Investigation of anisotropic spin phenomena in doped single nanocrystals probed by luminescence spectroscopy in a vector magnetic field

这个项目的总体目标是探索集体和个人的自旋效应在过渡金属掺杂的胶体纳米晶体的定义晶体和/或形状各向异性。这需要在方法上的主要创新，即在矢量磁场中对单个纳米晶体进行发光实验。作为一个模型系统，我们将主要集中在Mn 2+掺杂的II-VI型工程纳米晶体的纤锌矿或锌钛矿结构。主要的科学问题可以分为三个分项。在掺杂有过渡金属离子集合的纳米晶体中，旨在揭示晶体和/或形状各向异性对激子磁极化子复合物形成的影响-这种效应已经假设了十多年，但从未得到证实。因此，施加相对于主各向异性轴具有变化取向的磁场将允许有目的地稳定/不稳定磁极化子形成。此外，我们打算解决极化子的形成和发射线宽在个别纳米晶体的统计磁波动的作用，横向和纵向自旋波动之间的分离。本研究将探讨单一杂质掺杂奈米晶体，以阐明单原子掺杂奈米晶体中s-p及sp-d交换作用的共同作用。在这里，我们假设的最低激子状态良好建立的未掺杂的纳米晶体的精细结构最有可能被修改的情况下，过渡金属掺杂由于显着的sp-d交换相互作用。相对于Mn 2+的内部4 T1 - 6A 1跃迁仔细调节激子带隙将允许双发射，因为这些状态之间的能量转移相当快。计划研究单双发射纳米晶体，其中由于抑制的不均匀加宽，预期发射对温度和磁场的灵敏度增强。由于单激子-单掺杂剂相互作用导致激子-Mn 2+络合物内不同Mn 2+自旋态之间的显著能量分裂，因此对单原子掺杂纳米晶体中的双发射的研究可以揭示可能的自旋选择性能量转移。

The overall goal of this project is to explore collective and individual spin effects in transition metal doped colloidal nanocrystals of defined crystal and/or shape anisotropy. This requires a main innovation in methodology, namely luminescence experiments on single nanocrystals in a vector magnetic field. As a model system, we will predominantly concentrate on Mn2+-doped II-VI shaped-engineered nanocrystals of either wurtzite or zincblende structure. The main scientific questions can be split into three subitems. In nanocrystals doped with a collection of transition metal ions it is intended to unravel the impact of crystal and/or shape anisotropy on the formation of an exciton magnetic polaron complex – an effect which has been hypothesized since more than a decade, but never been proven. Hereby, the application of a magnetic field with varying orientation with respect to the dominant anisotropy axis will allow to purposely stabilize / destabilize magnetic polaron formation. We in addition intend to address the role of statistical magnetic fluctuations on polaron formation and emission linewidth in individual nanocrystals, separating between transversal and longitudinal spin fluctuations. Nanocrystals doped with single impurities will be investigated to elaborate the combined action of s-p and sp-d exchange interactions in single-atom doped nanocrystals. Here, we hypothesize that the fine structure of the lowest exciton state well-established for undoped nanocrystals has most likely to be revised in case of transition metal doping due to pronounced sp-d exchange interactions. Adjusting the exciton bandgap carefully with respect to the internal 4T1 – 6A1 transition of the Mn2+ will allow for dual emission because of the quite rapid energy transfer between these states. It is planned to study single dual emitting nanocrystals, where an enhanced sensitivity of the emission to temperature and magnetic field is expected due to the suppressed inhomogeneous broadening. As the single exciton – single dopant interaction leads to pronounced energy splitting between different Mn2+ spin states within the exciton - Mn2+ complex, the study of dual emission in single-atom doped nanocrystals may shed light on a possible spin-selective energy transfer.