Ultrafast transient pump-pump-probe spectroscopic studies in colloidal semiconductor heteronanostructures to follow processes involving multiple excitations

胶体半导体异质纳米结构中的超快瞬态泵浦探针光谱研究，以跟踪涉及多次激发的过程

• 批准号: 468735112
• 负责人: Krishan Kumar, Ph.D.
• 金额: --
• 依托单位: Institut für Physikalische und Theoretische Chemie
• 依托单位国家: 德国
• 项目类别: WBP Position
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/468735112?language=en
• 关键词: Ultrafast; transient; pump; probe; spectroscopic

Multiple excitation events are of highest relevance in light-harvesting applications, i.e., photocatalysis involving multielectron redox reactions. To achieve charge accumulation at the reaction center either several consecutive light-induced charge carrier transfer steps, each step initiated by absorption of a photon, or charge separation from multiple excited systems and quasi simultaneous multiple charge transfer to a reaction center have to occur. The majority of research reports on investigations of charge carrier dynamics solely under single excitation conditions. To overcome this limitation, this project aims to study the exciton and charge carrier dynamics in colloidal semiconductor nanostructures involving multiple excitations. Pump-pump-probe transient absorption spectroscopy will be applied to investigate the dynamics of consecutive light-induced electron transfer processes and processes in multiply excited nanostructures.The project will deliver insight into the electron transfer cascade beyond the initial electron transfer under in situ conditions. In the focus will be heteronanostructures, e.g., metal tipped CdSe@CdS nanorods, which have proven high efficiencies for photon-to-hydrogen conversion. The impact of the formation of an additional barrier for the charge separation at the semiconductor/metal interface due to charging of the metal particle after the first electron transfer step on the electron transfer process will be explored. The influence of structural factors on the second charge transfer step will be explored to complement the already available knowledge for the first charge transfer and support the design of optimized structures.The interaction of multiple excitons and their dynamics will be studied in heteronanostructures, e.g, CdSe@CdS nanorods. The choice of the excitation wavelength allows in heterostructures to control the initial localization of a generated exciton in a defined subdomain. Especially, the timescale of annihilation via Auger recombination (AR) of two initially spatially well-separated excitons will provide a fundamental understanding of the interaction of excitons in dependence on structural and electronic factors (volume and aspect ratio of the particle and band alignment) in the nanostructure. Further, interactions between multiple excitations in assemblies of semiconductor nanoparticles with varying degree of electronic coupling will be regarded. The coupling strength between neighboring particles can be tuned via modification of the surface ligands of the particles, which impacts exciton migration processes within the nanoparticle assembly. Exciton diffusion in the layer can lead to quenching of multiple excitations generated via AR. The results of these investigations will help to understand the relations between AR time scale and structure and will guide the design of structures with improved properties to enable future use of multiexcitons in light-harvesting applications.

多个激发事件在光捕获应用中具有最高的相关性，即，涉及多电子氧化还原反应的电子转移。为了在反应中心实现电荷积累，必须发生几个连续的光诱导电荷载流子转移步骤，每个步骤由光子的吸收引发，或者从多个激发系统分离电荷并准同时向反应中心转移多个电荷。大多数的研究报告调查的电荷载流子动力学仅在单一激发条件下。为了克服这一局限性，本项目旨在研究涉及多重激发的胶体半导体纳米结构中的激子和载流子动力学。泵浦-泵浦-探测瞬态吸收光谱将应用于研究连续光诱导电子转移过程和多重激发纳米结构中的过程的动力学。该项目将深入了解原位条件下初始电子转移之外的电子转移级联。重点将是异质纳米结构，例如，金属尖端的CdSe@CdS纳米棒，其已被证明对于光子到氢的转化具有高效率。将探讨在第一电子转移步骤之后由于金属颗粒的充电而在半导体/金属界面处形成用于电荷分离的额外势垒对电子转移过程的影响。我们将探索结构因素对第二步电荷转移的影响，以补充第一步电荷转移的现有知识，并支持优化结构的设计。我们将研究异质纳米结构（例如，CdSe@CdS纳米棒）中多个激子的相互作用及其动力学。激发波长的选择允许在异质结构中控制所产生的激子在限定的子域中的初始定位。特别是，湮灭的时间尺度通过俄歇复合（AR）的两个最初的空间分离的激子将提供一个基本的理解激子的相互作用依赖于结构和电子因素（体积和纵横比的颗粒和能带排列）的纳米结构。此外，多个激发在组件的半导体纳米粒子与不同程度的电子耦合之间的相互作用将被视为。相邻颗粒之间的耦合强度可以通过修饰颗粒的表面配体来调节，这会影响纳米颗粒组装体内的激子迁移过程。层中的激子扩散可导致经由AR产生的多个激发的淬灭。这些调查的结果将有助于了解AR时间尺度和结构之间的关系，并将指导具有改进性能的结构的设计，以使未来在光捕获应用中使用多激子。