Lanthanide-doped upconversion nanocrystals enable anti-Stokes emission with pump intensities several orders of magnitude lower than required by conventional nonlinear optical techniques. Their exceptional properties, namely large anti-Stokes shifts, sharp emission spectra and long excited-state lifetimes, have led to a diversity of applications. Here, we review upconversion nanocrystals from the perspective of fundamental concepts and examine the technical challenges in relation to emission colour tuning and luminescence enhancement. In particular, we highlight the advances in functionalization strategies that enable the broad utility of upconversion nanocrystals for multimodal imaging, cancer therapy, volumetric displays and photonics.
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The authors would like to acknowledge support through the Agency for Science, Technology and Research (A*STAR) (grant nos 122-PSE-0014 and 1231AFG028), the National Research Foundation and the Economic Development Board (Singapore-Peking-Oxford Research Enterprise), the National Natural Science Foundation of China (grant no. R-2014-S-009) through the NUS Research Institute at Suzhou, and the Australian Research Council (Centre of Excellence for Nanoscale BioPhotonics, grant no. CE140100003, and Future Fellowship, grant no. FT 130100517).
The authors declare no competing financial interests.
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Zhou, B., Shi, B., Jin, D. et al. Controlling upconversion nanocrystals for emerging applications. Nature Nanotech 10, 924–936 (2015). https://doi.org/10.1038/nnano.2015.251
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Up-conversion emission in transition metal and lanthanide co-doped systems: dimer sensitization revisited
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