TheCdAl2S4single crystal grown by the chemical transport reaction method in an excess sulfur atmosphere showed the intensive blue photoluminescence (PL) peaked at 462 nm at 280 K. TheCdAl2S4single crystal had the defect chalcopyrite structure, and the optical energy gap of the single crystal with the direct band structure was found to be 3.398 eV at 280 K, and to be 3.577 eV at 17 K. ©1997 American Institute of Physics.