Persistent luminescence in rare earth ion-doped gadolinium oxysulfide phosphors

A series of rare-earth ion-doped gadolinium oxysulfide phosphors Gd2O2S:RE3+, Ti, Mg (RE = Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb) were synthesized by solid-state reaction. The excitation and photoluminescence spectra, afterglow spectra, afterglow decay curves and thermoluminescence spectra of the phosphors were examined. According to the afterglow spectra, gadolinium oxysulfide doped with rare-earth ions were classified into three groups. When rare earth ions such as Eu3+, Sm3+, Dy3+, Ho3+, Er3+ and Tm3+ were introduced into the Gd2O2S host, their characteristic emission as well as that from Gd2O2S:Ti, Mg were observed. In case of Yb3+ and Nd3+, only the broadband luminescence of Gd2O2S:Ti, Mg was obtained. Gadolinium oxysulfide doped with Pr3+, Tb3+ and Ce3+ did not show afterglow emission. The calculated trap energy levels of the samples were compared. The role of Ti and Mg ions and a potential mechanism for persistent luminescence in the samples were discussed.