Enhancing the near-infrared photoluminescence and persistent luminescence properties of CaSnO3:Bi through modulating bismuth ion valence states via Mg²⁺ interstitial codoping

In this work, a series of near-infrared persistent luminescent phosphors CaSnO 3 :Bi,xMg 2 + were prepared via Mg 2+ co-doping, and the effects of Mg²⁺ doping on the structure, luminescence properties, Bi valence state, and defects of the phosphors were systematically studied. The results show that at low doping concentrations, Mg²⁺ primarily enters the CaSnO 3 lattice in an interstitial manner, leading to lattice expansion. The interstitial incorporation of Mg²⁺ introduces positive charges, which promotes the reduction of Bi³ ⁺ to Bi²⁺, thereby increasing the concentration of Bi²⁺ and enhancing the near-infrared photoluminescence efficiency of the phosphors. Moreover, Mg²⁺ codoping modified the defect distribution in the phosphor, which further enhances the near-infrared persistent luminescence intensity. Under the optimal Mg 2+ doping concentration, the photoluminescence intensity of the phosphor increased by 0.8 times, and the initial persistent luminescence brightness improved by 6.3 times compared to the Bi singly-doped sample. This study not only provides a new near-infrared persistent luminescent phosphor but also offers a novel strategy for regulating the valence state of Bi ions through interstitial codoping to prepare Bi 2+ -based near-infrared persistent phosphors.