Semiconductor nanorods (NRs) with strong fluorescence anisotropy are considered promising polarized light sources for liquid crystal displays. Here, we achieved a high fluorescence anisotropy value of 0.4 in the mixed-anion lead halide perovskite NRs, which constitutes a four-fold enhancement as compared to pristine CsPbBr₃ NRs. This was realized by substituting some smaller bromine anions with larger iodine anions in the orthorhombic CsPbBr₃ NRs via anion exchange. The resulting CsPbBr_1.2I_1.8 NRs kept a highly uniform length of ∼36 nm and width of ∼8.6 nm, and possessed a high emission quantum yield of 83%. On the basis of the DFT calculations, we attribute the improved polarized emission of the mixed-anion perovskite NRs to a moderate structural distortion of PbX₆ octahedra units in the orthorhombic perovskite lattice, which results in a preferred direction of the optical transition dipole moment along the Pb–X–Pb axis. Our study provides a guidance for design and fabrication of perovskite NRs with high fluorescence anisotropy.

中文翻译：

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混合阴离子卤化钙钛矿型纳米棒中的晶格畸变导致其高荧光各向异性

具有强荧光各向异性的半导体纳米棒（NRs）被认为是用于液晶显示器的有希望的偏振光源。在这里，我们在混合阴离子卤化铅钙钛矿NRs中获得了0.4的高荧光各向异性值，与原始CsPbBr ₃ NRs相比，它构成了四倍的增强。这是通过在正交晶体CsPbBr ₃ NRs中通过阴离子交换将一些较小的溴阴离子替换为较​​大的碘阴离子来实现的。所得的CsPbBr _1.2 I _1.8NRs保持〜36 nm的高度均匀的长度和〜8.6 nm的宽度的高度均匀，并具有83％的高发射量子产率。在DFT计算的基础上，我们将混合阴离子钙钛矿NRs的极化发射改善归因于正交晶钙钛矿晶格中PbX ₆八面体单元的适度结构畸变，这导致沿其光学跃迁偶极矩的首选方向Pb–X–Pb轴。我们的研究为具有高荧光各向异性的钙钛矿NRs的设计和制造提供了指导。