Type-II core/shell CdS/ZnSe nanocrystals: Synthesis, electronic structures, and spectroscopic properties
Type-II core/shell CdS/ZnSe nanocrystals: Synthesis, electronic structures, and spectroscopic properties
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DOI：
10.1021/ja068351m
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发表时间：
2007-09-26
影响因子：
15
通讯作者：
Klimov, Victor I.
中科院分区：
文献类型：
--
作者：
Ivanov, Sergei A.;Piryatinski, Andrei;Klimov, Victor I.
我们报告了一个两步合成的高度发光的CdS/ZnSe核/壳纳米晶体（发射量子产率高达50%），可以产生有效的空间分离的电子和空穴之间的核心和外壳（II型本地化制度）。我们的合成涉及到制造的cross-singony CdS核心颗粒，随后在非配位溶剂中的表面活性剂配体的存在下，用一层ZnSe包覆。不同的生长制度的ZnSe壳层的研究表明，获得高的发射效率的一种方法是通过合金化的CdS/ZnSe界面与CdSe，这导致形成一个中间ZnCdSe层与渐变的组合物。我们使用有效质量近似和应用一阶微扰理论来处理直接的电子-空穴耦合和核/壳界面极化效应，对这些核/壳纳米晶体进行理论建模。使用这个模型，我们确定的核/壳结构，导致在II型本地化制度的几何参数的范围。我们进一步应用该模型基于测量的发射波长来评估电子-空穴空间分离的程度（根据电子-空穴重叠积分来量化）。我们还讨论了这些纳米晶体在激光技术中的潜在适用性，特别是在II型纳米结构中的单激子光学增益的可能性。
We report a two-step synthesis of highly luminescent CdS/ZnSe core/shell nanocrystals (emission quantum yields up to 50%) that can produce efficient spatial separation of electrons and holes between the core and the shell (type-II localization regime). Our synthesis involves fabrication of cubic-singony CdS core particles that are subsequently overcoated with a layer of ZnSe in the presence of surfactant-ligands in a noncoordinating solvent. Studies of different growth regime of the ZnSe shell indicate that one approach to obtaining high emission efficiencies is through alloying the CdS/ZnSe interface with CdSe, which leads to the formation of an intermediate ZnCdSe layer with a graded composition. We perform theoretical modeling of these core/shell nanocrystals using effective mass approximation and applying first-order perturbation theory for treating both direct electron-hole coupling and the core/shell interface-polarization effects. Using this model we determine the range of geometrical parameters of the core/shell structures that result in a type-II localization regime. We further applied this model to evaluate the degree of electron-hole spatial separation (quantified in terms of the electron-hole overlap integral) based on measured emission wavelengths. We also discuss the potential applicability of these nanocrystals in lasing technologies and specifically the possibility of single-exciton optical gain in type-II nanostructures.