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Issue 25, 2019
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Size-dependent exciton substructure in CdSe nanoplatelets and its relation to photoluminescence dynamics

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Abstract

CdSe nanoplatelets can be synthesized with different lateral sizes; very small nanoplatelets have almost quantum dot like features (almost discrete exciton states), while very large ones are expected to have properties of colloidal quantum wells (exciton continuum). However, nanoplatelets can be in an intermediate confinement regime with a rich substructure of excitons, which is neither quantum dot like nor an ideal 2D exciton. In this manuscript, we discuss the experimental transition energies and relaxation dynamics of exciton states in CdSe platelets with varying lateral dimensions and compare them with a microscopic theoretical model including exciton–phonon scattering. The model takes special care of the interplay of confinement and Coulomb coupling in the intermediate regime showing strong changes with respect to simple weak or strong confinement models by solving the full four dimensional lateral factorization free exciton wavefunction. Depending on the platelet size broad resonances previously attributed to just ground and excited states are actually composed of a rich substructure of several exciton states in their temporal dynamics. We show that these factorization free exciton states can explain the spectral features observed in photoluminescence experiments. Furthermore we demonstrate that the interplay of exciton bright and dark states provides principle insights into the overall temporal relaxation dynamics, and allows tuning of the exciton cooling via lateral platelet size. Our results and theoretical approach are directly relevant for understanding e.g. the size tuneability of lasing, excitonic cooling dynamics or light harvesting applications in these and similar 2D systems of finite lateral size.

Graphical abstract: Size-dependent exciton substructure in CdSe nanoplatelets and its relation to photoluminescence dynamics

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Publication details

The article was received on 12 Apr 2019, accepted on 11 Jun 2019 and first published on 12 Jun 2019


Article type: Paper
DOI: 10.1039/C9NR03161H
Nanoscale, 2019,11, 12230-12241
  • Open access: Creative Commons BY license
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    Size-dependent exciton substructure in CdSe nanoplatelets and its relation to photoluminescence dynamics

    J. F. Specht, R. Scott, M. Corona Castro, S. Christodoulou, G. H. V. Bertrand, A. V. Prudnikau, A. Antanovich, L. D. A. Siebbeles, N. Owschimikow, I. Moreels, M. Artemyev, U. Woggon, A. W. Achtstein and M. Richter, Nanoscale, 2019, 11, 12230
    DOI: 10.1039/C9NR03161H

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