Crystal fields and dopant-ligand separations in cubic centres of rare-earth ions in fluorites

Phenomenological crystal-field parameters were calculated from spectroscopic data for Eu 3+ , Dy 3+ and Er 3+ in cubic sites in a number of fluorite-structure hosts. These values, and similar data from other calculations, were used to obtain, with the help of a semiempirical modelling procedure, the dopant-ligand distances in the corresponding centres. It is confirmed that significant local lattice collapse does take place in these centres. The final dopant-ligand distances calculated in this investigation compare favourably with relevant information collected by other methods.