The phosphorescent properties of Er³⁺ in Gd₂O ₂S by two-step absorption

We report on a novel luminescent phenomenon in Gd₂O₂S : Er,Yb prepared by a solid-state reaction. After irradiation at 980 nm, the afterglow emission of Er³⁺ is observed. X-ray diffraction, photoluminescent emission, long-lasting phosphorescence emission and decay curves were used to characterize the phosphor. It is found that the afterglow is improved with the co-doping of Ti⁴⁺ and Mg²⁺. Also the upconversion luminescent spectrum of Er³⁺ is changed. We ascribe this phenomenon to the change in the environment of activator ions. The phosphorescence properties of the sample are researched in detail. Due to the dependence of afterglow intensities on different irradiative powers, a possible two-step-absorption upconversion long-lasting phosphorescence mechanism is proposed. This kind of mechanism may overcome the shortcomings of the long persistent phosphors which are used for UV irradiation.