Hot-electron dynamics in quantum dots manipulated by spin-exchange Auger interactions

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Abstract

The ability to effectively manipulate non-equilibrium ‘hot’ carriers could enable novel schemes for highly efficient energy harvesting and interconversion. In the case of semiconductor materials, realization of such hot-carrier schemes is complicated by extremely fast intraband cooling (picosecond to subpicosecond time scales) due to processes such as phonon emission. Here we show that using magnetically doped colloidal semiconductor quantum dots we can achieve extremely fast rates of spin-exchange processes that allow for ‘uphill’ energy transfer with an energy-gain rate that greatly exceeds the intraband cooling rate. This represents a dramatic departure from the usual situation where energy-dissipation via phonon emission outpaces energy gains due to standard Auger-type energy transfer at least by a factor of three. A highly favourable energy gain/loss rate ratio realized in magnetically doped quantum dots can enable effective schemes for capturing kinetic energy of hot, unrelaxed carriers via processes such as spin-exchange-mediated carrier multiplication and upconversion, hot-carrier extraction and electron photoemission.

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Fig. 1: Auger-type energy-transfer processes in undoped and Mn-doped semiconductors.
Fig. 2: Subpicosecond energy-transfer dynamics in Mn-doped QDs revealed by TA studies.
Fig. 3: Spin-exchange Auger ionization of a Mn-doped QD due to ejection of a hot electron.

Data availability

The data that support the findings of this study are available from the authors on reasonable request.

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Acknowledgements

This work was supported by the Solar Photochemistry Program of the Chemical Sciences, Biosciences and Geosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy.

Author information

V.I.K. conceived the study. W.L. and J.L. synthesized the QDs and conducted their microstructural characterization. R.S. conducted the spectroscopic studies. R.S., I.R. and V.I.K. analysed the data. R.S. and V.I.K. performed theoretical modelling. V.I.K. wrote the manuscript with input from other co-authors.

Correspondence to Victor I. Klimov.

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Supplementary Information

Supplementary Notes 1–3 and Figs. 1–8.

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Singh, R., Liu, W., Lim, J. et al. Hot-electron dynamics in quantum dots manipulated by spin-exchange Auger interactions. Nat. Nanotechnol. 14, 1035–1041 (2019) doi:10.1038/s41565-019-0548-1

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