Determination of the excited states of the electron centers and recording-readout processes in the X-ray storage material BaFBr

在X射线成像材料的存储荧光粉中，X射线光子产生电子和空穴，这些电子和空穴被捕获在BaFBr：Eu^++>微晶中的空位和Eu^++>杂质处（存储过程），被捕获的电子的光激发引起电子和空穴在Eu杂质处的复合，从而发射紫外发光。记录该紫外发光并用于构建X射线图像（读出过程）。虽然在成像板的发明早期阶段已经提出了上述存储-读出机制，但是存储-读出过程目前仍然存在争议。为了建立清晰的机理模型，我尝试测量了俘获电子激发态的热稳定性，并阐明了电子和空穴的复合路径。为了进行这种测量，构建了用于红外发光的系统。主要结果如下：1）测量了F心的发光强度和寿命随温度的变化关系，得到了F心激发态的热激活能。2）首次测量了IP中F（F^-）中心的发光，并发现F（Br^-）中心不发射任何红外发光。这些结果表明，电子中心可以迁移的微晶中的IP和存储的图像的衰落可能是由迁移的空穴，热激活的浅陷阱空穴中心。

In the storage phosphor of the X-ray image material, the X-ray photons generate electrons and holes which are trapped at vacancies and Eu^<++> impurities in the micro crystals ofBaFBr : Eu^<++>(storage process) and photoexcitation of the trapped electron induces the recombination of the electrons and holes at Eu impurity, emitting the uv-luminescence. This uv-luminescence is recorded and is used to construct the X-ray image (readout process). Although the storage-readout mechanism described above has been proposed in the early stage of the invention of the imaging plate, the storage-readout process is still controversial at present. To establish the clear model for the mechanism, I tried to measured thermal stability of the excited state of the trapped electrons and also to clarify the recombination path of the electrons and holes. For this measurements, a system for the infrared luminescence was constructed. Results are summerized as follows.1) The temperature dependence of the luminescence intensity and its lifetime of the F center were measured and the thermal activation energy of the F centers in the excited state was obtained. This mechanism is identical to the that proposed by Takahashi.2) The F(F^-)-center luminescence in the IP was measured for the first time and it is also shown that F(Br^-) center does not emit any IR luminescence. These results shows that the electron center can migrate in the micro crystals in the IP and that the fading of the stored image might be induced by the migration of holes which are thermally activated in shallowly trapped hole centers.