Intrinsic Defects Drive Persistent Luminescence in Monoclinic SrAl2O4:Eu2+

The persistent luminescent phosphor SrAl 2 O 4:Eu 2+ shows a significantly long luminescent lifetime, making it an important material used for an array of applications. The origin of its long emission decay time has been suggested to stem from defects in the crystal structure. This study employs density functional theory with a hybrid exchange and correlation functional to study the energetics of charged vacancies in SrAl 2 O 4 and SrAl 2 O 4:Eu 2+ . The calculations indicate that defects are present in SrAl 2 O 4 regardless of the rare-earth ion, suggesting their intrinsic nature in this crystal system. Moreover, the defect states fall ≈0.67 eV below the bottom of the conduction band allowing them to act as electron traps, which is in accordance with the proposed persistence luminescent mechanism. These findings provide insight into the role of defects in persistent luminescent phosphor hosts and may aid the future design of long lifetime luminescent materials through defect chemistry.