ENERGY-TRANSFER PROCESSES IN ORGANIZED MEDIA - III - A 2-CENTER MODELFOR NONHOMOGENEOUS CRYSTALS

As part of a series of studies on energy transfer processes between op tical centers in condensed matter, an analysis is made of the problem of a crystalline system made up by a majority of regular optical cente rs and small amounts of defective optical centers. Within the conceptu al framework of the crystal model, analytic equations are derived that allow a direct connection between the microscopic study of the intera ction and kinetic type equations to describe the relaxation dynamics f rom excited states. As an example, Ln(3+) ions in elpasolite type latt ices are used, showing the biexponential character of the decay curves . These results can be used in the study of relaxation from excited st ates in crystals with heterogeneities due to crystallographic defects, trace impurities, or slightly distorted optical centers. (C) 1998 Ame rican institute of Physics.