, where hν = 1239.7/λ having the unit of eV, wavelength λ having the unit of nm and B being a constant. Finally, linear regression was performed for the linear portion of the (F (R ∞ )•hν) 1/2 vs. energy hν curve, and E g is the intercept of the straight line with the horizontal axis, which is around 1.21 eV.