[Synthesis and fluorescence properties of complexes of terbium with red fluorescence]

Two terbium complexes were synthesized, with dibenzoylmethane (HDBM) as the first ligand and 1,10-phenanthroline (phen), dipyrido[3,2-a:2',3'-c] quinoxaline as the second ligand. The studies of elemental analysis, rare earth complexometric titration, molar conduction, IR spectra, UV spectra, fluorescence excitation and emission spectra indicate that the complexes have the compositions of Tb (DBM)3 phen and Tb (DBM)3dpq. The results show that the rare earth ion (Tb3+) was bonded with the carbonyl oxygen atom of DBM and nitrogen atoms of phen and dpq. For the terbium complexes prepared by precipitation, the peak positions of the transitions were similar with the ones of the common complexes. The peaks at 490, 545, 586 and 621 nm were assigned to the D4 --> 7F6, 5D4 --> 7F6, D4 --> 7F6, 5D4 --> 7F6 transitions. For the fluorescence intensities of their 5D4 --> 7F6, 5D4 --> 7F5 and 5D4 --> 7F4 transitions were lower than that of the 5D4 --> 7F3 transition, the terbium complexes did not exhibit the characteristic fluorescence (green), but strong red fluorescence. The reason why terbium complexes exhibit the red fluorescence was investigated in the paper by studying the triplet state of ligands, the energy level transitions of complexes and the aggregation state of particles.