Synthesis of Mg-doped hierarchical ZnO nanostructures via hydrothermal method and their optical properties

• Hierarchical ZnO nanostructures can be obtained by doping Mg2+ in ZnO nanosheets.
• Lattice parameters are calculated by Rietveld analysis.
• Mg-doped ZnO has much higher absorption in UV region and visible region.
• Mg2+ doping can lead to a remarkable intensity in PL spectra.

Hierarchical flower-like ZnO nanostructures and Mg-doped ZnO flower-like hierarchical nanostructures composed of porous nanosheets were synthesized via a one-step hydrothermal method. In this method, Zn(NO3)2·6H2O was used as a precursor and Mg(NO3)2·6H2O was the dopant. FESEM, EDS, XRD, UV–vis absorption spectra and PL spectra were used to characterize the samples. It demonstrates that small portions of Mg are successfully incorporated into the lattice of the ZnO nanostructures. The incorporation of Mg into ZnO is supported by broadening and higher Bragg angle shift in XRD pattern and EDS analysis. Cell Parameters of hierarchical flower-like Mg-doped ZnO nanostructures are obtained from Rietveld analysis. The decrease of c-axis indicates that substitution by Mg2+ is the dominant doping form in the hierarchical ZnO nanostructures. PL spectra show that the effective Mg doping suppresses the near band gap emission and the green emission. The band edge emission shifts to the blue with increasing amount of Mg doping, reflecting the change in the excitons energy seen in the absorption spectra. The defect band is believed to be due to deep traps and becomes dominant at high levels of doping. All the results show that the molar ratio of Mg and Zn determines the structure, surface morphology and optical properties of the samples significantly.