Cr3+-Induced Structure Modulation and Near-Infrared Luminescence in Double Perovskite

Cr 3+ -doped lead-free halide double perovskites (DPs) have recently emerged as promising near-infrared (NIR) phosphors, owing to their tunable optical properties. Herein, we report a Cr 3+ -doped Cs 2 Ag 0.6 Na 0.4 In 0.9 Bi 0.1 Cl 6 system exhibiting dual-band luminescence under 405 nm excitation and NIR-only luminescence under 808 nm excitation. Increasing Cr 3+ concentration induces a redshift and attenuation in self-trapped excitons (STEs) luminescence, while Cr 3+ luminescence first increases and then decreases. The Tanabe–Sugano diagram ( D q / B ≈ 2.20) confirms the weak crystal field environment and spin-allowed 4 T 2 → 4 A 2 NIR transition. Multivariate regression reveals that Cr 3+ luminescence partly arises from the self-absorption process. First-principles calculations indicate that Cr significantly modifies the conduction band minimum, enhancing electron localization and reducing electron–hole wave function overlap, which in turn suppresses STEs luminescence. Combining experimental observations with first-principles calculations elucidates the luminescence pathways of Cr 3+ and STEs, offering insights into their distinct behaviors and interaction dynamics.