Radiative and Non-Radiative Lifetime Engineering of Quantum Dots in Multiple Solvents by Surface Atom Stoichiometry and Ligands.

CdTe quantum dots have unique characteristics that are promising for applications in photoluminescence, photovoltaics or optoelectronics. However, wide variations of the reported quantum yields exist and the influence of ligand-surface interactions that are expected to control the excited state relaxation processes remains unknown. It is important to thoroughly understand the fundamental principles underlying these relaxation processes to tailor the QDs properties to their application. Here, we systematically investigate the roles of the surface atoms, ligand functional groups and solvent on the radiative and non-radiative relaxation rates. Combining a systematic synthetic approach with X-ray photoelectron, quantitative FT-IR and time-resolved visible spectroscopies, we find that CdTe QDs can be engineered with average radiative lifetimes ranging from nanoseconds up to microseconds. The non-radiative lifetimes are anticorrelated to the radiative lifetimes, although they show much less variation. The density, nature and orientation of the ligand functional groups and the dielectric constant of the solvent play major roles in determining charge carrier trapping and excitonic relaxation pathways. These results are used to propose a coupled dependence between hole-trapping on Te atoms and strong ligand coupling, primarily via Cd atoms, that can be used to engineer both the radiative and non-radiative lifetimes.

碲化镉量子点具有独特的特性，在光致发光、光伏或光电子学应用中具有良好前景。然而，所报道的量子产率存在很大差异，并且预期会控制激发态弛豫过程的配体 - 表面相互作用的影响仍然未知。彻底理解这些弛豫过程背后的基本原理对于根据应用调整量子点的性质非常重要。在此，我们系统地研究了表面原子、配体官能团和溶剂对辐射和非辐射弛豫速率的作用。通过将系统的合成方法与X射线光电子能谱、定量傅里叶变换红外光谱和时间分辨可见光谱相结合，我们发现碲化镉量子点可以被设计为具有从纳秒到微秒的平均辐射寿命。非辐射寿命与辐射寿命呈反相关，尽管其变化要小得多。配体官能团的密度、性质和取向以及溶剂的介电常数在决定电荷载流子俘获和激子弛豫途径方面起着主要作用。这些结果被用于提出碲原子上的空穴俘获与主要通过镉原子的强配体耦合之间的耦合相关性，可用于设计辐射和非辐射寿命。