Shape-Dependent Linear Dichroism Spectra of Colloidal Semiconductor Nanocrystals
Shape-Dependent Linear Dichroism Spectra of Colloidal Semiconductor Nanocrystals
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胶体半导体纳米晶体的形状相关线性二色光谱
DOI：
10.1021/acs.langmuir.1c01155
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发表时间：
2021
期刊：
影响因子：
3.9
通讯作者：
Gao Xiaoqing
中科院分区：
文献类型：
--
作者：
Guo Jun;Chen Yan;Zhang Yadong;Xu Yiguo;Zhou Yunlong;Zhang Xiuwen;Gao Xiaoqing
半导体纳米晶体通常分散在溶剂中用于性质研究以及实际应用。然而，很少有人注意到它们在胶体溶液中的取向状态。在本文中，借助于线性二色性（LD）光谱，我们证明了具有高对称性的各向同性NC（即，量子点，QD）和各向异性NC（例如，量子棒，QR和纳米片，NPL），但在稀释浓度下随机分散，没有任何优先取向。同时，在高浓度下，各向异性的纳米粒子可以表现出沿沿着某一方向的净取向。例如，当溶液中CdSe量子棒（QRs）和纳米片（NPLs）的溶解度增加到一定值时，它们都表现出明显的沿溶液垂直方向的沿着择优取向。通过对QRs的LD谱的深入分析，发现QRs的第一激子跃迁是强量子限制的，而其高能激子跃迁是弱量子限制的。相比之下，NPL的LD谱表明它们的激子跃迁在空间空间中是各向同性的。这为了解各向异性半导体纳米粒子在溶液中的真实的状态提供了一个新的视角。
Semiconductor nanocrystals are normally dispersed in the solvent for property studies as well as practical applications. However, rare attention has been paid to their orientation status in the colloidal solution. Herein, with the help of linear dichroism (LD) spectroscopy, we demonstrate that isotropic NCs of high symmetry (i.e., quantum dots, QDs) and anisotropic NCs (e.g., quantum rods, QRs and nanoplates, NPLs) but under diluted concentration are randomly dispersed without any preferential orientation. Meanwhile, anisotropic NCs under a high concentration can behave with some net orientation along a certain direction. For example, CdSe quantum rods (QRs) and nanoplatelets (NPLs) both show an obviously preferred orientation along the vertical direction in solution when their solution absorbances increase to certain values. An in-depth analysis of QRs’ LD spectrum shows that the first excitonic transition of QRs is strongly quantumly confined while its higher-energy excitonic transitions are weakly quantumly confined. In contrast, the NPLs’ LD spectrum indicates that their excitonic transitions are isotropic in the spatial space. This work provides a new viewpoint of the real status of anisotropic semiconductor NCs in solution.