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

Area of Science:

• Materials Science
• Nanotechnology
• Biomedical Imaging

Background:

• Photon upconversion (UC) probes are crucial for advanced imaging techniques.
• Developing efficient and stable UC probes with near-infrared (NIR) emission remains a challenge.
• Quantum dots (QDs) offer tunable optical properties for various applications.

Purpose of the Study:

• To synthesize and characterize novel copper indium sulfide/zinc sulfide quantum dots (nCIS QDs) for NIR emission.
• To investigate the underlying mechanisms responsible for the observed optical properties, including UC.
• To demonstrate the potential applications of these nCIS QDs in high-contrast imaging.

Main Methods:

• Facile synthesis of nCIS QDs using a template-assisted cation-exchange reaction.
• Characterization of QD properties, including crystal structure, photoluminescence quantum yield (PLQY), Stokes shift, and fluorescence lifetime.
• Evaluation of UC capabilities and performance in NIR imaging under IR vision modules.

Main Results:

• Achieved NIR-I emission with a large Stokes shift (≈650 meV) and high PLQY (≈0.95).
• Identified a wurtzite crystal structure and deep defect states contributing to efficient UC via a self-trapping triplet-triplet annihilation mechanism.
• Demonstrated high-contrast NIR imaging, even with interference layers, showcasing the probe's robustness.

Conclusions:

• The developed nCIS QDs offer a facile synthesis route and exhibit excellent NIR emission properties.
• The unique optical characteristics are attributed to the template-assisted synthesis, resulting in deep defect states facilitating efficient UC.
• These nCIS QDs show significant promise for advanced biomedical imaging, particularly in surgical guidance and other in-vivo applications.