Roles of doping ions in persistent luminescence of SrAl2O4: Eu2+,RE 3+ phosphors

Abstract

The polycrystalline Eu2+ and Dy3+ codoped strontium aluminates SrAl2O4: Eu2+,Dy3+ were prepared by a solid-state reaction. The UV-excited photoluminescence, persistent luminescence, and thermoluminescence of the SrAl2O4: Eu2+,Dy3+ phosphors with different compositions and ion doping was studied and compared. The results showed that the Eu2+ ion doped in SrAl2O4: Eu2+,Dy3+ phosphors is not only the UV-excited luminescent center but also the persistent luminescent center. The Dy3+ ion introduced into SrAl2O4: Eu2+ crystal matrix can hardly yield any luminescence under UV excitation but acts as an electron trap with a suitable depth for persistent luminescence. The Dy3+ codoping would effectively enhance the persistent luminescence and thermoluminescence. Different codoping RE 3+ ions have a different effect on persistent luminescence. Only the RE 3+ ions (for example, Dy3+ and Nd3+), which have suitable optical electronegativity, can form suitable electron traps and effectively improve the persistent luminescence of SrAl2O4: Eu2+. Based on the above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.