Mechanism of long afterglow in SrAl2O4:Eu phosphors

Phosphors of SrAl2O4:Eu (SAO), B-doped (SBO), and B, F co-doped (SFO) were prepared by a high-temperature solid-state reaction method. The phosphors emit intense green light under UV excitation. SBO displayed significantly enhanced long afterglow. The decay time of SBO was 20 times bigger than that of SAO, while that of SFO was only 16% of that of SBO. The results suggest that B doping favors the formation of oxygen vacancies due to the unique bonding property of B. At the same time, B, F co-doping has the opposite effect, ascribed to the presence of F. The related partial density of state and the orbital structures were calculated using the first-principles density functional theory (DFT). The orbital structure of SBO showed that high partial density states are localized around the O vacancies, which can trap excited electrons, leading to improved long-afterglow luminescence.