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Dielectric nanostructures have demonstrated optical antenna effects due to Mie resonances. Previous work has exhibited enhancements in absorption, emission rates and directionality with practical limitations. In this paper, we present a Si mix antenna array to achieve a trifecta enhancement of ∼1200-fold with a Purcell factor of ∼47. The antenna design incorporates ∼10 nm gaps, within which fluorescent molecules strongly absorb the pump laser energy through a resonant mode. In the emission process, the antenna array increases the radiative decay rates of the fluorescence molecules via a Purcell effect and provides directional emission through a separate mode. This work could lead to novel CMOS-compatible platforms to enhance fluorescence for biological and chemical applications.

While structural colors are ubiquitous in nature, saturated reds are mysteriously absent. This long-standing problem of achieving Schrödinger’s red demands sharp transitions from “stopband” to a high-reflectance “passband” with total suppression of higher-order resonances at blue/green wavelengths. Current approaches based on nanoantennas are insufficient to satisfy all conditions simultaneously. Here, we designed Si nanoantennas to support two partially overlapping quasi–bound-states-in-the-continuum modes with a gradient descent algorithm to achieve sharp spectral edges at red wavelengths. Meanwhile, high-order modes at blue/green wavelengths are suppressed via engineering the substrate-induced diffraction channels and the absorption of amorphous Si. This design produces possibly the most saturated and brightest reds with ~80% reflectance, exceeding the red vertex in sRGB and even the cadmium red pigment. Its nature of being sensitive to polarization and illumination angle could be potentially used for information encryption, and this proposed paradigm could be generalized to other Schrödinger’s color pixels.

Bound-states-in-the-continuum (BIC) is an emerging concept in nanophotonics with potential impact in applications, such as hyperspectral imaging, mirror-less lasing, and nonlinear harmonic generation. As true BIC modes are non-radiative, they cannot be excited by using propagating light to investigate their optical characteristics. In this paper, for the 1st time, we map out the strong near-field localization of the true BIC resonance on arrays of silicon nanoantennas, via electron energy loss spectroscopy with a sub-1-nm electron beam. By systematically breaking the designed antenna symmetry, emissive quasi-BIC resonances become visible. This gives a unique experimental tool to determine the coherent interaction length, which we show to require at least six neighboring antenna elements. More importantly, we demonstrate that quasi-BIC resonances are able to enhance localized light emission via the Purcell effect by at least 60 times, as compared to unpatterned silicon. This work is expected to enable practical applications of designed, ultra-compact BIC antennas such as for the controlled, localized excitation of quantum emitters., The optically inaccessible bound-states-in-the-continuum (BIC) is probed via sub-1-nm electron beam, where the cathodoluminescence emissions from Si nanoantenna arrays are able to reveal the coherent interaction length of quasi-BIC resonances.

A Novel scalable approach using Terahertz (THz) waves together with the electromagnetic field simulation was applied to investigate four rabbits of eight rabbit corneas in vivo. One eye of each rabbits' corneas was edema induced; the other eye of the corneas served as the control. The simulation revealed the propagation of THz waves at a certain distance along the sub-surface of the cornea. THz spectra have been collected close to the corneal surface by deviating the direct reflection of the THz beam for the edema cornea, the reflected wave intensity for edema corneas is generally larger compared with the control cornea. Upon edema becomes severe at the end of the observation, the reflected wave intensities obtained by detector corresponding to the corneal deep stroma layer approach to the same value for all observed corneas. Good correlation is observed between central corneal thickness measurements and THz wave reflection signal intensities. Our results demonstrated that THz spectroscopy technique could obtain the information from different corneal sublayers.

Raman mapping was used to determine the lipid distribution inside human mesenchymal stem cells during induced adipogenesis by monitoring C-H stretching bands of the fats inside the lipid droplets. By incorporating deuterated glucose into the cell culture medium during induction it was possible to distinguish whether or not downstream metabolites, either in lipid droplets or in the cytoplasm, had been formed before or after the adipogenic cascade, because C-D stretching bands are 1/√2 shifted compared to the C-H bands. Thus, metabolites formed after the initiation of the process displayed both C-H and C-D stretching bands and so were forming during induced adipogenesis rather than prior to it. With the ability to distinguish small putative lipid drops formed by the induction of adipogenesis from those pre-formed in the cell, it was possible to analyze spectral changes occurring in the droplets at the earliest stages of adipogenesis. There were two key findings. Firstly, Raman spectra of lipid droplets evolved over time, suggesting that their composition at the early stages was not the same as at the later stages. Secondly, it was apparent that the proportion of unsaturated fats in droplets was higher at early stages than it was at later stages, suggesting that unsaturated fats arrive in the droplets faster than saturated ones.

Charge generation and recombination dynamics in organic photovoltaic bulk heterojunction films comprising the donor polymer, PDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene}), blended with the fullerene acceptor, PC71BM ([6,6]-phenyl C71-butyric acid methyl ester), have been studied. The charge-carrier generation process was studied using femtosecond transient absorption, and it was found that the efficiency of charge generation is not dominated by geminate recombination but rather is limited by exciton diffusion in the films. Highly sensitive nanosecond transient absorption (ns-TA) and time-resolved microwave conductivity (TRMC) were used to study charge recombination. From ns-TA measurements, we obtained a recombination rate constant of 1 × 10–9 cm3 s–1 and found that charge recombination is limited by the diffusion of charge carriers (Langevin-type recombination). TRMC signals were comparable with ns-TA on shorter time scales. However, in contr...

Polymer-grafted porous hollow silica nanoparticles prepared by reversible addition-fragmentation chain transfer polymerisation have an upper critical solution temperature of 45 °C. Conjugation of 5 nm gold nanoparticles onto polymer-grafted porous hollow silica nanoparticles enables remarkable specific photothermally-induced controlled release of encapsulated Rhodamine B by laser-stimulation at physiological temperature.

Electron transfer dynamics in the oxide layers of the working electrodes in both dye-sensitized solar cells and photocatalysts greatly influences their performance. A proper understanding of the distribution of surface and bulk energy states on/in these oxide layers can provide insights into the associated electron transfer processes. Metal ions like Iron (Fe), Copper (Cu) and Tin (Sn) doped onto TiO2 have shown enhanced photoactivity in these processes. In this work, the structural, optical and transient properties of Fe, Cu and Sn doped TiO2 nanocrystalline powders have been investigated and compared using EDX, Raman spectroscopy, X-ray Photoelectron spectroscopy (XPS), and Transient Absorption spectroscopy (TAS). Surface free energy states distributions were probed using Electrochemical Impedance spectroscopy (EIS) on Dye Sensitized Solar Cells (DSSC) based on the doped TiO2 photoanodes. Raman and XPS Ti2p3/2 peak shifts and broadening showed that the concentration of defects were in the order: Cu doped TiO2 > Fe doped TiO2 > Sn doped TiO2 > pure TiO2. Nanosecond laser flash photolysis of Fe and Cu doped TiO2 indicated slower transient decay kinetics than that of Sn doped TiO2 or pure TiO2. A broad absorption peak and fast transient decay at 430 nm for Fe doped TiO2 was ascribed to an increase in surface hole concentration resulting in poor current density in the Fe doped TiO2 photoanodes relative to pure TiO2, Sn or Cu doped anodes. The charge transfer capacitance and the calculated electron lifetimes correlated well with the trend in current density of the photoanodes (Sn > Cu > pure TiO2). The poor performance of Fe doped cells is due to faster recombination of injected electrons with surface holes while those of Sn and Cu were more influenced by the concentration of their bulk defects. These results demonstrate that the choice of selected metal ions doping onto TiO2 for a desired application should take into consideration the influence of bulk defect concentrations, the energy state distribution and the electron transfer properties in/on the oxide photoanodes.

Herein, we report the solution phase self-assembly between Eu(III) and a rigid ditopic tridentate terpyridine ligand which results in the formation of supramolecular metallo-networks in the solid state. Depending on the ligand to metal ratio used for the initial self-assembly process, the morphology of these materials can be altered from one-dimensional micron-sized fibres to a three-dimensional coordination network. The terpyridine-based ditopic ligand can act as an efficient sensitizer for Eu(III) emission whereby the emission lifetimes and ligand triplet state energies of the metallo-polymers strongly depend on the ligand to metal ratio. The obtained micron-sized fibres can act as an efficient optical wave-guide for Eu(III) emission.

A new class of soluble Eu(III) coordination polymers based on a tridentate ditopic pybox ligand has been developed displaying high metal emission quantum yields of up to 73% as well as a unique dynamic behaviour in solution.

Development of composite polymer/graphene oxide (GO) materials attracts significant attention due to their unique properties. In this work, highly ordered arrays of hollow microchambers made of composite polyelectrolyte/GO multilayers (PEGOMs) are successfully fabricated via layer-by-layer assembly on sacrificial or sustainable templates having imprinted patterns of microwells on their surface. Mechanical and optical properties of PEGOMs are studied by nanoindentation and near-infrared (NIR) absorption spectroscopy. Incorporation of three GO layers in between the polyelectrolyte multilayer stacks increases Young's modulus and critical stress of the microchambers by a factor of 5.6 and 2.6, respectively. Optical density of this PEGOM film is found to decrease gradually from 0.14 at λ = 800 nm to 0.06 at λ = 1500 nm. Remote opening of PEGOM microchambers with NIR laser beam is also demonstrated. One of the possible applications of the developed structures includes micropackaging and delivery systems in biological tissues with remote triggering.

Recently, donor-acceptor (D-A) copolymers have emerged a significant class of the materials for bulk-heterojunction (BHJ) solar cells. Among the possible D-A copolymers, diketopyrrolopyrrole (DPP)-based copolymers have been studied intensively as attractive materials for solar cells because of their low band gaps with wide-range absorption and high carrier mobility. In fact, DPP-based copolymers exhibited promising power conversion efficiency of ~8% [1]. In this study, we investigate the photoexcited-state dynamics in BHJ solar cells composed of the DPP-naphthalene copolymer (PDPP-TNT) [the inset of Fig. (a)] and PC71BM, using picosecond fluorescence and femtosecond transient absorption (TA) spectroscopies [2]. PDPP-TNT/PC71BM (1:2 by weight) blend films were prepared on glass substrates by spin-coating process from solutions in chloroform alone or a mixture of chloroform and o-dichlorobenzene (o-DCB) (4:1 by volume). The absorption spectrum of a blend film from chloroform alone is shown in Fig. (a). For TA measurements, 150-fs light pulse at 650 nm was used as a pump pulse. To detect the ground-state bleaching in PDPP-TNT, we used light pulse at 740 nm as a probe pulse. For the picosecond fluorescence measurements, 150-fs light pulse at 660 nm was used as an excitation light. A streak camera equipped with a monochromator was employed to monitor the fluorescence spectra [Fig. (a)] and kinetics of the PDPP-TNT polymer. Figure (b) shows the transient absorption kinetics of a neat PDPP-TNT film and the PDPP-TNT/PC71BM blend films (chloroform alone and chloroform & o-DCB) at a low excitation photon density (~ 100 nJ/cm2). The time profile for a neat PDPP-TNT film can be reproduced by single exponential decay (time constant: 175 ps), which is in good agreement with that of fluorescence. This result indicates that the observed signal originates from singlet excitons, and the absence of a long-lived component implies that charge carriers such as polaron pairs and triplet excitons are not efficiently photogenerated in the neat film. On the other hand, time profile for blend films can be reproduced by sum of exponential decay (time constant: 125 ps) and constant component. Therefore, in the blend films, the fast decay component can be interpreted as recombination of singlet excitons, and the long-lived one is attributable to the initially separated charge carriers. The signal due to charge carriers is more dominant in the blend film from a mix of chloroform and o-DCB than that from chloroform alone. This is consistent with the result from the photovoltaic measurement that more photocurrent is generated in the film from a mix of chloroform and o-DCB than in that from chloroform alone. Discussion on the diffusion length of singlet exciton in neat PDPP-TNT film will be also presented from the results of singlet–singlet annihilation analysis. Acknowledgement: The work was partly supported by the Strategic International Research Cooperative Program (SICP), Japan Science and Technology Agency (JST). Figure: (a) Molecular structure of PDPP-TNT and absorption spectrum of PDPP-TNT/PC71BM blend film from chloroform alone. Fluorescence spectra of the PDPP-TNT polymer. (b) Transient absorption kinetics of the neat and blend films. Reference [1] K. H. Hendriks, G. H. L. Heintges, V. S. Gevaerts, . M. Wienk, and R. A. J. Janssen, Angew. Chem. Int. Ed., 52, 8341 (2013). [2] H. Matsuzaki, A. Furube, R. Katoh, S. P. Singh, P. Sonar, E. L.Williams, C. Vijila, G. S. Subramanian, S. Gorelik, and J. Hobley, Jpn. J. Appl. Phys., 53, 01AB11 (2014). Figure 1