Interactions between rare earth ions in the ethyl sulphates

Abstract

The existing data on the interactions between a large number of different pairs of rare earth ions in ethyl sulphates is surveyed as a whole, and some comparisons are made with similar data for LaCl₃ and LaBr₃. Such an analysis of all of the data enables one to draw much firmer conclusions about the interaction mechanisms than a discussion of the results for any particular pair of ions. It is shown that exchange contributes very little to the interaction, and that electric multipole-multipole interaction contributions are negligible. This suggests that the sizeable nondipolar contribution to the interaction should be attributed to virtual phonon exchange (VPE). Estimates of this interaction based upon standard theories show that the interaction must be enhanced by a factor of 40-50 in order to agree with the experimental measurements. That this enhancement factor remarkably consistent for all of the data, and that one can invent a plausible model to account for the enhancement factor in terms of contributions from optical phonon modes, indicates that VPE interaction is the appropriate mechanism.