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

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.