The Eg value can be obtained by extrapolating the linear portion to the photon energy axis in that figure. Two absorption edges are observed at 5.0 eV and 5.2 eV in trace (a), and only one absorption edge can be found at 5.4 eV in trace (b). In the case of the 0-Pa film sample, the optical band-gap is found to shift from 5.4 eV to 5.0 eV or 5.2 eV due to the increase in ZnGa2O4:Cr3+ grain size and the change in the nature and strength of the interaction potentials between..the impurity and host materials, which increase the tailing of the absorption edge and hence reduces the band-gap [20].