Recent Progress in Rare Earth Micro/Nanocrystals: Soft Chemical Synthesis, Luminescent Properties, and Biomedical Applications

The recent progress on several soft chemical routes for the controlled synthesis of rare earth (RE) inorganic nano/microcrystals is reviewed. On the basis of the mechanism of luminescence, RE luminescence can be divided into down-conversion (DC) and up-conversion (UC) emission processes. In the light of DC and UC processes, two categories of RE phosphors can be obtained, DC phosphors and UC phosphors, which usually can be distinguished by the sorts of doped Ln3+ ions. Due to the various combinations of RE3+ ions for DC multicolor emissions, there are three doping systems for DC white light emissions, including monodoped, codoped, and tridoped materials. For these materials, the emission lines of each couple of doping ions will cover blue region and yellow region, respectively, and the emission intensities are comparable, resulting in white light emissions. A better understanding of the synthetic methodology will promote the systematic design of synthetic strategies and then direct us to produce nano/microcrystals with predesigned structures.