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 assynthesized 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. Ultravioletvisible 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.