JPH04283289A - Preparation of stimulable phosphor - Google Patents

Abstract

PURPOSE:To provide a stimulable phosphor with higher sensitivity, which comprises an alkaline earth metal halide activated with europium(Eu) and emits accelerated luminescence. CONSTITUTION:A mixture of the raw materials of a phosphor, which has stoichiometrically a relative proportion corresponding to compositional formula: (Ba1-aM<2>a)X2:cEu+dNH4X' (wherein M<2> is Be, Mg, Ca or Sr; X is F, Cl, Br or I; X' is Cl, Br or I; and c is a number in the range of 0.0001<=c<0.1), is fired at 500-1,100 deg.C in a neutral or reducing atmosphere to obtain a europium- activated alkaline earth metal halide represented by compositional formula: (Ba1-aM<2>a)(X1-eX'e)2:cEu2+ (wherein e is a number in the range of 0<=e<0.1). M<1>(monovalent metal) and/or M<3>(trivalent metal) may be used in place of M<2>.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a stimulable phosphor, in particular,
The present invention relates to a method for producing a stimulated phosphor of an alkaline earth metal halide activated with europium (Eu). X
Radiographic images such as line images are widely used for disease diagnosis. This X-ray image is a screen type in which X-rays that have passed through the subject are irradiated onto a phosphor layer (fluorescent screen), which generates visible light, and a film using silver salt is exposed and developed with this visible light. It was obtained as an X-ray photograph. No-screen type X-ray photography is also used. A method using stimulable phosphors has been proposed as a high-sensitivity, high-resolution X-ray system that replaces the method of indirectly or directly recording secondary images of radiation on a film coated with a silver salt photosensitive agent in the form of a sheet. It is being researched and developed. The basic system 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 maintained over a long period of time. When the phosphor in this state is irradiated with the first light that acts as excitation light,
The stored energy is released as second light (emits light). At this time, the first light is not limited to visible light;
A wide range of wavelengths from infrared to ultraviolet light can be used, but the choice of wavelength depends on the phosphor material used. There are also various types of second light, from infrared light to ultraviolet light, which also depends on the phosphor material used.

0002

[Prior Art] Halide-based phosphors activated with rare earth elements are known as stimulable phosphors, and one of them is a europium-activated alkaline earth metal (barium) composite halide phosphor (BaXX':Eu , However, X,
' is at least one kind of halogen selected from the group consisting of F, Cl 2 , Br and I). This phosphor emits near-ultraviolet light (stimulated luminescence) when excited by radiation such as X-rays, electron beams, and ultraviolet rays, and then by electromagnetic waves in the visible to infrared region. Since the intensity of stimulated luminescence is proportional to the intensity of X-rays, a plate (film) coated with phosphor is irradiated with X-rays that have passed through the subject, and this is scanned with a red or infrared laser to obtain the brightness. The exhausted luminescence is converted into an electrical signal using a photomultiplier tube, and this electrical 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. .

(Ba1-x-y-p Srx Cay, Eu p
2+)F(Cl1-a-bBra Ib) (However, x
, y, p, a and b are x+y+p≦1, y≦0.20
, 0.001≦p≦0.20 and a+b≦1) When excited by X-rays, ultraviolet rays, electron beams, etc., this phosphor emits near-ultraviolet light with an emission spectrum distribution peak around 390 nm. (instantaneous luminescence), so it has not only been put to practical use as a phosphor for X-ray intensifying screens, but also when excited by irradiating electromagnetic waves with a wavelength of 500 to 1000 nm after irradiation with X-rays, the emission spectrum distribution is around 580 nm. Since it exhibits near-ultraviolet light emission (stimulated light emission) with a peak of

[0004] The stimulable phosphor as disclosed in the above-mentioned Japanese Patent Publication No. 51-28591 is produced by mixing phosphor raw materials in a predetermined proportion and baking the mixture at a temperature of 600 to 1000°C for an appropriate period of time. Manufactured by.

[0005]

[Problem to be Solved by the Invention] When using a stimulable phosphor in an imaging plate for X-ray photography by molding or coating it, it is desirable to increase the stimulated luminescence intensity at the readout wavelength of the imaging plate (i.e. ,
By increasing the sensitivity of the phosphor to X-rays, it is possible to reduce the amount of X-rays to which the subject is exposed. Therefore, the present invention provides a method for producing a europium-activated alkaline earth metal halide stimulable phosphor with higher sensitivity.

[0006]

[Means for Solving the Problems] The above object is achieved by using (i) BaX2 (ii) EuX3 (iii) NH4X' (iv) M2X2 as raw materials, and stoichiometrically forming the composition formula (I) (Ba1 -a M2a)X2: cEu+dNH4
X'...(I) (wherein, M2 is Be, Mg, C
a, Sr, and X is F, Cl, Br
, I, X' is any of Cl, Br, I, a is a numerical value in the range of 0<a≦1, and c is a value in the range of 0.0001≦c≦0.1 It is a numerical value in the range, and d is a numerical value in the range of 0<d≦0.5. ) A phosphor raw material mixture is prepared so as to have a relative ratio corresponding to 5.
The composition formula (II
): (Ba1-a M2a) (X1-eX'e)2:
cEu2+...(II) (wherein, M2 is Be, M
g, Ca, Sr, and X is F, C
l, Br, I, and X' is Cl, Br
, I, a is a numerical value in the range of 0<a≦1, e is a numerical value in the range of 0≦e<0.1, and c is 0.0001≦c≦0. It is a numerical value in the range of 1. This is achieved by a method for producing a stimulable phosphor, which is characterized in that it is made into a europium-activated alkaline earth metal halide represented by:

[0007] During firing, it is preferable to add ammonium halide gas to the atmospheric gas to create a mixed gas atmosphere. In some cases, raw material (iii)
It is also possible to obtain a stimulable phosphor having a predetermined composition formula by using a mixed gas with ammonium halide gas during firing without using NH4X'. Ammonium halide gases include NH4Cl, NH4Br and NH4
In order to introduce these gases into a designated heating furnace, ammonium halide crystals are heated and sublimated, and then heated using an inert (neutral gas) (helium gas) or reducing gas carrier gas. Preferably, it is transported.

The object of the present invention can be achieved by using one or both of M1X and M3X3 as the raw material (v) instead of the raw material (iv) M2X2 in the above-mentioned method for producing a stimulable phosphor. be done. In such a case, (i) BaX2 (ii) EuX3 (iii) NH4X' (v) M1X and/or M3X3 are used as raw materials to stoichiometrically form the composition formula (III), (V) or ( VII)
(Ba1-f/2 M1f)X2: cEu+dN
H4X'... (III) (Ba1-3h/2 M3
h)X2:cEu+dNH4X'...(V)(Ba
1-(f/2+3h/2) M1f M3h )X2
: cEu+dNH4X'...(VII) (wherein, M1 represents an alkali metal selected from Li, Na, K, Rb, and Cs, and M3 represents Sc
, Y, Ce, Pr, Nd, Pm, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu
, Al, Ga, In, and Tl, and X represents F.
, Cl , Br , I, and X' is Cl
, Br, I. Also, f is 0<f≦0
．． 2, h is a numerical value in the range of 0<h≦0.2, c is a numerical value in the range of 0.0001≦c≦0.1, and d is a numerical value in the range of 0<d≦0. It is a numerical value in the range of .5. ) A phosphor raw material mixture is prepared so as to have a relative ratio corresponding to the composition formula (IV), ( VI) or (VIII) (Ba1
-f/2 M1f ) (X1-gX ′g )2:cE
u2+...(IV) (Ba1-3h/2 M3h)
(X1-i X'i)2:cEu2+...(VI)(
Ba1-(f/2+3h/2) M1f M3h)
(X1-j X'j)2:cEu2+...(VIII
) (wherein, M1 represents an alkali metal selected from Li, Na, K, Rb, and Cs, and M3 represents Sc
, Y, Ce, Pr, Nd, Pm, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu
, Al, Ga, In, and Tl, and X represents F.
, Cl , Br , I, and X' is Cl
, Br, I. Also, f is 0<f≦0
．． 2, h is a numerical value in the range of 0<h≦0.2, g is a numerical value in the range of 0≦g<0.1, and i is a numerical value in the range of 0≦i<0.1. is a numerical value in the range of , and j is 0≦
It is a numerical value in the range of j<0.1, and c is 0.0001≦
It is a numerical value in the range of c≦0.1. ) is a method for producing a photostimulable phosphor, characterized in that it is made into a europium-activated alkaline earth metal halide represented by:

Even in such a case, it is preferable to add ammonium halide gas to the atmospheric gas to create a mixed gas atmosphere during firing. In some cases, it is also possible to obtain a stimulable phosphor having a predetermined composition formula by using a mixed gas with ammonium halide gas during firing without using the raw material (iii) NH4X'. In any of the methods for producing stimulable phosphors, mixing is sufficiently carried out using conventional mixers such as various mixers, V-type blenders, ball mills, rod mills, and the like. If the above-mentioned raw materials are powders or the like, they can be dry mixed using these mixers. If these raw materials are dissolved in water or a solvent to form an aqueous solution or a solution, wet mixing can be performed using these mixers. Furthermore, raw material (i)
An aqueous solution of BaX2, an aqueous solution of raw material (iv) M2X2 or an aqueous solution of raw material (v) M1X, M3X3, and an aqueous activator solution of raw material (ii) EuX3 are wet mixed, dried, and then raw material (iii) NH4X' It is also possible to add powder and mix in a dry method. Further, when the activator raw material is used as a solution, a preparation containing the activator raw material solution may be dried in advance and then mixed and prepared. Note that during wet mixing, it is preferable to remove impurities by means such as filtration.

[0010] The mixed and prepared phosphor raw materials are placed in an alumina crucible,
It is placed in a heat-resistant container such as a quartz crucible or a quartz board, and then heated and fired in a firing furnace. As the neutral (inert) atmosphere in the firing atmosphere, nitrogen gas atmosphere, argon gas atmosphere, helium gas atmosphere, etc. are used, and as the reducing atmosphere, nitrogen gas containing 30% by volume or less of hydrogen gas is used. A mixed gas atmosphere of gas or inert gas is used. The optimum firing temperature differs depending on the type of phosphor raw material, composition (mixing ratio), etc., but as with conventional manufacturing methods, a range of 500 to 1100°C is appropriate.
A range of 0 to 950°C is preferred. Firing temperature is 500
If the temperature is lower than ℃, the diffusion of Eu will not be sufficient;
If the temperature exceeds 1100℃, the phosphor will melt.
Sensitivity is lost. The firing time varies depending on the type of phosphor raw material, composition (mixing ratio), amount filled into the heat-resistant container, firing temperature, etc., but is in the range of 1 minute to 12 hours.
Preferably it is 5 minutes to 2 hours. When pulverizing and classifying the obtained fired body, it is preferable to use it in an atmosphere of dry neutral gas (inert gas or nitrogen gas) to prevent moisture absorption.

[0011] Furthermore, when firing in a neutral or reducing atmosphere, an oxidizing atmosphere is created before firing to give a temperature of 200 to 75
It is desirable to remove organic impurities at a temperature of 0°C.

0012

[Function] The halogen element of the stimulable phosphor has the composition formula (II)
When X=X', the addition of NH4X' promotes concentration adjustment of X and diffusion of Eu, improving sensitivity. Furthermore, in the case of X≠X', by introducing a different type of halogen element, in addition to these promoting effects, the excitation spectrum can be changed. Changes in the spectrum can be controlled by the type and amount of halogen element added, firing conditions, etc.

[0013] If europium does not exist, photostimulability will not be expressed, and it is sufficient to have europium with 0.0001<c, and if c>0.1, concentration quenching (emitted light is absorbed by the phosphor) is sufficient. This is not preferable because a phenomenon in which c is lowered) occurs, and preferably 0.0005<c<0.01.

[0014]

EXAMPLES The present invention will be explained in detail below using embodiment examples and comparative examples. Example 1 Prepare powders of (i) BaBr2 powder; (ii) EuBr3 powder; (iii) NH4Br powder; (iv) CaBr2 powder; these powders were dry mixed in a ball mill for 6 hours, and the lid of the mill was opened. The mixture was vacuum dried at 110° C. for 2 hours, and further mixed in a ball mill for 6 hours. This mixed and prepared phosphor raw material mixed powder was placed in a quartz boat and fired in a tube furnace under the following conditions.

Firing temperature: 840° C. Firing time: 5 minutes Firing atmosphere: Helium gas flow...5 liters/min After firing, it was slowly 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 a phosphor powder. The stimulable phosphor produced in this way has the following composition: Ba0.99Ca0.01Br2:
It was 0.001Eu.

The obtained phosphor powder was placed in a measurement cell with a quartz glass window and irradiated with X-rays, and then a semiconductor laser (780 nm wavelength) was irradiated onto the phosphor in the measurement cell. The generated stimulated light was guided through a filter to a photomultiplier tube, and subjected to photoelectric conversion to determine the intensity of stimulated light emission (PSL). When the PSL intensity of BaBr2:0.001Eu, which will be described later, is 100, the PSL intensity of the obtained stimulable phosphor was 140.

Comparative Example 1 BaBr2:0 was prepared from (i) BaBr2 powder and (ii) EuBr3 powder by the above-mentioned procedure (under the same conditions).
．． 001Eu phosphor is manufactured and stimulated luminescence (
PSL) The intensity was determined and the value was set as 100. Comparative Example 2 The procedure of Example 1 (
Under the same conditions) Ba0.99Ca0.01Br2:
When a 0.001Eu phosphor was manufactured and the PSL intensity was determined in the same manner, it was 116.

Example 2 In Example 1, (iii) the NH4Br powder was removed and the three types of powder were dry mixed in a ball mill for 6 hours, the lid of the mill was opened and the mixture was vacuum dried at 110°C for 2 hours, and then for another 6 hours. Mixed in a ball mill. This mixed and prepared phosphor raw material mixed powder was placed in a quartz boat, placed in a tube furnace into which a mixed gas of helium gas and ammonium halide gas (NH4Br vapor) was introduced, and fired under the following conditions. Note that NH4Br vapor was generated by heating NH4Br powder to 400° C. and sublimating it in a separate electric furnace, and a carrier gas of helium gas was flowed thereto to flow the mixed gas in the tube furnace.

Firing temperature: 840° C. Firing time: 5 minutes Firing atmosphere: 5 liters/minute of helium gas flow containing NH4Cl vapor After firing, it was slowly 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 a phosphor powder. The composition of the stimulable phosphor produced in this way is Ba0.99Ca0
．． 01Br2:0.001Eu, and the stimulated luminescence intensity after X-ray irradiation was measured in the same manner as in Example 1, and the same results as in Example 1 were obtained.

Example 3 Instead of (iv) CaBr2 powder in Example 1, (
v) GdBr3 powder was prepared. Ba0.998Gd0.002Br2 according to the procedure of Example 1 (under the same conditions)
．． 002: 0.001Eu phosphor was manufactured. The stimulated luminescence (PSL) intensity after irradiation with a semiconductor laser (780 nm) after X-ray irradiation was 133.

Comparative Example 3 In the same manner as in Example 2 (iii) without adding and mixing NH4Br powder, Ba0.998Gd0.00
2Br2.002:0.001Eu phosphor is manufactured,
The PSL strength was found to be 108 in the same manner. Example 4 In addition to the four types of powder in Example 3, RbBr powder was additionally prepared, and Ba0.998Rb0.001Gd0.001 was obtained from these five types of powder using the procedure of Example 1 (under the same conditions).
Br2:0.001Eu phosphor was manufactured. Example 1
The PSL strength was determined in the same manner as 135.

Comparative Example 4 Ba0.998Rb0.001 was prepared in the same manner as in Example 4 (iii) without adding and mixing NH4Br powder.
When a Gd0.001Br2:0.001Eu phosphor was manufactured and the PSL intensity was determined in the same manner, it was 115. Example 5 (iii) In Example 1, Ba0.99Ca0.01Br0.95Cl0 was prepared using the procedure of Example 1 (under the same conditions) using NH4Cl powder instead of NH4Br powder.
．． 05:0.001Eu phosphor was manufactured. This PS
The L strength was 115.

Example 6 In place of (iv) CaBr2 powder in Example 1, P
Ba by the procedure of Example 1 (under the same conditions) using bBr
0.998Pb0.002Br2 :0.001Eu
A phosphor was produced. This PSL strength was 110. The above results are summarized in Table 1.

[0024]

[Table 1]

As can be seen from Table 1, when an alkaline earth metal or a monovalent (and/or trivalent) metal other than Ba is added, the PSL strength is slightly improved compared to when it is not added. Stimulable phosphors produced according to the present invention have improved PSL intensity by as much as 30-40%.

[0026]

[Effects of the Invention] As explained above, by using the manufacturing process of animium halide according to the method for manufacturing a photostimulable phosphor according to the present invention, compared to a photostimulable phosphor produced by a conventional manufacturing method, Stimulated luminescence intensity can be increased. If a highly sensitive stimulable phosphor can be obtained in this way, the X-ray exposure dose can be reduced, and the readout light of a semiconductor laser (wavelength 780nm) can be used, making it possible to make X-ray image reading devices more compact. can reduce costs.

Claims (4)

[Claims] Claim 1: Stoichiometrically the compositional formula (I) (Ba1-
a M2a )X2: cEu+dNH4X'...(
I) (where M2 is Be, Mg, Ca, Sr
, X is any of F, Cl, Br, I, X' is any of Cl, Br, I, and a is a numerical value in the range of 0<a≦1. Yes, c is a numerical value in the range of 0.0001≦c≦0.1, and d is 0
It is a numerical value in the range of <d≦0.5. ) A phosphor raw material mixture is prepared so as to have a relative ratio corresponding to 500 to 11 in an inert atmosphere or a reducing atmosphere.
By firing at a temperature in the range of 00°C, the composition formula (II): (Ba1-a M2a ) (X1-eX'e)2:
cEu2+...(II) (wherein, M2 is Be, M
g, Ca, Sr, and X is F, C
l, Br, I, and X' is Cl, Br
, I, a is a numerical value in the range of 0<a≦1, e is a numerical value in the range of 0≦e<0.1, and c is 0.0001≦c≦0. It is a numerical value in the range of 1. ) A method for producing a photostimulable phosphor, characterized in that it is made into a europium-activated alkaline earth metal halide represented by: [Claim 2] Stoichiometrically compositional formula (III) (Ba
1-f/2 M1f)X2: cEu+dNH4X
'... (III) (where M1 is Li, Na,
It represents an alkali metal selected from K, Rb, and Cs, and X is either F, Cl, Br, or I;
X' is any of Cl, Br, I, and f
is a numerical value in the range of 0<f<0.2, and c is 0.00
It is a numerical value in the range of 01≦c≦0.1, and d is 0<d≦0
．． It is a numerical value in the range of 5. ) A phosphor raw material mixture is prepared so as to have a relative ratio corresponding to the composition formula (IV): ( Ba1-f/2 M1f ) (X1-gX'g)
2:cEu2+...(IV) (wherein M1 is Li,
represents an alkali metal selected from Na, K, Rb, and Cs; X is either F, Cl, Br, or I; X' is any of Cl, Br, or I;
Further, f is a numerical value in the range of 0<f≦0.2, and g is
It is a numerical value in the range of 0≦g<0.1, and c is 0.000
It is a numerical value in the range of 1≦c≦0.1. ) A method for producing a photostimulable phosphor, characterized in that it is made into a europium-activated alkaline earth metal halide represented by: [Claim 3] Stoichiometrically the compositional formula (V) (Ba1-
3h/2 M3h)X2: cEu+dNH4X
'...(V) (where M3 is Sc, Y, Ce, P
r, Nd, Pm, Gd, Tb, Dy, Ho,
Er, Tm, Yb, Lu, Al, Ga, I
represents at least one trivalent metal selected from the group consisting of n, and Tl, X is either F, Cl, Br, or I, X' is any of Cl, Br, or I, and h is a numerical value in the range of 0<h≦0.2, c is a numerical value in the range of 0.0001≦c≦0.1, and d is a numerical value in the range of 0<d≦0.5. . ) A phosphor raw material mixture is prepared so as to have a relative ratio corresponding to 50% in an inert atmosphere or a reducing atmosphere.
By firing at a temperature in the range of 0 to 1100°C, composition formula (VI) is obtained.
: (Ba1-3h/2 M3h) (X1-i X'i
)2:cEu2+...(VI) (wherein, M3 is Sc
, Y, Ce, Pr, Nd, Pm, Gd, Tb
, Dy , Ho, Er , Tm , Yb , Lu ,
Represents at least one trivalent metal selected from the group consisting of Al, Ga, In, and Tl, and X represents F, C
l , Br , I, and X′ is Cl , B
r , I, and h is 0<h≦0.2
i is a numerical value in the range of 0≦i<0.1, and c is a numerical value in the range of 0.0001≦c≦0.1. ) A method for producing a photostimulable phosphor, characterized in that it is made into a europium-activated alkaline earth metal halide represented by: Claim 4: Stoichiometrically composed of formula (VII) (Ba
1-(f/2+3h/2) M1f M3h )X2
: cEu+dNH4X'...(VII) (wherein, M1 represents an alkali metal selected from Li, Na, K, Rb, and Cs, and M3 represents Sc
, Y, Ce, Pr, Nd, Pm, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu
, Al, Ga, In, and Tl, and X represents F.
, Cl , Br , I, and X' is Cl
, Br, I. Also, f is 0<f<0
．． 2, h is a numerical value in the range of 0<h≦0.2, c is a numerical value in the range of 0.0001≦c≦0.1, and d is a numerical value in the range of 0<d≦0. It is a numerical value in the range of .5. ) A phosphor raw material mixture is prepared so as to have a relative ratio corresponding to the composition formula (VIII): ( Ba1-(f/2+3h/2)
M1f M3h ) (X1-j X'j )2:cEu
2+...(VIII) (wherein, M1 represents an alkali metal selected from Li, Na, K, Rb, and Cs, and M3 represents Sc
, Y, Ce, Pr, Nd, Pm, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu
, Al, Ga, In, and Tl, and X represents F.
, Cl , Br , I, and X' is Cl
, Br, I. Also, f is 0<f≦0
．． h is a numerical value in the range of 0<h≦0.2, j is a numerical value in the range of 0≦j<0.1, and c is a numerical value in the range of 0.0001≦c. It is a numerical value in the range of ≦0.1. ) A method for producing a photostimulable phosphor, characterized in that it is made into a europium-activated alkaline earth metal halide represented by: