Superparticles made from colloidal nanocrystals have recently shown great promise in bridging the nanoscale and mesoscale, building artificial materials with properties designed from the bottom-up. As these properties depend on the dimension of the superparticle, there is a need for a general method to produce monodisperse nanocrystal superparticles. Here, we demonstrate an approach that readily yields spherical nanocrystal superparticles with a polydispersity as low as 2%. This method relies on the controlled densification of the nanocrystal-containing “source” emulsion by the swelling of a secondary “sink” emulsion. We show that this strategy is general and rapid, yielding monodisperse superparticles with controllable sizes and morphologies, including core/shell structures, within a few minutes. The superparticles show a high optical quality that results in lasing through the whispering-gallery modes of the spherical structure, with an average quality factor of 1600. Assembling superparticles into small clusters selects the wavelength of the lasing modes, demonstrating an example of collective photonic behavior of these artificial solids.

A recently developed emulsion-templated assembly method promises the scalable, low-cost, and reproducible fabrication of hierarchical nanocrystal (NC) superstructures. These superstructures derive properties from the unique combination of choices of NC building blocks and superstructure morphology and therefore realize the concept of “artificial solids”. To control the final properties of these superstructures, it is essential to control the assembly conditions that yield distinct architectural morphologies. Here, we explore the phase-space of experimental parameters describing the emulsion-templated assembly including temperature, interfacial tension, and NC polydispersity and demonstrate which conditions lead to the growth of the most crystalline NC superstructures or supercrystals. By using a combination of electron microscopy and small-angle X-ray scattering, we show that slower assembly kinetics, softer interfaces, and lower NC polydispersity contribute to the formation of supercrystals with grain sizes up to 600 nm, while reversing these trends yields glassy solids. These results provide a clear path to the realization of higher-quality supercrystals, necessary to many applications.

Amplification of enantiomeric excesses (ee) is routinely observed during chiral crystallization of conglomerate crystals for which the enantiomers undergo racemization in solution. Although routes comprising a combination of crystal growth and dissolution are frequently used to obtain enantiopure molecules, crystal growth by itself has rather been considered as a source of enantiomeric erosion and discounted as a potential source of enantiomeric amplification. Counterintuitively, we here demonstrate striking enantiomeric amplification during crystal growth for clopidogrel and tert-leucine precursors. Based on a mechanistic framework, we identify that the interplay between racemization and crystal growth rates elicits this surprising effect. The asymmetric amplification of the solid-phase ee can be enhanced by increasing the mass of grown material relative to the product such that small amounts of seeds of only 60% ee already result in virtually exclusive growth of the majority phase. These results impact our understanding of asymmetric amplification mechanisms during crystallization and offer a tangible basis for practical production of enantiopure molecules.