Enhanced upconversion of sub20 nm core/shell/shell nanophosphors for temperature and rhodamine B sensing

Abstract

Lanthanide-doped upconversion (UC) nanoparticles (NPs) have attracted great attention in many emerging applications. Although multilayer structures have been employed to strengthen UC intensity, balancing the energy transfer (ET) efficiency from sensitizer to activator as well as the back energy transfer (BET) efficiency remains a critical issue. Herein, the ET processes in the BaYF5-based core/shell/shell NPs are comprehensively manipulated, resulting in greatly enhanced UC intensity. By using the sub20 nm BaYF5:2Yb2Er@BaYbF5@BaYF5 nanostructure, the efficiencies of incident light absorption and ET from the sensitizer in the interlayer to the activator in the core are improved, while the BET is limited. The UC intensity of this nanostructure was approximately 3.7 times that of normal BaYF5:20Yb2Er@BaYF5 NPs. The isolation of Yb and Er can remarkably restrict the negative thermal quenching (NTQ) effect, resulting in improved temperature sensing performance. Moreover, the BaYF5:2Yb2Er@BaYbF5@BaYF5 NPs can be used for selective sensing of rhodamine B. Our results highlight the comprehensive manipulation of ET processes in a core/shell/shell nanostructure to significantly improve the UC intensity.