Spatially Partitioned Doping in Upconversion Nanoparticles for Efficient FRET‐Based ClO ⁻  Detection and Inflammation Grading Imaging

ABSTRACT Traditional low‐concentration lanthanide co‐doped upconversion systems face challenges due to random dopant distributions, leading to complex nonradiative decay pathways and uncontrolled donor‐acceptor distances in upconversion nanoparticles, which significantly limit their luminescence brightness and utility in Förster resonance energy transfer (FRET)‐based applications. This work proposes a universally applicable spatially partitioned doping structure (LiYbF 4 @LiYF 4 : A 3+ ) featuring a 100% Yb 3+ core for ultrafast Yb 3+ –Yb 3+ energy migration and interfacial dipole–dipole coupling to A 3+ , enhancing the luminescence brightness and FRET efficiency by simultaneously suppressing surface quenching pathways and detrimental back‐energy transfer, as well as confining activators spatially. Combined with Monte Carlo simulations, we reveal the microscopic energy migration‐transfer mechanism in partitioned structures, overcoming the limitations of conventional rate equations and establishing a programmable materials design platform that provides a theoretical basis and design tools.