JPH06128565A - Production of rare earth phosphate phosphor - Google Patents

Abstract

PURPOSE:To produce a substantially spherical phosphor having a stable particle diameter distribution with good reproducibility. CONSTITUTION:A process for producing a rare earth phosphate phosphor substantially represented by the general formula: (M1-x-yCexTby)PO4 (wherein M is at least one element selected from among La, Y and Gd, and x and y are numbers satisfying the formulas: x>0, y>0, and 0.1<=x+y<=0.7) by reacting a compound containing a rare earth element with a phosphoric acid compound in a solution, which comprises performing drying after the reaction in at least one state selected from among a sprayed state, a fluidized state and a frozen state.

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, for example, is used as the green light emitting component of the above-mentioned three-wavelength band fluorescent lamp. As a method for producing the rare earth phosphate phosphor, a rare earth element oxalate is roasted to obtain a rare earth oxide, and after mixing this with ammonium phosphate,
A method of obtaining a phosphor by firing at a temperature of 1000 to 1200 ° C. in a reducing atmosphere is well known.

However, in the above-mentioned method for producing a rare earth phosphate phosphor, since the shape of the rare earth oxide is a substantially rectangular and angular shape, when an oxide having such a shape is used as a raw material, The shape of the obtained phosphor is also rectangular and rectangular. When a phosphor film is formed using a phosphor having such a shape, there is a problem that a smooth phosphor screen cannot be obtained due to the influence of the particle shape. The roughness of the film surface of the phosphor screen causes a decrease in the luminous flux maintenance factor during the lighting of the lamp.

Also known is a method for producing a rare earth phosphate by reacting a phosphoric acid compound with an oxide or carbonate of a rare earth element in a solution. However, in this method for producing a rare earth phosphate, if the drying after the reaction is carried out by an ordinary drying method, the obtained rare earth phosphate will be solidified and aggregated, and the subsequent treatment steps will be difficult. However, there are problems that the phosphor characteristics vary greatly and that it is difficult to obtain a stable particle shape.

[0006]

As described above, according to the conventional method for producing a rare earth phosphate phosphor, the obtained phosphor has a rectangular rectangular shape, and a smooth phosphor screen is obtained. The problem is that the luminous flux maintenance factor decreases during lamp operation, or the rare earth phosphate aggregates and solidifies during the manufacturing process, resulting in low reproducibility of particle shape and phosphor characteristics. Was invited.

The present invention has been made in order to solve such a problem, and has made it possible to obtain a rare earth phosphate phosphor having a substantially spherical shape and a stable particle size distribution with good reproducibility. It is intended to provide a method of manufacturing a body.

[0008]

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: (M _1-xy Ce _x Tb _y ) PO ₄ (wherein M is La, Y and At least 1 selected from Gd
Represents the element of the species, where x and y are x> 0, y> 0, 0.1 ≦
x + y ≦ 0.7) represents a rare earth phosphate phosphor substantially represented by the following reaction in producing a compound containing a rare earth element and a phosphoric acid compound in a solution. The feature is that the subsequent drying is performed in one of a spraying state, a fluidized state and a frozen state.

In the production method of the present invention, a compound of a rare earth element such as a nitrate, an oxide, a carbonate or a chloride is first used as a raw material and at least one element selected from La, Y and Gd and Ce. Tb is prepared for each, and a phosphoric acid compound is added to an aqueous solution containing these in predetermined amounts. The phosphoric acid compound used may be either solid or liquid. However, 1.001-
It is preferable to add excessively in the range of 1.400 times.

Next, after the phosphoric acid compound is almost completely dissolved, the pH of the solution is adjusted to about 4 to 8 using, for example, NH ₄ OH solution. Adjusting the pH affects the size of the precipitate,
When adjusted to the alkaline side, the precipitated particles become large, which adversely affects the subsequent drying process. Then from room temperature to 100 ° C
After the reaction is carried out in a temperature range of about 2 hours or more, washing is performed. This washing is preferably repeated until the electric conductivity of the supernatant becomes 0.3 ms / cm or less. If the washing is insufficient, that is, if the amount of residual cations is large, coarse agglomerated particles are likely to be generated in the subsequent drying step.

After washing in this way, drying is carried out 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 having a uniform particle size, which facilitates the subsequent firing step (crystal growth step) and makes the particle shape spherical. It is possible to obtain a phosphor having a close particle size and a uniform particle size. The fluidized drying is
For example, it is a method of drying while moving the slurry to be dried on a disc. Freeze-drying is a method in which the slurry to be dried is frozen and then vacuumed to dry.

In the baking step after drying, after adding an alkali metal compound and a borate compound as a flux to the obtained rare earth phosphate, for example, in a reducing atmosphere containing nitrogen and hydrogen. , 1 ℃ to 1300 ℃ for 1 to 5 hours. Thereby, as described above, a phosphor having a particle shape close to a spherical shape and a uniform particle diameter can be obtained.

[0013]

EXAMPLES Examples of the present invention will be described below.

[0014] Example 1, Comparative Example 1 LaCl ₃ 137.4 g, in an aqueous solution containing CeCl ₃ 74.0 g and _{TbCl 3 37.1g, (NH 4)} 2 HPO 4 132.1g was added, to complete dissolution, NH ₄ After adjusting the pH to 7 with OH water, the mixture was reacted at room temperature for 24 hours. Then, the supernatant was washed until the electric conductivity was 0.3 ms / cm or less, and then filtered. The filter cake obtained by this filtration was freeze-dried under conditions of a trap temperature of -50 ° C.

Next, 30% by weight and 1.0% by weight of LiF and H ₃ BO ₃ , respectively, were added to the obtained soft rare earth phosphate and mixed by a dry method, then put in an alumina crucible, and nitrogen was added.
Firing was performed in a reducing atmosphere consisting of 95% by volume and 5% by volume of hydrogen at 1250 ° C. for 4 hours. The composition of the obtained phosphor is (La _0.56 Ce _0.30 Tb _0.14 ) PO ₄ .

The phosphor thus obtained exhibited green light emission with an emission peak wavelength around 545 nm when excited by ultraviolet rays. In addition, the fluorescent substance was used as a scanning electron microscope (SE
As a result of observation under M), it was confirmed that the particles had a uniform size and were substantially spherical.

The 50% D of the particle size distribution of this phosphor was measured and found to be 3.5 μm. Repeating the reproduction experiment twice under the above conditions and measuring 50% D of the particle size distribution of the phosphor obtained in each case, it was 3.5 μm for all, and the same value was obtained for all three times, and the stability of the particle size was obtained. Was confirmed to be high.

On the other hand, as a comparison with the present invention, using the same raw materials as in Example 1 above, the reaction, washing and filtration were carried out in the same manner, and the cake after filtration was dried with hot air at 100 ° C. Upon application, the obtained rare earth phosphate aggregated and solidified. Therefore, this solidified product was crushed in a mortar and then fired under the same conditions as in the above-mentioned example. The composition of the obtained phosphor is (La _0.56 Ce _0.30 Tb _0.14 ) PO ₄ .

When the phosphor according to this comparative example was observed with an SEM, it was found that spherical particles and spherical broken particles were mixed. In addition, 2
When 50% D of the particle size distribution of the phosphor obtained in the reproduction experiment was measured, the fluctuations were large, 2.5 μm, 4.0 μm and 3.4 μm.

Next, using the phosphor obtained in the above-mentioned example and the phosphor having 50% D of 3.4 μm in the above-mentioned comparative example,
Each of the fluorescent lamps was manufactured, and the emission intensity after 1000 hours of lighting was examined. When the emission intensity of the fluorescent lamp using the phosphor according to the comparative example was set to 100%, the fluorescent lamp using the phosphor according to the example showed a good luminous flux maintenance factor of 106%. Examples 2 to 4, Comparative Examples 2 to 4 Instead of the lanthanum-containing rare earth chloride raw material used in Example 1, carbonate raw materials (Example 2) and oxide raw materials (Example 3) shown in Table 1 were used. Using the nitrate raw materials (Example 4), reaction up to an aqueous solution was performed under the conditions shown in Table 1. Then, drying and firing were performed under the same conditions as in Example 1 to produce phosphors having the compositions shown in Table 1. In addition, as Comparative Examples 2 to 4, Comparative Example 1 using the same raw material
Phosphors were produced under the same conditions as above.

50% D of the particle size distribution of each of the phosphors of Examples 2 to 4 (including two reproduction experiments) and each of the phosphors of Comparative Examples 2 to 4 (including two reproduction experiments). The measurement results are shown in Table 2. Table 2 shows the emission intensity of each fluorescent lamp produced in the same manner as in Example 1 after 1000 hours of lighting. As is clear from Table 2, each of the phosphors of Examples 2 to 4 had a high particle diameter stability and an excellent luminous flux maintenance factor.

Example 5, Comparative Example 5 Y (NO ₃ ) ₃ 192.5 g, Ce (NO ₃ ) ₃ 65.2 g and Tb (N
O ₃ ) ₃ 34.5 g in (NH ₄ ) ₂ HPO ₄ 116.1
After g was added and completely dissolved, the pH was adjusted to 5.0 with NH ₄ OH water, and the mixture was reacted at 60 ° C. for 2 hours. Then, the supernatant was washed until the electric conductivity was 0.3 ms / cm or less, and then filtered. The filter cake obtained by this filtration was spray-dried using a conical dryer at a drying temperature of 130 ° C.

Next, to the obtained soft rare earth phosphate, 30% by weight and 1.0% by weight of LiCl and H ₃ BO ₃ , respectively, were added and mixed by a dry method, then put in an alumina crucible and the same as in Example 1. It was fired under the conditions. The composition of the obtained phosphor is
(Y _0.7 Ce _0.2 Tb _0.1 ) PO ₄ .

The phosphor thus obtained showed green light emission with an emission peak wavelength around 545 nm when excited by ultraviolet rays. When this phosphor was observed by SEM, it was confirmed that the particles had a uniform size and were substantially spherical.

The 50% D of the particle size distribution of this phosphor was measured and found to be 2.5 μm. Repeating the reproduction experiment twice under the above conditions and measuring 50% D of the particle size distribution of the phosphor obtained in each case, it was 2.5 μm for all, and the same value was obtained for all three times, and the stability of the particle size was obtained. Was confirmed to be high.

On the other hand, as a comparison with the present invention, a phosphor was prepared in the same manner as in Comparative Example 1 using the same raw material as in Example 5 above. The composition of the obtained phosphor is (Y _0.7 Ce _0.2 Tb
_0.1 ) PO ₄ .

When the phosphor according to Comparative Example 5 was observed with an SEM, spherical particles and spherical broken particles were mixed. Further, when the 50% D of the particle size distribution of the phosphor according to Comparative Example 5 and the phosphor obtained in two reproduction experiments under the same conditions were measured, they were 2.5 μm and 3.0 μm, respectively.
There was a large variation of m and 3.7 μm.

Next, the phosphor obtained in Example 5 described above,
Fluorescent lamps were produced using 50% D of the phosphor of 2.5 μm in Comparative Example 5, and the emission intensity after 1000 hours of lighting was examined. When the emission intensity of the fluorescent lamp using the phosphor according to Comparative Example 5 was 100%, the fluorescent lamp using the phosphor according to Example 5 showed a good luminous flux maintenance factor of 105%.

Examples 6 to 8 and Comparative Examples 6 to 8 Instead of the rare earth nitrate raw material containing yttrium used in Example 5, the oxide raw material (Example 6) and the chloride raw material (Example) shown in Table 1 were used. 7) and carbonate raw material (Example 8) were used, and the reaction up to the aqueous solution was performed under the conditions shown in Table 1. Then, drying and firing were performed under the same conditions as in Example 5 to produce phosphors having the compositions shown in Table 1. In addition, as Comparative Examples 6 to 8, phosphors were produced using the same raw material under the same conditions as in Comparative Example 5.

50% D of the particle size distribution of each of the phosphors of Examples 6 to 8 (including two reproduction experiments) and each of the phosphors of Comparative Examples 6 to 8 (including two reproduction experiments). The measurement results are shown in Table 2. Table 2 shows the emission intensity of each fluorescent lamp produced in the same manner as in Example 1 after 1000 hours of lighting. As is clear from Table 2, each of the phosphors of Examples 6 to 8 had high particle size stability and excellent luminous flux maintenance factor.

Example 9, Comparative Example 9 Gd ₂ (CO ₃ ) ₃ 86.5 g, Ce ₂ (CO ₃ ) ₃ 92 g and Tb ₂
To an aqueous solution containing (CO ₃ ) ₃ 62g, (NH ₄ ) ₂ HPO ₄ 98g
Was added and completely dissolved, and then the pH was adjusted to 4 with aqueous NH ₄ OH, and then the mixture was reacted at 40 ° C. for 10 hours. Then, the supernatant was washed until the electric conductivity was 0.3 ms / cm or less, and then filtered. The filter cake obtained by this filtration was subjected to fluidized drying using a disc dryer at a drying temperature of 280 ° C.

Next, Li ₂ CO ₃ and H ₃ BO ₃ were added to the obtained soft rare earth phosphate at 30% by weight and 1.0% by weight, respectively.
%, Add dry mix, put in an alumina crucible,
The firing was performed under the same conditions as in Example 1. The composition of the obtained phosphor is (Gd _0.35 Ce _0.40 Tb _0.25 ) PO ₄ .

The phosphor thus obtained exhibited green light emission with an emission peak wavelength around 545 nm when excited by ultraviolet rays. When this phosphor was observed by SEM, it was confirmed that the particles had a uniform size and were substantially spherical.

The 50% D of the particle size distribution of this phosphor was measured and found to be 2.0 μm. Repeating the experiment twice under the above conditions and measuring 50% D of the particle size distribution of the phosphor obtained in each case, it was 2.0 μm for all, and the same value was obtained for all three times, and the particle size stability Was confirmed to be high.

On the other hand, as a comparison with the present invention, a phosphor was prepared in the same manner as in Comparative Example 1 using the same raw material as in Example 9 above. The composition of the obtained phosphor is (Gd _0.35 Ce _0.40 Tb
_0.25 ) PO ₄ .

When the phosphor according to Comparative Example 9 was observed with an SEM, spherical particles and spherical broken particles were mixed. Further, when the 50% D of the particle size distribution of the phosphor according to Comparative Example 9 described above and the phosphor obtained in two reproduction experiments performed under the same conditions were measured, respectively, it was 2.0 μm.
The fluctuations were large at 3.0 μm and 4.0 μm.

Next, the phosphor obtained in Example 9 above,
Fluorescent lamps were prepared using the phosphors of 50% D of 2.0 μm in Comparative Example 9 above, and the emission intensity after 1000 hours of lighting was examined. When the emission intensity of the fluorescent lamp using the phosphor according to Comparative Example 9 was set to 100%, the fluorescent lamp using the phosphor according to Example 9 showed a good luminous flux maintenance factor of 104.5%.

Examples 10-12, Comparative Examples 10-12 In place of the gadolinium-containing rare earth carbonate raw materials used in Example 9, chloride raw materials (Example 10) and oxide raw materials (Example) shown in Table 1 were used. Example 11) and a nitrate raw material (Example 12) were used, and the reaction in an aqueous solution was performed under the conditions shown in Table 1. After this, drying under the same conditions as in Example 9,
By firing, phosphors having the compositions shown in Table 1 were produced. Further, as Comparative Examples 10 to 12, phosphors were produced under the same conditions as in Comparative Example 9 using the same raw materials.

A 50% D particle size distribution of each of the phosphors of Examples 10 to 12 (including two reproduction experiments) and each of the phosphors of Comparative Examples 10 to 12 (including two reproduction experiments) was used. The measurement results are shown in Table 2. Table 2 shows the emission intensity of each fluorescent lamp produced in the same manner as in Example 1 after 1000 hours of lighting. As is clear from Table 2, each of the phosphors of Examples 10 to 12 had a high particle size stability and an excellent luminous flux maintenance factor.

[0040]

[Table 1]

[Table 2]

[0041]

As described above, according to the method for producing a rare earth phosphate phosphor of the present invention, a phosphor having a particle shape close to a sphere and a uniform particle diameter can be reproducible in an easy process. It is possible to get well.

[0042]

Claims (1)

[Claims] 1. A general _{formula: (M 1-xy Ce x} Tb y) PO 4 ( wherein, M is at least one selected from La, Y and Gd
Represents the element of the species, where x and y are x> 0, y> 0, 0.1 ≦
x + y ≦ 0.7) represents a rare earth phosphate phosphor substantially represented by the following: when a compound containing a rare earth element and a phosphoric acid compound are reacted in a solution, A method for producing a rare earth phosphate phosphor, characterized in that the subsequent drying is performed in one of a sprayed state, a fluidized state and a frozen state.