The synthesis of colloidal core/shell nanocrystals has continually progressed to the point of true commercial-scale production. However, long term stability in ambient or aqueous conditions remains a significant challenge. This is especially the case for emergent, cadmium free nanocrystal systems, such as InP, which are utilized commercially only under stringent air and moisture free encapsulation. To improve long term ambient stability, the simple idea of growing thick epitaxial shells to passivate surface trap states and isolate the charge carriers creates new challenges as a result of increased lattice strain. Strain-induced dislocations at the core/shell interface have long been suggested as the major reason for lower fluorescence quantum yields in thick-shelled quantum dots. Unfortunately, directly characterizing these defects is difficult in nanocrystal systems compared to their bulk-epitaxial counterparts. To elucidate the impact of shell morphology and shell defects on the performance of colloidal quantum dots, we are utilizing a correlation strategy which allows for the interrogation of the single particle fluorescence dynamics and the atomic structure of the same quantum dot. This strategy has enabled the study of dark, non-emitting sub populations and has highlighted the effect of nanocrystal charging on the ensemble quantum yield. Correlation data will be presented which show the physical location of subtle and often overlooked surface defects in seeded CdSe/CdS nanorods and determine the charge carrier recombination mechanism and the type of blinking observed. Further, HRTEM, STEM-EDS and aberration-corrected STEM images of thick shelled InP/ZnSe and graded alloyed CdZnSeS/ZnS nanocrystals will be presented revealing further insight into the true physical structure of the shells and the need for improved synthetic strategies.

Impact of shell imperfections in colloidal quantum dots

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.