NOVEL BLUE-TO-GREEN PHOSPHOR OF CU-AL-S SYSTEM SENSITIZED WITH RARE-EARTH ELEMENTS

Single crystals with a new phase of the Cu-Al-S ternary system were grown from the starting composition of CuAl2S4 by chemical vapor transport. Transparent layered crystals were reproducibly obtained. The crystal symmetry was determined as trigonal, with lattice constants a = b = 13.001 +/- 0.002 angstrom, c = 12.043 +/- 0.002 angstrom, alpha = beta = 90-degrees and gamma = 120-degrees. The chemical formula of Cu2Al12S19 was suggested from electron probe microanalysis. The optical absorption edge was found to be 3.45 eV. Crystals doped with Eu and Ce rare-earth ions were found to emit strong luminescence at 515 nm and 466 nm, respectively in the blue-to-green region at room temperature.