Topology-driven energy transfer networks for upconversion stimulated emission depletion microscopy

Lanthanide-doped upconversion nanoparticles enable upconversion stimulated emission depletion microscopy with high photostability and low-intensity near-infrared continuous-wave lasers. Controlling energy transfer dynamics in these nanoparticles is crucial for super-resolution microscopy with minimal laser intensities and high photon budgets. However, traditional methods neglect the spatial distribution of lanthanide ions and its effect on energy transfer dynamics. Here, we introduce topology-driven energy transfer networks in lanthanide-doped upconversion nanoparticles for upconversion stimulated emission depletion microscopy with reduced laser intensities, maintaining a high photon budget. Spatial separation of Yb³⁺ sensitizers and Tm³⁺ emitters in 50-nm core-shell nanoparticles enhance energy transfer dynamics for super-resolution microscopy. Topology-dependent energy migration produces strong 450-nm upconversion luminescence under low-power 980-nm excitation. Enhanced cross-relaxation improves optical switching efficiency, achieving a saturation intensity of 0.06 MW cm^-2 under excitation at 980 nm and depletion at 808 nm. Super-resolution imaging with a 65-nm lateral resolution is achieved using intensities of 0.03 MW cm^-2 for a Gaussian-shaped excitation laser at 980 nm and 1 MW cm^-2 for a donut-shaped depletion laser at 808 nm, representing a 10-fold reduction in excitation intensity and a 3-fold reduction in depletion intensity compared to conventional methods. These findings demonstrate the potential of harnessing topology-dependent energy transfer dynamics in upconversion nanoparticles for advancing low-power super-resolution applications.