Crystalline scintillator materials comprising nano-scale particles of metal oxides, metal oxyhalides and metal oxysulfides are provided. The nano-scale particles are less than 100 nm in size. Methods are provided for preparing the particles. In one method, used to form oxyhalides and oxysulfides, metal salts are dissolved in water, and then precipitated out as fine particles using an aqueous base. After the particles are separated from the solution, they are annealed under a flow of a water saturated hydrogen anion gas, such as HCl or H.sub.2S, to form the crystalline scintillator particles. The other methods take advantage of the characteristics of microemulsion solutions to control droplet size, and, thus, the particle size of the final nano-particles. For example, in one method, a first micro-emulsion containing metal salts if formed. The first micro-emulsion is mixed with an aqueous base in a second micro-emulsion to form the final nano-scale particles.