Colloidal Cu-Zn-In-S-Based Disk-Shaped Nanocookies

We present a colloidal synthesis of quaternary Cu-Zn-In-S (CZIS) nanoplatelets (NPLs) by means of partial cation exchange. Starting with the synthesis of highly monodisperse binary CuS NPLs with lateral dimensions of similar to 64 nm and thickness of similar to 5 nm, we further performed a cation exchange reaction in which copper was partly replaced by indium, leading to Cu-In-S NPLs. To enhance the stability of the resulting NPLs and to improve their optical properties, we carried out the ZnS shell growth via both the heterogeneous nucleation of ZnS on the NPLs and via partial cation exchange on the surface of the particles. The latter reaction resulted, however, in rather an alloyed than the core/shell structure, whereas the reaction between zinc and sulfur precursors yielded unusual cookie-like hexagonal shaped structure, in which ZnS trigonal extensions grew only on one of the basal planes of the plates along the thickness direction. Upon ZnS growth, the lateral dimensions of the resulting core/shell CZIS/ZnS and alloyed CZIS NPLs distinctly increased to similar to 80 and similar to 75 nm, respectively. The analysis of the optical properties of the alloyed CZIS NPLs showed photoluminescence (PL) in the range from 780 to 820 nm depending on the reaction time and temperature. This PL signal originated mainly from small nanoparticles formed as a byproduct in the synthesis. In contrast to the alloyed NPLs, PL measurements of the core/shell CZIS/ZnS platelets showed a weak emission in the near-infrared region (PL maximum at approx. 1110 nm), which so far has rarely been reported for the copper chalcogenide-based two-dimensional structures.