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Spectral Tunable Room Temperature Superfluorescence

Kai Han, H Huang, Hao Liu, Ye Huang, Mingchen Li, Wenda Cui, Changqing Song, Zhongjie Xu, Tongcheng Yu, Chuan Guo

Published Jul 17, 2026• 0 citations
Publisher

Abstract

Abstract Superfluorescence (SF), a collective quantum phenomenon originating from correlated emitters, has historically required cryogenic temperatures or magnetic fields and been limited to narrowband Stokes-shifted emission. Although room-temperature SF has recently been realized in lanthanide-doped systems, active control over its spectral properties remains significant challenges. Here, we propose a state-entropy framework to reveal the coherence evolution and macroscopic dipole correlation in upconversion systems, providing a theoretical foundation for manipulating superradiant processes across a broad spectral range. Based on this framework, we designed an excitation strategy to decouple and regulate the distinct energy-population pathways, specifically excited-state absorption and energy transfer upconversion/cross-relaxation, in ~23 nm NaNdF₄ nanocrystals at room temperature. This approach enables multi-stage upconversion superfluorescence with tunable oscillations and nanosecond to sub-microsecond lifetimes. Most importantly, it substantially extends the accessible spectral window of room-temperature UC-SF from the previously reported two orange-red bands to six distinct emission bands covering the ultraviolet to the red (384-659 nm), accompanied by a wide-gamut wavelength-synthesized color evolution. Furthermore, cascaded excitation enables real-time emission enhancement by restoring the macroscopic dipoles correlation during the SF decay phase. This work demonstrates principles that may inform future designs of on-chip ultrafast optical computing based on spectrally tunable SF with encodable photonic emission.

DOI
10.21203/rs.3.rs-10365592/v1

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Abstract Superfluorescence (SF), a collective quantum phenomenon originating from correlated emitters, has historically required cryogenic temperatures or magnetic fields and been limited to narrowband Stokes-shifted emission. Although room-temperature SF has recently been realized in lanthanide-doped systems, active control over its spectral properties remains significant challenges. Here, we propose a state-entropy framework to reveal the coherence evolution and macroscopic dipole correlation in upconversion systems, providing a theoretical foundation for manipulating superradiant processes across a broad spectral range. Based on this framework, we designed an excitation strategy to decouple and regulate the distinct energy-population pathways, specifically excited-state absorption and energy transfer upconversion/cross-relaxation, in ~23 nm NaNdF₄ nanocrystals at room temperature. This approach enables multi-stage upconversion superfluorescence with tunable oscillations and nanosecond to sub-microsecond lifetimes. Most importantly, it substantially extends the accessible spectral window of room-temperature UC-SF from the previously reported two orange-red bands to six distinct emission bands covering the ultraviolet to the red (384-659 nm), accompanied by a wide-gamut wavelength-synthesized color evolution. Furthermore, cascaded excitation enables real-time emission enhancement by restoring the macroscopic dipoles correlation during the SF decay phase. This work demonstrates principles that may inform future designs of on-chip ultrafast optical computing based on spectrally tunable SF with encodable photonic emission.
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 antiStokes 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, and biophotonics, especially in deep tissue ultra-fast dynamic sensing.
Abstract Photon upconversion through lanthanide-doped nanoparticles is of great significance for various applications. However, the current development of upconversion nanoparticles is hindered by the low quantum efficiency and long radiative lifetimes of lanthanide ions, restricting their applications in time-dependent nanophotonics. Herein, we report ultrafast upconversion superfluorescence with a lifetime of sub-2.5 ns in lanthanide-doped nanoparticles at room temperature. Upon excitation with an 800-nm fs-pulsed laser, we achieve a large number ( N = 912) of correlated dipoles in Nd 3+ -concentrated nanoparticles, resulting in collective coherent emission with two orders of magnitude amplification in intensity and more than three orders of magnitude improvement in the radiative decay rate. Furthermore, we demonstrate that the control of excitation power and emitting sample length enables the lifetime manipulation of upconversion emission in a wide range from μs to sub-ns, accompanied by the typical superfluorescence signature of Burnham-Chiao ringing. These findings may benefit applications in many advanced technologies such as quantum counting and high-speed super-resolution bioimaging.
Superfluorescence (SF) in lanthanide doped upconversion nanoparticles (UCNPs) is a room-temperature quantum phenomenon, first discovered in 2022. In a SF process, the many emissive lanthanide ions within a single UCNP are coherently coupled by an ultra-short (ns or fs) high-power excitation laser pulse. This leads to a superposition of excited emissive states which decrease the emissive lifetime of the UCNP by a factor proportional to the square of the number of lanthanide ions which are coherently coupled. This results in a dramatic decrease in UCNP emission lifetime from the microsecond regime to the nanosecond regime. Thus SF offers a tantalizing prospect to achieving superior upconversion photon flux in upconversion materials, with potential applications such as imaging and sensing. This perspective article contextualizes how SF-UCNPs can be regarded as a second generation quantum technology, and notes several challenges, opportunities, and open questions for the development of SF-UCNPs.
Superfluorescence is a collective emission from several quantum emitters that initially have random phases and are then synchronized through vacuum field interactions. Despite its fascinating prospects in quantum information processing, optical computing and advanced photonic devices, a key challenge in harnessing superfluorescence is alleviating its reliance on cryogenic conditions. Recently, room-temperature superfluorescence has been successfully achieved using upconverted nanoparticles and quasi two-dimensional lead halide perovskites. These approaches, however, are restricted to a few specific material designs and unsuitable for wide promotion. Here, we report a universal strategy to elevate the operating temperature of superfluorescence. We reveal that the symmetry-protected optical bound state in the continuum (BIC) can break the size limitation of superfluorescence (λ^3) and correlate distant but similar emitters without violating the selection rules, significantly accelerating synchronization process and promoting the possibility of room-temperature superfluorescence. This effect has been experimentally verified using a series of BIC metasurfaces made of different lead halide perovskites. Key features such as the quadratic increase in transient peak intensity and the reduction in pulse width and build-up time at the BIC wavelength confirm the realization of room-temperature superfluorescence that is absent in the pristine material. A theoretical model is also built to explain the experimental observations. This research demonstrates that the operating temperatures of coherent macroscopic states can be effectively improved by artificial field, paving a critical step towards constructing building blocks for optical and quantum applications.
Superfluorescence (SF) in lanthanide doped upconversion nanoparticles (UCNPs) is a room-temperature quantum phenomenon, first discovered in 2022. In a SF process, the many emissive lanthanide ions within a single UCNP are coherently coupled by an ultra-short (ns or fs) high-power excitation laser pulse. This leads to a superposition of excited emissive states which decrease the emissive lifetime of the UCNP by a factor proportional to the square of the number of lanthanide ions which are coherently coupled. This results in a dramatic decrease in UCNP emission lifetime from the μs regime to the ns regime. Thus SF offers a tantalizing prospect to achieving superior upconversion photon flux in upconversion materials, with potential applications such as imaging and sensing. This perspective article contextualizes how SF-UCNPs can be regarded as a second generation quantum technology, and notes several challenges, opportunities, and open questions for the development of SF-UCNPs.
Superfluorescence (SF) originates from the spontaneous buildup of macroscopic coherence among initially incoherent emitters. Its formation is highly sensitive to dephasing and collective coupling in the system. Here, we observe room-temperature SF in CdS/CdSe/CdS spherical quantum wells. With increasing excitation fluence, the peak emission intensity shows a nearly quadratic increase, while the emission delay and pulse width decrease. Burnham-Chiao ringing is also observed, revealing the characteristic collective radiation dynamics of SF. Further experiments with stripe excitation show that shortening the excitation length L changes the dominant fast emission from amplified spontaneous emission to SF. More importantly, the threshold for SF under stripe excitation is only about 1/30 of that under spot excitation. This large reduction indicates that the propagating radiation field provided by spatially extended excitation favors the buildup of cooperative coherence. These findings provide direct experimental evidence for understanding ultrafast many-body coherence dynamics and offer a route to actively control collective emission at room temperature.