Cation exchange has become an interesting and useful process for structural and compositional modification of compound semiconductor nanocrystals, or quantum dots (QDs). In principal, this process could be used for heavy doping, alloying, and/or heterostructure formation, if the extent and distribution of exchanged cations can be controlled. In the present work, we examine the factors that control the exchange of Pb cations with Cd cations in PbS QDs. The effects of temperature, concentration, and composition of the ligand shell on the kinetics and extent of the exchange are investigated via electronic spectroscopy, atomic absorption spectrometry, and transmission electron microscopy. Whereas temperature can be used to increase the rate and extent of Pb exchange, very high temperatures (&gt;150 °C) also degrade the QDs and can lead to dissolution of the particles. Exchanging the ligands on the surface can also promote the exchange reaction, allowing use of lower reaction temperatures. Using these strategies, we have successfully demonstrated the production of thick, robust CdS shells surrounding PbS QDs. These thick shells can enhance the optical properties, and can modify the carrier distribution within the QDs and allow partial charge carrier separation within the particle.

Effective regulation of post-preparative cation exchange reactions in PbS quantum dots

249th National Meeting (2015)

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