Triangular-shaped Cu-Zn-In-Se-based nanocrystals with narrow near infrared photoluminescence

Tunable optical properties exhibited by semiconductor nanocrystals (NCs) in the near infrared (NIR) spectral region are of particular interest in various applications, such as telecommunications, bioimaging, photodetection, photovoltaics, etc. While lead and mercury chalcogenide NCs do exhibit exemplary optical properties in the NIR, Cu-In-Se (CISe)-based NCs are a suitable environment-friendly alternative to these toxic materials. Several reports of NIR-emitting (quasi)spherical CISe NCs have been published, but their more complex-shaped counterparts remain rather less explored. The emerging anisotropic nanomaterials have gained significant interest owing to their unique optical properties arising due to their specific shape. While several examples of non-spherical Cu-In-S-based NCs have been reported, examples of CISe-based anisotropic NCs are rather scarce, and those with intensive photoluminescence (PL) are not yet developed. In this work, we present a one-pot approach to synthesize quaternary Cu-Zn-In-Se (CZISe) triangular NCs with intensive PL in the NIR region. The NCs synthesized exhibit tetragonal crystal structure and, depending on the reaction conditions, are single triangular particles or stacks of triangular blocks of varied lateral sizes but rather uniform thickness. The synthesis involves the formation of In₂Se₃ seeds with subsequent incorporation of copper and growth of triangular CISe NCs, followed by the incorporation of zinc and the growth of a ZnS shell. Importantly, the PL band widths of the final core/shell heterostructured NCs are narrow, down to 102 meV, which is a rarely observed characteristic for this class of materials and can be attributed to their anisotropic shape and the absence of thickness and compositional inhomogeneities of their building blocks. The PL of the CZISe/ZnS NCs can be tuned in the range of 1082-1218 nm reaching a quantum yield of up to 40% by varying their size and composition. To the best of our knowledge, this is the farthest and the narrowest PL achieved for CISe-based NCs so far, which widens application perspectives of this material in NIR LEDs, bioimaging, and photovoltaics.