DETERMINATION OF OPTICAL GAIN OF SELF-TRAPPED EXCITON LUMINESCENCE INCDI2

Luminescence from self-trapped excitons in high-purity CdI2 has been s tudied at liquid nitrogen temperature under intense excitation by a pu lsed nitrogen laser. Luminescence intensity was carefully measured by changing excitation density and length of the excited region on a crys tal surface. Obtained results are well explained by introducing a stim ulated emission process into radiative decay channels of the self-trap ped excitons. The net optical gain depends strongly on the excitation density and is estimated as 6 cm(-1) in its maximum value which is ext remely smaller than the previously reported one. Discussions will be m ade on consistency among the excitation-density dependence, the excita tion-length dependence and the luminescence decay profiles.