RARE-EARTHS IN II-VI COMPOUNDS - NONLINEAR OPTICAL-EXCITATION PROCESSES AT LOW AND HIGH DOPING LEVELS

Based on a careful separation of the observed samarium sites in ZnS : Sm3+ bulk crystals, the optical properties of the dominant rare earth (RE) centers and their relative stability with respect to changes in the host lattice are reported. Based on non-linear optical processes at high excitation densities, the direct 4f-4f excitation channel is compared with energy transfer via the crystal. Developing a theoretical model for the non-exponential decay behaviour, connected with the indirect excitation channel, conclusions will be drawn on the complex nature of the RE sites involving other defects and impurities. Also in crystals with very low RE concentrations (1017 cm-3) these complex centers are observed and can be described by the same model. © 1989.