Twelve methods of determining energy band gap (E(g)) of semiconductors using diffuse reflectance spectroscopy have been applied in investigations of sonochemically produced antimony sulfoiodide (SbSI) consisting of nanowires. It has been proved that the best method of determining E(g) is based on simultaneous fitting of many mechanisms of absorption to the spectral dependence of Kubelka-Munk function evaluated from the diffuse reflectance data. It allows determining the values of indirect forbidden E(g), the Urbach energy, and the constant absorption/scattering of the examined semiconductor.

A novel sonochemical method for direct preparation of nanocrystalline antimony sulfoiodide (SbSI) has been established. The SbSI gel was synthesized using elemental Sb, S and I in the presence of ethanol under ultrasonic irradiation (35 kHz, 2 W/cm2) at 50 degrees C for 2 h. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and optical diffuse reflection spectroscopy (DRS). The SEM and HRTEM investigations exhibit that the as-prepared samples are made up of large quantity nanowires with diameters of about 10-50 nm and lengths reaching up to several micrometers and single-crystalline in nature.

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