Study of Lanthanide Complexes with BTFA in Silica Gels by Photoacoustic Spectroscopy

In this work, lanthanide beta-diketonate complexes Ln(btfa)(3)center dot 2H(2)O (Ln(3+): Eu3+, Sm3+, and Tb3+; btfa: 4,4,4-trifluoro-l-phenyl-1,3-butanedione) were incorporated into silica gels by a sol-gel method. Photoacoustic (PA) spectra of these complex-doped silica samples were measured and studied. The PA intensity of the beta-diketonate ligand is nearly the same for lanthanide complexes in wet gels. After heat treatment at 150 degrees C, however, the PA intensity of the ligand increases for Eu3+, Sm3+, and Tb3+ complexes in silica gels, respectively. Different PA intensities of the samples are interpreted by comparison with their luminescence spectra. The luminescence result is consistent with the PA spectra. The result indicates that lanthanide beta-diketonate complexes cannot be formed in silica gels without a suitable heat treatment. Moreover, the relaxation process model is proposed based on the PA and luminescence results.