Radiation induced defects and stimulated luminescence processes in Lanthanum Oxyhalide phosphors for lighting, CRT (Cathode Ray Tube) and medical applications

摘要

In order to understand the luminescence mechanism and luminescence centers in LaOCl, LaOBr and LaOBr:Tm, Thermally stimulated luminescence(TSL) and photoluminescence(PL) studies have been made on unirradiated and irradiated samples at room temperature. LaOCl revealed three glow peaks having their maxima at 355,390 and 410k while in LaOBr a shoulder at 335K and two glow peaks at 365 and 420k are observed. Incorporation of Tm in LaOBr resulted in significant changes in intensity. In addition, the shoulder at 335K gets suppressed and the 365 and 420K glow peaks shifted towards high temperatures to 380 and 430K. The shoulders at 355, 335K in LaOCl and LaOBr have been attributed to impurities while the glow peaks at 390 and 380K might originated due to radiative electron - hole recombination due to detrapping from chlorine and bromine ion vacancies. The high temperature glow peak at 420 and 430k might belong to F~+ centers being formed due to charge transfer between oxygen ion vacancies and excited electrons. The reflectance and photoluminescence studies supported these attributions as they revealed different emissions which may be responsible for color centers as well as luminescence centers.