Zinc oxide (ZnO) nanostructured films were prepared on quartz glasses by radio frequency magnetron sputtering deposition of ZnO films at different argon to oxygen (Ar/O2) gas ratios and post-treated in a reducing ambient at a low temperature. The effects of Ar/O2 gas ratio and substrate bias on the photoluminescence and structural properties were investigated. It was found that the formed ZnO nanostructures significantly depended on the O2 fraction. The crystallinities of the ZnO nanostructures were improved, and the green emission was enhanced with the decrease of the O2 fraction in the Ar/O2 mixtures. A green emission peak centered at 510 nm was obtained after the post-treatment. In addition, the applied substrate bias contributed to remarkably improving the crystallinity of the ZnO films. The strongest green emission was obtained from the ZnO nanostructures prepared from the ZnO film deposited in a pure Ar ambient with the substrate bias applied.