Journal of Luminescence (2012)

Temperature and wavelength dependent trap filling in M2Si5N8:Eu (M=Ca, Sr, Ba) persistent phosphors
Philippe F. Smet, Koen Van den Eeckhout, Adrie J.J. Bos, Erik van der Kolk, Pieter Dorenbos
Journal of Luminescence 132 (2012) 682-689

Abstract
The evaluation of persistent phosphors is often focused on the processes right after the excitation, namely on the shape of the afterglow decay curve and the duration of the afterglow, in combination with thermoluminescence glow curve analysis. In this paper we study in detail the trap filling process in europium-doped alkaline earth silicon nitrides (Ca2Si5N8:Eu, Sr2Si5N8:Eu and Ba2Si5N8:Eu), i.e., how the persistent luminescence can be induced. Both the temperature at which the phosphors are excited and the spectral distribution of the excitation light on the ability to store energy in the phosphors' lattices are investigated. We show that for these phosphors this storage process is thermally activated upon excitation in the lower 5d excited states of Eu2+, with the lowest thermal barrier for europium doped Ca2Si5N8. Also, the influence of co-doping with thulium on the trap filling and afterglow behavior is studied. Finally there exists a clear relation between the luminescence quenching temperature and the trap filling efficiency. The latter relation can be utilized to select new efficient 5d–4f based afterglow phosphors.

Keywords: Persistent luminescence; Afterglow; Thermoluminescence; Trap filling; Nitrides; Rare earth

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