JPH07133485A - Method for producing rare earth phosphate phosphor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for producing a rare earth phosphate phosphor capable of reproducibly obtaining a uniform crystal rare earth phosphate phosphor with a constant molar ratio of rare earth element and phosphorus. [Constitution] General formula: (La _1-xy Ce _x Tb _y ) PO ₄ (wherein
x and y are numbers satisfying x> 0, y> 0, and 0.1 ≦ x + y ≦ 0.8), in order to manufacture a rare earth phosphate phosphor, the lanthanum salt aqueous solution and the cerium salt are first prepared. Prepare an aqueous solution and an aqueous terbium salt solution,
Lanthanum phosphate, cerium phosphate and terbium phosphate are respectively synthesized by reacting these aqueous solutions with the phosphoric acid compound individually. These are mixed at a desired ratio to adjust the pH, dried to synthesize a rare earth phosphate having a desired composition, and the rare earth phosphate is fired in the air or a reducing atmosphere to produce a rare earth phosphate phosphor. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth phosphate phosphor used as a green light emitting component of a three-wavelength band fluorescent lamp.

[0002]

2. Description of the Related Art In recent years, as a fluorescent lamp for general illumination, a three-wavelength light emitting type fluorescent lamp which simultaneously satisfies high color rendering properties and high efficiency has been developed and has become popular. This three-wavelength band emission type fluorescent lamp mixes phosphors that emit light of each of blue, green and red colors, which have a relatively narrow band emission spectrum distribution, at an arbitrary ratio, and forms a phosphor film by this mixed phosphor. It is a fluorescent lamp that emits white light or a desired color.

A rare earth phosphate phosphor containing three kinds of rare earth elements, such as lanthanum, cerium and terbium, is used as a green light emitting component of the above-mentioned three-wavelength band emission type fluorescent lamp. The method for producing such a rare earth phosphate phosphor is roughly classified into a dry method and a wet method depending on the method for synthesizing the rare earth phosphate. In the dry method, a mixed oxide of rare earth and a phosphoric acid compound are mixed and the mixture is fired to obtain a rare earth phosphate. However, in this method, the obtained rare earth phosphate has a problem that it is very hard and it is difficult to perform firing to obtain a green light emitting phosphor without any treatment.

On the other hand, in the wet method, a phosphoric acid compound is added to an aqueous solution containing three kinds of rare earth elements such as lanthanum, cerium and terbium, and a rare earth phosphate is obtained by reacting the three kinds of rare earth elements with the phosphoric acid compound. There is. According to such a wet method, since the rare earth phosphate obtained is soft, it is possible to perform firing for obtaining the green light emitting phosphor without any treatment. However, in the above-mentioned conventional wet method, since three types of rare earth ions and phosphate ions react at a stroke to synthesize a rare earth phosphate, the molar ratio of rare earth element and phosphorus is such that a precipitation method such as a method of introducing a phosphate compound is used. However, there is a drawback that it easily changes depending on the conditions during the product formation reaction. As a result, it has been difficult to manufacture a phosphor having a constant molar ratio of rare earth element and phosphorus.

[0005]

As described above, in the method for producing a rare earth phosphate phosphor using the conventional wet method, the molar ratio of the rare earth element and phosphorus is likely to change and the phosphor having a constant molar ratio is used. Was difficult to manufacture. Then, another compound of rare earth is mixed with the variation of the molar ratio of the rare earth element and phosphorus, whereby a rare earth phosphate (phosphorus / rare earth ratio> 1) in which the molar ratio of phosphorus is larger than that of the rare earth element is produced. The problem was that it was easily synthesized. Such a rare earth phosphate having a phosphorus / rare earth ratio exceeding 1 is
It is known that the emission brightness decreases as the ratio increases.

The present invention has been made in order to solve such a problem, and enables to obtain a rare earth phosphate crystal having a uniform molar ratio of rare earth element and phosphorus with good reproducibility. Another object of the present invention is to provide a method for producing a rare earth phosphate phosphor, which is capable of stably obtaining good emission luminance characteristics.

[0007]

Means and Actions for Solving the Problems The method for producing a rare earth phosphate phosphor of the present invention comprises the following general formula: (La _1-xy Ce _x T _{b y} ) PO ₄ (where x and y are x> 0. , Y> 0, 0.1 ≦ x + y ≦ 0.
In the production of the rare earth phosphate phosphor substantially represented by (8), a lanthanum salt aqueous solution, a cerium salt aqueous solution and a terbium salt aqueous solution are prepared, and these aqueous solutions and phosphoric acid compounds are individually Let it react,
A step of synthesizing lanthanum phosphate, cerium phosphate and terbium phosphate, respectively, and mixing the lanthanum phosphate, cerium phosphate and terbium phosphate in a desired ratio to adjust pH and then drying to synthesize a rare earth phosphate having a desired composition. The method is characterized by including a step and a step of firing the rare earth phosphate in the air or a reducing atmosphere.

In the production method of the present invention, first, lanthanum, cerium and terbium salts such as chlorides, nitrates, carbonates, oxalates and oxides are prepared as raw materials, and these aqueous solutions are separately prepared. Create. The concentration of these aqueous solutions is preferably set in advance according to the composition of the target rare earth phosphate phosphor. Then, equimolar phosphoric acid compounds are individually dissolved in these aqueous solutions, and the lanthanum salt, cerium salt, terbium salt and phosphoric acid compound are individually reacted at a temperature of from room temperature to about 80 ° C. to give lanthanum phosphate, cerium phosphate and Terbium phosphate is synthesized separately. The phosphoric acid compound used may be either solid or liquid.

Next, lanthanum phosphate, cerium phosphate and terbium phosphate precipitated by the synthetic reaction are mixed. Adjust the pH of this mixture to the range of 6 to 8, stir for at least 1 hour and then dry. This drying step is preferably performed in one of a spraying state, a fluidized state and a frozen state. By using such a drying method, it is possible to obtain rare earth phosphate as fine agglomerated particles of uniform particle size, which facilitates the subsequent firing step (crystal growth step) and makes the particle shape close to a spherical shape. Moreover, it becomes possible to obtain a phosphor having a uniform particle size. In addition,
Fluidized drying is a method of performing drying while moving a slurry to be dried on a disc, for example. Freeze-drying is a method in which the slurry to be dried is frozen and then vacuumed to dry.

As described above, the reaction conditions are stabilized by individually reacting the lanthanum salt, the cerium salt, the terbium salt and the phosphoric acid compound, so that lanthanum phosphate, cerium phosphate and terbium phosphate having respective predetermined molar ratios can be obtained. Then, these are mixed at a desired ratio, and the mixture is subjected to pH adjustment and each treatment of drying, whereby a uniform rare earth phosphate crystal having a constant molar ratio of rare earth element and phosphorus can be obtained with good reproducibility. It will be possible.

After adding a boric acid compound or the like as a flux to the rare earth phosphate having a constant molar ratio of the rare earth element and phosphorus as described above, it is heated to 1000 in the atmosphere or a reducing atmosphere containing nitrogen and hydrogen. Bake at a temperature of ℃ to 1300 ℃ for 1 to 5 hours. This makes it possible to stably obtain a rare earth phosphate phosphor having a uniform crystal in which the molar ratio of the rare earth element and phosphorus is constant.

[0012]

EXAMPLES Examples of the present invention will be described below.

Example 1, Comparative Example 1 0.56 mol / l lanthanum chloride (LaCl ₃ ) aqueous solution and 0.14 mol
l / l cerium chloride (CeCl ₃ ) aqueous solution and 0.30 mol / l terbium chloride (TbCl ₃ ) aqueous solution were individually adjusted, and then equimolar diammonium hydrogen phosphate was added to each of these aqueous solutions. The reaction was carried out individually at 60 ° C. Then, after the precipitated lanthanum phosphate, cerium phosphate and terbium phosphate were mixed, the pH was adjusted to 8 and the mixture was stirred for 2 hours.

Then, the filter cake obtained by filtering the agitated product is dried at a drying temperature of 120 using a conical dryer.
After spray-drying at ℃, rare earth phosphate containing three kinds of rare earth elements, lanthanum, cerium and terbium was obtained. Lithium fluoride (Li
F) and boric acid (H ₃ BO ₄ ) are mixed at 30% by weight and 0.5% by weight, respectively, and the mixture is placed in an alumina crucible at 1300 ° C. in a reducing atmosphere consisting of 95% by volume of nitrogen and 5% by volume of hydrogen. The mixture was baked at the temperature of 2 hours to obtain a rare earth phosphate phosphor represented by (La _0.56 Ce _0.30 Tb _0.14 ) PO ₄ .

The rare earth phosphate phosphor thus obtained has a peak emission wavelength when excited by an ultraviolet ray of 254 nm.
It showed a green emission around 545 nm. When the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.00.

On the other hand, as a comparison with the present invention, one aqueous solution containing the same amounts of lanthanum chloride, cerium chloride and terbium chloride as in Example 1 was prepared and 1.0 mol of diammonium hydrogen phosphate was added thereto. The reaction was carried out at 60 ° C.
After the diammonium hydrogen phosphate was completely dissolved, the pH was adjusted to 8 and the mixture was stirred for 2 hours. Next, the filter cake obtained by filtering the agitated product was subjected to spray drying under the same conditions as in Example 1 to obtain a rare earth phosphate. This rare earth phosphate was fired under the same conditions as in Example 1 to produce a rare earth phosphate phosphor. When the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.05.

Next, using the rare earth phosphate phosphors obtained in Example 1 and Comparative Example 1 above, fluorescent lamps were produced and the emission brightness was measured. As a result, as compared with the fluorescent lamp using the phosphor of Comparative Example 1, the fluorescent lamp using the phosphor of Example 1 had an emission luminance improved by 2.5%.

Example 2, Comparative Example 2 A 0.20 mol / l lanthanum chloride aqueous solution, a 0.70 mol / l cerium chloride aqueous solution, and a 0.10 mol / l terbium chloride aqueous solution were individually prepared, and then these aqueous solutions were prepared. Equimolar diammonium hydrogen phosphate was added respectively and reacted individually at 40 ° C. Then, after the precipitated lanthanum phosphate, cerium phosphate and terbium phosphate were mixed, the pH was adjusted to 6 and the mixture was stirred for 3 hours.

Next, the filter cake obtained by filtering the agitated product is dried at a drying temperature of 120 using a conical dryer.
After spray-drying at ℃, rare earth phosphate containing three kinds of rare earth elements, lanthanum, cerium and terbium was obtained. The obtained rare earth phosphate was mixed with lithium fluoride and boric acid at 30% by weight and 0.5% by weight, respectively, and the mixture was placed in an alumina crucible, in a reducing atmosphere consisting of 95% by volume of nitrogen and 5% by volume of hydrogen, Firing was performed at a temperature of 1200 ° C. for 3 hours to obtain a rare earth phosphate phosphor represented by (La _0.20 Ce _0.70 Tb _0.10 ) PO ₄ .

The rare earth phosphate phosphor thus obtained has a peak emission wavelength of 254 nm when excited by an ultraviolet ray of 254 nm.
It showed a green emission around 545 nm. When the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.00.

On the other hand, as a comparison with the present invention, one aqueous solution containing the same amounts of lanthanum chloride, cerium chloride and terbium chloride as in Example 2 was prepared and 1.0 mol of diammonium hydrogen phosphate was added thereto. The reaction was carried out at 40 ° C.
After the diammonium hydrogen phosphate was completely dissolved, the pH was adjusted to 6 and the mixture was stirred for 3 hours. Next, the filter cake obtained by filtering the agitated product was spray-dried under the same conditions as in Example 2 to obtain a rare earth phosphate. This rare earth phosphate was fired under the same conditions as in Example 2 to prepare a rare earth phosphate phosphor. When the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.08.

Next, using the rare earth phosphate phosphors obtained in Example 2 and Comparative Example 2 above, fluorescent lamps were produced and the emission brightness was measured. As a result, the emission brightness of the fluorescent lamp using the phosphor of Example 2 was improved by 3.0% as compared with the fluorescent lamp using the phosphor of Comparative Example 2.

Example 3, Comparative Example 3 A 0.40 mol / l lanthanum chloride aqueous solution, a 0.45 mol / l cerium chloride aqueous solution, and a 0.15 mol / l terbium chloride aqueous solution were individually prepared, and then the respective aqueous solutions were prepared. Equimolar amounts of diammonium hydrogen phosphate were each added and reacted individually at room temperature. Then, after the precipitated lanthanum phosphate, cerium phosphate and terbium phosphate were mixed, the pH was adjusted to 7 and the mixture was stirred for 2 hours.

Next, the filter cake obtained by filtering the agitated product is dried at a drying temperature of 120 using a conical dryer.
After spray-drying at ℃, rare earth phosphate containing three kinds of rare earth elements, lanthanum, cerium and terbium was obtained. The obtained rare earth phosphate was mixed with lithium fluoride and boric acid at 30% by weight and 0.5% by weight, respectively, and the mixture was placed in an alumina crucible and calcined in the air at a temperature of 1250 ° C. for 5 hours, and (La _0.40 Ce A rare earth phosphate phosphor represented by _0.45 Tb _0.15 ) PO ₄ was obtained.

The thus-obtained rare earth phosphate phosphor has a peak emission wavelength when excited by an ultraviolet ray of 254 nm.
It showed a green emission around 545 nm. In addition, when the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.01.

On the other hand, as a comparison with the present invention, one aqueous solution containing the same amounts of lanthanum chloride, cerium chloride and terbium chloride as in Example 1 was prepared and 1.0 mol of diammonium hydrogen phosphate was added thereto. The reaction was carried out at room temperature.
After the diammonium hydrogen phosphate was completely dissolved, the pH was adjusted to 7 and the mixture was stirred for 3 hours. Next, the filter cake obtained by filtering the agitated product was spray-dried under the same conditions as in Example 3 to obtain a rare earth phosphate. This rare earth phosphate was fired under the same conditions as in Example 3 to prepare a rare earth phosphate phosphor. When the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.06.

Next, using the rare earth phosphate phosphors obtained in Example 1 and Comparative Example 1 above, fluorescent lamps were produced and the emission brightness was measured. As a result, as compared with the fluorescent lamp using the phosphor of Comparative Example 1, the emission brightness of the fluorescent lamp using the phosphor of Example 1 was improved by 1.5%.

Example 4, Comparative Example 4 A 0.30 mol / l lanthanum chloride aqueous solution, a 0.60 mol / l cerium chloride aqueous solution, and a 0.10 mol / l terbium chloride aqueous solution were individually prepared, and then these aqueous solutions were prepared. Equimolar diammonium hydrogen phosphate was added respectively and reacted individually at 50 ° C. Then, after the precipitated lanthanum phosphate, cerium phosphate and terbium phosphate were mixed, the pH was adjusted to 6 and the mixture was stirred for 2 hours.

Next, the filter cake obtained by filtering the agitated product is dried at a drying temperature of 120 using a conical dryer.
After spray-drying at ℃, rare earth phosphate containing three kinds of rare earth elements, lanthanum, cerium and terbium was obtained. The obtained rare earth phosphate was mixed with lithium fluoride and boric acid at 20% by weight and 0.5% by weight, respectively, and the mixture was placed in an alumina crucible and fired at a temperature of 1300 ° C. for 3 hours in the atmosphere, and (La _0.30 Ce A rare earth phosphate phosphor represented by _0.60 Tb _0.10 ) PO ₄ was obtained.

The rare earth phosphate phosphor thus obtained has a peak emission wavelength when excited by an ultraviolet ray of 254 nm.
It showed a green emission around 545 nm. When the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.00.

On the other hand, as a comparison with the present invention, one aqueous solution containing the same amounts of lanthanum chloride, cerium chloride and terbium chloride as in Example 4 was prepared and 1.0 mol of diammonium hydrogen phosphate was added thereto. The reaction was carried out at 50 ° C.
After the diammonium hydrogen phosphate was completely dissolved, the pH was adjusted to 6 and the mixture was stirred for 3 hours. Next, the filter cake obtained by filtering the agitated product was subjected to spray drying under the same conditions as in Example 4 to obtain a rare earth phosphate. This rare earth phosphate was fired under the same conditions as in Example 4 to prepare a rare earth phosphate phosphor. When the composition of this phosphor was analyzed, the molar ratio of the rare earth element to phosphorus was 1.12.

Next, using the rare earth phosphate phosphors obtained in Example 4 and Comparative Example 4 above, fluorescent lamps were produced and the emission brightness was measured. As a result, the emission brightness of the fluorescent lamp using the phosphor of Example 4 was improved by 3.5% as compared with the fluorescent lamp using the phosphor of Comparative Example 4.

[0033]

As described above, according to the method for producing a rare earth phosphate phosphor of the present invention, a uniform rare earth phosphate crystal having a constant molar ratio of rare earth element and phosphorus can be obtained with good reproducibility. It becomes possible. As a result, it becomes possible to stably produce a rare earth phosphate phosphor having good emission luminance characteristics.

[0034]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Iwasaki 1-7 Nisshin-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Toshiba Electronics Engineering Co., Ltd.

Claims (2)

[Claims] 1. A general _{formula: (La 1-xy Ce x} Tb y) PO 4 ( wherein, x and y are x> 0, y> 0, 0.1 ≦ x + y ≦ 0.
In order to produce a rare earth phosphate phosphor substantially represented by (8), a lanthanum salt aqueous solution, a cerium salt aqueous solution and a terbium salt aqueous solution are prepared respectively, and these aqueous solutions and phosphoric acid compounds are separately prepared. A step of reacting to synthesize lanthanum phosphate, cerium phosphate and terbium phosphate, respectively, and mixing the lanthanum phosphate, cerium phosphate and terbium phosphate in a desired ratio to adjust the pH, and then drying the rare earth phosphate having a desired composition. A method for producing a rare earth phosphate phosphor, comprising: a step of synthesizing a salt; and a step of firing the rare earth phosphate in the air or a reducing atmosphere. 2. The method for producing a rare earth phosphate phosphor according to claim 1, wherein the lanthanum salt, cerium salt and terbium salt is one selected from chloride, nitrate, carbonate, oxalate and oxide. A method for producing a rare earth phosphate phosphor, characterized by using.