Enrichment of molecular antenna triplets amplifies upconverting nanoparticle emission


Efficient photon upconversion at low light intensities promises major advances in technologies spanning solar energy harvesting to deep-tissue biophotonics. Here, we discover the critical mechanisms that enable near-infrared dye antennas to significantly enhance performance in lanthanide-doped upconverting nanoparticle (UCNP) systems, and leverage these findings to design dye–UCNP hybrids with a 33,000-fold increase in brightness and a 100-fold increase in efficiency over bare UCNPs. We show that increasing the lanthanide content in the UCNPs shifts the primary energy donor from the dye singlet to its triplet, and the resultant triplet states then mediate energy transfer into the nanocrystals. Time-gated phosphorescence, density functional theory, singlet lifetimes and triplet-quenching experiments support these findings. This interplay between the excited-state populations in organic antennas and the composition of UCNPs presents new design rules that overcome the limitations of previous upconverting materials, enabling performances now relevant for photovoltaics, biophotonics and infrared detection.

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Fig. 1: Dye-functionalized UCNPs, their mechanism of energy transfer, and the larger effective absorption cross-section of dyes relative to UCNPs.
Fig. 2: Time-gated photoluminescence as evidence of resonant triplet states.
Fig. 3: Evidence of triplet energy transfer to UCNPs.
Fig. 4: Upconverted performance improvements by enhancing the dye triplet population and coupling pathways.


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The authors thank S. Fischer, K. Raymond and K. Yao for helpful discussions, and T. Chen for her invaluable experimental assistance. This work was supported by the National Science Foundation SAGE IGERT fellowship (to D.J.G.) and the Chinese Scholarship Council fellowship (B.T.). Portions of this research were supported by the Global Research Laboratory (GRL) Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (no. 2016911815). This work was performed at the Molecular Foundry and was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy (contract no. DE-AC02-05CH11231). The computational work performed here was supported by the Director, Office of Science, Chemical Sciences, Geosciences and Biosciences Division of the US Department of Energy, under contract no. DEAC02-05CH1123.

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The scientific concepts, ideas and experimental designs were the result of interactions and discussions between D.J.G., P.J.S., B.E.C., N.J.B., E.M.C. and Y.D.S. D.J.G., E.M.C., N.A.T., C.A.T. and B.T. synthesized the nanoparticles. D.J.G., N.J.B. and E.S.B. conducted the spectroscopic measurements. D.J.G. and E.M.C. conducted the QY measurements. S.M.H. and J.B.N. performed the theoretical modelling. B.S. and S.A. conducted the electron microscopy. D.J.G., N.J.B., E.M.C., B.E.C. and P.J.S. wrote the paper, in coordination with all the authors.

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Correspondence to Emory M. Chan or Bruce E. Cohen or P. James Schuck.

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Supplementary Methods; Supplementary Figures 1–16; Supplementary Table 1; Supplementary discussion; and Supplementary references.

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Garfield, D.J., Borys, N.J., Hamed, S.M. et al. Enrichment of molecular antenna triplets amplifies upconverting nanoparticle emission. Nature Photon 12, 402–407 (2018). https://doi.org/10.1038/s41566-018-0156-x

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