Inhibiting concentration quenching in Yb3+-Tm3+ upconversion nanoparticles by suppressing back energy transfer
Dingxin Huang, Feng Li, Hans Ågren, Guanying Chen
Abstract
Abstract Lanthanide-doped upconversion nanoparticles are promising for applications ranging from biosensing, bioimaging to solid-state lasing. However, their brightness remains limited by the concentration quenching effect of lanthanide activator ions, which greatly restricts their utility. Here, we develop a heterogeneous core–shell–shell nanostructure based on hexagonal NaYF 4 , in which Tm 3+ activator and Yb 3+ sensitizer are separated into the core and inner shell, while the outmost shell is used to suppress surface quenching effects. We show that this design can alleviate the activator concentration quenching effect, resulting in optimal Tm 3+ concentration increasing from 1% to 8% at sub-100 W/cm 2 irradiance, compared with the canonical core-only NaYF 4 :Yb 3+ /Tm 3+ . Moreover, under high excitation irradiance (20 MW/cm 2 ), the optimal Tm 3+ concentration could be further increased to 50%. Mechanistic investigations reveal that the spatial separation of sensitizer and activator effectively suppresses the back energy transfer from Tm 3+ to Yb 3+ , driving the increase of optimal activator concentration. These findings enhance our understanding of lanthanide concentration quenching effect, unleashing opportunities for developing bright upconverting materials.