Korea Center for Artificial Photosynthesis, Center for Microcrystal Assembly, Department of Chemistry, Sogang University, Seoul 121-742, Korea.
J Am Chem Soc. 2012 Feb 8;134(5):2539-42. doi: 10.1021/ja211547s. Epub 2012 Jan 30.
The third-order nonlinear optical (3NLO) activity of PbS quantum dots (QDs) encapsulated in zeolite Y has been expected to depend sensitively on the countercation of the zeolite host. However, ion exchange of the pristine countercation, H(+), with other cations has not been possible because the framework decomposes and the QDs aggregate immediately when the PbS QD-incorporating zeolite Y with H(+) as the countercation is exposed to the atmosphere. We now report that when H(+) is transformed to NH(4)(+), the framework of PbS QD-containing zeolite Y does not undergo decomposition and the PbS QDs do not undergo aggregation to form larger QDs during the aqueous ion exchange of NH(4)(+) with alkali-metal ions (M(A)(+) = Li, Na(+), K(+), Rb(+)). The 3NLO activity of the M(A)(+)-exchanged PbS QD-incorporating zeolite Y film increases with increasing size of M(A)(+). The stabilization of the surface-bound exciton by the electron-rich framework oxide and electron-poor cation is proposed to be responsible for the increase. This is the first example of a method for systematically increasing the 3NLO activity of QDs dispersed in a dielectric matrix by systematically changing its properties. These results will serve as a guideline for future research and also promote applications of QD-incorporating zeolites in various fields.
在沸石 Y 中封装的 PbS 量子点 (QD) 的三阶非线性光学 (3NLO) 活性有望对沸石主体的抗衡离子敏感。然而，由于原始抗衡离子 H(+)的离子交换与其他阳离子不可能，因为当含有 H(+)作为抗衡离子的 PbS QD 沸石 Y 暴露于大气中时，骨架会分解并且 QD 会立即聚集。我们现在报告说，当 H(+)转变为 NH(4)(+)时，含 PbS QD 的沸石 Y 的骨架不会分解，并且在 NH(4)(+)与碱金属离子 (M(A)(+) = Li、Na(+)、K(+)、Rb(+))的水溶液离子交换过程中，PbS QD 也不会聚集形成更大的 QD。M(A)(+)交换的 PbS QD 掺入沸石 Y 薄膜的 3NLO 活性随 M(A)(+)尺寸的增加而增加。提出由富电子骨架氧化物和贫电子阳离子稳定表面结合激子是导致这种增加的原因。这是通过系统改变其性质来系统地提高分散在介电基质中的 QD 的 3NLO 活性的第一种方法的示例。这些结果将为未来的研究提供指导，并促进含 QD 沸石在各个领域的应用。
