EXCITONIC PROCESSES IN II-VI COMPOUNDS DOPED WITH TRANSITION-METAL AND RARE-EARTH IMPURITIES

Recently a new mechanism of the rare earth (RE) and transition metal (TM) intra-shell excitation was proposed. These ions can bind an exciton which forms an "external" excited state of the impurity. The role of such excitons in the photoluminescence excitation (PLE) is discussed. The mechanism of impurity Auger recombination is explained. This process is responsible for nonradiative recombination of bound excitons (BEs) due to an energy transfer to the impurity core states. Exciton binding is expected mostly for these RE and TM ions which can change their charge state in a given compound. It is shown that the photoionization (PI) process can be accompanied by exciton binding. Also, the recapture of the ionized carrier may proceed via the formation of the impurity BE state. In some cases direct recombination of such BE can be observed.