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High-efficiency photoemission from magnetically doped quantum dots driven by multi-step spin-exchange Auger ionization

Nature Photonics volume 16, pages 433–440 (2022)Cite this article

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Abstract

Materials displaying electron photoemission under visible-light excitation are of great interest for applications in photochemistry, photocathodes, advanced electron beam sources and electron microscopy. We demonstrate that in manganese-doped CdSe colloidal quantum dots (CQDs), two-step Auger up-conversion enables highly efficient electron photoemission under excitation with visible-light pulses. This effect is enabled by extremely fast, subpicosecond Auger-type energy transfer from excited manganese ions to an intrinsic CQD exciton. Since the rate of this process outpaces that of intraband cooling, the high-energy ‘hot’ electron produced by the first Auger-excitation step can be efficiently promoted further into the external ‘vacuum’ state via one more manganese-to-CQD energy-transfer step. This CQD ionization pathway exploits exceptionally large uphill energy gain rates associated with the spin-exchange Auger process and leads to photoemission efficiencies of more than 3%, orders of magnitude greater than in the case of undoped CQDs. We demonstrate that using this phenomenon, we can achieve high-yield production of solvated electrons (>3% internal quantum efficiency), which makes it of considerable utility in visible-light-driven reduction photochemistry.

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Fig. 1: Mechanisms for Auger-assisted photoemission and spin-exchange excitation transfer.
Fig. 2: Optical spectra and PL dynamics of undoped and Mn-doped CdSe/CdS CQDs.
Fig. 3: Auger recombination in Mn-doped and undoped CdSe/CdS CQDs.
Fig. 4: Experimental observations of electron photoemission from Mn-doped CdSe/CdS CQDs (sample s13).
Fig. 5: Generation of SEs using water-dispersed Mn-doped CdSe/CdS CQDs.

Data availability

Source data are provided for Figs. 2–5. The rest of the data are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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Acknowledgements

These studies were 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.

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Authors and Affiliations

  1. Chemistry Division, C-PCS, Los Alamos National Laboratory, Los Alamos, NM, USA

    Clément Livache, Whi Dong Kim, Ho Jin, Oleg V. Kozlov, Igor Fedin & Victor I. Klimov

  2. Center for High Technology Materials, University of New Mexico, Albuquerque, NM, USA

    Ho Jin

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Contributions

V.I.K. conceived the idea and coordinated the overall research effort. H.J. synthesized the Mn-doped CQDs and characterized their PL properties. I.F. fabricated the reference undoped CQDs. C.L. and O.V.K. conducted the TA studies and analysed the spectroscopic data. W.D.K. and C.L. conducted the SE experiments and analysed the data. C.L. and V.I.K wrote the manuscript with inputs from other authors.

Corresponding author

Correspondence to Victor I. Klimov.

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The authors declare no competing interests.

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Nature Photonics thanks Freddy Rabouw and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–9, Table 1 and refs.

Source data

Source Data Fig. 2

Sample spectra, time-resolved PL traces.

Source Data Fig. 3

1S state bleach dynamics for s0 and s13.

Source Data Fig. 4

Transient spectra for s13 and estimations of photoemission efficiencies.

Source Data Fig. 5

SE spectra and SE generation efficiency.

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Livache, C., Kim, W.D., Jin, H. et al. High-efficiency photoemission from magnetically doped quantum dots driven by multi-step spin-exchange Auger ionization. Nat. Photon. 16, 433–440 (2022). https://doi.org/10.1038/s41566-022-00989-x

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