By directly correlating nanoscale structure with function it is possible to address two key issues facing the predictive design and experimental realization of high-performing optical nanomaterials. Namely, one can assess (a) the origins of persistent performance heterogeneity in otherwise well-understood nanostructures that could inform development of materials with more uniform properties, and (b) the underlying nanoscale features responsible for specific unique properties whose origin may otherwise be attributable to several possible explanations and, thereby, not offering a clear choice for optimal target-material structure. Here, I will discuss our recent experiences using structure:function correlations to address both of these areas. First, I will elaborate on our effort to understand the origin of sub-unity quantum yields (QYs) in non-blinking CdSe/CdS “giant” quantum dots (gQDs). We initially hypothesized that some gQDs possessed 100% QYs, while others were simply non-emissive and, therefore, not contributing to our measurements of blinking behavior. However, by interrogating both atomic structure and photophysics at the level of single gQDs, we determined that the “heterogeneity” causing less-than-optimal QYs was not simply the presence of two populations of dots, i.e., always ‘on’ or always ‘off.’ Rather, our detailed analyses of fine atomic structure, chemical composition, and time-resolved single-photon photoluminescence data for the same individual nanocrystals revealed QY inhomogeneity across the population of gQDs. Essentially all nanocrystals were emissive and non-blinking, but each was characterized by its own QY that resulted from variations in the degree of charging, rather than from volume or clear structural inhomogeneity (Orfield et al. ACS Nano 2016, 10, 1960). Second, I will describe our recent insights into the role of core/shell interface abruptness on blinking and photobleaching behavior obtained through the first direct observation of this interface in gQDs. Finally, I will show how understanding structure:function correlations in asymmetric CdSe/CdS core/shell systems, e.g., seeded tetrapods, can be used to tune the efficiency, color and blinking behavior of multiexciton processes.

Correlating structure and function in symmetric and asymmetric core/shell optical nanomaterials

253rd National Meeting (2017)

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