Photoionization and luminescences in BaF2:Eu2+

The photoconductivity spectra of BaF2:Eu2+ shows that the "anomalous" emission usually observed in BaF2:Eu2+ is due to the fact that all the Eu2+ excited states are in the conduction band of the crystal. The red shifted emission is due to an impurity trapped exciton which is the lowest excited state of this system. A model for the photoconductive and luminescence behavior of BaF2:Eu2+ and SrF2:Eu2+ is given in terms of configuration coordinate diagrams. A broad blue band is also observed under high energy excitation (> 4 eV) and is interpreted as the emission of a perturbed self-trapped exciton.