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

Utilizing long-lived, ladder-like energy levels of Ln 3+, the intensity of anti-Stoke's luminescence of UCNPs is orders of magnitude more potent compared with those of conventional synthetic dyes or quantum dots (QDs).