Lanthanide charge transfer energies and related luminescence, charge carrier trapping, and redox phenomena

The energy of electron transfer from the valence band to a trivalent lanthanide ion provides information on the location of the ground state energy of the corresponding divalent lanthanide ion relative to the top of the valence band. It turns out that the 14 divalent lanthanides show a highly predictive pattern of the lowest 4f state energy location in compounds with the number n of electrons in the 4f shell. The lowest 4f state location controls important aspects like luminescence quantum efficiency, valence stability, and charge carrier trapping. An overview of our present state of knowledge is presented.