Recent advances in the synthesis and application of Yb-based fluoride upconversion nanoparticles

Lanthanide-doped upconversion nanoparticles are undergoing extensive investigations in many fields, particularly in biophotonics and photophysics. In an attempt to boost upconversion emission intensities, Yb-based fluoride crystals have been recently identified as more efficient alternatives to classical NaYF₄ crystals. Yb-Based fluoride crystals featuring a maximal occupancy of the host lattice by Yb³⁺ sensitizers facilitate the utilization of excitation light and promote energy transfer to upconverting activators, which contributes to a significant enhancement of upconversion luminescence. In this article, we present a survey of recent studies on chemical preparations of Yb-based fluoride nanoparticles with well-defined size and morphology. We show that these Yb-based upconversion nanoparticles are playing important roles in a few emerging applications such as optogenetics, biodetection and upconversion lasing.