Photoswitching the injected energy flux via core-sensitized energy migration upconversion for emission-varying STED microscopy

Stimulated emission depletion (STED) microscopy achieved with lanthanide-doped upconversion nanoparticles (UCNPs) exhibits many outstanding advantages such as low-power illumination, near-infrared (NIR) excitation, and high photostability. However, the available types of UCNP-STED probes are very limited and rely greatly on the specific depletion mechanism. Here, by combining the STED and the energy migration upconversion processes, emissions of Tb 3+ , Eu 3+ , Dy 3+ , and Sm 3+ distributed in the shell can all be depleted by interrupting the injected energy flux from the Tm 3+ -doped core nanoparticles. With the merit of the proposed strategy, new types of UCNP-STED probes are demonstrated to perform emission-varying STED imaging with one single, fixed pair of low-power NIR continuous wave lasers.