Photoluminescence due to exciton-exciton scattering in GaSe under picosecond laser excitations

Picosecond-laser-excited photoluminescence spectra in GaSe at room temperature have been measured and analyzed. Both spontaneous and stimulated emissions were attributed to the exciton-exciton scattering process in GaSe through a careful band-shape analysis. The exciton-photon coupling coefficient πα/ε=3.3×${10}^{\mathrm{-}3}$ was obtained from the spontaneous emission spectra fit. The stimulated emission is well explained by the optical gain mechanism arising from the reverse absorption process of the exciton-exciton scattering.