We investigate the geometry and electronic structures of α-Al2O3:VO + AlX systems based on first-principles calculations where VO represents one oxygen vacancy and AlX stands for IIIA atoms (B, Ga, In, and Tl) substituting of one Al atom. It is found that all the aluminates maintain the hexagonal symmetry as the pure α-Al2O3 structure and the lattice parameters a, b, and c are expanded with the increase of the IIIA atoms radius. The electronic property analysis indicates that the band gaps are considerably reduced and the reductions are also related to the radius of doping atoms. But unlike the situation of transition metal doped α-Al2O3 the decreases of the band gap are not due to the spreading of d states, but are mainly owing to the ns states at the bottom of the conduction band.
