Octahedral Distortion‐Induced Photoluminescence in Cs₂NaIn_<i>x</i>Bi_1−<i>x</i>Cl₆ Halide Double Perovskites

The halide perovskite materials have shown broadband light emission and there are multiple strategies to tweak the photoluminescence. Herein, a class of halide double perovskites Cs₂NaIn_xBi_1-xCl₆ that are chemically tuned via trivalent cation engineering to introduce octahedral distortion is reported. This distortion leads to improved light emission properties where the photoluminescence quantum yield improves from <1% for a symmetric-octahedra containing parent compounds to >6.5% in distorted-octahedra containing mixed-trivalent compounds. Using structural and optical studies including Raman spectroscopy, far-infrared absorption, and steady-state photoluminescence, the role of octahedral distortion in improving light emission in halide double perovskites is demonstrated. In addition, to emphasize the role of distortion, electric bias is intentionally applied to symmetric-octahedra containing parent compounds, and their role in the emission properties is investigated.