Factors affecting the metal-enhanced luminescence of lanthanide complexes by Ag@SiO2 nanoparticles

Abstract

Metal-enhanced luminescence (MEL) via Ag@SiO2 nanoparticles provides a promising strategy for the superior luminescence of lanthanide complexes. However, because of the delicate structure of the composites of Ag@SiO2 and complexes, it remains a great challenge to achieve the ideal MEL effect. Herein, five types of Ag@SiO2 nanoparticles with distinct core sizes (100 and 46 nm) and varied silica shell thickness (3, 24, 32, 52 and 55 nm) were prepared. Four kinds of lanthanide complexes RE(BA)3·H2O and RE(pyca)3·2H2O (RE = Eu and Tb, BA = benzoate, pyca = 2-pyrazine carboxylate) were synthesized. A series of REL3-Ag@SiO2 (L = BA−, pyca−) composite nanoparticles were prepared through the interaction of the Ag@SiO2 nanoparticles and the complexes. The adsorption of the complexes on the surface of Ag@SiO2 nanoparticles was confirmed by transmission electron microscope and energy dispersive X-ray spectroscopy. Luminescence property investigation showed that the factors affecting the MEL effect included the excitation and emission wavelength of lanthanide complexes, the kinds of lanthanide ions and organic ligands, as well as the core size and shell thickness of Ag@SiO2. Among these factors, the excitation wavelength of lanthanide complexes and the SiO2 shell thickness were found to play decisive roles. Finally, 25.92 times enhancement in luminescent intensity and 7.4 times increase in luminescence quantum yield can be achieved on Tb(BA)3·H2O by Ag@SiO2 with core size of 46 nm and shell thickness of 24 nm.