Achieving spin-triplet exciton transfer between silicon and molecular acceptors for photon upconversion


Inorganic semiconductor nanocrystals interfaced with spin-triplet exciton-accepting organic molecules have emerged as promising materials for converting incoherent long-wavelength light into the visible range. However, these materials to date have made exclusive use of nanocrystals containing toxic elements, precluding their use in biological or environmentally sensitive applications. Here, we address this challenge by chemically functionalizing non-toxic silicon nanocrystals with triplet-accepting anthracene ligands. Photoexciting these structures drives spin-triplet exciton transfer from silicon to anthracene through a single 15 ns Dexter energy transfer step with a nearly 50% yield. When paired with 9,10-diphenylanthracene emitters, these particles readily upconvert 488–640 nm photons to 425 nm violet light with efficiencies as high as 7 ± 0.9% and can be readily incorporated into aqueous micelles for biological use. Our demonstration of spin-triplet exciton transfer from silicon to molecular triplet acceptors can critically enable new technologies for solar energy conversion, quantum information and near-infrared driven photocatalysis.

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Fig. 1: State energies and spectra of the upconverting system.
Fig. 2: Quantification of the upconverted photoluminescence spectra.
Fig. 3: Kinetics of triplet energy transfer from Si NCs to 9EA.
Fig. 4: Using a kinetic model to fit time-resolved spectra.
Fig. 5: Si NC upconversion in an aqueous environment.

Data availability

Experimental data and fits to this data produced using the MATLAB software are available from the authors upon request.

Code availability

The MATLAB code used in the fitting analysis of transient absorption spectra is available from the authors upon request.


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S.T.R. and E.K.R. acknowledge support from the National Science Foundation (CHE-1610412), the Robert A. Welch Foundation (grant F-1885) and the Research Corporation for Science Advancement (grant no. 24489). E.K.R. also acknowledges partial support from a Leon O. Morgan fellowship. M.L.T. acknowledges an Air Force Office of Scientific Research (AFOSR) Award (FA9550-19-1-0092) for equipment, the DOE (DE-SC0018969) for salary support, and the Alfred P. Sloan Foundation. L.M. and D.C. acknowledge support from the National Science Foundation under CAREER award no. 1351386.

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Hydrogen-terminated Si NC were synthesized by D.C. P.X. and C.S.G. functionalized the Si NCs with organic ligands, characterized their steady-state properties and performed upconversion measurements. E.K.R. conducted transient absorption experiments and analysed the resulting data. L.M., M.L.T. and S.T.R. oversaw the project. P.X., E.K.R., L.M., M.L.T. and S.T.R. composed the manuscript.

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Correspondence to Lorenzo Mangolini or Ming Lee Tang or Sean T. Roberts.

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Supplementary Information

Supplementary methods, data, modelling, Figs. 1–12 and Tables 1–3.

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Xia, P., Raulerson, E.K., Coleman, D. et al. Achieving spin-triplet exciton transfer between silicon and molecular acceptors for photon upconversion. Nat. Chem. 12, 137–144 (2020).

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