Reversible nonradiative transfer of excitation energy in a system of strongly interacting particles

Theoretical and experimental studies on nonradiative energy transfer between impurity ions in crystal matrices are described. Particular attention is given to reversible energy transfer between two types of ions in the presence of an energy gap (Delta E) between the metastable states of these ions. Experimental results are presented on this type of energy transfer between Er(3+) ions in crystals of garnet structure. It is shown that the nature of this type of transfer is determined not only by the value of the Delta E/kT ratio (where kT is the energy of temperature activation) but also by the ratio of the concentrations of the various types of ions. The results may be helpful in designing laser matrices in which the sensitization principle is utilized.