Optical spectra, energy levels, and crystal-field analysis of tripositive rare-earth ions in Y2O3. IV. <i>C</i>3<i>i</i> sites

We report an analysis of new and previously existing optical absorption and fluorescence data, far-infrared data, and electronic Raman scattering data for Eu3+, Dy3+, and Er3+ in the C3i sites of Y2O3 and R2O3, where R=a rare earth. Our previous analysis of C2-site spectra yields an effective point-charge model for the host lattice that allows initial estimates to be calculated for the C3i-site crystal-field parameters Bkm. Best-fit values of B20, B40, and B43 are obtained for Eu, and best-fit values of all Bkm allowed by symmetry are obtained for Dy and Er. The best-fit Bkm are in relatively poor agreement with the model; in particular, B20 has the opposite sign from and B44 is much smaller than the model predictions. From the best-fit Bkm we obtain phenomenological crystal-field components Akm, from which we predict Bkm and C3i -site energy levels for the ground states of Tb3+, Ho3+, Tm3+, and Yb3+. While the effective point-charge model is apparently too crude to make accurate, quantitative, a priori predictions, the model and the data allow one to predict confidently the behavior of ions doped into C3i sites for which no data exist.

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