Spin Blockades to Relaxation of Hot Multiexcitons in Nanocrystals

Tufan Ghosh; Joanna Dehnel; Marcel Fabian; Efrat Lifshitz; Roi Baer; Sanford Ruhman

doi:10.1021/acs.jpclett.9b00992

Spin Blockades to Relaxation of Hot Multiexcitons in Nanocrystals

Tufan Ghosh, Joanna Dehnel, Marcel Fabian, Efrat Lifshitz^*, Roi Baer, Sanford Ruhman

^*Corresponding author for this work

Institute of Chemistry

Research output: Contribution to journal › Article › peer-review

14 Scopus citations

Abstract

The conjecture that, as in bulk semiconductors, hot multiexcitons in nanocrystals cool rapidly to the lowest available energy levels is tested here by recording the effects of a single cold "spectator" exciton on the relaxation dynamics of a subsequently deposited hot counterpart. Results in CdSe/CdS nanodots show that a preexisting cold "spectator exciton" allows only half of the photoexcited electrons to relax directly to the band-edge. The rest are blocked in an excited quantum state due to conflicts in spin orientation. The latter fully relax in this sample only after ∼25 ps as the blocked electrons spins flip, prolonging the temporal window of opportunity for harvesting the retained energy more than 100 fold! Common to all quantum-confined nanocrystals, this process will delay cooling and impact the spectroscopic signatures of hot multiexcitons in all envisioned generation scenarios. How the spin-flipping rate scales with particle size and temperature remains to be determined.

Original language	American English
Pages (from-to)	2341-2348
Number of pages	8
Journal	Journal of Physical Chemistry Letters
Volume	10
Issue number	10
DOIs	https://doi.org/10.1021/acs.jpclett.9b00992
State	Published - 16 May 2019

Bibliographical note

Funding Information:
S.R. holds the Lester Aronberg Chair in Chemistry. S.R. acknowledges financial support from the Israel Science Foundation (Grant # 163/16). R.B. gratefully acknowledges support of the Israel Science Foundation (ISF Grant No. 189-14) and the binational US−Israel Science Foundation (BSF Grant No. 2015687). T.G. thanks the Lady Davis Fellowship Trust and the Raymond and Janine Bollag Post-Doctoral Fellowship Fund for a fellowship. S.R. and T.G. thank Dr. O. Liubashevski and Dr. J. Dana for technical help. E.L. acknowledges financial support from the Israel Science Foundation Projects 914/15 and 1508/14. J.D. acknowledges the Marie-Sklodowska Curie action H2020-MSCA-ITN-642656 (PHONSI) for fellowship support.

Publisher Copyright:
© 2019 American Chemical Society.

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10.1021/acs.jpclett.9b00992

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title = "Spin Blockades to Relaxation of Hot Multiexcitons in Nanocrystals",

abstract = "The conjecture that, as in bulk semiconductors, hot multiexcitons in nanocrystals cool rapidly to the lowest available energy levels is tested here by recording the effects of a single cold {"}spectator{"} exciton on the relaxation dynamics of a subsequently deposited hot counterpart. Results in CdSe/CdS nanodots show that a preexisting cold {"}spectator exciton{"} allows only half of the photoexcited electrons to relax directly to the band-edge. The rest are blocked in an excited quantum state due to conflicts in spin orientation. The latter fully relax in this sample only after ∼25 ps as the blocked electrons spins flip, prolonging the temporal window of opportunity for harvesting the retained energy more than 100 fold! Common to all quantum-confined nanocrystals, this process will delay cooling and impact the spectroscopic signatures of hot multiexcitons in all envisioned generation scenarios. How the spin-flipping rate scales with particle size and temperature remains to be determined.",

author = "Tufan Ghosh and Joanna Dehnel and Marcel Fabian and Efrat Lifshitz and Roi Baer and Sanford Ruhman",

note = "Funding Information: S.R. holds the Lester Aronberg Chair in Chemistry. S.R. acknowledges financial support from the Israel Science Foundation (Grant # 163/16). R.B. gratefully acknowledges support of the Israel Science Foundation (ISF Grant No. 189-14) and the binational US−Israel Science Foundation (BSF Grant No. 2015687). T.G. thanks the Lady Davis Fellowship Trust and the Raymond and Janine Bollag Post-Doctoral Fellowship Fund for a fellowship. S.R. and T.G. thank Dr. O. Liubashevski and Dr. J. Dana for technical help. E.L. acknowledges financial support from the Israel Science Foundation Projects 914/15 and 1508/14. J.D. acknowledges the Marie-Sklodowska Curie action H2020-MSCA-ITN-642656 (PHONSI) for fellowship support. Publisher Copyright: {\textcopyright} 2019 American Chemical Society.",

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N2 - The conjecture that, as in bulk semiconductors, hot multiexcitons in nanocrystals cool rapidly to the lowest available energy levels is tested here by recording the effects of a single cold "spectator" exciton on the relaxation dynamics of a subsequently deposited hot counterpart. Results in CdSe/CdS nanodots show that a preexisting cold "spectator exciton" allows only half of the photoexcited electrons to relax directly to the band-edge. The rest are blocked in an excited quantum state due to conflicts in spin orientation. The latter fully relax in this sample only after ∼25 ps as the blocked electrons spins flip, prolonging the temporal window of opportunity for harvesting the retained energy more than 100 fold! Common to all quantum-confined nanocrystals, this process will delay cooling and impact the spectroscopic signatures of hot multiexcitons in all envisioned generation scenarios. How the spin-flipping rate scales with particle size and temperature remains to be determined.

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Spin Blockades to Relaxation of Hot Multiexcitons in Nanocrystals

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