Anomalous near-infrared emission and the underlying “structure-luminescence” correlation in the multi-peak emission system of KScF4:Yb3+,Mn2+

Abstract

Currently, research on near-infrared (NIR) phosphors predominantly focuses on doping with Cr³⁺ or rare earth ions. However, Mn²⁺ has recently emerged as a notable activator for NIR luminescence, providing a fresh perspective on achieving NIR emission. Herein, anomalous broadband NIR emission centered at ∼775 nm was achieved in a novel KScF₄:Yb³⁺,Mn²⁺ phosphor, exhibiting both Stokes and upconversion (UC) luminescence—an occurrence rarely reported in Mn²⁺-activated phosphors. Structural and spectral analysis revealed that the NIR emission was attributed to the super-exchange coupled Mn_Sc1–Mn_Sc2 dimers. Additionally, the phosphor exhibited an asymmetric visible Stokes emission consisting of three individual peaks at 540, 570 and 602 nm, originating from single Mn²⁺ ions at the K2, Sc2 and Sc1 sites, respectively. In contrast, the UC emission showed only a single visible peak at the Sc1 site. The distinct luminescence behaviors between UC and Stokes emissions, as well as between NIR and visible emissions, have been discussed in detail. The unique NIR properties of KScF₄:Yb³⁺,Mn²⁺ hold promise for applications in night vision, non-destructive testing, bio-imaging, and more. This work not only advances the fundamental understanding of Mn²⁺-activated NIR emission but also provides new insights for developing novel and environmentally friendly broadband NIR phosphors.