First-principles calculations of structural, electronic and optical properties of ZnGa2O4:Cr3+ system

ZnGa2O4 is an important cathodoluminescent material which exhibits good near-infrared long afterglow characteristics after being Cr-doped into Ga sites (ZGO: Cr). The band structure, crystal structure and optical properties of ZGO: Cr are investigated by using first-principles calculations based on density functional theory. It is found that, in the ZGO: Cr system, due to the presence of the Cr-O bond, the distortion of the local lattice goes up as the Cr3+ doping amount increases. Meanwhile, impurity levels appear near the Fermi level of the ZGO system, and the orbital controlling the conduction band bottom gradually moves from the Ga-4s orbital to the Cr-3d orbital. Consequently, the real optical band-gap of the ZGO: Cr system becomes narrower, and the absorption edge undergoes a red-shift. The density of states of all upward and downward atomic spins is distributed asymmetrically, indicating that ZGO: Cr exhibits a certain amount of spin polarization. Additionally, the static dielectric constant of the ZGO: Cr material system increases with the increase in the Cr3+ doping amount. According to the findings, adjustments can be made of the doping concentration and energy range in the optical applications of ZGO: Cr material system.