Surface Oxidation of Tris(diethylaminophosphine) Passivated PbSe Colloidal Quantum Dots

PbSe Quantum Dots (QDs) have a large exciton Bohr radius of 46 nm, a tunable bandgap between 0.28 eV and 1.2 eV and exhibit multiple exciton generation. These properties give PbSe QDs excellent potential as the active sensing materials in room-temperature radiation sensors. Surface oxidation severely impacts device quality by restricting the transport of charge carriers. Nanoparticle materials can have their ligand chemistry optimized to prevent surface oxidation. In this research, two precursors, one containing lead (II) oxide powder, oleic acid (OA), and 1-octadecene, while the other one containing selenium powder and tris(diethylaminophosphine) (TDP), were mixed in a glove box and transferred to a Schlenk line to dissolve. Reactions were processed in a batch microwave reactor. Material batches were synthesized using temperatures between 120 °C – 150 °C and holding times of 3 – 7 minutes. The reaction product was purified by adding a poor solvent and centrifuging. The PbSe QDs were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), UV-Vis-NIR spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The characterization data showed mostly uniform particles with spherical morphology. Both OA and TDP ligands were identified on the QD surface. A first exciton absorption peak was observed in the NIR region. The Pb:Se atomic ratio was found to be close to the ideal value of 1:1. A comparison of qualitative XPS data obtained from fresh and four-day-old material showed no signs of oxidation, which could be most easily observed in the Se 3d spectra. By combining OA and TDP as the passivating ligands, the characterization results demonstrated that the QD surface was successfully passivated.