On the phosphorescence mechanism in SrAl2O4:Eu and its codoped derivatives

The mechanism of phosphorescence in SrAl2O4:Eu,Dy material is discussed on the basis of a thermo-activated release of electrons trapped at oxygen vacancy sites. The depths and concentration of the electron traps are strongly affected by codoping with trivalent lanthanide cations Ln3+. This finding is rationalized by comparing the ionization potentials of the dopant cation Eu2+, the codopant cation Ln3+ and the substituted cation Sr2+. Such a use of ionization potentials provides a practical guide with which the variation of the phosphorescent decay time in the codoped derivatives of SrAl2O4:Eu is predicted.