Determination of Optical Gain of Self-Trapped Exciton Luminescence in CdI2

Abstract

Luminescence from self-trapped excitons in high-purity CdI 2 has been studied at liquid nitrogen temperature under intense excitation by a pulsed nitrogen laser. Luminescence intensity was carefully measured by changing excitation density and length of the excited region on a crystal surface. Obtained results are well explained by introducing a stimulated emission process into radiative decay channels of the self-trapped excitons. The net optical gain depends strongly on the excitation density and is estimated as 6 cm -1 in its maximum value which is extremely smaller than the previously reported one. Discussions will be made on consistency among the excitation-density dependence, the excitation-length dependence and the luminescence decay profiles.