Optical spectra, energy levels, and crystal-field analysis of tripositive rare-earth ions in Y2O3. IV. C3i sites

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Abstract
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.