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.