Luminescence due to exciton-electron and exciton-excitons collision in GaSe

Two emission bands are observed in GaSe under N2 laser excitation at 77 K and 4.2 K. The spectral-band shapes agree with the theoretical curves for exciton-electron and exciton-exciton collision processes. Stimulated emission is ascribed to the exciton-exciton collision process. The red-shift of the stimulated emission is explained by the reverse absorption of this process. The reverse absorption is observed in absorption spectra under intense excitation.