Fluorescence enhancement of europium complexes by core–shell Ag@SiO2 nanoparticles

•Three kinds of Ag@SiO2 with shell thickness of around 10, 15 and 25 nm were prepared.•Six complexes of europium with halo-benzoic acid were synthesized.•Ag@SiO2 nanoparticles can significantly enhance the fluorescence of the complexes.•When the thickness of SiO2 shell is 25 nm, enhancement of fluorescence is the biggest.•The order of enhancement for the complexes with different halogen atom is F < Cl < Br.

Three kinds of core–shell Ag@SiO2 nanoparticles with shell thickness of around 10, 15, and 25 nm, respectively, have been prepared by modified Stöber method and used for fluorescence enhancement. Six kinds of europium complexes with halobenzoic acid have been synthesized. Elemental analysis and lanthanide coordination titration show that the complexes have the compositions of Eu(p-XBA)3·H2O and Eu(o-XBA)3·2H2O (X = F, Cl, Br). The fluorescence spectra investigation indicates that the introduction of Ag@SiO2 nanoparticles into the europium complexes’ solution can significantly enhance the fluorescence intensities of the complexes. The sequence of enhancement factors for halobenzoic acid complexes with different halogen atoms is F < Cl < Br, and the fluorescence enhancement factors increase as the excitation wavelength of complexes increase. When the thickness of the SiO2 shell is 25 nm, the fluorescence intensity of the europium complexes can reach a maximum enhancement factor of 5.1. The fluorescence enhancement mechanism may be the metal-enhanced fluorescence resulting from surface plasmon resonance of nanoparticles. And the nanoparticles near the complexes can effectively prevent complexes from the interaction with the solvent molecules, leading to a decrease of nonradiative energy transfer and the suppression of luminescence quench.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide