Silica glass implanted with Zn ions of 60 keV to 1.0×1017 ions/cm2 was annealed in oxygen gas to form ZnO nanoparticles (NPs). In as-implanted state, the implanted Zn atoms form Zn metallic NPs inside of the silica. After annealing at 600 °C, ZnO NPs form on the surface, while Zn metallic NPs still remain in the deep region. At 700 °C, most of Zn atoms move to the surface to form the droplet-shaped ZnO NPs which show two photoluminescence bands, i.e., an exciton band at 375 nm and a defect band at ∼500 nm. The defect band almost disappears in the samples annealed at 600 °C, which include both ZnO NPs and Zn NPs.