How Surface Defects Shape the Excitons and Photoluminescence of Ultrasmall CdSe Quantum Dots

IF 7.2 2区材料科学 Q2 CHEMISTRY, PHYSICAL

Chemistry of Materials Pub Date : 2024-06-25 DOI:10.1021/acs.chemmater.4c00602

Torben Steenbock*, Emilia Drescher, Tobias Dittmann and Gabriel Bester,

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Abstract

Ultrasmall CdSe quantum dots (QDs) with diameters up to 2 nm show broad photoluminescence (PL) spectra presumably due to emission from band-edge excitons and defect states. However, the origin of the defect emission and the effect of defects on the band-edge excitons is not fully understood. Based on spin–orbit density functional theory and screened configuration interaction singles, we show that Cd-dimer and Se defects form in-gap defect states. In comparison with experiment, we discuss the role of deep and shallow defect states for the PL and cover the dependence of their contributions to the PL with respect to the QD size. Further, we observe that these defects lead to a localization of the molecular orbitals (MOs) involved in the band-edge excitons creating large electric dipoles in the MOs. In the excitonic states, these dipoles cause multiexponential PL decay from the band-edge states with a highly anisotropic polarization of the emission. The polarization is found to be very sensitive with respect to the exact composition of the surface.

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表面缺陷如何影响超小硒化镉量子点的激子和光致发光

直径达 2 纳米的超小型硒化镉量子点（QDs）显示出宽广的光致发光（PL）光谱，这可能是由于带边激子和缺陷态的发射所致。然而，缺陷发射的起源以及缺陷对带边激子的影响尚未完全明了。基于自旋轨道密度泛函理论和屏蔽构型相互作用单子，我们证明了镉-二聚体和硒缺陷会形成隙内缺陷态。通过与实验的比较，我们讨论了深缺陷态和浅缺陷态对光致发光的作用，并涵盖了它们对光致发光的贡献与 QD 尺寸的关系。此外，我们还观察到这些缺陷会导致参与带边激子的分子轨道（MO）局部化，从而在 MO 中产生大的电偶极子。在激子态中，这些偶极子会导致带边态多指数聚光衰减，并产生高度各向异性的极化发射。研究发现，偏振对表面的确切成分非常敏感。

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来源期刊

Chemistry of Materials 工程技术-材料科学：综合

CiteScore

14.10

自引率

5.80%

发文量

929

审稿时长

1.5 months

期刊介绍： The journal Chemistry of Materials focuses on publishing original research at the intersection of materials science and chemistry. The studies published in the journal involve chemistry as a prominent component and explore topics such as the design, synthesis, characterization, processing, understanding, and application of functional or potentially functional materials. The journal covers various areas of interest, including inorganic and organic solid-state chemistry, nanomaterials, biomaterials, thin films and polymers, and composite/hybrid materials. The journal particularly seeks papers that highlight the creation or development of innovative materials with novel optical, electrical, magnetic, catalytic, or mechanical properties. It is essential that manuscripts on these topics have a primary focus on the chemistry of materials and represent a significant advancement compared to prior research. Before external reviews are sought, submitted manuscripts undergo a review process by a minimum of two editors to ensure their appropriateness for the journal and the presence of sufficient evidence of a significant advance that will be of broad interest to the materials chemistry community.