Theoretical insight into optical properties of ZnGa2O4 transparent ceramic

Abstract

The spinel-type ZnGa 2 O 4 transparent ceramic with extremely wide infrared transmission range exhibited great potential applications in numerous fields. Based on the comparative study with MgAl 2 O 4 and ZnAl 2 O 4 , the optical properties of ZnGa 2 O 4 transparent ceramic in the entire wavelength range from ultraviolet to infrared were theoretically investigated by first-principles calculations. With the in-depth understanding of crystal, electronic, phonon structures and chemical bonding, the origin of the variations in the optical properties was clarified. Due to the inherent 3d 10 electronic configuration in both Zn and Ga, the significant p-d hybridization between Zn/Ga 3d states and O 2p states resulted in a smaller band gap and a higher refractive index of ZnGa 2 O 4 . The weaker tetrahedral Zn-O bond led to ZnGa 2 O 4 considerably broaden its infrared transmission range. The easily formed oxygen vacancy defect coupled with the intrinsic narrow band gap may provide opportunities for new functionalization of ZnGa 2 O 4 transparent ceramic. The comprehensive insight also offers guidance for designing novel transparent ceramics with desired optical properties. • Significant O 2p-Zn/Ga 3d hybridization resulted in a smaller band gap and a higher refractive index of ZnGa 2 O 4 . • Effective charge calculated from phonon frequency was used to evaluate the covalency of chemical bonds. • Weaker Zn-O bond and heavier cationic masses broaden infrared transmission range of ZnGa 2 O 4 . • Oxygen vacancy was easily formed in ZnGa 2 O 4 and defect level was generated in band structure.