Intrinsic Luminescences of KI Crystals

Abstract

Luminescences and their excitation spectra in KI crystals were studied at a temperature range of 5∼100 K. Under the excitation in the first exciton absorption band only one luminescence at 3.01 eV appeared at low temperatures. However, at high temperatures the 3.01 eV luminescence intensity decreased and instead the 3.31 eV luminescence appeared, while the sum of the yields of both the luminescences remained constant. The temperature dependences of these yields were dependent on the excitation energy in the exciton band. The 3.01 eV luminescence was attributed to self trapping of a free exciton to a triplet state of a self trapped exciton by a tunnel effect, and the 3.31 eV luminescence to also self trapping of the free exciton to another triplet state by a thermal transition. Probabilities of the two processes of self trapping were found to depend on excitation energy in the exciton band.