Dr. Kai Huang Profile

Dr. Kai Huang

at Univ of Massachusetts Chan Medical School

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Publications (3)

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Proceedings Article | 3 October 2022 Paper

Room temperature single nanocrystal anti-stokes shifted superfluorescence

Kory Green, Kai Huang, Gang Han, Hans Hallen, Shuang Fang Lim

Proceedings Volume 12228, 1222802 (2022) https://doi.org/10.1117/12.2634447

KEYWORDS: Neodymium, Nanocrystals, Upconversion, Luminescence, Ions, Doping, Optical computing, Erbium, Photonics, Near infrared

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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.

Proceedings Article | 1 August 2021 Presentation + Paper

Unidirectional optical mechano-sensing with upconversion nanoparticles

Kory Green, Brandon Long, Kai Huang, Gang Han, Hans Hallen, Shuang Fang Lim

Proceedings Volume 11825, 118250V (2021) https://doi.org/10.1117/12.2597041

KEYWORDS: Upconversion, Nanoparticles, Ytterbium, Nanocrystals, Erbium, Crystals, Biosensing, Haptic technology, Fiber optics, Fiber couplers

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Cells respond to forces, and their quantification can potentially inform on the role of mechanics in cell development, differentiation, tissue repair and homeostasis. Other force sensitive processes include cancer cell metastasis, heart development in embryos driven by fluid forces, and individual cell response to tension by enhancing microtubule growth and connections. Development of current mechano-sensing approaches has not yielded many options, especially in directional force measurement. We present a sharpened fiber-based approach for uniaxial forces. An upconversion nanoparticle (UCNP) is mounted on the tip of the fiber and optically accessed through the fiber, which is manipulated as a probe. In UCNPs, the modification of the crystal field via mechanical forces result in changes in emission intensity, spectral shifts, upconversion luminescence (UCL) lifetime and ratiometric UCL response. We report on a discernably large peak shift of between 5-10 nm, and an apparent phase transition, with increasing amount of applied force in the micro Newton regime, in a single direction. Moreover, the peak shift is linear to the applied compression force. We investigate the influence of the UCNP force sensing process using Raman spectroscopy.

Proceedings Article | 1 August 2021 Presentation + Paper

Single nanocrystal anti-stokes shifted superfluorescence

Kory Green, Kai Huang, Gang Han, Shuang Fang Lim

Proceedings Volume 11825, 118250U (2021) https://doi.org/10.1117/12.2597043

KEYWORDS: Neodymium, Nanocrystals, Erbium, Upconversion, Ytterbium, Ultrafast imaging, Nanoparticles, Luminescence, Ions, Nanoelectronics

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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 lanthanidedoped 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 upspeeded upconverted SF lifetimes at tens of nanoseconds scale should break through the key limitation in normal UCL. This will open up the opportunity to carry out high speed bioimaging using upconversion nanoparticles without compromising the imaging quality. In addition, our ultrafast upconverted SF will achieve fine temporal resolution control of highly dynamic physiological processes that have been constrained by normal UCL.

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