Manipulation of Bi3+/In3+ Transmutation and Mn2+-Doping Effect on the Structure and Optical Properties of Double Perovskite Cs2NaBi1-xInxCl6

The halide double perovskite family represented by A₂(B⁺,B³⁺)X₆ 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 Mn²⁺‐doped Cs₂NaBi_1‐xIn_xCl₆ 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 Bi³⁺/In³⁺ combination, the band gap increases with In³⁺ 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 Cs₂NaInCl₆, and a combination effect of absorption on Cs₂NaBi_1‐xIn_xCl₆ from both Cs₂NaBiCl₆ and Cs₂NaInCl₆. The associated Mn²⁺‐doped photoluminescence depending on the Bi³⁺/In³⁺ substitution is also addressed from the variation of the different Mn–Cl environment and neighboring‐cation effect.