Ultrafast carrier dynamics in core and core/shell CdSe quantum rods: Role of the surface and interface defects

Arianna Cretí, Marco Anni, Margherita Zavelani Rossi, Guglielmo Lanzani, Gabriella Leo, Fabio Della Sala, Liberato Manna, and Mauro Lomascolo
Phys. Rev. B 72, 125346 – Published 30 September 2005

Abstract

Femtosecond pump-probe spectroscopy, in the visible spectral range, is used to study fast processes after photoexcitation in quantum confined wurtzite CdSe core and CdSeCdSZnS core/shell nanorods. Effective-mass theory is applied to assign the energy levels in linear absorption spectra. Sequential bleaching of the excitonic states and photoinduced absorption are observed in the transmission difference spectra. A strong difference was found between the core and core/shell samples. In fact, in the transient transmission difference spectra, the decay time of the higher energy states is faster in the core than in the core/shell samples (200 fs versus 500 fs), due to the trapping in the unpassivated surface states of the bare core. Stimulated emission (SE) has been achieved in CdSe core and core/shell quantum rods at room temperature. As a striking feature, the SE is sustained for a shorter time in the core/shell sample (25 ps) compared with the core sample (50 ps). We demonstrate that this result is due to the competition between SE and photoinduced absorption from defect states in the midgap of the core/shell sample. Such midgap states are related to the formation of extended defects at the core/shell interface, due to lattice strain relaxation.

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  • Received 4 August 2004

DOI:https://doi.org/10.1103/PhysRevB.72.125346

©2005 American Physical Society

Authors & Affiliations

Arianna Cretí1,*, Marco Anni2, Margherita Zavelani Rossi1, Guglielmo Lanzani1, Gabriella Leo3, Fabio Della Sala4, Liberato Manna4, and Mauro Lomascolo5

  • 1ULTRAS-INFM National Laboratory for Ultrafast and Ultraintense Optical Science, Dipartimento di Fisica, Politecnico di Milano, Piazza L. Da Vinci 32, 20133 Milano, Italy
  • 2NNL National Nanotechnology Laboratory of INFM and Dipartimento di Ingegneria dell’Innovazione, Universitá degli Studi di Lecce, Via per Arnesano, I-73100 Lecce, Italy
  • 3ISMN-CNR, Institute for the Study of Nanostructured Materials, Via Salaria km 29,300 00016 Monterotondo Stazione Roma, Italy
  • 4NNL National Nanotechnology Laboratory of INFM, Università degli Studi di Lecce, Via per Arnesano, I-73100 Lecce, Italy
  • 5IMM-CNR, Istituto per la Microelettronica e Microsistemi, Campus Universitario, Strada Prov. per Monteroni, I-73100 Lecce, Italy

  • *Also at ISUFI Institute for Advanced Interdisciplinary Studies, Universitá degli Studi di Lecce, Via per Arnesano, 73100 Lecce, Italy. Electronic address: arianna.creti@le.imm.cnr.it

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Vol. 72, Iss. 12 — 15 September 2005

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