Plasmon enhanced upconversion emission in Tm3+/Yb3+/lithium niobate single crystal

Abstract

Light conversion efficiency, as the core issue of luminescence applications, has become the focus of upconversion (UC) study. Here, we have coated Au nano-films in different thicknesses on c-cut Tm3+/Yb3+/lithium niobate (LN) single crystal wafers, and discovered the luminescence intensity could be drastically enhanced by 15.1 and 26.5 folds for blue and red emission, respectively, in a proper Au thickness. Compared to the Au-free sample, optical measurements demonstrate a moderate enhancement of local optical power density. However, considering the non-linear relationship between the coating thickness and the enhancement factor, we attribute the drastic UC enhancement to the size-dependent localized surface plasmon resonance (LSPR); and accordingly, adopt an analytical optical absorption model to calculate the electron density of Au coating, which manipulates the resonance intensity and enhancement factor. The above explanation is further verified by the variation of LSPR frequency. These findings interpret the interaction between nano-scale Au coating and crystal surface, and demonstrate the feasibility and superiority of LSPR-enhanced UC luminescence in crystalline materials.