OSMAN Mohamed Abdelhameed Darweesh Assiut University, Faculty of Science

ZnS nanocrystals were prepared by chemical co-precipitation method. The effect of annealing temperature (Ta) on the morphological, structural and optical properties was investigated using x-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), UV-vis spectroscopy, selected area electron diffraction (SAED) and fourier transform infrared (FTIR) spectroscopy. Analysis of XRD patterns for as prepared and annealed samples showed that increasing Ta leads to an increase in the crystallite size (D) from 2.67 to 19.6nm. It is noticed that the obtained values of lattice parameters from HRTEM and SAED pattern are in good agreement with that deduced from XRD analysis. Furthermore, annealing process at 600oC and 700oC results in complete phase transformation, from as prepared ZnS cubic structure to ZnO hexagonal structure. Analysis of the XRD patterns, SAED, HRTEM and FTIR confirm this phase transition. Analysis of the optical absorption spectra indicates noticeable decrease in the direct band gap E_g^opt from 4.70 to 3.22eV with increasing Ta. This behavior is attributed to the enhancement in crystallinity and increase in particle size of ZnS nanoparticles. Moreover, UV photo-induced effect on the absorption edge was studied.