The Role of the Cu on OSL Emission in Gamma-LiAlO2:Cu Crystal

A large optically stimulated luminescence (OSL) response has been found from copper doped lithium aluminate (LiAlO2, LAO) which can be applicable in OSL dosimetry. After an irradiation at room temperature with x-rays, an optical absorption band peaking at 277 nm and a luminescence band near 354 nm appear which are assigned to Cu+ ions which occupy the Li+ sites. Based on the experimental study, we construct two models to study the optical spectra of Cu+ occupying the Li+ ion. One is an isolated defect in which Cu+ ions occupy the Li+ ions and present isolated CuLi. The other one is a CuLi bond with a neighboring lithium vacancy (CuLi-VLi). In this work, all calculations are based on density functionals theory (DFT). Advanced hybrid functionals is adopted to relieve the problem of DFT underestimating the band gap. We obtain the optical spectra containing electron‒phonon coupling, and the results are in good agreement with the experimental results. Furthermore, the optical properties of CuLi-VLi are investigated. We find the absorption and luminescence peak are located at 273 nm and 353 nm, which are assigned to the isolated CuLi, and the absorption band near 379 nm is assigned to the CuLi-VLi. To compare the relative stability of the two defects, we present the defect formation energies as a function of Fermi energy under Li-rich and Li-poor conditions, to demonstrate the isolated CuLi is more stable than CuLi-VLi for the Fermi level in the entire range of band gap under Li-rich condition.