Manipulation of Bi³⁺/In³⁺ Transmutation and Mn²⁺‐Doping Effect on the Structure and Optical Properties of Double Perovskite Cs₂NaBi_1‐<i>_x</i>In<i>_x</i>Cl₆

Abstract The halide double perovskite family represented by A 2 (B + ,B 3+ )X 6 can overcome the lead toxicity and enable generally large band gap engineering via B/B sites' transmutation or exotic dopants to fulfill the emerging applications in the optoelectronic fields. Herein, the design and the experimental synthesis of a new family of Mn 2+ ‐doped Cs 2 NaBi 1‐ x In x Cl 6 crystals with an intense orange‐yellow emission band are reported, and the phase formation stability is discussed via a combined experimental–theoretical approach. Depending on the manipulation of Bi 3+ /In 3+ combination, the band gap increases with In 3+ content, and a subsequent evolution from indirect to direct band gap is verified. First‐principles calculations and parity analyses indicate a parity forbidden effect on Cs 2 NaInCl 6 , and a combination effect of absorption on Cs 2 NaBi 1‐ x In x Cl 6 from both Cs 2 NaBiCl 6 and Cs 2 NaInCl 6 . The associated Mn 2+ ‐doped photoluminescence depending on the Bi 3+ /In 3+ substitution is also addressed from the variation of the different Mn–Cl environment and neighboring‐cation effect.