JPH069956A - Spherical sintered phosphor and its production - Google Patents

Abstract

PURPOSE:To obtain the title phosphor showing high-luminance stimulated luminescence by spray-drying a slurry containing specified phosphor particles and a binder to obtain spherical granules, removing the binder from the granules by heating, and firing them. CONSTITUTION:A mixture of a binder with particles of an alkaline earth metal fluorohalide phosphor activated by a rare earth element of the formula wherein MII is an alkaline earth metal; X is halogen; Ln is at least one rare earth metal element selected from among Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Sm and Gd, and 0<x<=0.2 is slurried in an organic solvent. The resulting slurry is spray-dried to obtain spherical granules, which are heated for 0.5-5hr at 200-500 deg.C to remove the binder therefrom and fired by heating for 0.5-5hr at 600-1300 deg.C. In this way, a substantially spherical sintered alkaline earth metal fluorohalide phosphor activated by a rare earth element can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphor and a method for producing the same, more specifically, the present invention relates to a rare earth element alkaline earth metal fluorohalide-based phosphor and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, when irradiated with radiation such as X-rays, electron beams and ultraviolet rays and then excited by electromagnetic waves (excitation light) in the visible or infrared region, it emits light in the near ultraviolet or blue region (stimulated emission). As a stimulable phosphor, a divalent europium-activated alkaline earth metal fluorohalide-based phosphor (M ^II
FX: Eu ²⁺ , M ^II are alkaline earth metals, and X is a halogen other than fluorine), and rare earth element-activated alkaline earth metal fluorohalide-based phosphors are well known. This phosphor is drawing attention as a phosphor for a radiation image conversion panel used in a radiation image conversion method using a stimulable phosphor.

Generally, the above-mentioned phosphors are produced by mixing the phosphor raw materials by a wet or dry method to prepare a raw material mixture, and then firing the mixture in a weak reducing atmosphere or a neutral atmosphere. The particle shape of the obtained phosphor is plate-like or amorphous having many irregularities on the surface.

As one of the methods for controlling the particle shape of the phosphor, there is a granulation technique utilizing spray drying, and this method can obtain spherical secondary particles. It is also known that the phosphor particles are molded and fired at a high temperature to sinter the primary particles of the phosphor to obtain a sintered body having various shapes such as a sheet shape.

Japanese Unexamined Patent Publication (Kokai) No. 62-86086 discloses a divalent europium-activated alkaline earth metal fluorohalide-based phosphor in which the particle shape is 1 in length and 1 in width and 1 in height. 2 and a substantially cubic phosphor having a ratio in the range of 0.5 to 2, and a method for producing the phosphor,
A method is described in which a phosphor raw material is dissolved in an aqueous solvent, the solution is rotatively dried under reduced pressure to prepare a raw material mixture, and then the raw material mixture is fired. The phosphor obtained by this method has a cubic shape and is not sintered.

Further, JP-A-2-167386 discloses a spherical aggregate containing plate-shaped or needle-shaped phosphor particles or a mixture of plate-shaped and needle-shaped phosphor particles together with a binder, Aggregates in which the plate-shaped and / or needle-shaped phosphor particles have an aspect ratio larger than 1: 1 and are randomly oriented inside the aggregate, and After forming a dispersion or slurry in which the individual phosphor particles are dispersed in a suitable liquid solvent containing a binder, the slurry is spray dried under conditions suitable to evaporate the liquid solvent. To form the spherical aggregates of the phosphor particles. What is obtained by this method is an aggregate of the phosphor containing the binder, and the phosphor itself remains in the shape of a plate and / or a needle.

[0007]

In the above-mentioned radiation image conversion method, it is desirable that the sensitivity is as high as possible in order to reduce the exposure dose of radiation such as X-rays. It is required that the stimulated emission luminance be as high as possible. Further, it is desirable that when the phosphor layer is formed, the shape of the phosphor particles is not changed (for example, agglomerates such as secondary particles are changed to primary particles). Further, in order to enhance the X-ray absorption ability of the phosphor, it is desirable that the spherical phosphor particles have a high density, which cannot be obtained by the phosphor aggregate.

An object of the present invention is to provide a spherical rare earth element-activated alkaline earth metal fluorohalide-based phosphor that exhibits stimulated luminescence with high brightness.

[0009]

Means for Solving the Problems Basic composition formula (I): M ^II FX: xLn (I) (where M ^II is at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca) Yes; X
Is at least one halogen selected from the group consisting of Cl, Br and I; Ln is Eu, Tb, Ce, T
at least one rare earth element selected from the group consisting of m, Dy, Pr, Ho, Nd, Yb, Er, Sm and Gd; and x is a numerical value in the range of 0 <x ≦ 0.2). A rare earth element activated alkaline earth metal fluoride halide phosphor, which is a substantially spherical sintered phosphor.

1) a step of adding a mixture of phosphor particles and a binder to an organic solvent to prepare a slurry, and then spray-drying the slurry to obtain a spherical granulated material; and 2) the granulated material. Is preferably heated in an oxidizing atmosphere, a neutral atmosphere, or under vacuum at a temperature in the range of 200 to 500 ° C. for 0.5 to 5 hours to remove the binder, and more preferably neutral. 600 to 130 in an atmosphere, a weak reducing atmosphere or an atmosphere containing a trace amount of oxygen.
And a step of firing at a temperature in the range of 0 ° C. for 0.5 to 5 hours.

According to the present invention, a slurry containing particles of a rare earth element-activated alkaline earth metal fluorohalide-based phosphor and a binder is spray-dried, and then the binder is removed (desorbed) by heating at a relatively low temperature. By performing the binder step) and the firing step at a high temperature, it is possible to obtain a phosphor having a substantially spherical shape in which primary particles and / or primary particles are sintered, and which has enhanced stimulated emission luminance.

The divalent europium-activated alkaline earth metal fluorohalide-based phosphor according to the present invention has a basic composition formula (I): M ^II FX: xLn (I) (where M ^II is Ba, At least one alkaline earth metal selected from the group consisting of Sr and Ca; X
Is at least one halogen selected from the group consisting of Cl, Br and I; Ln is Eu, Tb, Ce, T
at least one rare earth element selected from the group consisting of m, Dy, Pr, Ho, Nd, Yb, Er, Sm and Gd; and x is a numerical value in the range of 0 <x ≦ 0.2). It is a rare earth element activated alkaline earth metal fluoride halide phosphor.

Ln is preferably divalent europium (Eu ²⁺ ) or trivalent cerium (Ce ³⁺ ).
Further, a rare earth element-activated barium fluorohalide-based phosphor in which M ^II is Ba is particularly preferable, and part of Ba may be substituted with Sr and / or Ca. The phosphor may contain a small amount of the following components.

Sc described in JP-A-56-116777; B described in JP-A-57-23673; As described in JP-A-57-23675; Tetrafluoroboric acid compounds described in JP-A-59-27980; JP-A-59-47
Hexafluoro compounds described in JP 289;
V and C described in JP-A-59-56480
Transition metals such as r, Mn, Fe, Co and Ni;
9-75200, alkali metal halides (M ^I X ′; provided that M ^I is at least one alkali metal selected from the group consisting of Li, K and Rb, and X ′ is F, Cl. is at least one halogen selected from the group consisting of Br and I), divalent metal halides (M ^II 'X _"2; however, M ^II' is B
at least one divalent metal selected from the group consisting of e and Mg, X ″ is at least one halogen selected from the group consisting of F, Cl, Br and I) and a trivalent metal halide (M ^III X "'₃; provided that M
^III is at least one trivalent metal selected from the group consisting of Al, Ga, In and Tl, and X ″ ′ is F, C
at least one halogen selected from the group consisting of 1, Br and I); M ^II 'X' ₂ .M ^II 'X " ₂ (provided that M ^II is described in JP-A-61-2679. 'Is at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; X'and X "are at least one halogen selected from the group consisting of Cl, Br and I, respectively, and X '
≠ X ″); and LnX ″ ₃ described in Japanese Patent Application No. 60-106752 (where Ln is Y,
La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, D
y, Ho, Er, Tm, Yb, and at least one rare earth element selected from the group consisting of Lu; X ″ is a halogen selected from the group consisting of F, Cl, Br, and I).

The substantially spherical rare earth element-activated alkaline earth metal fluorohalide-based sintered phosphor of the present invention can be produced, for example, by the following method.

First, after mixing the phosphor particles and the binder, the mixture is added to an appropriate organic solvent and sufficiently mixed to prepare a slurry. The phosphor particles used in the present invention may have any shape such as a plate shape and an amorphous shape. The average particle size of the phosphor particles is preferably in the range of 0.1 to 50 μm.

Examples of the binder include nitrocellulose, ethyl cellulose, cellulose acetate, vinylidene chloride / vinyl chloride copolymer, polyalkyl (meth) acrylate, polyurethane, polyvinyl butyral, polyester, polystyrene, polyamide, polyethylene, polyvinyl chloride and epoxy resin. The synthetic polymer substance of Particularly preferred among such binders are polyalkyl (meth) acrylates, polyurethanes and polyvinyl butyral. In addition to these, synthetic polymer substances that can be dissolved in the following organic solvents such as polyvinyl acetate, vinyl chloride / vinyl acetate copolymer, cellulose acetate butyrate, polyvinyl alcohol and linear polyester can also be used.

Examples of the organic solvent include lower alcohols such as methanol, ethanol, n-propanol and n-butanol; chlorine atom-containing hydrocarbons such as methylene chloride and ethylene chloride; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; Mention may be made of esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate, butyl acetate; ethers such as dioxane, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether; and mixtures thereof.

The mixing ratio of the binder and the phosphor is generally 1 :.
It is selected from the range of 1 to 1: 500 (weight ratio), and in particular 1:
It is preferable to select from the range of 20 to 1: 100 (the same).

The slurry is then spray dried using a spray dryer. Various conditions such as temperature during spray drying, spray pressure and spray nozzle diameter are determined by the size of the phosphor particles,
It is appropriately adjusted depending on the type of solvent and the viscosity of the slurry. By spray drying, a spherical phosphor granule containing primary particles can be obtained.

Next, the spherical phosphor granules were put into a quartz boat,
It is filled in a heat-resistant container such as an alumina crucible or a quartz crucible and placed in the core of an electric furnace to remove the binder (debinding process). The heating temperature is suitably in the range of 200 to 500 ° C, preferably 250 to 400 ° C. The heating time varies depending on the filling amount of the granulated material, the type of binder, the heating temperature, etc., but is generally 0.5 to 5 hours. An oxygen atmosphere or an oxidizing atmosphere such as air is generally used as the atmosphere, but the atmosphere may be heated in a neutral atmosphere or vacuum. In the binder removal step, the binder in the granulated product is decomposed, oxidized and volatilized.

Further, the phosphor granulated product is fired in the core of an electric furnace (firing process). Firing temperature is 400-1300 ° C
Is suitable, and preferably in the range of 500 to 1000 ° C. The firing time varies depending on the filling amount of the granulated product, the firing temperature, the temperature at which the granules are taken out from the furnace, etc., but generally 0.5 to 10 hours is appropriate. As the firing atmosphere, a neutral atmosphere such as a nitrogen atmosphere or an argon gas atmosphere, a nitrogen atmosphere containing a small amount of hydrogen, a weak reducing atmosphere such as a carbon dioxide atmosphere containing carbon monoxide, or a trace oxygen introduction atmosphere is used. To be done.

In order to prevent excessive sintering of the phosphor in the firing step, a sintering inhibitor such as aluminum oxide may be added to and mixed with the granulated product prior to the binder removal step. Further, the binder removal step and the firing step may be continuously performed using the same electric furnace, or may be independently performed using different electric furnaces.

In this way, substantially spherical phosphor particles obtained by sintering the primary particles and / or the primary particles are obtained. The obtained phosphor may be subjected to various general operations in the production of the phosphor such as washing, drying, and sieving, if necessary.

In the method of the present invention, in addition to the above-mentioned phosphor, a lanthanum oxyhalide-based phosphor (LaOBr: Ce).
³⁺ ) and gadolinium oxyhalide-based phosphor (GdO
Cl: Ce ^3+, etc.) can be applied to a phosphor having a layered crystal structure and a plate-like particle shape.

[0026]

【Example】

Example 1 100 parts by weight of plate-like fine particles (BaFBr: 0.001 Eu ²⁺ , average particle size: 2 μm) of a divalent europium-activated barium fluorobromide phosphor and an acrylic resin (trade name: C
B-1 (manufactured by Sanyo Kasei Co., Ltd.) (2 parts by weight) was added to 34 parts by weight of methyl ethyl ketone, and the mixture was sufficiently stirred and mixed by a propeller mixer to prepare a slurry having a viscosity of 20 PS (25 ° C). Next, this slurry was spray-dried using a spray dryer (GS-32 type, manufactured by Yamato Scientific Co., Ltd.) under the following conditions. Spray nozzle diameter: 400 μm Slurry liquid transfer rate: 15 g / min Inlet temperature: 120 ° C. Outlet temperature: 85 ° C. Spraying pressure: 1 kg / cm ² Hot air flow rate: 0.5 m ³ / min

By spray drying, the diameter is 1 μm to 50 μm.
A spherical phosphor granule in the range of was obtained. Figure 1- (1)
Scanning electron micrographs (400 times, 2800 times) of the obtained phosphor granules are shown in (2).

Next, 100 parts by weight of the phosphor granules and 0.3 parts by weight of the sintering inhibitor (Al ₂ O ₃ ultrafine particles) were thoroughly mixed by dry shaking, and then the mixture was filled in a quartz boat. In a tubular furnace and heated in an oxygen atmosphere at a temperature of 350 ° C. for 2 hours to remove the binder. Further, the quartz boat was put in another tubular furnace and fired at a temperature of 850 ° C. for 2 hours in a nitrogen atmosphere. After allowing to cool to room temperature, the fired product was taken out of the furnace. In this way, a spherical phosphor in which the primary particles were sintered was obtained. FIG. 2 shows a scanning electron micrograph (2800 times) of the obtained phosphor.

[Example 2] The same as Example 1 except that polyvinyl butyral (trade name: Denka Butyral 3000-1, manufactured by Denki Kagaku Kogyo) was used in place of the acrylic resin. The slurry is prepared and spray-dried to give a diameter of 1 μm to 50 μm.
A spherical phosphor granule in the range of μm was obtained. Figure 1-
A scanning electron micrograph (2800 times) of the obtained phosphor granulation product is shown in (3). Further, the same operation as in the method of Example 1 was performed except that the heating temperature for removing the binder was set to 380 ° C. to obtain a spherical phosphor in which primary particles were sintered.

[Example 3] In Example 1, polyurethane was used instead of acrylic resin (trade name: Desmolac TP).
KL-5-2625, manufactured by Sumitomo Bayer Urethane Co., Ltd.
A slurry was prepared and spray-dried in the same manner as in the method of Example 1 except that
A spherical phosphor granule in the range of m was obtained. Figure 1-
A scanning electron micrograph (2800 times) of the obtained phosphor granules is shown in (4). Further, the same operation as in the method of Example 1 was performed except that the heating temperature for removing the binder was set to 380 ° C. to obtain a spherical phosphor in which primary particles were sintered.

[Embodiment 4] Plate-like fine particles (BaFBr _0.85 I _0.15 : 0.001 Eu ²⁺ , average particle diameter: 2 μm) of a divalent europium activated barium fluorobromide iodide phosphor as a phosphor in Embodiment 1. A slurry was prepared and spray-dried in the same manner as in Example 1 except that the above was used to obtain a spherical phosphor granule having a diameter in the range of 1 μm to 50 μm. Further, by performing the same operation as in the method of Example 1 except that the firing temperature was 840 ° C., a spherical phosphor in which primary particles were sintered was obtained.

[Embodiment 5] Plate-like fine particles (BaFBr _0.85 I _0.15 : 0.001 Eu ²⁺ , average particle diameter: 2 μm) of a divalent europium activated barium fluorobromide iodide phosphor as a phosphor in Embodiment 1. Using polyvinyl butyral (trade name: Denka Butyral 3000-1,
Spherical phosphor granules having a diameter in the range of 1 μm to 50 μm were obtained by preparing a slurry and performing spray drying in the same manner as in Example 1 except that Denki Kagaku Kogyo Co., Ltd.) was used. Obtained. Further, the same procedure as in Example 1 was carried out except that the heating temperature for removing the binder was 380 ° C. and the firing temperature was 840 ° C. Got the body

[Example 6] In Example 1, plate-like fine particles of a divalent europium-activated barium fluoroiodide phosphor as a phosphor (BaFI: 0.001Eu ²⁺ , average particle diameter: 2 µm)
The slurry was prepared and spray-dried in the same manner as in Example 1 except that
A spherical phosphor granule in the range of μm to 50 μm was obtained. Further, by performing the same operation as in the method of Example 1 except that the firing temperature was set to 820 ° C., a spherical phosphor in which primary particles were sintered was obtained.

[Embodiment 7] Plate-like fine particles (BaFCl: 0.001Eu ²⁺ , average particle diameter: 2 μm) of divalent europium activated barium fluorochloride phosphor as a phosphor in Example 1
Slurry was prepared and spray-dried in the same manner as in Example 1 except that m) was used to obtain spherical phosphor granules having a diameter in the range of 1 μm to 50 μm. Further, by performing the same operation as in the method of Example 1 except that the firing temperature was set to 880 ° C., a spherical phosphor in which primary particles were sintered was obtained.

[Embodiment 7] Embodiment 7 is carried out except that plate-like fine particles (BaFCl: 0.001 Ce ³⁺ , average particle diameter: 2 μm) of trivalent cerium-activated barium fluorochloride phosphor are used as the phosphor. By preparing the slurry and spray drying in the same manner as in Example 1, the diameter of 1
A spherical phosphor granule in the range of μm to 50 μm was obtained. Further, by performing the same operation as in the method of Example 1 except that the firing temperature was set to 880 ° C., a spherical phosphor in which primary particles were sintered was obtained.

[Comparative Example 1] Barium fluoride (BaF ₂ ) 8
7.7 g, barium bromide (BaBr ₂ ) 148.6 g and europium bromide (EuBr ₃ ) 0.196 g were added to distilled water (H ₂ O) 300 ml and mixed to give an aqueous solution. This aqueous solution was rotatively dried using a rotary evaporator at a pressure lower than atmospheric pressure by 600 mmHg and at a temperature of 90 ° C.

Next, the obtained phosphor raw material mixture was filled in an alumina crucible, which was placed in a high-temperature electric furnace and put in a carbon dioxide atmosphere containing carbon monoxide at a temperature of 900 ° C. for 1.5 minutes.
Burned for hours. After the firing was completed, the fired product was taken out of the furnace and cooled. The fired product is crushed to obtain a powdery divalent europium-activated barium fluorobromide phosphor (BaFBr: 0.02).
01Eu ²⁺ ) was obtained.

The obtained phosphor particles have a cubic shape, and the ratio of length (x), width (y) and height (z) is 1: 1 to 1.
It was in the range of 2: 0.5 to 2 (x: y: z). Also,
The particle size was in the range of about 2-15 μm. FIG. 3 shows a scanning electron micrograph (800 times) of the phosphor.

The phosphors of Examples 1 and 2 and Comparative Example 1 were irradiated with X-rays having a tube voltage of 80 kVp, and then excited by He-Ne laser light (632.8 nm) to stimulate the luminous intensity of phosphor particles. Was measured. The obtained results are summarized in Table 1.

Table 1 ────────────────────────── Relative stimulated emission luminance ────────────── ──────────── Example 1 130 Example 2 127 Comparative Example 1 100 ───────────────────────────

[Experimental Results] As is clear from the results shown in Table 1, the substantially spherical phosphor particles of the present invention (Example 1,
In the case of 2), the stimulated emission luminance was remarkably improved as compared with the known cubic phosphor particles (Comparative Example 1, corresponding to the example of JP-A-62-86086).

[0042]

According to the present invention, a slurry of a rare earth element-activated alkaline earth metal fluorohalide-based phosphor is spray-dried and then subjected to a binder removal step and a firing step so that the particle shape of the phosphor becomes spherical. In addition, the stimulated emission luminance can be significantly improved. Further, since the sintered phosphor of the substantially spherical particles of the present invention itself is not bound by a binder resin, when forming the phosphor layer on the support, an organic solvent (binding of phosphor particles to each other Even if the sintered phosphor particles of the present invention are dispersed in a binder (for containing a binder), the collapse or partial omission of the sintered body hardly occurs, and the original shape is maintained, so that the obtained fluorescence is obtained. There is also an advantage that there is little variation in the characteristics of the body layer. Further, since the substantially spherical phosphor of the present invention is a sintered body, it has an advantage that it becomes an aggregate having a high density, which improves the X-ray absorption ability.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of a spherical phosphor granule obtained after spray drying a slurry. (1) Example 1, magnification: 400 times (2) Example 1, magnification: 2800 times (3) Example 2, magnification: 2800 times (4) Example 3, magnification: 2800 times

FIG. 2 is a scanning electron micrograph of a spherical phosphor obtained by sintering the primary particles obtained in Example 1 (magnification: 28).
00 times).

FIG. 3 is a scanning electron micrograph of the cubic phosphor obtained in Comparative Example 1 (magnification: 800 times).

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[Procedure amendment]

[Submission date] February 17, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 4

[Correction method] Change

[Correction content]

Claims (7)

[Claims] 1. A basic composition formula (I): M ^II FX: xLn ... (I) (wherein M ^II is at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; X
Is at least one halogen selected from the group consisting of Cl, Br and I; Ln is Eu, Tb, Ce, T
at least one rare earth element selected from the group consisting of m, Dy, Pr, Ho, Nd, Yb, Er, Sm and Gd; and x is a numerical value in the range of 0 <x ≦ 0.2). A rare earth element activated alkaline earth metal fluoride halide phosphor, which is a substantially spherical sintered phosphor. 2. Ln in the composition formula (I) is Eu and / or
The phosphor according to claim 1, which is also Ce. 3. The average particle size of the phosphor is 1 to 100 μm.
The phosphor according to claim 1, which is in the range of. 4. A basic composition formula (I): M ^II FX: xLn ... (I) (wherein M ^II is at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; X
Is at least one halogen selected from the group consisting of Cl, Br and I; Ln is Eu, Tb, Ce, T
at least one rare earth element selected from the group consisting of m, Dy, Pr, Ho, Nd, Yb, Er, Sm and Gd; and x is a numerical value in the range of 0 <x ≦ 0.2). A step of preparing a slurry by adding a mixture of a rare earth element-activated alkaline earth metal fluorohalide-based phosphor particle and a binder to an organic solvent, and then spray-drying the slurry to obtain a spherical granule. , And the granules are heated at a temperature in the range of 200 to 500 ° C. for 0.5 to 5 hours to remove the binder, and then calcined at a temperature in the range of 600 to 1300 ° C. for 0.5 to 5 hours. The substantially spherical sintered rare earth element-activated alkaline earth metal fluorohalogenated phosphor according to claim 1, comprising: 5. The heating at a temperature in the range of 200 to 500 ° C. is performed in an oxidizing atmosphere, a neutral atmosphere or a vacuum, and the heating at a temperature in the range of 600 to 1300 ° C. is neutral. The method for producing a phosphor according to claim 4, which is carried out in an atmosphere, a weak reducing atmosphere or an atmosphere containing a trace amount of oxygen. 6. Ln in the above composition formula (I) is Eu and / or
Alternatively, the method for producing the phosphor according to claim 4, wherein the phosphor is Ce. 7. The average particle size of the phosphor particles is 0.1 to 5
The method for producing a phosphor according to claim 4, wherein the range is 0 μm.