Possibility of coherent light emission from excitons in crystalline GaTe

Free exciton photoluminescence (PL) spectra of crystalline GaTe has been studied as a function of continuous wave (cw) argon laser excitation intensity at T=6 K. When the excitation intensities are low (P4 W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$), the integrated PL intensities of free excitons for both singlet and triplet states increase approximately linearly with increasing excitation intensity. From about 4 to 9 W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, the peak energy redshift, the linewidth broadening, and the sharp increase of the integrated PL intensity of the exciton peaks are observed. These results are explained tentatively as large coherent emissions from excitons of GaTe. \textcopyright{} 1996 The American Physical Society.