Microwave-hydrothermal synthesis and photoluminescence characteristics of zinc oxide powders

A microwave-hydrothermal process for the synthesis of crystalline zinc oxide powders has been developed in this study. Well-crystallized zinc oxide powders exhibiting different morphology, crystallinity, and particle size have been successfully prepared by controlling the process temperature and molarity of NH₄OH in the starting solution. With increasing process temperature and NH₄OH molarity during synthesis, the morphology of ZnO powders changes from flowerlike agglomeration to a well-developed rodlike shape. The band gap of ZnO powders increases with a decrease in the molarity of NH₄OH during synthesis. Vacuum ultraviolet radiation (VUV) excited luminescence studies for ZnO powders reveal an excitation band at 161 nm possibly due to the absorption of O²⁻ 2p electrons in the valence band. The VUV excitation band of ZnO powders observed at 161 nm will be useful for excitation of gas-discharged plasma display devices.