Room Temperature Anti-Stokes Shifted Superfluorescence*

Superfluorescence (SF) is a unique optical phenomenon that consists of an ensemble of emitters coupling collectively to produce a short but extremely intense burst of light. SF has also only been realized in extreme conditions (at low temperatures of around 6 K). Moreover, no anti-Stokes shift SF has been discovered in either an ensemble of nanoparticles or at bulky crystal levels. We report on a new lanthanide-doped upconversion nanoparticles (UCNPs) as a medium to achieve cavity free anti-Stokes shifted SF at room temperature, culminating in rapid, intense, and narrow spectral peaks of upconverted SF. This is the first time that SF has been discovered in a single nanocrystal regime and is the smallest-ever SF media. We observed the resultant UCNP SF with an extremely narrow spectral width at single nanocrystal-level (full-width at half-maximum, FWHM = 2 nm), and to have a significantly shortened lifetime (τ = 46 ns, 10,000-fold accelerated radiative decay, when compared to the lifetime of τ = 455.8 μs of normal upconversion luminescence (UCL). The significantly up-speeded upconverted SF lifetimes at tens of nanoseconds scale should break through the key limitation in normal UCL, and enable high speed bioimaging without compromising imaging quality.