Colorless
CuAlS
2
was prepared by using either a small excess of Al or a deficiency of S or Cu. A stoichiometric ratio of the reactants or deficiency of Al yielded a green color product. These crystals showed ESR and optical absorption similar to iron‐doped crystals indicating that trace amounts of Fe+3 are responsible for the color. Crystals heated in the presence of elements such as Si or Cd lose their color and ESR spectrum, indicative of a reduction of Fe+3 to Fe+2. All as‐grown and most doped crystals were p‐type, while most crystals doped with a combination of Cd/Al were n‐type. Colorless
CuAlS
2
fluoresces with a broad peak at about 600 nm. The fluorescence may be stimulated by infrared after exposure to u.v. Mn‐doped crystals exhibit red‐orange fluorescence.