Therefore, the blue shift of the CTB is mainly
attributed to the enhancement of Eg. It can be confirmed by the results from Figs. 4 and 5. As for the intra-3d transitions, they are known to vary widely depending on the crystal field of the host material. The intra-3d transitions are not affected by varying the oxygen pressure from 1 to 0 Pa, indicating that the crystal field strength parameter 10Dq does not change. For ZnGa2O4:Cr3+ materials, Cr3+ substitutes for octahedral sites of Ga3+ in the host lattice.