Acoustic Phonon Contributions to the Emission Spectrum of Single CdSe Nanocrystals

Abstract

Narrow zero-phonon emission lines are observed in single CdSe/CdZnS core/shell colloidal nanocrystals over a range of cryogenic temperatures up to 40 K. These nanocrystals display dramaticaly improved spectral stability enabling the observation of acoustic phonon sidebands accompanying most zero-phonon lines. A discrete phonon mode is attributed to the electron coupling to the l = 0 acoustic breathing mode via the deformation coupling. The Huang−Rhys parameter, Sac, for this interaction is found to vary from 0.0016 to 0.09, demonstrating a wide dispersion in exciton−phonon coupling between different nanocrystals. Indeed, we observe single nanocrystals in which all acoustic phonon sidebands vanish, in close agreement with theoretical predictions that there should be negligible acoustic phonon coupling in an ideal spherical CdSe nanocrystal. Such nanocrystals are virtually decoupled from their environment, which is potentially useful for quantum technologies, such as single photon sources and quantum computing. In general, the ability to detect and quantify phonon interactions within single nanocrystals will provide significant insight into energy relaxation and dephasing processes in these systems.