DOUBLY-VALENT RARE-EARTH IONS IN HALIDE CRYSTALS

The results of extensive research into the properties of divalent rare-earth ions in halide crystals have been reported, particularly in the past 20 years, and yet no review of these data is available. This paper concentrates on the spectroscopic properties of divalent rare-earth ions in alkaline earth halides, alkali halides, and other halide crystals. Special emphasis is given to Eu2+, Sm2+ and Yb2+ which are the most-studied divalent rare-earth species. The optical properties of these ions in solution in halide crystals are summarized and aggregation and precipitation phenomena are described, using the results of EPR and ITC studies of aggregation kinetics.