Refractive index sensing using quasi-bound states in the continuum in silicon metasurfaces.

This work presents a bulk refractive index sensor based on quasi-bound states in the continuum (BICs) induced by broken symmetries in metasurfaces. The symmetry is broken by detuning the size and position of silicon particles periodically arranged in an array, resulting in multiple quasi-BIC resonances. We investigate the sensing characteristics of each of the resonances by measuring the spectral shift in response to changes in the refractive index of the surrounding medium. In addition, we reveal the sensing range of the different resonances through simulations involving a layer of deviating refractive index of increasing thickness. Interestingly, the resonances show very different responses, which we describe via the analysis of the near-field. This work contributes to the development of highly sensitive and selective BIC-based sensors that can be used for a wide range of applications.

Tunable emission from H-type supramolecular polymers in optical nanocavities.

H-type supramolecular polymers with preferred helicity and highly efficient emission have been prepared from the self-assembly of chiral tetraphenylene-based monomers. Implementation of the one-dimensional fibers into dielectric nanoparticle arrays allows for a significant reshaping of fluorescence due to weak light-matter coupling.

Enhancing Up-Conversion Luminescence Using Dielectric Metasurfaces: Role of the Quality Factor of Resonance at a Pumping Wavelength.

Photonic applications of up-conversion luminescence (UCL) suffer from poor external quantum yield owing to a low absorption cross-section of UCL nanoparticles (UCNPs) doped with lanthanide ions. In this regard, plasmonic nanostructures have been proposed for enhancing UCL intensity through strong electromagnetic local-field enhancement; however, their intrinsic ohmic loss opens additional nonradiative decay channels. Herein, we demonstrate that dielectric metasurfaces can overcome this disadvantage. A periodic array of amorphous-silicon nanodisks serves as a metasurface on which a layer of UCNPs is self-assembled. Sharp resonances supported by the metasurface overlap the absorption wavelength (λ = 980 nm) of UCNPs to excite them, resulting in the enhancement of UCL intensity. We further sharpen the resonances through rapid thermal annealing (RTA) of the metasurface, crystallizing silicon to reduce intrinsic optical losses. By optimizing the RTA condition (at 1000 °C for 20 min in N2/H2 (3 vol %) atmosphere), the resonance quality factor improves from 17.2 to 32.9, accompanied by an increase in the enhancement factor of the UCL intensity from 86- to over 600-fold. Moreover, a reduction in the intrinsic optical losses mitigates the UCL thermal quenching under a high excitation density. These findings provide a strategy for increasing light-matter interactions in nanophotonic composite systems and promote UCNP applications.

Room Temperature Exciton-Polariton Condensation in Silicon Metasurfaces Emerging from Bound States in the Continuum.

We show the first experimental demonstration of room-temperature exciton-polariton (EP) condensation from a bound state in the continuum (BIC). This demonstration is achieved by strongly coupling stable excitons in an organic perylene dye with the extremely long-lived BIC in a dielectric metasurface of silicon nanoparticles. The long lifetime of the BIC, mainly due to the suppression of radiation leakage, allows for EP thermalization to the ground state before decaying. This property results in a condensation threshold of less than 5 µJ cm-2, 1 order of magnitude lower than the lasing threshold reported in similar systems in the weak coupling limit.

Up-to-Five-Photon Upconversion from Near-Infrared to Ultraviolet Luminescence Coupled to Aluminum Plasmonic Lattices.

The incorporation of upconversion luminescence (UCL) materials into various plasmonic structures promotes light-matter interactions in nanophotonic systems. It has been experimentally demonstrated that UCL enhancement entailing two photons exhibits a quadratic dependence on the excitation intensity. However, in the field of plasmonics, there have not been sufficient studies on high-order multi-photon upconversion processes. We report up-to-five-photon UCL, wherein λ = 1550 nm near-infrared light is converted to 382 nm ultraviolet light, from core-inert shell nanoparticles coupled to aluminum plasmonic lattices. The five-photon UCL intensity of nanoparticles on the plasmonic lattice is over 800 times stronger than that on the flat glass. We demonstrate that the enhancement of UCL scales with the nth power of the local field enhancement for n-photon process. These findings give a strategy to obtain high-order multi-photon UPL with aluminum plasmonic nanostructures and can contribute to anti-counterfeiting application.

Collective plasmonic resonances enhance the photoluminescence of rare-earth nanocrystal films processed by ultrafast annealing.

Herein, we demonstrate that rapid thermal annealing allows achieving close-to-one photoluminescence quantum yield while preserving the transparency of rare-earth nanocrystal films, which further enables their integration with nanophotonics. The combination with periodic arrays of aluminum nanodisks that support collective plasmonic resonances leads to enhanced directional emission.

Controlling Exciton Propagation in Organic Crystals through Strong Coupling to Plasmonic Nanoparticle Arrays.

Exciton transport in most organic materials is based on an incoherent hopping process between neighboring molecules. This process is very slow, setting a limit to the performance of organic optoelectronic devices. In this Article, we overcome the incoherent exciton transport by strongly coupling localized singlet excitations in a tetracene crystal to confined light modes in an array of plasmonic nanoparticles. We image the transport of the resulting exciton-polaritons in Fourier space at various distances from the excitation to directly probe their propagation length as a function of the exciton to photon fraction. Exciton-polaritons with an exciton fraction of 50% show a propagation length of 4.4 µm, which is an increase by 2 orders of magnitude compared to the singlet exciton diffusion length. This remarkable increase has been qualitatively confirmed with both finite-difference time-domain simulations and atomistic multiscale molecular dynamics simulations. Furthermore, we observe that the propagation length is modified when the dipole moment of the exciton transition is either parallel or perpendicular to the cavity field, which opens a new avenue for controlling the anisotropy of the exciton flow in organic crystals. The enhanced exciton-polariton transport reported here may contribute to the development of organic devices with lower recombination losses and improved performance.

Random Lasing via Plasmon-Induced Cavitation of Microbubbles.

Numerous laboratories have observed random lasing from optically pumped solutions of plasmonic nanoparticles (NPs) suspended with organic dye molecules. The underlying mechanism is typically attributed to the formation of closed-loop optical cavities enabled by the large local field and scattering enhancements in the vicinity of plasmonic NPs. In this manuscript, we propose an alternative mechanism that does not directly require the plasmon resonance. We used high-speed confocal microspectroscopy to observe the photophysical dynamics of NPs in solution. Laser pulses induce the formation of microbubbles that surround and encapsulate the NPs, then sharp peaks <1.0 nm are observed that match the spectral signature of random lasing. Electromagnetic simulations indicate that ensembles of microbubbles may form optical corral containing standing wave patterns that are sufficient to sustain coherent optical feedback in a gain medium. Collectively, these results show that ensembles of plasmonic-induced bubbles can generate optical feedback and random lasing.

Evidence of the retardation effect on the plasmonic resonances of aluminum nanodisks in the symmetric/asymmetric environment.

A single metallic nanodisk is the simplest plasmonic nanostructure, but it is robust enough to generate a Fano resonance in the forward and backward scattering spectra by the increment of nanodisk height in the symmetric and asymmetric dielectric environment. Thanks to the phase retardation effect, the non-uniform distribution of electric field along the height of aluminum (Al) nanodisk generates the out-of-plane higher-order modes, which interfere with the dipolar mode and subsequently result in the Fano-lineshape scattering spectra. Meanwhile, the symmetry-breaking effect by the dielectric substrate and the increment of refractive index of the symmetric dielectric environment further accelerate the phase retardation effect and contribute to the appearance of out-of-plane modes. The experimental results on the periodic Al nanodisk arrays with different heights confirm the retardation-induced higher modes in the asymmetric and symmetric environment. The appearance of higher modes and blueshifted main dips in the transmission spectra prove the dominant role of out-of-plane higher modes on the plasmonic resonances of the taller Al nanodisk.

Evolutionary optimization of light-matter coupling in open plasmonic cavities.

Using a particle swarm optimization algorithm and finite-difference in time-domain simulations, we optimize the coupling strength between excitons in poly(3-hexylthiophene-2,5-diyl) (P3HT) and surface lattice resonances in open cavities defined by arrays of aluminum nanoparticles. Strong light-matter coupling and the formation of exciton-polaritons are demonstrated. Nanoparticle arrays with optimal dimensions have been fabricated and measured, validating the predictions by the numerical method. P3HT is a regioregular semiconducting polymer used as a donor material in acceptor-donor blends for organic photovoltaic applications. Our results demonstrate the efficacy of the proposed method for the optimization of light-matter coupling and its potential application for the enhanced performance of optoelectronic devices.

Broadband scattering by an aluminum nanoparticle array as a white pixel in commercial color printing applications.

Plasmonic color using metallic nanostructures has attracted considerable interest because of its subwavelength resolution and long sustainability. Significant efforts have been devoted to expanding the gamut of plasmonic color generation by tuning the composition, shape, and components in the primary pixel. In this study, we develop a novel and straightforward strategy for aluminum plasmonic color printing aimed at practical commercial applications. An array of aluminum nanodisks is designed for the broadband scattering of white pixels instead of the three primary colors. Examples presented include trademark and QR codes, which are common in the market of consumer advertising and item identification, that are encoded and fabricated in experiments with aluminum white color pixels to demonstrate feasibility. This simple and efficient strategy is compatible with cost-effective industrial fabrication methods, such as photolithography and nanoimprinting, and requires relatively simpler manufacturing procedures. Therefore, a new path is opened for the future with the extensive use of plasmonic color printing.

Home blood pressure on winter mornings could be exaggerated: A comparison with summer mornings.

PURPOSE: Self-measured blood pressure at home (HBP) is quite important for the management of hypertension. We hypothesized that winter HBP measured according to the recommendation of the guidelines, but not HBP measured inside bed before getting up, is elevated in response to cold ambient temperatures in winter. This study aimed to investigate differences in HBP measured before and after getting up in winter and summer.Methods: Hypertensive subjects whose blood pressure was stably controlled were enrolled (n = 46, 73 years). They were instructed to measure HBP while in bed just after waking (HBP-bed), in addition to the ordinary HBP measurement in the morning (HBP-morning) according to the guidelines. The mean value of HBP for 7 consecutive days before the day of a regular hospital visit was considered as the HBP of each subject, and characteristics of the winter and summer BPs were investigated.Results: HBP-morning was significantly higher (P < .001) in winter than in summer, but HBP-bed was lower in winter than in summer (P < .05). HBP-morning was significantly higher than HBP-bed in winter, while HBP-morning was not different from HBP-bed in summer, resulting in greater changes in HBP after getting up in winter than in summer (P < .0001). Changes in HBP after getting up were significantly correlated with serum creatinine levels and the urinary albumin-to-creatinine ratio.Conclusions: These findings imply that elevated HBP-morning in winter reflects the response of BP to cold after getting up. Seasonal profiles of HBPs before and after getting up should be noted in the management of hypertension.

Optical Responses of Localized and Extended Modes in a Mesoporous Layer on Plasmonic Array to Isopropanol Vapor.

Mesoporous silica features open and accessible pores that can intake substances from the outside. The combination of mesoporous silica with plasmonic nanostructures represents an interesting platform for an optical sensor based on the dependence of plasmonic modes on the refractive index of the medium in which metallic nanoparticles are embedded. However, so far only a limited number of plasmonic nanostructures are combined with mesoporous silica, including random dispersion of metallic nanoparticles and flat metallic thin films. In this study, we make a mesoporous silica layer on an aluminum nanocylinder array. Such plasmonic arrangements support both localized surface plasmon resonances (LSPRs) and extended modes which are the result of the hybridization of LSPRs and photonic modes extending into the mesoporous layer. We investigate in situ optical reflectance of this system under controlled pressure of isopropanol vapor. Upon exposure, the capillary condensation in the mesopores results in a gradual spectral shift of the reflectance. Our analysis demonstrates that such shifts depend largely on the nature of the modes; that is, the extended modes show larger shifts compared to localized ones. Our materials represent a useful platform for the field of environmental sensing.

Enhancing upconversion photoluminescence by plasmonic-photonic hybrid mode.

Upconversion photoluminescence (UCPL) of rare-earth ions has attracted much attention due to its potential application in cell labeling, anti-fake printing, display, solar cell and so forth. In spite of high internal quantum yield, they suffer from very low external quantum yield due to poor absorption cross-section of rare-earth ions. In the present work, to increase the absorption by rare earth ions, we place the emitter layer on a diffractive array of Al nanocylinders. The array is designed to trap the near infrared light in the emitter layer via excitation of the plasmonic-photonic hybrid mode, a collective resonance of localized surface plasmons in nanocylinders via diffractive coupling. The trapped near-infrared light is absorbed by the emitter, and consequently the intensity of UCPL increases. In sharp contrast to the pure localized surface plasmons which are bound to the surface, the hybridization with diffraction allows the mode to extend into the layer, and the enhancement up to 9 times is achieved for the layer with 5.7 µm thick. This result explicitly demonstrates that coupling the excitation light to plasmonic-photonic hybrid modes is a sensible strategy to enhance UCPL from a thick layer.

Enhanced absorption and photoluminescence from dye-containing thin polymer film on plasmonic array.

Thin films containing light emitters act as light-to-light converters that absorb the incident light and emit luminescence. This well-known phenomenon is photoluminescence (PL). When a photoluminescent film is notably thinner than the absorption length of emitters, it exhibits weak absorption of incident light. The absorption can be increased by depositing the thin film on a plasmonic array of metallic nanocylinders arranged with a specific periodicity. The array couples the incident light into the thin film, facilitating the plasmon-enhanced absorption by the emitters in the film. In this study, we demonstrate both experimentally and numerically the plasmon-enhanced absorption of a rhodamine 6G-containing film that is thinner than its absorption length using a periodic array of Al nanocylinders. The experimental results demonstrate that the spectrally integrated PL intensity is increased up to 3.78 times. In addition to enhanced absorption, the array is also found to diffract the PL into a direction determined by the periodicity, thereby facilitating the multiplied enhancement of PL. The combination of the two factors yields a PL intensity enhanced up to 10 times at a specific angle and wavelength. Numerical simulations combining the carrier kinetics with full-wave electromagnetics in the time-domain support the experimental observations.

Demonstration of temperature-plateau superheated liquid by photothermal conversion of plasmonic titanium nitride nanostructures.

A liquid can be heated up above its boiling point, known as superheating. In this metastable state, the liquid temperature keeps increasing as the liquid is being heated. In contrast, we experimentally demonstrate that the temperature of superheated water can be kept constant even at elevated heating power. Water heating is done by the photothermal conversion of plasmonic titanium nitride nanostructures on a sapphire substrate under the illumination of continuous wave laser irradiation. The temperature-constant superheating is also observed for ethylene glycol and 2-acetoxy-1-methoxypropane, and is attributed to the high thermal conductivity of the substrate. This unique superheating yet achieved by a simple method can be useful in optical trapping and various optical heating applications.

Hybrid Improper Ferroelectricity in (Sr,Ca)3Sn2O7 and Beyond: Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in n = 2 Ruddlesden-Popper Phases.

Hybrid improper ferroelectricity, which utilizes nonpolar but ubiquitous rotational/tilting distortions to create polarization, offers an attractive route to the discovery of new ferroelectric and multiferroic materials because its activity derives from geometric rather than electronic origins. Design approaches blending group theory and first principles can be utilized to explore the crystal symmetries of ferroelectric ground states, but in general, they do not make accurate predictions for some important parameters of ferroelectrics, such as Curie temperature ( TC). Here, we establish a predictive and quantitative relationship between TC and the Goldschmidt tolerance factor, t, by employing n = 2 Ruddlesden-Popper (RP) A3B2O7 as a prototypical example of hybrid improper ferroelectrics. The focus is placed on an RP system, (Sr1- xCa x)3Sn2O7 ( x = 0, 0.1, and 0.2), which allows for the investigation of the purely geometric (ionic size) effect on ferroelectric transitions, due to the absence of the second-order Jahn-Teller active (d0 and 6s2) cations that often lead to ferroelectric distortions through electronic mechanisms. We observe a ferroelectric-to-paraelectric transition with TC = 410 K for Sr3Sn2O7. We also find that the TC increases linearly up to 800 K upon increasing the Ca2+ content, i.e., upon decreasing the value of t. Remarkably, this linear relationship is applicable to the suite of all known A3B2O7 hybrid improper ferroelectrics, indicating that the  TC correlates with the simple crystal chemistry descriptor, t, based on the ionic size mismatch. This study provides a predictive guideline for estimating the TC of a given material, which would complement the convergent group-theoretical and first-principles design approach.

Dilated Cardiomyopathy with Eosinophilic Granulomatosis with Polyangiitis in Which Active Myocardial Inflammation Was Only Detected by Endomyocardial Biopsy.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare type of systemic vasculitis. Cardiac involvement is the main cause of death in patients with this disease. We herein report a case of congestive heart failure in a patient with EGPA. Neither 67Ga scintigraphy nor cardiac magnetic resonance imaging detected inflammation of the myocardium; however, myocardial biopsy revealed numerous infiltrating inflammatory cells, thereby fulfilling the criteria of inflammatory dilated cardiomyopathy. We improved the left ventricular systolic function by increasing the patient's prednisolone dosage. This case shows that in some cases the detection myocardial inflammation - which allows for appropriate therapy - may only be achieved by myocardial biopsy.

Collective plasmonic modes excited in Al nanocylinder arrays in the UV spectral region.

A periodic array of plasmonic nanocylinders can sustain both surface plasmon polaritons (SPPs) and optical diffraction in the plane of the array. Thus the optical energy can be efficiently trapped in the plane of the array, providing a good platform for controlling light. Plasmonic arrays have been investigated in the visible range, while studies in the ultraviolet (UV) range have been limited due to material-related restrictions and higher precision required for optical diffraction in the UV compared to that in the visible range. In this study, we fabricated periodic arrays of Al nanocylinders with periods comparable to optical wavelengths in the UV for simultaneous excitation of both SPPs and optical diffraction in the UV spectral region. We deposited UV-absorbing and highly luminous dielectric films on the arrays, observed enhanced photoluminescence of the film under UV laser excitation, and demonstrated that such periodic arrays can trap the UV light energy. Our findings show that periodic arrays of Al nanocylinders are useful for controlling UV light.

Evaluation of the reduction in central and peripheral arterial blood pressure following an oral glucose load.

The clinical significance of measuring central arterial blood pressure has been recently discussed. Although the postprandial reduction in blood pressure is well known, postprandial changes in central blood pressure have not been intensively studied. The present study investigated differences in the reduction of central and peripheral arterial blood pressure after administration of an oral glucose load.An oral glucose tolerance test (75 g) was performed in 360 participants in our physical checkup program. Brachial and central systolic blood pressures were assessed before and after the glucose load. Central arterial blood pressure was measured noninvasively using an automated device.The mean age was 53.6 ±â€Š8.2 years. Both brachial (127.9 ±â€Š17.7 to 125.0 ±â€Š16.3 mm Hg) and central arterial blood pressures were significantly decreased after an oral glucose load (118.9 ±â€Š17.9 to 112.8 ±â€Š16.8 mm Hg). The reduction in blood pressure was greater in central (7.3 ±â€Š11.5 mm Hg) than in brachial blood pressure measurements (3.4 ±â€Š11.3 mm Hg, P < .001). Extreme blood pressure reduction (>20 mm Hg) was recorded more frequently in central (n = 43, 12.3%) than brachial blood pressure measurements (n = 20, 5.6%).An oral glucose load decreases both central and brachial systolic blood pressure, with more pronounced effects on central blood pressure. Postprandial reductions in blood perfusion of the important organs such as the brain may be underestimated when postprandial BP reduction is assessed using brachial BP measurements.