Diffusion of Excitons in KI Crystals

Abstract

Under the excitations in the fundamental absorption bands, luminescence and excitation spectra for doped impurities as well as a self trapped exciton in a KI crystal are studied in detail at a temperature range of 5∼100 K. In doped crystals, impurity luminescences are induced instead of the intrinsic luminescence at 3.01 eV which comes from the self trapped exciton under the excitation in the first exciton absorption band. The induced impurity luminescence are confirmed to be due to collision of free excitons with doped impurities. The diffusion coefficient of the free exciton is found to be proportional to T^−1⁄2 below 40 K and above that temperature to T^1⁄2[exp(hω⁄kT)−1]. The value of the diffusion coefficient is estimated to be about 0.1 cm² sec⁻¹ at 5 K.