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In this study, a novel synthesis of ultrathin, highly uniform colloidal bismuth sulfohalide (BiSX where X = Cl, Br, I) nanowires (NWs) and NW bundles (NBs) for room‐temperature and solution‐processed flexible photodetectors are presented. High‐aspect‐ratio bismuth sulfobromide (BiSBr) NWs are synthesized via a heat‐up method using bismuth bromide and elemental S as precursors and 1‐dodecanethiol as a solvent. Bundling of the BiSBr NWs occurs upon the addition of 1‐octadecene as a co‐solvent. The morphologies of the BiSBr NBs are easily tailored from sheaf‐like structures to spherulite nanostructures by changing the solvent ratio. The optical bandgaps are modulated from 1.91 (BiSCl) and 1.88 eV (BiSBr) to 1.53 eV (BiSI) by changing the halide compositions. The optical bandgap of the ultrathin BiSBr NWs and NBs exhibits blueshift, whose origin is investigated through density functional theory‐based first‐principles calculations. Visible‐light photodetectors are fabricated using BiSBr NWs and NBs via solution‐based deposition followed by solid‐state ligand exchanges. High photo‐responsivities and external quantum efficiencies (EQE) are obtained for BiSBr NW and NB films even under strain, which offer a unique opportunity for the application of the novel BiSX NWs and NBs in flexible and environmentally friendly optoelectronic devices. [ABSTRACT FROM AUTHOR]

To understand the alkali-metal-dependent material properties of recently discovered AV3Sb5 (A = K, Rb, and Cs), we conducted a detailed electronic structure analysis based on first-principles density functional theory calculations. Contrary to the case of A = K and Rb, the energetic positions of the low-lying Van Hove singularities are reversed in CsV3Sb5, and the characteristic higher-order Van Hove point gets closer to the Fermi level. We found that this notable difference can be attributed to the chemical effect, apart from structural differences. Due to their different orbital compositions, Van Hove points show qualitatively different responses to the structure changes. A previously unnoticed highest lying point can be lowered, locating close to or even below the other ones in response to a reasonable range of bi- and uni-axial strain. Our results can be useful in better understanding the material-dependent features reported in this family and in realizing experimental control of exotic quantum phases. [ABSTRACT FROM AUTHOR]

Herein, the synthesis of novel, highly luminescent, and nearly monodisperse zero-dimensional (0D) cesium lanthanide chloride (Cs3LnCl6; Ln = Y, Ce, Gd, Er, Tm, Yb) colloidal nanocrystals (NCs) is reported for the first time. The Cs3LnCl6 NCs are synthesized using a heating-up method and exhibit highly uniform size and shape. The monoclinic-phase Cs3LnCl6 NCs contain completely isolated [LnCl6]3- octahedral units, resulting in 0D ternary metal halide structures. Therefore, these NCs exhibit deep-blue photoluminescence under ultraviolet excitation, and this photoluminescence can be tuned by changing the lanthanide cations within the [LnCl6]3- octahedral units. High photoluminescence quantum yields of up to 60% and 90% are observed for the Cs3YbCl6 and Cs3YCl6 NCs, respectively, at room temperature and under ambient conditions. The Cs3LnCl6 NCs exhibit characteristic optical and magnetic properties owing to the f-orbitals of the lanthanide elements. For example, near-infrared-to-visible upconversion luminescence appears when Cs3LnCl6 NCs are doped with Er3+ and Yb3+ ions. In addition, the Cs3GdCl6 NCs demonstrate paramagnetic properties owing to the unpaired electrons within the f-orbitals of the trivalent gadolinium ions. This study provides guidance for the rational design and synthesis of novel lanthanide-based 0D metal halide NCs, which can potentially be used as highly efficient, multifunctional NC emitters. [ABSTRACT FROM AUTHOR]

To understand the alkali-metal-dependent material properties of recently discovered AV 3 Sb 5 (A = K, Rb, and Cs), we conducted a detailed electronic structure analysis based on first-principles density functional theory calculations. Contrary to the case of A = K and Rb, the energetic positions of the low-lying Van Hove singularities are reversed in CsV 3 Sb 5 , and the characteristic higher-order Van Hove point gets closer to the Fermi level. We found that this notable difference can be attributed to the chemical effect, apart from structural differences. Due to their different orbital compositions, Van Hove points show qualitatively different responses to the structure changes. A previously unnoticed highest lying point can be lowered, locating close to or even below the other ones in response to a reasonable range of bi- and uni-axial strain. Our results can be useful in better understanding the material-dependent features reported in this family and in realizing experimental control of exotic quantum phases.