The important role of oxygen vacancies in Sr2MgSi2O7 phosphor

There have been some experimental suggestions about the correlation of the persistent luminescence (PL) mechanism of phosphors with host lattice defects. Oxygen vacancies have most often been invoked, but solid and direct evidence is scarce. We investigate the PL mechanism of Sr2MgSi2O7:Eu2+ on the basis of first-principles calculations of oxygen vacancies. We find that oxygen vacancies occur in a high concentration and introduce a dispersive empty defect band, which is distributed over a wide energy range and located from shallow to deep depth, explaining well the persistent luminescence emission with an intense intensity and a long-lasting duration. Our basic understanding of the general trend of the trap depth and density of O1, O2, and O3 vacancies is applicable to the assignment of the defect structures observe in thermoluminescence spectra. We also propose a possible PL mechanism for Sr2MgSi2O7:Eu2+ phosphor and provide some guides for the search and design of better PL materials.