JP3417831B2 - Manufacturing method of phosphor material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphor material, a method for producing the phosphor material, and a display device such as a phosphor display tube and a field emission display. 2. Description of the Related Art In an electron-beam-excited display device, when the phosphor screen is charged up, light emission is reduced. Therefore, it is necessary to release accumulated charges. The cathode ray tube has the back surface of the fluorescent screen (the surface facing the electron gun) to release the charge from the fluorescent screen.
Is provided with a conductive film made of, for example, aluminum. In a cathode ray tube, the electron beam is 10 kV or more, usually about 3 kV.
Since the electron beam is accelerated at a high speed by the anode voltage of 0 kV, the electron beam penetrates the conductive film and reaches the phosphor screen, so that the phosphor can be excited. However, a fluorescent display tube or a field emission display excites a phosphor with a low-speed electron beam accelerated by an anode voltage of 1 kV or less. In such a low-speed electron beam excited display, when a conductive film is formed on the surface of the fluorescent screen facing the cathode, the electron beam has no ability to penetrate the conductive film. As a result, the phosphor cannot be sufficiently excited. Therefore, the formation of a conductive film cannot be applied to a slow electron beam excitation display device. In order to solve this problem, a technique has been proposed in which a phosphor used in a low-speed electron beam excitation display device has conductivity to prevent charge-up of a phosphor screen. As one of them, development of a phosphor showing conductivity has been attempted. For example, blue-green light emitting ZnO: Zn exhibits conductivity. However, a conductive phosphor exhibiting a sufficient altitude and emitting a color other than blue-green has not been developed. For this reason, a color display cannot be manufactured using only the conductive phosphor. Further, use of a phosphor material in which a phosphor and a conductive substance are mixed has been studied. For example, there is an example in which a phosphor and a conductive substance such as In ₂ O ₃ are mixed. However, in such a phosphor material, the luminous efficiency decreases because the ratio of the phosphor decreases. [0005] Extended Abstracts of the 2nd Inte
rnational Conference on the Science and Technology
of Display Phoshors, Nov. 18 (1996), p. 319, discloses a ZnS: Ag, Cl phosphor material whose surface is coated with a conductive layer made of In ₂ O ₃ by a zolgel method. However, the phosphor particles used in this method are:
It is considered to have a particle shape close to a polyhedron synthesized by a normal flux method or the like. Therefore,
Even when the In ₂ O ₃ conductive layer is formed on the surface of the phosphor particles, the particle shape is maintained close to a polyhedron. If a phosphor layer is formed using a phosphor material having such a shape, packing of particles is poor and it is difficult to form a dense phosphor layer, which is disadvantageous in terms of luminance. In addition, since a high electric field tends to be applied to the projections due to unevenness on the phosphor screen, it is difficult to obtain uniform light emission. SUMMARY OF THE INVENTION An object of the present invention is to provide a phosphor material which can effectively prevent charge-up of a phosphor screen when applied to a slow electron beam excitation display device. It is in. Another object of the present invention is to provide a method for easily producing such a phosphor material. Still another object of the present invention is to provide a display device having a tendency layer made of the above-mentioned phosphor material and exhibiting good display characteristics. [0008] The phosphor material of the present invention comprises:
It has phosphor particles and a conductive layer formed on the surface of the phosphor particles, and the ratio of the minor axis to the major axis is 1.5 or less. The method for producing a phosphor material of the present invention comprises the steps of: generating a thermal plasma; supplying a conductive material into the thermal plasma to vaporize; supplying phosphor particles into the thermal plasma; And a step of cooling the phosphor particles to which the conductive material has adhered. A display device according to the present invention has a phosphor screen having an anode and a phosphor layer formed on the anode, and a cathode for emitting an electron beam for exciting the phosphor layer. The phosphor material is composed of phosphor particles and a conductive layer formed on the surface of the phosphor particles, and the ratio of the minor axis to the major axis is 1.5 or less. DETAILED DESCRIPTION OF THE INVENTION A phosphor material of the present invention has phosphor particles and a conductive layer formed on the surface of the phosphor particles, and has a ratio of a minor axis to a major axis of 1.5. It is as follows. This phosphor material is manufactured by a thermal plasma method, as described later in detail. In the present invention, conventionally known phosphors can be used as the phosphor particles which are the core of the phosphor material. It is preferable that the phosphor emits light with high efficiency by electron beam excitation. Further, when the phosphor is exposed to thermal plasma at several thousand degrees Celsius, at least the surface is dissolved without sublimation, vaporization or decomposition, but it is preferable that the phosphor does not easily react with the conductive material. Suitable phosphors include, specifically, rare earth oxide phosphors such as Y ₂ O ₃ : Eu; rare earth oxysulfide phosphors such as Gd ₂ O ₂ S: Pr and Y ₂ O ₂ S: T
m; Garnet-based phosphor such as Y ₃ Al ₅ O ₁₂ : T
b: Rare earth siliceous phosphor such as Y ₂ SiO ₅ : C
e. The phosphor particles have an average radius of 0.1 to 5 μm.
m is preferable. The average particle size can be determined by a Blaine method or a statistical method based on observation with an electron microscope. Phosphor particles having an average particle size of less than 0.1 μm have poor crystallinity, and thus are likely to reduce luminous efficiency.
On the other hand, when the phosphor layer is formed using phosphor particles having an average particle size exceeding 5 μm, irregularities are likely to be formed on the phosphor screen. Therefore, when the electron beam source (cathode) and the phosphor screen are close to each other as in a field emission display, the unevenness of the electric field intensity becomes large, so that light emission unevenness may occur. The ratio of the major axis to the minor axis of the phosphor particles is 1.5.
The following spherical shape is desirable. When the phosphor particles are spherical, the specific surface area of the phosphor particles is small, so that light scattering on the electric field surface between the phosphor particles and the conductive layer is reduced. As a result, the light emission can be efficiently extracted to the outside of the phosphor layer, and the apparent light emission efficiency increases. Also, if the phosphor particles are spherical and there are no extreme irregularities on the surface,
It is possible to suppress the occurrence of discharge and bright spots due to electric field concentration. In the present invention, the material of the conductive layer formed on the surface of the phosphor particles is not particularly limited, and may be indium oxide, indium tin oxide, tin oxide, zinc oxide, zinc chalcogenide, gallium nitride, indium nitride. And an inorganic material such as CdTe. The conductive material desirably has a high transmittance to an electron beam that excites the phosphor, and the average atomic weight of the constituent elements of the conductive wire material is preferably 70 or less. The electrical resistivity of the conductive layer is 10 ⁴ Ωcm or less,
Preferably, the resistance is not more than 10 ² Ωcm, and the resistance does not need to be extremely low. The conductive material preferably vaporizes when exposed to thermal plasma at several thousand degrees Celsius. This is because a uniform and thin conductive layer is formed on the surfaces of the phosphor particles by the thermal plasma method, and as a result, the above-described ratio between the minor axis and the major axis of the phosphor particles is preferably maintained. The thickness of the conductive layer on the surface of the phosphor particles is preferably not more than 10% of the particle diameter of the phosphor particles. If the thickness of the conductive layer exceeds 10% of the particle size of the phosphor particles, the absorption of electron beams may increase and the luminous efficiency may decrease. The thickness of the conductive layer is preferably 5 nm or more. This is because if the thickness of the conductive layer is less than 5 nm, the electric resistance of the conductive layer may increase, and the conductive layer may not function as a conductive layer. The phosphor material in which the uniform and thin conductive layer is formed on the surface of the phosphor particles as described above is a sphere having a ratio of the minor axis to the major axis of 1.5 or less, and is excited by a slow electron beam. Even in this case, charges can be effectively released through the conductive layer on the surface. In other words, the phosphor screen is composed of a large number of phosphor material particles, and if the conductive layers on the surface of the phosphor material are in contact with each other, the entire phosphor screen can be electrically connected,
The amount of conductive material can be reduced as much as possible. Therefore, it is possible to suppress a decrease in luminous efficiency due to charge-up while minimizing the absorption of electron beams by the conductive layer. Further, since the phosphor particles are coated with the inorganic material, an effect of suppressing the chemical deterioration of the phosphor particles can be expected. In the method of the present invention, a conductive layer is formed on the surface of the phosphor particles using thermal plasma. In the thermal plasma method, at least the surface of the phosphor particles is melted while the raw material particles of the phosphor are supplied and suspended in the thermal plasma set at a temperature equal to or higher than the melting point of the phosphor, and the phosphor particles fall. This is a method of cooling when exiting from thermal plasma. By such a method, spherical phosphor particles can be obtained. According to the present invention, in a state in which a conductive material is supplied into a thermal plasma and vaporized, the phosphor particles are supplied into the thermal plasma to dissolve the surface of the phosphor particles and to adhere to the surface of the phosphor particles. After depositing the conductive material, it is cooled.
By such a method, spherical phosphor particles having a conductive layer formed on the surface can be obtained. For producing the phosphor material of the present invention, for example, a high-frequency induction type thermal plasma apparatus shown in FIG. 1 is used. As shown in FIG. 1, a gas supply port 21 for supplying a plasma gas, for example, argon, is provided at an upper portion of the thermal plasma chamber 20, and the plasma gas flows downward from above. A cylinder 22 is provided below the gas supply port 21, and a high-frequency coil 23 is wound therearound. The plasma gas is supplied and the high frequency coil 23
, A plasma frame 24 is generated. A conductive material supply nozzle 25 and a phosphor particle supply nozzle 26 are provided at positions where the conductive material and the phosphor particles can be supplied into the generated plasma frame 24. First, a plasma gas is supplied into the chamber 20 and a high-frequency coil 23 is energized to generate a plasma frame 24. A conductive material is supplied and vaporized together with a carrier gas (for example, argon) into the generated plasma frame 24. Thereafter, a carrier gas (for example, argon) is supplied into the plasma frame 24.
At the same time, the raw material fluorescent particles are supplied and floated in the plasma frame 24. While suspended in the plasma frame 24, at least the surface of the phosphor particles is melted by the heat of the plasma and becomes spherical due to surface tension. Further, the vaporized conductive material adheres to the surface of the spherical phosphor particles. The spherical phosphor particles are cooled while falling from the plasma frame 24 and become spherical phosphor particles having a conductive layer formed on the surface. The obtained phosphor particles are collected by a collector such as a cyclone (not shown). By using the thermal plasma method as described above, a spherical phosphor material having a uniform and thin conductive layer formed on the surface can be manufactured in one step. The raw material phosphor particles used in this method are composed of the same base and activator as the target phosphor particles, but may have a different activator concentration from the target phosphor particles. Also,
When the base is a mixed crystal, the ratio of the mixed crystal of the raw material phosphor particles may be different from that of the target phosphor particles. It is effective to heat-treat the phosphor material obtained by the thermal plasma method at 800 to 1600 ° C. in order to improve the luminous efficiency. In the display device to which the present invention is applied, an anode having a phosphor layer and a cathode are provided to face each other, and when a voltage of 1 kV or less is applied between the anode and the cathode, the phosphor is emitted by the slow electrons emitted from the cathode. The display is performed by being excited and emitting light at this time. Such display devices include field emission displays and fluorescent display tubes. In the display device of the present invention, as described above, the phosphor material constituting the phosphor layer is composed of the phosphor particles and the conductive layer formed on the surface of the phosphor particles, and the ratio of the minor axis to the major axis is 1. 5
The following are used: A field emission display will be described as a specific example of the display device according to the present invention. FIGS. 2A and 2B show a main part of the field emission display. As shown in FIG. 2A, on the surface of the glass substrate 1, a phosphor screen composed of an anode 2 composed of a striped conductive layer and a phosphor layer 3 is formed. The phosphor layer 3 is formed by applying a phosphor material having a conductive layer formed on the surface of phosphor particles by an electrophoresis method, a slurry coating method, a sedimentation method, or the like. The thickness of the phosphor layer 3 is set to about 1 to 5 times the particle diameter of the phosphor material. On the other hand, on the opposing glass substrate 8, a cathode-side stripe-shaped semiconductor pattern 7 extending in a direction orthogonal to the anode 2 is formed. FIG.
FIG. 2B is an enlarged view of a portion on the cathode side in FIG. As shown in FIG. 2B, an insulating layer 5 that separates many cathodes 6 and individual cathodes 6 is formed at a position on the conductive pattern 7 that faces the anodes 2. The cathode 6 is a so-called Sp
It is an indt-type refrigeration electrode, for example, Mo is formed in a conical shape. On the insulating layer 5, a gate electrode 4 provided with a number of holes corresponding to the cathode 6 is formed. These members form a regular cathode array.
The cathode array and the phosphor screen face each other with a distance of 200 μm to 5 mm, and are vacuum-sealed. A voltage is applied to the cathode 6 so that the anode 2 has a positive potential of 1 kV or less, and a positive bias voltage for causing the gate electrode 4 to emit a field is applied.
As a result, electrons are emitted from the cathode 6, accelerated to reach the phosphor screen, and excite the phosphor. The excited phosphor is emitted and visible through anode 2 and glass substrate 1. Therefore, the two conductive patterns of the anode and the conductive pattern 7 on the cathode side are formed so as to be orthogonal to each other.
Accordingly, by applying the above-described voltage pulse to each electrode corresponding to a desired pixel, the pixel can emit light. By scanning each conductive pattern and performing this operation, a desired display can be obtained. Furthermore, if a pattern of phosphor layers emitting red, green and blue light is formed as the phosphor layer 3 formed on the anode 2, color display is possible. The glass substrate 1 needs to have high visible light transmittance in order to transmit light emitted when the phosphor is excited. The anode 2 is formed of a transparent conductive film such as ITO so as to transmit light emitted from the phosphor. The counter substrate is not limited to glass, and any material that can provide the required strength can be used. In the display device according to the present invention, since the phosphor layer is formed of a spherical phosphor material comprising phosphor particles having a conductive layer on the surface, it is possible to suppress a decrease in luminous efficiency due to charge-up. . Embodiments of the present invention will be described below. Example 1 Using the high-frequency induction type thermal plasma apparatus shown in FIG.
A phosphor material was manufactured as follows. Zinc oxide (ZnO) powder was used as a conductive material. Y as raw material phosphor
₂ O ₃ : Eu powder was used. This Y ₂ O ₃ : Eu powder had an average particle size of 0.5 μm as measured by the Blaine method. An argon gas at a flow rate of 10 L / min was supplied from the gas supply port 21 and flowed downward from above. The high frequency coil 23 surrounding this argon gas flow has a frequency of MHz,
A high-frequency power of 15 kW was applied to form a plasma frame 24. With argon gas at a flow rate of 20 L / min, Z
The nO powder was supplied into the plasma frame 24 from the upper supply nozzle 25 at a rate of 2 g / min, and was vaporized. Then, together with argon gas at a flow rate of 30 L / min, Y ₂ O
₃ : The Eu powder was supplied into the plasma frame 24 from the lower supply nozzle 26 at a supply rate of 5 g / min. After continuing this process for 30 minutes, the phosphor powder collected in a cyclone (not shown) provided downstream of the thermal plasma chamber was collected. When the average particle size of the obtained phosphor material was measured by the Blaine method, it was 0.8 μm. The ratio of major axis / minor axis was about 1.1. When the phosphor material was sliced and observed with a transmission electron microscope, the conductive layer on the surface was found to be about 50n.
m had a substantially uniform thickness. Using the obtained phosphor material, a field emission display was manufactured as follows.
A transparent conductive layer made of ITO was coated on a 2.5 cm square glass substrate. This glass substrate was placed on the bottom of the container. A dispersion obtained by dispersing a phosphor material in ethanol is put in a container, and the phosphor material is settled on a glass substrate.
The phosphor layer was formed at a coating amount of 5 mg / cm2. on the other hand,
A counter substrate as shown in FIG. 2B, on which a Spindt type cold cathode array made of Mo having a height of about 1 μm was formed. A field emission display (Example 1) was produced by opposing both substrates at a distance of 300 μm and sealing them by vacuum. For comparison, a phosphor powder as a raw material was used,
A field emission display (Comparative Example 1) was produced in the same manner as described above. In each of the displays of Example 1 and Comparative Example 1, +450 V was applied to the anode with respect to the cathode.
, Red light emission was observed. However, in Comparative Example 1, there was unevenness in luminance, and spots that did not emit light were observed. Further, a portion where the luminance fluctuated with time was observed. On the other hand, in Example 1, no luminance unevenness was observed, and light emission was stable. Furthermore, when the average luminance of the entire phosphor screen of both displays was compared, Example 1 was about 20 times that of Comparative Example 1. Example 2 Indium oxide (In ₂ O ₃ ) powder was supplied at a supply rate of 3 g / min, and tin oxide (SnO ₂ ) powder was supplied at a supply rate of 0.3 g / min with an argon gas flow rate of 20 L / min. The gas was supplied from the upper supply nozzle 25 into the plasma frame 24 and vaporized. Further, Y ₂ O ₂ S: Tm powder having an average particle size of 3.2 μm was mixed with argon gas at a flow rate of 30 L / min.
The gas was supplied from the lower supply nozzle 26 into the plasma frame 24 at a supply speed of g / min. Except for this, the phosphor material was manufactured in the same manner as in Example 1. The average particle size of the obtained phosphor material is 3.5 μm.
m. The surface conductive layer had a substantially uniform thickness of about 30 nm. 3.0 mg using the obtained phosphor material
Example 1 except that the phosphor layer was formed at a coating amount of / cm ^2.
A field emission display (Example 2) was produced in the same manner as in Example 1. For comparison, a raw material phosphor powder was used,
A field emission display (Comparative Example 2) was produced in the same manner as described above. In each of the displays of Example 2 and Comparative Example 2, +450 was applied to the anode with respect to the cathode.
When a voltage of V was applied, blue light emission was observed.
However, in Comparative Example 2, brightness unevenness was observed with the naked eye, and spots that did not emit light were observed. Further, a portion where the luminance fluctuated with time was observed. On the other hand, in Example 2, no remarkable luminance unevenness was recognized, and light emission was stable. Further, when the average heights of the entire phosphor screens of both displays were compared, Example 2 was about eight times as large as Comparative Example 2. Example 3 15 vol% N ₂ -85 vol% A at a flow rate of 20 L / min
g gallium nitride (GaN) powder along with the mixed gas
The gas was supplied from the upper supply nozzle 25 into the plasma frame 24 at a supply rate of g / min to be vaporized. In addition, the flow rate 30
With an argon gas of L / min, a Y ₃ Al ₅ O ₁₂ : Tb powder having an average particle diameter of 3.7 μm was supplied at a feed rate of 10 g / min.
It was supplied into the plasma frame 24 from the lower supply nozzle 26. Except for this, the phosphor material was manufactured in the same manner as in Example 1. The average particle size of the obtained phosphor material is 6.2 μm.
m. The surface conductive layer had a substantially uniform thickness of about 80 nm. Using the obtained phosphor material, 5.0 m
A field emission display (Example 3) was produced in the same manner as in Example 1 except that the phosphor layer was formed at an application amount of g / cm ² . For comparison, a phosphor powder as a raw material was used,
A field emission display (Comparative Example 3) was produced in the same manner as described above. In each of the displays of Example 3 and Comparative Example 3, +450 was applied to the anode with respect to the cathode.
When a voltage of V was applied, green light emission was observed.
However, in Comparative Example 3, luminance unevenness was observed with the naked eye, and spots that did not emit light were observed. Further, a portion where the luminance fluctuated with time was observed. On the other hand, in Example 3, no remarkable luminance unevenness was recognized, and light emission was stable. Furthermore, when the average luminance of the entire phosphor screen of both displays was compared, the average luminance of Example 3 was about 30 times that of Comparative Example 3. Examples 4 to 6 Phosphor materials were produced in the same manner as in Example 1 using phosphor particles and conductive materials shown in Table 1 below. The particle diameter of the obtained phosphor material and the thickness of the conductive layer are shown. Using the obtained phosphor material, a phosphor layer was formed with a predetermined coating amount to produce a field emission display.
Then, the average luminance of the entire phosphor screen of the display was examined. The results are summarized in Table 1. Note that L / L ₀ in Table 1 is the luminance L of a display manufactured using the phosphor material of the present invention composed of the phosphor particles having a conductive layer formed on the surface, and the L / L ₀ manufactured using the raw material phosphor powder. is the ratio between the luminance L ₀ of displays. As is clear from Table 1, displays made using the phosphor material of the present invention show high brightness. [Table 1] As described above in detail, according to the present invention, there is provided a phosphor material capable of effectively preventing charge-up of a phosphor screen when applied to a slow electron beam excitation display device. can do. Further, it is possible to provide a method capable of easily producing such a phosphor material.
Further, it is possible to provide a display device having a phosphor layer made of the above-described phosphor material and exhibiting good display characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a thermal plasma apparatus for producing a phosphor material of the present invention. FIG. 2 is a perspective view of a field emission display according to the present invention and an enlarged view showing a part thereof. DESCRIPTION OF SYMBOLS 20: Thermal plasma chamber 21: Gas supply port 22: Cylinder 23: High frequency coil 24: Plasma frame 25: Supply nozzle of conductive material 26: Supply nozzle of phosphor particles 1: Glass substrate 2: Anode 3 ... phosphor layer 4 ... gate electrode 5 ... insulating layer 6 ... cathode 67 ... conductor pattern 8 ... glass substrate

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Albesar Le Keiko 1 Tokoba, Komukai Toshiba-cho, Saisaki-ku, Kawasaki City, Kanagawa Prefecture (56) References JP-A 7-292354 (JP, A) JP-A-8-293275 (JP, A) JP-A-3-234789 (JP, A) JP-A-6-96670 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09K 11/00-11/89 H01J 29/20 H01J 31/12 H01J 31/15

Claims (1)

(57) a step of generating a [Claims 1. A thermal plasma, a step of vaporizing and supplying conductive material into the thermal plasma, before
Phosphor particles fed into the serial thermal plasma, characterized by a step of cooling the step of attaching the <br/> conductive material on its surface, the phosphor particles wherein the conductive material is adhered A method for producing a phosphor material.