Luminescent properties of europium and terbium complexes in mixed solvents

The luminescent properties of two water-soluble europium complexes and two organo-soluble terbium and europium complexes with ligands based on different N-heterocyclic ligands in various mixed solvents (light and heavy water, glycerol, methanol and ethanol) were studied in this work. The absorption, emission, and excitation luminescence spectra were obtained and analyzed. We calculated the asymmetry coefficient, the luminescence quantum yield, and the luminescence lifetime at various concentrations of mixed solvents. The luminescence quenching was found more noticeable in methanol than in ethanol for all studied complexes. We observed that the luminescence quantum yield in the water-containing solvents (methanol/water, methanol/heavy water, ethanol/heavy water) is almost independent of the water or heavy water concentration. We received that heavy water has less influence on luminescence quenching than water, since the vibrational frequencies of OH groups are higher than that of OD groups. Luminescence quenching by adding glycerol to the solvent is more effective for the studied organo-soluble complexes than for water-soluble ones. This effect can be explained by the fact that the ligand of organo-soluble complexes surrounds the rare earth ion more closely, thus preventing glycerol OH groups from entering the coordination zone of the ligand.