ON THE CORRELATION BETWEEN ENERGY STRUCTURE AND THE MECHANISM OF RECOMBINATION FOR RARE-EARTH IONS IN SOLIDS

An efficient mechanism of rare earth (RE) intra-ion excitation due to nonradiative bound exciton (BE) recombination is discussed. We first show that some RE ions, those which can change their charge state, bind excitons. RE bound excitons recombine nonradiatively due to the impurity Auger effect, i.e. energy transfer to core states, which results in core excitation, followed by an intra-ion emission. The correlation between the energy structure of an RE-BE system and the recombination mechanism is discussed from examples of Eu, Yb and Sm impurities in ZnS, and Eu in Ca(x)Cd(1-x)F2 crystals.