Abstract

The study of the energy-transfer processes is extended, within the conceptual framework of the crystal model, to the electric dipole-electric quadrupole and electric quadrupole-electric quadrupole interactions. The formalisms for the energy-transfer rates are deduced, applying a mixed scheme of Cartesian tensors which are used to establish the geometric aspects of the interaction, and spherical tensors for the electronic part. The dependence of these transfer rates with respect to the geometric factors is discussed, and they are compared with the electric dipole-electric dipole case. In general, and as a consequence of the intrinsically anisotropic character of the quadrupolar operator, the analysis shows formally that those rates are highly anisotropic, suggesting a more careful calculation and interpretation of the transfer rates in organized media, like crystalline phases. This type of analysis shows the faults of the models currently used and cited in the literature, and the importance of the anisotropic effect is illustrated with an application in elpasolite type lattices doped with Ln(3+) ions which occupy centrosymmetric sites. [S0163-1829(99)12835-2].