Near-Infrared and Visible Dual-Band Self-Trapped Exciton Emissions from Li⁺-Doped Cs₂NaScCl₆ Double Perovskites

Self-trapped excitons (STEs) have garnered significant attention due to their broadband emission and large Stokes shift. However, achieving multiband, particularly near-infrared (NIR) STE emissions remains a challenge, restricting their optoelectronic applications. Herein, we realize efficient dual-band STE emissions encompassing blue and NIR regions based on Cs2NaScCl6 double perovskites (DPs) via minor Li+-doping structural engineering. The dual-band emissions in the blue and NIR regions originated from the STE states associated with [ScCl6]3– and [NaCl6]5– octahedra, respectively. Li+ doping markedly enhanced the photoluminescence (PL) quantum yields of dual-band STE emissions from 3.2% and 2.7% to 98.2% and 45.4%, respectively. Steady-state/transient PL spectroscopies and density functional theory calculations revealed that Li+ doping intensified sublattice distortion and enhanced charge carrier localization within Cs2NaScCl6 DPs, thus boosting the dual-band STE emissions. These findings gain deep insights into STE manipulation in DPs through local structural engineering, thus stimulating the exploitation of DPs toward versatile applications.