5d-level energies ofCe3+and the crystalline environment. I. Fluoride compounds

Information on the position of all five $5d$ levels of ${\mathrm{Ce}}^{3+}$ in 17 different fluoride compounds has been collected. A model involving the polarizability of the fluoride ions, originally suggested by Morrison [J. Chem. Phys. 72, 1001 (1980)], is used to calculate the so-called spectroscopic polarizability ${\ensuremath{\alpha}}_{\mathrm{sp}}$ from the observed average energy of the 5d configuration. It will be compared with actual in-crystal fluoride ion polarizabilities. There appears a relationship between ${\ensuremath{\alpha}}_{\mathrm{sp}}$ and the types of cations present in the crystal structure. Small high valency cations tend to reduce the centroid shift. Large cations have the opposite effect. The size and the type of the fluoride ion coordination polyhedron around ${\mathrm{Ce}}^{3+}$ determine the crystal field splitting of the $5d$ levels. Combining the gained knowledge on centroid shift and crystal field splitting, the energy of the first $4\stackrel{\ensuremath{\rightarrow}}{f}5d$ transition in about 25 additional fluoride compounds will be interpreted.