Solvothermal synthesis, cubic structure and multicolor upconversion emission of ultrasmall monodisperse lanthanide-doped BaYF5 nanocrystals

Lanthanide (Ln(3+)) doped BaYF5 (Ln=Yb3+, Er3+, Tm3+) nanocrystals (NCs) with a mean size of approximately 10 nm are synthesized by a solvothermal method using oleic acid as a stabilizing agent at 210 degrees C. The size of BaYF5 NCs can be controlled by simply tuning the reaction parameters such as reaction temperature, reaction time and the molar ratio of F-/Y3+. The detailed structure investigation reveals that the as-synthesized BaYF5 NCs are in the cubic structure with space group Fm (3) over barm instead of the reported tetragonal structure. Ln(3+) cations occupy crystal lattice positions with lower point symmetry, which may lead to high upconversion efficiency under the excitation of a 980 nm diode laser. By adjusting the dopant concentrations of Yb3+, Er3+ and Tm3+, intense near-infrared, blue, yellow and white upconversion emissions are readily realized, respectively. The desirable property of the ultrasmall monodisperse NCs makes it the promising material for the applications in miniaturized solid-state light sources, multicolor three-dimensional display devices and fluorescent labels for biomedicine imaging. (C) 2011 Elsevier B.V. All rights reserved.