Study on the optical spectra for the Li defects and O-Li vacancy pair in gamma-LiAlO2 crystal

In the work, the optical properties and structure relaxation of lithium vacancy, lithium interstitial and O-Li divacancy have been studied based on density functional theory (DFT). The lattice structures of lithium vacancy, lithium interstitial and O-Li divacancy with different charges have been optimized. The divacancy lead to the large lattice distortion, and we explain the structure relaxation well based on the charge density and inter-distance. The optical spectra of the defects have been obtained considering the electron–phonon coupling. The calculated results indicate that the luminescence peaks near 4.13 eV and 1.24 eV are assigned to the lithium vacancy and O-Li vacancy pair, and absorption bands near 4.36 eV and 4.40 eV are attributed to the lithium vacancy and O-Li vacancy pair, respectively. The emission band near 4.06 eV is assigned to the lithium vacancy. For the lithium interstitial, we find that the charge transition energy level of lithium interstitial is a shallow donor level which is hardly involved in the optical transitions.