Crystal field in rare-earth fluorides-III. Analysis of experimental data for the alkaline earth fluorides

The superposition model and a recent experimental determination of the local distortion at substituted rare-earth ions in CaF2, SrF2 and BaF2 are employed to compared experimental results with ab initio calculations of crystal field parameters. It is shown that divalent and trivalent rare-earth ions have very similar n=4 and n=6 crystal field parameters and power laws. Strong experimental evidence is found for a power law of less than 6, in agreement with our theoretical prediction. Power laws also provide evidence that the spin-Hamiltonian parameter b4 depends quadratically on the crystal field, while b6 depends on its cube.