JPH10130641A - Tetradecahedral rare-earth-activated alkaline earth metal fluoride halide-accelerated phosphor and radiation image conversion panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the afterglow of accelerated phosphorescence of a radiation image conversion panel and improve the image quality by adding Mg to a specific tetradecahedral rare-earth-activated alkaline earth metal fluoride halide- accelerated phosphor and incorporating the phosphor contg. Mg into the panel. SOLUTION: This tetradecahedral rare-earth-activated alkaline earth metal fluoride halide-accelerated phosphor is represented by formula I (wherein M is an alkali metal; and (x), (y), (a), (b), and (c) are each a value satisfying the conditions of formula II). This phosphor is produced by using Ba, Ca, Eu, Mg, and an alkali metal halide. Usually, Mg is introduced into the phosphor by producing an accelerated phosphor contg. no Mg, mixing the phosphor with an Mg halide and fine alumina particles, etc., as a sintering inhibitor, and sintering the mixture. An accelerated phosphor layer is formed by causing a binder to contain and support the phosphor in a dispersion state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel tetrahedral rare earth activated alkaline earth metal fluorinated halide stimulable phosphor and a radiation image conversion panel using the stimulable phosphor. It is.

[0002]

2. Description of the Related Art As an alternative to the conventional radiographic method, there is known a radiation image recording / reproducing method using a stimulable phosphor as described in, for example, JP-A-55-12145. This method uses a radiation image conversion panel (a stimulable phosphor sheet) containing a stimulable phosphor, and transmits radiation transmitted through a subject or emitted from a subject to the stimulable phosphor of the panel. By absorbing the stimulable phosphor with electromagnetic waves (excitation light) such as visible light and infrared light in a time series manner, the radiation energy stored in the stimulable phosphor is absorbed by the body. The fluorescent light is emitted (stimulated emission light), the fluorescent light is read photoelectrically to obtain an electric signal, and a radiation image of a subject or a subject is reproduced as a visible image based on the obtained electric signal. . After the reading of the panel is completed, after the remaining image is deleted, the panel is prepared for the next photographing. That is, the radiation image conversion panel can be used repeatedly.

According to the above-described radiographic image recording / reproducing method, a radiation having a much smaller amount of exposure and a richer amount of information than a conventional radiographic method using a combination of a radiographic film and an intensifying screen. There is an advantage that an image can be obtained. Furthermore, while the conventional radiographic method consumes radiographic film for each photographing operation, this radiographic image conversion method uses a radiographic image conversion panel repeatedly, which also contributes to resource conservation and economic efficiency. It is advantageous.

A stimulable phosphor is a phosphor that emits stimulable light when irradiated with radiation and then with excitation light. However, in practice, the stimulable phosphor has a wavelength of 400 to 900 nm due to the excitation light. Phosphors that exhibit stimulated emission in the 500 nm wavelength range are commonly used. Examples of stimulable phosphors conventionally used in radiation image conversion panels include rare earth-activated alkaline earth metal fluorinated halide-based phosphors.

The radiation image conversion panel used in the radiation image recording / reproducing method has, as a basic structure, a support and a stimulable phosphor layer provided on the surface of the support. However, when the phosphor layer is self-supporting, a support is not necessarily required. The stimulable phosphor layer usually comprises a stimulable phosphor and a binder containing and supporting the stimulable phosphor in a dispersed state. However, as the stimulable phosphor layer, a layer composed of only an aggregate of the stimulable phosphor without a binder formed by a vapor deposition method or a sintering method is known. Also,
There is also known a radiation image conversion panel having a stimulable phosphor layer in which a polymer substance is impregnated in a gap between stimulable phosphor aggregates. In any of these phosphor layers, the stimulable phosphor has a property of exhibiting stimulable emission when irradiated with excitation light after absorbing radiation such as X-rays. The radiation emitted from the specimen
The radiation image is absorbed by the stimulable phosphor layer of the radiation image conversion panel in proportion to the radiation dose, and a radiation image of the subject or the subject is formed on the panel as a radiation energy accumulation image. This accumulated image can be emitted as stimulated emission light by irradiating the excitation light, and the accumulated image of radiation energy is imaged by photoelectrically reading the stimulated emission light and converting it into an electric signal. It is possible to do.

The surface of the stimulable phosphor layer (the surface not facing the support) is usually provided with a protective film such as a polymer film or an inorganic vapor-deposited film. Is protected from chemical alteration or physical impact.

The rare earth activated alkaline earth metal fluorohalide-based stimulable phosphor is excellent in sensitivity and, when used as a radiation image conversion panel, provides a radiation-reproduced image with high sharpness. Above, it can be said to be an excellent stimulable phosphor. However, as radiation image recording / reproducing methods have been put into practical use, demands for stimulable phosphors having higher performance have been increasing.

Japanese Patent Application Laid-Open No. Hei 7-233369 discloses the problem that the conventionally used rare earth activated alkaline earth metal fluorinated halide stimulable phosphor is composed of plate-like particles. In order to solve the problem, a rare earth activated alkaline earth metal fluorinated halide stimulable phosphor having a specific basic composition formula and having a tetradecahedral shape and a stimulable phosphor were irradiated with radiation. It is proposed to use it for an image conversion panel.

[0009]

SUMMARY OF THE INVENTION The present invention, when applied to a radiation image recording / reproducing method, is disclosed in Japanese Patent Laid-Open No.
Compared with the tetradecahedral rare earth activated alkaline earth metal fluorohalide-based stimulable phosphor specifically described in JP-A-233369, the stimulable phosphor has a reduced stimulable afterglow.
It is an object of the present invention to provide a tetrahedral rare earth activated alkaline earth metal fluoride halide stimulable phosphor.

That is, when the stimulable phosphor is irradiated with radiation energy, the stimulable phosphor accumulates radiation energy therein in accordance with the amount of the irradiated radiation energy, and thereafter, when irradiated with excitation light, the stimulable phosphor is stimulated. Although the phosphor emits light, the ordinary stimulable phosphor exhibits such a property that the stimulated emission continues for a short time after the irradiation of the excitation light is completed. In a radiation image conversion method (radiation image recording / reproduction method) using a radiation image conversion panel in which a stimulable phosphor is arranged in a planar layer as a recording medium, a laser beam is usually used as excitation light in the reproduction step. A method is used in which the stimulated emission is extracted while scanning the laser light on the surface of the panel, and the accumulated radiation image is read. Therefore, if the stimulating residual light continues for a long time compared to the scanning speed, the stimulating light emitted from the stimulable phosphor irradiated with the exciting light is irradiated with the exciting light immediately before, and then the excitation ends. The stimulable phosphor emitted from the stimulable phosphor is condensed in a state where the stimulable phosphor enters as noise, resulting in a deterioration in the quality of the finally obtained radiation image reproduced image. Therefore, in order to obtain a radiation image reproduction image having excellent image quality, it is desirable to reduce stimulating afterglow as much as possible. That is, an object of the present invention is to reduce the stimulable afterglow of the tetradecahedral rare-earth-activated alkaline earth metal fluorohalide-based stimulable phosphor without substantially reducing other properties of the phosphor. .

[0011]

SUMMARY OF THE INVENTION The present invention is basic formula _{(I): Ba 1-x} Ca x FBr 1-y I y: aEu, bM, cMg ... (I) [ however, M is an alkali metal ( Example, Li, K, Na, C
e), where x, y, a, b and c are each 0
≦ x ≦ 0.03, 0 <y ≦ 0.30, 0.0001 ≦ a
≦ 0.01, 0 ≦ b ≦ 0.001, and 0 <c ≦ 0.
It is a numerical value in the range of 1. ], And a radiation image conversion panel containing the same. The coefficients such as x, y, a, b, and c in the phosphor composition described in the present specification are numerical values obtained by analyzing the obtained phosphor. Since the composition changes before and after the firing step in the manufacture of the phosphor, the ratio of each component of each raw material used in the manufacture of the phosphor and the ratio of each component of the completed phosphor are slightly different.

In the above basic composition formula (I), x, y,
a, b, and c are each, in particular, 0.001 ≦ x ≦
0.02, 0.10 ≦ y ≦ 0.20, 0.001 ≦ a ≦
0.01, 0 <b ≦ 0.0003, and 0.001 <
It is preferable that the value be in the range of c ≦ 0.01. The stimulable phosphor of the above basic composition formula (I) may optionally include other alkaline earth metals such as strontium, as long as the basic properties of the stimulable phosphor are not changed.
Alternatively, other elements may be included. Also,
Two or more alkali metals may be combined.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The tetradecahedral rare earth activated alkaline earth metal fluoride halide stimulable phosphor of the present invention comprises barium, calcium, europium, magnesium and alkali metals (eg, Na, K, Li). , Cs) and the like, and further disclosed in JP-A-7-233.
It can be produced using a method according to the method described in JP-A-369-369. In order to introduce Mg into the tetradecahedral rare earth activated alkaline earth metal fluoride halide stimulable phosphor of the present invention, a halide of Mg is usually used as described above. The magnesium halide is usually prepared by preparing a tetrahedral rare earth activated alkaline earth metal fluorinated halide stimulable phosphor not containing the Mg halide, and then adding the magnesium halide and, for example, calcination. It is introduced into the intended stimulable phosphor using a method of adding and mixing alumina fine particles or the like used as an anti-binding agent, followed by baking.

The tetrahedral rare earth activated alkaline earth metal fluoride halide stimulable phosphor of the present invention is an intermediate polyhedron between a regular hexahedron and a regular octahedron, and usually has an aspect ratio of 1.0 to 1.0. 5.0 and the shape is the same as that shown in the photograph in the above-mentioned JP-A-7-733369.

In the radiation image storage panel of the present invention, the stimulable phosphor layer contains a tetradecahedral rare earth activated alkaline earth metal fluorohalide-based stimulable phosphor represented by the aforementioned basic composition formula. The stimulable phosphor layer is usually composed of a stimulable phosphor and a binder containing and supporting the stimulable phosphor in a dispersed state. The phosphor layer may further contain other stimulable phosphors and / or additives such as colorants.

Next, the method for producing the radiation image storage panel of the present invention will be described, taking as an example the case where the phosphor layer comprises a stimulable phosphor and a binder containing and supporting the stimulable phosphor in a dispersed state. The phosphor layer can be formed on a support by the following known method. First, a stimulable phosphor and a binder are added to a solvent and mixed well to prepare a coating solution in which the stimulable phosphor is uniformly dispersed in a binder solution.
The mixing ratio between the binder and the stimulable phosphor in the coating solution varies depending on the characteristics of the intended radiation image conversion panel, the type of the phosphor, and the like. Generally, the mixing ratio between the binder and the phosphor is 1%. It is selected from the range of 1: 1 to 1: 100 (weight ratio), and particularly preferably selected from the range of 1: 8 to 1:40 (weight ratio). The coating solution containing the phosphor and the binder prepared as described above is then uniformly applied to the surface of the support to form a coating film. This coating operation can be performed by using ordinary coating means, for example, a doctor blade, a roll coater, a knife coater, or the like.

The support can be arbitrarily selected from materials known as supports for conventional radiation image conversion panels. In a known radiation image conversion panel, a phosphor layer is provided to enhance the bond between the support and the phosphor layer or to improve the sensitivity or image quality (sharpness, granularity) of the radiation image conversion panel. A polymer material such as gelatin is applied to the surface of the support on the side to form an adhesion-imparting layer, or a light-reflective layer made of a light-reflective material such as titanium dioxide, or a light-absorbent material such as carbon black It is known to provide an absorption layer or the like. The support used in the present invention can also be provided with these various layers, and the configuration thereof can be arbitrarily selected depending on the desired purpose and application of the radiation image storage panel. Further, JP-A-58-20020
As described in JP-A No. 0, the surface of the support on the side of the phosphor layer (the surface of the support on the side of the phosphor layer, the adhesion-imparting layer, In the case where a layer or a light absorbing layer is provided, the surface thereof means fine irregularities.

After forming the coating on the support as described above, the coating is dried to complete the formation of the stimulable phosphor layer on the support. The thickness of the phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the kind of the phosphor, the mixing ratio of the binder to the phosphor, and the like.
mm. However, this layer thickness is preferably 50 to 500 μm. The stimulable phosphor layer does not necessarily need to be formed by directly applying the coating solution on the support as described above. For example, the stimulable phosphor layer may be separately applied on a sheet such as a glass plate, a metal plate, or a plastic sheet. After forming a phosphor layer by applying and drying a liquid, the phosphor layer may be joined to the support by pressing the phosphor layer on a support or using an adhesive.

As described above, usually, a protective film is provided on the phosphor layer. As the protective film, a film formed by applying a solution prepared by dissolving a transparent organic polymer substance such as a cellulose derivative or polymethyl methacrylate in an appropriate solvent onto the phosphor layer, or polyethylene. An organic polymer film such as terephthalate or a sheet for forming a protective film such as a transparent glass plate is separately formed and provided on the surface of the phosphor layer using a suitable adhesive, or an inorganic compound is deposited on the phosphor by vapor deposition or the like. A film formed on the layer is used. Further, the protective film may be formed of a coating film of a fluorine-based resin soluble in an organic solvent, in which a perfluoroolefin resin powder or a silicone resin powder is dispersed and contained.

For the purpose of improving the sharpness of the obtained image, at least one of the layers constituting the radiation image conversion panel of the present invention absorbs excitation light,
The stimulated emission light may be colored by a coloring agent that does not absorb the light, or an independent colored intermediate layer may be provided (see Japanese Patent Publication No. 54-23400).

According to the above-mentioned method, a tetrahedral rare earth activated alkaline earth metal fluorinated halide stimulable phosphor represented by the basic composition formula (I) and a dispersion containing the same in a dispersed state are provided on a support. The radiation image storage panel according to the present invention, which is provided with a phosphor layer made of a binder, can be manufactured.

[0022]

【Example】

Comparative Example 1 Ba _0.841 Ca _0.149 FBr _0.85 I _0.15 :
Production of 0.004Eu, 0.0001K 1) 1150 mL of BaBr ₂ aqueous solution (2.5 mol /
L), 72.37 g CaBr ₂ .2H ₂ O, 36 mL
Of EuBr ₃ (0.2 mol / L), 4.95 g of KBr, and 1812 mL of water were placed in a 4000 mL reaction vessel. The reaction mother liquor in the reaction vessel was kept at 60 ° C., and a screw-type stirring blade having a diameter of 60 mm was set to 500 mm.
The reaction mother liquor was stirred by rotation at rpm. 288 mL
3. An NH ₄ F aqueous solution (5 mol / mL) was placed in the above reaction mother liquor kept under stirring with a roller pump.
The mixture was injected at a flow rate of 8 mL / min to produce a precipitate.
After completion of the injection, the mixture was kept warm and stirred for 2 hours to mature the precipitate. Next, the precipitate was separated by filtration and washed with 2 L of methanol. Next, the washed precipitate was taken out,
For 4 hours to obtain 320 g of a phosphor precursor crystal (hereinafter, referred to as a BFB crystal). Observation of the obtained crystal with a scanning electron microscope revealed that most of the crystal was a tetrahedral crystal.

2) Take 20.6 g of the above-mentioned BFB crystal,
To this, the BaI ₂ 4.4g, the BaF ₂ 0.18g,
0.0012 g of KBr and 0.125 of ultrafine alumina powder for preventing a change in particle shape due to sintering during firing and a change in particle size distribution due to fusion between particles.
g was added and mixed in a mortar, then placed in a plastic bottle, shaken sufficiently, and stirred. This was taken and filled in a quartz boat. Using a tube furnace, in a nitrogen gas atmosphere, 800
The mixture was calcined at 2 ° C. for 2 hours to obtain europium-activated barium fluorobromide phosphor particles represented by the composition formula shown above. Observation of the obtained phosphor particles with a scanning electron microscope revealed that most of the particles were in the shape of a tetrahedron, like the raw material crystal.

Example 1 Ba _0.841 Ca _0.149 FBr
_0.85 I _0.15 : 0.004Eu, 0.0001K, 0.001 Production of Mg Using the BFB crystal obtained in Step 1) of Comparative Example 1, 0.0189 g (0.000 g) was added to the substance added thereto.
A tetrahedral europium-activated fluorobromide represented by the composition formula of the title was prepared in the same manner as in Comparative Example 1 except that MgBr ₂ (103 mol, the amount of Mg added to the phosphor matrix: 0.1 mol%) was added. Barium phosphor particles were obtained.

Example 2 Ba _0.841 Ca _0.149 FBr
_0.85 I _0.15 : 0.004Eu, 0.0001K, 0.005 Production of Mg Using the BFB crystal obtained in Step 1) of Comparative Example 1, 0.0945 g (0.000 g) was added to the substance to be added thereto.
A tetrahedral europium-activated fluorofluorobromide represented by the title composition formula was prepared in the same manner as in Comparative Example 1 except that MgBr ₂ was added in an amount of 514 mol (the amount of Mg added to the phosphor matrix: 0.5 mol%). Barium phosphor particles were obtained.

Example 3 Ba _0.841 Ca _0.149 FBr
Production of _0.85 I _0.15 : 0.004 Eu, 0.0001 K, 0.0010 Mg Using the BFB crystal obtained in the step 1) of Comparative Example 1, 0.189 g (0.00103 g) was added to the substance to be added thereto.
Mol, Mg added to phosphor matrix: 1.0 mol%)
In the same manner as in Comparative Example 1 except that MgBr ₂ was added, tetrahedral europium-activated barium fluorobromide phosphor particles represented by the title composition formula were obtained.

[Evaluation of the properties of the tetrahedral europium-activated barium fluorobromide stimulable phosphor] The tetradecahedral europium-activated barium fluorobromide stimulable phosphor obtained in each of the above Examples and Comparative Examples Were evaluated by the following methods. 1) Stimulated afterglow a) Semiconductor laser light (wavelength 680 nm) 10 seconds after irradiating a predetermined amount of phosphor with 300 mR of 80 kVp X-rays
At 5.9 J / m ² to excite the phosphor, and the photostimulated light emitted from the phosphor is filtered by an optical filter (B-41).
First, the amount of stimulated emission during excitation was measured by receiving light through a photomultiplier tube through 0). b) Next, the photostimulated light generated during the time 0.5 seconds after the end of the above excitation is received by the photomultiplier tube through the optical filter (B-410). Was measured for the amount of stimulated emission. c) The afterglow was obtained by calculation based on the following equation. Stimulated afterglow = log ₁₀ (Stimulated luminescence after excitation / Stimulated luminescence during excitation)

2) Ultraviolet fog value a) First, the amount of unfogged stimulated emission of each phosphor was measured by the above method 1) -a). b) Then, light from a white fluorescent lamp passed through a sharp cut filter (SC-46) was applied to the phosphor for 1200 minutes.
Irradiation for 10,000 lux-seconds eliminated residual radiation energy. Then, the phosphor was irradiated with 1.8 million lux-second ultraviolet light using a sodium lamp as a light source. Then
4. Apply semiconductor laser light (wavelength 680 nm) to this phosphor.
The phosphor is excited by irradiating 9 J / m ² and the photostimulated light emitted from the phosphor is received by a photomultiplier tube through an optical filter (B-410). The amount of stimulated emission was measured. c) Ultraviolet fog was obtained by calculation based on the following equation. UV fog value = (Stimulated luminescence after UV fog) /
(Unfogged photostimulated luminescence amount) UV fogging refers to a stimulable phosphor or a radiation image conversion panel using the stimulable phosphor placed under a fluorescent lamp or sunlight. This is a “fogging phenomenon” that occurs when the object is moved under such conditions. If the ultraviolet fogging is large, the image quality of the obtained radiographic image is degraded.

3) The stimulable afterglow and the UV fog value obtained for each phosphor are shown as a graph in FIG. 1 of the accompanying drawings based on the magnesium addition ratio. In FIG. 1, the ultraviolet fogging value (UV fogging value) is preferably on the smaller side (ie, the lower side in the graph), and the stimulus afterglow (PSL afterglow) is also on the smaller side (ie, the lower side in the graph). Preferably, there is. From the graph of FIG. 1, it can be seen that if the amount of addition is within a certain range, the addition of Mg is effective for reducing the afterglow afterglow without increasing ultraviolet fog much.

Example 4 Manufacture of Radiation Image Conversion Panel As a phosphor layer forming material, 358 g of a tetrahedral rare earth activated alkaline earth metal fluorohalide stimulable phosphor containing the above-mentioned Mg component, a polyurethane resin 15.8 g (Desmolac 4125, manufactured by Sumitomo Bayer Urethane Co., Ltd.) and 2.0 g of bisphenol A type epoxy resin were added to a mixed solvent of methyl ethyl ketone-toluene (1: 1), dispersed by a propeller mixer, and the viscosity was 25 to 30 PS. Was prepared. This coating solution was applied on a polyethylene terephthalate film with an undercoat using a doctor blade, and then dried at 100 ° C. for 15 minutes to obtain a film having a thickness of 200 μm.
A phosphor layer of μm was formed.

Next, as a protective film forming material, a fluororesin: fluoroolefin-vinyl ether copolymer (Lumiflon LF100 manufactured by Asahi Glass Co., Ltd.) 70 g, a cross-linking agent: isocyanate (Desmodur Z4370 manufactured by Sumitomo Bayer Urethane Co., Ltd.) 25 g, bisphenol A epoxy resin 5
g and 10 g of silicone resin fine powder (KMP-590, manufactured by Shin-Etsu Chemical Co., Ltd., particle size: 1-2 μm) were added to a mixed solvent of toluene-isopropyl alcohol (1: 1) to prepare a coating solution. This coating solution is applied to the phosphor layer formed in advance as described above using a doctor blade, and then heat-treated at 120 ° C. for 30 minutes to be heat-cured and dried. A membrane was provided. The radiation image conversion panel according to the present invention was obtained by the method described above.

[0032]

According to the present invention, when Mg is added as a trace component in the production of a tetrahedral europium-activated barium fluorobromide phosphor, the stimulable afterglow of the resulting stimulable phosphor becomes Reduce without significantly affecting other properties. Therefore, the radiation image conversion panel using the tetrahedral europium-activated barium fluorobromide phosphor of the present invention has a feature that the photostimulated afterglow is small.

[Brief description of the drawings]

FIG. 1 shows a photostimulable afterglow (PSL) of a tetrahedral europium-activated barium fluorobromide phosphor prepared in Examples and Comparative Examples.
It is a graph which displays afterglow) and an ultraviolet fog value (UV fog value) on the basis of a magnesium addition ratio.

Claims (3)

[Claims] 1. A basic formula _{(I): Ba 1-x} Ca x FBr 1-y I y: aEu, bM, cMg ... (I) [ However, M represents an alkali metal, x, y, a,
b and c are respectively 0 ≦ x ≦ 0.03, 0 <y ≦
0.30, 0.0001 ≦ a ≦ 0.01, 0 ≦ b ≦ 0.
001 and a numerical value in the range of 0 <c ≦ 0.1. ]
A tetrahedral rare earth activated alkaline earth metal fluorohalide-based stimulable phosphor represented by the formula: 2. The composition according to claim 1, wherein x, y, a,
b and c are respectively 0.001 ≦ x ≦ 0.0
2, 0.10 ≦ y ≦ 0.20, 0.001 ≦ a ≦ 0.0
1, 0 <b ≦ 0.0003 and 0.0001 <c ≦
The 14-hedral rare earth activated alkaline earth metal fluorinated halide stimulable phosphor according to claim 1, which has a numerical value in the range of 0.03. 3. A radiation image conversion panel comprising the tetrahedral rare earth activated alkaline earth metal fluorinated halide stimulable phosphor according to claim 1 or 2.