Korala Lasantha, Brock Stephanie L
Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA, TEL: (313) 577-3102, FAX: (313) 577-8822.
J Phys Chem C Nanomater Interfaces. 2012 Aug 16;116(32):17110-17117. doi: 10.1021/jp305378u. Epub 2012 Jul 18.
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.
透明的CdSe(ZnS)溶胶-凝胶材料因其强发光特性以及通过凝胶中预连线的纳米晶体(NC)网络进行电荷传输的潜力，在发光二极管(LED)等光电子应用中具有潜在用途。然而，典型的金属硫族化物凝胶合成方法得到的材料透明度较差。在这项工作中，通过时间分辨动态光散射(TRDLS)研究了以四硝基甲烷(TNM)作为氧化剂去除表面硫醇盐配体引发的两种尺寸的CdSe(ZnS)核壳纳米晶体聚集的机理和动力学；通过光吸收、透射电子显微镜(TEM)和小角X射线散射(SAXS)对所得凝胶的特性进行了探测。在低浓度的纳米晶体(约4×10(-7) M)下，对于特定的氧化剂浓度，较小的、发出绿色光的纳米晶体比较大的、发出橙色光的纳米晶体聚集得更快。聚集动力学对所得凝胶的宏观性质(即透明度)有显著影响，由于在凝胶点形成更大的聚集体并偏离反应受限簇聚集(RLCA)机制，凝胶的透明度随着氧化剂浓度的增加而降低。SAXS和TEM对凝胶结构的分析进一步证实了这一点。同样，较大的发出橙色光的颗粒在凝胶点也会产生更大的聚集体，导致透明度降低。控制硫族化物凝胶透明度的能力将使其性能得以调整，以满足光电子学中特定应用的需求。
