Redox-induced reversible luminescence switching of cerium-doped upconversion nanoparticles

Smart upconversion nanophosphors (UCNPs) that can be reversibly switched between two or more luminescent states by certain external stimuli have attracted considerable attention due to their great potential in biological applications. Here we report for the first time a type of redox-switchable UCNPs by codoping NaGdF4:Yb/Er nanorods with the redox-active Ce3+/Ce4+ ion pairs. A reversible switching of their UC luminescence intensity was observed upon the variation of the surrounding redox environments. We show solid proof that the luminescence switching is caused by the tailoring of the NaGdF4 host crystal structure in response to changing redox state of the codoped cerium ions. A proof-of-concept example is further demonstrated by using these UCNPs for probing the dynamical variation of redox environments in biological tissues. (C) 2016 Elsevier B.V. All rights reserved.