title: Exploring size and state dynamics in CdSe quantum dots using two-dimensional electronic spectroscopy.
abstract: Development of optoelectronic technologies based on quantum dots depends on measuring, optimizing, and ultimately predicting charge carrier dynamics in the nanocrystal. In such systems, size inhomogeneity and the photoexcited population distribution among various excitonic states have distinct effects on electron and hole relaxation, which are difficult to distinguish spectroscopically. Two-dimensional electronic spectroscopy can help to untangle these effects by resolving excitation energy and subsequent nonlinear response in a single experiment. Using a filament-generated continuum as a pump and probe source, we collect two-dimensional spectra with sufficient spectral bandwidth to follow dynamics upon excitation of the lowest three optical transitions in a polydisperse ensemble of colloidal CdSe quantum dots. We first compare to prior transient absorption studies to confirm excitation-state-dependent dynamics such as increased surface-trapping upon excitation of hot electrons. Second, we demonstrate fast band-edge electron-hole pair solvation by ligand and phonon modes, as the ensemble relaxes to the photoluminescent state on a sub-picosecond time-scale. Third, we find that static disorder due to size polydispersity dominates the nonlinear response upon excitation into the hot electron manifold; this broadening mechanism stands in contrast to that of the band-edge exciton. Finally, we demonstrate excitation-energy dependent hot-carrier relaxation rates, and we describe how two-dimensional electronic spectroscopy can complement other transient nonlinear techniques.
authors.affiliation: Department of Chemistry, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Justin R
authors.initials: JR
authors.lastname: Caram
authors.affiliation: Department of Chemistry, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Haibin
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Graduate Program in the Biophysical Sciences, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Dahlberg
authors.affiliation: Department of Chemistry, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Brian S
authors.initials: BS
authors.lastname: Rolczynski
authors.affiliation: Department of Chemistry, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Graham B
authors.initials: GB
authors.lastname: Griffin
authors.affiliation: Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Dmitriy S
authors.initials: DS
authors.lastname: Dolzhnikov
authors.affiliation: Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Dmitri V
authors.initials: DV
authors.lastname: Talapin
authors.affiliation: Department of Chemistry, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Engel
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D004583:Electrons; D010316:Particle Size; D045663:Quantum Dots; D011789:Quantum Theory; D018036:Selenium Compounds / Q000737:chemistry*; D013057:Spectrum Analysis; D013499:Surface Properties
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; C058667:cadmium selenide