Silica Nanoparticle Coating of NaYF4:(Yb3+, Er3+) Upconversion Phosphor

Abstract

To improve its light conversion efficiency, NaYF4:(Yb3+, Er3+) upconversion (UC) phosphor, which generates one visible photon by absorbing two or more near-infrared photons, was coated with SiO2 nanoparticles. The surface modification of phosphor was performed by using a modified sol-gel method as a function of the concentration of colloidal silica employed as the surface coating precursor. It was found that the PL intensities depend on the concentration of colloidal silica. When a 2.7 wt% concentration of colloidal silica was used, the NaYF4:(Yb3+, Er3+) phosphor exhibited a homogeneous coating with silica and an approximately 9% increase in the PL intensity, as compared with that of the non-coated sample of NaYF4:(Yb3+, Er3+) phosphor. This increase in the PL intensity can be explained by the suppression of the nonradiative recombination of electron-hole pairs via surface defects. The experimental results suggest that the surface modification of upconversion phosphors with a silica coating of the appropriate concentration is a simple and effective solution to improve the light conversion efficiency of upconversion phosphors used in optoelectronic devices.