In this paper, a water ethanol oleic acid system was developed to prepare LiREF4 nanocrystals with a controlled size and shape. The influence of LiOH concentration and temperature on the phase and shape evolution of the LiREF4 nanocrystals was systematically investigated and discussed. It was found that the LiOH concentration was the key factor responsible for the shape evolution and phase control for LiREF4 nanocrystals at selected temperatures. The LiYF4-LiLuF4 core-shell nanostructure was synthesized and characterized.