Keitel Robert C, Brechbühler Raphael, Cocina Ario, Antolinez Felipe V, Meyer Stefan A, Vonk Sander J W, Rojo Henar, Rabouw Freddy T, Norris David J
Optical Materials Engineering Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands.
J Phys Chem Lett. 2024 May 9;15(18):4844-4850. doi: 10.1021/acs.jpclett.4c00516. Epub 2024 Apr 29.
Most single quantum emitters display non-steady emission properties. Models that explain this effect have primarily relied on photoluminescence measurements that reveal variations in intensity, wavelength, and excited-state lifetime. While photoluminescence excitation spectroscopy could provide complementary information, existing experimental methods cannot collect spectra before individual emitters change in intensity (blink) or wavelength (spectrally diffuse). Here, we present an experimental approach that circumvents such issues, allowing the collection of excitation spectra from individual emitters. Using rapid modulation of the excitation wavelength, we collect and classify excitation spectra from individual CdSe/CdS/ZnS core/shell/shell quantum dots. The spectra, along with simultaneous time-correlated single-photon counting, reveal two separate emission-reduction mechanisms caused by charging and trapping, respectively. During bright emission periods, we also observe a correlation between emission red-shifts and the increased oscillator strength of higher excited states. Quantum-mechanical modeling indicates that diffusion of charges in the vicinity of an emitter polarizes the exciton and transfers the oscillator strength to higher-energy transitions.
大多数单量子发射体表现出非稳态发射特性。解释这种效应的模型主要依赖于光致发光测量，这些测量揭示了强度、波长和激发态寿命的变化。虽然光致发光激发光谱可以提供补充信息，但现有的实验方法无法在单个发射体强度发生变化（闪烁）或波长发生变化（光谱扩散）之前收集光谱。在这里，我们提出了一种实验方法来规避此类问题，从而能够收集单个发射体的激发光谱。通过对激发波长进行快速调制，我们收集并分类了单个CdSe/CdS/ZnS核/壳/壳量子点的激发光谱。这些光谱以及同时进行的时间相关单光子计数揭示了分别由电荷注入和俘获引起的两种不同的发射减少机制。在明亮发射期间，我们还观察到发射红移与更高激发态振子强度增加之间的相关性。量子力学建模表明，发射体附近电荷的扩散使激子极化，并将振子强度转移到更高能量的跃迁上。
