JPS5944332B2 - thermal fluorescent phosphor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermally fluorescent phosphor, and more particularly to a lithium borate-based thermally fluorescent phosphor.

Copper-activated lithium borate phosphor (Li2B407:C
There is u).

This phosphor, like lithium fluoride phosphor (LiF:Mg) and beryllium oxide phosphor (BeO), has low atomic numbers of its constituent elements and is close to the effective atomic number of living organisms, so it has radiation absorption properties. Thermal fluorescence dosimeters using this fluorophore have the advantage of being easy to measure the absorbed dose of living tissue, but the thermal fluorescence efficiency is extremely low, making it difficult to detect radiation. A curve that plots the low sensitivity and the intensity of the thermal fluorescence emitted when the phosphor is heated against the heating temperature (hereinafter this curve will be referred to as the "glow curve").
Its peak temperature is low, so it has the disadvantage of large fading when used as a thermal fluorescence dosimeter.
There were problems when using this phosphor as a thermal fluorescent dosimeter. The present invention uses a thermofluorescent fluorescent material whose effective atomic number is close to that of living tissue, whose radiation absorption characteristics are relatively similar to those of human soft tissue, and whose thermal fluorescent efficiency is higher than that of the Li2B407:CU phosphor. The purpose is to provide a light body.

A further object of the present invention is to provide a thermally fluorescent phosphor that has a higher main peak temperature in its glow curve and less fading than the Li2B407:CU phosphor.

In order to achieve the above object, the present inventors investigated various co-activators for Li2B4O7:CU phosphor, and found that if indium (In) is co-activated to Li2B407:CU phosphor, Li2B407:CU fluorophore will emit light. It is possible to obtain a thermofluorescent phosphor that exhibits thermal fluorescence with higher efficiency than that of a Li2B4O7:CU phosphor, and furthermore, by coactivating In and silicon (Si) to a Li2B4O7:CU phosphor, Li2B, O, :Cu phosphor can be obtained. In addition to exhibiting thermal fluorescence with higher efficiency than that of the photoreceptor, Li2B4
It was discovered that a thermally fluorescent phosphor having a main peak of the glow curve on the higher temperature side than the phosphor No. 07 and less fading could be obtained, and the present invention was completed.

The thermal fluorescent phosphor of the present invention has a compositional formula of It is expressed as

Particularly when paying attention to the thermal fluorescence intensity, X and y in the above composition formula are 3X10-4 and 3
It is more preferable that the Z value be in the range of x10-4≦y≦3X10-2, and in order to move the position of the main peak temperature of the glow curve to the high temperature side, the Z value should be in the range of 5×10-3≦z≦5X1.
More preferably, it is in the range of 0-2. The thermofluorescent phosphor of the present invention is manufactured by the manufacturing method described below. Commercially available lithium borate (Li2
Copper oxide (CuO) was used as the activator raw material.
) or a compound of copper that can easily be converted to CuO at high temperatures, indium oxide (In2O3) or In2 that can be easily converted to CuO at high temperatures.
Compounds of indium and silicon oxide (
SiO2) or a silicon compound that can be easily converted to SiO2 at high temperatures is used. The above raw materials are stoichiometrically Li
2B4O7:XCU. yIn,. ZSi (however, X, .
y and Z are each 10-5≦X≦5X0; y≦8X
10-2 and 0≦Z≦3×10-1).

Note that lithium borate (Li) is used as the starting material for the phosphor matrix.
2B4O7) instead of using lithium oxide (Li2O
) or lithium compounds that can be easily converted to Li2O at high temperatures, such as lithium carbonate (Li2CO3) and lithium nitrate (LiNO3), and high-temperature compounds such as boron oxide (B2O3), boric acid (H3BO3), and ammonium borate {(NH4)2B407}. easily B2O3
These raw materials are converted into Li2O using a boron compound that can be converted into
and B2Ol mole when converted to B2O3
It may be mixed with the above activator raw material at a ratio of 2 mol of 2O3.

After each raw material is thoroughly mixed using a mortar or the like, it is filled into a heat-resistant container such as an alumina crucible, a platinum crucible, or a quartz crucible, and fired.

Firing is performed in two ways as described below. One is to bake in air at a temperature of 750°C to 850°C for 30 minutes to 3 hours, and then rapidly cooled, and the other is to bake in air at a temperature of 950°C to 1000°C for 30 minutes to 2 hours.
After firing for a time and melting it, it is taken out on a metal plate such as stainless steel and rapidly cooled. The resulting glass-like fired product is crushed in a ball mill, mortar, etc., and then heated to 600°C to 800°C.
This method involves heat treatment at a temperature of 30 minutes to 2 hours, followed by rapid cooling.

Although either of the above two methods may be employed, better results can be obtained with the former method. Incidentally, if the fired product obtained by the above method is re-fired in an inert gas atmosphere such as argon gas, the thermal fluorescence intensity may be further increased. In this case, the firing temperature and firing time are suitably 750°C to 850°C for 30 minutes to 3 hours. After the above-mentioned firing, the fired product is washed and sieved to obtain a powder phosphor having a uniform particle size. , thus the composition formula L
i2B4O7:XCUlyIn. zSi (However, X.y
and z have the same definitions as above) is obtained.

C which is one of the activators in the thermally fluorescent phosphor of the present invention
As in the case of the Li2B4O7:CU phosphor, the concentration of u (x value) is such that when Z is 10-5 or less and when Z is 5X10-2 or more, the thermal phosphor efficiency of the obtained phosphor is The preferred range of X value is 10-5≦X〈5×10-2, which is extremely low and impractical for use in thermal fluorescence dosimeters.
Particularly good results can be obtained when the range is 3 x 10-4 x ≦ 8 x 10-3.

Figure 1 shows Ll2B, which is one of the thermofluorescent phosphors of the present invention.
4O7: 0.003Cu. 2 is a graph showing the relationship between the concentration (y value) of In, which is a co-activator, and the thermal fluorescence intensity in a yIn phosphor.

The vertical axis of the graph is expressed as a relative value when the thermal fluorescence intensity when n is not included (y-0) is taken as 100, and the thermal fluorescence intensity is the height of the peak of the glow curve that appears at approximately 145°C. It is compared with As is clear from Figure 1, Ll2
B4O7: 0.001Cu. As the y value increases in the yIn phosphor, the thermal fluorescence intensity gradually increases, reaching 3 x 10-3
The thermal fluorescence intensity reaches a maximum near this point, but as the y value increases further, the thermal fluorescence intensity decreases, and when the y value exceeds 8X10-2, it becomes lower than that of the Ll2B4O7:0.001CU phosphor that does not coactivate In. This tendency is almost the same regardless of the concentration of Cu as an activator, and in addition to In as a co-activator, Si
When using , the main peak temperature of the glow curve moves to a higher temperature side, but when comparing the height of the main peak of the glow curve, the relationship between In concentration (y value) and thermal fluorescence intensity is almost the same as that shown in Figure 1. The results showed the same trends as shown in . In this way, Li2B4O
7: By coactivating In to the CU fluorophore, Li2
The thermal fluorescence intensity of the B4O7:CU phosphor can be increased, but the range of In concentration (y value) in which a higher thermal fluorescence intensity can be obtained than that of the Li2B4O7:CU phosphor is O<y≦
8×10−2, and a more preferable In concentration range is 3×
10-4≦y≦3X10-2. Figure 2: Thermofluorescent phosphor of the present invention and conventionally known Li2B4O7:CU
The glow curves of the phosphors are shown, and curves A, b, e and d are Ll2B4O7:0.003Cu, . 0
．． 0021n phosphor, Ll2B4O7:0.003Cu
10.0021n10.005Si phosphor, Ll2B4
O7: 0.003Cu, 0.0021n,. 0.015
Glow curves of Si phosphor and Ll2B4O7:0.003Cu phosphor.

As is clear from Fig. 2, co-activation of n to the Li2B4O7:Cu phosphor increases the thermal fluorescence intensity, but the peak temperature of the glow curve is approximately 145°C, similar to the Li2B4O7:Cu phosphor. Its position does not change much. However, when Li2B4O7:CU is co-activated with Inl and Si at the same time, for example, as shown in curve b in Figure 2,
In addition to this, a glow curve peak appears near 230°C, and as the amount of Si added (z value) increases, the glow peak near 230°C becomes relatively higher than the glow peak near 145°C. The main peak of the glow curve is approximately 230℃
Move to. The glow peak near 230°C is relatively higher than that near 145°C, and the main peak is when the z value is 5X10-3 or more, and when the z value increases further, the main peak is 230°C. The glow peak intensity near 145°C becomes relatively stronger than that near 145°C.

However, when the z value exceeds approximately 10-2, the glow curve hardly changes, and when the z value exceeds approximately 5X10-2, the thermal fluorescence intensity gradually weakens to 3X10-1.
In the above, the thermal fluorescence intensity of the obtained phosphor is Li2B4O7
: It is weaker than that of CU phosphor, which is not preferable. Therefore, in the case of a phosphor that uses Si as a co-activator together with In, S
The i concentration (z value) is preferably 3X10-1 or less, particularly preferably in the range of 5X10-3 x Z<5X10-2. In addition, in order to shift the main peak of the glow curve of the Li2B4O7:CU phosphor to the high temperature side, it is necessary to coactivate In and Si.
:When a CU phosphor is coactivated with only In or only Si, no shift in the peak position of the glow curve is observed, so Si added as a coactivator is combined with In to create a new trap. It seems that it forms the
To shift the position of the main peak of the glow curve of the Li2B4O7:CU phosphor, In and S are used as in the phosphor of the present invention.
Similar results can be obtained by coactivating silver (Ag) and Si instead of coactivating i.

As described above, the thermal fluorescent phosphor of the present invention has a sensitivity 4 to 5 times that of the conventionally known Li2B4O7:CU phosphor, and is also more sensitive than the Li2B4O7:Cu phosphor. The main park of the glow curve is located on the higher temperature side.

Therefore, by using the phosphor of the present invention as a thermal fluorescent dosimeter, it is possible to measure lower doses of radiation than with a thermal fluorescent dosimeter using a Li2B4O7:Cu phosphor. Thermal fluorescence dosimeters also have good fading characteristics. Next, the present invention will be explained with reference to Examples.

Example 1 The above phosphor raw materials were thoroughly mixed in a ball mill, then filled into an alumina crucible, placed in a high-temperature electric furnace, and heated at 830 °C in air.
It was baked for 2 hours at a temperature of °C.

The obtained baked product was crushed, washed with warm water, dried, and sieved to make the particle size uniform.Ll2B4O7:
A 0.003Cu10,002n phosphor was obtained.

The thus obtained phosphor exhibits thermal fluorescence with a glow curve peak at approximately 145°C, and the thermal fluorescence intensity after irradiation with 60C0 gamma rays is Ll when compared in terms of peak height.
It was about 4.8 times that of 2B4O7:0.003Cu. This Li2B4O7:0.003Cu10.002
The glow curve of the 1n phosphor is shown by curve a in FIG. Example 2 Ll2B4O7:0.003CU10.003In,
A 0.015Si phosphor was obtained.

The phosphor obtained in this way exhibits thermal fluorescence with a main peak of the glow curve at approximately 230°C, and the thermal fluorescence intensity after irradiation with 60C0 gamma rays is compared with the height of the main peak: Ll2B4O7 : Approximately 5 that of 0.003CU phosphor
Li2B4O7:0.0 times the fading characteristics
It was significantly improved compared to that of the 03Cu phosphor. This Ll2B4O7:0.003CU10.003In, 0
．． The glow curve of the 015Si phosphor is shown by curve C in FIG. Example 3 After thoroughly mixing the above phosphor raw materials in a ball mill, Ll2B4O7:0,001CU10.0011 was prepared in the same manner as in Example 1, except that it was fired at 800°C for 2 hours.
n phosphor was obtained.

The phosphor thus obtained exhibits thermal fluorescence with a glow curve peak at approximately 145°C, and the intensity of the glow curve after irradiation with 60C0 gamma rays is L when compared in terms of peak height.
12B4O7: It was about 4 times that of the 0.001Cu phosphor.

Example 4 Ll2B4O7: 0.0005CU, 0.0005I was prepared in the same manner as in Example 3 except that the above phosphor raw materials were used.
n,0.02Si phosphor was obtained.

The phosphor obtained in this way exhibits thermal fluorescence with a main peak of the glow curve at approximately 230°C, and the thermal fluorescence intensity after irradiation with 60C0 gamma rays is compared with the height of the main peak: Ll2B4O7 :0.0005Cu phosphor is about 3.5 times that of phosphor, and the fading property is also Ll2B4O7
: It was significantly improved compared to that of the 0.0005CU phosphor.

[Brief explanation of drawings]

Figure 1 shows In, which is a co-activator for the thermofluorescent phosphor of the present invention.
It is a graph showing the relationship between density (y value) and thermal fluorescence intensity.

Claims (1)

[Claims] 1. The compositional formula is Li_2B_4O_7:xCu, yIn, zSi (where x, y) and z are each 10^-^5≦x≦5×
10^-^2, 0<y≦8×10^-^2 and 0≦z≦3×10^-^1) . 2 The above x, y, and z are respectively 3×10^-^4≦x≦8×10^-^3, 3×10^
-^4≦y≦3×10^-^2 and 5×10^-^3
The thermofluorescent phosphor according to claim 1, wherein the number satisfies the following condition: ≦z≦5×10^-^2.