Synthesis of orange-red-emitting Eu2+, Pr3+ codoped SrS long afterglow phosphor

We describe the synthesis and properties of an orange-red-emitting SrS:Eu2+,Pr3+ phosphor showing a long afterglow of greater than 1000 min under visible light. The SrS:Eu2+,Pr3+ phosphor was synthesized by reduction of SrSO4:Eu3+,Pr3+ formed by liquid phase reaction. The SrS:Eu2+,Pr3+ phosphor showed orange-red emission with a peak wavelength of 611 nm. The excitation band of the phosphor was in the range of visible light above 440 nm. The optimum reaction conditions were achieved under a reducing atmosphere at 1400 °C for 2 h. The optimum quantity of activator was obtained for Eu/Sr and Pr/Sr atomic ratios of 0.00002 and 0.0010, respectively. The afterglow time for the SrS:Eu2+,Pr3+ phosphor after irradiation for 5 min at 1000 lux under a D65 lamp was greater than 1000 min, which was 7 times longer than that obtained with a commercially available CaS afterglow phosphor.