Oxynitride nanoparticles, methods of preparation thereof, and methods of use thereof are disclosed. One representative oxynitride nanoparticle includes a M.sub.xO.sub.yN.sub.z nanoparticle, where x is in the range of about 1 to 3, y is in the range of about 0.5 to less than 5, and z is in the range of about 0.001 to 0.5.