Hollow ZnO microspheres self-assembled from rod-like nanostructures: morphology-dependent linear and Kerr-type nonlinear optical properties

Abstract

Hollow nanostructures have attracted attention because of their unique physiochemical properties and broad potential applications in electronics, optics and photonics. In this study, a facile hydrothermal approach was developed to fabricate hollow ZnO microspheres via self-assembled rod-like nanostructures. The morphology-controlled synthesis was conducted by altering hydrothermal treatment temperature (150, 200 and 250 °C) in solutions containing zinc acetate dihydrate precursor and glycerol as the stabilizing agent. The morphological observations indicated that hydrothermally grown ZnO architectures could be reasonably adjusted by modulating hydrothermal reaction temperature. Possible growth routes are proposed to elucidate the formation process of ZnO microspheres with the rod-like nanostructures. Morphology-dependent absorbance and emission along with red-shifts with improved crystalline qualities were observed with increasing hydrothermal growth temperature. Kerr-type nonlinear optical characteristics examined using single-beam Z-scan technique in the near infrared spectral range under nanosecond Nd-YVO4 laser pulses showed positive values of nonlinear refraction providing an evidence of self-focusing behaviors at the excitation wavelength of 1064 nm in all the samples studied. The highest Kerr-type nonlinear susceptibility was estimated to be 2.31 × 10–6 esu for hollow ZnO microspheres grown at 250 °C, suggesting synergistic effects of surface morphologies on optical nonlinearities.