Elimination of Photon Quenching by a Transition Layer to Fabricate a Quenching‐Shield Sandwich Structure for 800 nm Excited Upconversion Luminescence of Nd 3+ ‐Sensitized Nanoparticles

Nd3+-sensitized quenching-shield sandwich-structured upconversion nanoparticles are reported, which exhibit highly efficient upconversion photoluminescence under excitation by an 800 nm continuous-wave laser. The transition-layer structure is essential to bridge energy transfer from the sensitizer to the activator and simultaneously block energy back-transfer from the activator to the sensitizer. These 800 nm-excited upconversion nanoparticles are a key step toward the development of upconversion nanophosphors for biological applications.