title: Sub-Picosecond Auger-Mediated Hole-Trapping Dynamics in Colloidal CdSe/CdS Core/Shell Nanoplatelets.
abstract: Quasi-two-dimensional colloidal nanoplatelets (NPLs) have recently emerged as a class of semiconductor nanomaterials whose atomically precise monodisperse thicknesses give rise to narrow absorption and emission spectra. However, the sub-picosecond carrier dynamics of NPLs at the band edge remain largely unknown, despite their importance in determining the optoelectronic properties of these materials. Here, we use a combination of femtosecond transient absorption spectroscopy and nonadiabatic molecular dynamics simulations to investigate the early time carrier dynamics of CdSe/CdS core/shell NPLs. Band-selective probing reveals sub-picosecond Auger-mediated trapping of holes with an effective second-order rate constant of 3.5 ± 1.0 cm2/s. Concomitant spectral blue shifts that are indicative of Auger hole heating are found to occur on the same time scale as the sub-picosecond trapping dynamics, whereas spectral red shifts that emerge at low excitation densities furnish an electron-cooling time scale of 0.84 ± 0.09 ps. Finally, nonadiabatic molecular dynamics simulations relate the observed sub-picosecond Auger-mediated hole-trapping dynamics to a shallow trap state that originates from the incomplete passivation of dangling bonds on the NPL surface.
authors.affiliation: Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , 21 Nanyang Link, Singapore 637371.
authors.forename: Shuo
authors.initials: S
authors.lastname: Dong
authors.affiliation: Departments of Chemistry, and Physics and Astronomy, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Sougata
authors.initials: S
authors.lastname: Pal
authors.affiliation: Institute of Materials Research & Engineering, A*STAR , 2 Fusionopolis Way, Innovis #08-03, Singapore 138634.
authors.forename: Jie
authors.initials: J
authors.lastname: Lian
authors.affiliation: Institute of Materials Research & Engineering, A*STAR , 2 Fusionopolis Way, Innovis #08-03, Singapore 138634.|Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543.
authors.forename: Yinthai
authors.initials: Y
authors.lastname: Chan
authors.affiliation: Departments of Chemistry, and Physics and Astronomy, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Prezhdo
authors.affiliation: Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , 21 Nanyang Link, Singapore 637371.
authors.forename: Zhi-Heng
authors.initials: ZH
authors.lastname: Loh
keywords: Auger carrier heating; carrier cooling; femtosecond transient absorption spectroscopy; quantum wells; ultrafast carrier dynamics