JP2003171660A - Oxygen introduced rare earth activated alkaline earth metal halogen fluoride-based stimulable phosphor, its manufacturing method and radiation image conversion panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an oxygen introduced rare earth activated alkaline earth metal halogen fluoride-based stimulable phosphor with good yield and to provide a radiation image conversion panel having good brightness and structural mottle by using the stimulable phosphor. <P>SOLUTION: The method for manufacturing an oxygen introduced rare earth activated alkaline earth metal halogen fluoride-based stimulable phosphor which has a phosphorus content of ≤50 ppm and is represented by formula (1): Ba<SB>(1-x)</SB>M<SB>2(x)</SB>FBr<SB>(y)</SB>I<SB>(1-y)</SB>: aM<SB>1</SB>, bLn, cO (wherein M<SB>1</SB>is at least one element to be selected from Li, Na, K, Rb or Cs; M<SB>2</SB>is at least one element to be selected from Be, Mg, Sr or Ca; Ln is at least one element to be selected from Ce, Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er and Yb; x, y, a, b, and c are 0≤x≤0.3, 0<y≤0.3, 0≤a≤0.05, 0<b≤0.2, and 0<c≤0.1, respectively) comprises removing a solvent from a reaction fluid having a barium concentration of ≥3.3 mol/L to obtain a stimulable phosphor precursor. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an oxygen-introduced rare earth activated alkaline earth metal fluorohalide stimulable phosphor, and a stimulable phosphor precursor and stimulable phosphor obtained by the method. The present invention relates to a phosphor, and further to a radiation image conversion panel using the stimulable phosphor.

[0002]

2. Description of the Related Art Radiation images such as X-ray images are widely used in the fields of disease diagnosis and the like. This X-ray image can be obtained by irradiating the phosphor layer (fluorescent screen) with X-rays that have passed through the subject to generate visible light, which is the same as when taking a normal photo. Then, a so-called radiographic method is widely used in which a silver halide photographic light-sensitive material (hereinafter, also simply referred to as a light-sensitive material) is irradiated and then developed to obtain a visible silver image.

However, in recent years, a new method of directly taking out an image from a phosphor layer has been proposed instead of an image forming method using a light-sensitive material having a silver halide salt.

As this method, the radiation that has passed through the subject is absorbed by the phosphor, and then the phosphor is excited by, for example, light or thermal energy, and the radiation energy accumulated by the phosphor is absorbed. Is emitted as fluorescence and this fluorescence is detected and imaged.

Specifically, for example, US Pat. No. 3,85
A radiation image conversion method using a stimulable phosphor as described in JP-A No. 9,527 and JP-A No. 55-12144 is known.

This method uses a radiation image conversion panel containing a stimulable phosphor, and the radiation transmitted through the object is applied to the stimulable phosphor layer of the radiation image conversion panel to apply the radiation to each part of the object. Accumulates radiation energy corresponding to the radiation transmission density, and then accumulates in the stimulable phosphor by time-sequentially exciting the stimulable phosphor with electromagnetic waves (excitation light) such as visible light and infrared rays. The emitted radiation energy is emitted as stimulated emission, and the signal depending on the intensity of this light is photoelectrically converted to obtain an electric signal,
This signal is sent to a recording material such as a silver halide photographic light-sensitive material,
The image is reproduced as a visible image on a display device such as a CRT.

According to the above-mentioned radiographic image reproduction method, the radiographic image has much smaller exposure dose and more information than the radiographic method using the conventional combination of radiographic film and intensifying screen. Has the advantage that

As described above, the stimulable phosphor is a phosphor that exhibits stimulated emission when irradiated with excitation light after being irradiated with radiation, but in practice, the excitation light has a wavelength in the range of 400 to 900 nm. Therefore, a phosphor that exhibits stimulated emission in the wavelength range of 300 to 500 nm is generally used.

A radiation image conversion panel using these stimulable phosphors releases radiation energy by scanning excitation light after storing radiation image information. Therefore, radiation images can be stored again after scanning. It can be used repeatedly. In other words, in the conventional radiographic method, the radiographic film is consumed for each photographing, whereas in the radiographic image conversion method, the radiographic image conversion panel is repeatedly used. It is advantageous.

The radiation image conversion panel comprises a support and a stimulable phosphor layer provided on the surface thereof, or a self-supporting stimulable phosphor layer, and the stimulable phosphor layer is usually stimulable. Some include a fluorescent substance and a binder that dispersively supports the fluorescent substance, and some include only an aggregate of the stimulable fluorescent substance formed by a vapor deposition method or a sintering method. Also known is one in which the gap between the aggregates is impregnated with a polymer substance. Further, on the surface of the stimulable phosphor layer opposite to the support side,
Usually, a protective film composed of a polymer film or a vapor deposition film of an inorganic material is provided.

As the stimulable phosphor used in the radiation image conversion panel, there are disclosed in JP-A Nos. 55-12145 and 55-55.
160078, 56-74175, 56-11.
No. 6777, No. 57-23673, No. 57-2367.
5, No. 58-206678, No. 59-27289.
No. 59, No. 59-27980, No. 59-56479, No. 59-56480 and the like, rare earth element-activated alkaline earth metal fluorohalide-based phosphors; JP-A-59-75
No. 200, No. 60-84381, No. 60-10675
No. 2, No. 60-166379, No. 60-221483
No. 60-228592, No. 60-228593
No. 61-23679, No. 61-120882,
JP-A-61-2120883, JP-A-61-120885, JP-A-61-235486 and JP-A-61-235487, and the divalent europium-activated alkaline earth metal fluoride halide phosphors; JP-A-55-12144; Rare earth element-activated oxyhalide phosphor described in JP-A-58-6.
Cerium-activated trivalent metal oxyhalide phosphor described in 9281; Bismuth-activated alkali metal halide phosphor described in JP-A-60-70484; JP-A-60-1
Nos. 41783 and 60-157100, the divalent europium-activated alkaline earth metal halophosphate phosphors;
A divalent europium-activated alkaline earth metal haloborate phosphor described in JP-A-60-157099;
0-217354, divalent europium-activated alkaline earth metal hydrohalide phosphor;
-21173 and 61-21182, cerium-activated rare earth compound halide phosphors; JP-A-61-4
Cerium-activated rare earth halophosphate phosphor described in JP-A-0390; divalent europium-activated cerium rubidium halide phosphor described in JP-A-60-78151; divalent europium-activated phosphor described in JP-A-60-78151. Examples include europium-activated composite halide phosphors.

Among these, divalent europium-activated alkaline earth metal fluorohalide-based phosphors containing iodine, rare earth element-activated oxyhalide phosphors containing iodine, and bismuth-activated alkali metal halide fluorescents containing iodine. Photostimulable phosphors such as system phosphors are well known, but high-luminance photostimulable phosphors are still required.
Further, as the use of a radiation image conversion method utilizing a stimulable phosphor has progressed, there has been a further demand for improvement in the image quality of the obtained radiation image, for example, improvement in sharpness and graininess.

The above-described method for producing a stimulable phosphor is a method called a solid phase method or a sintering method, in which pulverization after firing is indispensable, and the particle shape that affects sensitivity and image performance is It has a problem that it is difficult to control. Among the means for improving the image quality of a radiation image, making the particle size of the stimulable phosphor fine particles and the particle size of the finely divided stimulable phosphor particles uniform, that is,
It is effective to narrow the particle size distribution.

JP-A-7-233369 and 9-291.
The method for producing a stimulable phosphor from a liquid phase disclosed in, for example, No. 278 is a method for obtaining a fine-particle stimulable phosphor precursor by adjusting the concentration of a phosphor raw material solution. It is effective as a method for producing a stimulable phosphor powder having a uniform distribution.

However, there is an increasing demand for a radiation image conversion panel capable of obtaining a high quality image for accurate diagnosis, and further for a stimulable phosphor for realizing the radiation image conversion panel. In particular, in order to obtain an effective image while reducing the exposure dose, there is a strong demand for a high-luminance photostimulable phosphor. Further, there is a strong demand for a stimulable phosphor having good image quality characteristics for diagnosis. In particular, there is a strong demand for improvement of the structural mottle caused by the structural disorder of the phosphor layer, which greatly affects the graininess.

The alkaline earth metal fluoroiodide-based stimulable phosphor produced in the above liquid phase is advantageous in terms of brightness and graininess, but when a precursor crystal is obtained in the liquid phase, Have a problem like In the case of producing alkaline earth metal fluoroiodide-based stimulable phosphor particles in a liquid phase, it is disclosed in JP-A-10-88.
No. 125 and No. 9-291278, 1) Barium iodide is dissolved in water or an organic solvent, and a solution of inorganic fluoride is added while stirring this solution.

2) A method in which ammonium fluoride is dissolved in water and a solution of barium iodide is added while stirring this solution is effective.

However, in the method 1), it is necessary to allow an excess amount of barium iodide to exist in the solution. Therefore, the stoichiometry of the charged barium iodide and the barium fluoroiodide obtained after solid-liquid separation is used. The ratio is often a small value of around 0.4. That is, the yield of the stimulable phosphor of the alkaline earth metal fluoroiodide system is often about 40% with respect to the charged barium iodide. Further, the method 2) also requires an excess amount of barium iodide with respect to the inorganic fluoride, and the yield is low. As described above, the liquid phase synthesis of barium fluoride iodide has a problem of low yield and poor productivity. When the concentration of barium iodide in the mother liquor is lowered to increase the yield, the particles are enlarged, which is not preferable in terms of image quality characteristics.

As an attempt to increase the yield of rare earth activated alkaline earth metal fluoride halide stimulable phosphors, particularly alkaline earth metal fluoride iodide stimulable phosphors, Japanese Patent Laid-Open No. Hei 1 (1994) -31868 has been proposed.
The basic composition formula BaFI: xLn was obtained by adding the concentration of the reaction mother liquor and the fluorine source to No. 1-29324 and then concentrating the mixture.
A method for obtaining a rare earth-containing angular barium fluoroiodide crystal satisfying (Ln: at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb) is disclosed. There is.

As a result of the additional test conducted by the present inventors, although BaFI prismatic crystals were produced as described, the productivity was remarkably low because of concentration by natural evaporation, which is not industrially practical. Do you get it. Further, it was found that the obtained rectangular crystals also have a large grain size and a broad grain size distribution, and therefore have poor image characteristics, particularly structural mottle, and cannot be put to practical use.

[0021]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to obtain an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide stimulable phosphor having a small particle size in good yield. The purpose of the present invention is to provide a radiation image conversion panel having excellent brightness and structural mottle by using a stimulable phosphor.

[0022]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in view of the above problems, and as a result, controlling the phosphorus concentration in the stimulable phosphor has a particle diameter within an appropriate range. It is possible to obtain a stimulable phosphor having high brightness and high image quality, particularly good structure mottle, and by the manufacturing method within the scope of the present invention, a stimulable phosphor having good image characteristics can be inexpensively and stably produced in a large amount. The inventors of the present invention have found that they can be obtained and have reached the present invention.

Specifically, the object of the present invention has been achieved by the following constitution. 1) The general formula (1) having a phosphorus content of 50 ppm or less, characterized in that a stimulable phosphor precursor is obtained by removing a solvent from a reaction liquid having a barium concentration of 3.3 mol / L or more. A method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor represented by:

2) The mass after removal of the solvent is 0.97 or less with respect to the mass before removal, and the oxygen-introduced rare earth-activated alkaline earth metal fluorohalide system bright as described in 1) above. Method for producing exhaustible phosphor.

3) The method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluoride halide stimulable phosphor as described in 1) or 2) above, wherein the removal of the solvent is carried out under reduced pressure.

4) The method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor as described in 1) or 2) above, wherein the solvent is removed by aeration of dry gas.

5) The method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor as described in 1) or 2) above, wherein the solvent is removed by forming a liquid film.

6) An oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor precursor obtained by the production method described in any one of 1) to 5) above.

7) An oxygen-introduced rare earth-activated alkaline earth metal halogen fluoride obtained from the oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor precursor described in 6) above. Compound-based stimulable phosphor.

8) A radiation image conversion panel comprising a phosphor layer containing the oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor described in 7) above.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION A typical embodiment of the method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor of the present invention will be described in detail below.

The photostimulable phosphor of the present invention has a composition substantially represented by the above general formula (1), but in addition to this, it may contain a trace amount of aluminum or silicon.

In the present invention, the concentration of phosphorus in the stimulable phosphor is preferably 50 ppm or less, more preferably 30 ppm or less. In order to obtain the above composition, the phosphorous content in the stimulable phosphor precursor (hereinafter, also simply referred to as a phosphor precursor) is preferably 50 ppm or less, and more preferably in the phosphor precursor. The amount of phosphorus is preferably 30 ppm or less. The phosphorus content is preferably as low as possible.

In order to control the amount of phosphorus in the stimulable phosphor and the phosphor precursor, there can be mentioned a method of controlling the phosphorus concentration in the barium halide as a raw material.

In order to measure the amount of phosphorus in the stimulable phosphor and the phosphor precursor, it is preferable to use inductively coupled plasma emission spectroscopy (hereinafter referred to as ICP-AES).
A predetermined amount of the stimulable phosphor or phosphor precursor whose phosphorus content is to be measured is weighed out, heated and dried repeatedly with hydrochloric acid, and the residue is dissolved with hydrochloric acid and water to obtain a constant volume. . By measuring the phosphorus concentration in this liquid, the phosphorus content in the stimulable phosphor and the phosphor precursor can be known.

Regarding ICP-AES measurement, an analysis wavelength of 213.618 nm and an output of 1.3 kW are preferably used, and it is preferable to quantify by a calibration curve method.

The photostimulable phosphor of the present invention is disclosed in Japanese Patent Publication No.
It is also possible to use a so-called solid phase method in which the powder raw materials described in JP-A-29406 and JP-A-6-29412 are mixed and heated, but the liquid phase method is used from the viewpoint of controlling the particle size of the phosphor. It is preferable to see.

For the production of the phosphor precursor by the liquid phase method, the precursor production method described in JP-A-10-140148 and the precursor production apparatus described in JP-A-10-147778 can be preferably used. Here, the phosphor precursor refers to a state in which the substance of the general formula (1) has not been subjected to a high temperature of 600 ° C. or higher, and exhibits almost no stimulated luminescence or instantaneous luminescence.

The method for producing the stimulable phosphor precursor by the liquid phase method will be described below. First, the raw material compounds other than the fluorine compound are dissolved in an aqueous solvent. That is, B
aI ₂ and Ln halide, and optionally M ₂
Halide, and further a halide of M ₁ and mixed thoroughly placed in an aqueous solvent, is dissolved, to prepare an aqueous solution. However, the quantitative ratio of the BaI ₂ concentration and the aqueous solvent is adjusted so that the BaI ₂ concentration is 3.3 mol / L or more. At this time, if desired, a small amount of acid, ammonia,
Alcohol, water-soluble polymer, water-insoluble metal oxide fine particle powder and the like may be added. The BaI ₂ concentration is preferably 3.3 mol / L or more and 5.0 mol / L or less. This aqueous solution (reaction mother liquor) is maintained at 50 ° C.

Next, an aqueous solution of inorganic fluoride (ammonium fluoride, alkali metal fluoride, etc.) is injected into the stirred and maintained aqueous solution at 50 ° C. using a pipe with a pump or the like. This injection is preferably carried out in the areas where the stirring is particularly vigorous. By injecting this inorganic fluoride aqueous solution into the reaction mother liquor, the phosphor precursor crystals corresponding to the above general formula (1) are precipitated.

Next, the solvent is removed from the reaction solution. The time of removing the solvent is not particularly limited. It may be any time from the start of the addition of the inorganic fluoride solution to the solid-liquid separation. Most preferred is a mode in which the removal is started immediately after the addition of the inorganic fluoride solution is completed. The amount of solvent removed is preferably 3% or more in terms of mass ratio before and after removal. Below 3%,
In some cases, the crystals do not have the desired composition. Therefore, the removal amount is preferably 3% or more, more preferably 5% or more. Further, even if it is removed too much, the viscosity of the reaction solution may excessively increase, which may cause inconvenience in handling. Therefore, the removal amount of the solvent is preferably 50% or less in terms of mass ratio before and after removal.

The time required for removing the solvent not only greatly affects the productivity but also the shape and particle size distribution of the particles are influenced by the method for removing the solvent, and therefore the method for removing must be properly selected. Generally, in removing the solvent, a method of heating the solution and evaporating the solvent is selected. This method is also useful in the present invention. By removing the solvent, the precursor having the intended composition can be obtained. Further, in order to improve productivity and to keep the particle shape appropriate, it is preferable to use other solvent removal methods in combination. The method of removing the solvent used in combination is not particularly limited. It is also possible to select a method using a separation membrane such as a reverse osmosis membrane. In the present invention, it is preferable to select the following removal method from the viewpoint of productivity.

1. Aeration of dry gas The reaction vessel is of a closed type, and at least two or more holes are provided to allow the gas to pass therethrough, and the dry gas is aerated from there. The type of gas can be arbitrarily selected. From the perspective of safety
Air and nitrogen are preferred. Depending on the saturated vapor content of the gas to be vented, the solvent is entrained in the gas and removed. In addition to the method of ventilating the voids of the reaction vessel, a method of ejecting gas as bubbles in the liquid phase to absorb the solvent in the bubbles is also effective.

2. Decompression As is well known, decompression reduces the vapor pressure of the solvent. The solvent can be removed efficiently by lowering the vapor pressure. The degree of reduced pressure can be appropriately selected depending on the type of solvent. When the solvent is water 8.65 × 10
⁴ Pa or less is preferable.

3. By enlarging the liquid film evaporation area, the solvent can be removed efficiently. As in the present invention, when a reaction vessel having a constant volume is heated and stirred to carry out the reaction, the heating method is to immerse the heating means in a liquid or to attach the heating means to the outside of the vessel. Is common. According to this method, the heat transfer area is limited to the portion where the liquid and the heating means come into contact with each other, and the heat transfer area is reduced as the solvent is removed, so that the time required for solvent removal is prolonged. To prevent this, use a pump or stirrer to spray on the wall of the reaction vessel,
A method of increasing the heat transfer area is effective. A method of forming a liquid film by spraying a liquid on the wall surface of the reaction container in this manner is known as a "wetting wall". As a method for forming the wetting wall, in addition to a method using a pump, JP-A-6-33562.
Nos. 7 and 11-235522 may be used.

These methods may be used alone or in combination. A combination of a method of forming a liquid film and a method of reducing the pressure in the container, a combination of a method of forming a liquid film and a method of aerating a dry gas are effective. The former is particularly preferable, and the method described in JP-A-6-335627 is preferably used.

Next, the above phosphor precursor crystal is filtered,
Separate from the solution by centrifugation or the like, thoroughly wash with methanol or the like, and dry. A sintering inhibitor such as alumina fine powder or silica fine powder is added to and mixed with the dried phosphor precursor crystal, and the sintering inhibitor fine powder is uniformly attached to the crystal surface. By selecting the firing conditions,
It is also possible to omit the addition of the sintering inhibitor.

Next, the phosphor precursor crystals are filled in a heat-resistant container such as a quartz port, an alumina crucible, or a quartz crucible, and placed in the core of an electric furnace to perform firing while avoiding sintering. The firing temperature is suitably in the range of 400 to 1300 ° C, preferably 500 to 1000 ° C. The firing time varies depending on the filling amount of the phosphor raw material mixture, the firing temperature, the temperature at which the material is taken out of the furnace, etc., but is generally 0.5 to
12 hours is appropriate.

As the firing atmosphere, 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, or a weak reducing atmosphere such as a carbon dioxide atmosphere containing carbon monoxide is used. To be done.
In the present invention, firing in a weak reducing atmosphere is preferred.

In addition, the amount of oxygen in the stimulable phosphor can be controlled by setting the atmosphere in which a trace amount of oxygen is introduced during firing. It is also possible to perform firing by the method described in JP-A-2000-8034.

The phosphor particles (crystals) according to the present invention preferably have an average particle size of 1 to 10 μm and are monodisperse. The average particle size is 1 to 5 μm, and the average particle size distribution (%). Is 2
0% or less is preferable, and especially the average particle size is 1 to 3 μm.
It is preferable that m and the average particle size distribution be 15% or less. The average particle diameter is obtained by randomly selecting 200 particles from an electron micrograph of particles (crystals) and calculating the average by volume particle diameter in terms of sphere.

As the support used in the radiation image conversion panel of the present invention, various polymer materials are used. In particular, in terms of handling as an information recording material, a material which can be processed into a flexible sheet or web is preferable, and in this respect, a cellulose acetate film, a polyester film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyamide film, A plastic film such as a polyimide film, a triacetate film or a polycarbonate film is preferable.

The layer thickness of these supports varies depending on the material of the support used and the like, but is generally 80-100.
0 μm, and more preferably 8 from the viewpoint of handling.
It is 0 to 500 μm. The surface of these supports may be a smooth surface, or may be a matte surface for the purpose of improving the adhesiveness with the stimulable phosphor layer.

Further, these supports may be provided with an undercoat layer on the surface on which the stimulable phosphor layer is provided for the purpose of improving the adhesiveness with the stimulable phosphor layer. The undercoat layer preferably contains a polymer resin that can be crosslinked with a crosslinking agent.

The polymer resin that can be used in the undercoat layer is not particularly limited, but examples thereof include polyurethane, polyester, vinyl chloride copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer. Polymers, vinyl chloride-acrylonitrile copolymers, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyral, cellulose derivatives (nitrocellulose, etc.), styrene-butadiene copolymers, various synthetic rubber resins, phenolic resins, epoxy resins , Urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin and the like. Among them, polyurethane, polyester, vinyl chloride copolymer,
Examples thereof include polyvinyl butyral and nitrocellulose. The average glass transition temperature (Tg) of the polymer resin used in the undercoat layer is preferably 25 to 200 ° C.

The crosslinking agent which can be used in the undercoat layer is not particularly limited, and examples thereof include polyfunctional isocyanates and their derivatives, melamine and its derivatives, amino resins and their derivatives, and the like. It is preferable to use a polyfunctional isocyanate compound, and examples thereof include Coronate HX and Coronate 3041 manufactured by Nippon Polyurethane Company.

The subbing layer can be formed on the support by the following method, for example. First, the above-mentioned polymer resin and a cross-linking agent are added to a suitable solvent, for example, the solvent used in the preparation of the stimulable fluorescent layer coating solution described below, and this is mixed sufficiently to prepare an undercoat layer coating solution. .

The amount of the crosslinking agent used varies depending on the characteristics of the intended radiation image conversion panel, the type of material used for the stimulable phosphor layer and the support, the type of polymer resin used for the undercoat layer, etc. Considering the maintenance of the adhesive strength of the stimulable phosphor layer to the support, it is preferably added at a ratio of 50% by mass or less with respect to the polymer resin, particularly 15 to 50.
It is preferably mass%.

The film thickness of the undercoat layer is the desired characteristics of the radiation image conversion panel, the types of materials used for the stimulable phosphor layer and the support, the types of polymer resins and crosslinking agents used for the undercoat layer, and the like. It is preferably 3 to 50 μm, and particularly preferably 5 to 40 μm, though it depends on the above.

In the present invention, examples of the binder used in the stimulable phosphor layer include proteins such as gelatin, polysaccharides such as dextran, or natural polymer substances such as gum arabic, and polyvinyl butyral and poly. Vinyl acetate, nitrocellulose, ethyl cellulose,
Binders represented by synthetic polymeric substances such as vinylidene chloride / vinyl chloride copolymer, polyalkyl (meth) acrylate, vinyl chloride / vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, linear polyester, etc. Although it can be mentioned, it is preferable that the binder is a resin containing a thermoplastic elastomer as a main component, and examples of the thermoplastic elastomer include polystyrene-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, and polyurethane-based thermoplastics described above. Thermoplastic elastomer, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, polybutadiene-based thermoplastic elastomer, ethylene vinyl acetate-based thermoplastic elastomer, polyvinyl chloride-based thermoplastic Elastomers, natural rubber-based thermoplastic elastomer, fluorine rubber thermoplastic elastomer,
Examples thereof include polyisoprene-based thermoplastic elastomers, chlorinated polyethylene-based thermoplastic elastomers, styrene-butadiene rubber, and silicone rubber-based thermoplastic elastomers.

Of these, the polyurethane-based thermoplastic elastomer and the polyester-based thermoplastic elastomer have good dispersibility because they have a strong binding force with the phosphor.
In addition, it is also preferable because it is rich in ductility and the flexibility of the radiation intensifying screen becomes good. In addition, these binders may be crosslinked with a crosslinking agent.

The mixing ratio of the binder to the stimulable phosphor in the coating liquid varies depending on the set value of the haze ratio of the intended radiation image conversion panel, but is preferably 1 to 20 parts by mass with respect to the phosphor, and Is more preferably 2 to 10 parts by mass.

As a protective layer provided on a radiation image conversion panel having a coating type phosphor layer, ASTM D-1003 is used.
The haze ratio measured by the method described in 5 is 5% or more, 6
Polyester film, polymethacrylate film, nitrocellulose film, cellulose acetate film, etc. having an excitation light absorption layer of less than 0% can be used, but stretched films such as polyethylene terephthalate film and polyethylene naphthalate film are transparent. , Preferred as a protective layer in terms of strength, further, on these polyethylene terephthalate film or polyethylene terephthalate film, a metal oxide,
A vapor-deposited film obtained by vapor-depositing a thin film of silicon nitride or the like is more preferable from the viewpoint of moisture resistance.

The haze ratio of the film used in the protective layer can be easily adjusted by selecting the haze ratio of the resin film to be used, and a resin film having an arbitrary haze ratio can be easily obtained industrially. it can. As a protective film for a radiation image conversion panel, one having a very high optical transparency is supposed. As such a highly transparent protective film material, various plastic films having a haze ratio in the range of 2 to 3% are commercially available. A preferable haze ratio is 5% or more and less than 60%, and more preferably 10% or more and less than 50%. If the haze ratio is less than 5%, the effect of eliminating image unevenness and linear noise is low, and if it is 60% or more, the effect of improving sharpness is impaired, which is not preferable.

The film used for the protective layer can have optimum moisture resistance by laminating a plurality of resin films or vapor-deposited films obtained by vapor-depositing metal oxides on the resin film in accordance with the required moisture resistance. In consideration of preventing moisture absorption and deterioration of the stimulable phosphor, the water vapor permeability is at least 5.0 g /
It is preferably m ² · day or less. The method for laminating the resin film is not particularly limited, and any known method may be used.

Further, by providing the excitation light absorption layer between the laminated resin films, the excitation light absorption layer is protected from physical impact and chemical alteration, and stable plate performance can be maintained for a long time, which is preferable. Further, the excitation light absorption layer may be provided at a plurality of positions, or the adhesive layer for laminating may contain a coloring material to form the excitation light absorption layer.

The protective film may be adhered to the stimulable phosphor layer via an adhesive layer, but the structure is provided so as to cover the phosphor surface (hereinafter, also referred to as sealing or sealing structure). Is more preferable.

When sealing the phosphor plate,
Although any known method may be used, the outermost resin layer on the side of the moisture-proof protective film in contact with the phosphor sheet is a resin film having heat-fusible properties, so that the moisture-proof protective film can be fused, This is one of the preferable modes in that the sealing work of the phosphor sheet is made efficient. Furthermore, the moisture-proof protective film is arranged on the upper and lower sides of the phosphor sheet, and the peripheral edge thereof is an area outside the peripheral edge of the phosphor sheet, and the upper and lower moisture-proof protective films are heated and fused by an impulse sealer or the like. The sealing structure is preferable because moisture can be prevented from entering from the outer peripheral portion of the phosphor sheet.

Furthermore, when the moisture-proof protective film on the support surface side is a laminated moisture-proof film formed by laminating one or more layers of aluminum film, it is possible to more reliably reduce the ingress of moisture and to seal this film. The stopping method is preferable because it is easy in terms of work. In the method of heat fusion with the impulse sealer, heat fusion in a reduced pressure environment is more preferable in terms of preventing displacement of the phosphor sheet in the moisture-proof protective film and eliminating moisture in the atmosphere.

The resin layer, which is the outermost layer having the heat-fusible property, on the side of the moisture-proof protective film in contact with the phosphor surface and the phosphor surface may or may not be adhered. The term "non-adhesive" as used herein means that, even if the phosphor surface is microscopically in point contact with the moisture-proof protective film, the phosphor surface and the moisture-proof protective film are almost discontinuous optically and mechanically. It is a state that can be treated as a body. In addition, the above-mentioned resin film having heat-fusible property is a resin film that can be fused by a commonly used impulse sealer, and for example, ethylene vinyl acetate copolymer (EVA), polypropylene (PP) film, polyethylene (PE) ) Films and the like can be mentioned, but the present invention is not limited thereto.

Examples of the organic solvent used for preparing the coating liquid for the stimulable phosphor layer include lower alcohols such as methanol, ethanol, isopropanol and n-butanol,
Acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate, n-butyl acetate, dioxane, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, etc., Examples thereof include aromatic compounds such as triol and xylol, halogenated hydrocarbons such as methylene chloride and ethylene chloride, and mixtures thereof.

The coating liquid contains a dispersant for improving the dispersibility of the phosphor in the coating liquid, and a binding force between the binder and the phosphor in the stimulable phosphor layer after formation. Various additives such as a plasticizer for improving the composition may be mixed.

Examples of dispersants used for such purpose include phthalic acid, stearic acid, caproic acid, lipophilic surfactants and the like.

Examples of the plasticizer include phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate, diphenyl phosphate; phthalic acid esters such as diethyl phthalate and dimethoxyethyl phthalate; ethyl phthalyl ethyl glycolate and butyl glycolate. Glycolic acid esters such as phthalylbutyl; and polyesters of triethylene glycol and adipic acid, polyesters of polyethylene glycol and aliphatic dibasic acids such as polyesters of diethylene glycol and succinic acid, and the like.

In order to improve the dispersibility of the stimulable phosphor particles, a dispersant such as stearic acid, phthalic acid, caproic acid or a lipophilic surfactant is added to the coating liquid for the stimulable phosphor layer. You may mix.

The coating liquid for the stimulable phosphor layer is prepared, for example, by a ball mill, a bead mill, a sand mill, an attritor,
It is carried out using a dispersing device such as a three-roll mill, a high-speed impeller disperser, a Kady mill, or an ultrasonic disperser.

A coating film is formed by uniformly coating the coating liquid prepared as described above on the surface of a support described later. As a coating method that can be used, usual coating means, for example, a doctor blade, a roll coater,
A knife coater, a comma coater, a lip coater, etc. can be used.

The coating film formed by the above means is then heated and dried to complete the formation of the stimulable phosphor layer on the support. The film thickness of the stimulable phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of the stimulable phosphor, the mixing ratio of the binder and the phosphor, etc., but is usually 1
0 to 1000 μm, more preferably 10 to 500
μm.

[0079]

EXAMPLES The present invention will be illustrated below with reference to Examples.
The present invention is not limited to these.

Example 1 [Preparation of Radiation Image Conversion Panel] << Formation of Undercoat Layer >> The undercoat layer coating solution described below was formed using a doctor blade on a foamed polyethylene terephthalate film (manufactured by Toray Industries, Inc.). 188E60
L) and dried at 100 ° C. for 5 minutes to form an undercoat layer having a dry film thickness of 30 μm.

(Undercoat layer coating liquid) Polyester resin dissolved product (Vylon 55SS, Toyobo Co., solid content 35%) 28
To 8.2 g, 0.34 g of β-copper phthalocyanine dispersion product
(Solid content 35%, pigment content 30%) and 11.22 g of a polyisocyanate compound (Coronate HX manufactured by Nippon Polyurethane Industry Co., Ltd.) as a curing agent were mixed and dispersed with a propeller mixer to prepare an undercoat layer coating solution.

<< Preparation of Phosphor Sheet >> (Preparation of Phosphor Precursor) In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, a BaI ₂ aqueous solution was placed in a pressure vessel having two holes. (4 mol / L)
2500 ml and EuI ₃ aqueous solution (0.2 mol / L) 2
6.5 ml was added. Furthermore, 992 g of potassium iodide was added to the aqueous solution. The reaction mother liquor in this reactor was kept warm at 83 ° C. with stirring. Ammonium fluoride aqueous solution (1
600 ml (0 mol / L) was injected into the reaction mother liquor using a roller pump to form a precipitate. The concentration of phosphorus in BaI ₂ used here was 28 ppm.
After completion of the injection, dry air was aerated at a rate of 10 l / min for 20 minutes. The mass ratio of the solution before and after aeration was 0.94. The mixture was stirred at the same temperature for 90 minutes. After stirring for 90 minutes, it was filtered and washed with 2000 ml of ethanol. The mass of the recovered precursor was measured and compared with the amount of BaI ₂ charged to determine the yield. The precipitate obtained by the above operation was subjected to X-ray diffraction measurement. X-ray is Cu-K
α rays were used. Then, the average particle size of the obtained precipitate was measured.

(Preparation of Phosphor) In order to prevent changes in particle shape due to sintering during firing and changes in particle size distribution due to fusion between particles, 0.1% by mass of ultrafine alumina powder was added. Then, the mixture was thoroughly stirred with a mixer to uniformly deposit the ultrafine alumina powder on the crystal surface. This is filled in a quartz boat, and using a tube furnace under hydrogen gas atmosphere,
The mixture was baked at 850 ° C. for 2 hours to prepare europium-activated barium fluoroiodide phosphor particles.

(Measurement of Phosphorus Concentration in Phosphor Precursor) 2 g of a sample was placed in a 100 ml Teflon (R) heatable beaker, and hydrochloric acid (EL grade manufactured by Kanto Chemical Co., Inc.) was added to 20 ml.
ml was added, heating was carried out, and drying was carried out until the water content disappeared.
Further, hydrochloric acid addition and heat drying were repeated twice. Next, the sample was dissolved using 5 ml of the above-mentioned hydrochloric acid and ultrapure water to make 50 ml in total.

The obtained solution was analyzed by using an ICP emission spectrometer (Seiko Denshi KK, SPS4000). Analysis wavelength and output are 213.618n
m, 1.3 kW. The phosphorus content was determined by a calibration curve method using an atomic absorption analysis reagent (manufactured by Kanto Chemical Co., Inc.) as the standard solution.

(Preparation of Phosphor Layer Coating Solution) 300 g of europium-activated barium fluoroiodide phosphor particles prepared above
And polyester resin (byron 530 manufactured by Toyobo Co.,
Solid content 30%, solvent: methyl ethyl ketone / toluene =
5/5) 52.63 g and methyl ethyl ketone 0.1
3 g, toluene 0.13 g and cyclohexanone 41.
It was added to 84 g of the mixed solvent and dispersed by a propeller mixer to prepare a phosphor layer coating solution. The solvent ratio of cyclohexane in the phosphor layer coating liquid was 53% by mass.

(Formation of Phosphor Layer) The above-prepared phosphor layer coating solution was coated on the above-formed undercoat layer with a doctor blade so that the film thickness was 180 μm,
A phosphor layer was formed by drying at 100 ° C. for 15 minutes to prepare a phosphor sheet.

The residual solvent amount in the phosphor layer was measured by the method described below, and as a result, the residual amount of cyclohexanone was 5
It was 60 mg / m ² .

<< Preparation of Moisture-Proof Protective Film >> As the protective film on the phosphor layer coated surface side of the phosphor sheet prepared above, one having the following constitution (A) was used.

Structure (A) NY15 /// VMPET12 /// VMPET12 /
// PET12 /// CPP20 NY: Nylon PET: Polyethylene terephthalate CPP: Casting polypropylene VMPET: Alumina-deposited PET (commercially available product: manufactured by Toyo Metallizing Co., Ltd.) μm).

The above "///" means a dry lamination adhesive layer, and the thickness of the adhesive layer is 3.0 μm. The used adhesive for dry lamination is
A two-component reactive urethane adhesive was used.

The protective film on the back surface side of the support of the phosphor sheet is CPP 30 μm / aluminum film 9 μm /
A dry laminated film having a structure of polyethylene terephthalate 188 μm was used. The thickness of the adhesive layer in this case was 1.5 μm, and a two-component reactive urethane adhesive was used.

The phosphor sheet prepared above was cut into squares each having a side of 20 cm, and the peripheral edge portion was fused and sealed under reduced pressure using an impulse sealer using the moisture-proof protective film prepared above. Thus, a radiation image conversion panel was produced. The distance from the fusion portion to the peripheral edge of the phosphor sheet was 1 mm. The heater of the impulse sealer used for fusing has a width of 3 mm.

[Evaluation of Radiation Image Conversion Panel] The following measurements were performed on the produced radiation image conversion panel.

(Measurement of Luminance) For each radiation image conversion panel, the luminance was measured by irradiating the X-ray of a tube voltage of 80 kVp from the rear surface side of the phosphor sheet support, and then the panel was irradiated with He.
-Operated by Ne laser light (633 nm) to be excited, and stimulated emission emitted from the phosphor layer is received by a light receiver (spectral sensitivity S-
(5) Photoelectron multiplier tube, and measure its intensity,
This was defined as brightness, and the brightness of the radiation image conversion panel of Example 1 was set to 1.00 and displayed as a relative value.

(Measurement of Structural Mottle) X-rays are exposed to the obtained radiation image conversion panel under the photographing conditions of 80 kV and 200 mas. The signal is read with Regius 150 (manufactured by Konica) to obtain signal value data. From this data, Wiener spectrum data for each spatial frequency is obtained. The value of 0.2 line / mm is read to obtain the structure mottle value. The value of the structure mottle was shown as a relative value, with the result of Example 1 being 100.

Example 2 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (Preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

After the addition of ammonium fluoride was completed, the pressure in the reaction vessel was adjusted to 7.45 × 10 using a circulation aspirator.
The pressure was reduced to ⁴ Pa, and the solvent was concentrated under reduced pressure for 15 minutes. The mass ratio of the reaction solution before and after the concentration was 0.92. Other than this, the same operation as in Example 1 was performed to obtain a precipitate. Example 1
The yield was calculated in the same manner as above, and the X-ray diffraction and average particle size of the precipitate were measured.

Example 3 A radiation image conversion panel was prepared in the same manner as in Example 1 except that the (preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

After the addition of ammonium fluoride was completed, the reaction solution was sprayed on the wall surface of the reaction vessel using a pump to evaporate the solvent while forming a liquid film. This operation was performed for 15 minutes. The mass ratio of the reaction solution before and after the concentration was 0.94. Other than this, the same operation as in Example 1 was performed to obtain a precipitate. The yield was calculated in the same manner as in Example 1, and the precipitate was subjected to X-ray diffraction and average particle size measurement.

Comparative Example 1 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (Preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

To synthesize a europium-activated barium fluoroiodide stimulable phosphor precursor, 2500 ml of BaI ₂ aqueous solution (4 mol / L) and EuI ₃ aqueous solution (0.
26.5 ml of 2 mol / L) was put into the reactor. The BaI ₂ used here is the same as that used in Example 1,
It contains 28 ppm of phosphorus. Further, 332 g of potassium iodide was added to the aqueous solution. The reaction mother liquor in this reactor was kept warm at 83 ° C. with stirring. 250 ml of an aqueous solution of ammonium fluoride (10 mol / L) was injected into the reaction mother liquor using a roller pump to form a precipitate. After the injection was completed, the mixture was stirred at the same temperature for 90 minutes. After stirring for 90 minutes, it was filtered and washed with 2000 ml of ethanol. The mass of the recovered precursor was measured and compared with the amount of BaI ₂ charged to determine the yield. X-ray diffraction measurement was performed on the precipitate obtained by the above operation. Then, the average particle size of the obtained precipitate was measured.

Comparative Example 2 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (Preparation of phosphor precursor) was changed to the following, and the brightness and structural mottle were measured. It was

A precipitate was obtained in the same manner as in Comparative Example 1 except that the amount of ammonium fluoride aqueous solution injected into the reaction mother liquor was 600 ml. The yield was calculated in the same manner as in Example 1,
The precipitate was subjected to X-ray diffraction, average particle size measurement, and phosphorus concentration measurement.

Comparative Example 3 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (preparation of phosphor precursor and phosphor) in Example 1 was changed to the following, and the radiation and structure mottles were changed. The measurement was performed.

A precipitate was obtained in the same manner as in Example 1 except that BaI ₂ containing 52 ppm of phosphorus was used. The yield was calculated in the same manner as in Example 1, and the precipitate was subjected to X-ray diffraction and average particle size measurement.

Comparative Example 4 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (Preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

A precipitate was obtained in the same manner as in Example 1 except that BaI ₂ containing 65 ppm of phosphorus was used. The yield was calculated in the same manner as in Example 1, and the precipitate was subjected to X-ray diffraction and average particle size measurement.

Example 4 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

A precipitate was obtained in the same manner as in Example 1 except that BaI ₂ containing 18 ppm of phosphorus was used. The yield was calculated in the same manner as in Example 1, and the precipitate was subjected to X-ray diffraction and average particle size measurement.

Example 5 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (Preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

A precipitate was obtained in the same manner as in Example 1 except that BaI ₂ containing 10 ppm of phosphorus was used. The yield was calculated in the same manner as in Example 1, and the precipitate was subjected to X-ray diffraction and average particle size measurement.

Example 6 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

A precipitate was obtained in the same manner as in Example 1 except that BaI ₂ containing 40 ppm of phosphorus was used. The yield was calculated in the same manner as in Example 1, and the precipitate was subjected to X-ray diffraction and average particle size measurement.

Example 7 A radiation image conversion panel was prepared in the same manner as in Example 1 except that (Preparation of phosphor precursor) was changed to the following, and the luminance and structural mottle were measured. It was

After adding ammonium fluoride, the pressure inside the reaction vessel was set to 7.45 × 10 ⁴ Pa, the reaction solution was sprayed on the wall surface of the reaction vessel using a pump, and the solvent was removed while forming a liquid film. . This operation was performed for 7 minutes. The mass ratio of the reaction solution before and after the concentration was 0.92. Other than this, Example 1
The same operation as above was performed to obtain a precipitate. The yield was calculated in the same manner as in Example 1, and the precipitate was subjected to X-ray diffraction and average particle size measurement.

Table 1 shows the radiation image conversion panels of Examples (the present invention) and Comparative Examples and the results of their evaluation and measurement. From the result of X-ray diffraction measurement, the diffraction line at 2θ = 29.4 ° was identified as the peak of barium fluoride as a by-product.

[0118]

[Table 1]

The structural mottle of Comparative Example 2 could not be evaluated because the brightness was not sufficient.

As is clear from the table, by removing the solvent from the reaction solution, it is possible to obtain a stimulable phosphor precursor in a high yield while preventing the particles from becoming large, and to increase the phosphorus concentration. By controlling, it can be seen that the radiation image conversion panel produced from the phosphor from the phosphor precursor has good brightness and good structural mottle.

[0121]

Industrial Applicability According to the present invention, a stimulable phosphor precursor can be obtained in high yield while preventing the particles from being enlarged, and by controlling the phosphorus concentration, the brightness and the structure mottle can be improved. A radiation image conversion panel could be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G01T 1/00 G01T 1/00 B G21K 4/00 G21K 4/00 MF term (reference) 2G083 AA03 BB01 DD02 DD11 DD12 EE02 EE03 EE10 4G076 AA05 AA07 AA08 AA19 DA11 4H001 CA04 CA08 CF01 XA04 XA09 XA12 XA20 XA35 XA38 XA53 XA56 YA00 YA03 YA11 YA19 YA37 YA55

Claims (8)

[Claims] 1. A stimulable phosphor precursor obtained by removing a solvent from a reaction solution having a barium concentration of 3.3 mol / L or more, wherein the phosphorus content is 50 ppm or less. A method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor represented by (1). General formula (1) Ba _(1-x) M _{2 (x)} FBr _(y) I _(1-y) : a
M ₁ , bLn, cO (wherein M ₁ is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs, and M ₂ is selected from the group consisting of Be, Mg, Sr and Ca) At least one alkaline earth metal, Ln is Ce, Pr, S
m, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er
And at least one rare earth element selected from the group consisting of Yb, and x, y, a, b and c are each 0 ≦ x.
≦ 0.3, 0 <y ≦ 0.3, 0 ≦ a ≦ 0.05, 0 <b
≦ 0.2 and 0 <c ≦ 0.1. ) 2. The oxygen-introduced rare earth-activated alkaline earth metal fluoride halide system according to claim 1, characterized in that the mass after removal of the solvent is 0.97 or less with respect to the mass before removal. Method for producing exhaustible phosphor. 3. The method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor according to claim 1, wherein the removal of the solvent is performed under reduced pressure. 4. The method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluoride halide stimulable phosphor according to claim 1, wherein the solvent is removed by aeration of dry gas. 5. The method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluorohalide stimulable phosphor according to claim 1 or 2, wherein the solvent is removed by forming a liquid film. 6. An oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor precursor, which is obtained by the production method according to any one of claims 1 to 5. 7. An oxygen-introduced rare earth-activated alkaline earth metal halogen fluoride obtained from the oxygen-introduced rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor precursor according to claim 6. Compound-based stimulable phosphor. 8. A radiation image conversion panel comprising a phosphor layer containing the oxygen-introduced rare earth activated alkaline earth metal fluorohalide stimulable phosphor according to claim 7.