Electronic structure and optical properties of F centers in α-alumina

We use a state-of-the-art GW Bethe-Salpeter equation (BSE) formalism to study electronic structure and optical properties of oxygen vacancies (F centers) in alpha-alumina. The density functional theory (DFT) + GW formalism has been employed to compute the charge transition levels (CTLs) for oxygen vacancies. We propose a reformulation of the DFT+GW approach to calculate these CTLs. Our new approach allows for transparent application of electrostatic corrections required in finite supercell calculations using periodic boundary conditions. We find that F centers in this material introduce deep donor levels, (+2/+1) at 2.4 eV, and a (+1/0) level at 3.9 eV above the valence band maximum. We also study F-center absorption and emission processes using constrained DFT and BSE. Our calculated absorption and emission energies are in excellent agreement with experiments and provide an unambiguous interpretation of the same.