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.