Understanding Persistent Luminescence: Rare-Earth- and Eu²⁺-doped Sr₂MgSi₂O₇

Similar to many other Eu²⁺,RE³⁺-co-doped persistent luminescence materials, for Sr₂MgSi₂O₇:Eu²⁺,RE³⁺ the initial intensity and duration of persistent luminescence was also found to depend critically on the rare-earth (RE) co-doping. An enhancement of 1 - 2 orders of magnitude in these properties could be obtained by Dy³⁺ co-doping whereas total quenching of persistent luminescence resulted from the use of Sm³⁺ and Yb³⁺. To solve this drastic disparity, the effects of the individual RE³⁺ ions were studied with thermoluminescence (TL) spectroscopy to derive information about the formation of traps storing the excitation energy. The charge compensation defects were concluded to be the origin of the complex TL glow curve structure. The tuning of the band gap of the Sr₂MgSi₂O₇ host and especially the position of the bottom of the conduction band due to the Eu²⁺,RE³⁺ co-doping was measured with the synchrotron radiation vacuum UV (VUV) excitation spectra of the Eu2+ dopant. The model based on the evolution of the band gap energy with RE³⁺ co-doping was found to explain the intensity and duration of the persistent luminescence.