Concentration-gradient neodymium (III)-doped fluoride nanoparticles with NIR-to-NIR down-conversion and NIR-to-visible up-conversion luminescence

The rational exploration of lanthanide-doped fluoride nanoparticles (NPs) is of great significance for advanced optical applications. Herein, the concentration-gradient Nd3+-doped NaGdF4 NPs and NaGdF4:3%Nd@NaGdF4 core-shell NPs were synthesized. The prepared NPs exhibits intense near-infrared emission upon 794 nm excitation, the concentration quenching of Nd3+ ions in the NaGdF4 host is ascribed to the dipole-dipole interaction. The fluorescence lifetime and luminescence efficiency of NPs are remarkably improved through coating the inert shell. In addition, the NaGdF4:3%Nd@NaGdF4 NPs displays obvious up-conversion luminescence under 808 nm laser irradiation, and the double-photon process is responsible for it. This research manifests that the title NPs is a potential dual-mode luminescent nanomaterial for advanced optical applications, especially photobiological application.