Optical Evidence of Charge Trapping at Lanthanide Codopants in SrAl₂O₄:Eu,Ln (Ln = Nd, Sm, Dy) Persistent Phosphors

Abstract In this work, the absorption spectra of metastable Dy²⁺, Nd²⁺, and Sm²⁺ are identified in SrAl₂O₄:Eu,Ln persistent phosphors after excitation with blue light, thereby confirming that the persistent luminescence is indeed due to a charge transfer between the two lanthanide dopants. In contrast to previous studies relying on X‐ray absorption spectroscopy to observe charge transfers between dopants, here low‐energy light is exclusively employed to probe for changes in the absorption spectrum of the phosphor, thereby only minimally affecting the state of the phosphor. Optical bleaching in combination with thermoluminescence measurements allowed to assign which optically active trapping centers contribute to the afterglow of the persistent phosphors.