JP2002265940A - Method for producing rare earth-activated fluorinated barium halide fluorescent substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a rare earth-activated fluorinated barium halide fluorescent substance which has no worsened performances in erasure and image-storage even after treated in a burning process. SOLUTION: The method for producing a rare earth-activated fluorinated barium halide fluorescent substance has a batch type burning process that a raw material mixture for the fluorescent substance is put to burn in a burning furnace and removed out of the furnace, which is then prepared for the next raw material mixture to put, comprising a cleaning process between a burning process and the next one so that a substance adhering to the burning furnace may be removed or inactivated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth-activated barium fluorohalide-based phosphor useful as a stimulable phosphor for a radiation image conversion panel.

[0002]

2. Description of the Related Art As an alternative to the conventional radiographic method, a radiation image recording / reproducing method using a stimulable phosphor (hereinafter sometimes simply referred to as "phosphor") is known. 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, the panel is prepared for the next photographing after the remaining image (afterimage) is deleted. 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 shot, the radiographic image recording / reproducing method uses a radiographic image conversion panel repeatedly, which leads to resource conservation and economic efficiency. Is also 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 barium fluorinated halogenated phosphors.

[0005] Rare earth activated barium fluoride halide phosphors are generally produced by the following method. First, a phosphor material mixture is uniformly mixed in a dry state (dry method) or a slurry state in which the phosphor materials are uniformly mixed, and then dried (wet method) to prepare a phosphor material mixture. Do.

Next, usually, the obtained phosphor raw material mixture is placed in a firing furnace, and is heated at a temperature close to the melting point of the host crystal (BaFX or the like) in a neutral or weakly oxidizing atmosphere at almost atmospheric pressure. Firing is performed over a long time (firing step). If desired
The fired product obtained once may be fired again. By the firing step, the activator element (Eu or the like) diffuses into the host crystal at the same time that the host crystal of the phosphor grows, and further, an F ⁺ center serving as a source of a stimulating center is generated. Therefore, the firing step is an important step that affects the emission characteristics of the phosphor. Then, the fired material after firing is cooled and subjected to a treatment such as washing, classification and the like as necessary to become a phosphor.

On the other hand, in order to mass-produce the phosphor, generally, a phosphor material mixture is put into a firing furnace in one firing furnace, fired, the fired material after firing is taken out of the firing furnace, and the next fluorescent material is fired. It is performed by repeating a batch-type firing step of preparing for the introduction of the body material mixture. At this time, the halide and the like sublimated during the firing may adhere to the inner wall of the firing furnace, particularly to a low-temperature portion thereof. Such a deposit absorbs a small amount of oxygen to be introduced at the time of the subsequent baking, and causes a reduction in the amount of oxygen distributed to the phosphor raw material mixture.
It is considered that the erasing characteristics and the afterimage characteristics of the phosphor depend on the amount of oxygen at the time of firing, and when the amount of oxygen supplied to the phosphor raw material mixture decreases, the erasing characteristics and the afterimage characteristics deteriorate. Will be lost.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and achieve the following objects. That is, an object of the present invention is to provide a method for producing a rare earth activated barium fluorohalide-based phosphor in which the erasing characteristics and the afterimage characteristics are not deteriorated even after a firing step.

[0009]

Means for solving the above problems are as follows. That is, <1> a phosphor raw material mixture is charged into a firing furnace, which is fired to take out a fired material after firing, and a rare earth activated fluorine having a batch-type firing process for preparing the next phosphor material mixture input. In the method for producing a barium halide halide-based phosphor, between one firing step and the next firing step,
A method for producing a rare earth-activated barium fluorohalide-based phosphor, comprising a cleaning step of removing or inactivating deposits adhering to the inside of the firing furnace.

<2> The rare earth activated barium fluoride halide system according to <1>, wherein the cleaning step is a step of flowing an oxygen-containing gas into the firing furnace maintained at a certain temperature or higher. This is a method for producing a phosphor. <3> The method for producing a rare earth-activated barium fluoride halide phosphor according to <1>, wherein the cleaning step is a step of evacuating the inside of the firing furnace. <4> The method according to <1>, wherein the cleaning step is a step of rubbing an inner wall of the firing furnace with a rubbing unit. is there.

<5> The cleaning step includes the following A
<2> The method for producing a rare earth activated barium fluorinated halogenated phosphor according to <1>, wherein two or more of steps C to C are performed in any combination. A Step of pouring an oxygen-containing gas into the firing furnace maintained at a certain temperature or higher B Step of evacuating the inside of the firing furnace C Step of rubbing the inner wall of the firing furnace with a rubbing means

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. The method for producing a rare earth activated barium fluorinated halogen-based phosphor of the present invention (hereinafter, simply referred to as “the production method of the present invention”) is a production method capable of producing the phosphor excellent in erasing characteristics and afterimage characteristics. . The rare-earth-activated barium fluorohalide-based phosphor (hereinafter, may be simply referred to as a phosphor) is, for example, one represented by the following basic composition formula (1). ^{_{(Ba 1-a, M II}} a) FX: zLn ··· (1) (M II represents at least one rare earth element selected from Sr and Ca, Ln is Ce, Pr, Sm, E
represents at least one rare earth element selected from the group consisting of u, Tb, Dy, Ho, Nd, Er, Tm and Yb. X represents at least one halogen element selected from the group consisting of Cl, Br, and I. a represents a numerical value of 0 ≦ a <1, and z represents a numerical value of 0 <z ≦ 0.2. )

A in the basic composition formula (1) is 0 ≦ a ≦ 0.
It is preferably a numerical value of 5. Ln is preferably a rare earth element of Eu or Ce. Further, the basic composition formula (1) does not indicate that the composition has a stoichiometric molar ratio of F: X = 1: 1.
^{_{(Ba 1-a, M II}} a) shows that a compound of PbFCl type crystal structure represented by FX. Generally, BaF
In X-crystal X ^- is a vacancy ions F ⁺ (X ^-)
A state in which many centers are generated is preferable from the viewpoint of increasing the stimulating efficiency with respect to light of 600 to 700 nm. At this time, F is X
Often slightly more than

Although omitted in the basic composition formula (1), if necessary, various additives are added in the mixing step to add a stimulable phosphor represented by the following basic composition formula (2). It may be. (Ba _1-a , M ^II _a ) FX · wN ^I · xN ^II · yN ^III · bA: zLn (2)

In the basic composition formula (2), M ^II , Ln, X and a, z are the same as those in the basic composition formula (1). N ^I represents at least one kind of alkali metal compound selected from the group consisting of Li, Na, K, Rb and Cs, and N ^II represents at least one kind of alkaline earth metal compound selected from the group consisting of Mg and Be. N ^{II I}
Represents at least one trivalent metal compound selected from the group consisting of Al, Ga, In, Tl, Sc, Y, La, Gd and Lu. The above trivalent metal compound is disclosed in
It is preferable to use a halide as described in JP-A-9-75200, but it is not limited thereto. A represents a metal oxide such as Al ₂ O ₃ , SiO ₂ and ZrO ₂ . BaFX volume average particle diameter of the primary particles in preventing sintering between particles in the following ultrafine particles _{0.1μm (Ba 1-a, M} II a) preferably has a low reactivity with FX, in particular Al ₂ O ₃ is preferred.

Further, b, w, x and y are the charged amounts (molar amounts) when the number of moles of (Ba _1-a , M ^II _a ) FX is 1, and 0 ≦ b ≦ 0.5, 0 ≦ w
≤2, 0≤x≤0.3, and 0≤y≤0.3, respectively. These figures do not necessarily represent the element ratios contained in the final composition for additives that are reduced by baking or subsequent washing. Also,
Some remain as added compounds in the final composition, while others react with BaFX or become incorporated.

FIG. 1 shows an example of a manufacturing apparatus that can be used in the manufacturing method of the present invention. In FIG. 1, reference numeral 10 denotes a firing furnace, in which a furnace core tube 12 as a firing portion is disposed so as to penetrate in the left-right direction in the drawing. Firing furnace 10
A heat source 14 is disposed inside and outside the furnace core tube 12, and the inside of the baking furnace 10 is heated by the heat source 14 and housed in a boat (firing vessel) 16 which is put into the furnace core tube 12. The phosphor raw material mixture 18 is configured to be fired.

A gas introduction / exhaust pipe 20 communicates with the furnace core tube 12 via a valve 22 so that gas can be introduced and exhausted into the furnace core tube 12 so that the atmosphere inside the furnace core tube 12 can be appropriately adjusted. I have. When gas is introduced from the gas introduction / exhaust pipe 20 to adjust the atmosphere inside the furnace core tube 12,
It is desirable to use a device that can accurately measure the gas flow rate, such as a mass flow controller.

The opening at the left end in the drawing of the furnace core tube 12 is closed by a sample supply / discharge lid 24 so that a boat (firing vessel) 16 can be inserted while ensuring the inside tightness of the furnace core tube 12 during firing. Have been.

The boat (fired vessel) 16 is made of a heat-resistant vessel such as a quartz boat, an alumina crucible, a quartz crucible, a silicon carbide vessel, or the like. Further, as the heat source 14, any conventionally known heat source can be used, and for example, a known electric heater can be adopted.

A sealing lid 30 is fixed to the opening at the right end of the furnace core tube 12 in the drawing, and the internal sealing of the furnace core tube 12 during firing is secured by the sealing lid 30. Hermetic lid 3
The material of No. 0 is generally a metal such as stainless steel or a ceramic such as quartz or alumina, but is preferably made of a heat insulating material. Here, the heat insulating material is, for example, ceramics having low thermal conductivity (zirconia, mica, etc.)
And porous ceramics, or those having a multilayer structure thereof.

The shape of the furnace core tube 12 may be any of a cylindrical shape, a rectangular tube shape, and the like. The size of the furnace core tube 12 is appropriately set according to the purpose, but the diameter of the cross section (if not cylindrical, the diameter of a circle corresponding to the area of the cross section) is in the range of about 50 to 2000 mm. Selected from 100-
A range of about 1200 mm is preferable. Also, the furnace core tube 12
It is desirable to secure a volume of the fired portion of 2 to 500 liters per 1 kg of the phosphor raw material mixture to be fired, and preferably a volume of the fired portion of 5 to 50 liters. If the volume of the fired portion is less than 2 liters per 1 kg of the phosphor raw material mixture, the phosphor raw material mixture is densely packed in a narrow space, and it becomes difficult to perform uniform firing as a whole. May be 5
If it exceeds 00 liters, the halogen atmosphere that evaporates is too low, and the stimulable light emission amount and erasing characteristics of the obtained stimulable phosphor may be deteriorated.

In firing the phosphor raw material mixture 18, first, the phosphor raw material mixture 18 is placed in a boat (firing vessel) 1.
6 and the sample supply / discharge port lid 24 is opened and placed at a predetermined position inside the furnace core tube 12. Then, the sample supply / discharge lid 24 is closed, gas is appropriately exhausted and / or introduced by the gas introduction / exhaust pipe 20, and heat is applied from the heat source 14 while the atmosphere inside the furnace core tube 12 is kept in a predetermined state. Perform baking. The firing conditions (atmosphere, temperature,
The time, the firing temperature, the number of steps in the atmosphere, etc.) may be appropriately set according to the purpose.

After firing, the boat (firing vessel) 16 containing the phosphor raw material mixture 18 is taken out with the sample supply / discharge port lid 24 opened, and the desired rare earth activated alkaline earth metal fluoride halide fluorescent material is obtained. The body is manufactured.

The manufacture of a phosphor using the above-described manufacturing apparatus is performed as follows. Hereinafter, a series of steps including a mixing step, a sintering step, and a cooling step are shown, but the production method of the present invention is not limited to these series of steps, and any one of the steps may be omitted, Other steps can be added. For example, a washing step, a drying step,
General various steps such as a sieving step can also be provided.
Hereinafter, each step will be described separately.

<Mixing Step> The mixing step is a step of preparing a phosphor raw material mixture by mixing phosphor raw materials. Examples of the phosphor material include the following materials (1) to (5). (1) BaF ₂ , BaCl ₂ , BaBr ₂ , BaI ₂ , Ba
At least one barium halide selected from the group consisting of FBr, BaFCl and BaFI. However, at least one is a material containing F. (2) CaF ₂ , CaCl ₂ , CaBr ₂ , CaI ₂ , Sr
F ₂ , SrCl ₂ , SrBr ₂ , SrI ₂ , MgF ₂ , Mg
At least one alkaline earth metal halide selected from the group consisting of Cl ₂ , MgBr ₂ and MgI ₂ . (3) CsCl, CsBr, CsI, NaCl, NaB
r, NaI, KCl, KBr, KI, RbCl, RbB
r, RbI, RbF, CsF, NaF, KF, LiF,
At least one alkali metal halide selected from the group consisting of LiCl, LiBr and LiI. (4) At least one metal oxide selected from the group consisting of Al ₂ O ₃ , SiO ₂ and ZrO ₂ . (5) At least one compound selected from the group consisting of rare earth element compounds such as halides, oxides, nitrates and sulfates. If desired, ammonium halide (NH ₄ X ′, where X ′ represents F, Cl, Br or I) or the like may be used as a flux.

The method of preparing the phosphor material mixture can be appropriately selected from known mixing methods. For example, the phosphor material mixture is prepared by the following methods (i) to (iv). You may. (I) A preparation method in which the phosphor raw materials (1) to (5) are weighed and simply mixed. (Ii) The phosphor raw materials (1) to (4) are weighed and mixed,
After heating this mixture at a temperature of 100 ° C. or higher for several hours,
A preparation method in which the phosphor material (5) is mixed with the obtained heat-treated product. (Iii) A preparation method in which the phosphor raw materials (1) to (5) are mixed, and the mixture is heated at a temperature of 100 ° C. or higher for several hours. (Iv) The phosphor materials (1) to (4) are mixed in the form of a suspension, and the suspension is heated, preferably 50 to 20.
A preparation method in which the phosphor material (5) is mixed with the obtained dried product after drying under reduced pressure, vacuum drying, spray drying and the like at 0 ° C.

Further, as a modification of the above-mentioned 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) includes the phosphor raw materials (1) and (5). Heating the suspension,
Preferably after heating to 50 to 200 ° C. or after drying under reduced pressure, vacuum drying, spray drying and the like under the heating,
Preparation method (iv-3) in which the phosphor raw materials (2) to (4) are added and mixed into the obtained mixture can also be suitably exemplified.

Further, a tetrahedral rare earth-activated alkaline earth metal fluorohalide-based stimulant having a controlled particle shape and particle aspect ratio described in JP-A-7-233369 and JP-A-10-195431 is disclosed. Method for producing luminescent phosphor, ie, method for preparing phosphor mixture (i)
In addition to (iv-4), various conditions such as a preparation method (v) using a means capable of imparting a shearing force when mixing phosphor materials, addition of each phosphor material, and timing of mixing are also defined. It can also be prepared by the preparation method (vi) using a controllable means.

The mixing apparatus used for the mixing in the preparation methods (v) and (vi) can be appropriately selected from known mixing apparatuses, and examples thereof include various mixers, V-blenders, ball mills, and the like. Rod mills and the like can be mentioned.

In the production of the phosphor, various additives as described below can be added for the purpose of further improving the stimulating light emission amount, the erasing characteristics and the like. For example, JP-A-57-2
No. 3673, As described in JP-A-57-23675, Tetrafluoroboric acid compound described in JP-A-59-27980, JP-A-59-472
Hexafluoro compound described in JP-A-89-89,
-56480, V, Cr, Mn, Fe, C
transition metals such as o and Ni, or BeX " ₂ described in JP-A-59-75200 (where X" is F, Cl, B
represents at least one halogen atom selected from the group consisting of r and I).

When the above-mentioned additive component is added, the additive component is added when the phosphor raw materials are weighed and mixed or before firing,
Mixed.

<Firing Step> The firing step will be described with reference to FIG. However, the present invention is not limited to the apparatus shown in FIG. The firing step is performed by charging the phosphor raw material mixture 18 into the furnace core tube 12 which is a firing portion. More specifically, the phosphor raw material mixture 18 is accommodated in a boat (firing vessel) 16, charged into the furnace core tube 12, and the inside of the firing furnace 10 is heated to a high temperature by heat from the heat source 14. Of the phosphor material mixture 1
8 is obtained.

The firing temperature is preferably in the range of 500 to 1100 ° C., more preferably in the range of 700 to 1000 ° C., and even more preferably in the range. The firing temperature is 500
If the temperature is lower than 0 ° C., the diffusion of the activator element in the host crystal and the generation of F ⁺ , which is a source of the photostimulated center, may be insufficient.
If it exceeds 100 ° C., the host crystal may be melted.

The firing time during the firing depends on the filling amount of the phosphor raw material mixture, the firing temperature or the temperature of taking out of the furnace, and is generally preferably 1 to 10 hours.
More preferably, 1 to 5 hours. If the baking time is less than 1 hour, the diffusion of the activator element in the host crystal and the generation of F ^{+ which} is a source of the stimulating center may be insufficient, and the baking is performed for more than 10 hours. However, further changes in the properties of the phosphor are small, which may lower the productivity.

The atmosphere in the furnace core tube 12 at the time of firing is preferably an atmosphere using a neutral or slightly oxidizing atmosphere gas. Examples of the neutral atmosphere gas include an inert gas such as He, Ne, Ar, and N ₂ . The slightly oxidizing atmosphere gas is produced by introducing 0.1 to 200 ml, preferably 1 to 100 ml, of oxygen from the gas inlet / outlet pipe 20 at a firing temperature of room temperature per 1 liter of the firing partial volume of the firing furnace. . For the remaining part, an inert gas such as He, Ne, Ar, or N ₂ is introduced. When the oxygen introduction amount is less than 0.1 ml, the effect of improving the erasing characteristics of the stimulable phosphor may not be sufficiently obtained. When the oxygen introduction amount exceeds 200 ml, the stimulable luminescence amount is significantly reduced. There is.

As a method for introducing oxygen into the neutral gas,
It is not particularly limited and can be appropriately selected from known introduction methods.
Once the inside of the furnace tube 12 is evacuated to a state close to vacuum,
It is preferable that a predetermined amount of oxygen and a neutral gas be introduced, and the sintering be performed in a weakly oxidizing atmosphere. By doing so, the required amount of oxygen can be accurately introduced, and the influence of other gases can be minimized.

That is, by specifying the baked partial volume of the sintering furnace per 1 kg of the luminescent material mixture to be baked and the amount of oxygen introduced per 1 liter of the baked partial volume, the stimulating fluorescent The amount of oxygen necessary to improve the body's elimination properties can be introduced. Further, by replacing the gas in the furnace core tube 12 with a gas containing a predetermined amount of oxygen, the amount of oxygen in the furnace core tube 12 can be introduced so as to be changed stepwise or continuously.

For example, a desired amount of oxygen can be introduced by the following operation. First, a boat (firing vessel) 16 containing a phosphor raw material mixture 18 is put into the firing furnace 12 that has reached the firing temperature, and immediately after that, the gas is evacuated and exhausted by the gas introduction / exhaust pipe 20 for several minutes. Remove air inside. In this case, as for the degree of vacuum, baking can be performed in a state close to a vacuum state, but in order to make the amount of oxygen in the atmosphere an accurate amount, 0.13 hPa
(0.1 torr) or less.

Next, a predetermined amount of oxygen is supplied into the furnace core tube 12 and charged to a desired pressure. As described above, the amount of oxygen introduced is preferably 0.1 to 200 ml per 1 liter of the fired partial volume of the furnace core tube, and the amount of oxygen introduced is indicated by the volume at the firing temperature. After accurately introducing a predetermined amount of oxygen into the furnace core tube 12, the neutral gas is further charged into the furnace core tube 12, and the pressure in the furnace core tube 12 is reduced to about 1
013 hPa (1 atm), that is, near atmospheric pressure, and a weakly oxidizing atmosphere can be used.

When the inside of the furnace core tube 12 is adjusted to a weakly oxidizing atmosphere, oxygen may be introduced instead of oxygen using, for example, a gas containing oxygen such as air or an inert gas. As the introduction amount of the gas containing oxygen such as the air, it is generally preferable to introduce a gas amount necessary for obtaining the same oxygen amount as in the case of introducing oxygen. 1
More preferably 0.5 to 1000 ml per liter,
Most preferred is 5-500 ml.

It is not always necessary to introduce oxygen into the furnace core tube 12 after evacuation to a vacuum state.
(013 hPa, 1 atm) A small amount of oxygen may be simply introduced into the furnace core tube 12 under a neutral gas or a weakly oxidizing atmosphere, or a gas containing oxygen such as air may be introduced into the furnace core tube 12. During the introduction, the oxygen may be introduced so as to increase the amount of oxygen in the furnace core tube 12.

When the firing is performed twice or more, for example, after the phosphor raw material mixture 18 is once fired, the fired material is taken out of the firing furnace and allowed to cool.
After pulverizing into a fine powder using a known pulverizer such as a ball mill, a tube mill, or a centrifugal mill, the pulverized material is again put into a baking furnace, and baking is repeated. It is preferable to adjust the firing conditions.

In particular, once the phosphor raw material mixture is
After firing at a firing temperature of 1300 ° C. (first firing), the fired product is taken out and pulverized in the same manner as described above, and the pulverized product is heated at a temperature lower than the firing temperature, preferably 4 ° C.
It is more preferable to further bake at a temperature of 00 to 1000 ° C. By performing calcination as described above, a powdery stimulable phosphor can be obtained.

<Cooling Step> In the cooling step, the temperature may be lowered inside the firing furnace 10 or may be taken out of the firing furnace 10 to lower the temperature. A method of forcibly lowering the temperature while controlling the temperature using a cooling means such as a means may be used. However, from the viewpoint of shortening the cooling time and stably producing a stimulable phosphor having sufficient characteristics, a method of cooling at a desired temperature is preferable.

Further, as an initial stage of the cooling step, it is preferable to provide a step of gradually cooling the inside of the firing furnace 10.
The slow cooling may be performed immediately after the phosphor raw material mixture 18 is fired, but is preferably performed after a certain time has passed while removing and replacing the atmosphere while maintaining the temperature at a certain temperature.

In the slow cooling, the temperature is controlled by controlling a gentle temperature gradient from the start until a predetermined temperature is reached. In particular, slow cooling is effective in improving the light emission characteristics of the stimulable phosphor.
It is preferable that the heating is performed at a temperature lowering rate of 2 to 5 ° C./min until the temperature at the end of the firing becomes lower by 20 to 300 ° C.

In the cooling step, the temperature of the fired product finally becomes 2
It is preferably carried out until the temperature becomes 00 ° C. or lower, more preferably 100 ° C. or lower.

The phosphor produced by the above production method is
It has a sufficient amount of stimulated emission, has sufficient erasing characteristics, and can stably form a high-quality image.
Various characteristics originally required for the phosphor are not reduced at all.

When mass-producing the phosphor, a series of steps including the mixing step, the sintering step, and the cooling step are repeated many times. In this case, in the firing step, a batch-type firing step of charging the phosphor raw material mixture, firing it, taking out the fired material after firing, and preparing for the next charging of the phosphor raw material mixture is repeatedly performed. Then, in each firing step, the halide and the like contained in the phosphor raw material mixture sublime and adhere to the inner wall portion of the firing furnace (core tube). If this deposit is left, the deposit absorbs oxygen introduced during firing in the subsequent firing step, and the amount of oxygen to be supplied to the phosphor raw material mixture is reduced. The characteristics and afterimage characteristics deteriorate, which is not preferable. Therefore, the following cleaning step is provided between one baking step and the next baking step to remove or inactivate the attached matter.

<Cleaning Step> As described above, the cleaning step is a step of removing or inactivating deposits adhered to the inner wall of the firing furnace 10 (furnace tube 12). The cleaning step can be performed, for example, by at least one step selected from the following steps A to C. All of the following steps A to C are performed after the boat 16 (fired product) is taken out of the firing furnace 10. A Step of pouring an oxygen-containing gas into a firing furnace maintained at a certain temperature or higher (hereinafter, referred to as “Step A”) B Step of evacuating the firing furnace (hereinafter, referred to as “Step B”) C A step of rubbing the inner wall of the furnace with a rubbing means (hereinafter, referred to as “step C”) By any one of the above steps A to C, the attached matter can be removed or inactivated. In the baking step, the above-mentioned problem that the attached matter absorbs the introduced oxygen does not occur, and sufficient oxygen can be supplied to a new (next) phosphor raw material mixture. By providing such a cleaning step, a phosphor having good erasing characteristics and good afterimage characteristics can be obtained.

In step A, the heating furnace 10 is
Is maintained at a certain temperature or higher, and with the sample supply / discharge lid 24 opened, one end is connected to an air compressor, and the other end of a Hastelloy tube (not shown) provided with a spout at the other end is connected to a furnace core tube. 12, the air compressor is operated, and air (oxygen-containing gas) flows into the furnace core tube 12 from the Hastelloy tube outlet. The oxygen-containing gas introduced into the firing furnace 10 has a high temperature, and this oxygen-containing gas causes
Halides and the like adhered to the inner wall of the furnace core tube 12 (adhered matter)
Is oxidized and inactivated, and / or re-sublimated and exhausted.

As the oxygen-containing gas to be introduced, air or a mixed gas containing oxygen can be used. When preparing a mixed gas containing oxygen, the oxygen concentration in the oxygen-containing gas is preferably set to 20 to 100%. The introduction of the oxygen-containing gas can be performed by an oxygen-containing gas cylinder equipped with a pressure control valve. The flow rate of the oxygen-containing gas to be introduced is 5 to 5000 l / m.
It is preferably set to in.

As described above, when performing the step A, the firing furnace 10
Is maintained at a certain temperature or higher, but the fixed temperature is not particularly limited, and may be, for example, minus one with respect to the temperature set in the above-mentioned firing step (the temperature at the time of firing).
It can be 0 ° C. or higher. When the temperature is equal to or higher than the temperature, oxidation, inactivation, and / or re-sublimation of a halide or the like attached to the inner wall of the furnace core tube 12 is promoted. The constant temperature is more preferably the temperature at the time of firing, and even more preferably the temperature plus 10 ° C. or more with respect to the temperature at the time of firing. -10 ° C to the temperature during firing
Even if the amount is less than the above, a certain cleaning effect can be obtained, but the cleaning efficiency may decrease due to low reactivity with oxygen.

The temperature inside the firing furnace 10 is 1200 ° C.
Or less, more preferably 1000 ° C. or less. When the internal temperature exceeds 1200 ° C., the load on the heat source 14 (such as an electric heater) of the firing furnace 10 increases, which may shorten the life of the heat source and increase the manufacturing cost (such as electricity cost).

The execution time of the step A depends on the amount of the deposits in the firing furnace, but is preferably 0.1 to 50 hours, more preferably 0.5 to 20 hours. If the execution time is less than 0.1 hour, the removal or inactivation of deposits may be insufficient, and if it exceeds 50 hours,
There is no effect of removing the deposit any more, and the productivity may decrease.

In the above step A, the oxygen-containing gas was introduced from the Hastelloy pipe with the sample supply / discharge port lid 24 opened, and discharged from the opening of the furnace core tube 12 on the sample supply / discharge port lid 24 side. The oxygen-containing gas may be introduced into the furnace core tube 12 with the supply / discharge port lid 24 closed, and may be stopped in the furnace core tube 12 and left as it is. Also in this case, the deposits can be deactivated by the high-temperature oxygen retained in the furnace core tube 12.

In step B, the baking furnace 10 (furnace tube 12) is sealed, and the gas adhering to the inner wall of the baking furnace 10 (furnace tube 12) is sucked by evacuating the gas from the gas introduction / exhaust tube 20. Remove.

The degree of vacuum of the firing furnace 10 (furnace core tube 12) is preferably 0.13 hPa (0.1 torr) or less. If it exceeds 0.13 hPa, it may not be possible to suck the attached matter. Further, the temperature in the firing furnace 10 during vacuum suction is preferably set to be higher than or equal to the firing temperature and lower than or equal to 1200 ° C.

The execution time of the step B depends on the amount of the deposits in the firing furnace, but is preferably 0.1 to 50 hours, more preferably 0.5 to 20 hours. If the execution time is less than 0.1 hour, the removal of the deposits may be insufficient, and if it is more than 50 hours, there is no effect of removing the deposits further, and the productivity may decrease.

In the step C, the inner wall of the baking furnace 10 (furnace core tube 12) is rubbed by a rubbing tool (rubbing means) to discharge the deposits to the outside of the baking furnace 10.

As a rubbing tool for rubbing the inner wall of the firing furnace 10 (furnace tube 12), a brush or the like can be used. In addition, in combination with the suction nozzle, the efficiency of removing adhering substances can be increased. Further, upon rubbing, rubbing can be performed using an abrasive or the like.

The cleaning step may be performed every time after the baking step, or may be performed once every time the baking step is performed n times (n: natural number). For example, if the amount of the deposit is small in one baking process, the cleaning process may not be performed every time. From the viewpoint of manufacturing efficiency, the cleaning process is performed every time the amount of the deposit reaches the amount to be removed. It can be carried out. That is, if the number of firing steps in which the amount of adhered substances is to be removed is measured and n is set to the number, the phosphor can be manufactured efficiently.
For example, in the case where the amount of the adhered substance reaches the amount to be removed after three firing steps, the firing step is performed three times (n = 3).
It can be set as appropriate, such as performing a cleaning step once each time it is performed. Although it depends on the firing conditions and the like, n is preferably 1 to 10.

On the other hand, even when the firing step is performed in two or more steps for one phosphor raw material mixture, a cleaning step must be provided between a certain firing step and the next firing step. Can be. Even in one baking process, it is considered that deposits are generated over time. Therefore, if the cleaning process is performed in the middle of the process of manufacturing one baking product, similarly, the attachments in the baking furnace may be performed. Deposits can be removed or inactivated, and a phosphor excellent in erasing characteristics and afterimage characteristics can be manufactured. More specifically, the boat 10 (fired product) is taken out of the firing furnace 10 during the firing step, a cleaning step is performed, and then the boat 10 is put into the firing furnace 10 and the firing step is performed again.

Each cleaning step is the same every time (A
To C), it may be different for each cleaning step. In other words, in each cleaning step, step A
To C can be arbitrarily selected. In addition, two or more steps A to C can be arbitrarily combined in one cleaning step. For example, after the process A, the process C is performed, or the process A, the process B, and the process C are performed.
Or in this order. As described above, by arbitrarily combining two or more of the steps A to C, it is possible to more sufficiently remove or inactivate the deposits attached to the inner wall of the firing furnace.

[0066]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. (Example 1) <Mixing step> BaFBr: Eu prepared in advance and Ba
FI: Eu raw powder (Eu activation amount 5 × 10 ⁻³ mol, K, Cs and Ca as additives are each 1 × 10 ⁻³ mol)
Are mixed so that the composition ratio of Br and I becomes 85:15, and further, in order to prevent sintering during firing, 1% by mass of ultrafine alumina particles are added, and the mixture is sufficiently mixed with a mixer. A was obtained.

<Firing Step> 3 kg of the phosphor raw material mixture A was placed in a quartz boat (firing vessel) 16 and the temperature in the furnace was set to 830 ° C. using the firing furnace 10 (furnace tube 12) in a nitrogen atmosphere containing a trace amount of oxygen. And baked for 2 hours. After firing, the quartz boat 16 (fired product) was moved to a cooling chamber 28 in which a trace amount of oxygen was contained in advance, and was cooled for 30 minutes. After cooling,
The quartz boat 16 (fired product) was taken out of the cooling chamber 28.

<Cleaning Step> Thereafter, the firing furnace 10
With the sample supply / discharge port lid 24 opened while the temperature inside the furnace is maintained at 830 ° C., the other end of the Hastelloy tube connected to the air compressor at one end is inserted into the furnace core tube 12 and air (oxygen Containing gas) was introduced. The air volume is
The air flow was adjusted so as to be sufficiently distributed in the furnace. It was left for 1 hour in that state.

Thereafter, the Hastelloy tube was taken out of the firing furnace 10, a new phosphor raw material mixture was placed in a quartz boat 18, and fired in the same manner using the firing furnace 10. The above series of steps was repeated, and 10 continuous firings were performed.

(Example 2) In this example, the mixing step and the baking step were performed in the same manner as in Example 1, and then the following cleaning step was performed. <Cleaning Step> After firing, the sample supply / discharge port lid 24 is closed while the firing furnace is kept at 830 ° C., the valve 22 is opened, and the inside of the furnace core tube 12 is exhausted by the vacuum pump through the gas introduction / exhaust tube 20. Left for 1 hour. Ten minutes after the start of evacuation, no change in the degree of vacuum was observed, and the ultimate degree of vacuum was 0.013 hPa (0.01 torr). Thereafter, the valve 22 is closed, and the connection of the gas introduction / exhaust pipe 20 is switched from the vacuum pump to the N ₂ gas cylinder.
2 was opened and N ₂ gas was introduced to return the inside of the furnace core tube 12 to atmospheric pressure. Thereafter, the sample supply / drain cover 24 is opened, and the new phosphor material mixture is accommodated in the quartz boat 18 and the firing furnace 10 is opened.
Was similarly baked. The above series of steps was repeated, and 10 continuous firings were performed.

(Embodiment 3) In this embodiment, the mixing step and the baking step were performed in the same manner as in Embodiment 1, and thereafter, the following cleaning step was performed. <Cleaning Step> After the firing, the sample supply / discharge port lid 24 is opened while the firing furnace 10 is maintained at 830 ° C., and the furnace core tube 12 (the firing furnace 10) is heated with a metal heat-resistant brush (rubbing means).
The inner wall was rubbed to remove attached matter. The deposits stored in the furnace core tube 12 were removed via a suction tube. Thereafter, the sample supply / discharge lid 24 was opened, the new phosphor raw material mixture was accommodated in a quartz boat 18, and similarly fired using the firing furnace 10. Repeat the above series of steps,
Ten continuous firings were performed.

(Comparative Example 1) Ten firings were performed in the same manner as in Example 1 except that the cleaning step was not performed.

In each of Examples 1 to 3 and Comparative Example 1, the erasing characteristics and the afterimage characteristics were evaluated with respect to the prepared phosphors.

<Erasing Characteristics Evaluation> The following erasing values were measured to evaluate the erasing characteristics. (Erased value) Visible light (erasing light) is applied to the phosphor particles for which the amount of stimulated emission has been measured, and then the secondary emission is performed again. A value standardized by the amount of initial photostimulated light emission. Under the same evaluation conditions, the smaller the value, the better the erasing characteristics. (Evaluation method) 200 mg of phosphor particles were uniformly packed in a black cylindrical holder (recess opening 10 mmφ, depth 1 mm). The phosphor surface of the opening of the holder was irradiated with X-rays having a tube voltage of 80 kVp through a 3 mm-thick Al filter by an X-ray generator (MG164, manufactured by Philips) through a 3 mm-thick Al filter in a dark room. Twenty seconds later, a 660 nm wavelength semiconductor laser (ML-1016R, manufactured by Mitsubishi Electric Corporation) is uniformly spread over the phosphor surface to generate an excitation energy of 4.3 J.
/ M ² , and at that time, photostimulated light emitted from the phosphor surface is converted into an optical filter (B-41 manufactured by HOYA).
0) through a photomultiplier tube (Hamamatsu Photonics: R-
1848) and the amount of stimulated emission (initial) was measured. Subsequently, using a three-wavelength fluorescent light bulb (Prince Electric Co., Ltd .: FLR505T5EX-L), 300,000 lx
After irradiating the light amount of 200 sec, the light is further irradiated with a light amount of 200,000 lx sec (a total of 500,000 lx sec) through a sharp cut filter (N-039, manufactured by Nitto Resin Co., Ltd.) that cuts short-wave light from 480 nm. , Erased. This was read with a semiconductor laser under the same conditions as above, and the amount of stimulated emission (after erasure) at that time was measured. The value obtained by standardizing the amount of stimulated light emission after erasing by the amount of initial stimulated light emission was expressed as an erased value.

<Evaluation of Afterimage Characteristics> The following afterimage values were measured to evaluate the afterimage characteristics. (Afterimage value) After the phosphor particles that have been subjected to X-ray irradiation, photostimulated luminescence measurement, and erasure have passed for a predetermined time at a predetermined temperature and then subjected to secondary excitation again, the luminescence amount (afterimage aging) (After-stimulated light emission) means a value standardized by the initial amount of stimulated light. Under the same evaluation conditions, the smaller the value, the better the afterimage characteristics. (Evaluation method) The phosphor particle holder whose erased value was measured
It was allowed to elapse for 2 hours in a thermostat at 60 ° C. This was read with a semiconductor laser under the same conditions as in the erasure measurement, and the amount of stimulated emission (after image lapse) at that time was measured. The value obtained by standardizing the amount of stimulated emission after the lapse of the afterimage with the amount of initial stimulated emission was expressed as an afterimage value.

Table 1 shows the measurement results of the erase value and the afterimage value in Examples 1 to 3 and Comparative Example 1.

[0077]

[Table 1]

From Table 1, it can be seen that in the phosphors of Examples 1 to 3, the erased value and the afterimage value did not change significantly even after 10 firing steps, that is, the erase characteristics and the afterimage characteristics changed significantly. Was not observed, and good results were obtained. On the other hand, in Comparative Example 1, both the erase value and the afterimage value deteriorated (increased) each time, and in the fourth baking, both the erase value and the afterimage value deteriorated to twice or more the first time. It continued to worsen every time until the tenth time. From the above, it is apparent that according to the manufacturing method of the present invention, the erasing characteristics and the afterimage characteristics do not deteriorate even if the firing step is repeatedly performed.

[0079]

According to the present invention, it is possible to provide a method for producing a rare earth-activated barium fluorohalide-based phosphor in which the erasing characteristics and the afterimage characteristics are not deteriorated even after the firing step.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an apparatus for producing a rare earth-activated barium fluorohalide-based phosphor to which the production method of the present invention can be applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Firing furnace 12 Furnace tube 14 Heat source 16 Boat (firing container) 18 Phosphor raw material mixture 20 Gas introduction / exhaust pipe 22 Valve 24 Sample supply / discharge port lid 30 Sealed lid

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G21K 4/00 G21K 4/00 LF term (reference) 2G083 AA03 BB01 CC02 DD20 EE04 4H001 CA08 XA03 XA04 XA09 XA11 XA12 XA13 XA17 XA19 XA20 XA21 XA31 XA35 XA37 XA38 XA39 XA49 XA53 XA55 XA56 XA57 XA64 XA71 XA81 YA58 YA59 YA60 YA62 YA63 YA65 YA66 YA67 YA68 YA69 YA70

Claims (5)

[Claims] 1. A phosphor raw material mixture is charged into a firing furnace,
This is fired to take out the fired material after firing, and in a method for producing a rare earth activated barium fluoride halide-based phosphor having a batch-type firing step in preparation for charging the next phosphor raw material mixture, Producing a rare earth activated barium fluorohalide-based phosphor characterized by providing a cleaning step for removing or inactivating deposits adhering to the inside of the baking furnace between the baking step and the next baking step. Method. 2. The rare-earth activated barium fluorohalide-based phosphor according to claim 1, wherein the cleaning step is a step of flowing an oxygen-containing gas into the firing furnace maintained at a certain temperature or higher. Manufacturing method. 3. The method of claim 1, wherein the cleaning step is a step of evacuating the inside of the firing furnace. 4. The method according to claim 1, wherein the cleaning step is a step of rubbing the inner wall of the firing furnace with a rubbing means. . 5. The rare earth activated barium fluorinated halogenated phosphor according to claim 1, wherein the cleaning step is performed by arbitrarily combining two or more of the following steps A to C. Production method. A Step of pouring an oxygen-containing gas into the firing furnace maintained at a certain temperature or higher B Step of evacuating the inside of the firing furnace C Step of rubbing the inner wall of the firing furnace with a rubbing means