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. Despite our recently published works showing that room temperature anti-Stokes shifted SF were achieved in a few randomly assembled or even single lanthanide-doped upconversion nanoparticle (UCNP), the coupling required to produce and optimize Burnham-Chiao ringing (echoing of pulses) is not understood. Such ringing could be particularly useful to provide timing and multiplexing in potential applications as an alternative light source device. We previously found a lack of Burnham Chiao ringing in single nanocrystals, but strong ringing in a random cluster. The ordered assembly of these crystals will not only create a SF superburst, but also enable understanding of the periodicity of the Burnham Chiao ringing. This work explores SF microrod (MR) and microplate (Mplate), with enhanced SF performance and the closely spaced assembly of MR/Mplate result in a greater active volume, which gives rise to greater Burnham-Chiao ringing.
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 biophotonics, 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.
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. Despite our recently published works showing that room temperature anti-Stokes shifted SF were achieved in a few randomly assembled or even single lanthanide-doped upconversion nanoparticle (UCNP), the coupling required to produce and optimize Burnham-Chiao ringing (echoing of pulses) is not understood. Such ringing could be particularly useful to provide timing and multiplexing in potential applications as an alternative light source device. We previously found a lack of Burnham Chiao ringing in single nanocrystals, but strong ringing in a random cluster. The ordered assembly of these crystals will not only create a SF superburst, but also enable understanding of the periodicity of the Burnham Chiao ringing. This work explores SF microrod (MR), with enhanced SF performance and the closely spaced assembly of MR result in a greater active volume, which gives rise to greater reabsorption of the initial emission, which is then re-emitted, leading to greater oscillatory fluorescence or Burnham Chiao ringing. We also correlate the MR dimension and orientation with the corresponding SF spectral properties.
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.
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.
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.
The combination of resonance Raman with deep UV excitation, DUVRR, gives greater selectivity and eliminates background fluorescence, enabling sensitive detection of UV absorbing nucleotide bases and amino acids. We demonstrate this combination with our 3D nanopore structure design. Resonance Raman is specific to a molecule absorbing at the excitation, while plasmon resonance of a small, shape-, index- and size- tuned metal dramatically increases the electric field strength in the active region. The 3D nanostructure exploits nanopores that retain the advantages of small-gap antennas but increases the ease of fabrication, availability, and detection volume compared to conventional plasmon-based designs, such as gaps between two particles, by being inherently single particle, with edge enhancement open to diffusion, and by possessing a large number of pores per particle. We show the large local field enhancement (hot spots) of the pores. Comparisons with an Al and silica coated/uncoated microsphere template with/without nanopores clearly show a significant blue shift of the 280 nm peak to (the more useful) 265 nm, in the presence of a hollow sphere with nanopores. Raman measurement of Tryptophan on an aluminum nanopore structure with excitation from our tunable OPO system in the visible and deep UV region indicate visible excitation causes more fluorescence and is less specific for the tryptophan, even displaying a Raman peak at the silicon substrate, while the deep-UV Raman spectra, at an energy close to the nanopore resonance, shows no substrate signal and peaks with close correlation to the known tryptophan vibrations.
Methylation in DNA is a controlling factor in gene expression, embryonic development, and has been found to be important in infections and cancer. From a basic biology point of view, great heterogeneity has been found in methylation levels within tissues, so questions arises as to how and why. We show that methylated-DNA (m-DNA) can be distinguished from non-methylated (n-DNA) with nano-bowtie- and resonance- enhanced Raman spectra. By tuning the bowtie antenna to the resonance wavelength, both gains can be realized. Two additional Raman peaks in the 1200 – 1700 cm-1 band appear with methylation: one at 1239 cm-1 and the other at 1639 cm-1; a weak peak near 1000 cm-1 also appears with methylation. We also find that the two spectral features, although the latter with slight modification, can be used to distinguish the methylation state even when the DNA is denatured, as we show when we induce crystallization of the salts in the solution with increased excitation power, or allow it to happen naturally via solvent evaporation, and the DNA is trapped within the salt crystals. A comparison between liquid/solution to dried/denatured state m-DNA shows a general broadening of the larger lines and a transfer of spectral weight from the ~1470 cm-1 vibration to two higher energy lines. The applicability of the resonance-Raman in these spectra is shown by demonstrating that the Raman spectral characteristics hardly change as the Raman resonance in excitation wavelength is approached. Finally, we comment on real signal gain in this double-resonance system.
Infrared excited and visible emitting upconverting nanoparticles show potential applications in the fields of photovoltaics, and in single molecule bio-imaging. We show enhanced upconversion luminescence, of up to 50-fold, at the single particle level, via subwavelength interference of the infrared excitation and visible emission. Single particle upconverted spectra and time-resolved decay, correlated with AFM, show enhanced emission at 545nm and 650 nm, whereby the magnitude of the enhancement is dependent on the thickness of the interference layer, and on the excitation intensity. We correlate our experimental results with finite element modeling showing both enhanced excitation and emission as a function of the interference layer thickness.
Photothermal treatment is a valuable part of cancer therapies, in which the temperature of the heated region must rise to at least 40-45°C for protein destruction to occur[1, 2]. In practice, heating temperature distributions are typically non-uniform, resulting in incomplete kill of cancer cells. Gold nanorods (AuNRs) show strong absorption in the near infrared which leads to a strong plasmonic photothermal (PPT) effect. However, basic scientific understanding of AuNR local temperature and heat transfer to local surroundings has not been investigated in detail. In our study, the near infrared (NIR) excited Upconversion nanoparticle (UCNP)-AuNR nanostructure combines the powerful diagnostic and thermal sensing capacity of UCNPs, with the known therapeutic property of AuNRs. We show enhanced upconverted emission with AuNRs coupling, improving diagnostic capacity of the construct. We demonstrate mapping of the temperature profile within tumor tissue phantom medium, at high spatial and temporal sensitivity.
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