Rare earth fluorides upconversion nanophosphors: from synthesis to applications in bioimaging

Rare-earth (RE) fluoride upconversion nanoparticles (UCNPs), when excited by lower-energy photon radiation, exhibit a unique narrow higher energy output emission. This unique luminescent property makes the UCNPs promising bioimaging probes with fascinating features, including low autofluorescence, less scattering and absorption, and deep penetration in biological samples. This highlight aims to focus on the representative established methodologies for the preparation and surface modification of these UCNPs and their applications as luminescent labels.