Isolated Defects in Sr2MgSi2O7: A DFT Study

The modifications in the crystal and electronic structure due to the Eu2+ luminescent centre and isolated vacancies in the Sr2MgSi2O7(:Eu2+) persistent luminescence material were calculated using the density functional theory (DFT). The exact role of defects in the storage of excitation energy is currently not well understood. They can be formed e.g. due to charge compensation and preparation conditions. The probability of vacancy formation was studied using the total energy of the defect containing host. The most significant structural modifications due to defects in the environment of the Eu2+ luminescent centre were found with the introduction of the strontium vacancy. Electron traps were created by Eu2+ and the strontium as well as oxygen vacancy, whereas the strontium, magnesium and silicon vacancies created also shallow hole traps in the material. The electron traps close to the conduction band can contribute to the persistent luminescence efficiency since they are readily bleached by the thermal energy at room temperature. However, too shallow or deep traps can decrease this efficiency. The role of the intrinsic defects and dopants in the energy storage of the persistent luminescence materials was discussed. PACS: Type pacs here, separated by semicolons.