Ligand-capped nanocrystals (NCs) of lead halide perovskites, foremost fully inorganic CsPbX₃ NCs, are the latest generation of colloidal semiconductor quantum dots. They offer a set of compelling characteristics—large absorption cross section, as well as narrow, fast, and efficient photoluminescence with long exciton coherence times—rendering them attractive for applications in light-emitting devices and quantum optics. Monodisperse and shape-uniform, broadly size-tunable, scalable, and robust NC samples are paramount for unveiling their basic photophysics, as well as for putting them into use. Thus far, no synthesis method fulfilling all these requirements has been reported. For instance, long-chain zwitterionic ligands impart the most durable surface coating, but at the expense of reduced size uniformity of the as-synthesized colloid. In this work, we demonstrate that size-selective precipitation of CsPbBr₃ NCs coated with a long-chain sulfobetaine ligand, namely, 3-(N,N-dimethyloctadecylammonio)-propanesulfonate, yields monodisperse and sizable fractions (>100 mg inorganic mass) with the mean NC size adjustable in the range between 3.5 and 16 nm and emission peak wavelength between 479 and 518 nm. We find that all NCs exhibit an oblate cuboidal shape with the aspect ratio of 1.2 × 1.2 × 1. We present a theoretical model (effective mass/k·p) that accounts for the anisotropic NC shape and describes the size dependence of the first and second excitonic transition in absorption spectra and explains room-temperature exciton lifetimes. We also show that uniform zwitterion-capped NCs readily form long-range ordered superlattices upon solvent evaporation. In comparison to more conventional ligand systems (oleic acid and oleylamine), supercrystals of zwitterion-capped NCs exhibit larger domain sizes and lower mosaicity. Both kinds of supercrystals exhibit superfluorescence at cryogenic temperatures—accelerated collective emission arising from the coherent coupling of the emitting dipoles.

中文翻译：

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单分散长链磺基甜菜碱封端的CsPbBr ₃纳米晶体及其超荧光组装。

卤化钙钛矿的配体封端纳米晶体（NCs），最主要是完全无机的CsPbX ₃NC是最新一代的胶体半导体量子点。它们具有一系列引人注目的特性-大的吸收截面，以及窄的，快速的和有效的光致发光以及激子相干时间长-使其在发光器件和量子光学中的应用具有吸引力。单分散和形状均匀，尺寸可调，可扩展且坚固耐用的NC样品对于揭示其基本光物理特性以及使其投入使用至关重要。迄今为止，尚未报道满足所有这些要求的合成方法。例如，长链两性离子配体赋予了最耐用的表面涂层，但以合成胶体的尺寸均匀性降低为代价。在这项工作中，我们证明了CsPbBr _3的尺寸选择性沉淀涂有长链磺基甜菜碱配体即3-（N，N-二甲基十八烷基氨基）丙烷磺酸盐的NCs产生单分散级分和相当大的级分（无机质量> 100 mg），平均NC大小可在3.5至16 nm范围内调节发射峰值波长在479至518 nm之间。我们发现所有NC均显示长方比为1.2×1.2×1的扁长方体形状。我们提出了一个理论模型（有效质量/ k·p）解释了各向异性的NC形状，并描述了吸收光谱中第一和第二激子跃迁的尺寸依赖性，并解释了室温激子的寿命。我们还显示，溶剂蒸发后，均匀的两性离子封端的NC容易形成长程有序超晶格。与更常规的配体体系（油酸和油胺）相比，两性离子封端的NC的超晶表现出较大的畴尺寸和较低的镶嵌性。两种超晶在低温下均表现出超荧光-由发射偶极子的相干耦合引起的加速的集体发射。