title: Multiexciton Absorption Cross Sections of CdSe Quantum Dots Determined by Ultrafast Spectroscopy.
abstract: Multiexciton absorption cross sections are important for analysis of a number of experiments, including multiple exciton generation and stimulated emisson. We present a rigorous method to determine these cross sections using transient absorption (TA) measurements. We apply the method to CdSe quantum dots (QDs) and core-shell (CdSe)ZnS QDs. The method involves measuring TA dynamics for various excitation intensities over a broad time range and analyzing the experiments in terms of a kinetic multiexciton model taking into account all contributions to the signal. In this way, we were able to quantify exciton and multiexciton absorption cross sections at different spectral positions. The absorption cross sections decrease with increasing number of excitations, qualitatively in agreement with the state-filling effective mass model but showing a slower decrease. The cross sections for single-exciton to biexciton absorption range between 57 and 99% of the ground to single-exciton cross section.
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Nils
authors.initials: N
authors.lastname: Lenngren
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Tommy
authors.initials: T
authors.lastname: Garting
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Kaibo
authors.initials: K
authors.lastname: Zheng
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.|Department of Chemistry, Qena Faculty of Science, South Valley University , Qena 83523, Egypt.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Abdellah
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Noëlle
authors.initials: N
authors.lastname: Lascoux
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Fei
authors.initials: F
authors.lastname: Ma
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Arkady
authors.initials: A
authors.lastname: Yartsev
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Karel
authors.initials: K
authors.lastname: Žídek
authors.affiliation: Department of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden.
authors.forename: Tõnu
authors.initials: T
authors.lastname: Pullerits
keywords: CdSe; absorption cross sections; femtosecond spectroscopy; multiexciton; quantum dots; transient absorption