Physical Review B (2011)

Luminescence and x-ray absorption measurements of persistent SrAl2O4:Eu,Dy powders: Evidence for valence state changes
Katleen Korthout, Koen Van den Eeckhout, Jonas Botterman, Sergey Nikitenko, Dirk Poelman, Philippe Smet
Physical Review B 84 (2011) 85140

Abstract
The development of new efficient afterglow phosphors is currently hampered by a limited understanding of the persistent luminescence mechanism. Radioluminescence and x-ray absorption measurements on the persistent phosphor SrAl2O4:Eu,Dy were combined to reveal possible valence state changes for the rare earth (co)dopants. Traps in the phosphor material are quickly filled when exposing thermally emptied SrAl2O4:Eu,Dy powder to x-rays. On the same time scale, a partial oxidation of Eu2+ to Eu3+ is observed by XANES (x-ray absorption near-edge spectroscopy), while for the trivalent dysprosium the valence state remains unchanged. The impact of these observations on the recently proposed models for persistent luminescence is discussed.

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