Temperature dependence of the threshold and mechanisms of lasing in CdS single crystals subjected to one-photon excitation

The temperature dependences of the pump intensity I_th corresponding to the lasing threshold were determined in the range 4.2 K≤T≤300 K for CdS single crystals with different levels of losses in the case of one-photon pumping with nitrogen laser radiation. The temperature dependence I_th(T) was nonmonotonic. An analysis of the dependences I_th(T) was made using the available theoretical treatments and a comparison of the experimental and calculated subthreshold emission spectra indicated competition between three lasing mechanisms, which changed with temperature, took place under the experimental conditions. These mechanisms were exciton-phonon, exciton-exciton, and exciton-electron inelastic scattering. In particular, the fall of I_th recorded under certain conditions on increase in temperature could be attributed to spectral degeneracy of two or three of these mechanisms.