JPH0468077A - Preparation of phosphor powder - Google Patents

Abstract

PURPOSE:To prepare a crystalline phosphor powder improved in luminance and resistance to deterioration of luminance by mixing two specified compds., an org. silicon compd. and a solvent, gelling the mixture, removing the solvent and firing the residue. CONSTITUTION:A soln. is prepd. by mixing a compd. (i) giving a rare-earth element ion functioning as a luminescent center of a phosphor, such as Tb, Ce, Nd, Pr, Dy, Eu, Sm or Tm (e.g. Tb4O7), a compd. (ii) giving other rare-earth element ion (e.g. Sc, Y, La, Gd or Lu) forming a mother crystal of which the atomic ratio of element (ii) to element (i) is 1.95-1.70/0.05-0.30, an org. silicon compd. and a solvent. The soln. is gelled as such or treated with a precipitant to form a composite precipitate. By removing the solvent, a powdery material which is at least partially amorphous is obtd. Then, it is calcined to prepare a crystalline phosphor powder.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is used in cathode ray tubes, fluorescent lamps, etc.
This invention relates to a method for producing phosphor powder that emits light when energy from electron beams, ultraviolet rays, etc. is applied.

[Prior Art] Conventionally, when synthesizing a rare earth silicate phosphor, the raw material rare earth oxide and silicon dioxide are uniformly mixed and heated to a high temperature to promote a solid phase reaction. We have phosphor powder.

For example, as disclosed in Japanese Patent Publication No. 4G-37670, in the case of lanthanum and yttrium silicate phosphors, rare earth oxides and silicon dioxide, which serve as luminescent centers and base materials, are completely mixed and heated at 1000 to 1500°C. After firing, the phosphor is obtained by mechanically crushing it into a fine powder. In addition, a rare earth nitrate aqueous solution and an oxalate aqueous solution are mixed to form an oxalate coprecipitate, which is mixed with silicon dioxide and then fired to obtain a phosphor.

[Problems to be Solved by the Invention] In the conventional manufacturing method, variations in the surface shape of the powder particles due to the type of raw material silicon dioxide, lot differences, etc. greatly affect the progress of the solid phase reaction. The disadvantage is that the properties are extremely dependent on the raw materials.

In addition, in the method of producing a coprecipitate of oxalate, as shown in the above publication, it is necessary to mix silicon dioxide at a ratio of about 1.5 mol to 1.0 mol of rare earth oxide. be. This is because when using a solid phase reaction, taking into account that there is a large difference between the melting points of rare earth oxides (oxalates) and silicon dioxide, excess silicon dioxide is used to allow the reaction to proceed throughout the material. This is because it is necessary to add it. When silicon dioxide is added in excess, the amount is set so that the luminescence intensity of the final product, the phosphor, is maximized. However, if excess silicon dioxide is present, a foreign phase component with a stoichiometric ratio other than the desired host crystal composition will be mixed in, causing brightness degradation and large variations in grain size due to the heterogeneous crystal phase. It has been found that this has an adverse effect on the lifespan of the phosphor.

[Means for Solving the Problems] In order to solve the above-mentioned problems, an example is known in which a light-emitting thin film of a composite oxide is formed using a sol-gel method (Japanese Patent Laid-Open No. 1-109641). Publication, Ellzer M.

Rabinovich et al., American Ceramics
Society Bulletin (Am, Ceram, Soc,
Bull 1. ), 66 [101 (1987) P, 150
5-1509).

However, when fluorescent integrated products are manufactured using these techniques, priority is given to formability into a thin film, and there is a problem in that sufficient brightness cannot be achieved for use in cathode ray tubes or fluorescent lamps. The inventors of the present invention conducted further intensive studies and arrived at the present invention.

That is, the present invention provides a compound that provides one or more rare earth element ions that can become the luminescent center of a phosphor, a compound that provides other rare earth element ions that form a mother crystal, and an organosilicon compound, depending on the composition of the target compound. Prepare a solution mixed in a corresponding stoichiometric ratio, gel it as it is, or add a precipitant to form a composite precipitate, then remove the solvent to form a powder that is wholly or partially amorphous. The present invention relates to a method for producing a phosphor powder, which includes a step of heating and firing the powder to obtain a crystalline powder.

[Function] In the present invention, a compound giving a rare earth element ion and an organosilicon compound are uniformly mixed in a solution state in a stoichiometric ratio corresponding to the composition of the desired compound to obtain a phosphor powder with a homogeneous composition. Therefore, it is possible to change the desired single composition without the need for excessive silicon dioxide at the time of raw material input, and without the contamination of foreign phase components.

[Example] In the present invention, compounds that provide one or more rare earth element ions (hereinafter also referred to as luminescence center ions) that can become the luminescence center of a phosphor, and other rare earth element ions (hereinafter also referred to as luminescence center ions) that can form the mother crystal
Hereinafter, a compound giving a parent crystal ion (also referred to as a mother crystal ion) and an organosilicon compound are used.

As a specific example of the luminescent center ion, for example, Tb%
Examples include ions such as Ce5Nds Pr5Dys ELISS1% TI, and one or more of these may be used.

Specific examples of the mother crystal ions include Sc,
Ions include Y, La, Cd5Lu, etc.
One or more of these may be used.

As compounds (raw materials) that provide these rare earth element ions, not only inorganic salts such as oxides, chlorides, nitrates, and acetates, but also alkoxides and esters can be used.

Specific examples of the organosilicon compound include, for example, the alkoxide tetranidoxinran<(C2H5O)
4S+) (hereinafter referred to as TE01), tetramethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. Among these, from a practical standpoint, TE01 is particularly preferred since it has a low melting point and is inexpensive. In addition, ethyl silicate, which is a silicate ester,
Methyl silicate and the like can also be used as organosilicon compounds.

In the present invention, a solution is prepared in which a compound that provides the luminescent center ion, a compound that provides the host crystal ion, and a compound that is intended to be an organosilicon compound (silicate) are mixed in a stoichiometric ratio.

The stoichiometric ratio is the rare earth element silicate (Scz 5ins, Y25ins, Y25ins,
Laz 5IOsSGdz 5ins, Scz 5i
207, Y251207, Laz 5i2e7, etc.) is such that a part of the rare earth element is replaced with a rare earth element serving as a luminescent center ion.

The degree of substitution is changed as appropriate from luminous efficiency and other points of view, but usually the atom ratio of the rare earth element serving as the mother crystal ion/the rare earth element serving as the luminescent center ion is 1.95/
The ratio is 0.05 to 1.70/0.30.

For example, in Y/Tb, the atom ratio is 1.85/0.15
It is preferable that

The method for preparing the solution includes, for example, weighing the compound that will become the luminescent center ion and the compound that will become the mother crystal ion so that the proportions are as described above, and adding this to a nitric acid aqueous solution (
Concentration: 1.0-1.5M), ethanol (special grade 99.
5%) to a concentration of 0.2 to 0.5 mol/Ω, and then add a mixed solution of an organosilicon compound and ethanol (concentration ratio organosilicon compound/EtO
An example of a method is to add H-1/1 to 1/3 or so) to have the composition of the silicate and thoroughly stir and mix.

Next, the solution may be gelled as it is, or a precipitant may be added to form a composite precipitate containing each component.

The above-mentioned "gelling as it is" means that the solution is heated to 60 to 10
By holding the mixture at 0° C. for 24 to 48 hours, the alkoxide is hydrolyzed and gelled in a uniform state.

Examples of the precipitating agent to be added when forming the composite precipitate include aqueous ammonia, triethanolamine,
Examples include urea. These precipitants are gradually added while stirring vigorously until the pH of the mixed solution changes from an acidic range to an alkaline range.

Next, the solvent is removed from the gel or precipitate-containing material so that the average particle size of all or part of the amorphous particles is 0.
．． Make it into a fine powder of about 5 to 1.0.

The reason why all or part of the fine powder is amorphous is that the gel or precipitate is generally amorphous, and when heated to about 200° C., a part of it crystallizes.

As the removal method, for example, 150 to 200'C
Methods include heating for 24 to 48 hours.

Note that it may be filtered before heating.

The fine powder is then heated and fired to form a crystalline powder.

For example, the fine powder is packed in an aluminum pot, heated at 200 to 1000°C for 2 to 10 hours to decompose organic components, and then heated to 1300 to 160°C.
It is carried out at 0°C, more preferably at 1500 to 1600°C. There is no particular limit to the firing time, but it is usually 1 to IO.
time, more preferably 4 to 6 hours.

Furthermore, the firing atmosphere may be controlled as necessary.

For example, the target compound is Y25105: Tb
In the case of Y25i052Ce, it is preferable to use a reducing atmosphere such as N2-N2 mixed gas.

Since the average particle size of the phosphor powder synthesized through the above steps is about 4 to 7 f, it can be used without pulverization, and the phosphor has improved brightness and brightness life.

Hereinafter, the present invention will be explained in more detail based on Examples.

Example 1 Yttrium oxide (Y203.
99.99%) and terbium oxide (T
b407.99.9%) were mixed and stirred, and 45 ml of concentrated nitric acid (HNO3, 85%) was added and dissolved to prepare a nitrate aqueous solution. Additionally, TE01 ((C2
N50) 4 Sl, 99.999%) 20.83 g and 80 ml of ethanol were mixed, and this was added to the nitrate aqueous solution and thoroughly stirred. After mixing thoroughly until homogeneous, the mixture was heated to 80°C to cause a polycondensation reaction by hydrolysis.
The mixture was aged for 48 hours at 200° C. and further dried at 200° C. for 24 hours to remove the solvent. When the obtained powder was examined by X-ray diffraction, it was found to be completely amorphous.

The powder was packed in an aluminum crucible, heated and decomposed in the atmosphere at 800°C for 4 hours, and then heated in a weak reducing atmosphere (N2-
Firing was performed at 1550° C. for 4 hours in a N2 mixed gas atmosphere.

It was confirmed from the results of X-ray diffraction that the obtained phosphor powder was monoclinic Y2510S. Moreover, the average particle size was about 6 grains. This substance is a phosphor that exhibits green color with Tb3+ as the emission center when excited by ultraviolet rays or electron beams.

The luminance characteristics of this material with respect to current density were measured using a demountable luminance measurement device and irradiated with an electron beam at an excitation voltage of 20 kV. The results are shown in Figure 1.

Furthermore, using the same device, the time change in brightness (brightness deterioration characteristics) in response to electron beam irradiation with an excitation voltage of 20 kV was also measured. The results are shown in Figure 2.

Note that the vertical axis in FIG. 1 is luminance, and the vertical axis in FIG. 2 is relative luminance (Ht)/lo x 100). 1(tN is the brightness after one hour, io is the initial brightness.

Example 2 22.02 yttrium oxide in 400 ml of distilled water
g and 45 ml of concentrated nitric acid, and then add cerium nitrate (Ce(NOx)3 8H20, 99,9%).
2.17 g was added and completely dissolved to prepare a nitrate aqueous solution. Another TE0120.83 g and 20 ml of ethanol were mixed, and this was added to the nitrate aqueous solution and sufficiently stirred until it became homogeneous. In addition, 0
．． When IN aqueous ammonia was added little by little with vigorous stirring until the pH reached 9, a white precipitate of the complex hydroxide salt was generated. Further, stirring was continued for 0.5 hour at room temperature to sufficiently advance the precipitation reaction, and the resulting precipitate was filtered and dried at 200° C. for 24 hours to remove the remaining solvent. The obtained powder is placed in a weak reducing atmosphere (N2-N2
By firing at 1500° C. for 6 hours in a mixed gas atmosphere, a phosphor powder with an average particle size of about 6 mm was obtained. The powder thus obtained is Y25ins:Ce, which is a phosphor that emits blue light with Ce as the emission center when excited by an electron beam.

Example 3 Sotrium chloride (isotrium) in 300 ml of special grade ethanol
56.12 g of Y (J3 °6H20,99,9%) and ichterhium salt (TbCf3 7H20,9
9.9%) 5.87g was dissolved.

Separately, 20.83 g of TE01 and 50 ml of ethanol were mixed, and this was added to the chloride ethanol solution and thoroughly stirred. After sufficiently uniformly mixing, Example 1 will be described below.
It was gelled and dried under the same conditions. The obtained powder was thermally decomposed in the air at 400°C for 8 hours, and then fired at 1550°C for 4 hours in a weakly reducing atmosphere (N2-N2 mixed gas atmosphere) to obtain a phosphor powder with an average particle size of about 7m. I got it. When the properties of the obtained powder were investigated, it showed the same properties as in Example 1.

Example 4 Europium oxide (Eu20
3.99.9%) was added, and since there was no need for atmosphere control, the average particle size force (approximately A phosphor powder was produced.The resulting powder Cma Y2510S
: Eu and is a phosphor that emits red light with Eu3+ as the emission center due to electron beam excitation.

Example 5 Scandium oxide (5c20
s, 99.9%) 12.76 and terbium oxide 2
．． 80 g was added and stirred, and 45 ml of concentrated nitric acid was added and dissolved therein to prepare a nitric acid aqueous solution. Another one;:TE
Add a solution of 841.87 g of O8 and 100 ml of ethanol to the aqueous nitric acid solution and mix thoroughly with stirring.
In the same manner as in Example 1, a phosphor powder having an average particle size of about 5-50 mm was produced.

The obtained phosphor powder is Scz 5i207:Tb, which emits green light with Tb3+ as the emission center when excited by X-rays, ultraviolet rays, or electron beams.

Comparative Example 1 Yttrium oxide 201119g, Terbium oxide 2
．． 80g and silicon dioxide (Si02.99.5%)
Put 6.34g into a ball mill pot and add 1 part of ethanol.
00 ml was added and mixed for 10 hours. After taking out the resulting mixture from the ball mill pot and thoroughly drying it,
It was packed in an aluminum tube and fired at 1550° C. for 4 hours in a slightly reducing atmosphere. After cooling, it was pulverized to produce phosphor powder. The obtained phosphor is Y25i05:Tb, which emits green light when excited by an electron beam.

The brightness characteristics and brightness deterioration characteristics with respect to current density of the obtained phosphor were investigated in the same manner as in Example 1. The results are shown in Figures 1 and 2, respectively.

Comparative Example 2 Yttrium oxide 20.89g in 10100O distilled water
and 2.80 g of terbium oxide were mixed and stirred, and 45 ml of concentrated nitric acid was added and dissolved to prepare a nitrate aqueous solution.

Separately, oxalic acid hydrate (C
2H204/2H20, reagent special grade) 45. A solution in which OOg was dissolved was prepared, and when the nitrate aqueous solution was added to this oxalic acid aqueous solution, a white precipitate was generated. This precipitate was washed and filtered, and then dried in an oven.

The obtained powder was thermally decomposed at 1000℃ for 2 hours to obtain a composite oxide of yttrium and terbium, and silicon dioxide 6
The mixture was placed in a ball mill pot with 4 g of J and 50 ml of ethanol and mixed for 10 hours. Then, after drying,
The mixture was fired at 1550° C. for 3 hours in a weakly reducing atmosphere, cooled, and then ground to obtain a phosphor powder.

The obtained phosphor exhibited the same characteristics as Comparative Example 1.

[Effects of the Invention] As described above, according to the method of the present invention, it is possible to uniformly mix a compound that provides rare earth element ions and an organosilicon compound in a solution, thereby producing a homogeneous phosphor powder. particles can be obtained. As a result, the luminance is improved and a phosphor with excellent luminance deterioration characteristics can be used.

[Brief explanation of drawings]

FIG. 1 is a graph showing the luminance characteristics with respect to current density of the phosphors of Example 1 and Comparative Example 1, and FIG.
and a graph showing the luminance deterioration characteristics of the phosphor of Comparative Example 1. Representative Masuo Oishi

Claims (1)

[Claims] (1) A compound that provides one or more rare earth element ions that can become the luminescent center of the phosphor, a compound that provides other rare earth element ions that form the mother crystal, and an organosilicon compound,
Prepare a solution mixed in a stoichiometric ratio corresponding to the composition of the target compound, and either gel it as it is or add a precipitant to form a composite precipitate, and then remove the solvent to dissolve all or part of it. A method for producing a phosphor powder, comprising the step of preparing an amorphous powder and heating and baking it to obtain a crystalline powder.