Multi-Band Excitation of NIR-II Lanthanide Nanoparticles via Multiple-Dye Cascade Sensitization

Lanthanide-doped downshifting nanoparticles (DSNPs) emitting in the near-infrared-II (NIR-II) window offer distinct advantages for deep-tissue optical applications, yet their practical utility is fundamentally constrained by excitation limited to a few discrete wavelengths. Here, we report a multi-band-driven lanthanide nanoparticle platform enabled by a multiple-dye sensitization strategy. By integrating three complementary organic dyes-tropolone (Trop), cyanine 3 (Cy3), and IR806-the excitation window of DSNPs is expanded sixfold, across the ultraviolet-visible-near-infrared (UV-Vis-NIR) region from 270 nm to 1030 nm. While Trop and IR806 exhibit efficient sensitization, IR806 further acts as an energy-transfer bridge, enabling efficient cascaded energy transfer and markedly enhanced NIR-II emission for the Cy3 sensitization (efficiency increased from ∼6% to 70%). This modular strategy affords tunable NIR-II emission from 1060 nm to 1525 nm, providing unprecedented flexibility in excitation and emission wavelength selection for advanced optical applications.