Abstract
Strain can have a large influence on the properties of materials at the nanoscale. The effect of lattice strain on semiconductor devices has been widely studied, but its influence on colloidal semiconductor nanocrystals is still poorly understood. Here we show that the epitaxial deposition of a compressive shell (ZnS, ZnSe, ZnTe, CdS or CdSe) onto a soft nanocrystalline core (CdTe) to form a lattice-mismatched quantum dot can dramatically change the conduction and valence band energies of both the core and the shell. In particular, standard type-I quantum-dot behaviour is replaced by type-II behaviour, which is characterized by spatial separation of electrons and holes, extended excited-state lifetimes and giant spectral shifts. Moreover, the strain induced by the lattice mismatch can be used to tune the light emission—which displays narrow linewidths and high quantum yields—across the visible and near-infrared part of the spectrum (500–1,050 nm). Lattice-mismatched core–shell quantum dots are expected to have applications in solar energy conversion, multicolour biomedical imaging and super-resolution optical microscopy.
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Acknowledgements
The authors would like to thank Hong Yi, Zhong L. Wang, Yong Ding and A. Kumbhar for assistance with transmission electron microscopy, K. Hardcastle for help with powder X-ray diffraction, and R. Dickson, T. Lian, A. Issac and P. Nicovich for help in fluorescence lifetime data measurements. This work was supported by the NIH Roadmap Initiative in Nanomedicine through a Nanomedicine Development Centre award (PN2EY018244), and was also supported in part by NIH grants (P20 GM072069, R01 CA108468, U01HL080711 and U54CA119338), and by the DOE Genomes to Life (GTL) Program. A.M.S. acknowledges the Whitaker Foundation for generous fellowship support and S.M.N is a Distinguished Scholar of the Georgia Cancer Coalition (GCC).
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A.M.S. and S.M.N. conceived and designed the experiments. A.M.S. performed the experiments. A.M.S. and S.M.N. analysed the data. A.M.M. contributed materials/analysis tools. A.M.S. and S.M.N. co-wrote the paper.
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Smith, A., Mohs, A. & Nie, S. Tuning the optical and electronic properties of colloidal nanocrystals by lattice strain. Nature Nanotech 4, 56–63 (2009). https://doi.org/10.1038/nnano.2008.360
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DOI: https://doi.org/10.1038/nnano.2008.360
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