JP3781486B2 - Rare earth activated barium fluoride halide phosphor powder and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a powder comprising fine particles of rare earth activated barium fluorohalide-based stimulable phosphor particles, and a production method suitable for advantageously producing the phosphor powder.
[0002]
[Prior art]
As an alternative to the conventional radiographic method using a photographic film, a radiation image conversion method using a stimulable phosphor has been developed and has been widely used in recent years. This method uses a radiation image conversion panel (accumulative phosphor sheet) containing a stimulable phosphor, and the radiation transmitted through the subject or emitted from the subject is stimulated by the panel. The radiation energy stored in the stimulable phosphor is absorbed by the body, and then the stimulable phosphor is excited in time series with electromagnetic waves (excitation light) such as visible light and infrared rays. It emits as fluorescence (stimulated luminescence light), photoelectrically reads this fluorescence to obtain an electrical signal, and then reproduces a radiographic image of a subject or subject as a visible image based on the obtained electrical signal. . The panel which has been read is prepared for the next photographing after the remaining image is erased. That is, the radiation image conversion panel can be used repeatedly.
[0003]
Stimulable phosphors are phosphors that exhibit stimulating luminescence when irradiated with excitation light after being irradiated with radiation, but in practice, wavelengths of 300 to 500 nm are obtained by excitation light having a wavelength in the range of 400 to 900 nm. Phosphors that exhibit a range of stimulated luminescence are generally utilized. And as a ru photostimulable phosphor conventionally used for a radiation image conversion panel, the following composition formula (I):
Ba _1-x M ^II _x FX: aM ^I , bLn (I)
(Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Mg, Ca and Sr; X represents at least one halogen selected from the group consisting of Cl, Br and I; ^I represents at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; and Ln is selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb Represents at least one rare earth metal; and x, a, and b are numerical values that satisfy the conditions of 0 ≦ x ≦ 0.5, 0 <a ≦ 0.05, and 0 <b ≦ 0.2, respectively. is there.)
The rare earth activated barium fluoride halide phosphor represented by the following formula is most commonly used.
[0004]
The radiation image conversion panel used in the radiation image conversion method includes, as its basic structure, a support and a photostimulable phosphor layer provided on the surface thereof. However, a support is not necessarily required when the phosphor layer is self-supporting.
The photostimulable phosphor layer is usually composed of a photostimulable phosphor and a binder containing and supporting the phosphor in a dispersed state. However, as the photostimulable phosphor layer, a layer composed only of an aggregate of stimulable phosphors without containing a binder, which is formed by a vapor deposition method or a sintering method, is known. A radiation image conversion panel having a stimulable phosphor layer in which a polymer substance is impregnated in a gap between aggregates of stimulable phosphors is also known.
[0005]
[Problems to be solved by the invention]
As the use of a radiation image conversion method using a stimulable phosphor progresses, improvement in the image quality of the obtained radiation image, for example, improvement in sharpness and graininess, is further demanded.
Various means for improving the image quality of the radiation image are conceivable. Among them, the fine phosphor particles are made fine and the particle size of the fine phosphor particles is made uniform, that is, the particle size distribution is changed. It is effective to make it narrow. For this purpose, first, it is necessary to suppress as much as possible the agglomeration of the phosphor powder by sintering, which is likely to occur during the firing of the phosphor powder.
[0006]
That is, the photostimulable phosphor is generally obtained by reacting a phosphor raw material in an aqueous solution to obtain a reaction product crystal, and then firing the reaction product (phosphor precursor) at a high temperature, It is manufactured using a method of pulverizing and classifying it using a sieve or the like. However, in this method, there is a problem that in the high-temperature firing step of the phosphor precursor, the precursor crystals are sintered, and the obtained phosphor is easily obtained as a lump. This phosphor lump is finely divided by pulverization. However, excessive pulverization tends to cause deterioration of the properties of the resulting phosphor particles (such as a decrease in sensitivity). It is desirable to keep it. And conventionally, in order to suppress the occurrence of sintering in the firing step of the phosphor precursor, by mixing fine particles of a sintering inhibitor such as aluminum oxide and zirconium oxide with the crystalline phosphor precursor, A method of spotting on the surface and suppressing sintering by the action of the spotted aluminum oxide or zirconium oxide has been generally used.
Spotting by mixing aluminum oxide and zirconium oxide fine particles on the phosphor precursor crystal is effective for preventing sintering, but the phosphor precursor crystals and the sintering inhibitor fine particles are uniform. In addition, the mixing operation becomes complicated, and in particular, when a large amount of sintering inhibitor fine particles are added, the uniform spotting is not easy.
[0007]
[Means for Solving the Problems]
Composition formula (I):
Ba _1-x M ^II _x FX: aM ^I , bLn (I)
(Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Mg, Ca and Sr; X represents at least one halogen selected from the group consisting of Cl, Br and I; ^I represents at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; and Ln is selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb Represents at least one rare earth metal; and x, a, and b are numerical values that satisfy the conditions of 0 ≦ x ≦ 0.5, 0 <a ≦ 0.05, and 0 <b ≦ 0.2, respectively. is there.)
A powder of a rare earth activated fluoride barium halide phosphor represented in, the powder surface, aluminum, zirconium, titanium, coated with film of oxides of any element of the contact and barium A rare earth-activated barium fluorohalide phosphor powder obtained by firing, characterized in that:
[0008]
The oxide-coated phosphor powder has the composition formula (I):
Ba _1-x M ^II _x FX: aM ^I , bLn (I)
(However, M ^II , X, M ^I , Ln, and x, a, and b have the same meaning as described above.)
An alkoxide of any element of aluminum, zirconium, titanium, silicon and barium is attached to the surface of the precursor powder of the rare earth-activated barium fluoride halide phosphor represented, and then the alkoxide is hydrolyzed And then calcining the precursor powder.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A typical embodiment of the method for producing the rare earth activated barium fluorohalide phosphor of the present invention will be described in detail below.
[0010]
First, in accordance with a conventional method, in an aqueous solvent, barium halide (BaX ₂ : X is the one described in the composition formula (I): and, if desired, CaX ₂ , SrX ₂ , or alkali metal halide, etc. An additive), a rare earth element (Ln in the composition formula (I)) halide, and an inorganic fluoride (ammonium fluoride, alkali metal fluoride, etc.) are reacted to produce a phosphor precursor crystal.
[0011]
The phosphor precursor crystal can also be produced in a mixed solvent of water and an organic solvent as described in the specification of Japanese Patent Application No. 8-131057.
That is, first, an organic solvent (alcohol-based, ketone-based, ether-based, ester-based, etc.) that is compatible with water is placed in a reaction vessel, and this organic solvent is kept at 20 to 80 ° C. Separately, barium halide (BaX ₂ : X is as described in composition formula (I), and optionally further additives such as CaX ₂ , SrX ₂ , or alkali metal halide) and rare earth elements (composition) An aqueous solution or an aqueous organic solvent solution in which the halide of Ln) of formula (I) is dissolved, and an aqueous solution or an aqueous organic solvent solution of inorganic fluoride (ammonium fluoride, alkali metal fluoride, etc.) are prepared. These are simultaneously added to the organic solvent with stirring. By the simultaneous addition of the phosphor raw material to the organic solvent, they react immediately and the phosphor precursor crystals are deposited. The reaction mixture is further stirred in the above temperature range, and the precipitated crystals are aged. Thereafter, the precipitated crystals are collected by filtration, washed thoroughly with an organic solvent or an aqueous organic solvent, and then dried to obtain the desired phosphor precursor crystals. The central particle diameter of the phosphor precursor crystal is preferably in the range of 0.1 to 8 μm .
[0012]
Then, the dried crystals (phosphor precursor crystals), firing the aluminum used as a coating agent of the phosphor of the present invention, zirconium, titanium, readily the oxide of any element of the 及 beauty barium Deposit changing compounds. Preferred examples of such compounds, aluminum, zirconium, titanium, alkoxides of any element of the 及 beauty barium (e.g., methoxide, ethoxide, propoxide, isopropoxide, carbon atoms such as sec- butoxide 1 -6 lower alkyl oxides).
A preferred method for the attachment of these alkoxides to the phosphor precursor crystals is immersion of the precursor crystals in an alkoxide organic solvent solution. Alternatively, the alkoxide organic solvent solution may be sprayed onto the precursor crystal. In addition, when making the alkoxide organic solvent solution adhere to the surface of a precursor crystal | crystallization using this spraying, it is desirable to spray uniformly on the surface of a precursor crystal | crystallization.
[0013]
The phosphor precursor crystal with the alkoxide attached to the surface is then hydrolyzed by contact with water and then baked according to a conventional method.
Firing is performed by filling the phosphor precursor crystal in a heat-resistant container such as a quartz boat, an alumina crucible, or a quartz crucible, and placing the phosphor precursor crystal in the core of an electric furnace. The baking temperature is suitably from 400 to 1300 ° C, preferably in the range of 500 to 1000 ° C (particularly around 700 to 900 ° C). The firing time is generally 0.5 to 12 hours (particularly 1 to 5 hours), although it varies depending on the filling amount of the phosphor raw material mixture, the firing temperature and the temperature of taking out from the furnace. The firing atmosphere may be a neutral atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere, a nitrogen gas atmosphere containing a small amount of hydrogen gas, a weakly reducing atmosphere such as a carbon dioxide atmosphere containing carbon monoxide, or a small amount of oxygen introduced. The atmosphere is used.
[0014]
Since the alkoxide is decomposed into the oxide by the hydrolysis described above, the powder surface is uniformly coated with the oxide film of the alkoxide, and therefore the agglomeration due to sintering is small (eg, the center particle diameter is 10 μm or less). A barium halide based photostimulable phosphor powder is obtained. If desired, the obtained phosphor powder may be classified using a sieve or the like.
[0015]
【Example】
[Example 1]
In a glove box in which the internal atmosphere was replaced with nitrogen, 0.52 g, 1.56 g, 2.60 g, and 5.20 g of aluminum tri-sec-butoxide (manufactured by Kanto Chemical Co., Inc.) were weighed separately, and this was sec. -Diluted with butanol to prepare 300 mL of aluminum tri-sec-butoxide solution.
Separately prepared 100 g of europium-activated barium fluorobromide fluoride (BaFBr: 0.001 Eu ²⁺ , stimulable phosphor) having a central particle diameter of 5 μm was added to the above aluminum tri-sec-butoxide solution ( 300 mL), vigorously stirred, and fully dispersed to obtain a suspension of phosphor precursor crystal powder having aluminum tri-sec-butoxide adsorbed on the surface.
[0016]
Separately, 0.54 g, 1.62 g, 2.70 g, and 5.40 g of water were respectively added to sec-butanol (50 mL) to prepare a mixture of the phosphor precursor crystal suspension. Each was added sequentially at room temperature to hydrolyze aluminum tri-sec-butoxide. This addition was carried out by stirring the suspension and adding the mixed solution thereto at a flow rate of 0.1 mL / min using a cylinder pump. After addition of the mixed solution, stirring was continued for 1 hour at room temperature for further aging, and then the treated phosphor precursor crystals were separated using suction filtration.
20 g of the separated phosphor precursor crystals were weighed and baked in a nitrogen atmosphere at 850 ° C. to shine bright europium-activated barium fluoride bromide (BaFBr: 0.001 Eu ²⁺ ) whose surface was coated with aluminum oxide. An exhaustive phosphor powder was obtained.
[0017]
[Example 2]
In a glove box where the internal atmosphere was replaced with nitrogen, 0.38 g, 1.14 g, 1.90 g and 3.80 g of zirconium tetrapropoxide (Aldrich) were weighed separately and diluted with propanol. A 300 mL zirconium tetrapropoxide solution was prepared.
Separately prepared 100 g of europium activated barium fluorobromide bromide (BaFBr: 0.001 Eu ²⁺ , stimulable phosphor) having a central particle diameter of 5 μm was added to the above zirconium tetrapropoxide solution (300 mL). The mixture was sufficiently stirred and dispersed sufficiently to obtain a suspension of phosphor precursor crystal powder having zirconium tetrapropoxide adsorbed on the surface.
[0018]
Separately, propanol (50 mL) was prepared by adding 0.29 g, 0.88 g, 1.46 g, and 2.92 g of water to each of the above phosphor precursor crystal suspensions. Zirconium tetrapropoxide was hydrolyzed by sequential addition at room temperature. This addition was carried out by stirring the suspension and adding the mixed solution thereto at a flow rate of 0.1 mL / min using a cylinder pump. After addition of the mixed solution, stirring was continued for 1 hour at room temperature for further aging, and then the treated phosphor precursor crystals were separated using suction filtration.
20 g of the separated phosphor precursor crystals were weighed and baked in a nitrogen atmosphere at 850 ° C., and the brightness of europium-activated barium fluoride bromide (BaFBr: 0.001 Eu ²⁺ ) whose surface was coated with zirconium oxide. An exhaustive phosphor powder was obtained.
[0019]
[Example 3]
Titanium tetraisopropoxide (manufactured by Wako Pure Chemical Industries, Ltd.) was weighed 0.37 g, 1.12 g, 1.87 g, and 3.74 g, respectively, in a glove box in which the internal atmosphere was replaced with nitrogen. A 300 mL titanium tetraisopropoxide solution was prepared by diluting with isopropanol.
Separately prepared 100 g of europium-activated barium fluorobromide fluoride (BaFBr: 0.001 Eu ²⁺ , stimulable phosphor) having a center particle diameter of 5 μm was added to the above titanium tetraisopropoxide solution (300 mL). ), Vigorously stirred, and sufficiently dispersed to obtain a suspension of phosphor precursor crystal powder having titanium tetraisopropoxide adsorbed on the surface.
[0020]
Separately, a mixture of 0.45 g, 1.35 g, 2.25 g, and 4.50 g of water was added to isopropanol (50 mL), and these were added to each of the phosphor precursor crystal suspensions. Titanium tetraisopropoxide was hydrolyzed by sequential addition at room temperature. This addition was carried out by stirring the suspension and adding the mixed solution thereto at a flow rate of 0.1 mL / min using a cylinder pump. After addition of the mixed solution, stirring was continued for 1 hour at room temperature for further aging, and then the treated phosphor precursor crystals were separated using suction filtration.
20 g of the separated phosphor precursor crystal is weighed and calcined in a nitrogen atmosphere at 850 ° C., whereby europium-activated barium fluorobromide (BaFBr: 0.001 Eu ²⁺ ) whose surface is coated with titanium oxide. The photostimulable phosphor powder was obtained.
[0021]
[Example 4 (however, it is not an example of the present invention but a reference example) ]
Tetraethoxysilane (manufactured by Kanto Chemical Co., Inc.) was weighed separately for 0.36 g, 1.09 g, 1.82 g, and 3.64 g in a glove box substituted with nitrogen inside, and diluted with ethanol. 300 mL of tetraethoxysilane solution was prepared.
Separately prepared 100 g of europium activated barium fluorobromide bromide (BaFBr: 0.001 Eu ²⁺ , stimulable phosphor) having a center particle size of 5 μm was added to the tetraethoxysilane solution (300 mL). Then, the suspension was vigorously stirred and dispersed sufficiently to obtain a suspension of phosphor precursor crystal powder having tetraethoxysilane adsorbed on the surface.
[0022]
Separately, 0.60 g, 1.79 g, 2.99 g, and 5.98 g of water were added to ethanol (50 mL), respectively, and these were added to each of the above phosphor precursor crystal suspensions. Were added in order at room temperature to hydrolyze tetraethoxysila. This addition was carried out by stirring the suspension and adding the mixed solution thereto at a flow rate of 0.1 mL / min using a cylinder pump. After addition of the mixed solution, stirring was continued for 1 hour at room temperature for further aging, and then the treated phosphor precursor crystals were separated using suction filtration.
20 g of the separated phosphor precursor crystal was weighed and calcined in a nitrogen atmosphere at 850 ° C., whereby europium-activated barium fluorobromide (BaFBr: 0.001 Eu ²⁺⁾ whose surface was coated with silicon oxide. ) Photostimulable phosphor powder was obtained.
[0023]
[Example 5]
In a glove box where the internal atmosphere was replaced with nitrogen, 2.00 g of barium metal was dissolved in isopropanol to obtain a 100 mL isopropanol solution containing barium isopropoxide. This solution was weighed separately at 4.5 mL, 13.4 mL, 22.3 mL, and 44.6 mL, respectively, and diluted with isopropanol to prepare 300 mL of barium isopropoxide solution.
Separately prepared 100 g of europium-activated barium fluorobromide bromide (BaFBr: 0.001 Eu ²⁺ , stimulable phosphor) having a central particle diameter of 5 μm was prepared in the above barium isopropoxide solution (300 mL). The mixture was thoroughly stirred and dispersed sufficiently to obtain a suspension of phosphor precursor crystal powder having barium isopropoxide adsorbed on the surface.
[0024]
Separately, 0.12 g, 0.35 g, 0.59 g, and 1.17 g of water were added to isopronol (50 mL), respectively, and these were added to the suspension of the phosphor precursor crystals. Barium isopropoxide was hydrolyzed by adding to each at room temperature. This addition was carried out by stirring the suspension and adding the mixed solution thereto at a flow rate of 0.1 mL / min using a cylinder pump. After addition of the mixed solution, stirring was continued for 1 hour at room temperature for further aging, and then the treated phosphor precursor crystals were separated using suction filtration.
20 g of the separated phosphor precursor crystal is weighed and calcined in a nitrogen atmosphere at 850 ° C., whereby europium-activated barium fluorobromide (BaFBr: 0.001 Eu ²⁺ ) whose surface is coated with barium oxide. The photostimulable phosphor powder was obtained.
[0025]
[Comparative Example 1]
Ultrafine particles (center particle diameter: about 0) are prepared on 20 g of a pre-prepared precursor crystal of europium-activated barium fluorobromide (BaFBr: 0.001 Eu ²⁺ , stimulable phosphor) having a center particle diameter of 5 μm. 0.02 μm) of aluminum oxide was added and mixed well. This mixture was fired in a nitrogen atmosphere at 850 ° C. to obtain a photostimulable phosphor powder of europium activated barium fluorobromide (BaFBr: 0.001 Eu ²⁺ ) spotted with aluminum oxide on the surface. .
[0026]
[Center particle diameter of phosphor powder after firing]
The center particle diameters of the phosphor powders obtained after firing in Examples 1 to 5 and Comparative Example 1 were measured. The result is shown in FIG. The horizontal axis of FIG. 1 represents the amount of metal oxide coated or spotted on the surface of the phosphor powder, and the amount of the metal oxide is obtained by immersing phosphor precursor particles in the examples. The value is based on the assumption that the entire amount of alkoxide in the alkoxide solution is adsorbed on the surface of the phosphor precursor particles and hydrolyzed.
As can be seen from FIG. 1, when compared with the same amount of oxide used, when the metal oxide is deposited on the surface of the phosphor powder using the hydrolysis of alkoxide according to the present invention, the conventional aluminum oxide It can be seen that, compared to the use of ultrafine particles, at least the same and many more excellent anti-sintering effects have been achieved.
[0027]
[Example 6]
The surface was changed in the same manner as in Example 1 except that the precursor crystal was changed to cerium-activated barium fluorobromide (BaFBr: 0.001 Ce ³⁺ , stimulable phosphor) having a center particle diameter of 5 μm. A stimulable phosphor powder of europium-activated barium fluorobromide (BaFBr: 0.001 Ce ³⁺ ) coated with aluminum oxide was obtained.
Stimulation of the obtained photostimulable phosphor was suppressed as in Example 1.
[0028]
[Example 7]
The surface was changed in the same manner as in Example 2 except that the precursor crystal was changed to cerium-activated barium fluorobromide (BaFBr: 0.001 Ce ³⁺ , stimulable phosphor) having a center particle diameter of 5 μm. A stimulable phosphor powder of europium-activated barium fluorobromide (BaFBr: 0.001 Ce ³⁺ ) coated with zirconium oxide was obtained.
Stimulation of the obtained photostimulable phosphor was suppressed as in Example 2.
[0029]
[Example 8 (however, it is not an example of the present invention but a reference example) ]
The surface was changed by the same operation as in Example 4 except that the precursor crystal was changed to cerium-activated barium fluorobromide (BaFBr: 0.001 Ce ³⁺ , photostimulable phosphor) having a center particle diameter of 5 μm. A stimulable phosphor powder of europium-activated barium fluorobromide (BaFBr: 0.001 Ce ³⁺ ) coated with silicon oxide was obtained.
Stimulation of the obtained photostimulable phosphor was suppressed as in Example 4.
[0030]
【The invention's effect】
As a sintering inhibitor in the preparation of a rare earth activated fluoride barium halide stimulable phosphor powders obtained aluminum, zirconium, titanium, by oxidation of the alkoxide of any element of the contact and barium oxide By using the product so as to cover the surface of the powder, sintering of the phosphor particles during firing can be effectively suppressed.
[Brief description of the drawings]
FIG. 1 is a graph showing fluctuations in the particle size (center particle size) of a phosphor powder after firing a stimulable phosphor of the same particle size treated with the present invention and a known sintering inhibitor.

Claims (6)

Composition formula (I):
Ba _1-x M ^II _x FX: aM ^I , bLn (I)
(Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Mg, Ca and Sr; X represents at least one halogen selected from the group consisting of Cl, Br and I; M ^I represents at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; and Ln is selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb Represents at least one rare earth metal; and x, a, and b are numerical values that satisfy the conditions of 0 ≦ x ≦ 0.5, 0 <a ≦ 0.05, and 0 <b ≦ 0.2, respectively. is there.)
A powder of a rare earth activated fluoride barium halide phosphor represented in, the powder surface, aluminum, zirconium, is coated with an oxide film of any element of titanium, you and barium A rare earth-activated barium fluoride halide phosphor powder obtained by firing. Rare earth activated fluoride barium halide phosphor powder according to claim 1 oxide film coating the phosphor powder is a coating of aluminum oxide or oxide zirconium beam.   2. The rare earth-activated barium fluorohalide phosphor powder according to claim 1, wherein the phosphor powder has a center particle diameter of 0.1 to 8 [mu] m. Composition formula (I):
Ba _1-x M ^II _x FX: aM ^I , bLn (I)
(Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Mg, Ca and Sr; X represents at least one halogen selected from the group consisting of Cl, Br and I; ^I represents at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; and Ln is selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb Represents at least one rare earth metal; and x, a, and b are numerical values that satisfy the conditions of 0 ≦ x ≦ 0.5, 0 <a ≦ 0.05, and 0 <b ≦ 0.2, respectively. is there.)
In aluminum on the surface of the precursor powder of a rare earth activated fluoride barium halide phosphor represented, zirconium, allowed to attach titanium, an alkoxide of any element of the contact and barium, hydrolyzing the alkoxide And then firing the precursor powder, a method for producing a rare earth-activated barium fluorohalide phosphor powder. Alkoxide to adhere to the phosphor precursor powder, method for producing a rare earth activated fluoride barium halide phosphor powder according to claim 4 which is an aluminum alkoxide or zirconium alkoxy de.   The rare earth-activated barium fluorohalide phosphor powder according to claim 4, wherein the alkoxide is attached to the surface of the phosphor precursor by immersing the precursor in the solution. Manufacturing method.

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