Growth and properties of ZnO nanoblade and nanoflower prepared by ultrasonic pyrolysis

ZnO nanoblades and nanoflowers are synthesized using zinc acetate dihydrate Zn(CH3COO)2∙2H2O dissolved in distilled water by ultrasonic pyrolysis at 380–500°C. Thermogravimetry-differential scanning calorimetry, x-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and low-temperature photoluminescence (PL) were used to characterize the thermal properties, crystalline and optical features of the ZnO nanostructures. The results showed that at 400°C the formation of nanoblades resulted from the simultaneous precipitation and nucleation in zinc acetate precursor. At an elevated temperature of 450°C, decomposition was almost advanced and thus the size of nanopetal became smaller and aggregates became larger by as much as 60nm. The formation of aggregates is explained in terms of random nucleation model. Through PL measurement, nanoblade showed a strong near band-edge emission with negligible deep-level emission and free exciton band-gap energy Eg(0)=3.372eV and Debye temperature β=477±65K by the fitting curve of free exciton peak as a function of temperature to Varshni equation, Eg(T)=Eg(0)−αT2∕(β+T), which are very close to bulk ZnO.