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.