In this communication we describe a technique for measuring the absolute quantum yields (QYs) of upconverting nanomaterials based on the use of a commercially available fluorimeter and an integrating sphere. Using this setup, we have successfully acquired luminescence efficiency data (pump laser, absorbed pump, and visible emitted intensities) for lanthanide-doped upconverting nanoparticles. QYs in the range of 0.005% to 0.3% were measured for several NaYF(4): 2% Er(3+), 20% Yb(3+) nanoparticles with particle sizes ranging from 10 to 100 nm while a QY of 3% was measured for a bulk sample.

Upconverting lanthanide-doped nanocrystals were synthesized via the thermal decomposition of trifluoroacetate precursors in a mixture of oleic acid and octadecene. This method provides highly luminescent nanoparticles through a simple one-pot technique with only one preparatory step. The Er3+, Yb3+ and Tm3+, Yb3+ doped cubic NaYF4 nanocrystals are colloidally stable in nonpolar organic solvents and exhibit green/red and blue upconversion luminescence, respectively, under 977 nm laser excitation with low power densities.

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