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This work studies extinction properties of ZnSe quantum dots terminated with either Se-surface or Zn-surface (Se-ZnSe or Zn-ZnSe QDs). In addition to commonly observed photoluminescence quenching by anionic surface sites, Se-ZnSe QDs are found to show drastic signatures of Se-surface states in their UV-visible (Vis) absorption spectra. Similar to most QDs reported in literature, monodisperse Zn-ZnSe QDs show sharp absorption features and blue-shifted yet steep absorption edge respect to the bulk bandgap. However, for monodisperse Se-ZnSe QDs, all absorption features are smeared and a low-energy tail is identified to extend to an energy window below the bulk ZnSe bandgap. Along increasing their size, a cyclic growth of ZnSe QDs switches their surface from Zn-terminated to Se-terminated ones, which confirms that the specific absorption signatures are reproducibly repeated between those of two types of the QDs. Though the extinction coefficients per unit of Se-ZnSe QDs are always larger than those of Zn-ZnSe QDs with the same size, both of them approach the same bulk limit. In addition to contribution of the lattice, extinction coefficients per nanocrystal of Zn-ZnSe QDs show an exponential term against their sizes, which is expected for quantum-confinement enhancement of electron-hole wavefunction overlapping. For Se-ZnSe QDs, there is the third term identified for their extinction coefficients per nanocrystal, which is proportional to the square of size of the QDs and consistent with surface contribution.

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Publication history
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Acknowledgements

Publication history

Received: 30 December 2019
Revised: 04 February 2020
Accepted: 06 February 2020
Published: 26 February 2020
Issue date: March 2020

Copyright

© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020

Acknowledgements

This work was funded by the National Key Research and Development Program of China (No. 2016YFB0401600), the National Natural Science Foundation of China (No. 91833303), Joint NSFC-ISF Research (No. 21761142009), and the education department of Fujian Province (No. JA13013).

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