Optically stimulated detrapping during charging of persistent phosphors

Persistent phosphors, also called glow-in-the-dark materials, are a specific class of luminescent materials having the unique ability to emit light long after the excitation ended. For many applications in the visible spectrum, such as in emergency signage or road marks, the storage capacity of the Eu super(2+) based phosphors should further be increased. In this work we show that the excitation of the europium center in Sr sub(2) MgSi sub(2) O sub(7):Eu,Dy by near-UV light not only leads to charge trapping, but also to optically stim-ulated release of previously trapped charges and subsequent luminescence (OSL). The experimental evidence for OSL at the excitation wavelength is supported by a model assuming local trapping and an additional detrapping rate proportional to the excitation intensity. In this way, the characteristics of both the charging and afterglow behaviour can be explained. The storage capacity of a persistent phosphor is thus not only controlled by the trap density and the trap depth, but also by the sensitivity to optically stimulated detrapping at the excitation wavelength.