Synthesis of Colloidal Upconverting NaYF4: Er3+/Yb3+ and Tm3+/Yb3+ Monodisperse Nanocrystals

The synthesis, characterization, and spectroscopy of upconverting lanthanide-doped NaYF₄ nanocrystals (NCs) is presented. The monodisperse\ncubic NaYF₄ NCs were synthesized via a thermal decomposition reaction of trifluoroacetate precusors in a mixture of technical grade chemicals,\noctadecene and the coordinating ligand oleic acid. In this straightforward method, the dissolved precursors are added slowly to the reaction\nsolution through a stainless-steel canula resulting in highly luminescent nanocrystals with an almost monodisperse particle size distribution.\nThe NCs were characterized through the use of transmission electron microscopy, selected area electron diffraction, ¹H NMR, powder X-ray\ndiffraction, and high-resolution luminescence spectroscopy. The NaYF₄ NCs are capable of being of dispersed in nonpolar organic solvents\nthus forming colloidally stable solutions. The colloids of the Er³⁺, Yb³⁺ and Tm³⁺, Yb³⁺ doped NCs exhibit green/red and blue upconversion\nluminescence, respectively, under 980 nm laser diode excitation with low power densities.