Superfluorescence (SF) is a unique quantum optics phenomenon arising from the assembly of self-organized and cooperatively coupled emitters. SF produces a short and intense burst of light, ideal for various applications in nanophotonics and optical computing. However, due to the prerequisite for cooperative emitter coupling, SF was conventionally observed in a Stokes-shifted manner under cryogenic conditions in limited systems (for example, atomic gases and perovskite-nanocrystal superlattices). Here we show that room-temperature anti-Stokes-shift SF is achieved in a few randomly assembled or in a single lanthanide-doped upconversion nanoparticle. Moreover, upconverted SF has a 10,000-fold accelerated nanosecond lifetime (τ = 46 ns of SF versus τ = 455.8 μs for normal upconversion luminescence), overcoming the slow decay of conventional upconversion systems. Therefore, the conceptual room-temperature anti-Stokes-shift SF not only lays the foundation for ultrafast upconversion but it also paves a straightforward way to a wide variety of applications that have been limited by the existing SF system.

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