ANALYSIS OF CUBIC CRYSTAL-FIELD PARAMETERS FOR GD3+ IN ALKALINE EARTH FLUORIDES

The optical spectra of the alkaline-earth fluorides doped with Ge 3+ (MeF2:Gd3+, where Me represents Ca, Sr, or Ba) at octahedral sites are analyzed to determine the effect of lattice size on the cubic crystalfield parameters. The point-charge model predicts a linear dependence of the first-order crystal-field splitting on B0 4 which in turn varies inversely with the Gd3+-F - separation to the fifth power (A-5). The slopes of plots of log b40 vs log b40 yield values of -2.1, -2.7, and 0 for the 8S7/2, 6P 7/2, and 6P5/2 multiplets, respectively. This apparent discrepancy is resolved by the inclusion of crystal-field interactions in all orders between the 8S and 6(P, I, D) multiplets. The A40〈r4〉) vs logR plot is found to be -1.8 which agrees with the EPR result to within experimental error. The disagreement with the point-charge model is examined.