JPH0341187A - Phosphor with accelerated phosphorescence and its preparation - Google Patents

Abstract

PURPOSE:To cause accelerated phosphorescence to occur when irradiated with a radiation and improve the sensitivity by mixing raw materials corresponding to a specific formula of compsn. and sintering the mixture in a reducing atmosphere. CONSTITUTION:Raw materials, in which the ratio among the components contained corresponds to the formula of compsn. of a phosphor to be produced, are mixed, and sintered at 600-1000 deg.C for 1-12hr in a reducing atmosphere, such as N2 atmosphere contg. 30vol.% or lower H2 or a mixed gas of CO with N2, to produce the phosphor which comprises a crystal having the compsn. of the formula (wherein MA and MB are each Mg, Ca, Sr, or Ba; MC is Li, Na, K, Rb, or Cs; XA, XB, and XC are each Cl, Br, or I, and XA and XB are different from each other; 0.4<(x)<0.6; 0<(y)<0.1; and 0.0001<(z)<0.02), stores energy in the crystal when irradiated with a radiation, and shows accelerated phosphorescence by photoexcitation.

Description

[Detailed Description of the Invention] [Summary] For the purpose of improving the luminescence sensitivity of the mixture for photostimulable luminescence, (MAXAz)(1x)(MIIXB2)x(Mc
Using a crystal represented by Xc)y:zBi, a photostimulable fluorophore is constructed which is characterized by accumulating energy in the crystal by irradiation with radiation and emitting photostimulable light by photoexcitation.

However, MA and MB are elements consisting of any one of Mg, Ca, Sr, and Ba, MC is an element consisting of any one of Li, Na, K, Rh, and Cs, XA XB Xc is CCBr, There is no case where XA and X11 are the same in any of the halogen elements I.

X is in the range of 0.4 < x < Q, 6, y is in the range of Q <
The range is y<0.1, and Z is the range 0.0001<z<0.02.

[Industrial application field]

The present invention relates to a photostimulable fluorophore with improved luminescence sensitivity and a method for producing the same.

An X-ray image conversion sheet using photostimulable fluorophore is combined with a digital image processing device to constitute an X-ray photography system.

That is, although X-rays are used in a wide range of fields such as human body diagnosis and material forensics, their greatest use is in X-ray diagnosis.

Diagnosis is performed by taking X-ray photographs and fluoroscopy, but since X-rays are radiation and are harmful to the human body, it is necessary to reduce the exposure dose as much as possible. Improvements have been made to increase sensitivity, and inspections can now be performed using an incomparably smaller amount of X-rays than in the past.

However, if you try to increase the sensitivity of the film, it is inevitable that the image quality will deteriorate.

On the other hand, recently developed X-ray photography systems use an X-ray image conversion sheet and a computer to process images. Specifically, they use an X-ray image conversion sheet instead of conventional film to take images. , the X-ray image imprinted on the sheet is converted into an electrical signal using a laser beam, and then this signal is processed by a computer, and this information is converted into the intensity of the laser beam to create a normal photograph. An X-ray photograph is formed by transferring it to film.

According to such a method, a clear image can be obtained with a dose that is several tenths or less compared to the conventional method.

The X-ray image conversion sheet is a sheet that uses photostimulable fluorophore as a photosensitive material, which can temporarily store radiation energy and then emit fluorescence again when excited by heat or light.

The present invention relates to a photostimulable fluorophore used in such an X-ray image conversion sheet and a method for producing the same.

[Conventional technology]

X-ray image conversion sheets are made by baking a mixture of alkaline earth metal halides and europium halides (Eu) on a transparent resin film such as polyethylene terephthalate film (hereinafter commonly referred to as Mylar) in a reducing gas. A divalent europium-activated alkaline earth metal halide phosphor is prepared, a visible photostimulable fluorophore is mixed with a binder and applied onto a base film, and an adhesive is applied on top of this. It is used in sheet form by pasting a thin film of Mylar.

Various studies have already been conducted on such photostimulable fluorophores, and divalent europium-activated barium chloride bromide (BaCE Br
: Eu2”) has been announced.For example, (JP-A-6L
-78892).

The principle of photostimulable fluorescence is that when a phosphor crystal is irradiated with X-rays, electrons in the valence band are excited to the conduction band, but immediately become impurity units in the forbidden band. Depress and stabilize.

This corresponds to the accumulation record of X-ray energy.

Next, when a laser beam is irradiated for reading, the electrons in the impurity level absorb the energy of the laser beam and are excited to the conduction electron band, and then fall back to the valence band, but at this time, the fluorescence is emitted. The body emits fluorescence, and its brightness is proportional to the amount of captured electrons in the impurity level.

Based on the above, the surface of the X-ray image conversion sheet is scanned with a tiny spot (100 μm in diameter) of laser light, the fluorescence emission of each pixel is detected using an interference filter, and then converted into an electronic signal using a photomultiplier tube. It is to be recorded.

In such photostimulable fluorophores, Eu'' is an effective element in forming luminescent centers, and is produced by reduction of Eu compounds such as europium bromide (EuBri).

Specifically, barium chloride (BaCl1z), barium bromide (BaBrz), and EuBr are dissolved in distilled water and then evaporated to dryness, and this mixture is converted into a mixed gas stream of hydrogen (N2) and nitrogen (N2). BaCI Br:Eu" by reduction firing at a temperature of 800-900'C
A photostimulable fluorophore consisting of is formed.

Next, after crushing this phosphor, this powder and binder (
For example, make a coating solution by kneading polymethyl methacrylate (PMMA) and a solvent (for example, toluene), apply this uniformly on a resin film, dry the solvent, and then apply a resin film (for example, Mylar) on top of this. ) is attached to make the xilIA double image conversion sheet.

The photostimulable fluorophore forming the conventional X-ray image conversion sheet is thus converted into divalent E+i activated barium chloride bromide CBa.
The basic composition formula is C1Br:Eu''), and a photostimulable fluorophore having the following composition formula has also been proposed.

(Special Publication No. 5l-28591) (Ba+-a-b-p Sr x Ca y Eu p
”)F(CI+-a-b Br@I) However, x +y +p ≦1. y≦0.20
o, oot ≦p ≦0.20, a + b
≦1 However, there is a strong desire to further reduce the amount of irradiated X-rays, and there is still a need for improvements in the layer.

[Problem to be solved by the invention]

As the frequency of use of X-ray image sheets increases in medical diagnosis, material forensics, etc., there is a growing demand to further reduce the amount of X-rays irradiated.

Therefore, the challenge is to put photostimulable fluorophores with even higher sensitivity into practical use.

[Means to solve the problem]

The above problem is (MAX XAz ) (l x) (M"X'
z)x(McXc) 3': zBi
-(1) However, MA and M8 are elements consisting of any one of Mg, Ca, Sr, and Ba, and MC is an element consisting of any one of Li, Na, K, Rh, and Cs. XA, Xl, and XC are halogen elements consisting of any one of C1, Br, and 4, and there is no case where XA and X11 are the same.

X is in the range of 0.4 < x < 0.6, y is in the range of O <
Using a crystal in the range of y < 0.1 and 2 in the range of 0.0001 < z < 0.02, energy is accumulated in this crystal by irradiation with radiation, and photostimulable light emission is generated by photoexcitation. This production method involves mixing the phosphor raw materials so that the composition ratio corresponds to the composition formula (1), and then converting this mixture into a reducible fluorophore. The problem of photostimulable luminescence can be solved by sintering in an atmosphere and using a manufacturing method to obtain the mixture.

[Effect]

The present invention is a method for increasing the sensitivity of conventional photostimulable fluorophores whose basic composition is BaCQ Br:Eu". In addition to controlling the valence by changing the activating element that is the center of luminescence from Eu to Bi, , in which some of the constituent elements are replaced with elements of the same group.

The method is as follows.

I, Partial replacement of constituent elements, II) Part of Ba is replaced with MgCa, which is the same group a in the periodic table,
Replace with either Sr.

These elements are shown as MA and Ml in formula (1).

1-2) Partial substitution is performed by adding ■ to a halogen element consisting of Br and Cf.

The visible elements are shown in formula (1) as XA, Xs, )<c.

(2) Atomic valence control, 1l-1) Adding a monovalent element to trivalent Bi makes it substantially equivalent to bivalent Bi.

Here, the monovalent elements are Li, Na, and K.

Rb and Cs are suitable, and these elements are shown as Mc in formula (1).

As described above, the ionic radius of the atoms constituting the photostimulable fluorophore is changed and the activating element is changed from the conventional Eu to Bi to control the valence. The number of impurity levels that form photoextension increases, and therefore the number of electrons trapped by radiation irradiation increases, making it possible to achieve higher sensitivity.

Next, as for the production method of the photostimulable fluorophore, the phosphor raw materials are weighed as shown in the composition formula shown in formula (1), and then mixed using various ξxer 5V type blenders, ball mills, rod mills, etc. Mixing is done using a machine.

Incidentally, since the phosphor raw material is hygroscopic, it is preferable to carry out the adjustment and mixing in a dry atmosphere or an inert gas atmosphere.

Next, the mixed phosphor raw materials were placed in alumina crucible 1 and crucible 2.
The material is filled into a heat-resistant container such as a quartz boat and placed in a firing furnace for firing. However, when firing in the air, the phosphor is oxidized, so firing is performed in a reducing atmosphere or an inert atmosphere.

Here, as the reducing atmosphere, a nitrogen gas (N2) atmosphere containing 30% by volume or less of hydrogen gas (N2), a mixed gas of -carbon oxide (CO) and N2, etc. are used.

Next, the firing temperature varies depending on the type and composition of the phosphor raw material, but the same temperature as before is used, which is <600-1000'C.
Particularly suitable is 700 to 950'C.

In addition, the firing time depends on the type and composition of the phosphor raw material, the firing temperature,
It takes 1 to 12 hours, although it varies depending on the degree of filling of the container.

Furthermore, since the phosphor obtained by sintering is sintered, it requires pulverization and classification, but since moisture absorption occurs in this process as well, it is necessary to carry out the process in a dry atmosphere.

〔Example〕

Example 1: ((BaCIz)o, as(BaBr
z) o, 5s (NaCI) o, o.

2:. , ooIBi ] Each raw material was weighed so that the molar ratio would reach the target composition ratio, and mixed in a bowl for 12 hours.

Here, Bi is added as B1Cl, 1 or old 203.

The phosphor raw material made in this way was put into a quartz boat,
This was maintained at 882°C and t(
Place the e-gas in a tube furnace at a flow rate of 101/min, and
Firing was carried out for 0 minutes, and after the firing was completed, it was cooled to room temperature in the same atmosphere.

Since the obtained phosphor was sintered, it was ground in a mortar made of Ll to give (BaCIz)o, 4s(BaBrz)o, 5s(Na
CI) o, ooz: Powder (■) having a composition ratio of 0.001Eli was obtained.

Next, this phosphor powder is irradiated with X-rays, which have a wavelength of 7
A semiconductor laser of 80 nm was irradiated, and the resulting stimulated light with a wavelength of 400 nm was detected using a photomultiplier tube.

Examples 2 to 15: Raw materials were weighed in the same manner as in Example 1 to achieve the target composition ratio, and fired in the same manner as in Example 1 to produce phosphors having a composition ratio of 1 to 0.

(BaCIz) o, as (BaBrz) o,
ss (NaCI) 0.002 (BaCIz) o,
so (BaBrz) 0.5o (LiCI) o
, ooz (BaC1z) o, so (rlaBr
z) o, so (K C1) 0.002 (BaC
1z)o, 45(BaBrz)o, 5s(RhBr)
o, 002 (BaClz) o, so (BaBr
z) o, so (CsCI)o. 002(BaC1
z) o, 45 (BaBrz) o, ss (C
sBr) o, ooz(BaC1z)o, as(Ba
Brz) o, 5s (Cs I) o, ooz (BaC1□
) 0.45 (BaBrz) o, ss (RbBr
) o, oos(Ba(', lz) o, as (
BaBrz) o, ss (RbBr) o, o
＋.

(BaCIz) o, so (BaBrz) o,
so (CsC1) o, ooz:. ,. . , Bi...■ :o,. . Ji...■:. ,ooosBi...■ ' o,ooIBi...■: o,oo+8! ...■ ' o,ooIBi ...■:. ,. . IBi...■:. ,ooIBi...■;. , ooIBi ... [phase] o, oosRi ... ■ (CaCIz) o, 5o (SrBrz) o, 5o (
C3CI) o, ooz: o, ooJi...
@ (MgC1z)o, 5o(BaBrz)o, 5o(Rb
Br) o, ooz : o, oo+Bi...@ (BaCIz) o, 5o (BaBrz) o, 5o (Cs
CI) o, oz: o, oo+Bi... [phase] (BaC1z) o, 4s (BaBrz) o, 5s (Rb
Br) o, oz :O, GOIIlt...■ The above phosphor powder is irradiated with X-rays, and the wavelength is 780.
The sample was irradiated with a 400 nm wavelength semiconductor laser, and the resulting stimulated light with a wavelength of 400 nm was detected using a photomultiplier tube.

Comparative example: ((BaCIz)o, 5o(BaBrz)
o, so: 0.001t! Production Example of Ll) As in Example 1, raw materials were weighed so as to have the target composition ratio, fired as in Example 1, and then ground to produce a phosphor having a conventional composition ratio.

Next, this phosphor powder is irradiated with X-rays, which have a wavelength of 7
A semiconductor laser of 80 nm was irradiated, and the resulting stimulated light with a wavelength of 400 nm was detected using a photomultiplier tube, and this sensitivity was defined as the standard sensitivity.

Table 1 compares the sensitivity of this comparative example with the sensitivities of Examples (1) to (2).

Table 1 As can be seen from the results, it is possible to obtain sensitivity superior to the conventional one depending on the composition, and it is found that it is advantageous for readout using a semiconductor laser.

[Effects of the Invention] By implementing the present invention, stimulated luminescence at a wavelength of 780 nm, which is advantageous for readout using a semiconductor laser, has been improved, so the amount of X-ray irradiation for diagnosis can be reduced.

Claims (2)

[Claims] (1) A photostimulable fluorophore comprising a crystal represented by the following compositional formula, which stores energy in the crystal upon irradiation with radiation and emits stimulable light upon photoexcitation. (M^AX^A_2) (1-x) (M^BX^B_2)
x(M^CX^C)y:zBi...(1) However, M^A and M^B are magnesium (Mg), calcium (
Ca), strontium (Sr) or barium (Ba)
), M^C is an element consisting of any one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs), X ^A, X^B, X^C are chlorine (Cl), bromine (Br)
Or, it is a halogen element such as iodine (I), and there is no case where X^A and X^B are the same. x is in the range of 0.4<x<0.6; y is in the range of 0<y<0.1; z is in the range of 0.0001<z<0.02. (2) After mixing the phosphor raw materials so as to have a composition ratio corresponding to the composition formula (1) described in claim (1), the mixture is sintered in a reducing atmosphere to produce photostimulable luminescence. 1. A method for producing a phosphor, characterized by obtaining a phosphor exhibiting .