JP3877470B2 - Method for producing barium fluorohalide phosphor - Google Patents

Description

【００６５】
前記表１より明らかなように、焼成後、一定温度に維持しながら前記焼成時の雰囲気を除去した後、前記焼成時の雰囲気と異なる雰囲気に置換して徐冷を行った実施例１の本発明の製造方法では、十分な輝尽発光量と消去性能を有する輝尽性蛍光体を製造することができた。
一方、焼成後に、焼成時の雰囲気と異なる雰囲気に置換して徐冷を行わなかった比較例１では、十分な輝尽発光量、消去性能を有する輝尽性蛍光体を製造することはできなかった。
【００６６】
【発明の効果】
本発明のバリウムフルオロハライド蛍光体の製造方法によれば、十分な輝尽発光量が得られ、さらに容易に消去しうる十分な消去性能を有する輝尽性蛍光体を安定に製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a photostimulable phosphor that retains a part of irradiated radiation energy for a certain period and emits light by a specific electromagnetic wave. Specifically, the present invention relates to a method for producing a barium fluorohalide-based photostimulable phosphor having good light emission performance and erasing performance.
[0002]
[Prior art]
Conventionally, a divalent europium-activated barium fluorohalide phosphor (BaFX: Eu) that emits light (instantaneous light emission) from the near-ultraviolet region to the blue region when excited by radiation such as X-rays, γ-rays, electron beams, or ultraviolet rays.²⁺, Where X represents a halogen atom other than fluorine. And is used as a phosphor for a radiation intensifying screen used for X-ray imaging or the like.
Furthermore, in recent years, when the phosphor is irradiated with radiation such as X-rays, γ-rays, electron beams, or ultraviolet rays, and then excited by electromagnetic waves (excitation light) in a wavelength region extending from visible rays to infrared rays, It has been found that it exhibits light emission in the wavelength range (stimulated light emission), and such a phosphor is useful as a phosphor useful for a radiographic image conversion technique that substitutes for conventional radiography in radiography. It has attracted a lot of attention.
[0003]
This radiation image conversion technique uses a radiation image conversion panel (accumulative phosphor sheet) in which a phosphor layer containing a stimulable phosphor is provided on a support, and the radiation or subject transmitted through the subject. After the radiation emitted from the panel is absorbed by the photostimulable phosphor on the panel, the photostimulable phosphor is excited in time series using an electromagnetic wave (excitation light) selected from a wavelength range from visible light to infrared. The radiation energy stored in the photostimulable phosphor is emitted as fluorescence (stimulated luminescence), and an electrical signal is obtained by photoelectrically reading, and the obtained electrical signal is imaged. is there.
[0004]
By using this radiation image conversion panel, it is possible to form an image with a smaller exposure amount than in the conventional radiography method, and the obtained image can be processed by a computer. Abundant radiographic images can be obtained, and a defective image can be relieved.
[0005]
The divalent europium activated barium fluorohalide phosphor (BaFX: Eu)²⁺), In particular, a phosphor containing iodine as a part of the halogen atom X has high stimulated emission luminance, and as the iodine content increases, the peak of the stimulated excitation spectrum shifts to the longer wavelength side. Depending on the content, it has been proposed to use in combination with a laser having an emission wavelength in the red region, such as a He—Ne laser, or a semiconductor laser having an emission wavelength in the red or infrared region.
[0006]
Since the radiation image conversion panel itself hardly deteriorates even when irradiated with radiation and electromagnetic waves, it can be used repeatedly for a long time. Usually, the reading operation of the radiation energy accumulated in the radiation image conversion panel is performed by scanning the radiation image conversion panel using laser light.
However, in practice, it is not possible to emit the accumulated radiation energy only by scanning the laser beam. For example, in order to forcibly emit the remaining radiation energy, for example, JP-A-56-11392 As described in the publication, there has been proposed a method of erasing remaining radiation energy by irradiating the entire radiation image conversion panel with light in the excitation wavelength region of stimulated emission after reading.
[0007]
However, a radiation image conversion panel using a stimulable phosphor containing iodine usually has several seconds using, for example, a white fluorescent lamp, as in the case of erasing the radiation energy accumulated in the stimulable phosphor. The remaining radiation energy cannot be removed sufficiently by simply irradiating with light for a short period of time from several minutes, and a part of the radiation energy remaining over time after erasing (afterimage) The problem was that it was recognized.
[0008]
When the radiation image conversion panel is used repeatedly, such erasing performance and afterimage characteristics are factors that adversely affect the image quality of the formed image. On the other hand, if the erasure time is increased for the purpose of complete erasure, the time required from reading to erasing in the reading device becomes longer, not only causing a decrease in the processing capability of the device itself, but also the erasing device in the apparatus excessively generates heat. Therefore, it is not preferable in terms of durability and power saving of the apparatus.
[0009]
On the other hand, the divalent europium activated barium fluorohalide phosphor is generally produced by the following method.
First, the phosphor raw material mixture is uniformly mixed in a dry state (dry method) or a slurry state in which the phosphor raw material is uniformly mixed and then dried (wet method) to prepare the phosphor raw material mixture. Do.
Next, usually, the obtained phosphor raw material mixture is fired at a temperature close to the melting point of the base crystal (BaFX or the like) for several hours in a neutral atmosphere or a weak reducing atmosphere at almost atmospheric pressure (firing step) ). If desired, the fired product once obtained may be refired. As a result of the firing process, the host crystal of the phosphor grows, and at the same time, the activator element (Eu, etc.) diffuses into the host crystal and further becomes a source of the stimulating center.⁺A center is also generated. Therefore, the firing process is an important process that affects the light emission characteristics of the phosphor.
Further, after firing, the obtained phosphor is subjected to treatments such as washing and classification as necessary.
[0010]
Further, in JP-A-7-233369 and JP-A-10-195431, a tetrahedral rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor (hereinafter referred to as a phosphor) having a controlled particle shape and particle aspect ratio (hereinafter referred to as a phosphorescent phosphor). , Simply referred to as “a tetrahedral phosphor”).
In the radiation image conversion panel provided with the photostimulable phosphor layer containing the tetrahedral phosphor, the tetrahedral phosphor itself is not isotropic in the photostimulable phosphor layer, and is directional. Since the arrangement is small, the spread of excitation light and stimulated emission in the lateral direction within the layer is reduced, and the sharpness of the image formed on the radiation image conversion panel can be improved.
Although the tetrahedral phosphor obtained by the manufacturing method described in the above publication has relatively high light emission characteristics and sharpness, a sufficient amount of stimulated luminescence is not yet obtained as a phosphor used in the radiation conversion method. In addition, since it does not have sufficient erasing performance that can be easily erased, further improvement in performance has been desired.
There has also been a demand for the establishment of a production method having excellent production stability that has a sufficient amount of stimulated light emission and can sufficiently improve the erasing performance.
[0011]
[Problems to be solved by the invention]
An object of the present invention is to solve the conventional problems and achieve the following objects. That is, the present invention provides a method for producing a barium fluorohalide phosphor, which can stably produce a photostimulable phosphor having a sufficient amount of photostimulated luminescence and sufficient erasability that can be easily erased. For the purpose.
[0012]
[Means for Solving the Problems]
As a result of intensive studies on a production method capable of stably producing a barium fluorohalide-based photostimulable phosphor, the present inventors have further clarified that after firing the phosphor raw material mixture at a constant temperature in the firing step, By removing the atmosphere at the time of firing while maintaining the temperature, substituting with an atmosphere different from the atmosphere and performing slow cooling, it is possible to improve the photostimulable emission amount and erasing performance of the stimulable phosphor. The headline and the present invention were completed.
Means for solving the above-mentioned problems are as follows. That is,
[0013]
<1> Barium represented by the following composition formula (I), comprising a mixing step of preparing a phosphor raw material mixture by mixing phosphor raw materials and a baking step of baking the phosphor raw material mixture to obtain a fired product. In the method for producing a fluorohalide phosphor, after the firing step, the phosphor raw material mixture is fired, the atmosphere during firing is removed while maintaining a constant temperature, and an atmosphere different from the atmosphere during firing is replaced. It is a method for producing a barium fluorohalide phosphor characterized by performing slow cooling.
(Ba_1-a, M^II _aFX ・ bM^I・ CM^IIIDA: xLn ... Composition formula (I)
[Where M^II _aRepresents at least one alkaline earth metal selected from the group consisting of Sr, Ca and Mg,^IRepresents at least one alkali metal compound selected from the group consisting of Li, Na, K, Rb and Cs;^IIIIs a compound of at least one trivalent metal selected from the group consisting of Al, Ga, In, Tl, Sc, Y, Cd, and Lu (provided that Al₂O_ThreeIs excluded). X represents at least one halogen selected from the group consisting of Cl, Br, and I. Ln represents at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm, and Yb. A is Al₂O_Three, SiO₂, ZrO₂Represents at least one metal oxide selected from the group consisting of a, b, c, d, and x represent 0 ≦ a ≦ 0.3, 0 ≦ b ≦ 2, 0 ≦ c ≦ 2, 0 ≦ d ≦ 0.5, and 0 <x ≦ 0.2, respectively. ]
[0014]
<2> The method for producing a barium fluorohalide phosphor according to <1>, wherein a firing temperature when the phosphor raw material mixture is fired at a constant temperature is 400 to 1000 ° C.
<3> The method for producing a barium fluorohalide phosphor according to <1> or <2>, wherein slow cooling is performed at a temperature lowering rate of 0.2 to 5 ° C./min.
<4> The barium fluoro according to any one of <1> to <3>, wherein the temperature difference between the atmosphere temperature after replacing the atmosphere during firing and the atmosphere temperature at the end of annealing is 50 to 300 ° C. This is a method for producing a halide phosphor.
[0015]
<5> The method for producing a barium fluorohalide phosphor according to any one of <1> to <4>, wherein the slow cooling time in the firing step is 30 to 180 minutes.
<6> In the firing step, after 1/3 to 1 of the firing time for firing the phosphor raw material mixture at a constant temperature, the atmosphere during firing is removed, and the atmosphere is replaced with an atmosphere different from the atmosphere <1 It is a manufacturing method of the barium fluorohalide fluorescent substance in any one of>-<5>.
<7> The above-mentioned <1> to <1>, wherein the atmosphere during firing is a neutral or weakly reducing atmosphere, and after the atmosphere during firing is removed, the atmosphere during firing is replaced with an oxidizing atmosphere and then gradually cooled. 6> The method for producing a barium fluorohalide phosphor according to any one of 6).
[0016]
<8> The method for producing a barium fluorohalide phosphor according to <7>, wherein the oxidizing atmosphere is a weak oxidizing atmosphere containing 0.1 to 200 ml of oxygen per liter of the oxidizing atmosphere.
<9> Using a furnace having a firing partial volume of 2 to 500 L with respect to 1 kg of the phosphor material mixture, firing the phosphor material mixture in the furnace and removing the atmosphere during firing, In any one of the above items <1> to <8>, 0.1 to 200 ml of oxygen is introduced into 1 L of the firing partial volume of the furnace at a firing temperature, and an inert gas is further introduced to form an oxidizing atmosphere. It is a manufacturing method of described barium fluorohalide fluorescent substance.
<10> The method for producing a barium fluorohalide phosphor according to any one of <1> to <9>, wherein the atmosphere is removed to a vacuum state of 1 torr or less.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing the barium fluorohalide phosphor of the present invention, after the mixing step of mixing the phosphor raw materials, in the firing step, the phosphor raw material mixture is fired at a constant temperature and maintained at a constant temperature during the firing. After the atmosphere is removed and replaced with an atmosphere different from the above atmosphere, slow cooling is performed.
In addition, a cooling step may be provided after the firing step, and other steps may be provided as necessary.
Hereinafter, the method for producing the barium fluorohalide phosphor of the present invention will be described in detail.
[0018]
-Mixing process-
First, a phosphor material mixture is prepared by a mixing process of mixing desired phosphor materials. Examples of the phosphor material include the following materials (1) to (5).
(1) BaF₂, BaCl₂, BaBr₂And BaI₂At least one barium halide selected from the group consisting of
(2) CaF₂, CaCl₂, CaBr₂, CaI₂, SrF₂, SrCl₂, SrBr₂, SrI₂, MgF₂MgCl₂, MgBr₂And MgI₂At least one alkaline earth metal halide selected from the group consisting of
(3) At least one selected from the group consisting of CsCl, CsBr, CsI, NaCl, NaBr, NaI, KCl, KBr, KI, PbCl, PbBr, PbI, PbF, CsF, NaF, KF, LiF, LiCl, LiBr, and LiI Alkali metal halides.
(4) Al₂O_Three, SiO₂And ZrO₂At least one metal oxide selected from the group consisting of:
(5) At least one compound selected from the group consisting of rare earth elements such as halides, oxides, nitrates and sulfates.
If desired, further ammonium halide (NH_FourX ', where X' represents F, Cl, Br or I. ) Etc. may be used as flux.
[0019]
In preparing the phosphor raw material mixture, a desired raw material is arbitrarily selected from each of the raw materials (1) to (5), and the stoichiometry is set so as to have a relative ratio corresponding to the composition formula (I). The basis weight is mixed and a phosphor material mixture of phosphor materials is prepared.
[0020]
The method for preparing the phosphor material mixture can be appropriately selected from known mixing methods. For example, the phosphor material mixture can be prepared by the following methods (i) to (iv). Good.
(I) A preparation method in which the phosphor raw materials (1) to (5) are weighed and simply mixed.
(Ii) The phosphor materials (1) to (4) are weighed and mixed, and the mixture is heated at a temperature of 100 ° C. or higher for several hours, and then the phosphor material (5) is mixed with the obtained heat-treated product. Preparation method to do.
(Iii) A preparation method in which the phosphor raw materials (1) to (5) are mixed, and this mixture is heated at a temperature of 100 ° C. or higher for several hours.
(Iv) The phosphor raw materials (1) to (4) are mixed in the form of a suspension, and the suspension is heated, preferably at 50 to 200 ° C. under reduced pressure, vacuum, and sprayed. A preparation method of mixing the phosphor raw material (5) with the obtained dried product after drying by drying or the like.
[0021]
Further, as a modified method of the preparation method (iv), the phosphor raw materials (1) to (5) are mixed in a suspension state, and the suspension is dried. The preparation method (iv-2), The suspension containing the phosphor raw materials (1) and (5) was heated, preferably dried at 50 to 200 ° C. or under reduced pressure, vacuum drying, spray drying, or the like. Thereafter, in the preparation method (iv-3) in which the phosphor raw materials (2) to (4) are added and mixed in the obtained mixture, or when the phosphor raw material ( 1) and (2) are mixed in the state of a suspension, and after adding the phosphor raw materials (3) to (4) after primary firing, the suspension is heated, preferably 50 to 200. Preparation method of drying by vacuum drying, vacuum drying, spray drying, etc. at 0 ° C., and mixing the phosphor raw material (5) with the obtained dried product iv-4), etc. are also favorably used.
[0022]
Further, a tetrahedral rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor with controlled particle shape and particle aspect ratio described in JP-A-7-233369 and JP-A-10-195431 In other words, in addition to the preparation methods (i) to (iv-4) of the phosphor raw material mixture, a preparation method (v) using a means capable of imparting a shearing force when mixing the phosphor raw materials. ), And can be prepared by a preparation method (vi) using means capable of controlling various conditions such as addition of each phosphor raw material and timing of mixing.
[0023]
The mixing device used for mixing in the preparation methods (v) and (vi) can be appropriately selected from known mixing devices such as various mixers, V-type blenders, ball mills, rod mills and the like. Can be mentioned.
[0024]
-Baking process-
Next, a firing process in which the phosphor material mixture obtained in the mixing process is fired to obtain a fired product will be described.
In the method for producing a barium fluorohalide phosphor of the present invention, after the mixing step described above, a firing step including the following steps is provided.
That is, after the firing step of firing the obtained phosphor raw material mixture at a constant temperature is completed, the atmosphere in the firing step is removed while maintaining the constant temperature, and the atmosphere is replaced with an atmosphere different from the atmosphere (substitution) Stage) and slow cooling (slow cooling stage).
[0025]
Firing of the phosphor raw material mixture obtained in the mixing step is performed by filling the phosphor raw material mixture into a heat-resistant container such as a quartz boat, an alumina crucible, a quartz crucible, or a silicon carbide container and placing it in a furnace core. To do.
[0026]
As a furnace used for firing, a furnace having a firing partial volume of 2 to 500 L (liter) per 1 kg of the phosphor raw material mixture is required, and among them, a furnace having a firing partial volume of 5 to 50 L is preferable.
When the firing partial volume is less than 2 L with respect to 1 kg of the phosphor raw material mixture, the phosphor is densely packed in a narrow space, and it may be difficult to perform uniform firing overall. If it exceeds 500 L, the volatile halogen atmosphere is too low, and the photostimulable luminescence amount and erasing characteristics of the resulting photostimulable phosphor may deteriorate.
[0027]
Firing in the firing step is performed at a constant temperature, and the firing temperature at this time is preferably 400 to 1000 ° C, more preferably 600 to 900 ° C.
When the firing temperature is less than 400 ° C., it becomes the source of the diffusion of the activator element in the host crystal and the bright center.⁺May be insufficient, and if it exceeds 1000 ° C., the base crystal may melt.
[0028]
The firing time in the firing stage varies depending on the filling amount of the phosphor raw material mixture, the firing temperature, the temperature taken out from the furnace, and the like, but is generally preferably 0.5 to 6 hours, and more preferably 1 to 3 hours.
When the firing time is less than 0.5 hours, F serves as a source of diffusion of the activator element in the host crystal and a bright center.⁺May be insufficient, and even if the baking is performed for more than 6 hours, there is little change in the characteristics of the phosphor and productivity may be reduced.
[0029]
As an atmosphere in the furnace in the firing step, any of a neutral atmosphere, a weak reducing atmosphere, and an oxidizing atmosphere can be selected.
Examples of the neutral atmosphere or the weak reducing atmosphere include a neutral atmosphere such as a nitrogen gas atmosphere and an argon gas atmosphere, a weak nitrogen gas atmosphere containing a small amount of hydrogen gas, and a carbon dioxide atmosphere containing carbon monoxide. A reducing atmosphere may be mentioned. When a trivalent europium compound is included as the rare earth element of the phosphor material, the trivalent europium is reduced to divalent europium in the firing step.
[0030]
As the oxidizing atmosphere, it is preferable to use a slightly oxidizing atmosphere gas.
Examples of the slightly oxidizing atmosphere gas include weakly oxidizing atmosphere gas containing 100 to 100,000 ppm, preferably 150 to 50,000 ppm of oxygen in an inert gas (neutral gas) per unit volume. For example, He, Ne, Ar, N₂And a weakly oxidizing atmosphere gas containing the above-mentioned concentration of oxygen in an inert gas.
[0031]
The amount of oxygen introduced is preferably 0.1 to 200 ml, more preferably 0.2 to 100 ml, at room temperature with respect to 1 L (liter) of the firing partial volume of the furnace.
If the amount of oxygen introduced is less than 0.1 ml, the effect of improving the erasing performance and residual characteristics of the stimulable phosphor may not be sufficiently obtained. May decrease.
[0032]
After the firing step, the atmosphere in the firing step is removed and replaced with an atmosphere different from the atmosphere. This atmosphere removal and replacement is performed while maintaining the inside of the furnace at a constant temperature while being cut off from the outside air.
[0033]
When removing the atmosphere at the firing stage, it is preferable to remove the atmosphere in the furnace by evacuating it while shutting off from the outside air, and to remove the atmosphere close to the vacuum. It is more preferable to use a vacuum state of 1 torr or less from the standpoint of adjusting the amount.
[0034]
The removal of the atmosphere during firing is preferably performed after 1/3 to 1 of the firing time at a constant temperature in the production method of the present invention is completed.
If the atmosphere is removed in less than 1/3 of the time required for the firing step, the emission characteristics of the resulting photostimulable phosphor may deteriorate.
[0035]
The atmosphere used when substituting with an atmosphere different from the atmosphere of the firing stage is preferably an oxidizing atmosphere, and the atmosphere of the firing stage is neutral or weakly reducing atmosphere, and after removing this, the atmosphere is replaced with an oxidizing atmosphere. Thus, it is preferable to shift to the slow cooling stage.
Further, the oxidizing atmosphere is more preferably a weak oxidizing atmosphere, more preferably a weak oxidizing atmosphere containing 0.1 to 200 ml of oxygen per liter of oxidizing atmosphere, and containing 1 to 100 ml of oxygen. A weakly oxidizing atmosphere is most preferred.
For example, He, Ne, Ar, N₂And a weakly oxidizing atmosphere gas containing the above-mentioned concentration of oxygen in an inert gas.
In addition, when an oxidizing atmosphere is used in the firing stage, it is preferable to use an inert weak oxidizing atmosphere rather than the atmosphere.
[0036]
The method for introducing oxygen in the case where an oxidizing atmosphere is used in the above-described firing step, or when the atmosphere during firing is replaced with an oxidizing atmosphere or a weakly oxidizing atmosphere is not particularly limited, and is publicly known. Although it can be selected as appropriate from among the introduction methods, it is preferable to evacuate the inside of the furnace to a state close to a vacuum and then introduce a predetermined amount of oxygen to make the inside of the furnace a desired weakly oxidizing atmosphere. By doing so, the necessary oxygen amount can be introduced accurately, and at the same time, the influence of other gases can be minimized.
That is, by specifying the firing volume of the furnace per 1 kg of the phosphor material mixture to be fired and the amount of oxygen introduced into 1 L of the firing material volume, the stimulating performance of the stimulable phosphor can be reduced in the firing process of the phosphor material mixture. The amount of oxygen necessary to improve can be introduced. In this case, it is most preferable to use a furnace having a firing partial volume of 5 to 50 L with respect to 1 kg of the phosphor raw material mixture.
Further, by replacing the gas in the furnace with a gas containing a predetermined amount of oxygen, the oxygen amount in the furnace can be introduced in a stepwise or continuous manner.
[0037]
For example, a desired amount of oxygen can be introduced by the following operation.
First, after the phosphor raw material mixture is put into an electric furnace that has reached the firing temperature, or after the firing stage is finished, vacuum exhaust is immediately performed for several minutes to remove air in the furnace core.
Next, a predetermined amount of oxygen is supplied into the furnace and filled to a desired pressure. The amount of oxygen introduced at this time is as described above, and this amount of oxygen introduced is measured as the oxygen partial pressure at the firing temperature.
After accurately introducing a predetermined amount of oxygen into the furnace, the furnace is further filled with an inert gas (neutral gas), and the pressure in the furnace is set to about 760 torr (1 atm), that is, near atmospheric pressure, An oxidizing atmosphere can be obtained.
[0038]
When the inside of the furnace is adjusted to an oxidizing atmosphere, oxygen may be introduced using, for example, a gas containing oxygen such as air or an inert gas instead of oxygen.
As the introduction amount of the gas containing oxygen such as air, it is generally preferable to introduce a gas amount necessary for the oxygen amount equal to that when oxygen is introduced. On the other hand, 0.5 to 1000 ml is more preferable, and 5 to 500 ml is most preferable.
[0039]
It is not always necessary to introduce oxygen into the furnace after evacuating to a vacuum state. Instead, a small amount of oxygen is introduced into the furnace core in a neutral gas or weakly oxidizing atmosphere at atmospheric pressure (1 atm). Alternatively, the oxygen amount in the furnace may be increased while introducing a gas containing oxygen such as air into the furnace.
[0040]
In the case of performing the firing step twice or more, for example, after the phosphor raw material mixture is once fired, the fired product is taken out from the electric furnace and allowed to cool, and if necessary, a mortar, ball mill, tube mill, centrifuge After pulverizing into a fine powder using a known pulverizer such as a mill, the pulverized product is again placed in an electric furnace and firing is repeated, and the firing conditions of the final firing (at the time of final firing) are adjusted to the firing conditions. Thereafter, it is preferable to perform slow cooling by removing the atmosphere during firing and substituting with an atmosphere different from the atmosphere.
Among them, after the phosphor raw material mixture is once fired at a firing temperature of 900 to 1300 ° C. (first firing), the fired product is taken out and pulverized in the same manner as described above, and this pulverized product is lower than the firing temperature. It is more preferable that the baking is further performed at a temperature, preferably 400 to 1000 ° C., and then the atmosphere is removed and replaced, followed by slow cooling. By passing through the firing step as described above, a powdered fired product, that is, a stimulable phosphor can be obtained.
[0041]
As described above, after the firing step, the atmosphere in the furnace is removed and replaced, and then the annealing step is performed. The slow cooling step may be performed immediately before the completion of the firing step at a constant temperature, but as described above, after a predetermined time has passed while the atmosphere is removed and replaced while maintaining the constant temperature. It is preferable.
The predetermined time is preferably 0 to 240 minutes, more preferably 30 to 180 minutes.
If the predetermined time exceeds 180 minutes, the light emission characteristics of the obtained photostimulable phosphor may be deteriorated.
[0042]
In the slow cooling step, the temperature is lowered by controlling a gentle temperature gradient from the start temperature to a predetermined temperature. In this case, the temperature lowering rate is preferably 0.2 to 5 ° C./min, and more preferably 0.5 to 3 ° C./min.
If the temperature lowering rate is less than 0.2 ° C./min, the light emission characteristics may be deteriorated, and if it exceeds 5 ° C./min, the erasing characteristics may not be improved sufficiently.
[0043]
Moreover, it is preferable to perform slow cooling until it becomes the temperature 50-300 degreeC lower than the said slow cooling start temperature, and it is more preferable to carry out until it becomes a temperature lower 100-250 degreeC.
If the temperature difference between the start and end of slow cooling is less than 50 ° C., the erasing characteristics may not be sufficiently improved, and if it exceeds 300 ° C., the light emission characteristics may be deteriorated.
[0044]
Furthermore, after the atmosphere replacement, the slow cooling time for lowering from the start temperature to a predetermined temperature is preferably 30 to 180 minutes, and more preferably 60 to 150 minutes.
If the slow cooling time is less than 30 minutes, the erasing characteristics may not be improved sufficiently, and if it exceeds 180 minutes, the light emitting characteristics may be deteriorated.
[0045]
-Cooling process-
In the production method of the present invention, in the firing step, the photostimulable phosphor that has finished the slow cooling step is transferred to a cooling step and cooled to room temperature.
[0046]
The cooling step is not particularly limited and can be appropriately selected from known cooling methods. For example, the cooling step can be performed by cooling, quenching, or the like. In particular, in a state where the fired product after firing is shielded from the outside air, the atmosphere in the firing process is removed, and cooling is performed by replacing with a vacuum state or an atmosphere different from the atmosphere in the firing process, or the atmosphere in the firing process is removed. The first atmosphere is replaced with a first atmosphere different from the atmosphere in the firing step, the first cooling is performed, the first atmosphere is removed, the second atmosphere is replaced, and the second cooling is performed. It is preferred to carry out the method.
[0047]
In this case, it may be carried out immediately after the gradual cooling step of the firing step, but the firing step is completed from the viewpoint of producing a photostimulable phosphor having a sufficient amount of stimulated light emission and erasing performance. It is preferable that the first cooling start point is a desired constant temperature, and the process proceeds to the cooling step from the time when the first cooling start point is reached. The first cooling start point refers to the furnace temperature or the fired product surface temperature.
[0048]
-Others-
Furthermore, after the cooling step, various general steps such as a washing step, a drying step, and a sieving step can be provided as necessary.
[0049]
Examples of the apparatus used for removing the atmospheric gas in the furnace include a rotary pump and an aspirator. Among them, a rotary pump is preferable in terms of exhaust speed and ultimate vacuum.
[0050]
-Stimulable phosphor-
By the production method of the present invention, a barium fluorohalide-based stimulable phosphor represented by the following composition formula (I) can be produced stably.
In addition, the photostimulable phosphor produced by the production method of the present invention has a sufficient amount of stimulated light emission, has sufficient erasing performance and afterimage characteristics, and can stably form a high-quality image. it can.
[0051]
(Ba_1-a, M^II _aFX ・ bM^I・ CM^IIIDA: xLn ... Composition formula (I)
[0052]
Where M^II _aRepresents at least one alkaline earth metal selected from the group consisting of Sr, Ca and Mg,^IRepresents at least one alkali metal compound selected from the group consisting of Li, Na, K, Rb and Cs;^IIIIs a compound of at least one trivalent metal selected from the group consisting of Al, Ga, In, Tl, Sc, Y, Cd, and Lu (provided that Al₂O_ThreeIs excluded).
Where M^IM, an alkali metal compound represented by^IIIAre represented by halides, oxides, sulfides, carbonates and the like.
[0053]
In the formula, X represents at least one halogen selected from the group consisting of Cl, Br, and I. Ln represents at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm, and Yb. A is Al₂O_Three, SiO₂, ZrO₂Represents at least one metal oxide selected from the group consisting of
A, b, c, d, and x are 0 ≦ a ≦ 0.3, 0 ≦ b ≦ 2, 0 ≦ c ≦ 2, 0 ≦ d ≦ 0.5, and 0 <x ≦ 0.2, respectively. To express.
[0054]
In the production of the photostimulable phosphor represented by the composition formula (I), various additive components such as the following may be added for the purpose of further improving the photostimulated luminescence amount, the erasing performance and the remaining characteristics. it can.
For example, B described in JP-A-57-23673, As described in JP-A-57-23675, tetrafluoroboric acid compound described in JP-A-59-27980, JP-A-59- Hexafluoro compounds described in Japanese Patent No. 47289, transition metals such as V, Cr, Mn, Fe, Co, Ni described in Japanese Patent Laid-Open No. 59-56480, or BeX described in Japanese Patent Laid-Open No. 59-75200 ”₂(Where X ″ represents at least one halogen atom selected from the group consisting of F, Cl, Br and I).
[0055]
When the additive component is added, the additive component is added and mixed when the phosphor material is weighed and mixed or before firing.
[0056]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
Example 1
<Mixing process>
Distilled water (H₂O) In 1760 ml, barium bromide (BaBr)₂) Aqueous solution (2.5 mol / L) 1200 ml, europium bromide (EuBr)_Three) Aqueous solution (0.2 mol / L) 40 ml, calcium bromide dihydrate (CaBr)₂・ 2H₂O) 0.85 g was added, stirred and mixed to obtain a suspension (BaBr).₂Concentration: 1.0 mol / L).
This suspension was kept at 60 ° C., and the suspension was stirred while rotating a screw type stirring blade having a diameter of 60 mm at a rotation speed of 500 rpm.
On the other hand, 150 ml of an aqueous ammonium fluoride solution (10 mol / ml) and 150 ml of water are mixed, and 300 ml of this mixed solution is injected into the suspension under stirring at a liquid feed rate of 5 ml / min with a roller pump. To produce a precipitate.
After completion of the injection, the mixture was further stirred for 2 hours while stirring, and the precipitate was aged.
[0057]
Next, the produced precipitate was collected by filtration and washed with 2 L of methanol. The washed precipitate was taken out and vacuum-dried at 120 ° C. for 4 hours to obtain crystals of europium-activated barium fluorobromide (BaFBr: Ca, Eu phosphor precursor). The yield was about 330 g.
Further, as a result of observation with a scanning electron microscope, it was confirmed that it was a tetrahedral crystal, and this crystal was further measured with a light diffraction particle size distribution measuring instrument (LA-500, manufactured by Horiba, Ltd.). The average crystal size was 4.9 μm.
[0058]
100 g of europium-activated barium fluorobromide (BaFBr: Ca, Eu phosphor precursor) crystal obtained from the above, 21.2 g of barium fluoroiodide (BaFI), 0.06 g of cesium bromide (CsBr) In order to prevent changes in crystal shape and particle size distribution due to interparticle fusion during firing, 1% by weight of ultrafine powder of alumina is added and stirred thoroughly with a mixer on the crystal surface. It was made to adhere uniformly and the phosphor raw material mixture was obtained.
[0059]
<Baking process>
After filling 100 g of the obtained phosphor raw material mixture (BaFBrI: Eu phosphor precursor) into a quartz boat, it was put into a furnace core (calcined partial volume: 1.3 L) capable of being evacuated and immediately evacuated. The degree of vacuum in the furnace core was about 0.1 torr in a minute. Next, nitrogen gas was charged until the inside of the furnace was at atmospheric pressure (760 torr) to obtain a neutral atmosphere. Firing was performed for 2 hours at a temperature of 850 ° C. in an electric furnace in a neutral atmosphere (firing step).
After finishing the firing step, while maintaining at 850 ° C., evacuate by a rotary pump, and after 30 minutes while substituting an oxidizing atmosphere containing 6 ml of oxygen per liter of atmosphere (substitution step), 850 ° C. As a slow cooling start point, the temperature was gradually lowered under a temperature gradient of 2.2 ° C./min, and slow cooling was performed for 90 minutes until reaching 650 ° C. (slow cooling stage).
[0060]
<Cooling process>
After the slow cooling, the atmosphere was removed by vacuum using a rotary pump, and the atmosphere was rapidly cooled to room temperature under the vacuum atmosphere. )
[0061]
(Comparative Example 1)
In the firing step of Example 1, the evacuation was carried out while maintaining the temperature at 850 ° C., the substitution step for replacing with an oxidizing atmosphere, and the slow cooling step for gradually lowering the temperature and performing the slow cooling were not performed. Except that, a tetrahedral BaFBrI: Eu stimulable phosphor (2) was obtained in the same manner as in Example 1.
[0062]
(Measurement of photostimulated luminescence)
Using the photostimulable phosphors (1) and (2), after irradiating an X-ray having a tube voltage of 80 KVp with 100 mR, an irradiation energy of 4.3 J / m²Were excited by irradiating LD (wavelength 660 nm), and the emitted stimulated emission light was received by a photomultiplier tube through a filter (B-410), and the amount of stimulated emission was measured. The measured results are shown in Table 1 below.
This value indicates that the greater the amount of stimulated light emission, the greater the value.
[0063]
(Evaluation of erase performance)
Using the photostimulable phosphors (1) and (2), after irradiating an X-ray having a tube voltage of 80 KVp with 100 mR, an irradiation energy of 4.3 J / m²The LD (wavelength 660 nm) was excited by excitation, and the photostimulated luminescence emitted from the photostimulable phosphor was received by a photomultiplier tube through a filter (B-410). The initial photostimulated luminescence was measured.
After measuring the initial photostimulated luminescence amount, the white fluorescent lamp was used to perform an erasing operation by irradiating each photostimulable phosphor with light at 5000 lux for 70 seconds, and then again by the same method as above. Laser irradiation was performed after irradiation of the line, and the amount of stimulated luminescence after erasure of the stimulable phosphor was measured.
The erasing characteristic is represented by an erasing value calculated from the following. The smaller this value, the better the erasing characteristic. The calculation results are shown in Table 1 below.
Erase value = (stimulated luminescence after erasure / initial photostimulated luminescence)
[0064]
[Table 1]

[0065]
As is clear from Table 1, after firing, the atmosphere at the time of firing was removed while maintaining a constant temperature, and then the steel was replaced with an atmosphere different from the atmosphere at the time of firing and gradually cooled. In the production method of the invention, a photostimulable phosphor having a sufficient photostimulated luminescence amount and erasing performance could be produced.
On the other hand, in Comparative Example 1 in which annealing was not performed by substituting with an atmosphere different from the atmosphere at the time of firing, a photostimulable phosphor having a sufficient amount of stimulated light emission and erasing performance could not be produced. It was.
[0066]
【The invention's effect】
According to the method for producing a barium fluorohalide phosphor of the present invention, it is possible to stably produce a photostimulable phosphor having a sufficient amount of photostimulated luminescence and a sufficient erasability that can be easily erased. .

Claims (10)

A barium fluorohalide fluorescence represented by the following composition formula (I), comprising: a mixing step of preparing a phosphor raw material mixture by mixing phosphor raw materials; and a baking step of baking the phosphor raw material mixture to obtain a fired product. In the method for producing a body, after the firing step, the phosphor raw material mixture is fired, the atmosphere at the time of firing is removed while maintaining a constant temperature, and an atmosphere different from the atmosphere at the time of firing is replaced with slow cooling. A method for producing a barium fluorohalide phosphor, which is performed.
(Ba _1-a , M ^II _a ) FX · bM ^I · cM ^III · dA: xLn Composition formula (I)
[Wherein M ^II _a represents at least one alkaline earth metal selected from the group consisting of Sr, Ca and Mg, and M ^I is selected from the group consisting of Li, Na, K, Rb and Cs. M ^III represents at least one trivalent metal compound selected from the group consisting of Al, Ga, In, Tl, Sc, Y, Cd, and Lu (wherein Al ₂ O ₃ is excluded). X represents at least one halogen selected from the group consisting of Cl, Br, and I. Ln represents at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm, and Yb. A represents at least one metal oxide selected from the group consisting of Al ₂ O ₃ , SiO ₂ , and ZrO ₂ . a, b, c, d, and x represent 0 ≦ a ≦ 0.3, 0 ≦ b ≦ 2, 0 ≦ c ≦ 2, 0 ≦ d ≦ 0.5, and 0 <x ≦ 0.2, respectively. ] The method for producing a barium fluorohalide phosphor according to claim 1, wherein a firing temperature when firing the phosphor raw material mixture at a constant temperature is 400 to 1000 ° C. The method for producing a barium fluorohalide phosphor according to claim 1 or 2, wherein slow cooling is performed at a temperature lowering rate of 0.2 to 5 ° C / min. The method for producing a barium fluorohalide phosphor according to any one of claims 1 to 3, wherein the temperature difference between the atmosphere temperature after replacing the atmosphere during firing and the atmosphere temperature at the end of slow cooling is 50 to 300 ° C. . The method for producing a barium fluorohalide phosphor according to any one of claims 1 to 4, wherein the slow cooling time in the firing step is 30 to 180 minutes. 6. The firing process according to claim 1, wherein in the firing step, after finishing 1/3 to 1 of the firing time for firing the phosphor raw material mixture at a constant temperature, the atmosphere during firing is removed and replaced with an atmosphere different from the atmosphere. The manufacturing method of the barium fluoro halide phosphor in any one. The atmosphere during firing is a neutral or weak reducing atmosphere, and after the atmosphere during firing is removed, the atmosphere during firing is replaced with an oxidizing atmosphere, and then slow cooling is performed. A method for producing the barium fluorohalide phosphor described. The method for producing a barium fluorohalide phosphor according to claim 7, wherein the oxidizing atmosphere is a weak oxidizing atmosphere containing 0.1 to 200 ml of oxygen per liter of the oxidizing atmosphere. Using a furnace having a firing partial volume of 2 to 500 L with respect to 1 kg of the phosphor raw material mixture, after firing the phosphor raw material mixture in the furnace and removing the atmosphere at the time of firing, first, the firing temperature in the furnace The barium fluorohalide fluorescence according to any one of claims 1 to 8, wherein 0.1 to 200 ml of oxygen is introduced into 1 L of the firing partial volume of the furnace, and an inert gas is further introduced to form an oxidizing atmosphere. Body manufacturing method. The method for producing a barium fluorohalide phosphor according to any one of claims 1 to 9, wherein the atmosphere is removed to a vacuum state of 1 torr or less.