Photoacoustic and fluorescence studies of silica gels doped with rare earth salicylic acid complexes

Photoacoustic spectroscopy (PAS) is useful in the study of non-crystalline solids. By using PA amplitude and phase spectra, together with IR and fluorescence spectra, the variation of the energy levels and luminescence efficiencies and the intramolecular relaxation processes of silica gels doped with rare earth complexes with salicylic acid have been studied in comparison with their corresponding pure complexes. After the complexes are doped into silica gels, the PA and emission peaks of the ligands show a shift, but the peaks of rare earth ions do not apparently shift. The complex molecules are dispersed in the silica gel, this reduces concentration quenching. In addition, the relatively rigid host structure of silica gel limits the vibrations of the ligands, which decreases the non-radiative transition and increases the lifetime of Tb3+.