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Optical properties of vacancies in aluminum oxide (α−Al2O3) from first principles

Christoph Wilhelmer1,*, Mark E. Turiansky2,†, Dominic Waldhör1, Lukas Cvitkovich1,‡, Chris G. Van de Walle2, and Tibor Grasser1,§

  • *Contact author: wilhelmer@iue.tuwien.ac.at
  • †Present Address: US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA.
  • ‡Present Address: University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany.
  • §Contact author: grasser@iue.tuwien.ac.at
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Phys. Rev. Materials 9, 096202 – Published 30 September, 2025

DOI: https://doi.org/10.1103/5kvl-hktd

Abstract

We employ first-principles calculations based on hybrid density functional theory to investigate the structural and optical properties of the oxygen vacancy (VO) and aluminum vacancy (VAl) in α−Al2O3, the most stable (corundum) phase of alumina. Our calculations facilitate the identification of experimental excitation and luminescence spectra with specific electronic transitions at the vacancy sites. The absorption line shape for excitation of an electron at VO0 to the conduction-band minimum (CBM) is in excellent agreement with the 6.1 eV band detected by optical absorption spectroscopy, and we find that the 5.9 eV absorption band is generated by an internal electron transition at VO0. We confirm that the slowly decaying 3.0 eV emission band of the F center is due to a triplet-singlet transition at VO0. Our calculations also reveal that the 4.8 eV/5.4 eV absorption and 3.8 eV emission bands assigned to the F+ center are generated by internal transitions at VO+1. The line shape for the excitation of an electron from VO+1 to the CBM agrees well with an absorption band at 6.4 eV, while the recombination of an electron with VO+2 also produces luminescence around 3.8 eV, but with a considerably broader line shape. For Al vacancies, we confirm that the most prevalent configuration in α−Al2O3 is a split-vacancy configuration VAl,s, and we calculate migration barriers for different directions in the corundum crystal. We predict absorption and emission spectra for the excitation and recombination of an electron localized at VAl−3 and VAl,s−3 sites with the CBM. The line shapes of the two VAl configurations overlap and are considerably broader than the spectra corresponding to VO.

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Phys. Rev. Materials 9, 096202– Published 30 September, 2025
  • Received 16 June 2025
  • Accepted 12 September 2025
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