4f and 5d levels of Ce3+ in D2 eightfold oxygen coordination
  The effects on the 4f and 5d levels of Ce3+ of its first coordination shell geometry 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 CeO8 cube that are found to shift the lowest 4f-5d transition to the red are the symmetric Ce-O bond compression and the tetragonal symmetric bond bending. These results are analyzed in terms of centroid and ligand field stabilization energy differences. The splittings of the upper 5d levels and of the 4f levels are also discussed. 
Luis Seijo and Zoila Barandiaran
cond-mat.mtrl-sci physics.chem-ph