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

The rational exploration of lanthanide-doped fluoride nanoparticles (NPs) is of great significance for advanced optical applications. Nevertheless, developing highly efficient near-infrared (NIR) emitting NPs that can be excited by NIR light remains a considerable challenge. Herein, the concentration-gradient Nd³⁺-doped NaGdF₄ NPs and NaGdF₄:3%Nd@NaGdF₄ core-shell NPs were synthesized. The prepared NPs exhibits intense NIR 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.