Structural, Electronic, and Optical Properties of Er3+-Doped Sc2O3 with Different Er3+ Concentrations: A First-Principles Study

Abstract Er3+-doped Sc2O3 (Er:Sc2O3), featuring low phonon energy, high thermal conductivity, and excellent optical properties, has become a promising laser gain material. Nevertheless, the microscopic mechanisms associated with its structural stability, electronic characteristics, and optical response remain insufficiently understood. In this study, the structural, electronic, electron localization, and optical properties of Er:Sc2O3 at different doping concentrations were systematically investigated through first-principles calculations based on density functional theory. The CALYPSO method was employed to predict the stable crystal structures, and subsequent calculations were performed using the VASP package within the generalized gradient approximation (GGA) + U framework. The results reveal that Er3+ substitution induces local lattice distortion and symmetry reduction from the cubic Ia3̅ phase to the trigonal R3̅ phase. Moreover, all optimized structures remain dynamically stable according to phonon dispersion calculations. Electronic structure analysis suggests that Er-related 4f states introduce impurity energy levels into the band gap and gradually reduce the band gap width with increasing doping concentration, while the insulating nature of the system is preserved. Additionally, the electron localization function and Bader analysis specify that the bonding characteristics remain predominantly ionic. Furthermore, Er3+ doping modifies the dielectric response and shifts the absorption edge toward lower energy, resulting in an expanded optical absorption range, as reflected in optical calculations. These findings provide a theoretical reference for understanding the microscopic effects of Er:Sc2O3.