The Tauc relation 𝛼(hν) = A (hν -Eg) n where 𝛼 is the absorption coefficient, hν is the energy (in eV), A being the energy-dependent constant is used to determine the optical band gap in eV from the absorption spectra. The value of n is 1/2 for direct transitions, which is used in this case. For high photon energies, the absorption coefficient is proportional to the optical energy band gap (Eg). For direct transitions between conduction and valence bands, no change in the electron wave vector is assumed, and the absorption coefficient for (E= hv) for direct transitions can be expressed as eq 1.