Effects of composition and reduction conditions on persistent luminescence of SrAl2O4:Eu,Dy prepared via a solid-state reaction

SrAl2O4:Eu,Dy is a representative persistent luminescent phosphor that has been widely investigated. However, the mechanism of its long-lasting action has not been fully elucidated. With the aim of providing new insights into trapping in the phosphor by elucidating the relationship between trap creation and preparation conditions, SrAl2O4:Eu,Dy phosphors with different nominal Sr:Al compositions were prepared via a solid-state reaction and heating under different reducing conditions. The photoluminescence (PL) and persistent luminescence (PersL) emission and excitation spectroscopy of the phosphors, as well as their afterglow and thermoluminescence (TL) characteristics, were studied. SrxAl2O4:Eu2+,Dy3+ with x = 0.79-0.89 prepared via preheating in air and post-reduction showed the best afterglow properties. The PersL excitation spectra of these phosphors featured the same characteristic peaks, which were attributed to oxygen vacancies (electron traps) induced by Sr deficiencies. The TL measurements revealed that co-doping with Dy3+ ions increased the number of trapped electrons in preexisting oxygen vacancies with trap depths of similar to 0.53 eV and stabilized traps with depths of similar to 0.61 eV via interactions with pre-existing oxygen vacancies that increase in number with Sr deficiency and preheating in air.