The use of the varied chemical reactivity of precursors to drive the production of a desired nanocrystal architecture has become a common method to grow thick-shell graded alloy quantum dots (QDs) with robust optical properties. Conclusions on their behavior assume the ideal chemical gradation and uniform particle composition. Here, advanced analytical electron microscopy (high-resolution scanning transmission electron microscopy coupled with energy dispersive spectroscopy) is used to confirm the nature and extent of compositional gradation and these data are compared with performance behavior obtained from single-nanocrystal spectroscopy to elucidate structure, chemical-composition, and optical-property correlations. Specifically, the evolution of the chemical structure and single-nanocrystal luminescence was determined for a time-series of graded-alloy “CdZnSSe/ZnS” core/shell QDs prepared in a single-pot reaction. In a separate step, thick (∼6 monolayers) to giant (>14 monolayers) shells of ZnS were added to the alloyed QDs via a successive ionic layer adsorption and reaction (SILAR) process, and the impact of this shell on the optical performance was also assessed. By determining the degree of alloying for each component element on a per-particle basis, we observe that the actual product from the single-pot reaction is less “graded” in Cd and more so in Se than anticipated, with Se extending throughout the structure. The latter suggests much slower Se reaction kinetics than expected or an ability of Se to diffuse away from the initially nucleated core. It was also found that the subsequent growth of thick phase-pure ZnS shells by the SILAR method was required to significantly reduce blinking and photobleaching. However, correlated single-nanocrystal optical characterization and electron microscopy further revealed that these beneficial properties are only achieved if the thick ZnS shell is complete and without large lattice discontinuities. In this way, we identify the necessary structural design features that are required for ideal light emission properties in these green-visible emitting QDs.

中文翻译：

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壳组成和形态在实现绿色发射“巨大”量子点的单发射体光稳定性中的作用

利用前驱物不同的化学反应性来驱动所需纳米晶体结构的生产已成为生长具有坚固光学性能的厚壳分级合金量子点（QD）的常用方法。关于它们行为的结论假定理想的化学梯度和均匀的颗粒组成。在这里，使用先进的分析电子显微镜（高分辨率扫描透射电子显微镜与能量色散光谱法结合）来确认组成级配的性质和程度，并将这些数据与单纳米晶体光谱法获得的性能进行比较，以阐明结构，化学性质。组成和光学属性相关性。特别，确定了在单锅反应中制备的梯度合金“ CdZnSSe / ZnS”核/壳量子点的时间序列的化学结构和单纳米晶体发光的演变。在一个单独的步骤中，通过连续的离子层吸附和反应（SILAR）过程，将厚的（〜6个单层）到巨型的（> 14个单层）ZnS壳添加到合金化QD中，并且该壳对光学性能的影响也进行了评估。通过基于每个粒子确定每个组成元素的合金化程度，我们观察到单罐反应的实际产物在Cd中的“分级”较少，而在Se中则比预期的要高，其中Se遍布整个结构。后者表明硒的反应动力学比预期的要慢得多，或者硒有能力从初始有核的核中扩散出来。还发现，随后需要通过SILAR方法生长较厚的纯相ZnS壳，才能显着减少闪烁和光漂白。然而，相关的单纳米晶体光学表征和电子显微镜进一步表明，只有在厚厚的ZnS壳完整且没有大的晶格不连续性的情况下，才能获得这些有益的性能。通过这种方式，我们确定了这些绿色可见发光QD中理想发光特性所需的必要结构设计特征。相关的单纳米晶体光学表征和电子显微镜进一步揭示，只有在厚厚的ZnS壳完整且没有大的晶格不连续性的情况下，才能获得这些有益的性能。通过这种方式，我们确定了这些绿色可见发光QD中理想发光特性所需的必要结构设计特征。相关的单纳米晶体光学表征和电子显微镜进一步揭示，只有在厚厚的ZnS壳完整且没有大的晶格不连续性的情况下，才能获得这些有益的性能。通过这种方式，我们确定了这些绿色可见发光QD中理想发光特性所需的必要结构设计特征。