Crystalline scintillator materials comprising nano-scale particles of metal halides are provided. The nano-scale particles are less than 100 nm in size. Methods are provided for preparing the particles. In these methods, ionic liquids are used in place of water to allow precipitation of the final product. In one method, the metal precursors and halide salts are dissolved in separate ionic liquids to form solutions, which are then combined to form the nano-crystalline end product. In the other methods, micro-emulsions are formed using ionic liquids to control particle size.