Lanthanide Sensitizers for Large Anti-Stokes Shift Near-Infrared-to-Visible Triplet–Triplet Annihilation Photon Upconversion

The upconversion of near-infrared (NIR) to visible (vis) photons is of interest for display technologies and energy conversion. Although triplet–triplet annihilation (TTA) offers a mechanism for upconversion that works efficiently at low incident irradiance flux densities, current strategies for NIR–vis upconversion based on TTA have fundamental limitations. Herein, we report a strategy for NIR–vis TTA based on lanthanide-containing complexes to sensitize the upconversion. We demonstrate a β-diketonate complex of Yb³⁺ paired with rubrene that emits yellow (λ_em = 559 nm) under NIR excitation (λ_exc = 980 nm). This corresponds to an exceptional anti-Stokes shift of just less than 1 eV. Thus, lanthanide complexes could unlock high-performance NIR–vis upconversion, with lanthanide sensitizers overcoming the energy loss, reabsorption, and short triplet lifetime that fundamentally limit porphyrin, nanocrystals, and direct S₀–T₁ sensitizers.