Aggregation Kinetics of Metal Chalcogenide Nanocrystals: Generation of Transparent CdSe(ZnS) Core(shell) Gels.
Aggregation Kinetics of Metal Chalcogenide Nanocrystals: Generation of Transparent CdSe(ZnS) Core(shell) Gels.
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DOI：
10.1021/jp305378u
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发表时间：
2012-08-16
影响因子：
3.7
通讯作者：
Brock, Stephanie L.
中科院分区：
文献类型：
--
作者：
Korala, Lasantha;Brock, Stephanie L.
透明CdSe（ZnS）溶胶-凝胶材料由于其强大的发光特性和通过凝胶的预连接纳米晶体（NC）网络传输电荷的潜力，在光电应用中具有潜在的用途，如发光二极管（led）。然而，典型的金属硫系凝胶合成产生的材料透明度较差。本文采用时间分辨动态光散射（TRDLS）技术研究了四硝基甲烷（TNM）作为氧化剂去除表面硫化物配体引发的两种尺寸的CdSe（ZnS）核（壳）纳米碳的聚集机理和动力学；采用光学吸收、透射电子显微镜（TEM）和小角x射线散射（SAXS）对所得凝胶进行了表征。在低浓度的NCs（约4 × 10−7 M）下，对于特定的氧化剂浓度，较小的绿色排放的NCs比较大的橙色排放的NCs聚集得更快。聚集动力学对所得凝胶的宏观性质（即透明度）有显著影响，随着氧化剂浓度的增加，凝胶的透明度随着凝胶点形成更大的团簇而降低，这是由于在凝胶点形成更大的团簇聚集（RLCA）机制的转变。凝胶结构的SAXS和TEM分析进一步证实了这一点。同样，较大的橙色发射颗粒也会在凝胶点产生较大的聚集体，导致透明度降低。控制硫系凝胶透明度的能力将使其性能得以调整，以满足光电子学中的特定应用需求。
Transparent CdSe(ZnS) sol-gel materials have potential uses in optoelectronic applications such as light emitting diodes (LEDs) due to their strong luminescence properties and the potential for charge transport through the prewired nanocrystal (NC) network of the gel. However, typical syntheses of metal chalcogenide gels yield materials with poor transparency. In this work, the mechanism and kinetics of aggregation of two sizes of CdSe(ZnS) core(shell) NCs, initiated by removal of surface thiolate ligands using tetranitromethane (TNM) as an oxidant, were studied by means of time-resolved dynamic light scattering (TRDLS); the characteristics of the resultant gels were probed by optical absorption, transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). At low concentrations of NCs (ca. 4 × 10−7 M), the smaller, green-emitting NCs aggregate faster than the larger, orange-emitting NCs, for a specific oxidant concentration. The kinetics of aggregation have a significant impact on the macroscopic properties (i.e. transparency) of the resultant gels, with the transparency of the gels decreasing with the increase of oxidant concentration due the formation of larger clusters at the gel point and a shift away from a reaction limited cluster aggregation (RLCA) mechanism. This is further confirmed by the analyses of the gel structures by SAXS and TEM. Likewise, the larger orange-emitting particles also produce larger aggregates at the gel point, leading to lower transparency. The ability to control the transparency of chalcogenide gels will enable their properties to be tuned in order to address application-specific needs in optoelectronics.
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