NIR‐I‐Responsive Single‐Band Upconversion Emission through Energy Migration in Core–Shell–Shell Nanostructures

Here we report a new strategy to tune both excitation and emission peaks of upconversion nanoparticles (UCNPs) into the first infrared biowindow (NIR‐I, 650–900 nm) with high NIR‐I‐to‐NIR‐I upconversion efficiency. By introducing the sensitizer Nd3+, activator Er3+, energy migrator Yb3+ and energy manipulator Mn2+ into specific region to construct proposed energy migration processes in the designed core–shell–shell nanoarchitecture, back energy transfer (BET) from activator to sensitizer or migrator can be greatly blocked and the NIR‐to‐red upconversion emission can be efficiently promoted. Consequently, BET‐induced photon quenching and the undesired green‐emitting radiative transition are entirely eliminated, leading to high‐efficiency single‐band red upconversion emission upon 808 nm NIR‐I laser excitation. Our findings provide insights into fundamental lanthanide interactions and advance the development of UCNPs for bioapplications with techniques that overturn traditional limitations. To regulate the excitation and emission peaks of upconversion nanoparticles (UCNPs) into the NIR‐I bio‐window, a new type of high‐efficiency NIR‐I‐to‐NIR‐I UCNPs has been developed based on the elaborate combination of high‐content Nd3+ sensitization, Yb‐mediated energy migration, Mn2+‐assisted exchange‐energy transfer and core‐multishell construction that exhibit intense single‐band red luminescence upon 808 nm NIR‐I laser excitation.