Cerium doped crystals

The invention relates generally to crystals that allow selected wavelengths of light to pass therethrough, and more particularly, to optical band-pass or rejection filters that operate in the ultraviolet (UV) spectrum. A crystal having good optical transmission between 260 nm and 280 nm and strongly absorbing at 285 nm and higher, which is nonhydroscopic and stable at temperatures to 250° C. An example of such a crystal is Cerium doped YLiF. These properties make YLiFcrystals doped with Ce excellent materials for use as UV filters in the missile early warning spectral band. Optical devices including missile detection systems are also provided.