5d-level energies ofCe3+and the crystalline environment. III. Oxides containing ionic complexes

Information on the energy of $5d$ levels of ${\mathrm{Ce}}^{3+}$ ions coordinated by ${\mathrm{CO}}_{3}^{2\ensuremath{-}},$ ${\mathrm{SO}}_{4}^{2\ensuremath{-}},$ ${\mathrm{PO}}_{4}^{3\ensuremath{-}},$ ${\mathrm{BO}}_{3}^{3\ensuremath{-}},$ and ${\mathrm{SiO}}_{4}^{4\ensuremath{-}}$ ionic complexes or by neutral water molecules in oxide compounds will be presented and systematically analyzed. The average energy of the $5d$ configuration of excited ${\mathrm{Ce}}^{3+}$ is shifted towards lower energy relative to the free ion value. This centroid shift depends on the binding strength of the oxygen ligands in these ionic complexes. It will be analyzed by means of a model which provides a parameter that is directly related to the polarizability of the oxygen ligands. A qualitative relationship with the electronegativity of the cations in the compounds will be demonstrated. Crystal-field splitting of the $5d$ levels is interpreted in terms of the type and size of anion polyhedron coordinating the ${\mathrm{Ce}}^{3+}$ ion. All data indicate that crystal-field splitting behaves independently from the centroid shift. By combining centroid shift and crystal-field splitting, the redshift of the first electric dipole-allowed $\mathrm{fd}$ transition in ${\mathrm{Ce}}^{3+}$-doped oxide compounds will be interpreted.