JPH0525476A - Production of stimulable phosphor - Google Patents

Abstract

PURPOSE:To produce a stimulable phosphor of a barium halide activated with europium (Eu) and a highly sensitive stimulable phosphor. CONSTITUTION:Phosphor materials are mixed together in a relative ratio corresponding to the formula (I):BaX2:xEu+yNH4X' (wherein X is F, Cl, Br or I, and X' is Cl, Br or I) and fired at 500-1000 deg.C in an oxidizing atmosphere, a neutral atmosphere or a reducing atmosphere to obtain an europium-activated barium halide of formula (II): Ba(X1-zX'z)2:xEu2+ (wherein 0<z<0.1 and 0.0001<x<0.1). Alternatively, the phosphor materials are mixed together in a relative ratio corresponding to the formula (III):BaX2:xEu and fired in a gas containing an ammonium halide gas to form a phosphor of formula (II).

Description

Detailed Description of the Invention

[0001]

The present invention relates to a stimulable phosphor, particularly,
The present invention relates to a method for producing a phosphor that stimulates and emits barium halide activated by europium (Eu). Radiation images such as X-ray images are widely used for disease diagnosis and the like. This X-ray image is a screen type that irradiates the phosphor layer (fluorescent screen) with X-rays that have passed through the subject, produces visible light from this, and exposes and develops a film using silver salt with this visible light. It was obtained as an X-ray photograph. In addition, no-screen type X-ray photographs are also used. A method of using a stimulable phosphor as an X-ray system with high sensitivity and high resolution is an alternative to the method of recording a secondary image of radiation indirectly or directly on a film coated with such a silver salt sensitizer. Researched and developed. A basic method of such a method is proposed in US Pat. No. 3,859,527. When the phosphor used in this system receives the energy of radiation such as X-rays (when it is irradiated), the phosphor accumulates energy in the crystal and its state is relatively stable. It is maintained for a long time. When the phosphor in this state is irradiated with the first light that acts as excitation light, the stored energy becomes second light and is emitted (emits light). At this time, the first light is not limited to visible light, and light having a wide range of wavelengths from infrared rays to ultraviolet rays can be used, but the wavelength selection depends on the phosphor material used. Also, there are various types of second light from infrared to ultraviolet,
This also depends on the phosphor material used.

[0002]

2. Description of the Related Art A rare earth element-activated halide phosphor is known as a stimulable phosphor, and one of them is a europium-activated alkaline earth (barium) composite halide phosphor (BaXX ': Eu, However, X, X'are F, Cl, Br
And at least one halogen selected from the group consisting of I). This phosphor exhibits near-ultraviolet emission (stimulated emission) when excited by radiation such as X-rays, electron beams and ultraviolet rays and then excited by electromagnetic waves in the visible or infrared region. Since the intensity of stimulated emission is proportional to the intensity of X-rays, a plate (film) coated with a phosphor is irradiated with X-rays that have passed through the subject, and this is scanned with a red or infrared laser to obtain a bright emission. The exhaust emission is converted into an electric signal by a photomultiplier tube, and the electric signal is image-processed to obtain an X-ray photograph. As a stimulable phosphor used in such a radiation image conversion method, for example, a divalent europium-activated divalent metal fluorohalide phosphor represented by the following formula is proposed in Japanese Patent Publication No. 51-28591. There is.

(Ba _1-xyp Sr _x Ca _y , Eu _p ²⁺ ) F (Cl _1-ab Br _a I _b ) (where x, y, p, a and b are x + y + p ≦ 1, y ≦ 0.20,
This is a number that satisfies the conditions 0.001 ≤ p ≤ 0.20 and a + b ≤ 1) 39 when excited by X-rays, ultraviolet rays, electron beams, etc.
Since it exhibits near-ultraviolet emission (instantaneous emission) having a peak of emission spectrum distribution near 0 nm, it is not only practically used as a phosphor for X-ray intensifying screens, but also has a wavelength of 500 to 1000 nm after X-ray irradiation. 58 when excited by radiating electromagnetic waves
Since it exhibits near-ultraviolet emission (stimulated emission) having a peak of emission spectrum distribution near 0 nm, a He-Ne laser (wavelength 63
It can be used as an X-ray image conversion sheet (imaging plate) with scanning irradiation of 3 nm).

The photostimulable phosphor as disclosed in Japanese Patent Publication No. 51-28591 mentioned above is prepared by mixing phosphor raw materials in a predetermined composition and firing the mixture at a temperature of 600 to 1000 ° C. for an appropriate time. Manufactured by.

[0005]

When used as an imaging plate for X-ray photography by molding or coating a stimulable phosphor, the stimulable luminescence intensity at the readout wavelength of the imaging plate is increased (ie, ,
It is possible to reduce the X-ray dose to the subject by increasing the sensitivity of the phosphor to X-rays. Therefore, the present invention is to provide a method for producing a more sensitive europium-activated barium halide stimulable phosphor.

[0006]

[Means for Solving the Problems] The above-mentioned object is to use (i) BaX ₂ (ii) EuX ₃ (iii) NH ₄ X'as a raw material in a stoichiometric composition formula (I) BaX ₂ : xEu ＋ yNH ₄ X '... (I) (In the formula, X is one of F, Cl, Br, I, and X'is Cl,
Either Br or I, and x is 0.0001 <x <0.
(1) and y is a numerical value in the range of 0 <y <0.1). The phosphor raw materials are mixed and prepared so as to have a relative ratio, and this mixture is mixed in an oxidizing atmosphere, a neutral atmosphere or in a reducing atmosphere and baked at a temperature in the range of 500 to 1000 ° C., formula _{(II) Ba (X 1-} z X 'z) 2: xEu 2 + ...... (II) ( wherein, X is Is one of F, Cl, Br, I, and X'is Cl,
Any one of Br and I, and z is a numerical value in the range of 0 <z <0.1, and x is a numerical value in the range of 0.0001 <x <0.1). This is achieved by a method for producing a stimulable phosphor, which is characterized by using barium oxide.

Mixing is performed by various mixers which are ordinary mixers.
Sufficiently performed with a V-type blender, a ball mill, a rod mill or the like. If the above three kinds of raw materials are powders or the like, they can be dry-mixed by these mixers. If these raw materials are made into an aqueous solution or solution in which water or a solvent is dissolved, they can be wet-mixed by a mixer. Further, the raw material (i) an aqueous solution of BaX ₂ and the raw material (ii) Eu
It is also possible to mix the activator aqueous solution of X _{3 in} a wet manner and dry it, and then add the powder of the raw material (iii) NH ₄ X ′ and mix it in a dry manner. Note that it is preferable to remove impurities by means such as filtration during wet mixing.

A phosphor raw material prepared by mixing is used as an alumina crucible,
It is put in a heat-resistant container such as a quartz crucible or a quartz boat, and heated in a firing furnace to be fired. At that time, the firing atmosphere may be an oxidizing atmosphere, a neutral (inert) atmosphere or a reducing atmosphere, and the oxidizing atmosphere may be the atmosphere or a mixed gas of oxygen and an inert gas. As the (inert) atmosphere, a nitrogen gas atmosphere,
An argon gas atmosphere, a helium gas atmosphere, or the like is used, and as the reducing atmosphere, a mixed gas atmosphere of nitrogen gas containing 30% by volume or less of hydrogen gas or an inert gas is used. The optimum firing temperature varies depending on the type of phosphor raw material, composition (mixing ratio), etc., but is preferably in the range of 500 to 1000 ° C. as in the conventional production method.
The range of 700 to 950 ° C is preferable. The firing time depends on the type of phosphor raw material, composition (mixing ratio), filling amount in the heat-resistant container,
Depending on the firing temperature and the like, it is in the range of 5 minutes to 12 hours, preferably 5 minutes to 2 hours. When pulverizing and classifying the obtained fired body, it is preferable to place it in an atmosphere of dry neutral gas (inert gas or nitrogen gas) in order to prevent moisture absorption.

Further, the above-mentioned object is to use (i) BaX ₂ (ii) EuX ₃ as a raw material in a stoichiometric composition formula (III) BaX ₂ : xEu (III) (wherein X is one of F, Cl, Br, I, and x is
The phosphor raw materials are mixed and prepared so as to have a relative ratio corresponding to 0.0001 <x <0.1), and this mixture is mixed with an atmosphere of a neutral gas or a reducing gas and an ammonium halide gas. in the middle, and then calcined at a temperature in the range of 500 to 1000 ° C., formula _{(II) Ba (X 1-} z X 'z) 2: xEu 2 + ...... (II) ( wherein, X is F, Cl, Br, or I, X'is Cl,
Any one of Br and I, and z is a numerical value in the range of 0 <z <0.1, and x is a numerical value in the range of 0.0001 <x <0.1). This can also be achieved by a method for producing a stimulable phosphor, which is characterized by using barium oxide.

Ammonium halide (NH ₄ X) gas includes
There are NH ₄ F, NH ₄ Cl, NH ₄ Br, and NH ₄ I gases.To introduce these gases into the designated heating furnace, the ammonium halide crystals are heated away from the heating zone of the mixture.・
It is preferable to sublimate and continuously convey by a carrier gas such as a neutral gas (helium gas) or a reducing gas. If the firing temperature is lower than 500 ° C., the crystallinity of the BaBr ₂ matrix and the diffusion of Eu are not sufficient, while if it exceeds 1000 ° C., the phosphor melts, resulting in loss of sensitivity. It is preferably 700 to 950 ° C. On the other hand, the sublimation temperature of ammonium halide crystals is lower than the firing temperature and is 350 to 600 ° C.

[0011]

[Function] The halogen element of the stimulable phosphor is X in the composition formula (II).
= 'For, NH ₄ X' X diffusion of X concentrations preparation and Eu by adding is promoted, the sensitivity is enhanced. Also, X ≠
In the case of X ′, introduction of a different halogen element can change the excitation spectrum in addition to these promoting effects. The change in spectrum can be controlled by the type of halogen element, the amount of halogen element added, the firing conditions, and the like.

If europium does not exist, the photostimulability is not expressed, and if 0.0001 <x of europium is sufficient,
When x> 0.1, the concentration quenching (a phenomenon in which the phosphor absorbs and reduces the emission) appears, which is not preferable.
0.0005 <x <0.01.

[0013]

EXAMPLES The present invention will be described in detail below with reference to the accompanying drawings by way of example embodiments and comparative examples of the present invention. Example 1 1000 g BaBr ₂ powder, 2.6 g EuBr ₃ powder, 30 g NH 3
₄ Cl powder was dry-mixed with a ball mill for 6 hours, the lid of the mill was opened as it was, dried under vacuum at 110 ° C. for 2 hours, and further mixed with a ball mill for 6 hours. The phosphor raw material mixed powder thus prepared was put in a quartz boat and fired in a tube furnace under the following conditions.

Firing temperature: 845 ° C. Baking time: 5 minutes Firing atmosphere: Helium gas flow ... 5 liters / min

After firing, the material was gradually cooled to room temperature in an atmosphere of helium gas flow. Since the obtained fired phosphor was sintered, it was ground in an agate mortar to obtain phosphor powder. The photostimulable phosphor thus produced has a composition of Ba (Br _1-00.4 C
l _{0 04) 2:.} a 0.002 Eu ^2+, as follows by measuring the stimulated emission spectrum after X-ray irradiation results shown in Figure 1 was obtained.

The obtained phosphor powder is put in a measuring cell having a quartz glass window, irradiated with X-rays, and then the light of a halogen lamp (light source) is dispersed by a spectroscope to fluoresce the measuring cell. Irradiated the body. The generated photostimulated light was guided to a photomultiplier tube through a filter, and photoelectrically converted to obtain photostimulated luminescence intensity.

For comparison, BaBr ₂ : 0.002Eu ²⁺ phosphor powder was manufactured by the same procedure without addition of NH ₄ Cl powder, and the stimulated emission spectrum after X-ray irradiation was measured to obtain the result. As shown in FIG. As is clear from FIG. 1, the stimulated emission intensity was improved over the entire range by incorporating the step of adding ammonium chloride in the manufacturing process.

Example 2 1000 g BaBr ₂ powder, 2.6 g EuBr ₃ powder and 30 g NH 3
₄ Br powder was dry-mixed with a ball mill for 6 hours, the mill lid was opened as it was, dried at 110 ° C. for 2 hours under vacuum, and further mixed with a ball mill for 6 hours. The phosphor raw material mixed powder thus prepared was put in a quartz boat and placed in a tube furnace in Example 1
It was fired under the same conditions below.

Firing temperature: 845 ° C. Baking time: 5 minutes Firing atmosphere: Helium gas flow ... 5 liters / min

After firing, the material was gradually cooled to room temperature in a helium gas flow atmosphere. Since the obtained fired phosphor was sintered, it was ground in an agate mortar to obtain phosphor powder. The stimulable phosphor produced in this manner has a composition of BaBr ₂ : 0.002.
It was Eu ²⁺ , and the stimulated emission spectrum after X-ray irradiation was measured in the same manner as in Example 1, and the results shown in FIG. 1 were obtained. There is no change in the distribution of the excitation spectrum as compared with the case where NH ₄ Br is not added, but the sensitivity can be increased about 1.4 times and the firing time can be shortened to several minutes to 1 hour.

Example 3 1000 g BaBr ₂ powder, 2.6 g EuBr ₃ powder and 30 g NH 3
₄ I powder was dry-mixed with a ball mill for 6 hours as in Example 1, the mill lid was opened as it was, vacuum-dried at 110 ° C. for 2 hours, and further mixed with a ball mill for 6 hours. The mixed phosphor raw material powder thus prepared was put in a quartz boat and fired in a tube furnace under the same conditions as in Example 1.

Firing temperature: 845 ° C. Baking time: 5 minutes Firing atmosphere: Helium gas flow ... 5 liters / min

After firing, it was gradually cooled to room temperature under a helium gas flow atmosphere. Since the obtained fired phosphor was sintered, it was ground in an agate mortar to obtain phosphor powder. The photostimulable phosphor thus produced has a composition of Ba (Br _1-00.4 C
l _{0 04) 2:.} a 0.002 Eu ^2+, the results shown by the broken line in FIG. 1 by measuring the stimulated emission spectrum after X-ray irradiation in the same manner as in Example 1 were obtained. The excitation spectrum shifts to the longer wavelength side than in the cases of Examples 1 and 2.

Example 4 1000 g of BaBr ₂ powder and 2.6 g of EuBr ₃ powder were dry mixed in a ball mill for 6 hours, and the mill lid was opened as it was.
It was vacuum dried at 0 ° C. for 2 hours, and further mixed by a ball mill for 6 hours. This mixed and prepared phosphor raw material mixed powder (composition ratio BaBr
₂ : 0.002 Eu ²⁺ ) was put into a quartz boat, and the quartz boat was put into a tube furnace into which a mixed gas of helium gas and ammonium halide gas (vapor of NH ₄ Cl) was introduced, and fired under the following conditions. Incidentally, NH ₄ Cl NH ₄ Cl vapors in a separate electric furnace
The powder was heated to 400 ° C. to be sublimated and generated, and a carrier gas of helium gas was flown therein to flow as a mixed gas in a tube furnace.

Baking temperature: 845 ° C. Baking time: 5 minutes Baking atmosphere: Helium gas flow containing NH ₄ Cl vapor ... 5 liters / minute

After firing, the material was gradually cooled to room temperature in an atmosphere in which only helium gas was flowed. Since the obtained fired phosphor was sintered, it was ground in an agate mortar to obtain phosphor powder. The composition of the stimulable phosphor produced in this manner is Ba (Br
_1-00.4 Cl _{0 04) 2:.} A 0.002 Eu ^2+, the same results as in Example 1 by measuring the stimulated emission spectrum after X-ray irradiation in the same manner as in Example 1 were obtained.

Example 5 The phosphor raw material mixed powder (5 g) mixed and prepared in Example 4 was put into a quartz boat 1, and ammonium bromide (NH ₄ Br) crystal powder (15 g) was added to three quartz boats 2A and 2B. It was divided into 2C and put. These quartz boats were spaced apart from the long quartz reaction tube 3 as shown in FIG. This reaction tube 3
(Electric) heating furnace 4 is heated to
Was maintained at 845 ° C and the sublimation zone B was maintained at 500 ° C. With the helium gas (10 l / min) flowing into the reaction tube 3, the reaction tube was slowly inserted into the heating furnace 4,
As shown in FIG. 2, the quartz boat 1 is in the calcined soaking zone A,
Moreover, the quartz boat 2A was made to come to a position near the sublimation zone. Move the reaction tube 3 little by little (to the right in the drawing),
The quartz boats 2A, 2B, and 2C were sequentially moved to the sublimation temperature zone to sublimate ammonium bromide and continuously supplied as a gas to the raw material mixed powder of the quartz boat 1. In this way, firing was performed for 2 hours, and after firing, helium gas was caused to flow in the opposite direction to gradually cool the fired body to room temperature.

Since the fired phosphor obtained is sintered,
It was crushed in an agate mortar to obtain a phosphor powder. The stimulable phosphor produced in this manner has a composition of BaBr ₂ : 0.002Eu ²⁺
Then, the stimulated emission spectrum after X-ray irradiation was measured in the same manner as in Example 1, and the same result as in Example 2 was obtained.

As a comparative example regarding the gas supply of ammonium bromide (NH ₄ Br), as shown in FIG. 3, ammonium bromide crystal powder (15 g) was put in one quartz boat 2.
It was arranged near the quartz boat 1 of the phosphor raw material mixed powder (5 g). The firing soaking temperature A of the heating furnace 3 is set to 845 ° C.,
In addition, helium gas (10 liters / minute) was passed through the reaction tube 3. Slowly insert this reaction tube into the heating furnace 4,
Quartz boats 1 and 2 were fired as shown in FIG.
I brought it in and baked it for 2 hours. After firing, helium gas was continuously flowed to gradually cool the fired body to room temperature. Since the obtained fired phosphor was sintered, it was ground in an agate mortar to obtain a phosphor powder, and the phosphor sensitivity was measured. Taking the sensitivity of this comparative example as 100, the sensitivity in the case of the present invention was 120. The reason why the sensitivity of the comparative example is low is that the sublimation temperature is lower than the firing temperature, so that ammonium bromide is sublimated all at once at the start of firing and the ammonium bromide gas cannot be continuously supplied during the firing period. Therefore, in the present invention, the ammonium halide gas is continuously supplied.

Example 6 At the time of wet mixing, the raw materials in an aqueous solution state (BaBr ₂ aqueous solution and
(EuBr ₃ aqueous solution) was mixed as an aqueous solution, and dried by heating using a vacuum dryer. A rotary evaporator may be used for drying. After drying, ammonium halide was added and mixed. In addition, before adding and mixing, baking may be performed at 500 ° C. or lower in the air after being dried to some extent. Then, the phosphor powder obtained by firing under the same conditions as in Example 1 had the same properties as in Example 2.

Example 7 1000 g of BaBr ₂ powder and 2.6 g of EuBr ₃ powder were dry-mixed in a ball mill, vacuum-dried, and calcined in the air at 500 ° C. for 3 hours. By baking in such an oxidizing atmosphere, it is possible to remove organic impurities and prevent blackening of the phosphor. Crush this fired body and add 30g to it.
NH ₄ Cl powder was added and mixed. Then, Example 1
The phosphor powder obtained by firing under the same conditions as above had the same characteristics as in Example 1.

[0032]

As described above, by using the ammonium halide production process according to the method for producing a stimulable phosphor according to the present invention, compared with the stimulable phosphor produced by the conventional production method. The stimulated emission intensity can be increased. If a highly sensitive photostimulable phosphor can be obtained in this way, the exposure dose of X-rays can be reduced, and the read-out light of a semiconductor laser (wavelength 780 nm) can be adopted, so that the X-ray image reading apparatus can be made compact. And cost reduction.

[Brief description of drawings]

FIG. 1 is a graph showing a fluorescence spectrum of a stimulable phosphor at stimulated emission intensity.

FIG. 2 is a schematic view of a heating device for firing a stimulable phosphor according to the present invention.

FIG. 3 is a schematic view of a heating device when firing a stimulable phosphor as a comparative example.

[Explanation of symbols]

1 ... Quartz boat of phosphor raw material mixed powder 2, 2A, 2B, 2C ... Quartz boat of ammonium bromide crystal powder 3 ... Reaction tube 4 ... Heating furnace A ... Firing soaking zone B ... Sublimation zone

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masami Hasegawa             1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture             Within Fujitsu Limited (72) Inventor Soichiro Hidaka             1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture             Within Fujitsu Limited

Claims (4)

[Claims] 1. A stoichiometric composition formula (I) BaX ₂ : xEu + yNH ₄ X ′ (I) (wherein X is any one of F, Cl, Br, I, and X ′ is Cl. ,
Either Br or I, and x is 0.0001 <x <0.
(1) and y is a numerical value in the range of 0 <y <0.1). The phosphor raw materials are mixed and prepared so as to have a relative ratio, and this mixture is mixed in an oxidizing atmosphere, a neutral atmosphere or in a reducing atmosphere and baked at a temperature in the range of 500 to 1000 ° C., formula _{(II) Ba (X 1-} z X 'z) 2: xEu 2 + ...... (II) ( wherein, X is Is one of F, Cl, Br, I, and X'is Cl,
Br, I, and z is a numerical value in the range 0 <z <0.1, and x is a numerical value in the range 0.0001 <x <0.1) A method for producing a stimulable phosphor, which comprises using barium. 2. The mixing of the phosphor raw materials is performed by wet and / or
Alternatively, the manufacturing method according to claim 1, which is performed in a dry method. 3. A stoichiometric composition formula (III) BaX ₂ : xEu (III) (wherein X is F, Cl, Br or I, and x is
The phosphor raw materials are mixed and prepared so as to have a relative ratio corresponding to 0.0001 <x <0.1), and this mixture is mixed with a neutral gas or a reducing gas and an ammonium halide gas in an atmosphere of a mixed gas. in the middle, and then calcined at a temperature in the range of 500 to 1000 ° C., formula _{(II) Ba (X 1-} z X 'z) 2: xEu 2 + ...... (II) ( wherein, X is F, Cl, Br, or I, X'is Cl,
Br, I, and z is a numerical value in the range 0 <z <0.1, and x is a numerical value in the range 0.0001 <x <0.1) A method for producing a stimulable phosphor, which comprises using barium. 4. The ammonium halide gas is NH ₄ X.
(X is any one of F, Cl, Br, I) is generated by sublimation at a position away from the heating zone of the mixture, and the mixture is continuously supplied to the mixture with the carrier gas of the neutral gas or the reducing gas. The method according to claim 3, further comprising: