巨壳层CdSe/CdS纳米晶：激子与壳层声子耦合的共振拉曼光谱研究
Giant-Shell CdSe/CdS Nanocrystals: Exciton Coupling to Shell Phonons Investigated by Resonant Raman Spectroscopy
摘要：
半导体纳米晶体中激子和声子之间的相互作用在激子能谱和动力学中起着至关重要的作用，因此在它们的光学性质中起着至关重要的作用。我们利用共振拉曼光谱研究了巨壳结构的CdSe/CdS核壳纳米晶体中激子2声子的耦合。利用CdS的光学声子（LO）与其第一次多重散射（2LO）的强度比来计算Huang-Rhys参数。我们使用了四个不同的激发波长的范围内，从CdS壳吸收的发病以及以上的CdS壳的带边，以深入了解高能量激子跃迁的CdS LO声子的共振效应。各向同性的球形巨壳纳米晶体表现出一贯更强的激子-声子耦合相比，各向异性棒形的点在棒（DiR）架构，和2LO/LO强度比接近CdS带边的激发波长降低。球形巨壳层纳米晶体中强的激子-声子耦合与电子波函数的离域有关。此外，我们观察到的GS纳米晶体的径向呼吸模式和它们的泛音，通过超低频拉曼光谱与非共振激发，使用激光能量远低于异质纳米晶体的带隙，并强调高阶之间的差异，
英文摘要：
The interaction between excitons and phonons in semiconductor nanocrystals plays a crucial role in the exciton energy spectrum and dynamics, and thus in their optical properties. We investigate the exciton2 phonon coupling in giant-shell CdSe/CdS core-shell nanocrystals via resonant Raman spectroscopy. The Huang-Rhys parameter is evaluated by the intensity ratio of the longitudinal-optical (LO) phonon of CdS with its first multiscattering (2LO) replica. We used four different excitation wavelengths in the range from the onset of the CdS shell absorption to well above the CdS shell band edge to get insight into resonance effects of the CdS LO phonon with high energy excitonic transitions. The isotropic spherical giant-shell nanocrystals show consistently stronger exciton-phonon coupling as compared to the anisotropic rod-shaped dot-in-rod (DiR) architecture, and the 2LO/LO intensity ratio decreases for excitation wavelengths approaching the CdS band edge. The strong exciton-phonon coupling in the spherical giant-shell nanocrystals can be related to the delocalization of the electronic wave functions. Furthermore, we observe the radial breathing modes of the GS nanocrystals and their overtones by ultralow frequency Raman spectroscopy with nonresonant excitation, using laser energies well below the band gap of the heteronanocrystals, and highlight the differences between higher order
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