JPH1129324A - Cubic crystal of bafi containing rare earth element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cubic crystal of BaFI having uniform form and particle diameter by mixing a BaI2 aqueous solution containing a rare earth element with an aqueous solution of NH4 F having a specific concentration and concentrating the mixture by heating. SOLUTION: The objective BaFI cubic crystal containing rare earth element and expressed by the compositional formula of BaFI:xLn (Ln is at least one kind of rare earth element selected from Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb; 0<x<=0.1) is produced by mixing an aqueous solution of BaI2 containing at least one kind of rare earth element selected from Ce, Pr, Sm, Eu, Gd, Tm and Yb with an aqueous solution of NH4 F in such a manner as to get the Ba concentration of <=3.0 mol/L and an F/Ba molar ratio of 0.5-0.7 and concentrating the obtained mixture to a Ba concentration of >=3.2 mol/L under heating at >=70 deg.C. A fluorescent material is produced by heat-treating the cubic crystal in an inert gas atmosphere at 800-850 deg.C for 1-5 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel rare earth element-containing BaFI prismatic crystal useful as a raw material for a stimulable phosphor and a method for producing the same.

[0002]

2. Description of the Related Art Conventional methods for producing a rare earth element-containing BaFI crystal useful as a raw material for a stimulable phosphor include barium fluoride,
After mixing barium iodide, a halide of a rare earth element, or the like in a dry manner, or suspending and mixing in a solution, the mixture is fired and pulverized. Since the shape and particle size of the crystals obtained in this way are non-uniform, there is a problem that the phosphor layer obtained when applying a phosphor using this as a raw material becomes non-uniform. As a technique capable of solving such a problem, a method for manufacturing a tetrahedron is used in JP-A-7-233369. However, as for the BaFI system, no crystals of any shape can be obtained, not to mention tetradecahedral crystals, within the range of the synthesis conditions described in JP-A-7-233369.

[0003]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a novel rare earth element containing a uniform shape and particle size.
An object of the present invention is to provide a BaFI prismatic crystal and a method for producing the same.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention has been made by variously examining the reaction conditions of BaI ₂ and NH ₄ F, and has completed the present invention. x
Ln (where Ln is Ce, Pr, Sm, Eu, Gd, T
at least one selected from the group consisting of b, Tm and Yb
Represents a kind of rare earth element, and x represents a numerical value in a range represented by 0 ≦ x ≦ 0.1. ) Is a rare earth element-containing BaFI prismatic crystal represented by Ce), Pr, Sm, Eu, Gd, T
at least one selected from the group consisting of b, Tm and Yb
The Ba concentration in the aqueous solution of BaI ₂ containing the rare earth element and the aqueous solution after mixing is 3.0 mol / L or less, and the molar ratio of F / Ba is
An aqueous NH ₄ F solution whose concentration and concentration are adjusted so as not to exceed 0.7 is mixed, and the Ba concentration is adjusted to 3.
This is a method for producing a rare earth element-containing BaFI square crystal, which is characterized in that the crystal is precipitated by concentrating to 2 mol / L or more.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, a BaI ₂ aqueous solution containing a rare earth element and an NH ₄ F aqueous solution are prepared. In this case, the most important is the concentration of the liquid. However, the individual concentrations of the BaI ₂ aqueous solution and the NH ₄ F aqueous solution containing the rare earth element are not important. After mixing both solutions, adjust the concentrations of both solutions so that the Ba concentration in the mixed solution becomes 3.0 mol / L or less. It is important to. Ba concentration in the mixture is 3.
If it exceeds 0 mol / L, the crystal growth becomes non-uniform, and only aggregated plate-like crystals can be obtained. Although there is no lower limit of the Ba concentration in the mixed solution, crystals are precipitated by concentration, and therefore, it is advantageous that the concentration does not exceed 3.0 mol / L, as close as possible, in order to minimize the cost of concentration. Next important is the molar ratio of F / Ba to be mixed. F / Ba molar ratio is 0.5 ~
Must be set to 0.7. From the formula of BaFI, it is considered that the F / Ba molar ratio is advantageously 1.0, but it has been found that the yield is actually lowered when the F / Ba molar ratio is set to 1.0. The upper limit of the F / Ba molar ratio is 0.7, and if it exceeds this, the crystal grain size becomes extremely small and the yield decreases. Although there is no lower limit of the F / Ba molar ratio, it is preferable that the molar ratio be set to 0.5 or more, since too low a ratio is unsuitable for commercial production from the viewpoint of production speed due to loss of Ba.

Next, an aqueous solution of BaI ₂ containing a rare earth element and an aqueous solution of NH ₄ F are mixed with stirring. As a mixing method at this time, an NH ₄ F aqueous solution may be added to a BaI ₂ aqueous solution containing a rare earth element, or vice versa, or both may be simultaneously dropped and added to a container. Regardless of the method used for mixing, a gel-like precipitate is generated during mixing, but this disappears during the subsequent heating and concentration process, which affects the properties of the finally obtained rare earth element-containing BaFI square crystals. do not do. There is also no limitation on the mixing speed, and the mixing may be performed at once in a short time, or may be performed while dropping over time.
The temperature at the time of mixing is not particularly limited. However, since heating and concentration are performed as an operation subsequent to mixing, the production time can be reduced by heating at the time of mixing.

Next, the mixed aqueous solution is concentrated by heating. The heating temperature needs to be 70 ° C. or higher, and if it is heated and concentrated at a temperature lower than 70 ° C., fine aggregated crystals are precipitated, which is not preferable. When the concentration is continued, the gel precipitate generated in the mixing step disappears when the Ba concentration is approximately 2.8 mol / L. When the concentration is further continued, precipitation of a new crystal starts when the concentration exceeds 3.2 mol / L. Aging is performed at a temperature of 70 ° C. or more for about one hour from the start of the precipitation of the crystals to complete the precipitation of the crystals.

Crystals precipitated after heating and aging for about one hour are separated from the mother liquor by filtration or the like. The separated crystals are washed with a water-soluble organic solvent such as methanol, ethanol or acetone and then dried. When used as a phosphor, a heat treatment is further performed under an inert gas atmosphere at a temperature of 800 to 850 ° C. for 1 to 5 hours in order to improve the emission characteristics.

A novel rare earth element-containing BaFI prismatic crystal represented by the basic composition formula BaFI: xLn of the present invention will be described below. Ln is Ce, Pr, Sm, Eu, Gd, Tb, Tm
And at least one rare earth element selected from the group consisting of Yb and Yb, and x represents a numerical value in the range of 0 <x ≦ 0.1.
Ln acts as an activator and x represents its concentration. Even if the value of x exceeds 0.1, there is no improvement in the luminance of the phosphor.
1 or less. When the ratio of the shortest side to the longest side of the novel rare-earth element-containing BaFI prismatic crystal of the present invention is 0.5 or more, it means that the crystal must have a certain thickness or more. That is, when the thickness of the crystal is smaller than a certain limit, the cohesive strength is increased and the dispersibility is deteriorated. When applying the particles as a phosphor to any surface, there is a great merit that particles having good dispersibility can be applied uniformly. The value indicating the limit of the thickness of the crystal, that is, the ratio of the shortest side to the longest side of the prismatic crystal is 0.5 or more. Also, Ce, Pr, Sm, Eu, Gd, Tb, represented by Ln
At least one rare earth element selected from the group consisting of Tm and Yb is effective as an activator for the stimulable phosphor. Among them, Eu is particularly effective and practical.

[0010]

The embodiments of the present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these. It was heated to (Example 1) with stirring 80 ° C. Put solution 200ml of concentration 3.0 mol / L of BaI ₂ containing Eu beaker to 0.03 mol / L of 500 ml. While stirring, NH 3
50 ml of an aqueous solution having a concentration of ₄ F of 6.0 mol / L was introduced for 10 seconds. The formation of a gel-like precipitate was observed at the same time as the introduction. Immediately after the addition was completed, the Ba concentration of the mixed solution was 2.4 mol / L, and the F / Ba molar ratio was 0.5. Concentration by spontaneous evaporation was performed while heating at 80 ° C. was continued. When the Ba concentration of the mixed solution reached about 2.8 mol / L, the gel-like precipitate generated immediately after the introduction completely disappeared, and the solution became transparent. Further concentration was continued, and when the Ba concentration of the mixed solution reached about 3.2 mol / L, crystals started to precipitate. After further aging at 80 ° C. for 1 hour, the crystals were filtered off with a Buchner funnel and washed with ethanol. The crystals were further dried at 100 ° C. for 10 hours to obtain 83.1 g of Eu-containing BaFI square crystals. The shape of the obtained crystal is shown in FIG. 1 (Photo 1). The length of one side of the crystal was approximately 10 to 20 μm, the ratio of the shortest side to the longest side of all the crystals in this photograph was 0.5 or more, and the shape was a clean corner.

(Example 2) Synthesis was performed in exactly the same manner as in Example 1 except that the amount of the 6.0 mol / L aqueous NH ₄ F solution was changed to 70 ml, to obtain 87.3 g of Eu-containing BaFI prismatic crystals. Was.
The Ba concentration of the mixed solution immediately after the end of the charging was 2.22 mol / L,
The F / Ba molar ratio was 0.7. The grain size and the shape of the obtained crystals were exactly the same as in Example 1, and the ratio of the shortest side to the longest side of all the crystals was 0.5 or more, and the shape was a clean angular shape.

Comparative Example 1 Synthesis was performed in exactly the same manner as in Example 1 except that the amount of the 6.0 mol / L aqueous NH ₄ F solution was changed to 100 ml, to obtain 54.3 g of Eu-containing BaFI prismatic crystals. Was. Immediately after the addition was completed, the Ba concentration of the mixed solution was 2.0 mol / L, and the F / Ba molar ratio was 1.0. Although the shape of the obtained crystal was square, the length of one side of the crystal particle was about 1 μm and the crystal was strongly aggregated. Further, the yield was as low as 65% of Example 1.

(Comparative Example 2) Synthesis was carried out in the same manner as in Example 1 except that the concentration of the BaI ₂ aqueous solution was increased and the Ba concentration of the mixed solution immediately after the introduction was changed to 3.2 mol / L. Eu
The resulting BaFI crystal was obtained. The shape of the obtained crystal is shown in FIG. 2 (Photo 2). The shape of the crystals was not square but plate-like and very strongly aggregated.

(Comparative Example 3) In a 500 ml eggplant type flask
200 ml of 3.0 mol / L BaI ₂ aqueous solution containing 0.03 mol / L Eu
A 6.0 mol / L NH ₄ F aqueous solution (50 ml) was charged, and the mixture was concentrated under reduced pressure using a rotary evaporator. The temperature at this time was kept at 60 ° C. As in Example 1, formation of a gel-like precipitate, dissolution of the gel-like precipitate, and precipitation of crystals were observed. Example 1
The crystals were separated by filtration, washed and dried in the same manner as described above to obtain 73.6 g of Eu-containing BaFI crystals. Fine particles of the obtained crystals were aggregated in a lump, and no angular crystals were obtained.

[0015]

Industrial Applicability According to the present invention, it is possible to synthesize a rare earth element-containing BaFI prismatic crystal having a uniform shape and particle size, and its industrial utility is extremely large.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of the shape of the Eu-containing BaFI prismatic crystal of the present invention obtained in Example 1.

FIG. 2 is an electron micrograph of the shape of the Eu-containing BaFI crystal obtained in Comparative Example 2.

Claims (3)

[Claims] 1. The basic composition formula BaFI: xLn (where Ln is C
e represents at least one rare earth element selected from the group consisting of Pr, Sm, Eu, Gd, Tb, Tm and Yb, and x represents a numerical value in the range of 0 <x ≦ 0.1. ) A rare earth element-containing BaFI prismatic crystal represented by). 2. The rare earth element-containing BaFI prismatic crystal according to claim 1, wherein the ratio of the shortest side to the longest side of the prismatic crystal is 0.5 or more. 3. Ce, Pr, Sm, Eu, Gd, Tb,
A BaI ₂ aqueous solution containing at least one rare earth element selected from the group consisting of Tm and Yb;
a concentration is 3.0 mol / L or less and the molar ratio of F / Ba is 0.7
Is mixed with an aqueous solution of NH ₄ F whose concentration and concentration have been adjusted so as not to exceed 300 ° C., and heated at 70 ° C. or higher while the Ba concentration is 3.2 mol.
A method for producing a rare earth element-containing BaFI prismatic crystal, wherein the crystal is precipitated by concentrating the solution to at least / L or more.