Fabrication and Optical Properties of Large-Scale Nutlike ZnO Microcrystals via a Low-Temperature Hydrothermal Route

Large-scale uniform nutlike ZnO microcrystals are successfully synthesized via a facile hydrothermal process. Field emission scanning electron microscopy and transmission electron microscopy results reveal that the as-prepared ZnO products have average lengths of 2.2 μm and diameters of 1.8 μm, possessing a wurtzite structure. The evolution process of the nutlike ZnO microcrystals has been viewed by FESEM characterization, and the results reveal that the reaction time plays a crucial role in determining the final size and shape of the samples. It is also found that the existence of triethanolamine (TEA) is vital to the formation of the complex microcrystals formed from self-assembled nanoparticles, and a possible formation mechanism is proposed. Optical properties of the ZnO sample are also investigated by PL spectroscopy. It is found that the intensity of the visible emission shows an obvious decrease after the nutlike ZnO is annealed in air for 90 min. Moreover, the UV emission is further identified to originate from the recombination of the radiative free exciton and the donor bound excition by the temperature-dependent PL spectra.