This collaborative report from the Cossairt (IMOD; University of Washington), Li (University of Washington), Seidler(University of Washington) and Toney (IMOD; CU Boulder) groups describes how a combination of atomistic synthesis, computation, X-ray measurement, and physical and electronic structure characterization reveals those features of synthetic control that influence photoluminescence properties in colloidal quantum dots.

Quantum Dots, also called semiconductor nanocrystals, are semiconducting particles a few nanometers across. They are often called “artificial atoms”, because they exhibit quantum mechanical effects in their optical and electronic properties, more similar to those of a single atom than other structures of a similar size. These quantum mechanical properties make them particularly interesting materials for applications in optoelectronic technologies, such as displays and LEDs.

An approach called colloidal quantum dot synthesis provides a suspension of these artificial atoms that can then readily be processed into electronic and device systems. Key to this approach is ensuring that the size, shape, composition, surface properties and stability of the quantum dot is uniform throughout the suspension, otherwise the properties of the materials will be poorly controlled.

One of the most effective approaches to maintaining uniform control over the synthesis and properties of colloidal quantum dots is the core-shell class of materials. These modular systems have a structure analogous to that of an orange, where the core is the fruit inside and the shell is the skin of the orange. Both the core and shell are made from semiconducting materials, but you can vary the size, thickness and chemical composition of both the core and the shell, and this controls the quantum properties of the material.

To better understand the features of core-shell colloidal quantum dots and how they correlate to and can be used to control the material properties of the system, this IMOD team assembled expertise in synthesis, computational modeling, and physical and electronic characterization to comprehensively examine the interface between the core and shell. Previous efforts to examine this extremely thin layer have encountered problems, and only through this collaborative and multi-faceted approach, made possible by the IMOD Center, was it possible to effectively study how the structure of these layers influence the properties.

This method to investigate the thin layer between the core and the shell not only provides an opportunity to refine this specific system, but can also be used more broadly by the research community to enhance the understanding of these important optoelectronic materials.