Persistent and Photostimulated Red Emission in CaS:Eu2+,Dy3+ Nanophosphors

The persistent and near-infrared photostimulated optical properties of CaS nanoparticles and CaS:Eu2+ and CaS:Eu2+,Dy3+ nanophosphors are presented. Proposed mechanisms are elucidated for both phenomena by carrying out wavelength-resolved, thermally stimulated luminescence (TSL) and photostimulated luminescence (PSL) measurements. After UV (254 nm) irradiation, blue persistent and near-infrared photostimulated luminescence is obtained due to the presence of intrinsic defects in CaS nanoparticles. By introducing Eu2+ as a dopant, the formation of shallow traps below the conduction band is observed and red persistent and near-infrared PSL is obtained. Dy3+ is added as a codopant to create shallow and near-infrared photostimulated deeper traps, lengthening the strong red persistent luminescence to 5 h and PSL time to 18 min.