Precision Colloidal Synthesis: How Far Can it take us in Realizing Advanced Quantum Light Sources?

Core/shell heterostructuring of semiconductor quantum dots (QDs) provides a convenient platform for exploring the limits of synthetic control over quantum optical properties. Even “simple” control of component composition and feature size in a nano-heterostructure affords opportunities for band-structure engineering, which leads to altered photoluminescence properties, including emission color, lifetime, photostability, etc. More interestingly, however, colloidal synthesis provides possibilities for nearly-atomically precise manipulation of the core/shell interface. This can include alloying, introduction of defects or dopants, and selective facet growth. Here, I will describe several examples of how advanced colloidal synthesis can be used to finely tune nanoscale heterostructure to realize novel properties: dual-color emission, charged-state versus excitonic emission, and resistance to photobleaching by either dimming or catastrophic failure. First, we show that adventitious or intentional introduction of hole traps at the InP/CdSe QD interface, as well as arm length and arm diameter tuning in CdSe/CdS core/arm tetrapods, can provide conditions for realizing two-color excitonic or multi-excitonic emission, respectively, both potentially characterized by suppressed blinking. Second, we assign for the first time the synthesis-structure-function correlations for non-blinking CdSe/CdS core/shell QDs to define the limits of “on-demand” single-photon production under thermal or high-photon-flux stress. The new insights show, e.g., the relationships between shell defects and charged-state emission and between interfacial alloying and photobleaching resistance, each precisely controlled by synthesis conditions. Taken together, the different nano-heterostructure systems reveal the opportunity for achieving designed quantum optical properties through synthesis, while the remaining limitations expose where alternative strategies might be needed to realize, e.g., transform-limited, ultrafast single-photon emitters.