Cascade Lanthanide-Triplet Energy Transfer for Nanocrystal-Sensitized Organic Photon Upconversion

Sensitized organic photon upconversion via triplet-triplet annihilation (TTA) shows significant potential for energy conversion and photocatalysis, but achieving efficient upconversion across multiple wavelengths with single-wavelength near-infrared (NIR) excitation remains a daunting challenge. Here, we report a strategy utilizing lanthanide-doped nanocrystals (LnNCs) to sensitize TTA upconversion in multiple organic emitters under NIR excitation, achieving an anti-Stokes shift of up to 1.1 eV. This approach leverages a cascade lanthanide-triplet energy transfer design, adopting an interfacial energy transfer pathway via lanthanide ions to surface energy relay molecules for extended triplet sensitization. It allows consecutive transfer of photon energy from LnNCs to TTA emitters, mitigating energy mismatch between the triplet levels of emitters and excitation photon energies. The use of LnNCs enhances energy transfer efficiency through the unique spin-orbital coupling and narrow-band absorption properties of lanthanide ions. Our approach offers tunable upconversion emission, minimized energy loss during sensitization, and improved chemical stability of LnNCs. Additionally, we demonstrate the utility of this system in NIR-induced photopolymerization, showcasing its potential for applications such as 3D printing and photocatalysis.