Temperature dependence of direct and indirect band gaps of Bi13I2S18 hexagonal rod crystals

Single crystals of Bi13I2S18 have been grown by chemical vapor transport method. The band-edge properties of Bi13I2S18 are evaluated using temperature-dependent optical absorption and thermal modulated reflectance (TR) measurements in the temperature range between 30 and 300 K. Single-crystal X-ray diffraction of different orientations showed structural anisotropy and identified the crystalline phase of the as-grown Bi13I2S18 hexagonal micro pillars. According to transmission and TR measurements, the Bi13I2S18 hexagonal rod is confirmed to be an indirect semiconductor that simultaneously possesses indirect (E-g(ind) at similar to 0.73 eV) and direct (E-g(d) at similar to 1.06 eV) optical gaps. The averaged value of direct and indirect gaps is close to 1 eV that may efficiently absorb the sunlight spectrum for solar energy application. Temperature-energy variation and line-width broadening behavior (TR) of the band-edge transition of Bi13I2S18 are also analyzed and discussed herein. (C) 2017 Elsevier B.V. All rights reserved.