Research Institute for Physical Chemical Problems of the Belarusian State University, 220006 Minsk, Belarus.
Nanoscale. 2017 Nov 23;9(45):18042-18053. doi: 10.1039/c7nr05065h.
We study the influence of surface passivating ligands on the optical and structural properties of zinc blende CdSe nanoplatelets. Ligand exchange of native oleic acid with aliphatic thiol or phosphonic acid on the surface of nanoplatelets results in a large shift of exciton transition energy for up to 240 meV. Ligand exchange also leads to structural changes (strain) in the nanoplatelet's core analysed by wide-angle X-ray diffraction. By correlating the experimental data with theoretical calculations we demonstrate that the exciton energy shift is mainly caused by the ligand-induced anisotropic transformation of the crystalline structure altering the well width of the CdSe core. Further the exciton reduced mass in these CdSe quantum wells is determined by a new method and this agrees well with the expected values substantiating that ligand-strain induced changes in the colloidal quantum well thickness are responsible for the observed spectral shifts. Our findings are important for theoretical modeling of other anisotropically strained systems and demonstrate an approach to tune the optical properties of 2D semiconductor nanocrystals over a broad region thus widening the range of possible applications of AB nanoplatelets in optics and optoelectronics.
我们研究了表面钝化配体对闪锌矿型 CdSe 纳米板光学和结构性质的影响。通过在纳米板表面上将原本的油酸与脂肪族硫醇或膦酸进行配体交换，可使激子跃迁能发生高达 240meV 的大幅移动。配体交换还会导致通过广角 X 射线衍射分析得出的纳米板核心的结构变化（应变）。通过将实验数据与理论计算相关联，我们证明激子能量移动主要是由配体诱导的晶体结构各向异性转变引起的，从而改变了 CdSe 核心的势阱宽度。此外，我们还通过一种新方法确定了这些 CdSe 量子阱中的激子有效质量，这与预期值非常吻合，证实了胶体量子阱厚度因配体应变而发生的变化是导致观察到的光谱移动的原因。我们的发现对于各向异性应变系统的理论建模很重要，并展示了一种在较宽的区域内调节二维半导体纳米晶体光学性质的方法，从而拓宽了 AB 纳米板在光学和光电子学中应用的范围。
