Tunable and ultra-broad plasmon enhanced upconversion emission of NaYF4:Yb3+, Er3+ nanoparticles deposited on Au films with papilla Au nanoparticles

Abstract

Rare earth ions doped upconversion nanoparticles have broad applications ranging from biological imaging to solar energy conversion. However, the application of upconversion nanoparticles has been limited due to their low upconversion efficiencies. In this paper, two kinds of Au films with tunable and broad surface plasmonic absorptions were used to enhance the upconversion emission of NaYF₄:Yb³⁺, Er³⁺ nanoparticles, respectively. The results demonstrated that the upconversion enhancement is highly dependent on the topography of Au films. About 77 and 40-fold enhancement were obtained for the green and red UC emissions of NaYF₄:Yb³⁺, Er³⁺ nanoparticles on the irregular and random Au particles. About 121 and 78-fold enhancement were obtained for the green and red UC emissions of NaYF₄:Yb³⁺, Er³⁺ nanoparticles on continuous Au films with papilla Au nanoparticles, respectively. In contrast to that of NaYF₄:Yb³⁺, Er³⁺ nanoparticles deposited on quartz substrate, and the corresponding UC efficiency of NaYF₄:Yb³⁺, Er³⁺ nanoparticles on irregular and random Au particles and continuous Au films with papilla Au nanoparticles increased by 50% and 100%, respectively. The enhancement of UC emission may be attributed to the increase of radiative decay rate and the enhancement of excitation field.