Halide perovskite materials recently attracted wide attention for light-emitting applications. The intense white light emission and excited state lifetimes greater than 1 μs are the hallmarks of a good light-emitting material. Here, we provide a clear design strategy to achieve both of these aforementioned properties in a single material via the introduction of octahedral asymmetry in halide double perovskites Cs₂AgMCl₆ through iso-trivalent substitution at the M site. In the substituted Cs₂AgMCl₆, the presence of mixed M³⁺ sites distorts the [AgCl₆]^5- octahedra, affecting the parity of the valence and conduction band edges and thereby altering the optical transitions. The distortion also creates a local polarization that leads to an effective photogenerated carrier separation. Considering perovskite series with three M³⁺ cations, namely Bi³⁺, In³⁺ and Sb³⁺, the mixed trivalent cationic compounds with specific ratios of In³⁺ and Bi³⁺ show white light emission with intensity nearly 150 times larger than that of the parent compounds, and are characterised by excited state lifetimes nearing 1 μs. Using single crystal X-ray diffraction, far-infrared absorption, steady-state and time-resolved photoluminescence, bias-dependent photoluminescence, P-E loop traces and density-functional theory calculations, we hence demonstrate the role of octahedral distortion in enhancing white light emission and excited state lifetimes of halide double perovskites.

卤化物钙钛矿材料最近在发光应用中引起了广泛关注。强烈的白光发射和大于 1 μs 的激发态寿命是良好发光材料的标志。在这里，我们提供了一个明确的设计策略，通过在 M 位点进行异三价取代，在卤化物双钙钛矿 Cs ₂ AgMCl _{6 中}引入八面体不对称性，从而在单一材料中实现上述两种特性。在取代的 Cs ₂ AgMCl _{6 中}，混合 M ³⁺位点的存在扭曲了 [AgCl ₆ ] ^5-八面体，影响价带和导带边缘的奇偶性，从而改变光学跃迁。畸变还会产生局部极化，导致有效的光生载流子分离。考虑具有三个M ³⁺阳离子，即Bi ³⁺、In ³⁺和Sb ^{3+ 的}钙钛矿系列，具有特定比例的In ³⁺和Bi ³⁺的混合三价阳离子化合物显示出强度比母体化合物大近 150 倍的白光发射，其激发态寿命接近 1 μs。使用单晶 X 射线衍射、远红外吸收、稳态和时间分辨光致发光、偏置相关光致发光、PE 环迹线和密度泛函理论计算，我们因此证明了八面体畸变在增强白光发射中的作用和卤化物双钙钛矿的激发态寿命。