Correlation of Surface Composition to Optical Properties of CdSe Nanocrystals

Understanding the role that surface chemistry plays in modifying the optical properties of quantum dots (QDs) has been an active field of research for some time now.  Recently, one of the goals of many research groups involve possessing systematic control of the ligand exchange process which can provide the ability to tailor the surface with a specific amount of surface ligand, thereby having unparalleled control over the optical properties.  In this presentation, we will discuss our efforts towards investigating controlled efforts of ligand exchange in CdSe QDs.  Most notably, we focus on the trioctylphosphine oxide (TOPO) coated CdSe system with efforts towards exchanging phosphine oxide derivatives onto the QD surface.  Using a combination of nuclear magnetic resonance and infrared spectroscopy and thermogravimetric analysis, we probe the extent of ligand exchange of a function of incoming ligand concentration and QD particle size.  We also discuss the effects of multiple washing of the QDs during the cleaning process – QD materials that still possess quantum confinement like features, yet is not dispersible in typical organic solvent.  Titrations of ligands from the excessively cleaned materials lead to dispersed QDs.  During the course of these measurements, we will discuss the impact these surface chemistry treatments have on the photoluminescence of these materials.