Size controlled synthesis of monodisperse PbTe quantum dots: using oleylamine as the capping ligand

Abstract

We report a simple method to synthesize monodisperse hydrophobic PbTe quantum dots followed by a stability study of the as-synthesized quantum dots in air. We provide evidence that air-stable PbTe quantum dots can be synthesized using this method. PbCl₂ complexed with oleylamine was used as the Pb precursor. Tellurium powder dissolved in tri-n-octylphosphine was used as the Te precursor. Oleylamine was used as the only capping ligand. The size and shape of the PbTe quantum dots were controlled by changing variables such as injection temperature, growth temperature, and growth time. Both Pb to oleylamine and Pb to Te feed mole ratios have been examined to obtain the optimal synthetic conditions. The PbTe quantum dots can be changed from hydrophobic to hydrophilic through ligand exchange using 4-mercaptopyridine to replace oleylamine as the capping ligand. The colloidal PbTe quantum dots were characterized by transmission electron microscopy, high resolution transmission electron microscopy, selected area X-ray diffraction, energy-dispersive X-ray spectroscopy, FT-IR spectrometer, ³¹PNMR spectrometer, and powder X-ray diffraction. The sizes of the PbTe quantum dots synthesized ranged from 2.6 nm to 14.0 nm with a relative standard deviation of ∼5.6 to 9.1%. The shape of the PbTe quantum dots was either spherical (<∼9 to 10 nm) or cubic (>∼9 to 10 nm).