Abstract

Here CdS_xSe_1-x nanocrystals were studied and characterized by resonant Raman scattering, low frequency inelastic scattering, pressure tuned Raman scattering and photoluminescence. Ordinary Raman scattering and low frequency inelastic scattering were used for composition and size characterization. In the photoluminescence spectra we found that the deep defects where symbatic for compositions in the range close to CdS. For intermediate compositions down to CdSe no marked change in the defect peak positions were observed. This behavior is similar to the bulk case.¹ Also the pressure coefficients in our measurements reflected this peculiarity. Resonant Raman scattering at different pressures was applied to examine the electron phonon interaction in the framework of the one dimensional configuration model. We found that the coupling strength (Huang-Rhys parameter) is larger than expected from theory and might indicate an extrinsic effect such as a point defect.² The pressure dependence of the coupling was also compared with bulk CdS calculated from phonon replicas of the green defect line 3 and we found the same tendency of weakening with pressure. In the case of nanocrystals we were able to observe this beyond the phase transition point of bulk due to their higher stability or superpressure effects.

© 1993 Optical Society of America