Study on silicon oxide coated on silver nanocrystal to enhance fluorescence intensity of rare earth complexes

Twelve kinds of rare earth complexes were synthesized using halo-benzoic acid as anion ligand and Sm3+ and Dy3+ as central ions, respectively. The complexes were characterized by elemental analysis, rare earth coordination titration and electrospray ionization mass spectra, from which the compositions of the complexes were confirmed to be RE(p-FBA)3·H2O, RE(p-ClBA)3·2H2O, RE(p-BrBA)3·H2O, RE(o-FBA)3·2H2O, RE(o-ClBA)3·H2O, RE(o-BrBA)3·H2O (RE=Sm3+, Dy3+). Besides, IR spectra and UV-visible absorption spectroscopy indicated that the carboxyl oxygen atoms of ligands coordinated to the rare earth ions. Moreover, Ag@SiO2 core-shell nanoparticles (NPs) were prepared via a modified Stöber method. The average diameters of silver cores were typically between 60 nm and 70 nm, and the thicknesses of the SiO2 shells were around 10 nm, 15 nm and 25 nm, respectively. The influence of Ag@SiO2 NPs on the luminescence properties of the rare earth complexes showed that the luminescence intensities of rare earth complexes were enhanced remarkably. As the thickness of SiO2 shell increases in the range of 10-25 nm, the effect of metal-enhanced fluorescence become obvious. The mechanism of the changes of the fluorescence intensity is also discussed.