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Excitonic pathway to photoinduced magnetism in colloidal nanocrystals with nonmagnetic dopants

Nature Nanotechnology volume 13, pages 145–151 (2018)Cite this article

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Abstract

Electronic doping of colloidal semiconductor nanostructures holds promise for future device concepts in optoelectronic and spin-based technologies. Ag+ is an emerging electronic dopant in iii–v and ii–vi nanostructures, introducing intragap electronic states optically coupled to the host conduction band. With its full 4d shell Ag+ is nonmagnetic, and the dopant-related luminescence is ascribed to decay of the conduction-band electron following transfer of the photoexcited hole to Ag+. This optical activation process and the associated modification of the electronic configuration of Ag+ remain unclear. Here, we trace a comprehensive picture of the excitonic process in Ag-doped CdSe nanocrystals and demonstrate that, in contrast to expectations, capture of the photohole leads to conversion of Ag+ to paramagnetic Ag2+. The process of exciton recombination is thus inextricably tied to photoinduced magnetism. Accordingly, we observe strong optically activated magnetism and diluted magnetic semiconductor behaviour, demonstrating that optically switchable magnetic nanomaterials can be obtained by exploiting excitonic processes involving nonmagnetic impurities.

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Fig. 1: Optical properties of Ag-doped CdSe NCs.
Fig. 2: SEC of Ag:CdSe NCs.
Fig. 3: DMS physics in Ag-doped NCs.
Fig. 4: Photoinduced paramagnetization of Ag-doped CdSe NCs.

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Acknowledgements

Q.D. and J.Z. acknowledge support from the National Natural Science Foundation of China (grants 51372025, 91323301 and 51631001). A.C. and M.Z.-R. acknowledge support from the project MIUR-PRIN 2015WTW7J3. Work at the National High Magnetic Field Laboratory is supported by the US National Science Foundation (DMR-1157490), the State of Florida, and the US Department of Energy.

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Authors and Affiliations

  1. Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano, Italy

    Valerio Pinchetti, Monica Lorenzon, Mauro Fasoli, Francesco Meinardi & Sergio Brovelli

  2. Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, China

    Qiumei Di & Jiatao Zhang

  3. Dipartimento di Fisica, Politecnico di Milano, Milano, Italy

    Andrea Camellini

  4. Dipartimento di Energia, Politecnico di Milano and IFN-CNR, Milano, Italy

    Margherita Zavelani-Rossi

  5. National High Magnetic Field Laboratory, Los Alamos, NM, USA

    Scott A. Crooker

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  1. Valerio Pinchetti
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Contributions

S.B. conceived this study. Q.D. and J.Z. developed and synthesized the samples and performed the structural and analytical characterization. V.P. and M.L., with the assistance of M.F. and F.M., performed the optical and spectroelectrochemical measurements. A.C., V.P. and M.Z.-R. collected and analysed the transient transmission data. V.P. and S.A.C. performed the magneto-optical experiments. V.P., S.A.C. and S.B. analysed the data. V.P. and S.B. wrote the paper in consultation with all authors.

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Correspondence to Jiatao Zhang or Sergio Brovelli.

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Supplementary Figures 1–10, Supplementary Table 1, Supplementary discussion.

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Pinchetti, V., Di, Q., Lorenzon, M. et al. Excitonic pathway to photoinduced magnetism in colloidal nanocrystals with nonmagnetic dopants. Nature Nanotech 13, 145–151 (2018). https://doi.org/10.1038/s41565-017-0024-8

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