Photoacoustic and luminescence properties study on energy transfer and relaxation processes of Tb(III) complexes with benzoic acid

The photoacoustic (PA) amplitude spectra of Tb(Benz)3, Tb(Benz)3Phen and Tb(Benz)3Bpy complexes (Benz: benzoic acid; Phen: 1,10-phenanthroline; Bpy: 2,2′-bipyridine) have been measured, and the PA phase data of the different complexes calculated. The PA amplitude spectra combined with the luminescence spectra reflected the variation of the luminescence properties, and the PA phase is directly relative to the relaxation time. The luminescence intensity and the PA phase data increase when the second ligand Bpy is introduced, while they decrease greatly when Phen is added. These results are due to the different intramolecular energy transfer processes. Compared with Tb(Benz)3, the energy gap between Tb3+ and Bpy is more suitable for energy transfer, while the energy gap between Tb3+ and Phen is so small that the thermally activated Tb3+-to-Phen inverse energy transfer rate increase more. The models of energy transfer and relaxation processes of Tb(Benz)3Bpy and Tb(Benz)3Phen are established.