Photoluminescence and gain of CdS and CdSe single crystals under electron-beam excitation conditions

An investigation was made of the photoluminescence spectra of cadmium sulfide and selenide single crystals (77 and 4.2°K) and of the spectra of the gain α(ħω) during excitation of the same crystals with electron beams of 20 keV energy (77°K). The experimental and calculated gain profiles were compared on the assumption of the exciton–phonon interaction between carriers. A correlation was found between the photoluminescence and gain spectra. Gains up to 70 cm^–7 were obtained for CdS crystals whose 77°K photoluminescence spectra included a strong (compared with the edge luminescence) band due to A free excitons, and there was clear evidence of transitions assisted by one or two longitudinal optical phonons. In the case of CdSe crystals grown by the sublimation of a powder in an argon stream the maximum gain and full agreement between the experimental and calculated gain profiles were obtained when these crystals were grown in the temperature range 800–900°C.