Red photostimulated luminescence and afterglow in CaS:Eu2+, Mn2+ phosphors

In afterglow phosphors, luminescence appears and can be observed with the naked eye for minutes to hours or more, even after photoexcitation ceases. Red afterglow and photostimulated luminescence (PSL) at 650 nm are studied in CaS:Eu2+, Mn2+ phosphors. Infrared light at 980 nm from a laser diode induces the red PSL for 990 s. Two types of trap states are found to be present in the phosphors by using thermoluminescence (TL). Deep trap states are reflected in a TL peak in the temperature region of 520 K, and are related to PSL. Shallow trap states reflected in the other TL peak at 250 K are related to afterglow. The intensity dependence of photoexcitation on PSL shows that carriers are more easily accumulated in the deep trap states than shallow trap states. Experiments of electron paramagnetic resonance are conducted to discuss the possible origins of PSL and the afterglow.