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. The nature of traps responsible for persistent and near‐infrared photostimulated luminescence in CaS nanoparticles and CaS:Eu2+ and CaS:Eu2+,Dy3+ nanophosphors is addressed using wavelength‐resolved, thermally stimulated luminescence measurements. After UV irradiation (254 nm), CaS:Eu2+,Dy3+ shows a strong red persistent luminescence for 5 h, photostimulated emission for 18 min.