Surface Coating Effect on Structural, Optical and Photoluminescence Properties of Eu3+ Doped Yttrium Fluoride Nanoparticles

Europium doped yttrium fluoride (YF3:Eu) nanoparticles(core-NPs) with and without a passive layer of LaF3 coating around the core-NPs were prepared by simple polyol process. The surface of these luminescent core/shell-NPs was additionally functionalized with amorphous silica. The phase purity, crystalinity, shapes and size of the as-prepared core and their respective core/shell-NPs were determined by X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM). The as-prepared core/shell-NPs were successfully grafted with silica layer as verified by Fourier transform infrared spectroscopy (FTIR). As observed from absorption spectra, the energy band gap was decreased after core/shell formation because of increase in grain size of the luminescent-NPs. The core/shell-nanostructure synthesized by this method exhibited a remarkable enhancement than their respective core-NPs. However, the emission intensity was suppressed after silica surface coating because of non-radiative transitions effect. The presence of silanol (Si-OH) groups on their surfaces not only results in high solubility in aqueous solvents, but also allows further conjugation with biomolecules such as antigens, antibodies and oligonucleotides, which pave the way for potential bio-applications of the core/shell/SiO2-NPs.