Using DFT (GGA-PBE), we calculate the electronic structureofa120-atom α-Al2O3 supercell for four defect families: Frenkel-pair-like defects, oxygen vacancies, vacancies around an interstitial Te atom, and substitution of O by Te. The pristine gap is 6.17 eV. Oxygen vacancies narrow the gap monotonically (4.36 → 2.21 eV), whereas Te-containing configurations show a nonmonotonic response (2.66 to 1.12 eV) controlled by the local Te coordinationrather thanbythe defect count. The in-gap states do not by themselves establish a conducting filament.