Institut des
NanoSciences de Paris
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Soutenance de thèse de Violette Steinmetz - Lundi 5 octobre 2020 à 14 h

Violette Steinmetz, doctorante dans l’équipe Photonique et cohérence de spin (PHOCOS) soutient sa thèse le lundi 5 octobre 2020 à 14 h.

Sorbonne Université - Campus Pierre et Marie Curie - Paris, France - Amphithéâtre Charpak

Propriétés optiques et excitoniques de nanocristaux colloïdaux 2D : hétéro-structures CdSe/CdTe et nanoplaquettes pérovskite CsPbBr3

JPEG Figure

a) Sketch of the CdSe/CdTe core/crown nanoplatelet geometry and diagram of the single carriers energy levels for both the core and crown domains. (b) Absorption and photo-luminescence spectra of a dense film of CdSe/CdTe nanoplatelets at T = 10 K.

Abstract

Colloidal nanoplatelets (NPLs) are 2D crystalline objects, chemically synthesized, and stabilized by a shell of ligands. Strong and homogeneous quantum confinement in the thickness direction leads to interesting properties for a large field of applications ranging from light display to lasing material. An understanding of the fundamental mechanisms at play in these structures is necessary to consider any of these applications. In this context, this PhD is dedicated to the study of the excitonic properties of two different types of NPLs. First, we study CdSe/CdTe core/crown hetero-NPLs, which support indirect excitons (electron being confined in the CdSe core and the hole being confined in the CdTe crown). Single object spectroscopy allows us to highlight how the strong LO phonon/exciton coupling and the spectral diffusion shape the emission spectrum. Then, measurements of the degree of polarization and time-resolved photoluminescence carried out as a function of the magnetic field allow us to unravel the electronic fine structure of these hetero-NPLs (two linear bright states split by an energy 50 microeV dominate the emission). A long spin relaxation lifetime (> 500 ns) is also evidenced at 1.6 K. Finally, a preliminary study on CsPbBr3 perovskite NPLs is conducted. We perform a structural characterization of these objects through optical measurements coupled to TEM imaging and highlight the difference between NPLs, characterized by 1D confinement, and nanosticks, where 2D confinement is at play. The exciton recombination dynamics are also studied and compared to the existing models describing the energy relaxation within the fine structure manifold.

Jury

  • Mme Emmanuelle Deleporte (LuMin, Université Paris-Saclay, rapporteure)
  • M. Philippe Tamarat (LP2N, Bordeaux, rapporteur)
  • Mme Paulina Plochocka (LNCMI, Toulouse, examinatrice)
  • M. Jérôme Tignon (LPENS, Paris, examinateur)
  • M. Laurent Legrand (Directeur de thèse)
  • M. Thierry Barisien (Co-encadrant)