First-principles study on stability of Li, Na and Ca in Lu2SiO5

Lu2SiO5:Ce (LSO:Ce) is a well-known scintillator with high light yield, fast decay time and high density. In experiments, Li, Na and Ca are reported to influence its light yield and thermoluminescence intensity related to the oxygen vacancies in the host. The stability of Li, Na and Ca ions in LSO has been investigated using the density functional theory. Li and Na ions have lower formation energies at substitutional sites than interstitial sites. The formation energy of the defect complex of Na and the oxygen vacancy is lower than the isolated oxygen vacancy. Ca ions are found to be stable at interstitial sites and the complex of Ca and the oxygen vacancy is not as stable as the isolated oxygen vacancy. Some shallow thermodynamic transition levels are introduced by substituents. The dopants are responsible for some unoccupied states above the top of the valence band and occupied states below the bottom of the conduction band.