Boosting Dye‐Sensitized Luminescence by Enhanced Short‐Range Triplet Energy Transfer

Abstract Dye‐sensitization can enhance lanthanide‐based upconversion luminescence, but is hindered by interfacial energy transfer from organic dye to lanthanide ion Yb³⁺. To overcome these limitations, modifying coordination sites on dye conjugated structures and minimizing the distance between fluorescence cores and Yb³⁺ in upconversion nanoparticles (UCNPs) are proposed. The specially designed near‐infrared (NIR) dye, disulfo‐indocyanine green (disulfo‐ICG), acts as the antenna molecule and exhibits a 2413‐fold increase in luminescence under 808 nm excitation compared to UCNPs alone using 980 nm irradiation. The significant improvement is attributed to the high energy transfer efficiency of 72.1% from disulfo‐ICG to Yb³⁺ in UCNPs, with majority of energy originating from triplet state (T₁) of disulfo‐ICG. Shortening the distance between the dye and lanthanide ions increases the probability of energy transfer and strengthens the heavy atom effect, leading to enhanced T₁ generation and improved dye‐triplet sensitization upconversion. Importantly, this approach also applies to 730 nm excitation Cy7‐SO₃ sensitization system, overcoming the spectral mismatch between Cy7 and Yb³⁺ and achieving a 52‐fold enhancement in luminescence. Furthermore, the enhancement of upconversion at single particle level through dye‐sensitization is demonstrated. This strategy expands the range of NIR dyes for sensitization and opens new avenues for highly efficient dye‐sensitized upconversion systems.