Formation and migration of VK centers from localized excitons in NaCl:I− and NaCl:I−,Tl+ crystals

Abstract

We have investigated the temperature dependence of the decay profiles of the localized exciton luminescence related to the I− center in single-doped NaCl:I− and co-doped NaCl:I−,Tl+ crystals. At the temperature region below 160 K, the localized exciton luminescence exhibits almost single-exponential decay profiles regardless of single- or co-doped crystals, reflecting the radiative and nonradiative transitions inside the exciton localized at the I− center. Above 200 K, the decay profiles change to non-single-exponential decay profiles even in the single-doped NaCl:I− crystal. The non-single-exponential decay profiles in NaCl:I− relate to the formation of the VK center. The non-single-exponential decay profiles in the co-doped crystal are faster than those in the single-doped crystal. The faster decay profiles of the localized exciton luminescence in the co-doped crystal are attributed to the energy transfer process through migration of the VK center to the Tl+ center. The decay profiles are analyzed on the basis of the rate equations considering the formation and migration of the VK center, which are discussed through thermally activated processes.