Photostimulated luminescence excited by infrared LEDs in CaS:Eu2+ red afterglow phosphors

Red photostimulated luminescence (PSL) at 650 nm appears under the excitation by using an infrared (IR) light-emitting diode at 940 nm in CaS:Eu2+ afterglow phosphors. The effect of doping of Dy3+ ions, alkali metal ions or Cl- ions in CaS:Eu2+ on afterglow or photostimulation is investigated. Afterglow temporal decays and thermoluminescence glow curves suggest that Dy3+ ions and alkali metal ions induce different types of defects in the phosphor, and enhance the afterglow independently. Doping of Cl- ions is found to enhance the photostimulation by the IR excitation. Even if the phosphor is irradiated with IR light for some seconds, the afterglow decay curve is the same as when it is not irradiated with IR light. Trap states responsible for the photostimulation are different from those responsible for the afterglow. The red photostimulation appears under the excitation at 940 nm, after the phosphor is left in the dark for 60 min. Its intensity is 68% of the red PSL generated after being left in the dark for 10 min. It is considered that the PSL decreases little, when the sample is kept in the dark.