Theoretical Studies of Electronic and Optical Properties of Bixbyite and Fluorite Polymorphs of Sb-Doped Y2O3.

Sb-doped Y₂O₃, a compound with excellent optical properties, is used in laser applications. Recently, it has been found that it coexists in two distinct polymorphs upon doping with various levels of Sb. Therefore, the electronic structure and optical properties of Sb-doped Y₂O₃ corresponding to two distinct phases, i.e., bixbyite and fluorite, are explored in this paper using the CASTEP density functional theory (DFT) code. Sb is substituted at Y sites in pure Y₂O₃ in both phases, and the corresponding band structure, density of states, and various optical properties, namely the dielectric function, refractive index, reflectivity, and optical loss functions, are investigated. The results reveal that Sb-doped Y₂O₃ in fluorite phase is conductive for 12.5% doping but shows a small gap of 0.45 eV in the case of 25% Sb doping. Moreover, the fluorite phase of Sb-doped Y₂O₃ has defect states in the bandgap above the Fermi level, while the bixbyite phase exhibits insulating behavior. Moreover, the bandgap of the bixbyite phase steadily decreases with increasing Sb doping concentration. The results for the optical properties reveal that new kinds of excitation and plasmonic states emerge in Sb-doped bixbyite Y₂O₃ whereas no such transitions appear upon doping of the fluorite structure. [ABSTRACT FROM AUTHOR]