Research On Synthesis And Luminescence Properties Of Europium And Terbium Complexes

In this article, six new kinds of ternary rare earth complexes were synthesized by introducing benzoylacetone (BA) as the first ligand and 1,10-phenanthroline (Phen), triphenylphosphine oxide (TPPO), 2,2'-bipyridyl(Bipy) as the second ligand, which were Eu(BA)3Phen, Eu(BA)3(TPPO)2, Eu(BA)3Bipy, Tb(BA)3Phen, Tb(BA)3(TPPO)2 and Tb(BA)3Bipy, respectively. Then, in order to systematically study of energy transfer process of these rare earth complexes, structure and luminescence properties were characterized by plenty of measurement methods and discussed in details.1) Eu(BA)3Phen,Eu(BA)3(TPPO)2 and Eu(BA)3Bipy were synthesized. Structure and composition were characterized by elemental analysis, Infrared absorption spectrum (IR) and Hermogravimetric-Differential scanning calorimeters (TG-DSC), which indicated that these Eu(III) complexes did not contain water or solvent molecules. By analysis of Ultraviolet and Visible Spectrophotometer (UV-vis), it can be concluded that the first ligand and the second ligand belonged to Eu(III) complexes participate in energy absorption. And, through calculation of the absorption edge in UV-vis, the optical band gaps of these Eu(III) complexes were gained, which were 3.06eV, 3.0eV and 3.03eV, respectively. It can be seen that these optical band gaps were nearly identical, which should belong to the singlet state of the first ligand BA. According to the cyclic voltammetry curves, band gaps of the Eu(III) complexes were calculated as 1.58eV, 1.66eV and 1.77eV, respectively, which were corresponding to f→f electronic transitions of Eu(III) complexes. In photoluminescence spectra and fluorescence spectra, it can be seen that the three kinds of the Eu(III) complexes exhibited fluorescence emission peaks at 615nm that was corresponding to characteristic luminescence of europium ion, which were red light-emitting material.2) Three kinds of the terbium(III) complexes of Tb(BA)3Phen, Tb(BA)3(TPPO)2 and Tb(BA)3Bipy were synthesized. The properties were characterized by elemental analysis, IR, TG-DSC, UV-vis, cyclic voltammetry, photoluminescence spectra and fluorescence spectra. The optical band gaps of the Tb(III) complexes are 3.23eV, 3.21eV and 3.22eV, respectively, which should belong to the first ligand BA. The f→f electronic transitions of Tb(III) complexes corresponding to the band gaps (2.01eV, 1.90eV and 1.87eV) were gained by analysis of cyclic voltammetry curves. In photoluminescence spectra and fluorescence spectra, it can be seen that the three kinds of the Tb(III) complexes exhibit the fluorescence emission peaks at 543nm that is corresponding to characteristic luminescence of terbium ion, which are green light-emitting material.3) The luminescence mechanism of the Eu(III) complexes and the Tb(III) complexes had also been discussed in this article. It can be inferred that the second ligands (Phen, TPPO, Bipy) of rare earth complexes can affect their luminescent properties. Based on the Kasha rule, the energy band structure model of the rare earth complexes had been set up. The energy levels of singlet state of BA,Phen,TPPO and Bipy were estimated by referencing their absorbance edge in UV-vis spectra, and their intramolecular energy transfer models had also been set up. The results showed that the fluorescence yield of the rare earth complexes does not only depend on the energy difference between the triplet state (T1) of the ligand and the lowest excited state of the rare earth ions, but also depend on the energy difference between the singlet state (S1) of the second ligand and the singlet state (S1) of the first ligand. The appropriate energy difference can contribute to an effective intramolecular energy transfer.