where E is Photon energy (eV), h is Planck's constant (4.132  10 -15 eV.s), υ is the frequency (s -1 ), c is photon velocity (nm), λ is the wavelength (nm), α is absorption coefficients from absorption mode, B is constant, and Eg is bandgap (eV), A is absorbance value, l is sample width (cm), R is reflectance value, K is absorption coefficient from reflectance mode, and S is scattering coefficient from reflectance mode. For direct and indirect bandgaps, r is equal to 2 and ½, respectively.