Collective blinking of upconversion emission in lanthanide-doped nanocrystals

Abstract Fluorescence blinking, often regarded as a limitation for stable emitters, can enable super-resolution localization microscopy and serve as a versatile reporter of the photophysical states of quantum emitters and their interactions with local environment. However, conventional blinking emitters are typically single quantum systems with Stokes-shifted fluorescence, making them susceptible to autofluorescence background, weak signal, and irreversible photodegradation under prolonged excitation. In contrast, single lanthanide-doped upconversion nanocrystals are effectively background-free anti-Stokes emitters and demonstrate robust resistance to photodegradation, yet they are generally considered non-blinking owing to the presence of a large ensemble of uncorrelated emitting lanthanide ions within a single nanocrystal. Here we report the discovery and control of collective blinking in the upconversion luminescence of thousands of lanthanide ions within a single nanocrystal. The blinking exhibits a high on–off intensity ratio up to 25, persists for over 15 h (over 10,000 cycles) without discernible photodegradation, and can be reversibly controlled by adjusting the excitation power. We propose a universal, activator-independent mechanism for the upconversion blinking, in which a single quencher, likely generated via a cooperative multi-ion process, intercepts delocalized excitation energy within the Yb 3+ sensitizer network and darkens the whole nanocrystal. Benefiting from the high-contrast, long-term photostable blinking and background-free emission, we achieve low-power super-resolution localization microscopy that resolves and localizes individual nanocrystals in dense aggregates with a mean resolution of 12.6 nm and a mean localization precision of 1.2 nm. This work establishes a general strategy to realize and control collective blinking in photostable multi-emitter nanosystems, opening new opportunities in nanoscience, bioimaging, and quantum technologies.