Lanthanide-doped luminescent nanocrystals have great potential as biological luminescent labels, but their use has been limited because of most of these nanocrystals are hydrophobic. In this work, water soluble LaF3:Eu3+ down-conversion nanocrystals were prepared by encapsulated individual nanocrystals with polyvinylpyrrolidone (PVP). Their morphology, surface structure and luminescence properties were explored in detail. The results indicate that these nanocrystals can be readily dispersed in water, forming a stable and transparent colloidal solution. The colloidal solution displayed unique red luminescence with high emission intensity under ultraviolet excitation. These results suggest that these nanocrystals have great potential as luminescent labeling materials for biological applications. (C) 2010 Elsevier B. V. All rights reserved.