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

Abstract

The persistent and near‐infrared photostimulated optical properties of CaS nanoparticles and CaS:Eu 2+ and CaS:Eu 2+ ,Dy 3+ 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 Eu 2+ as a dopant, the formation of shallow traps below the conduction band is observed and red persistent and near‐infrared PSL is obtained. Dy 3+ 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.