Quantum size effect on ZnO nanoparticle-based discs synthesized by mechanical milling

► Homogenously sized ZnO nanoparticles were synthesized via milling process. ► The UV blue shift resulted from the quantum size effect in the ZnO nanoparticle. ► The milling process had a significant effect on the grain crystallinity. ► Most optical properties were attributed to the defects introduced into the sample.