Silver(I) cations exchange rapidly at room temperature with Cd2+ and Pb2+ cations in metal chalcogenide quantum dots. While cadmium/silver exchange was demonstrated more than a decade ago, lead/silver exchange was reported only recently. When cation exchange occurs in these nano-sized crystals, strain fields build up near the domain boundaries that form. In the case of Ag+ exchange in CdSe, this strain is so significant that partial exchange within quantum dots of a typical 3-6 nm size appears to be impossible. Contrarily, partial exchange is readily achieved and observed in PbS quantum dots as Ag+ ions are gradually added to the sample. This fundamentally different behavior during incomplete exchange has important implications for the spectroscopic properties of quantum dot ensembles as well as for the homogeneity of the sample. We present electronic spectra from both CdSe and PbS quantum dots as Ag+ ions are gradually incorporated and highlight the observed differences. In addition, high resolution transmission electron microscope images (with STEM-EDS mapping) and x-ray diffraction data will be presented to support the conclusions drawn from the spectroscopic study. Finally, we will discuss the limitations that are imposed by these phenomena on the ability to carry out post-preparative compositional transformations of quantum dots.

Fundamental differences in the cation exchange behaviors of cadmium- and lead chalcogenide quantum dots

253rd National Meeting (2017)

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