Lv Liulin, Liu Shaojie, Li Jiongzhao, Lei Haixin, Qin Haiyan, Peng Xiaogang
Key Laboratory of Excited-State Materials of Zhejiang Province, and Department of Chemistry, Zhejiang University, Hangzhou 310027, China.
J Am Chem Soc. 2022 Sep 21;144(37):16872-16882. doi: 10.1021/jacs.2c05151. Epub 2022 Sep 6.
Zinc-blende CdSe, CdS, and CdSe/CdS core/shell nanocrystals with a structure-matched shape (cube-shaped, edge length ≤30 nm) are synthesized via a universal scheme. With the edge length up to five times larger than exciton diameter of the bulk semiconductors, the nanocrystals exhibit novel properties in the weakly confined size regime, such as near-unity single exciton and biexciton photoluminescence (PL) quantum yields, single-nanocrystal PL nonblinking, mixed PL decay dynamics of exciton and free carriers with sub-microsecond monoexponential decay lifetime, and stable yet extremely narrow PL full width at half maximum (FWHM < 0.1 meV) at 1.8 K. Their monodisperse edge length, shape, and facet structure enable demonstration of unexpected yet size-dependent PL properties at room temperature, including unusually broad and abnormally size-dependent PL FWHM (∼100 meV), nonmonotonic size dependence of PL peak energy, and dual-peak single-exciton PL. Calculations suggest that these unusual properties should be originated from the band-edge electron/hole states of the dynamic-exciton, whose exciton binding energy is too small to hold the photogenerated electron-hole pair as a bonded Wannier exciton in a weakly confined nanocrystal.
通过一种通用方法合成了具有结构匹配形状（立方体形，边长≤30 nm）的闪锌矿结构的CdSe、CdS和CdSe/CdS核壳纳米晶体。由于边长比体相半导体的激子直径大五倍，这些纳米晶体在弱受限尺寸区域表现出新颖的性质，例如接近单位的单激子和双激子光致发光（PL）量子产率、单纳米晶体PL不闪烁、激子和自由载流子的混合PL衰减动力学以及亚微秒单指数衰减寿命，并且在1.8 K时具有稳定且极窄的PL半高宽（FWHM < 0.1 meV）。它们单分散的边长、形状和晶面结构使得在室温下能够展示出意想不到的尺寸依赖性PL性质，包括异常宽且异常依赖尺寸的PL FWHM（~100 meV）、PL峰值能量的非单调尺寸依赖性以及双峰单激子PL。计算表明，这些不寻常的性质应源于动态激子的带边电子/空穴态，其激子结合能太小，无法在弱受限纳米晶体中将光生电子 - 空穴对保持为束缚的万尼尔激子。
