𝜌 (𝜔) is the density of states. The higher is the interaction of the electric field of the incident light with the dipole moment, the higher will be the rate of optical transition. The absorption intensity is proportional to |𝛤 12 | 2 . Therefore, an increased intensity in the absorption spectra is a measure of intensity of positive ion vacancy that has been created. This explains the fact that 1% Mn doping has caused more positive ion (Ni +2 ) vacancies compared to higher doping leading to a reduction in band gap.