Abstract
The static refractive index no of different types of materials, like semiconductors, insulators, oxides, thin-films, and glasses, has been reported in many publications in attempts to estimate how it can be correlated to the optical bandgap. Reviewing of the previous studies to correlate the optical refractive index and energy gap led to concluded that Reddy Ahmmed approximation was selected to develop a new realized form that can give a good fit to the experimental data and, hence, be used directly as an accurate formula in the theoretical studies. The obtained formula correlates the optical/static refractive index to the energy bandgap and the oxygen atom's electronegativity. Such a new relation has been used to calculate the refractive indices for more than 96 materials (elements/compounds) with a high agreement with the experimental data.