Single-crystal growth and optical properties of undoped and Ce3+ doped CaGa2S4

To improve the crystallinity of CaGa2S4 single crystals, we have grown the crystals under various conditions by the horizontal Bridgman method using a travelling temperature gradient. If we lower the growth speed to < 0.5 cm/h while keeping the growth temperature close to but a little higher than the melting point, cracks and voids in the crystals are substantially reduced. A carbon boat is adopted in order to avoid the reaction of an ampoule with the material solution, which is found effective to improve the quality of a grown crystal. However, an absorption band with a peak at 3.2 eV newly emerges to turn a grown crystal yellowish. Absorption spectra of Ce3+-doped crystals are also measured. As a result, the energy separation between the 5d sublevels of Ce3+ ion, i.e., T-2g and E-g is first estimated as 0.8 eV. (C) 2002 Elsevier Science B.V. All rights reserved.