Synthesis, Optical Properties, and Ethanol-Sensing Properties of Bicone-like ZnO Microcrystals via a Simple Solution Method

Large-scale uniform bicone-like ZnO microcrystals were successfully synthesized via a simple solution method at lower temperature (80 °C). The as-prepared bicones, composed of two cones, possess a single-crystal hexagonal structure and grow along the [0001] direction. The influence of the reactant concentration on the size and shape of the ZnO samples has been studied in detail, and the results revealed that reactant concentration plays a crucial role in determining the final morphologies of the samples. The growth process of the bicone-like ZnO microcrystals was viewed by field emission scanning electron microscopy (FESEM) characterization, and a possible formation mechanism was proposed. Optical properties of the bicone-like ZnO microcrystals were also investigated by photoluminescence (PL) spectroscopy. The room-temperature PL spectrum of the bicone-like ZnO microcrystals shows a strong UV emission peak. The UV emission is further identified to originate from the radiative free exciton recombination by temperature-dependent PL. In addition, the bicone-like ZnO microcrystals exhibit excellent sensing properties toward ethanol gas at an operating temperature of 300 °C. The response and recovery times are 2 and 3 s, respectively. These results indicate that the bicone-like ZnO microcrystals have potential applications in fabricating optoelectronic devices and gas sensors.