The almost hidden role of deep traps when measuring afterglow and thermoluminescence of persistent phosphors

Although the luminescence characteristics of persistent phosphors have been extensively investigated, the physical mechanism underlying their afterglow is not yet fully understood. Many variables influence the outcome of thermoluminescence, charging and afterglow experiments, hampering a correct interpretation. Here we investigate the role of deep, thermally stable traps in SrAl2O4:Eu2+,Dy3+ which received little attention in previous studies. We demonstrate that these traps have a considerably higher trapping cross-section than the shallow traps, which are responsible for the persistent luminescence. This affects the charging dynamics of the shallow traps significantly and should therefore be considered in behavioral studies of these phosphors.