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

ABSTRACT 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.