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^<++>的微晶体中的空位和Eu^<++>杂质处（存储过程），被捕获电子的光激发诱导电子和空穴在Eu杂质处重新组合，发出紫外线发光。这种紫外线发光被记录下来，并用于构建x射线图像（读出过程）。虽然上述存储读出机制在成像板发明初期就已提出，但目前存储读出过程仍存在争议。为了建立清晰的机理模型，我试图测量被困电子激发态的热稳定性，并澄清电子与空穴的复合路径。为此，建立了红外发光测量系统。结果总结如下。1)测量了F中心发光强度和寿命与温度的关系，得到了激发态F中心的热活化能。该机制与takahashi提出的相同。2)首次测量了IP中的F（F^-）中心发光，也表明F（Br^-）中心不发出任何红外发光。结果表明，电子中心可以在微晶体中迁移，而存储图像的衰落可能是由于在浅阱空穴中心被热激活的空穴迁移引起的。

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.