ZnO crystal as a potential damage-recoverable window material for fusion reactors

Hydrothermal-grown bulk zinc oxide (ZnO) single crystals are investigated before and after 1-keV hydrogen-ion and deuterium-ion plasma irradiation. A decrease in optical transmittance, red-shifting of ultraviolet (UV) emission peaks, and shortening of UV emission lifetimes are observed from the bulk crystals immediately after irradiation. The results are attributed to the radiation-induced defects formed by hydrogen implantation. Although these defects immediately affect the optical properties of the single crystals, the optical transmittances and photoluminescence emissions recover days after irradiation. Our observations show the potential properties of a bulk ZnO single crystal as a damage-recoverable window material in high-flux-radiation environments such as those of fusion reactors.