Giant-Shell CdSe/CdS Nanocrystals: Exciton Coupling to Shell Phonons Investigated by Resonant Raman Spectroscopy

• Main Authors: Lin, Miao-Ling, Miscuglio, Mario, Polovitsyn, Anatolii, Leng, Yuchen, Martín-García, Beatriz, Moreels, Iwan, Tan, Ping-Heng, Krahne, Roman
• Format: Journal Article
• Language: English
• Published: 24-04-2020
• Subjects: Physics - Chemical Physics; Physics - Materials Science
• DOI: 10.48550/arxiv.2004.11625

J. Phys. Chem. Lett. 2019 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