Near-Infrared Emissive CuInS₂/ZnS Quantum Dot-Embedded Polymer Scaffolds for Photon Upconversion Imaging

A facile synthesis and application of photon upconversion (UC) probes, CuInS₂/ZnS quantum dots (nCIS QDs) is presented, which exhibits near-infrared (NIR) spectral emission. The nCIS QDs are synthesized via a template-assisted cation-exchange reaction during a heating process, resulting in NIR-I emission with a large Stokes shift (≈650 meV) and a high photoluminescence quantum yield (PLQY, ≈0.95). This behavior is attributed to a template-assisted cation-exchange mechanism that produces a wurtzite crystal structure and deep defect states, leading to a relatively long fluorescence lifetime (≈5 µs). The quantum confinement effect allows for the emission of light at different wavelengths by adjusting the size of the nanocrystals. Moreover, their deep defect states facilitate photon UC via a self-trapping triplet-triplet annihilation mechanism. The promising potential of the nCIS QDs is explored in UC imaging, demonstrating high-contrast NIR imaging under IR vision modules, even in the presence of interference layers. It suggests potential applications in surgical guidance and future biomedical imaging.