Crystal size dependence of the persistent phosphorescence in Sr ₂ZnSi₂O₇: Eu²⁺, Dy³⁺

There has been considerable interest recently in materials which show prolonged persistent phosphorescence following short periods of excitation; the persistence has been reported in a large variety of phosphor materials including sulfides, oxides, and complex silicates and aluminates. The phosphorescence has generally been attributed to the presence of traps in most instances produced by a co-dopant ion. In this paper, we investigate the behavior of the persistent phosphorescence as a function of phosphor particle size and find that the persistence time increases as a function of decreasing particle size. The increase in time is attributable to an increase in surface trapping levels commensurate with changes in the surface to volume ratio in the phosphor particles.