4f and 5d Levels of Ce3+ in D2 8-fold oxygen coordination

The effects of the first coordination shell geometry of the trivalent Cerium ion (Ce3+) on its 4f and 5d levels in Ce-doped oxides with a D2 8-fold site, like garnets, are studied with embedded cluster, wave function based ab initio methods. The only deformations of a D2 CeO8 moiety that are found to shift the lowest 4f → 5d transition to the red (longer wavelengths) are the symmetric Ce–O bond compression and the tetragonal symmetric bond bending. In a first approximation, the lowest 5d level of Ce3+ in garnets can be understood as resulting from the cubic Eg level with a strong Eg × eg Jahn–Teller coupling. These results are analyzed in terms of 5d − 4f centroid energy differences and ligand field stabilizations. The splittings of the upper 5d levels and of the 4f levels are also discussed.

► The 4f and 5d levels of Ce3+ in 8-fold oxygen coordination of D2 symmetry, like garnets, are calculated ab initio. ► Their variations under six independent D2 distortions of a CeO8 cubic moiety are shown. ► The calculations are high-level wave function theory calculations done on a (CeO8)13− cluster embedded in a general cubic confinement potential. ► The only distortions that significantly red shift the lowest 4f–5d transition are the symmetric Ce–O bond compression and the tetragonal symmetric bond bending. ► The lowest 5d level of Ce3+ in garnets can be understood as resulting from an Eg cubic level under a strong Jahn–Teller Eg × eg coupling.