Tailoring ZnSe-CdSe Colloidal Quantum Dots via Cation Exchange: From Core/Shell to Alloy Nanocrystals
Tailoring ZnSe-CdSe Colloidal Quantum Dots via Cation Exchange: From Core/Shell to Alloy Nanocrystals
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DOI：
10.1021/nn402931y
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发表时间：
2013-09-01
期刊：
影响因子：
17.1
通讯作者：
Donega, Celso de Mello
中科院分区：
文献类型：
--
作者：
Groeneveld, Esther;Witteman, Leon;Donega, Celso de Mello
本文报道了用Cd~(2+)阳离子交换(CE)对胶体锌硒纳米晶(NCS)中锌离子的研究。我们的结果表明，ZnSe NCS中的CE是一个热激活的各向同性过程。CE效率(即溶液中最初存在的Cd-Sol中的Cd-Sol离子的分数)随着温度的升高而增加，并且还依赖于Cd-Sol/ZnSe的比例。有趣的是，反应温度可以作为一个敏感的参数来调整产物(Zn，Cd)Se NCS的组成和元素分布。当温度为150℃时，得到的是ZnSe/CdSe核/壳异质结纳米管(HNCs)，而较高的温度(200℃和220℃)得到的是(Zn1-xCdx)Se梯度合金NCS，随着温度的升高，NCS的梯度变得越来越平坦，直到T>；=240℃时才得到均匀的NCS。值得注意的是，顺序加热(150℃后220℃)会得到壳层较厚的ZnSe/CdSe核/壳HNC，而不是(Zn1-xCdx)Se梯度合金NCS。250℃下的热处理使ZnSe/CdSe核/壳HNC转变为(Zn1-xCdx)Se均匀合金NCS，同时保持NC形状。提出了锌硒纳米管中阳离子交换的一种机制，即在纳米管表面发生快速的阳离子交换，随后是由Frenkel缺陷引起的相对较慢的热激活固相阳离子扩散。结果表明，胶体ZnSe NCS中的阳离子交换为调节胶体ZnSe-CdSe NCS的电子和空穴波函数的性质和局域化机制以及光电性质提供了一个非常灵敏的工具。
We report a study of Zn2+ by Cd2+ cation exchange (CE) in colloidal ZnSe nanocrystals (NCs). Our results reveal that CE in ZnSe NCs is a thermally activated isotropic process. The CE efficiency (i.e., fraction of Cd2+ ions originally in solution, Cd-sol, that is incorporated in the ZnSe NC) increases with temperature and depends also on the Cd-sol/ZnSe ratio. Interestingly, the reaction temperature can be used as a sensitive parameter to tailor both the composition and the elemental distribution profile of the product (Zn,Cd)Se NCs. At 150 degrees C ZnSe/CdSe core/shell hetero-NCs (HNCs) are obtained, while higher temperatures (200 and 220 degrees C) produce (Zn1-xCdx)Se gradient alloy NCs, with increasingly smoother gradients as the temperature increases, until homogeneous alloy NCs are obtained at T >= 240 degrees C. Remarkably, sequential heating (150 degrees C followed by 220 degrees C) leads to ZnSe/CdSe core/shell HNCs with thicker shells, rather than (Zn1-xCdx)Se gradient alloy NCs. Thermal treatment at 250 degrees C converts the ZnSe/CdSe core/shell HNCs Into (Zn1-xCdx)Se homogeneous alloy NCs, while preserving the NC shape. A mechanism for the cation exchange in ZnSe NCs is proposed, in which fast CE takes place at the NC surface, and is followed by relatively slower thermally activated solid-state cation diffusion, which is mediated by Frenkel defects. The findings presented here demonstrate that cation exchange in colloidal ZnSe NCs provides a very sensitive tool to tailor the nature and localization regime of the electron and hole wave functions and the optoelectronic properties of colloidal ZnSe-CdSe NCs.