Persistent luminescence of Eu2+ and Na+ doped alkaline earth aluminates

The luminescence and afterglow properties of the Eu2+ and Na+ doped alkaline earth aluminates, stoichiometric and non-stoichiometric (MxAl2O4:Eu2+, Na+; M=Ca or Sr, x=0.97, 1.00 or 1.03, X-Na=0.02), were studied. Broad band luminescence and afterglow of the Eu2+ ion were observed in the blue (lambda(max) = 440 nm) and green (lambda(max)=520 nm) region for the calcium and strontium aluminates, respectively Both Na+ co-doping and strontium excess quenched the afterglow efficiently The results supported the mechanism of the persistent luminescence where the cation vacancies act as traps. The results for the calcium aluminates were ambiguous, probably due to the slightly larger ionic radius of the Na+ with respect to that of Ca2+. The sodium ions may not fit into the calcium sites and thus form (an) independent compound(s).