It is clear that ZnO can emit luminescence over the entire visible region. Radiative transition via matrix, impurities, and
defect states (native point defects) seems to be the plausible explanation of the PL emission in the given sample. ZnO has a number of deep defect states between the valance band and the conduction band, commonly identified native defects in ZnO are Oxygen vacancies (Vo), Zinc vacancies (VZn), Oxygen interstitials (Oi), Zinc interstitials (Zni), Oxygen antisites (OZn), and Zinc antisites (ZnO) . The concentration of these deep levels or native point defects in ZnO depends on their formation energy and at thermodynamic equilibrium the concentration can be given as