Structural Insights into Giant Core‐Shell Copper Iron Sulfide‐Zinc Sulfide Nanocrystals

Abstract CuFeS₂ nanocrystals have emerged as promising candidates for applications in photovoltaics, spintronics, and bioimaging due to their high absorption coefficients and tunable quantum confinement effects. This study focuses on the synthesis and characterisation of giant CuFeS₂/ZnS core/shell nanocrystals. The development of giant core/shell nanocrystals is a significant step toward addressing limitations such as poor luminescence and non‐radiative recombination in CuFeS₂ nanocrystals. A novel ZnS shell growth protocol is employed to passivate surface defects and enhance photostability without introducing toxic heavy metals like cadmium. X‐ray crystallography confirmed the formation of a sharp CuFeS₂/ZnS interface as well as improved crystallinity. Optical analysis reveals a bandgap as low as 0.5 eV, extending the reach of core/shell architectures into the near‐infrared region. Transmission electron microscopy analysis highlights diverse morphologies and a well‐defined core‐shell structure, with an average size of 26 nm and a uniform ZnS shell of ∼3 nm. The study underscores the potential of CuFeS₂/ZnS nanocrystals as environmentally friendly, efficient, and scalable alternatives to traditional heavy‐metal‐based nanocrystals. By overcoming challenges in synthesis, this work introduces a novel class of giant nanocrystals with enhanced optical and structural properties, paving the way for advanced optoelectronic and biomedical applications.