JPH0333187A - Phosphor exhibiting accelerated phosphorescence and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a phosphor exhibiting accelerated phosphorescence with improved luminous sensitivity by mixing raw materials of phosphor so as to provide the proportions corresponding to a specified constitutional formula and sintering the mixture in a reducing atmosphere. CONSTITUTION:Raw materials of phosphor are mixed so as to provide the proportions corresponding to a constitution of formula I (wherein MA and MB are each Mg, Ca, Sr or Ba; MC is Li, Na, K or Rb; MD is Sc, Y, La, Gd or Lu; XA to XD are each Cl, Br or I except for the case where XA and XB are the same; 0.4<x<0.6: 0<y<0.2; -0.5<delta<0.5; 0.001<z<0.05), and the mixture is sintered in a reducing atmosphere, thus giving a phosphor exhibiting accelerat ed phosphorescence which consists of crystals having a constitution of the formu la, stores energy in the crystals when irradiated with a radiation, emits light with accelerated phosphorescence when excited with light, and has improved luminous sensitivity.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to improve the luminescence sensitivity of a phosphor that exhibits photostimulable luminescence.
)(1-y)(MCXc-(1+δ)M”
A photostimulable firefly characterized by using a crystal represented by zEu!+, storing energy in the crystal by irradiation with radiation, and emitting photostimulable light by photoexcitation. Constitutes a light body.

[Industrial application field]

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

An X-ray image conversion sheet using a photostimulable phosphor 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 improve sensitivity, and compared to the past, inspections can now be performed using a smaller amount of X-rays without causing compression.

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 less than several tenths of a liter compared to the conventional method.

As you can see, the X-ray image conversion sheet is a sheet that uses a photostimulable phosphor 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 phosphor constituting 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, the stimulable phosphor 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 phosphors, and divalent europium-activated barium chloride bromide (BaCI Br) is a photostimulable phosphor with excellent properties.
: nu"") 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 the impurity level in the forbidden band is immediately excited. It becomes depressed and stabilizes.

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 per impurity unit.

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 stimulable phosphors, Eu" is an effective element in forming luminescent centers, and is produced by reduction of Eu compounds such as europium bromide (EuBr+).

Specifically, barium chloride (BaCl), barium bromide (BaBrz), and BaBr2 are dissolved in distilled water, then evaporated to dryness, and this mixture is dissolved into hydrogen (H) and nitrogen (N).
A photostimulable phosphor made of BaCI Or :Eu'' is formed by reduction firing at a temperature of 800 to 900° C. in a mixed gas flow of step t).

Next, after crushing this phosphor, this powder and binder (
For example, make a coating liquid by kneading polymethyl methacrylate (PMMA) and a solvent (e.g. toluene), apply this uniformly on a resin film, dry the solvent, and then apply a resin film (e.g. mylar) on top of this. ) is attached to make an X-ray image conversion sheet.

However, there is a strong desire to further reduce the amount of irradiated X-rays, and improvements are being sought.

[Problem to be solved by the invention]

Medical diagnosis and materials! 1M! As the frequency of use of X-ray image sheets increases, there is a growing demand to further reduce the amount of X-rays irradiated.

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

[Means to solve the problem]

The above problem is ((1-x)MAXA□ ・xM”X”□) (1-
y) (MCXC・(1+δ) ”XD:l) y/
2: zEu2+ (1) However, MA and Ml are magnesium (Mg), calcium (C
a) MA and MB are magnesium (Mg), calcium (
MC is lithium (Li) or barium (Ba), M
C is an element consisting of either lithium (Li) or sodium (Na), and Me is an element consisting of scandium (Sc) or yttrium (Y
).

An element consisting of lanthanum (La), gadolinium (Gd) or lutesilanthane (La), XA
, Xll, XC, and XD are halogen elements consisting of chlorine (Clfi), bromine (Br), or iodine (1), and there is no case where XA and Xl 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 < 0.2, δ in the range -0.5 < δ < 0.5, and 2 in the range 0.0001 < z < 0.05, this is achieved by irradiation with radiation. It is a photostimulable phosphor that stores energy in a crystal and emits photostimulable light upon photoexcitation, and the manufacturing method is such that the composition ratio corresponds to the composition formula (1). This problem can be solved by a method of manufacturing a phosphor that exhibits stimulable luminescence by mixing phosphor raw materials and sintering the mixture in a reducing atmosphere.

[Effect]

The present invention is based on "BaCI Br: tiu"& 1lt
As a method of increasing the sensitivity of the conventional photostimulable phosphor (c), some of the constituent elements are replaced with elements of the same group, and valence control is performed.

The method is as follows.

■, Partial replacement of constituent elements, If) A part of Ba is Mg, which belongs to the same group IIa in the periodic table.

Replace with either Ca or Sr.

In formula (1), these elements are shown as MA and M''.

1 2) Br, Cm! Partial substitution is performed by adding ■ to the halogen element consisting of.

In formula (1), the elements are XA , XB , X
Shown as C.

(2) Valency control, 1l-1) Replace divalent Ba with a monovalent element and a trivalent element.

Here, as a monovalent element, L t + Na + K
+Rb is suitable, and the element to be detected is MC in formula (1).
It was shown as

In addition, trivalent elements include Sc, Y, and La.

Gd and Lu are suitable, and the element is M in formula (1).
Indicated as O.

Next 1. In order to make a construct with such valence control neutral, it is necessary to adjust the number of added atoms, and this number is expressed as δ in equation (1).

By changing the ionic radius of the atoms constituting the photostimulable phosphor as described above and controlling the valence, the number of impurity levels forming the photostimulable phosphor increases, and therefore the radiation Since the number of electrons trapped by irradiation increases, higher sensitivity becomes possible.

Next, huh! The method for producing the stimulable phosphor is to weigh the phosphor raw materials as shown in the composition formula shown in equation (1), and use a conventional mixer, type blender, Pall kil, Ronde kettle, etc. Mixing is performed using a mixer.

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 a 20,000-inch alumina crucible.
The Eu-activated alkaline earth composite halide phosphor of the present invention uses divalent Eu as an activator, so it is filled in a heat-resistant container such as a quartz boat and placed in a firing furnace for firing. It is necessary to reduce the trivalent Eu added as divalent Eu.

Therefore, it is essential to use a reducing atmosphere, such as 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.

Next, the firing temperature varies depending on the type and composition of the phosphor raw material, but the same temperature as in the past is used, from <600 to 1000°C, and 700 to 950°C is particularly suitable.

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: ((BaC1z)o, 4s(BaBrz
) o, 5o (LiCI 5cC1z) o, ozs:
O,0OZELI] (D production example molar ratio, target value m
Each raw material was weighed so as to match the acid ratio, and mixed in a bowl for 12 hours.

Here, Eu is added from EuCl3 as a raw material.

The phosphor raw material made in this way was put into a quartz boat,
This was kept at 882°C, and He containing 20% by volume of N2 was heated.
Place the gas in a tube furnace with a flow rate of 101/min,
Firing was carried out for several minutes, and after the firing was completed, it was cooled to room temperature in the same atmosphere.

The obtained phosphor was sintered, so it was crushed in a Baba mortar to give (BaC1z)o, 4s(BaBrz)o, 5o(Li
C1-3cCI3) o, ozs:. , 002EL
A powder (■) having a composition ratio of I 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 11: Raw materials were weighed in the same manner as in Example 1 to achieve the target composition ratios, and fired in the same manner as in Example 1 to produce phosphors having composition ratios of ① to ②.

(BaC1z)o, as(BaBrz)o, 5a(Na
C11, acls) o, ozs: o, ooJu
”'■(BaCIz)o,
4s(BaBrz)o, 4s(K CI 5cC1t
) o, os: o, oosEu
...■(BaC1z)ols(BaBrz
)ols(K Br -5cBr3)o, os: o
, ootEu
... ■ (BaC1z) o, N5 (BaBrz) o, 5
o(RbCI ・YCl3)0.025: o, o
BEu...,■
(BaC1z)o, N5(BaBrz)o, 5o(Rb
Br -YBr3) o, ozs: o, o6zEu
・,,■(Ba
C1z) o, so (BaBrz) 0.45 (
NaC16,q ・LuCl:+) 0.025: o
, ooJLI
-(D(BaC1z)o, N5(BaBrz)o, 5o
(LiC1-LuC1:+)o, ozs: o, oo
Ju-@(Ba
C1z)o, 4s(BaBrz)o, 5o(RbC1-
LaC13) o, ozs: o, (,6zEu
・・・――■(BaC1x
)o, 4s(BaBrz)o, 4s(RbC1-LaC
1:+) o, os: o, oozBu
”'(1!D(BaC1t)o
, 4o(BaBrz)o, 4s'(RbCI La
C13) o, ots: o, ooz, Eu
A phosphor powder with a phosphor size of 780n111 was irradiated with X-rays, and the resulting stimulated light with a wavelength of 400nm was detected using a photomultiplier tube.

Comparative example: ((BaC1z)o, 5o(BaBrz)o
,so: O,0OIt! Production example of u) The raw materials were weighed so that the target composition ratio was obtained in the same manner as in Example 1, and the same method as in Example 1 was performed by baking and pulverizing.
I made a certain amount of phosphor.

Table 1 Next, this phosphor powder was irradiated with X-rays, and the wavelength was 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).

As can be seen from this result, superior sensitivity can be obtained depending on the composition, and in particular, those in which BaCl and BaBr are replaced with RbCl and LaCl3 have improved sensitivity, which is advantageous for readout with a semiconductor laser. I understand that.

〔Effect of the invention〕

By implementing the present invention, stimulated luminescence at a wavelength of 780 nm, which is advantageous for readout using an 11 semiconductor laser, has been improved, so the amount of X-ray irradiation for diagnosis can be reduced.

Claims (2)

[Claims] (1) A photostimulable phosphor 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. {(1-x)M^AX^A_2・xM^BX^B_2}
(1-y)・{M^CX^C・(1+δ)M^DX^D
＿3｝y/2:zEu^2^+(1)...(1) However, M^A and M^B are magnesium (Mg), calcium (
Ca), strontium (Sr) or barium (Ba)
), M^C is an element consisting of lithium (Li), sodium (Na), potassium (K), or rubidium (Rb), M^b is scandium ( Sc), Yttrium (Y),
An element consisting of lanthanum (La), gadolinium (Gd) or lutetium (Lu), X^A,
^B, X^C, and X^D are halogen elements consisting of chlorine (Cl), bromine (Br), or iodine (I), and there is no case where X^A and X^B are the same. x is in the range 0.4<x<0.6, y is in the range 0<y<0.2, δ is in the range -0.5<δ<0.5, z is 0.0001<z<0 In the range of .05, the value of . (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 .