PbWO4闪烁晶体的发光动力学模型

在对PbWO₄闪烁晶体的光谱特性、发光衰减及其温度依赖以及热释光的研究基础上,并结合理论计算,提出了PbWO₄晶体发光的动力学模型,给出了PbWO₄晶体的基本能带结构及激子发光中心能态、陷阱能级在能隙中的位置。用此模型可以完整说明PbWO₄的发光过程,特别是导致室温下发光效率低的原因。最后还对其主发射成分蓝、绿发光中心的起源作了简要讨论。

A Model of the Luminescence Dynamics of PbWO4 Scintillator

On the ground of the study of the luminescence spectral properties, the temperature dependence of the intensity, the decay of the luminescence, and the thermoluminescence of PbWO₄ scintillating crystals, combining the results from the theoretical calculations of its electronic structure, a model of the luminescence dynamics of PbWO₄ scintillator is suggested with the fundamental band structure, the states of the excitonic luminescence centers, and the position of the trap levels in the band gap defined. According to the theoretical calculations, the band gap is 4.4eV, consistent with the fact that the 265nm excitation band is corresponding to the band transition. The stronger 310nm excitation band originates from the exciton whose binding energy is 0.41eV. The energy difference between the ground state and the excited state is 2.88eV and 2.38eV respectively for blue (430nm) and green (520nm) emission centers. The thermal activation energy for the blue and green emission centers is 0.18eV and 0.13eV respectively calculated from the temperature dependence of the luminescence intensity. The thermoluminescence curves indicate that several types of electronic traps exist in the band gap with the energy depth of 0.42, 0.60, 0.65eV and the deepest 1eV or so. With this dynamical model, the luminescence process of PbWO₄ can be fully explained, especially for the causation of the low luminescence efficiency at room temperature because of the strong thermal quenching. On the other hand, according to our study on the luminescence of PbWO₄ annealed in different atmosphere, we suggested that the green emission center is "WO₄^2-+Oi"where Oi is oxygen interstitial, instead of "WO³⁺F" where F is an oxygen vacancy holding two electrons, and the blue emission center is some kind of combination center with the form of "WO₄^2-+some intrinsic defects".