Photoacoustic spectroscopy study on lanthanide complexes with aromatic carboxylic acid in silica gels

Using a sol-gel process, lanthanide complexes Ln (Sal)(3)center dot H2O (Ln(3+) : Nd3+, Tb3+; Sal: salicylic -acid) are incorporated into silica gels by the hydrolysis and condensation of tetraetboxysilane (TEOS). After heat treatment at 150 degrees C for the lanthanide complexes in gels, the photoacoustic (PA) intensity of the ligand changes remarkably, while this difference can not be observed for the samples without heat treatment. Different PA intensities of lanthanide complexes in silica gels can be interpreted by comparison them with their luminescence spectra. The formation of lanthanide complex in silica gel is discussed by two aspects: radiative and nonradiative processes.