JP2008063574A - Europium-activated yttrium oxide and process for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a red phosphor suitable for electron beam-excited light emitting elements such as field emission displays (FEDs). <P>SOLUTION: Provided is a europium-activated yttrium oxide which has a median diameter in the range of 2 to 8 μm as measured by a laser diffraction/scattering method and a (δ2θ)cosθ of 0.083 degree at the largest calculated from a diffraction peak from a 440 face measured by an X-ray diffraction method (wherein θ represents a diffraction angle; and δ2θ represents a half value width (degree) of a diffraction peak). The europium-activated yttrium oxide can be produced by mixing a europium-containing yttrium compound and a flux together in an aqueous system to prepare slurry, spray drying the slurry to obtain spherical secondary particles, and then firing the obtained secondary particles so that the median diameter after the firing becomes 0.65 to 0.75 time of the median diameter before the firing to bring the median diameter after the firing to 2-8 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to europium-activated yttrium oxide useful as a red phosphor used in an electron beam-excited light emitting device such as a field emission display (FED) and a method for producing the same.

Examples of red phosphors used in electron beam-excited light-emitting devices include europium-activated yttrium oxysulfide (Y _1-x Eu _x ) ₂ O ₂ S and europium-activated yttrium oxide (Y _1-x Eu _x ) ₂ O _3. ing.
Europium activated yttrium oxysulfide has been widely used as a red phosphor for image display so far. When this is used for a field emission display (FED), (1) an acceleration voltage of 5 to 10 kV used in the FED is used. Excitation with a moderate degree of electron beam makes it difficult to obtain sufficient light emission luminance, (2) Contamination with cathode due to containing sulfur, and (3) Deterioration of luminance due to electron beam irradiation are a concern. Has been. Europium-activated yttrium oxide does not contain sulfur because it does not contain sulfur, but its emission characteristics are not sufficient, and studies are being made to improve emission brightness and lower emission start voltage. . For example, a manufacturing method for refiring (annealing) in a reducing atmosphere is known for lowering the emission start voltage (see Patent Document 1). In addition, regarding a method for producing a rare earth oxide by a spray drying method, for example, a production method is known in which a rare earth oxalate produced under specific production conditions is spray dried under specific conditions and then fired (Patent Document 2). reference). Furthermore, there is known a manufacturing method for obtaining a phosphor by thermally decomposing fine droplets made of a solution containing a constituent metal element of the phosphor (see Patent Document 3).

JP 2000-265168 A Japanese Patent Laid-Open No. 9-71415 JP 2001-220580 A

Although the red phosphor described in Patent Document 1 can reduce the light emission start voltage, further improvement in light emission luminance is required for use as a red light emitting element of a field emission display (FED). . In general, in order to improve the light emission luminance, it is advantageous to improve the crystallinity of the phosphor powder. In order to improve crystallinity, firing at a high temperature is a preferable production condition. However, the improvement in crystallinity by high-temperature firing tends to produce a coarse sintered body due to the inter-particle sintering, resulting in deterioration of powder characteristics such as dispersibility. Therefore, if the generated coarse particles are pulverized to adjust the particle size, intra-particle distortion due to pulverization occurs, resulting in deterioration of crystallinity. Thus, improvement of crystallinity and improvement of dispersibility (suppression of interparticle sintering) are contradictory requirements, and a phosphor that satisfies these requirements and a method for producing the same are demanded.

The present inventor conducted various studies to find a yttrium oxide-based red phosphor having a good balance between crystallinity and dispersibility. After the europium-containing yttrium compound and the flux were mixed in an aqueous system to form a slurry. , Spray drying to obtain spherical secondary particles, and then firing the resulting secondary particles so that the median diameter after firing is 0.65 to 0.75 times the median diameter before firing It was found that the europium-activated yttrium oxide obtained by setting the median diameter later to 2 to 8 μm satisfies the above-mentioned conflicting characteristics at the same time, thereby completing the present invention.

That is, the present invention has a median diameter measured by the laser diffraction / scattering method in the range of 2 to 8 μm and is calculated from the diffraction peak from the 440 plane measured by the X-ray diffraction method (δ2θ) cosθ (where, The europium-activated yttrium oxide is characterized in that θ is a diffraction angle and δ2θ is a half-value width (deg) of a diffraction peak at most 0.083 deg.

Furthermore, the present invention is a method for producing the above yttrium oxide, wherein a europium-containing yttrium compound and a flux are mixed in an aqueous system to form a slurry, followed by spray drying to obtain spherical secondary particles, which are then obtained. The secondary particles are fired so that the median diameter after firing is 0.65 to 0.75 times the median diameter before firing, and the median diameter after firing is 2 to 8 μm. A method for producing yttrium oxide.

The europium-activated yttrium oxide of the present invention is a phosphor suitable for pasting because it is excellent in emission luminance due to electron beam irradiation because of improved crystallinity, and is in a monodispersed state having an appropriate median diameter. is there.

The present invention is europium activated yttrium oxide having a median diameter measured by a laser diffraction / scattering method in the range of 2 to 8 μm and calculated from a diffraction peak from 440 plane measured by an X-ray diffraction method (δ2θ). ) Cos θ (where θ is the diffraction angle, and δ 2θ is the half width (deg) of the diffraction peak), which is 0.083 deg at most.

In the present invention, the median diameter and (δ2θ) cosθ are measured by the following methods, respectively.

(Measurement method of median diameter)
The median diameter is measured with a laser diffraction / scattering particle size distribution analyzer (model number: LA950) manufactured by Horiba. As the dispersion medium, a 0.2% sodium hexametaphosphate aqueous solution is used. The median diameter is calculated on a volume basis with the refractive index of the sample being 1.82 and the refractive index of the dispersion medium being 1.33.

(Measuring method of (δ2θ) cosθ)
Using a powder X-ray diffraction measurement device (model number: RINT1000, X-ray source: CuKα) manufactured by Rigaku Denki, a step scan was performed at an angle range of 47.8 ° ≦ 2θ ≦ 49.2 ° at 0.01 ° / 10 sec. The diffraction peak position (2θ) from the 440 plane is obtained by the peak top method, the half width (integral width) δ2θ is obtained from the integrated intensity, and (δ2θ) cos θ (deg) is calculated.

The europium activated yttrium oxide of the present invention has a median diameter calculated by the above method in the range of 2 to 8 μm. By making the median diameter in the above range, it becomes suitable for pasting. When the median diameter is smaller than 2 μm, it is difficult to form monodispersed particles with little sintering. When the median diameter is larger than 8 μm, voids are likely to be generated in the particles, and it is difficult to form dense particles.

Further, in the europium activated yttrium oxide of the present invention, (δ2θ) cosθ calculated by the above method is 0.083 deg at most. In general, the Scherrer formula is applied using the value of (δ2θ) cosθ to estimate the crystallite size Lc (= Kλ _CuKα1 / (δ2θ) cosθ, where K = 0.9 for powder) Can do. In the case of the present invention, when expressed in Lc estimated in this way, Lc ≧ 95.7 nm. However, the diffraction peak broadening (δ2θ) includes not only broadening due to the finite crystallite size but also broadening due to crystal distortion, and when the diffraction peak broadening is small, it was calculated by the above method ( If δ2θ) cos θ is 0.083 deg at most, it cannot be ignored. That is, it is not always appropriate to discuss crystallinity by the value of Lc to which the above Scherrer formula is applied. Crystal strain is also important as a measure of crystallinity. In the present invention, the value of (δ2θ) cos θ is used as a measure that reflects both the crystallite size and the nonuniform strain of the crystal. When (δ2θ) cos θ is larger than 0.083 deg, the crystallinity is not sufficient, and therefore the emission luminance is inferior.

In the europium activated yttrium oxide of the present invention, it is essential that the median diameter and (δ2θ) cosθ satisfy the above range at the same time. In order to make the median diameter in the range of 2 to 8 μm, for example, it is achieved by suppressing the inter-particle sintering by firing at a low temperature, but in this case, only those having low crystallinity can be obtained. However, (δ2θ) cos θ is larger than 0.083 deg. Moreover, in order to make (δ2θ) cosθ within the specified range of the present application, it is achieved by firing at a high temperature. In this case, the interparticle sintering proceeds, and the median diameter is larger than 8 μm. Become. In the method of the present invention, firing is performed in a balance between both, and as described later, firing is performed, for example, in the temperature range of the melting point of the flux to 1500 ° C., preferably the melting point of the flux to 1400 ° C.

When the amount of europium contained as an activator is in the range of 0.03 to 0.20 in terms of molar ratio (Eu / Y), emission luminance corresponding to the content of europium is obtained, and the color of the emission color Since the thing excellent also in purity is obtained, it is preferable.

The following present invention is a method for producing the above-mentioned europium-activated yttrium oxide, wherein the europium-containing yttrium compound and the flux are mixed in an aqueous system to form a slurry, followed by spray drying to obtain spherical secondary particles, The obtained secondary particles are fired so that the median diameter after firing is 0.65 to 0.75 times the median diameter before firing, and the median diameter after firing is 2 to 8 μm. Do

In the production method of the present invention, first, a europium-containing yttrium compound and a flux are mixed in an aqueous system to form a slurry, which is then spray-dried to obtain spherical secondary particles. The europium-containing yttrium compound referred to in the present invention includes, in addition to the yttrium / europium composite compound in which europium is solid-solved inside the yttrium compound, a compound in which the europium compound is adsorbed on the surface of the yttrium compound, and a mixture of the yttrium compound and the europium compound. To do.

Examples of the europium-containing yttrium compound include europium hydroxide-containing yttrium hydroxide, europium-containing yttrium hydroxide, and europium oxalate-containing yttrium oxalate. Europium hydroxide-containing yttrium hydroxide neutralizes nitrate solution containing yttrium and europium with ammonia water, europium-containing yttrium hydroxide oxide is filtered through dehydrated europium hydroxide-containing yttrium hydroxide, and then heated partly dehydrated europium oxalate The contained yttrium oxalate can be produced by adding an oxalic acid solution to a nitrate solution containing yttrium and europium. Among these, it is preferable to use europium hydroxide-containing yttrium hydroxide obtained by neutralization with aqueous ammonia. Reaction conditions such as neutralization temperature and neutralization time can be appropriately set. The europium hydroxide-containing yttrium hydroxide obtained by neutralization is appropriately filtered and washed with water.

Next, the europium-containing yttrium compound and the flux are mixed in an aqueous system to form a slurry. Examples of the flux that can be used include lithium fluoride, sodium fluoride, potassium fluoride, potassium phosphate, sodium phosphate, sodium chloride, lithium chloride and the like. These can be used alone or in combination. be able to. Among these, it is preferable to use lithium fluoride and / or potassium phosphate. Lithium fluoride is preferably used because the flux hardly remains in the phosphor obtained after firing. Further, potassium phosphate is preferable because crystallization is promoted with a small addition amount. Furthermore, it is preferable to use lithium fluoride and potassium phosphate together because the particle shape tends to be spherical. The amount of the flux used is preferably in the range of 0.1 to 15 mol% with respect to the europium-containing yttrium compound. When the flux is used beyond this range, a coarse phosphor is easily generated. Also, the flux component remaining in the phosphor increases, which is undesirable because it adversely affects crystallization. By using an appropriate amount of the flux, crystallization during firing is promoted, so that the firing temperature can be lowered and inter-particle sintering can be suppressed.

The slurry is spray-dried to obtain spherical secondary particles. There are various types of spray dryers such as a four-fluid nozzle method, a two-fluid nozzle method, and a disk atomizer method. In the present invention, a four-fluid nozzle method that easily generates secondary particles in the above range is used. Is preferred. Spherical secondary particles having a desired median diameter can be obtained by appropriately setting conditions such as slurry (oxide conversion) concentration, spray air discharge amount, temperature and the like according to the spray dryer to be used.

Next, the obtained spherical secondary particles are fired so that the median diameter after firing is 0.65 to 0.75 times the median diameter before firing, and the median diameter after firing is set to 2 to 8 μm. Of europium activated yttrium oxide. The firing atmosphere includes an oxidizing atmosphere containing oxygen such as the air, or a neutral atmosphere containing a non-oxidizing / non-reducing gas such as nitrogen, and can be set as appropriate. An oxidizing atmosphere such as the air is preferable. The spherical secondary particles are densified by firing. By firing so that the ratio of the median diameter of the spherical secondary particles before and after firing is in the above range, the spherical secondary particles are densified, and europium-activated yttrium oxide in which inter-particle sintering is suppressed is obtained. Moreover, when the median diameter of the spherical secondary particles after firing is set to 2 to 8 μm, it is suitable for pasting. The firing temperature can be appropriately set according to the type and amount of the flux used, but a temperature range of the melting point of the flux to 1500 ° C., preferably the melting point of the flux to 1400 ° C. is preferred. When the firing temperature is lower than the above range, densification is insufficient and it is difficult to obtain desired crystallinity. On the other hand, if the firing temperature is higher than the above range, the crystal distortion increases due to the progress of inter-particle sintering, and the dispersibility tends to be poor. The europium-activated yttrium oxide obtained in this way is excellent in crystallinity, and when (δ2θ) cosθ is used as a measure of crystallinity, the value is 0.083 deg at most.

When the particles are slightly sintered due to firing, the particles can be pulverized to the same degree by crushing. Further, when the crystal distortion in the particles is increased by pulverization and as a result, the value of (δ2θ) cosθ is increased, recalcination (annealing) can be performed at a temperature lower than the temperature at the time of firing.

The europium-activated yttrium oxide of the present invention is excellent in emission luminance by electron beam excitation and has a median diameter suitable for pasting, so that it is a flat panel display utilizing an electron beam excitation luminescence phenomenon, for example, a field emission display. It is suitable for a red phosphor used for (FED). There are two types of FEDs, low voltage type using an electron beam accelerated by a voltage of 100 to 3000V as an excitation source and high voltage type using an electron beam accelerated by a voltage of 3000V or more as an excitation source. Yes. The red phosphor of the present invention can be used in any of the above-mentioned types because good light emission can be obtained even with an electron beam accelerated at least at about 1000V.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

Example 1
(Generation of yttrium hydroxide containing europium hydroxide)
125 g of yttrium oxide powder with a purity of 4N and 9.741 g of europium oxide powder with a purity of 4N were weighed in a 1 (l) beaker, and 400 (ml) of pure water was added and stirred to form a slurry. Concentrated nitric acid (specific gravity 1.38) 261 (ml) was dispersed and added to this slurry with stirring to dissolve it. After cooling, the insoluble residue was filtered off by natural filtration, and then pure water was added to dilute to 1 (l) to obtain a nitrate aqueous solution containing yttrium and europium. Next, 6.3 (l) of pure water and 343 (ml) of 25% ammonia water were added to a glass reaction vessel having a volume of 10 (l), and the temperature was raised to 70 ° C. while stirring. Nitrate aqueous solution of yttrium and europium was added all at once, and the liquid volume was adjusted to 8 (l) with pure water. It was kept for 5 hours while maintaining 70 ° C., and then washed with filtered water to obtain yttrium hydroxide containing europium hydroxide containing homogeneously yttrium and europium.

(Generation of spherical secondary particles)
Europium hydroxide-containing yttrium hydroxide and pure water obtained in the previous step were placed in a commercially available juice mixer and stirred to obtain a slurry having a concentration of 8.25 wt% in terms of oxide. K ₃ PO _{4 in an} amount of P / (Eu + Y) = 0.5 (mol%) was dissolved in 200 (ml) pure water and added to the slurry with stirring. After adjusting the pH of the slurry to 8 with dilute acetic acid solution, pure water was added to make the slurry concentration 5.0 wt% in terms of oxide. The dispersion slurry was sprayed with a Fujisaki Electric spray dryer (4-fluid nozzle system, with cyclone system classification function: MDL-50C), air discharge amount 100 (l / min), drying temperature 200 ° C., spray amount 30 (ml / Minute), and double hydroxide monodispersed spherical secondary particles having a median diameter of 6.97 μm were recovered with a cyclone.

(Baking)
60 g of the obtained spherical secondary particles were calcined in the atmosphere at a temperature of 1380 ° C. for 5 hours using an alumina crucible having a capacity of 100 (ml).

(Pulverization)
The fired product was pulverized with a centrifugal pulverizer (manufactured by Nippon Seiki Co., Ltd.) to obtain europium activated yttrium oxide (sample A) of the present invention.

Example 2
Spherical secondary particles having a median diameter of 9.32 μm were obtained in the same manner as in Example 1 except that the slurry concentration of europium hydroxide-containing yttrium hydroxide was 7.5 wt%. Further, the subsequent firing and pulverization were carried out in the same manner as in Example 1 to obtain europium activated yttrium oxide (sample B) of the present invention.

Example 3
Spherical secondary particles having a median diameter of 4.12 μm were obtained in the same manner as in Example 1 except that the slurry concentration of europium hydroxide-containing yttrium hydroxide was 2.5 wt%. Further, subsequent firing and pulverization were performed in the same manner as in Example 1 to obtain europium-activated yttrium oxide (sample C) of the present invention.

Comparative Example 1
The spray dryer is made by Niro Co., Ltd .: Mobile minor type (atomizer type), spray drying conditions: oxide equivalent slurry concentration of spray liquid 5wt%, liquid feed amount 30 (ml / min), dryer inlet temperature 230 ° C, outlet Spherical secondary particles having a median diameter of 12.8 μm were obtained in the same manner as in Example 1 except that the temperature was 100 ° C. Further, subsequent firing and pulverization were performed in the same manner as in Example 1 to obtain a europium-activated yttrium oxide (sample D) as a comparative sample.

Comparative Example 2
Spherical secondary particles (cyclone carryover product) having a median diameter of 2.53 μm were collected using a bag filter in the same manner as in Example 1. Further, subsequent firing and pulverization were performed in the same manner as in Example 1 to obtain a europium-activated yttrium oxide (sample E) as a comparative sample.

Comparative Example 3
In Example 1, a comparative sample of europium activated yttrium oxide (Sample F) was obtained by the same treatment as in Example 1 except that the firing temperature was 1200 ° C. and the firing was performed for 5 hours.

Comparative Example 4
In Example 1, the same procedure as in Example 1 was conducted except that the firing temperature was 1100 ° C. and the firing was performed for 5 hours to obtain a europium activated yttrium oxide (sample G) as a comparative sample.

Comparative Example 5
Using a mortar, 6.25 g of 4N purity yttrium oxide powder and 0.4871 g of europium oxide powder were mixed well. Into this, 30.57 g of sodium chloride and 1.508 g of lithium fluoride were mixed as a flux until homogeneous. The amount of the flux used was a mixed flux of NaCl / (Y + Eu) = 900M% and LiF / (Y + Eu) = 100M%. This mixture was placed in an alumina crucible and baked in an electric furnace at a temperature of 1250 ° C. for 50 hours. After cooling, the remaining flux was dissolved and removed in hot water and washed with filtered water. It dried at the temperature of 110 degreeC, and obtained the europium activated yttrium oxide (sample H) of the comparative sample.

Comparative Example 6
Using a mortar, 6.25 g of 4N purity yttrium oxide powder and 0.4871 g of europium oxide powder were mixed well. To this, 16.983 g of sodium chloride and 7.538 g of lithium fluoride were mixed as a flux until homogeneous. The amount of the flux used is a mixed flux of NaCl / (Y + Eu) = 500 M% and LiF / (Y + Eu) = 500 M%. This mixture was placed in an alumina crucible and baked in an electric furnace at a temperature of 1250 ° C. for 50 hours. After cooling, the remaining flux was dissolved and removed in hot water and washed with filtered water. It dried at the temperature of 110 degreeC, and obtained the europium activated yttrium oxide (sample I) of the comparative sample.

Comparative Example 7
In an agate mortar, 5.5 g of 4N purity yttrium oxide powder, 0.44 g of 4N purity europium oxide powder, 2.65 g of sodium carbonate, 4.8 g of sulfur, and 0.515 g of flux (K ₃ PO ₄ ) are precisely weighed. Mixed thoroughly. The mixture was placed in an alumina crucible and capped. The lid was sealed with inorganic cement and then fired at 1150 ° C. for 2 hours in an air atmosphere. After cooling, it was sufficiently washed with pure water to obtain europium-activated yttrium oxysulfide (sample J) having a median diameter of 7.10 μm. X-ray diffraction analysis of Sample H confirmed that it was a Y ₂ O ₂ S single phase.

Using the samples A to I obtained in Examples 1 to 3 and Comparative Examples 1 to 6, the median diameters (D ₀ and D), (δ 2θ) cos θ and electron beam excitation luminescence luminance before and after firing were measured. The results are shown in Table 1. The median diameter and (δ2θ) cosθ were measured by the method described above, and the electron beam excited luminescence brightness was measured by the following method. Furthermore, scanning electron micrographs of Samples A to I are shown in FIGS.

(Measuring method of luminance excited by electron beam)
A measurement plate obtained by allowing a slurry in which 0.1 g of a sample is dispersed in 100 (ml) of pure water to spontaneously settle on a 10 mm × 10 mm aluminum plate is sufficiently vacuum-dried, and then the pressure is 3 to 5 × 10 ^−6. The sample was irradiated with an electron beam accelerated at an acceleration voltage of 5 kV under a high vacuum of Pa, and the emission spectrum from the sample was measured using a multichannel spectrometer. The Y value (emission luminance) in the CIE 1931 color system was determined from the obtained emission spectrum. In Table 1, the comparative sample J is expressed as a relative value with the light emission luminance of 100.

As can be seen from FIGS. 1-9, the europium-activated yttrium oxide of the present invention (samples A to C) is in a dense and monodispersed state, whereas the comparative sample is in a monodispersed state. There are voids inside (sample D), or interparticle sintering has advanced (sample E), and the particles are not sufficiently densified (samples F and G). (Samples H and I).

Further, from Table 1, the median diameter is in the range of 2 to 8 μm, and the europium activated yttrium oxide (samples A to C) of the present invention in which (δ2θ) cos θ is 0.083 deg at most is the median diameter and ( Compared with comparative samples D, E, F, G, H, and I that do not satisfy the range of δ2θ) cosθ at the same time, it was found that the emission luminance by electron beam excitation was excellent.

The europium activated yttrium oxide of the present invention is useful as a red phosphor for an electron beam-excited light emitting device such as a field emission display (FED).

2 is a scanning electron micrograph showing the particle shape of sample A. FIG. 3 is a scanning electron micrograph showing the particle shape of Sample B. FIG. 3 is a scanning electron micrograph showing the particle shape of sample C. FIG. 3 is a scanning electron micrograph showing the particle shape of sample D. FIG. 4 is a scanning electron micrograph showing the particle shape of sample E. FIG. 4 is a scanning electron micrograph showing the particle shape of sample F. FIG. 3 is a scanning electron micrograph showing the particle shape of sample G. FIG. 3 is a scanning electron micrograph showing the particle shape of sample H. FIG. 4 is a scanning electron micrograph showing the particle shape of Sample I.

Claims (5)

The median diameter measured by the laser diffraction / scattering method is in the range of 2 to 8 μm, and is calculated from the diffraction peak from the 440 plane measured by the X-ray diffraction method (δ2θ) cosθ (where θ is the diffraction angle, δ2θ Europium-activated yttrium oxide, characterized in that the half-value width (deg) of the diffraction peak is at most 0.083 deg. A europium-containing yttrium compound and a flux are mixed in an aqueous system to form a slurry, followed by spray drying to obtain spherical secondary particles, and then the median diameter after firing of the obtained secondary particles is the median before firing. A method for producing europium-activated yttrium oxide, characterized by firing so as to be 0.65 to 0.75 times the diameter, and setting the median diameter after firing to 2 to 8 μm. The method for producing europium-activated yttrium oxide according to claim 2, wherein the europium-containing yttrium compound is europium hydroxide-containing yttrium hydroxide obtained by neutralizing an aqueous solution containing yttrium and europium with ammonia water. The method for producing europium-activated yttrium oxide according to claim 2, wherein the pulverization is performed after firing. The method for producing europium-activated yttrium oxide according to claim 2, wherein the flux is lithium fluoride and / or potassium phosphate.

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