Abstract
Upconversion nanocrystals convert infrared radiation to visible luminescence, and are promising for applications in biodetection1,2,3, bioimaging4,5,6,7, solar cells8,9,10 and three-dimensional display technologies8,9,11. Although the design of suitable nanocrystals has improved the performance of upconversion nanocrystals10,12,13,14, their emission brightness is limited by the low doping concentration of activator ions needed to avoid the luminescence quenching that occurs at high concentrations15,16. Here, we demonstrate that high excitation irradiance can alleviate concentration quenching in upconversion luminescence when combined with higher activator concentration, which can be increased from 0.5 mol% to 8 mol% Tm3+ in NaYF4. This leads to significantly enhanced luminescence signals, by up to a factor of 70. By using such bright nanocrystals, we demonstrate remote tracking of a single nanocrystal with a microstructured optical-fibre dip sensor. This represents a sensitivity improvement of three orders of magnitude over benchmark nanocrystals such as quantum dots17.
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Acknowledgements
The authors thank D. Birch, D. Inglis, N. Vella, A. Nadort, R. Field, M. Nguyen, D. Liu, C. Yan and J. Shen (Olympus Australia) for sample characterization, H. Ebendorff-Heidepriem for providing the suspended-core fibres, which were fabricated at the OptoFab node of the Australian National Fabrication Facility (ANFF), and A. Nechaev (Lomonosov Moscow State University of Fine Chemical Technologies, Russia) for bulk crystal preparation. J.Z. acknowledges a Macquarie University Research Excellence Scholarship, and D.J. and J.P. acknowledge support from the Australian Research Council (DP1095465, LP130100517). P.X. acknowledges support from the ‘973 program’ of China (2011CB707502, 2011CB809101) and T.M. acknowledges the support of an ARC Federation Fellowship.
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D.J. and T.M. conceived the project, designed the experiments and supervised the research. J.Z., E.S., Y.Lu and D.J. were primarily responsible for data collection and analysis. D.J., E.G., J.Z. and T.M. prepared figures and wrote the main manuscript text. J.Z., E.G., A.Z. and D.J. were primarily responsible for supporting information and numerical simulations. All authors contributed to data analysis, discussions and manuscript preparation.
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Zhao, J., Jin, D., Schartner, E. et al. Single-nanocrystal sensitivity achieved by enhanced upconversion luminescence. Nature Nanotech 8, 729–734 (2013). https://doi.org/10.1038/nnano.2013.171
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DOI: https://doi.org/10.1038/nnano.2013.171
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