A SHELL-MODEL FOR CROSS-RELAXATION IN ELPASOLITE CRYSTALS - APPLICATION TO THE P-3(0) AND (1)G(4) STATES OF CS(2)NAY(1-X)PR(X)CL(6)

A model for cross relaxation in high symmetry systems is developed. Th e positions of all acceptor ions and all multipole-multipole interacti ons may be included. The geometric factors are explicitly considered. A feature of the model is that it enables decay rates and the form of decay curves to predicted a priori if the exponential decay curves of very dilute and stoichiometric materials are experimentally accessible . The model is applied to the title system and excellent agreement wit h experiment is achieved.