KR930003387B1 - Process for the preparation of luminous materials - Google Patents

Abstract

The fluorescent material is mfd. by (a) dissolving 50 g La2O3 and 0.6 g Ce2O3 into 100 ml thick nitric acid, (b) adding 100 g oxalic acid to the mixture to precipitate La/Ce coprecipitation cpd., (c) firing the La/Ce cpd. at 100 deg.C for 2 hr to obtain La/Ce oxide, (d) heat-treating the mixture of La/Ce oxide and 30 g NH4Br at 400 deg.C for 2 hr to obtain LaOBr:Ce fluorescent material, and (e) adding 11 g KBr and 5 g KF as a flux to the fluorescent material, and then firing it under HBr + H2 gas at 1000 deg.C for 2 hr.

Description

[Name of invention]

Manufacturing method of phosphor

Detailed description of the invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth oxidized halide phosphor, and more particularly, to a method for producing a rare earth oxidized halide phosphor revived with a rare earth element having excellent crystal form used in an apparatus for storing and reproducing images.

Rare earth oxidized halide phosphors such as La, Gd, and Lu, which are generally revived by Ta, Er, Tm, and Ce, are excited by electromagnetic waves such as visible or infrared rays after being irradiated with light such as X-rays, cathode rays, and UV rays. It is used to store and reproduce an image of an X-ray imaging tube, an X-ray sensitizer, a fluorescent screen, etc. as a phosphor that emits light stimulated over a UV region to a blue region.

Rare earth oxidized halide phosphors revived with a rare earth element represented by the general formula LnOX: M ³⁺ (wherein Ln is a rare earth element such as La, Gd and Y, X is a halogen element such as Cl, Br, or I, and M ³⁺ is a rare earth activator such as Tb, Tm, and Ce.) Was prepared by two methods, a gaseous reaction process and a molten salt process.

For example, US Pat. No. 3,607,770 obtains good crystals of rare earth oxyhalide and rare earth oxides in a gas phase reaction process, and US Patent Application No. 769,940 describes a novel manufacturing method by a molten salt process.

However, the LnOX: M ³⁺ phosphors produced by the above two methods had low luminous efficiency due to the incomplete growth of thin particles of elliptical shape, and KBr was added as a flux for crystal growth, but the average particle size was about 3 to 5 μm. It is not suitable when crystals of large particles are required.

Therefore, in order to manufacture LnOX: M ³⁺ phosphors having normal crystal growth and having large grains, a method of increasing the firing temperature or extending the firing time was adopted, but there was no practical value in terms of ease of manufacture and manufacturing cost. There is an uneconomic problem.

It is an object of the present invention to provide a method for producing a LnOX: M ³⁺ phosphor which has crystals of large particles without changing firing temperature and time and promotes crystal growth to prevent a decrease in luminous efficiency.

In order to achieve the above object, the rare earth oxidizing halide phosphor of the present invention comprises the steps of mixing the raw materials, the first crystallization step and the second crystallization step, at least one of the steps of adding a flux It is characteristic in that it does.

The preparation method of the LnOX: M ³⁺ phosphor of the present invention is as follows.

Conventional LnOX: M ³⁺ phosphors have two processes when produced by the gas phase reaction process method. Hereinafter, the LaOBr: Ce phosphor will be described as an example.

(1) A process

A process is a process of manufacturing a fluorescent substance after mixing a raw material and passing through one baking process.

[Departure material]

La ₂ O ₃

Ce ₂ O ₃ raw material mixture → firing process → LaOBr: Ce ³⁺ phosphor

NH ₄ Br

KBr

(2) B process

Process B is a process of manufacturing a phosphor through a three-step baking process of converting a raw material mixture into an oxide, a first crystallization step, and a second crystallization step.

(Starting material)

LaOBr: Ce phosphors can be produced from the above two steps, and the difference between the two steps depends on the number of steps of firing process.

In the present invention, by adopting the B step of the A, B process to achieve a predetermined object by adding a novel material acting as a flux in the second crystallization step.

Therefore, the process B will be described in detail as follows.

Lanthanum oxide (La ₂ O ₃ ) and cerium oxide (Ce ₂ O ₃ ) are dissolved in concentrated nitric acid and boiled for several minutes to increase dissolution.

[Conversion step to oxide]

Thereafter, the mixture was cooled at 50 to 60 ° C., diluted with an appropriate amount of pure water, and 120 to 200% of oxalic acid was added to precipitate the coprecipitation compound of La and Ce.

After that, the coprecipitated compound is allowed to stand for a certain time, and the supernatant is washed several times by draining to separate from water and dried at 100 ° C in air. The dried oxalate co-precipitation compound of La and Ce was calcined at 1000 ° C. for 1 to 2 hours to be converted into the oxide form of La and Ce, and then uniformly mixed with NH ₄ Br, and then heated at 1 to 400 to 500 ° C. Heat treatment for 2 hours to give LaOBr: Ce ³⁺ phosphor having incomplete crystals. (First crystallization step)

Subsequently, the obtained phosphor particles were calcined by simultaneously adding KBr and KF as fluxes under a reducing gas of N ₂ or CO ₂ and HBr atmosphere (secondary crystallization step).

In this case, the addition amount of KBr and KF is preferably 0.05 to 0.6 mol based on 1 mol of La ₂ O ₃ . If it is more than 0.6 mole, the light emission luminance is lowered.

The preferred embodiment of the present invention having the above features will be described in detail.

EXAMPLE

50 g of La ₂ O ₃ (purity: 99.99%) and 0.5856 g of Ce ₂ O ₃ (purity; 99.9%) are dissolved in 100 ml of concentrated nitric acid, and 100 g of oxalic acid is slowly added under stirring to precipitate the coprecipitation compound of La and Ce. The precipitated coprecipitation compound is washed several times with pure water, separated from water, and dried at 100 ° C.

The co-precipitation compound of La and Ce thus obtained was calcined at 100 ° C. for 2 hours to be converted into La and Ce oxide, and then NH ₃ Br 30g was mixed and heat-treated at 400 ° C. for 2 hours to first crystallize LnOBr: Ce phosphor was obtained.

The resulting phosphor is unstable in crystals and emits poor light, so that in order to promote crystal growth of the final calcined product under HBr and H ₂ gas atmosphere, KBr 11g and KF 5g are simultaneously added and calcined at 1000 ° C. for 2 hours to secondary crystallization. LaOBr: Ce phosphor was obtained.

Comparative Example

In the same manner as in Example, but only KBr was added as a flux to obtain LaOBr: Ce phosphor. Table 1 shows the result of comparing the phosphor thus obtained and the phosphor obtained in the example.

TABLE 1

Characteristics of LaOBr: Ce ³⁺ Phosphors

Note: 1); C.C measurement

2); MCPD Measurement

As can be seen from Table 1, it was confirmed that the phosphor obtained by simultaneous addition of KBr and KF as a flux formed a good crystal having a size of about 3 μm in average particle diameter and about 6% in light emission luminance.

In addition, the phosphor prepared by adding KF should be processed for 2 hours by raising the firing temperature in the final firing step from 1000 ° C. to 1200 ° C. in order to produce particles similar to the particle size of the phosphor prepared by adding KF. The use of KF is very effective because it is not economical in terms of cost and ease of manufacture.

As described above, according to the present invention, a phosphor obtained by simultaneously adding KBr and KF in the final firing step as a flux through a three-step firing process, which is larger than the phosphor prepared by the conventional manufacturing method and has an average particle diameter of about 3 A large crystal shape of about μm was obtained, and the luminous efficiency was improved, resulting in an increase in brightness of about 6%, which is very economical in terms of manufacturing cost and ease of manufacture.

Claims (5)

A method for producing a rare earth oxidized halide phosphor that has been revived from a rare earth element, the method comprising mixing raw materials, a first crystallization step, and a second crystallization step, wherein the flux is applied in at least one of the steps. A method for producing a rare earth oxidized halide phosphor, which is added. The method of claim 1, wherein the first crystallization step is to add the oxalic acid to the raw material mixture to precipitate and dry the coprecipitation compound, mixed with ammonium bromide and calcined for 1 to 2 hours at 400 to 500 ℃ Method for producing a rare earth oxidized halide phosphor. The method of claim 1, wherein the second crystallization step is characterized in that the calcined product obtained in the first crystallization step is fired for 30 minutes to 3 hours at 800 to 1200 ℃ under N ₂ or CO ₂ atmosphere and HBr atmosphere A method of producing a rare earth oxidized halide phosphor. 2. The method of claim 1, wherein KBr and KF are used in combination as the flux. 5. The method of claim 4, wherein the addition amount of the KBr and KF is in the range of 0.05 to 0.6 moles, respectively, based on 1 mole of La ₂ O ₃ .