In recent years, persistent phosphors have been studied by many
investigators in the effort to develop the phosphors with colorful
emissions [1] for more applications, e.g., in vivo biomedical
imaging [2,3]. The phosphorescence examination is also an effective
way to analyze the charge transfer among the trapping defects [1].
Optical charging process in phosphorescence may provide important
facts that reveal the trapping mechanism. In our previous work [4],
we have observed a slowly rising time dependence of the photoluminescence
of SrAl2O4:Eu,Dy during the excitation period, which
was attributed to a trap charging process.