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.