Lead chalcogenide nanocrystals are an excellent material for infrared optoelectronics and have recently been commercialized in low-cost near-infrared cameras. However, they still remain limited by the absorption-extraction compromise and low photoluminescence quantum yields. One solution to these limitations is to combine an infrared plasmonic material with the lead chalcogenide into a core/shell nanocrystal, which will allow for exciton-plasmon coupling and optical enhancements via the Purcell effect. Doped plasmonic nanocrystals, such as copper chalcogenides, are good plasmonic materials for this purpose because they have plasmonic energies tunable throughout the near-infrared. Therefore, lead and copper chalcogenide core/shell nanocrystals, such as Cu2-xS/PbS, are very desirable as a model system to controllably couple excitons and plasmons to enhance the optical properties of infrared nanocrystals. We developed a novel synthetic method for Cu2-xS/PbS core/shell nanocrystals, which deposits a PbS shell while maintaining the plasmonic character of the Cu2-xS cores. Typical shell synthetic methods avoid homogenous nucleation of the shell material by the slow addition of precursors over a long reaction time. However, long reaction times (~hours) do not work for Cu2-xS/PbS core/shell nanocrystals due to a Cu-to-Pb cation exchange, which destroys the plasmonic character of the Cu2-xS cores. By simultaneously mixing the precursors with the Cu2-xS cores, and limiting the reaction times and temperatures, we were able to deposit the PbS shell before cation exchange could destroy the Cu2-xS plasmon. PbS nanocrystals do homogenously nucleate, but they can be removed using size-selective precipitation. The effect of the PbS shell on the energy and intensity of the plasmon depends on the ligand type and copper vacancy concentration of the initial Cu2-xS cores. This synthesis is the first step toward the realization of infrared exciton-plasmon coupling in uniform core/shell nanocrystals using doped plasmonic semiconductors.

Synthesis of Cu2-xS/PbS core/shell nanocrystals for infrared exciton-plasmon coupling

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.