a crystal filter and a method of making a crystal filter capable of transmitting radiation within a particular pass band is disclosed . the crystal filter is particularly appropriate for a uv detection system , where the pass band is between about 200 to about 350 nm . a uv detection system incorporating the crystal filter is also described . one embodiment of crystal filter is formed from a single - crystal transparent host , such as a fluoride host , codoped with lanthanide or actinide fluorides and lanthanide or actinide nitrides , oxides , borides , carbides or hydroxides . filter crystals according to the present invention can be grown by various crystal growth methods , including czochralski and bridgeman crystal growth methods .