Photoionization behavior of Eu2+-doped BaMgSiO4 long-persisting phosphor upon UV irradiation

Abstract The fluorescence, phosphorescence and thermoluminescence properties of Eu-doped BaMgSiO4 phosphors sintered in air and in a reducing atmosphere were investigated. Phosphorescence of phosphor sintered in a reducing atmosphere can last for 1.5 h at a recognizable intensity level, whereas phosphorescence of air-sintered phosphor can only persist for 6 min. In addition, a distinction between the shape of the fluorescence spectrum and its corresponding phosphorescence spectrum is observed in the former case. Ionization of Eu2+ to Eu3+ upon UV irradiation is observed in the phosphor prepared in a reducing atmosphere, but there is no indication that the photogenerated Eu3+ cannot change back to its divalent state at room temperature after the excitation source is switched off. In addition, phosphor sintered in a reducing atmosphere shows photochromism upon UV irradiation. No such photoionization and photochromism behavior is observed for the air-sintered phosphor. A possible Eu2+ photoionization mechanism is constructed on the basis of these experimental observations. The photoionization mechanism presented can also successfully explain the fluorescence and phosphorescence behavior of Eu in BaMgSiO4.