Rare earth fluoride nano-/microcrystals: synthesis, surface modification and application

This feature article highlights the recent advances on the chemical synthesis, surface modification and applications of rare earth fluoride nano-/microcrysals. In the past decade, great progress in the size and shape control of rare earth fluoride nano-/microcrystals has been made by developing solution phase-based methods such as thermal decomposition, hydro(solvo)thermal reaction, hydrothermal in situ conversion route, and ionic liquids-based synthesis. The main challenge of fluoride nanocrystals for biological applications is that it is hard to obtain ideal nanocrystals with smaller size (sub-50 nm), higher luminescence yield, better dispersity and stability in aqueous solvents, and superior biocompatibility. In order to overcome these shortcomings, a series of strategies of surface modification have been outlined in this review. Finally, we introduce the application of rare earth fluorides, with special emphasis on β-NaY(Gd)F 4 : Yb 3+ , Er 3+ upconversion nanopaticles (UCNPs) in biomedical applications including biological labels, multimodal bioimaging, photodynamic therapy and drug delivery. This feature article highlights the recent advances on the chemical synthesis, surface modification and applications of rare earth fluoride nano-/microcrysals.