Synthesis and Optical Properties of Solid and Hollow ZnO Microspheres Prepared by Hydrothermal Method
Keywords:ZnO microsphere, growth mechanism, optical properties
AbstractWe successfully synthesized solid and hollow ZnO microspheres by a template-free hydrothermal method on the substrate of porous alumina membranes. The morphology of prepared sample was characterized by scanning electron microscopy and transmission electron microscopy. The growth mechanism of the synthesized ZnO microspheres is discussed in detail. At step 1, solid ZnO microspheres were prepared by the thermal decomposition of the Zn(OH)2 microspheres synthesized under the mixture of Zn(NO3)2·6H2O, C6H12N4, and C6H5Na3O7·2H2O solution. The quantity of C6H5Na3O7·2H2O dopant will greatly affect the morphology of the prepared sample by controlling ZnO nucleation and growth rate. At step 2, hollow ZnO microspheres were prepared by removing the Zn(OH)2 cores in an alkaline solution. The proper pH value also plays a key role in preparing hollow ZnO microspheres with high quality. Compared with hollow nanostructure, the solid ZnO microsphere shows the relatively strong Raman peaks at 437 cm-1, which suggests that the prepared solid spheres should have the better crystal quality. Photoluminescence spectra show that the solid ZnO microspheres have the relatively strong ultraviolet (UV) peak at ~ 380 nm attributed to the recombination of free exciton, and the weak green peak owing to the low surface-to-volume ratio.
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