Colloidal synthesis and optical properties of all-inorganic low-dimensional cesium copper halide nanocrystals

Low-dimensional metal halides have recently attracted extensive attention owing to their unique structure and photoelectric properties. Herein, we report the colloidal synthesis of all-inorganic low-dimensional cesium copper halide nanocrystals (NCs) by adopting a hot-injection approach. Using the same reactants and ligands, but different reaction temperatures, both 1D CsCu${}_2$I${}_3$ nanorods and 0D Cs${}_3$Cu${}_2$I${}_5$ NCs can be prepared. Density functional theory indicates that the reduced dimensionality in 1D CsCu${}_2$I${}_3$ compared to 0D Cs${}_3$Cu${}_2$I${}_5$ makes the excitons more localized, which accounts for the strong emission of 0D Cs${}_3$Cu${}_2$I${}_5$ NCs. Subsequent optical characterization reveals that the highly luminescent, strongly Stokes-shifted broadband emission of 0D Cs${}_3$Cu${}_2$I${}_5$ NCs arises from the self-trapped excitons. Our findings not only present a method to control the synthesis of low-dimensional cesium copper halide nanocrystals but also highlight the potential of 0D Cs${}_3$Cu${}_2$I${}_5$ NCs in optoelectronics. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)