Doping Effect On The Modulation Of LiF Luminescent Properties And Vacancy Effect

Lithium fluoride (LiF) has been widely used in various technologicalapplications such as in x-ray monochromators, as a filter for ultraviolet radiation, andin thermoluminescent (TL) dosimetry. Owing to its highest sensitivity, especially, LiFco-doped with Mg, Cu and P stimulated extensive interest in the radiation dosimetryin the past decades. However, there are no consistent views about impurity Cu and Pon the roles of TL properties. Some authors proposed that Cu acts as a luminescentcenter, while others take the opposite view. As for Cu impurity, its ion size (0.96) islarger than that of Li+(0.68). It was usually thought that LiF cannot be doped withCu+，Under irradiation, on the other hand, there exists a common defect of Livacancy (VLi) and thus a complex defect of Cu-VLidipole may be introduced in thedoping system. The impurity P may also affect Cu to doping in LiF. The complexdefects may play an important modulation role on TL sensitivity. Our results providecorresponding theoretical basis for controllable doping in experiments. The mainworks are as follows:(1) We present a detailed investigation on LiF:Cu in the presence of VLiby usingfirst-principles method. The defect structure has been determined from the formationenergy. It is shown that the presence of VLileads to a decrease of the formationenergies of Cu, in favor of Cu doping into LiF. The electronic structure and opticalproperties of the doped system were systematically studied, which can be largelymodulated by VLi. A new absorption peak is obtained at9.3eV in LiF:Cu with anadjacent VLito Cu, which is in good agreement with experimental observation.(2) Based on first-principles method within the framework of the densityfunctional theory, we studied different defects structure of the impurities Cu and Pdoped LiF. From the formation energy, we can deduce that the nearest neighbor Pmake the Cu easier to doping into LiF crystal. The electronic structure and opticalproperties of the doped system were systematically studied. A new absorption peak is obtained at250nm in LiF:Cu,P, which is in good agreement with experimentalobservation.