Elucidation of the electron transfer mechanism in Eu2+ and Sm3+ codoped CaF2: A step towards better understanding of trapping and detrapping in luminescent materials

Many-electron multiconfigurational ab initio calculations are combined with x-ray spectroscopy to scrutinize a popular model for electron transfer in lanthanide-doped crystals which hypothesizes that the electrons are conveyed by the conduction band of the host. Contrary to this accepted picture, our combined theoretical-experimental effort shows that the reversible electron phototransfer from Eu2+ to Sm3+ in CaF2 is direct, from metal to metal. It is theoretically predicted and experimentally verified that visible light induces the reverse electron transfer.