Mechanism of persistent luminescence in Sr2MgSi2O7 : Eu2+; Dy3+

A recently developed method to determine the energy levels of divalent lanthanide ions relative to the conduction band and valence band of host compounds is applied to Sr(2)MgS(2)iO(7) doped with Eu2+ and Dy3+. The level locations are not consistent with the widely adopted and generally believed mechanism of persistent luminescence in Eu2+ and Dy3+, doped aluminates and silicates. A new mechanism of persistent luminescence is proposed. In this mechanism Eu3+ and Dy2+ are the stable trapping centers and not Eu+ and Dy4+ as in the existing mechanism.