Low-temperature liquid-phase formation of environmentally stable copper halide nanocrystal superlattices and their application to anticounterfeiting patterns

Nanocrystal superlattices have the potential to create a new class of semiconductor materials by combining the photophysical properties of individual nanocrystals with bulk-like structure performance. However, the princi-ples underlying the direct formation of superlattices in liquid phase have not been thoroughly investigated, particularly, those consisting of exciton self-trapping metal halides. Here, we explore the formation of Cs3Cu2Br5 nanocrystal superlattices via liquid-phase crystallization of growing nanocrystals over a reaction period of only a few seconds. Importantly, the reaction temperature and the precursor concentration were found to be key pa-rameters governing the concomitant nanocrystal growth and superlattice formation. The resulting Cs3Cu2Br5 superlattices had a well-defined face-centered cubic structure and emitted a single-band bright blue emission when exposed to 280 nm light. Owing to their advantages, such as low toxicity, reabsorption-free, narrow ab-sorption, strong emission, and high environmental stability, the Cs3Cu2Br5 superlattices were applicable to anti -counterfeiting applications. Our findings shed light on the liquid-phase assembly of nanocrystals into super -lattices and highlight the potential applications of the superlattices.