Luminescence study of Eu3+−O2− associates in fluorides: CaF2, RbCdF3 and RbCaF3

Abstract The luminescence spectra and quantum efficiency of the Eu 3+ ion in some fluoride systems, viz. CaF 2 , RbCdF 3 and RbCaF 3 , are reported. The presence of oxygen in the lattice strongly influences the luminescence of the Eu 3+ ion. Several Eu 3+ centers are observed which are due to associates of Eu 3+ ions with O 2− ions of F − sites in the lattice. The quantum efficiency of the Eu 3+ luminescence under CT (oxygen to europium) excitation ( q CT ) depends on the crystal structure of the host material. In CaF 2+ , the lattice is not able to counteract the expansion in the excited state, giving rise to a low q CT value ( $ 15%). As a result of a beneficial orientation of the second coordination sphere of the Eu 3+ ion in the perovskite lattice (RbCdF 3 and RbCaF 3 ), the q CT value amounts to about 70%. So far, this value is the highest reported for the Eu 3+ ion in compounds of divalent cations. Still this value is far from 100% which points to the fact that the effectively positive charge of the Eu 3+ ion sets an upper limit to the q CT value.