Correlation between the 5d-level position of Ce3+ and of the other Ln3+ ions in solids

The experimental values of the lowest 4f–5d transitions of the lanthanide ions Ln3+ have recently been found to show a linear dependence as a function of the corresponding transition energy of the Ce3+ ion for a series of different hosts. We explain this behavior on the basis of an interaction between the induced multipole moments on the ligands and the electrons on the metal, decreasing the energy difference between the 4fn−15d and 4fn configurations with respect to the free ions.