Near infrared photostimulated persistent luminescence and information storage of SrAl₂O_4:Eu²⁺, Dy³⁺ phosphor

The phosphor Sr_0.97Al₂O₄:0.01Eu²⁺, 0.02Dy³⁺ was synthesized by a high temperature solid state reaction in a reducing atmosphere. After charging by ultraviolet radiation, the persistent luminescence decay was divided into different time ranges and well-fitted by a biexponential function, but the two lifetimes became longer with time of persistent luminescence decay. The fractional amplitude of the shorter lifetime increased with time, whereas that of the longer lifetime decreased. The change in lifetime has been associated with the emptying of a pseudo-continuum of trap states either from different traps or different levels of the same trap species. The investigation in photostimulated persistent luminescence indicated the sample could emit bright persistent luminescence again under infrared light excitation after the UV light-excited persistent luminescence had decayed completely. The NIR photostimulation exhibited a continuous broad band, with maximum at 760 nm, representing the emptying of filled traps into the conduction band. These results also infer that the traps are pseudo-continuous but the assignment of Dy²⁺ as the trapped species cannot be excluded. The read-in and write-out properties of the phosphor have been elucidated and these convey applications in information storage and retrieval.