The compound BaZrSi 3O 9 is isomorphous with benitoite. Under cathode-ray excitation it shows an emission with a maximum at 285 nm. This emission is ascribed to the Zr 4+ ions. Activation with Ti 4+ or Eu 2+ yields efficient photoluminescent phosphors. It is further shown that the blue-green emission observed for a number of zirconium compounds is due to Ti 4+ impurities and that the Zr 4+ emission itself lies in the ultraviolet.