JPH05247461A - Phosphor and radiation image conversion panel - Google Patents

Abstract

PURPOSE:To provide a new phosphor which exhibits accelerated phosphorescence. CONSTITUTION:A phosphor exhibiting accelerated phosphorescence is based on a fluorite-type fluoride, activated by a rare earth element, and represented by the compsn. formula: MIIF2.xMIF:yA... [wherein MII is an alkaline earth metal; MI is an alkali metal; A is Ce, Pr, Sm, Eu, Gd, Tb, Tm, or Yb; 0<x<=0.5; and 0<y<=0.1]. A radiation image conversion panel has a phosphor layer contg. this phosphor.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a novel photostimulable phosphor,
And a radiation image conversion panel having a stimulable phosphor layer containing the stimulable phosphor.

[0002]

2. Description of the Related Art As a method replacing the conventional radiographic method, for example, a radiation image recording / reproducing method using a stimulable phosphor as described in JP-A-55-12145 is known. This method uses a radiation image conversion panel (stimulable phosphor sheet) containing a stimulable phosphor, and the radiation transmitted through the subject or emitted from the subject is stimulable fluorescence of the panel. Radiation energy accumulated 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 to excite the radiation energy accumulated in the stimulable phosphor. It emits fluorescence (stimulated luminescence), photoelectrically reads this fluorescence to obtain an electric signal, and then reproduces a radiation image of a subject or a subject as a visible image based on the obtained electric signal. .. The panel that has finished reading is prepared for the next shooting after the remaining image is erased. That is, the radiation image conversion panel can be repeatedly used.

According to the above-mentioned radiographic image recording / reproducing method, compared with the conventional radiographic method using a combination of a radiographic film and an intensifying screen, the radiation dose is much smaller and the amount of information is large. There is an advantage that an image can be obtained. Further, 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 photostimulable phosphor is a phosphor that exhibits photostimulated luminescence when irradiated with excitation light after being irradiated with radiation, but in practical use, it is 300 to 300 nm by excitation light having a wavelength in the range of 400 to 900 nm. Phosphors that exhibit stimulated emission in the wavelength range of 500 nm are commonly used. An example of the stimulable phosphor that has been conventionally used in a radiation image conversion panel is a divalent europium-activated alkaline earth metal halide phosphor. 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, the support is not always necessary. The stimulable phosphor layer is
Usually, it comprises a stimulable phosphor and a binder containing and supporting the stimulable phosphor in a dispersed state. However, it is known that the stimulable phosphor layer is composed of only aggregates of the stimulable phosphor without containing a binder formed by a vapor deposition method or a sintering method. Further, a radiation image conversion panel having a stimulable phosphor layer in which a polymer substance is impregnated in a gap between aggregates of the stimulable phosphor is also known. In any of these phosphor layers, the stimulable phosphor has a property of absorbing stimulated radiation such as X-rays and then exhibiting stimulated emission upon irradiation with excitation light. Radiation emitted from the specimen is absorbed by the photostimulable phosphor layer of the radiation image conversion panel in proportion to the radiation dose, and the radiation image of the subject or the subject is formed on the panel as an accumulated image of radiation energy. .. This accumulated image can be emitted as stimulated emission light by irradiating the excitation light,
By photoelectrically reading this stimulated emission light and converting it into an electric signal, it becomes possible to form an accumulated image of radiation energy.

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 a vapor deposition film of an inorganic substance, and the phosphor layer Protects against chemical alteration or physical shock.

A large number of phosphors have been found so far in various applications. However, only a few kinds of phosphors having the above-described stimulability have been confirmed. Therefore, it is still important to search for a phosphor showing a stimulable level that can be practically used.

The present inventor, in the course of research for searching for a new stimulable phosphor, has a fluorite-type fluoride (eg, composition) which has been conventionally known as a substance (ion conductor) exhibiting ion conductivity. As the formula, CaF ₂ · 0.01Na,
It has been found that a novel compound obtained by activating a substance represented by (4) with a rare earth element exhibits stimulability.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel phosphor having stimulability (stimulable phosphor).

[0009]

[Means for Solving the Problems] Composition formula (I): M ^II F ₂ · xM ^I F: yA (I) [wherein M ^II is an alkaline earth metal, M ^I is an alkali metal, and A Is Ce, Pr, Sm, Eu, Gd, T
represents b, Tm, or Yb, and x and y represent numerical values of 0 <x ≦ 0.5 and 0 <y ≦ 0.1, respectively. ] A radiographic image conversion panel having a rare earth element-activated fluorite-type fluoride-based stimulable phosphor represented by: and a phosphor layer containing the stimulable phosphor.

In the composition formula (I), M ^II is preferably Mg, Ca, Sr or Ba, and M ^I is preferably Na or Li, in consideration of the intensity of the stimulated emission obtained. A is preferably Eu or Ce. Further, it is preferable that x is a numerical value in the range of 0.001 ≦ x ≦ 0.2 and y is 0.001 ≦ x ≦ 0.05.

The rare earth element-activated fluorite-type fluoride-based stimulable phosphor represented by the composition formula (I) of the present invention comprises: 1) an alkaline earth metal fluoride, an alkali metal fluoride and a rare earth element A step of preparing a mixture of phosphor raw materials made of a fluoride, and 2) applying 400 to 130 to the phosphor raw material mixture under a weakly reducing or neutral atmosphere or a trace oxygen introducing atmosphere.
And a step of baking at a temperature in the range of 0 ° C. for 0.5 to 10 hours. The method for producing the rare earth element-activated fluorite-type fluoride-based stimulable phosphor of the present invention will be described in detail below.

First, as a phosphor material, 1) an alkaline earth metal fluoride (such as SrF ₂ ), 2) an alkali metal fluoride (such as NaF), and 3) a rare earth element fluoride (such as CeF ₃ ) To prepare. In some cases, a known flux may be used.

In the production of the phosphor, first, the above-mentioned 1) fluoride of alkaline earth metal, 2) fluoride of alkali metal, and 3) fluoride of rare earth element are stoichiometrically described above. A mixture of phosphor raw materials is prepared by weighing and mixing so that the relative ratio corresponds to the formula (I).

The phosphor raw material mixture is prepared by i) simply mixing the phosphor raw materials 1) to 3) above, ii) first mixing the phosphor raw materials 1) to 2) above, and mixing the mixture at 100 ° C. After heating for several hours at the above temperature, the phosphor material of the above 3) is mixed with the obtained heat-treated product, iii) The phosphor materials of the above 1) to 2) are first mixed in a suspension state, This suspension is heated (preferably 50 to 200).
It may be carried out by any method such as drying under reduced pressure at a temperature of ℃), vacuum drying, spray drying, etc., and then mixing the dried material with the phosphor raw material of the above 3).

As a modification of the method ii), a method of mixing the phosphor raw materials 1) to 3) and subjecting the mixture to the heat treatment may be used. Further, as a modification of the above method iii), a method of mixing the phosphor raw materials of the above 1) to 3) in a suspension state and drying this suspension may be used. Alternatively, the phosphor raw material of 2) above may be added to and mixed with the mixture after heat treatment or after drying, or when the firing is performed twice or more, the phosphor raw material of 2) above may be added after the primary firing. Good. In any of the above methods i), ii), and iii), various mixers, V-type blenders, ball mills, rod mills, and other ordinary mixers are used for mixing.

Next, the phosphor raw material mixture prepared as described above is filled in a heat-resistant container such as a quartz boat, an alumina crucible, a quartz crucible, and placed in the core of an electric furnace for firing. 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, and the like, but 0.5 to 10 hours is generally suitable. As the firing atmosphere,
A nitrogen gas atmosphere, a neutral atmosphere such as an argon gas atmosphere, a nitrogen gas atmosphere containing a small amount of hydrogen gas, a weak reducing atmosphere such as a carbon dioxide atmosphere containing carbon monoxide, or a trace oxygen introduction atmosphere is used. ..

After the phosphor raw material mixture is once fired as described above, the fired product is taken out of the electric furnace and allowed to cool, and if necessary, a mortar, ball mill, tube mill,
It is also possible to pulverize into a fine powder using an ordinary pulverizer such as a centrifugal mill, and then put the pulverized product into an electric furnace for re-firing (secondary calcination). The firing temperature for re-firing is 400
〜1300 ℃ is suitable, and the firing time is 0.5〜.
10 hours is appropriate, and the firing atmosphere may be the above-mentioned weak reducing atmosphere or neutral atmosphere, or the atmosphere into which a trace amount of oxygen has been introduced.

A powdery phosphor is obtained by the above firing. The obtained phosphor may be subjected to various general operations in the production of the phosphor such as washing, drying and sieving, if necessary. Since the phosphor is easily decomposed by warm water, washing is performed with an organic solvent such as acetone, ethyl acetate or ethanol.

By the production method described above, the composition formula (I): M ^II F ₂ · xM ^I F: yA (I) [wherein M ^II is an alkaline earth metal, M ^I is an alkali metal, And A is Ce, Pr, Sm, Eu, Gd, T
represents b, Tm, or Yb, and x and y represent numerical values of 0 <x ≦ 0.5 and 0 <y ≦ 0.1, respectively. ] The rare earth element activated fluorite type fluorinated stimulable phosphor represented by the following formula is obtained.

Next, a method for manufacturing the radiation image storage panel of the present invention will be described.

The photostimulable phosphor layer of the radiation image storage panel of the present invention is a layer containing the rare earth element-activated fluorite-type fluoride-based photostimulable phosphor represented by the general formula (I), and is usually , Consisting of a stimulable phosphor and a binder that contains and supports the stimulable phosphor in a dispersed state, but if necessary, is composed of only aggregates of the stimulable phosphor without a binder. Alternatively, it may be a phosphor layer in which a polymer substance is impregnated in the gap between aggregates of the stimulable phosphor.

Next, the method for producing the radiation image storage panel of the present invention will be described by taking the case where the phosphor layer is composed of a stimulable phosphor and a binder containing and supporting the phosphor in a dispersed state as an example.

The phosphor layer can be formed on the support by the following known method. First, a stimulable phosphor and a binder are added to a solvent and mixed sufficiently to prepare a coating solution in which the stimulable phosphor is uniformly dispersed in a binder solution. The mixing ratio of the binder and the stimulable phosphor in the coating liquid varies depending on the characteristics of the intended radiation image conversion panel, the kind of the phosphor, etc., but generally the mixing ratio of the binder and the phosphor is 1 It is preferably selected in the range of 1 to 1: 100 (weight ratio), and particularly preferably in 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 an ordinary coating means such as a doctor blade, a roll coater or a knife coater.

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 in order to strengthen the bond between the support and the phosphor layer, or to improve the sensitivity or image quality (sharpness, graininess) of the radiation image conversion panel. The surface of the side support is coated with a polymer substance such as gelatin to form an adhesion-imparting layer, or a light-reflecting layer made of a light-reflecting substance such as titanium dioxide, or a light-absorbing substance made of a light absorbing substance such as carbon black It is known to provide an absorbing layer and the like. The support used in the present invention can also be provided with these various layers, and their configuration can be arbitrarily selected according to the desired purpose and application of the radiation image conversion panel. Further, JP-A-58-20020
As described in Japanese Unexamined Patent Publication (Kokai) No. 0, the surface of the support on the side of the phosphor layer (adhesion-imparting layer, light reflection When a layer, a light absorption layer, or the like is provided, it means the surface thereof), and fine irregularities may be formed.

After forming the coating film on the support as described above, the coating film is dried to complete the formation of the stimulable phosphor layer on the support. The layer thickness of the phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of phosphor, the mixing ratio of the binder and the phosphor, etc., but is usually 20 μm to 1
mm. However, this layer thickness is preferably 50 to 500 μm. The stimulable phosphor layer does not necessarily have to be formed by directly applying the coating liquid on the support as described above, and for example, a sheet such as a glass plate, a metal plate or a plastic sheet may be separately formed. After forming the phosphor layer by applying the coating solution onto the substrate and drying it, the phosphor layer is pressed onto the support or an adhesive is used to bond the support and the phosphor layer. Good.

As described above, a protective film is usually provided on the phosphor layer. The protective film is formed by applying a solution prepared by dissolving a transparent organic polymer substance such as a cellulose derivative or polymethylmethacrylate in an appropriate solvent onto the phosphor layer, or polyethylene. An organic polymer film such as terephthalate or a protective film forming sheet such as a transparent glass plate is separately formed and provided on the surface of the phosphor layer with an appropriate adhesive, or an inorganic compound is deposited by vapor deposition or the like. What was formed into a film on the layer is used. Further, it may be a protective film formed of a coating film of an organic solvent-soluble fluorine-based resin, 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 above layers constituting the radiation image storage panel of the present invention absorbs excitation light,
It may be colored with a coloring agent that does not absorb stimulated emission light, and an independent coloring intermediate layer may be provided (see Japanese Patent Publication No. 54-23400).

According to the above method, the rare earth element-activated fluorite-type stimulable stimulable phosphor of the compositional formula (I) and the binder which contains and supports it in a dispersed state are formed on the support. The radiation image storage panel of the present invention provided with a phosphor layer can be manufactured.

[0029]

【Example】

Example 1 Strontium fluoride (SrF ₂ ) 50
g, sodium fluoride (NaF) 0.167 g (SrF
1 mol% with respect to ₂ ) and cerium fluoride (CeF
₃ ) 0.758 g (1 mol% with respect to SrF ₂ ) was thoroughly mixed with a ball mill, and the mixture was charged into a quartz boat and put into a tube electric furnace, and the mixture was heated to 90 ° C. under a nitrogen atmosphere.
It was baked at a temperature of 0 ° C. for 5 hours. After firing, the quartz boat was taken out of the electric furnace and cooled to room temperature in a nitrogen atmosphere. The obtained baked product was crushed and then sieved. Thus, the cerium-activated strontium fluoride / sodium fluoride phosphor (SrF ₂ .0.01NaF: 0.
01Ce) was obtained.

[Examples 2 to 4] In Example 1, the amount of sodium fluoride (NaF) was 0.0835 g (SrF).
0.5 mol% based on ₂ ), 0.501 g (3 mol% based on SrF ₂ ) and 1.67 g (10 mol% based on SrF ₂ ) and the method of Example 1. By performing the same operation, the following various cerium-activated strontium fluoride / sodium fluoride phosphors were obtained. Example 2: SrF ₂ · 0.005NaF: 0.01C
e Example 3: SrF ₂ · 0.03NaF: 0.01Ce Example 4: SrF ₂ · 0.1NaF: 0.01Ce

[Comparative Example 1] A cerium-activated strontium fluoride phosphor (SrF ₂ : 0.0.5) was obtained by performing the same operation as in Example 1 except that sodium fluoride was not used. 01Ce) was obtained.

[Evaluation of phosphors] 40K for each of the above phosphors
After irradiation with X-rays of Vp at 30 mR for 30 seconds, He-
Excited by irradiating Ne laser light (633 nm), and photostimulated luminescence emitted from the phosphor is received by a photomultiplier tube through a filter (blue-transmissive bandpass filter), thereby stimulating the luminescence intensity of the phosphor. Was measured. The stimulated emission peaks were all 428 nm. The stimulated emission intensity of each phosphor was measured based on the height of this stimulated emission peak. The obtained results are summarized in relative values and shown in Table 1.

Table 1 Example Phosphor composition Photostimulated luminescence (relative value) 1 SrF ₂ · 0.01NaF: 0.01Ce 26.9 2 SrF ₂ · 0.005NaF: 0.01Ce 17.9 3 SrF ₂ · 0.03NaF: 0.01Ce 25.6 4 SrF ₂ · 0.1NaF: 0.01 Ce 23.1 Ratio 1 SrF ₂ : 0.01Ce 1.0

[Examples 5 to 14] In Example 1, strontium fluoride, sodium fluoride and cerium fluoride were appropriately changed, and the rare earth element-activated fluorite-type fluoride stimulant shown in Table 2 below was used. A phosphor was obtained.

Table 2 Example Phosphor composition Photostimulated luminescence (relative value) 5 MgF ₂ .0.01LiF: 0.01Eu 6.9 6 MgF ₂ .0.01NaF: 0.01Eu 4.3 7 CaF ₂ .0.01LiF: 0.01Eu 2.8 8 CaF ₂ .0.01NaF: 0.01Eu 5.4 9 CaF ₂ .0.01NaF: 0.01Ce 2.6 10 SrF ₂ .0.01LiF: 0.01Eu 6.7 11 SrF ₂ .0.01NaF: 0.01Eu 7.6 12 BaF ₂ · 0.01LiF: 0.01Eu 5.1 13 BaF ₂ · 0.01NaF: 0.01Eu 3.1 14 BaF ₂ · 0.01NaF: 0.01Ce 2.8 Ratio 1 SrF ₂ : 0.01Ce 1.0

CaF ₂ .0.01Na of Example 8 above
The stimulated emission spectrum and stimulated excitation spectrum of F: 0.01Eu are shown in FIGS. 1 and 2, respectively.

Next, an example of manufacturing a radiation image conversion panel will be described.
[Example 15] As a phosphor layer forming material, the cerium-activated strontium fluoride / sodium fluoride phosphor obtained in Example 1 (SrF ₂ /0.01NaF:0.01Ce)
356 g, polyurethane resin (Desmolac 4125 manufactured by Sumitomo Bayer Urethane Co., Ltd.) 15.8 g, and bisphenol A type epoxy resin 2.0 g were added to a mixed solvent of methyl ethyl ketone-toluene (1: 1), dispersed by a propeller mixer, and the viscosity was increased. A coating solution of 25 to 30 PS was prepared. After applying this coating solution onto a polyethylene terephthalate film with an undercoat using a doctor blade, 1
It was dried at 00 ° C for 15 minutes to form a phosphor layer.

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

[Examples 16 to 28] The same operation as in Example 15 except that the rare earth element-activated fluorite-type fluorinated stimulable phosphor obtained in Examples 2 to 14 was used as the phosphor. Then, a radiation image conversion panel including a support, a stimulable phosphor layer and a protective layer was obtained.

[0040]

INDUSTRIAL APPLICABILITY The novel rare earth element-activated fluorite-type fluoride-based photostimulable phosphor of the present invention exhibits high photostimulated luminescence, and is advantageous, for example, in the form of a radiation image conversion panel or the like and in a radiation image recording / reproducing method. Available.

[Brief description of drawings]

FIG. 1 is a stimulated emission spectrum of CaF ₂ .0.01NaF: 0.01Eu.

FIG. 2 is a stimulated excitation spectrum of CaF ₂ .0.01NaF: 0.01Eu.

Claims (2)

[Claims] 1. A composition formula (I): M ^II F ₂ · xM ^I F: yA (I) [wherein M ^II is an alkaline earth metal, M ^I is an alkali metal, and A is Ce, Pr. , Sm, Eu, Gd, T
represents b, Tm, or Yb, and x and y represent numerical values of 0 <x ≦ 0.5 and 0 <y ≦ 0.1, respectively. ] The photostimulable phosphor represented by 2. A radiation image conversion panel having a phosphor layer containing a stimulable phosphor, wherein the stimulable phosphor has a composition formula (I): M ^II F ₂ .xM ^I F: yA (I) [I However, M ^II is an alkaline earth metal, M ^I is an alkali metal, and A is Ce, Pr, Sm, Eu, Gd, T.
represents b, Tm, or Yb, and x and y represent numerical values of 0 <x ≦ 0.5 and 0 <y ≦ 0.1, respectively. ] A radiation image conversion panel characterized by being a stimulable phosphor represented by