f d transition energies of divalent lanthanides in inorganic compounds

The systematic in the 4f n → 4f n−1 5d transition energy of divalent lanthanides in inorganic compounds has been studied. Energies were derived from excitation and optical absorption spectra gathered from the literature. Going through the lanthanide series from La2+ to Yb2+, a characteristic variation is observed similar to that known for the trivalent lanthanides and the free atoms and free ions. Once the transition energy is known for one lanthanide in a compound, that of all others in that same compound can be predicted. The value for the Stokes shift between fd excitation and df emission appears independent of the lanthanide ion. For Gd2+ to Yb2+ both the spin-forbidden and the spin-allowed fd-transition energies are discussed.