chemical formula: Y ₂ O ₂ S: Eu It is. 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 an irradiation time of 0.1 to 20 μs, and emits red light.

  In the Eu-activated yttrium oxysulfide phosphor, Eu is an activator that forms a luminescent center and has a high transition probability, so that high luminous efficiency can be obtained. The trivalent Eu, which is an activator, is preferably contained in a range of 4 to 7% by weight with respect to yttrium (Y) constituting the base of the phosphor. A more preferable Eu content is 6 to 7% by weight with respect to Y. If the Eu content is outside this range, the light emission luminance and light emission chromaticity decrease, which is not preferable. Thus, by increasing the content ratio of Eu as an activator, loss of photoelectric conversion with respect to input energy can be reduced even in pulsed electron beam excitation in a high energy density region.

  In addition, this phosphor has a content ratio of elements other than the matrix constituent elements (Y, O, S) and activator elements (Eu) existing on the surface (for example, silicon used for surface treatment). Is less than 1% by weight. That is, the surface treatment of the phosphor usually performed is omitted, and elements other than the matrix constituent elements (Y, O, S) and the activator element (Eu) are 1% by weight or more on the particle surface of the phosphor. Is configured not to exist.

  The Eu-activated yttrium oxysulfide phosphor thus configured can be manufactured, for example, by the method shown below.

That is, yttrium oxide (Y ₂ O ₃ ) and europium oxide (Eu ₂ O ₃ ) are weighed so as to have a desired composition and mixed. This mixture and an appropriate amount of sulfur powder are mixed well and then filled into a heat-resistant container such as an alumina crucible or a quartz crucible. This is baked by heating at 1180 ° C. for 4 hours in an air atmosphere.

  Next, the obtained fired product is washed with water and dried, and then subjected to sieving to remove coarse particles as necessary. Thus, an Eu-activated yttrium oxysulfide phosphor is obtained without surface treatment.

  By using the obtained Eu-activated yttrium oxysulfide phosphor and forming a phosphor layer using a known printing method, a red light emitting device can be formed. In order to form a phosphor layer by a printing method, an Eu-activated yttrium oxysulfide phosphor is mixed with a binder solution made of, for example, polyvinyl alcohol, n-butyl alcohol, ethylene glycol, water, etc., and a binder solution made of ethyl cellulose. To prepare a phosphor paste, and this phosphor paste is applied onto 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.

  The red light emitting device having the Eu-activated yttrium oxysulfide phosphor layer thus formed is irradiated with a pulsed electron beam having an acceleration voltage of 5 to 15 kV, more preferably 7 to 13 kV and an irradiation time of 0.1 to 20 μs. It is an element that emits red light. The Eu-activated yttrium oxysulfide phosphor is not subjected to a surface treatment with a processing agent such as silica, and the element resulting from the surface treatment does not substantially exist on the phosphor surface. That is, the content ratio of elements other than yttrium (Y), oxygen (O), sulfur (S), and activator element (Eu), which are host constituent elements existing on the surface of Eu-activated yttrium oxysulfide phosphor, Since it is less than 1% by weight, charge-up and temperature rise are further reduced, and red light emission with high luminous efficiency, high luminance and long life is realized.

  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 composed of the red light emitting element of the first embodiment described above, the acceleration voltage is 5 to 15 kV and the irradiation time is 0.1. Irradiation with a pulsed electron beam of ˜20 μs provides good display characteristics with high brightness and high color purity.

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

Example 1
Using 1000 g of yttrium oxide (Y ₂ O ₃ ), 6.8 g of europium oxide (Eu ₂ O ₃ ), and 1200 g of sulfur powder, heating and firing were performed at 1180 ° C. for 240 minutes by a conventional method. Subsequently, the obtained fired product was washed with water, dried and further sieved to obtain an Eu-activated yttrium oxysulfide phosphor having an average particle size of 5 μm. In Example 1, no surface treatment was performed on the obtained phosphor particles. In the comparative example, the obtained phosphor particles were subjected to surface treatment using colloidal silica. That is, colloidal silica (particle size 20 to 150 nm) was added to the liquid in which the phosphor particles were suspended in water at a ratio of 1 to 2% by weight, followed by filtration and drying.

  For the Eu-activated yttrium oxysulfide phosphors obtained in Example 1 and the comparative example, the silicon content present on the surface was measured by X-ray photoelectron spectroscopy (XPS). While it is almost 0 (less than 1% by weight), it is 10% by weight in the phosphor of the comparative example, and 1% by weight of elements other than the matrix and the activator element resulting from the surface treatment on the surface of the phosphor. I found out that it exists.

  Next, a paste was prepared using the Eu-activated yttrium oxysulfide phosphor obtained in Example 1 and the comparative example, and after forming a coating layer by screen printing, the resin in the paste was decomposed by baking. A phosphor layer having a predetermined thickness was formed. The thickness of the phosphor layer was 10 μm. Thereafter, an aluminum metal back layer was formed on the phosphor layer by a lacquer method to obtain a light emitting device.

Next, for the light-emitting elements obtained in Example 1 and the comparative example, the light emission luminance and the luminance linearity γ with respect to the input current density were examined. The light emission luminance was measured by irradiating each light emitting element with an electron beam having an acceleration voltage of 10 kV and a current density of 15 mA / cm ² . The light emission luminance was obtained as a relative value when the luminance of the light emitting element of the comparative example was 100. γ was calculated from the result of measuring the luminance at a current density of 0 to 15 mA / cm ² . These measurement results are shown in Table 1.

  As is clear from Table 1, the light emitting device obtained in Example 1 has higher emission luminance when irradiated with an electron beam having a low acceleration voltage (15 kV or less) and a high current density than that of the comparative example. In addition, the value of γ is large and it has good light emission characteristics.

Example 2
The Eu-activated yttrium oxysulfide phosphor (Y ₂ O ₂ S: Eu) obtained in Example 1 was used as the red-emitting phosphor, and the silver- and aluminum-activated zinc sulfide phosphor (ZnS) was used as the blue-emitting phosphor. : Ag, Al) was used as the green light-emitting phosphor, and copper and aluminum activated zinc sulfide phosphors (ZnS: Cu, Al) were respectively 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 red light emitting device of the present invention, when an electron beam with an acceleration voltage of 15 kV or less and an irradiation time of 0.1 to 20 μs is irradiated, it has high brightness, good color purity, low temperature quenching and long life. Red light emission can be obtained. By using such a red light emitting element, a thin flat display device having high luminance and excellent display characteristics can be realized.

It is sectional drawing which shows schematically FED which is the 2nd 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 (3)

A light-emitting element mainly composed of yttrium oxysulfide phosphor activated with trivalent europium, which emits red light when excited by an electron beam with an acceleration voltage of 15 kV or less and an irradiation time of 0.1 to 20 μs,
A red light-emitting element, wherein a content ratio of an element other than an element constituting the matrix and an activator of the phosphor existing on the phosphor surface is less than 1% by weight.   2. The red light emitting device according to claim 1, wherein the activation amount of the europium is 4 to 7% by weight with respect to yttrium constituting the base of the phosphor. 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 15 kV or less and an irradiation time of 0.1 to 20 μs are irradiated to the phosphor layer. 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;
3. The field emission display device according to claim 1, wherein the red light emitting phosphor layer includes the red light emitting element according to claim 1.

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