LUMINESCENCE STUDY OF EU-3+-O-2- ASSOCIATES IN FLUORIDES - CAF2, RBCDF3 AND RBCAF3

The luminescence spectra and quantum efficiency of the Eu3+ ion in some fluoride systems, viz. CaF2, RbCdF3 and RbCaF3, are reported. The presence of oxygen in the lattice strongly influences the luminescence of the Eu3+ ion. Several Eu3+ centers are observed which are due to associates of Eu3+ ions with O2- ions of F- sites in the lattice. The quantum efficiency of the Eu3+ luminescence under CT (oxygen to europium) excitation (q(CT)) depends on the crystal structure of the host material. In CaF2, the lattice is not able to counteract the expansion in the excited state, giving rise to a low q(CT) value (approximately 15%). As a result of a beneficial orientation of the second coordination sphere of the Eu3+ ion in the perovskite lattice (RbCdF3 and RbCaF3), the q(CT) value amounts to about 70%. So far, this value is the highest reported for the Eu3+ 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 Eu3+ ion sets an upper limit to the q(CT) value.