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The separation of colloidal nanocrystals from their original synthesis medium is an essential process step towards their application, however, the costs on a preparative scale are still a constraint. A new combination of approaches for the purification of hydrophobic Quantum Dots is presented, resulting in an efficient scalable process in regard to time and solvent consumption, using common laboratory equipment and low-cost materials. The procedure is based on a combination of solvent-induced adhesion and solid phase extraction. The platform allows the transition from manual handling towards automation, yielding an overall purification performance similar to one conventional batch precipitation/centrifugation step, which was investigated by thermogravimetry and gas chromatography. The distinct miscibility gaps between surfactants used as nanoparticle capping agents, original and extraction medium are clarified by their phase diagrams, which confirmed the outcome of the flow chemistry process. Furthermore, the solubility behavior of the Quantum Dots is put into context with the Hansen solubility parameters framework to reasonably decide upon appropriate solvent types.
Here, we report on the recent advancements in the synthesis and optical properties of novel core-shell CdSe semiconductor nanocrystals (SCNC) with either a thick monolithic shell of CdS or thin multi-shells of succeeding CdS and ZnS monolayers, characterized by steady state and time-resolved fluorescence spectroscopy at the ensemble level. SCNC samples, chosen upon the size of their photoluminescence quantum yield (PL QY), were subsequently investigated at the single particle level using a custom build confocal laser scanning microscope to obtain information on brightness, blinking behavior, and decay kinetics of single SCNCs and correlate these properties with their surface morphology. The results of this study can help to identify new synthetic routes and surface modifications to colloidally and photochemically stable SCNCs with a PL QY of close to unity.