Influence of reaction parameters on crystal phase growth and optical properties of ultrasonic assisted hydro- and solvothermal synthesized sub-micrometer-sized CdS spheres

Sub-micrometer-sized CdS spheres were synthesized by hydrothermal and solvothermal reactions using Cd(NO3)2.4H2O and CH4N2S raw materials at a constant stoichiometric 1 : 2, Cd : S molar ratio. Various conditions such as solvent type (water and/or ethanol), reaction time and temperature were examined for the synthesis of the targets. The synthesized materials were characterized by powder X-ray diffraction (PXRD) technique and fourier-transform infrared (FTIR) spectroscopy. Crystal structure study was performed in a comparison mode to investigate the crystalline phase purity and growth of the obtained CdS materials when the reaction conditions were changed. The PXRD data indicated that the as-synthesized materials were crystallized well in a hexagonal crystal system with the space group P63mc. However, the crystal phase growth study showed that a cubic crystal system of CdS was obtained as a second crystal phase in the mixture. The morphologies of the synthesized materials were studied by field emission scanning electron microscopy (FESEM) technique. The data showed that the reaction solvent had a critical influence on the morphology of the obtained materials. Ultraviolet-visible spectra showed that the synthesized CdS materials had strong light absorption in the ultraviolet-visible light regions. The calculated direct optical band gap energies of the obtained materials were in the ranges of 1.90-2.30 eV.