Facile synthesis of ZnO nanostructures and investigation of structural and optical properties

• ZnO nanostructures were synthesized by chemical bath deposition method.
• Particle’s shape and sizes were controlled by varying the HMT concentrations.
• Effect of particle’s sizes was observed in the band gap (shift) and photoluminescence.
• HMT is an effective suppressor of ZnO directional growth.
• Shape evolution of ZnO particles can be tailored by varying the HMT concentrations.

ZnO nanostructures were synthesized by chemical bath deposition method, using zinc nitrate [Zn(NO3)2] and hexa-methylene-tetra-amine [(HMT),C(H2)6N4] as precursors. Controlled size and shape evolution of ZnO nanostructures were achieved by changing the HMT concentration from 0.025 M to 0.1 M, whereas Zn(NO3)2 concentration kept constant. X-ray diffraction (XRD) and Raman study confirmed the formation of single crystalline, hexagonal wurtzite ZnO structure. Sharp peaks in Raman spectra, corresponding to E2(low) and E2(high) referred to wurtzite structure with higher order of crystallinity. Transmission electron microscopy (TEM) revealed that the shape and size of the nanostructures reduced, with increasing concentration of HMT. Further, effect of structure's size was observed in the band gap (shift). Photoluminescence study showed two peaks at ~ 380 nm and ~ 540 nm corresponding to the band to band transition and defect transitions. Modifications of properties are explained in detail on the basis of shape and size change of the structures and possible mechanism is discussed.