Room Temperature Single Nanocrystal Anti-Stokes Shifted Superfluorescence

Abstract: Superfluorescence (SF) is a unique quantum mechanical behavior arising from the self-organization between emitters, thus forming a cooperatively coupled assembly. In contrast to isotropic spontaneous emission or normal fluorescence, SF produces a short but intense burst of light, which makes it ideal for a wide variety of applications in photonics, electronics, and optical computing. Due to the prerequisite of cooperative emitter coupling, SF has been conventionally observed under cryogenic conditions in limited systems, such as atomic gases, and a few bulk material systems. Here we show lanthanide-doped upconversion nanoparticles (UCNPs) as a medium to achieve anti-Stokes shift SF at room temperature. We observe such room temperature upconverted SF in a few nanoparticles assembly, and in a single nanoparticle, the latter of which is the smallest-ever SF media. In particular, we found that under near-infrared light (800 nm) excitation, each lanthanide ion in a single UCNP nanocrystal can be considered as an individual emitter that interact with each other to establish coherence and to enable anti-Stokes shift SF emission. More importantly, when compared to the microsecond scale slow lifetime of typical upconversion luminescence, the upconverted SF has a 10,000-fold accelerated lifetime (τ = 46 ns of SF v.s. τ = 455.8 μs of normal upconversion luminescence). When taken together, the observed ultrafast upconverted SF in both UCNP assembly and single nanocrystals under NIR light excitations, is uniquely well-positioned for applications in on-chip optical computing, optical timers, and biophotonics, especially in deep tissue ultra-fast dynamic sensing.

Bio: Following completion of a Ph.D. at the University of Cambridge, UK, 2004, Shuang Fang Lim served in a postdoctoral Research Position at Princeton University from 2004-2008.

She is the first to report on the observation of solid state anti-Stokes shifted room temperature superfluorescence (SF) in the smallest-ever observed SF media at the single nanocrystal-level. Prior to her findings, SF has only been realized in extreme conditions (at low temperatures of around 6 K), thus limiting the feasibility of its practical applications. Her research also showed that the nanocrystals can produce a pulse sequence with a fixed time interval, known as Burnham-Chiao ringing, indicating that they could potentially become quantum optical timers.

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