Enhancing Upconversion Luminescence Emission of Rare Earth Nanophosphors in Aqueous Solution with Thousands Fold Enhancement Factor by Low Refractive Index Resonant Waveguide Grating

Abstract

The enhancement of upconversion luminescence (UCL) of rare earth doped upconversion nanoparticles (UCNPs) in aqueous solution is particularly important and urgently required for a broad range of biomedical applications. Herein, an effective approach to achieve highly enhanced UCL from NaYF4:Yb3+,Tm3+ UCNPs in aqueous solution is presented. We demonstrate that UCL of these UCNPs can be enhanced more than 104-fold by using a mesoporous silica low refractive index resonant waveguide grating (low-n RWG) in contact with aqueous solution, which makes it well-suited for biomedical applications. The structure parameters of the low-n RWG are tuned via rigorous coupled-wave analysis simulation to ensure strong local excitation field to form atop the TiO2 surface of the low-n RWG, where UCNPs are deposited. As the low-n RWG is excited by a near-infrared laser at 976 nm to match its guided mode resonance (GMR) condition, UCL emitted from UCNPs is greatly enhanced thanks to the strong interaction between excitation lo...