Roles of doping ions in persistent luminescence of SrAl2O4:Eu2+, RE3+ phosphors

The polycrystalline Eu2+ and RE3+ co-doped strontium aluminates SrAl2O4:Eu2+, RE3+ were prepared by solid state reactions. The UV-excited photoluminescence, persistent luminescence and thermo-luminescence of the SrAl2O4:Eu2+, RE3+ phosphors with different composition and doping ions were studied and compared. The results showed that the doped Eu2+ ion in SrAl2O4:Eu2+, Dy3+ phosphors works as not only the UV-excited luminescent center but also the persistent luminescent center. The doped Dy3+ ion can hardly yield any luminescence under UV-excitation, but can form a electron trap with appropriate depth and greatly enhance the persistent luminescence and thermo-luminescence of SrAl2O4:Eu2+. Different co-doping RE3+ ions showed different effects on persistent luminescence. Only the RE3+ ion (e.g. Dy3+, Nd3+), which has a suitable optical electro-negativity, can form the appropriate electron trap and greatly improve the persistent luminescence of SrAl2O4:Eu2+. Based on above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.