Measuring exciton-phonon coupling in semiconductor nanocrystals

Abstract

At low excitation density, the dynamics of excitons in semiconductor nanocrystals are largely dictated by their interactions with the underlying atomic lattice. This exciton-phonon coupling is responsible, for example, for absorption and luminescence linewidths at elevated temperatures, relaxation processes following optical excitation, and even degradation of quantum coherent applications. Characterizing and understanding exciton-phonon coupling is therefore central to guiding rational design of colloidal nanocrystal materials and their device applications. In this review, we compare different spectroscopic methods of measuring exciton-phonon interactions and the complementary information that they provide. We emphasize the development of a new technique, termed multi-dimensional coherent spectroscopy, that circumvents many of the limitations of traditional methods.

An Exact Expression for Multidimensional Spectroscopy of a Spin‐Boson Hamiltonian

“…Exciton coupling to LO phonons in CdSe quantum dots was studied by us [ 57 ] and others [ 58–61 ] using MDCS, in which LO phonons manifested as clear sidebands adjacent to the exciton peak in the 2‐D spectra. A nonlinear analogue to phonon replicas [ 56,62 ] in linear absorption or luminescence spectra, these sidebands additional exhibit coherent dynamics that provide direct insight into the microscopic parameters of exciton‐phonon coupling.…”