Hexagonal crown-capped NaYF4:Ce3+/Gd3+/Dy3+ microrods: Formation mechanism, energy transfer and luminescence properties

In this work, hexagonal crown-capped beta-NaYF4:Ce3+/Gd3+/Dy3+ microrods with remarkably uniform morphology and size have been successfully synthesized for the first time via a facile hydrothermal route. The phase and morphology evolution of beta-NaYF4 crystals are carefully tracked during hydrothermal growth by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron diffraction (TEM), respectively. The possible growth mechanism of hexagonal crown-capped NaYF4 microrods has been proposed. Furthermore, the luminescence properties of beta-NaYF4:Ce3+/Gd3+/Dy3+ are systemically investigated by the photoluminescence excitation spectra, emission spectra and decay curves. Impressively, upon the allowed Ce3+ 4f-5d electronic transition excitation, the efficient energy transfer from sensitizer (Ce3+) to activator (Dy3+) occurs via energy migration process Ce3+ -> (Gd3+)(n) -> Dy3+, in which Gd3+ ions act as bridge centers to induce intense yellow luminescence from Dy3+ activators. (C) 2015 Elsevier B.V. All rights reserved.