Band Gap Engineering of ZnO Nanocrystallites Prepared via Ball-Milling

Zinc oxide (ZnO) nanostructures have become the foremost prevalent metal oxide materials for technological applications due to their tunable optical properties. However, a simple, cheap and green method is required for the mass production of these nanostructures. In the present investigation ball-milling technique was used to tune the band gap of ZnO nanocrystallites. Samples were synthesized using metallic Zn powder and distilled water via wet-milling followed by dry-milling. The crystallite size of the ZnO samples were determined in the range of 24.9 - 22.0 nm depending on the dry milling time. UV-vis absorbance measurements and Kubelka-Munk theory were used to calculate the band gap of the ZnO nanocrystallites. The energy band gap of the samples was successfully tuned in the range of 3.15 - 3.02 eV depending on the nanocrystallite size. This behavior was explained by the surface states and energy traps on the band edge, created by delocalization of molecular orbitals.