Fluorescence enhancement of Tb3+ complexes by adding silica-coated silver nanoparticles

Six kinds of terbium ternary complexes with halo-benzoic acids were synthesized. Their compositions were determined by C, H elemental analyzer and EDTA titration. The infrared spectra, ultraviolet absorption spectra, and fluorescence spectra were also measured to identify the complexes. Elemental analysis showed that the compositions of these complexes were Tb(p-BrBA)(3)center dot H2O, Tb(p-ClBA)(3)center dot 2H(2)O, Tb(p-FBA)(3)center dot H2O, Tb(o-FBA)(3)center dot 2H(2)O, Tb(o-ClBA)(3)center dot H2O, and Tb(o-BrBA)(3)center dot H2O, respectively. The monodispersed Ag@SiO2 core-shell nanoparticles with silica thicknesses of 10, 15, and 25 nm were successfully prepared and characterized by transmission-electron microscopy. Fluorescence intensities of the complexes were detected before and after Ag@SiO2 core-shell nanoparticles were added; the enhancement times were related to the silica-shell thickness. The fluorescence enhancement times were largest when the thickness of the silica shell was 25 nm. The mechanism may be attributed to the localized surface-plasmon resonance. Furthermore, the enhancement effect of terbium fluoro-benzoate complexes was the strongest in these complexes. This result may be attributed to the hydrogen bond between the hydroxyl on the surface of the silica shell and the fluorine atom.