The band gap obtained for 1% doping was 2.9 eV which is low value compared to that reported for pure NiO (Fig ). However, on increasing the doping concentration to 3 and 5 % the band gap obtained as representative of the host material NiO. This indicates that the lower doping of 1% Mn has been able to create Ni +2 vacancies making it a p-type semiconductor. The positive ion vacancies are generated to compensate for the extra charges carried by Mn +3 or Mn +4 . The Mn +2 ions mainly replace the Ni +2 causing comparatively less perturbations in the lattice. The positive ion vacancy again is an effective negative ion which causes the nearby positive ions to move inward and negative ions to move outwards creating polarization. The diploe moment due to this polarization again interacts with the electric field of the incoming light wave. As per Fermi's Golden Rule the rate of optical transition is given by