Vacuum ultraviolet spectra of CaF_2:Eu^+3 and CaF_2:Sm^+3

Abstract
Vacuum ultraviolet absorption spectra due to 4ƒ→5d transitions in Eu+3 and Sm+3 ions in a CaF2 host lattice is presented. A tendency of dopant (Eu+3) clustering is tentatively identified at a relatively low impurity concentration.