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Simultaneous phase and size control of lanthanide doped upconversion nanocrystals

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Document pages: 9 pages

Abstract: Doping is a widely used technical process in material science. It involves combining atoms or ions of appropriate elements into the main lattice to produce hybrid materials with ideal properties and functions. For nanocrystalline materials, doping is of fundamental importance for stabilizing specific crystal phase 1, changing electronic properties 2, 3 and 4, modulating magnetism 5 and adjusting emission properties 6, 7, 8 and 9. Here, we describe a material system in which doping affects the growth process, so as to simultaneously control the crystal phase, size and light emission characteristics of the resulting nanocrystals. We show that NaYF4 nanocrystals can reasonably adjust the size (less than 10 nm), phase (cubic or hexagonal) and up conversion rate of 10,11,12 Eission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF4 upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels12 to volumetric three-dimensional displays13.

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