Photoacoustic spectroscopy study on the co-fluorescence effect of Eu-La-Hba solid complexes

The photoacoustic (PA) spectra of Eu³⁺-La³⁺-Hba complexes are reported (Hba: benzoic acid). It is found that the PA intensity of the ligand bears a relation to the energy transfer processes. For Eu³⁺-La³⁺-Hba coprecipitates, with increasing the concentration of La³⁺, the PA intensity in the region of the ligand absorption decreases firstly, then increases. It is indicated that the addition of the second rare earth ion La³⁺-changes the relaxation processes of the complexes. The changes of fluorescence spectra turn out to be complementary to the PA spectra. The intramolecular energy transfer and intermolecular energy transfer processes in the coprecipitates are discussed.