Microstructural Analysis and the Multicolor UV/Violet/Blue/Green/Yellow PL Observed from the Synthesized ZnO Nano-leaves and Nano-rods

We report the synthesis of zinc oxide (ZnO) nano-leaves and nano-rods under high and extremely high alkaline experimental conditions, via a simple and low-temperature method. By performing transmission electron microscopy it is found that the nano-leaves and nano-rods grow along the (001) direction. Anisotropic, i.e., hkl-dependent line-shape broadening is observed in ZnO powder diffraction patterns. Rietveld analysis using Fullprof with model for handling the anisotropic size-like broadening is performed on these diffraction patterns. The refinement showed that ZnO powders belong to the hexagonal ZnS structure type with space group P63mc, and confirmed that the nano-leaves and nano-rods are oriented along the (001) direction. Results of visualization in 3D of the average crystallite shape obtained from refinement of spherical harmonics coefficients showed elongated shapes in the both samples, exhibiting a slight twisting for nano-leaves. Diffuse reflectance measurements reveal that the optical band-gap energies found for the ZnO nano-leaves and nano-rods is somewhat smaller than a wide-direct band gap of 3.37 eV. We argued that well defined and strong photoluminescence (PL) bands in the visible part that belong to the defects may influence the observed displacement of a ultraviolet (UV) near-band-edge emission, and which is related with obtained slightly lower band-gap energies than the established band gap of bulk ZnO. We discuss processes behind the multicolor UV/violet/blue/green/yellow emission band in PL spectra.