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Photochemical upconversion of near-infrared light from below the silicon bandgap


Photochemical upconversion is a strategy for converting infrared light into more energetic, visible light, with potential applications ranging from biological imaging and drug delivery to photovoltaics and photocatalysis. Although systems have been developed for upconverting light from photon energies in the near-infrared, upconversion from below the silicon bandgap has been out of reach. Here, we demonstrate an upconversion composition using PbS semiconductor nanocrystal sensitizers that absorb photons below the bandgap of silicon and populate violanthrone triplet states below the singlet oxygen energy. The triplet-state violanthrone chromophores luminesce in the visible spectrum following energy delivery from two singlet oxygen molecules. By incorporating organic chromophores as ligands onto the PbS nanocrystals to improve energy transfer, we demonstrate that violanthrone upconverts in the absence of oxygen by the triplet–triplet annihilation mechanism. The change in mechanism is shown by exploiting the magnetic field effect on triplet–triplet interactions.

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Fig. 1: A cartoon showing the energy flow and mechanism of nanocrystal-sensitized PUC.
Fig. 2: Upconversion below the silicon bandgap.
Fig. 3: Absorption and emission spectra of the PbS nanocrystals, TTCA ligands and V79.
Fig. 4: Energy transfer kinetics in the PbS NC/TTCA/V79 PUC system.
Fig. 5: The effect of oxygen on PUC with V79.

Data availability

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


  1. 1.

    Ravetz, B. D. et al. Photoredox catalysis using infrared light via triplet fusion upconversion. Nature 565, 343–346 (2019).

    ADS  Article  Google Scholar 

  2. 2.

    Khnayzer, R. S. et al. Upconversion-powered photoelectrochemistry. Chem. Commun. 48, 209–211 (2012).

    Article  Google Scholar 

  3. 3.

    Schulze, T. F. & Schmidt, T. W. Photochemical upconversion: present status and prospects for its application to solar energy conversion. Energy Environ. Sci. 8, 103–125 (2015).

    Article  Google Scholar 

  4. 4.

    Cheng, Y. Y. et al. Improving the light-harvesting of amorphous silicon solar cells with photochemical upconversion. Energy Environ. Sci. 5, 6953–6959 (2012).

    Article  Google Scholar 

  5. 5.

    Park, Y. I., Lee, K. T., Suh, Y. D. & Hyeon, T. Upconverting nanoparticles: a versatile platform for wide-field two-photon microscopy and multi-modal in vivo imaging. Chem. Soc. Rev. 44, 1302–1317 (2015).

    Article  Google Scholar 

  6. 6.

    Wen, S. et al. Future and challenges for hybrid upconversion nanosystems. Nat. Photon. 13, 828–838 (2019).

    ADS  Article  Google Scholar 

  7. 7.

    Schmidt, T. W. & Castellano, F. N. Photochemical upconversion: the primacy of kinetics. J. Phys. Chem. Lett. 5, 4062–4072 (2014).

    Article  Google Scholar 

  8. 8.

    Pedrini, J. & Monguzzi, A. Recent advances in the application triplet–triplet annihilation-based photon upconversion systems to solar technologies. J. Photon. Ener. 8, 8–16 (2017).

    Google Scholar 

  9. 9.

    Mongin, C., Garakyaraghi, S., Razgoniaeva, N., Zamkov, M. & Castellano, F. N. Direct observation of triplet energy transfer from semiconductor nanocrystals. Science 351, 369–372 (2016).

    ADS  Article  Google Scholar 

  10. 10.

    Huang, Z. et al. Hybrid molecule-nanocrystal photon upconversion across the visible and near-infrared. Nano Lett. 15, 5552–5557 (2015).

    ADS  Article  Google Scholar 

  11. 11.

    Wu, M. et al. Solid-state infrared-to-visible upconversion sensitized by colloidal nanocrystals. Nat. Photon. 10, 31–34 (2016).

    ADS  Article  Google Scholar 

  12. 12.

    Huang, Z. & Lee Tang, M. Semiconductor nanocrystal light absorbers for photon upconversion. J. Phys. Chem. Lett. 9, 6198–6206 (2018).

    Article  Google Scholar 

  13. 13.

    Nienhaus, L., Wu, M., Bulović, V., Baldo, M. A. & Bawendi, M. G. Using lead chalcogenide nanocrystals as spin mixers: a perspective on near-infrared-to-visible upconversion. Dalton Trans. 47, 8509–8516 (2018).

    Article  Google Scholar 

  14. 14.

    Garakyaraghi, S., Mongin, C., Granger, D. B., Anthony, J. E. & Castellano, F. N. Delayed molecular triplet generation from energized lead sulfide quantum dots. J. Phys. Chem. Lett. 8, 1458–1463 (2017).

    Article  Google Scholar 

  15. 15.

    Mongin, C., Moroz, P., Zamkov, M. & Castellano, F. N. Thermally activated delayed photoluminescence from pyrenyl-functionalized CdSe quantum dots. Nat. Chem. 10, 225–230 (2018).

    Article  Google Scholar 

  16. 16.

    Kroupa, D. M. et al. Control of energy flow dynamics between tetracene ligands and PbS quantum dots by size tuning and ligand coverage. Nano Lett. 18, 865–873 (2018).

    ADS  Article  Google Scholar 

  17. 17.

    Nishimura, N. et al. Photon upconversion utilizing energy beyond the band gap of crystalline silicon with a hybrid TES-ADT/PbS quantum dots system. Chem. Sci. 10, 4750–4760 (2019).

    Article  Google Scholar 

  18. 18.

    Askes, S. H. C. & Bonnet, S. Solving the oxygen sensitivity of sensitized photon upconversion in life science applications. Nat. Rev. Chem. 2, 437–452 (2018).

    Article  Google Scholar 

  19. 19.

    Baluschev, S., Katta, K., Avlasevich, Y. & Landfester, K. Annihilation upconversion in nanoconfinement: solving the oxygen quenching problem. Mater. Horiz. 3, 478–486 (2016).

    Article  Google Scholar 

  20. 20.

    Svagan, A. J. et al. Photon energy upconverting nanopaper: a bioinspired oxygen protection strategy. ACS Nano 8, 8198–8207 (2014).

    Article  Google Scholar 

  21. 21.

    Kang, J.-H. & Reichmanis, E. Low-threshold photon upconversion capsules obtained by photoinduced interfacial polymerization. Angew. Chem. Int. Ed. 51, 11841–11844 (2012).

    Article  Google Scholar 

  22. 22.

    Fückel, B. et al. Singlet oxygen mediated photochemical upconversion of NIR light. J. Phys. Chem. Lett. 2, 966–971 (2011).

    Article  Google Scholar 

  23. 23.

    Ogryzlo, E. A. & Pearson, A. E. Excitation of violanthrone by singlet oxygen. a chemiluminescence mechanism. J. Phys. Chem. 72, 2913–2916 (1968).

    Article  Google Scholar 

  24. 24.

    Trupke, T., Green, M. A. & Würfel, P. Improving solar cell efficiencies by up-conversion of sub-band-gap light. J. Appl. Phys. 92, 4117–4122 (2002).

    ADS  Article  Google Scholar 

  25. 25.

    Saritaş, M. & McKell, H. D. Absorption coefficient of Si in the wavelength region between 0.80–1.16 μm. J. Appl. Phys. 61, 4923–4925 (1987).

    ADS  Article  Google Scholar 

  26. 26.

    Engel, T. & Reid, P. Physical Chemistry 3rd edn, Ch. 35, 997 (Pearson Education, 2013).

  27. 27.

    Samia, A. C. S., Chen, X. & Burda, C. Semiconductor quantum dots for photodynamic therapy. J. Am. Chem. Soc. 125, 15736–15737 (2003).

    Article  Google Scholar 

  28. 28.

    Stern, H. L. et al. Identification of a triplet pair intermediate in singlet exciton fission in solution. Proc. Natl Acad. Sci. USA 112, 7656–7661 (2015).

    ADS  Article  Google Scholar 

  29. 29.

    Matsui, Y. et al. Exergonic intramolecular singlet fission of an adamantane-linked tetracene dyad via twin quintet multiexcitons. J. Phys. Chem. C 123, 18813–18823 (2019).

    Article  Google Scholar 

  30. 30.

    Merrifield, R. E. Theory of magnetic field effects on the mutual annihilation of triplet excitons. J. Chem. Phys. 48, 4318–4319 (1968).

    ADS  Article  Google Scholar 

  31. 31.

    Atkins, P. & Evans, G. Magnetic field effects on chemiluminescent fluid solutions. Mol. Phys. 29, 921–935 (1975).

    ADS  Article  Google Scholar 

  32. 32.

    Iwasaki, Y., Maeda, K. & Murai, H. Time-domain observation of external magnetic field effects on the delayed fluorescence of N,N,N',N'-tetramethyl-1,4-phenylenediamine in alcoholic solution. J. Phys. Chem. A 105, 2961–2966 (2001).

    Article  Google Scholar 

  33. 33.

    Monroe, B. M. photochemical estimation of oxygen solubility. Photochem. Photobiol. 35, 863–865 (1982).

    Article  Google Scholar 

  34. 34.

    Zamani-Khamiri, O. & Hameka, H. Spin-orbit contribution to the zero-field splitting of the oxygen molecule. J. Chem. Phys. 55, 2191–2197 (1971).

    ADS  Article  Google Scholar 

  35. 35.

    Frazer, L., Gallaher, J. K. & Schmidt, T. W. Optimizing the efficiency of solar photon upconversion. ACS Energy Lett. 2, 1346–1354 (2017).

    Article  Google Scholar 

  36. 36.

    Schulze, T. F. et al. Photochemical upconversion enhanced solar cells: effect of a back reflector. Aust. J. Chem. 65, 480–485 (2012).

    ADS  Article  Google Scholar 

  37. 37.

    Stanley, C. P. et al. Singlet molecular oxygen regulates vascular tone and blood pressure in inflammation. Nature 566, 548–552 (2019).

    ADS  Article  Google Scholar 

  38. 38.

    Kakuichi, M., Kasatani, K. & Morita, Y. Preparation of nanoparticles of a violanthrone derivative with properties of J-like aggregates. Trans. Mater. Res. Soc. Jpn. 37, 471–474 (2012).

    Article  Google Scholar 

  39. 39.

    Dover, C. B. et al. Endothermic singlet fission is hindered by excimer formation. Nat. Chem. 10, 305–310 (2018).

    Article  Google Scholar 

  40. 40.

    Hu, L. et al. Graphene doping improved device performance of ZnMgO/PbS colloidal quantum dot photovoltaics. Adv. Funct. Mater. 26, 1899–1907 (2016).

    Article  Google Scholar 

  41. 41.

    Beygi, H., Sajjadi, S. A., Babakhani, A., Young, J. F. & van Veggel, F. C. J. M. Surface chemistry of as-synthesized and air-oxidized PbS quantum dots. Appl. Surf. Sci. 457, 1–10 (2018).

    ADS  Article  Google Scholar 

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This work was supported by the Australian Research Council (Centre of Excellence in Exciton Science CE170100026). The research used facilities supported by Microscopy Australia at the Electron Microscope Unit (EMU) and the Solid State and Elemental Analysis Unit within the Mark Wainwright Analytical Centre (MWAC) at UNSW Sydney.

Author information




E.M.G., S.K.K.P., S.N. and T.I. performed the optical measurements and analysed the data. S.H. and Z.L.T. synthesized the PbS material. J.E.A. and A.J.P. synthesized the TTCA ligands. J.H.C. performed theoretical analysis of the magnetic field effects. S.C. and R.D.T. performed the TEM measurements. T.W.S. conceived the experiments and wrote the manuscript.

Corresponding author

Correspondence to Timothy W. Schmidt.

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Supplementary Information

Supplementary Figs. 1–9, Tables 1–3 and text.

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Gholizadeh, E.M., Prasad, S.K.K., Teh, Z.L. et al. Photochemical upconversion of near-infrared light from below the silicon bandgap. Nat. Photonics 14, 585–590 (2020).

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