Engineering the Upconversion Nanoparticle Excitation Wavelength: Cascade Sensitization of Tri‐doped Upconversion Colloidal Nanoparticles at 800 nm

Cascade‐sensitized 800 nm excited tri‐doped upconversion nanoparticles (UCNPs) are developed for the first time. This novel class of UCNPs employ Nd3+ as an 800 nm photon sensitizer and Yb3+ as a bridging ion, and show strong upconversion emission without photobleaching. They outperform classical 980 nm excited UCNPs in regard to significantly decreased NIR photon absorption in water and decreased laser‐induced water heating effects.