Title : Structural and Optical Properties of ZnO Nano-Powder Synthesized by Combustion and Sol-gel Method
ZnO is considered as the most important chemical compounds due to their distinctive properties owing to its wide band gab and large exciton binding energy. It is well known that the structural and the optical properties of ZnO differ by different methods of preparation. X-ray diffraction (XRD) and Transmission electron microscopy (TEM) were used to determine the structure properties of un-doped ZnO powders. Ultraviolet visible spectroscopy (UV-Vis) and Photoluminescence spectroscopy (PL) were used to determine the optical properties of un-doped ZnO powders prepared by both sol-gel and combustion method. The obtained results from ZnO synthesized by the sol- gel method showed that the crystallite size of ZnO was increases by increasing of the annealing temperature. Also, little change in the lattice parameter was observed when the annealing temperature increased, this change may be attributed to the change of particle size and quantum size effects. It is observed also that similar structure of ZnO prepared by sol-gel and combustion can be obtained at particular conditions. TEM studies showed that the ZnO nanocrystals are irregularly spherical with average diameter of 32 nm which is similar to the calculated crystallite size from the XRD data. The calculated energy band gab of ZnO prepared by sol-gel method is found to be increased with increasing the annealing temperature. There was a clear difference between the two PL spectra obtained from ZnO synthesized by a different method which is assigned to be due to complicated defect chemistry relevant to the experimental process. Also, the concentration and the type of defect are basically associated with preparation method.