Synthesis of hexagonal-phase NaYF4:Yb,Er and NaYF 4:Yb,Tm nanocrystals with efficient up-conversion fluorescence

Abstract

IR-to-visible up-conversion fluorescent nanocrystals of hexagonal-phase NaYF4:20 %Yb,2 %Er and NaYF4:20%Yb,2%Tm have been synthesized by decomposition of multiprecursors of CF3COONa, (CF 3COO)3Y, (CF3COO)3Yb, and (CF 3COO)3Er/(CF3COO)3Tm in oleylamine at 330 °C. The average particle size is 10.5±0.7 nm (from random measurements of 200 particles from five transmission electron microscopy images) and 11.1±1.3 nm (from dynamic-light-scattering measurements). The upconversion fluorescence intensity of the hexagonal nanocrystals in this work is much higher than that of other cubic-phase NaYF4:Yb,Er nanocrystals, including the ones in this work (by a factor of 7.5). Mechanisms for nucleation and growth of the hexagonal-phase nanoparticles are proposed. These nanocrystals are easily dispersed in organic solvents, producing a transparent colloidal solution. The hydrophobic surfaces of the particles are made hydrophilic using a bipolar surfactant. These nanoparticles and their dispersions in various media have potential applications in optical nanodevices and bioprobes. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.