The effect of Ag content on the electronic structure and optical property of α-Fe₂O₃

The electronic structure and optical properties of Ag-doped α-Fe₂O₃ with different Ag contents (1.67 mol%, 3.33 mol%, 5.00 mol% and 6.67 mol%) were studied by density-functional theory (DFT). α-Fe₂O₃ has the characteristics of semimetal after Ag doping, and the semimetal property increases with increasing Ag contents. Doped Ag loses less electrons for Ag-doped α-Fe₂O₃ than corresponding Fe (replaced iron) for pure α-Fe₂O₃, which led the weaker Ag-O bond than Fe-O bond before Ag doping. However, the number of losing electrons for Ag increases gradually with the increase of Ag content. For optical properties, it is found that the peaks of imaginary parts of dielectric function and extinction coefficient for Ag-doped α-Fe₂O₃ shift to low energy (red shift) relative to those of pure α-Fe₂O₃. In the ultraviolet range (200 nm-380 nm), Ag doping reduces the optical absorption intensity. However, the optical absorption is enhanced steeply with the increase of Ag contents in the wavelength of 420 nm to 1400 nm. The optical absorption intensity of 3Ag-doped and 4Ag-doped α-Fe₂O₃ is similar in the visible range, suggesting that excessive Ag concentration (over 3 Ag) has little effect on the optical absorption property.