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Photonic crystals

Yongjoon Heo, Su Yeon Lee, Ji-Won Kim, Tae Yoon Jeon, Shin-Hyun Kim
Inverse opals have been used for structural coloration and photonic applications owing to their photonic bandgap properties. When the photonic structures contain planar defects, they provide defect modes, which are useful for lasing, sensing, and waveguiding. However, it remains a challenge to insert a planar defect into inverse opals in a reproducible manner. Here, we report a new method for producing planar-defect-inserted inverse opals using sequential capillary wetting of colloidal crystals and creating micropatterns through photolithography...
November 22, 2017: ACS Applied Materials & Interfaces
Fan-Li Meng, Jiao-Jiao Wu, Er-Fei Zhao, Yan-Zhen Zheng, Mei-Lan Huang, Li-Ming Dai, Xia Tao, Jian-Feng Chen
Integration of the upconversion effect in perovskite solar cells (PSCs) is a facile approach towards extending the spectral absorption from the visible to the near infrared (NIR) range and reducing the non-absorption loss of solar photons. However, the big challenge for practical application of UCNCs in planar PSCs is the poor compatibility between UCNCs and the perovskite precursor. Herein, we have subtly overcome the tough compatibility issue using a ligand-exchange strategy. For the first time, β-NaYF4:Yb,Er UCNCs have been embedded in situ into a CH3NH3PbI3 layer to fabricate NIR-enabled planar PSCs...
November 22, 2017: Nanoscale
Biting Zhu, Qianqian Fu, Ke Chen, Jianping Ge
Nitrogen adsorption-desorption for mesopore characterization requires the using of expensive instrument, time-consuming process and consumption of liquid nitrogen. Here, a new method was developed to measure the pore parameters through mixing of mesoporous substance with supersaturated SiO2 colloidal solution at different temperatures, followed by quick measurement of reflection changes of the precipitated liquid photonic crystals. Pore volumes and diameters of mesoporous silica were measured according to the positive correlation between unit mass reflection change (Δλ/m) and pore volume (V), and the negative correlation between average absorption temperature (T) and pore diameter (D)...
November 21, 2017: Angewandte Chemie
Qingyang Wei, Tianyu Ma, Tianpeng Xu, Ming Zeng, Yu Gu, Tiantian Dai, Yaqiang Liu
Modern positron emission tomography (PET) detectors are made from pixelated scintillation crystal arrays and readout by Anger logic. The interaction position of the gamma-ray should be assigned to a crystal using a crystal position map or look-up table. Crystal identification is a critical procedure for pixelated PET systems. In this paper, we propose a novel crystal identification method for a dual-layer-offset LYSO based animal PET system via Lu-176 background radiation and mean shift algorithm. Single photon event data of the Lu-176 background radiation are acquired in list-mode for 3 hours to generate a single photon flood map (SPFM)...
November 21, 2017: Physics in Medicine and Biology
Lihui Lin, Yanxin Lu, Mengmeng Yuan, Fenghua Shi, Haixia Xu, Yihang Chen
Graphene plasmons, owing to their diverse applications including electro-optical modulation, optical sensing, spectral photometry and tunable lighting at the nanoscale, have recently attracted much attention. One key challenge in advancing this field is to precisely control the propagation of graphene plasmons. Here, we propose an on-chip integrated platform to engineer the wave front of the graphene plasmons through a metasurface with a refractive index of zero. We demonstrate that a well-designed graphene/photonic-crystal metasurface can possess conical plasmonic dispersion at the Brillouin zone center with a triply degenerate state at the Dirac frequency, giving rise to the zero-effective-index of graphene plasmons...
November 21, 2017: Nanoscale
Bjoern Delfs, Andreas Alexander Schoenfeld, Daniela Poppinga, Ralf-Peter Kapsch, Ping Jiang, Dietrich Harder, Bjoern Poppe, Hui Khee Looe
The optical density (OD) of EBT3 radiochromic exposed to absorbed doses to water up to D = 20 Gy in magnetic fields of B = 0.35 and 1.42 T was measured in three colour channels. A 7 cm wide water phantom with fixed film holder was placed in magnetic fields and was irradiated by a 6 MV photon beam whose axis was directed at right angles with the field lines. The doses at the film position at water depth 5 cm were measured with a calibrated ionization chamber when the magnet was switched off and were converted to the doses in presence of the magnetic field via the monitor units and by a Monte Carlo-calculated correction accounting for the slight change of the depth dose curves in magnetic fields...
November 20, 2017: Physics in Medicine and Biology
Yosuke Terada, Kenji Miyasaka, Keisuke Kondo, Norihiro Ishikura, Takuya Tamura, Toshihiko Baba
Silica-clad silicon photonic crystal waveguides (PCWs) are promising components for various applications because of their simple fabrication and generation of slow light. However, an optical loss higher than 4 dB occurs when they are simply coupled to input/output silicon wire waveguides. To reduce the optical loss, we proposed a junction structure in which light in the waveguide is first coupled to a high-group-velocity radiation mode at an expanded core and subsequently converted to the slow-light mode in a tapered core of the PCW...
November 15, 2017: Optics Letters
Nicola Coluccelli, Christopher R Howle, Kenneth McEwan, Yuchen Wang, Toney Teddy Fernandez, Alessio Gambetta, Paolo Laporta, Gianluca Galzerano
We demonstrate a fiber-format system for dual-comb coherent anti-Stokes Raman scattering spectroscopy. The system is based on two ytterbium fiber (Yb) femtosecond lasers at repetition frequencies of 94 MHz, a Yb amplifier, and a photonic crystal fiber for spectral broadening and generation of pulses with a central wavelength of 1040 nm and durations in the sub-20-fs regime. We observed Raman spectra of acetonitrile and ethyl acetate with spectral coverage from 100 to 1300  cm(-1), resolution of 8  cm(-1), and a signal-to-noise ratio of around 100, when averaging over 10 acquisitions...
November 15, 2017: Optics Letters
Tatsunosuke Matsui, Kazuya Tsukuda
We report the direct experimental observation of electrically tunable photonic nanojets (PNJs) generated from self-assembled liquid crystal (LC) microdroplets formed by dispersing nematic LCs in polymer matrix. Optical measurements were performed with a home-built laser-scanning confocal microscope system. PNJs with subwavelength beam waists were successfully obtained from LC microdroplets of 5 μm diameter, similar to those from SiO2 microspheres of the same size. By applying external voltage of a few volts, some of major properties of PNJs, such as beam length and brightness, are tuned...
November 15, 2017: Optics Letters
Francesco Talotta, Jean-Louis Heully, Fabienne Alary, Isabelle M Dixon, Leticia Gonzalez, Martial Boggio-Pasqua
The N→O linkage photoisomerization mechanism in a ruthenium nitrosyl complex, [RuCl(NO)(py)4]2+, for which a quasi complete photoconversion between the stable nitrosyl (N-bonded) and metastable isonitrosyl (O-bonded) isomers has been observed under continuous irradiation of the crystal at 473 nm (Cormary et al., Acta Cryst. B 2009, 65, 612-623), is investigated using multiconfigurational second-order perturbation theory (CASPT2). The results support efficient intersystem crossing pathways from the initially excited singlet states to the lowest triplet excited state of metal-to-ligand charge transfer character (3MLCT)...
November 14, 2017: Journal of Chemical Theory and Computation
Chengeng Zeng, Paul E Kinahan, Hua Qian, Robert L Harrison, Kyle M Champley, Lawrence R MacDonald
The goal for positron emission tomography (PET)/X is measuring changes in radiotracer uptake for early assessment of response to breast cancer therapy. Upper bounds for detecting such changes were investigated using simulation and two image reconstruction algorithms customized to the PET/X rectangular geometry. Analytical reconstruction was used to study spatial resolution, comparing results with the distance of the closest approach (DCA) resolution surrogate that is independent of the reconstruction method...
October 2017: Journal of Medical Imaging
Shiva Abbaszadeh, Garry Chinn, Craig S Levin
The kinematics of Compton scatter can be used to estimate the interaction sequence of inter-crystal scatter interactions in 3-D position-sensitive cadmium zinc telluride (CZT) detectors. However, in the case of intra-crystal scatter in a "cross-strip" CZT detector slab, multiple anode and cathode strips may be triggered, creating position ambiguity due to uncertainty in possible combinations of anode-cathode pairings. As a consequence, methods such as energy-weighted centroid are not applicable to position the interactions...
November 13, 2017: Physics in Medicine and Biology
Chang Xu, Wan-Ying Zhang, Qiong Ye, Da-Wei Fu
Switchable materials, due to their potential applications in the fields of sensors, photonic devices, digital processing, etc., have been developed drastically. However, they still face great challenges in effectively inducing multiple molecular switching. Herein organic-inorganic hybrid compounds, an emerging class of hydrosoluble optoelectronic-active materials, welcome a new member with smart unique optical/electrical (fluorescence/dielectric) dual switches (switching ON/OFF), that is, [C5H13NBr][Cd3Br7] (1) in the form of both a bulk crystal and an ultraflexible monodirectional thin film, which simultaneously exhibits fast dielectric/fluorescent dual switching triggered by an optical/thermal/electric signal with a high signal-to-noise ratio of 35 (the highest one in the known optical/dielectric dual molecular switches)...
November 13, 2017: Inorganic Chemistry
Yusuke Nagai, Chen Shao-Chieh, Kotaro Kajikawa
A random laser of a photonic crystal fiber (PCF) with holes filled with laser dye-doped nematic liquid crystal (NLC) is reported. When the excitation polarization was along the PCF axis, the measured laser threshold was 80  μJ/mm(2) per pulse, which is much lower than the previously reported random laser of PCF filled with laser dye-doped organic solvent. This low threshold is due to the high refractive index of the NLC, which produces a greater scattering efficiency. In contrast, when the excitation polarization is perpendicular to the PCF axis, the threshold was much higher or the laser oscillation was absent...
November 10, 2017: Applied Optics
Izabela Kaminska, Danek Elbaum, Bozena Sikora, Przemysław Kowalik, Jakub Mikulski, Zofia Felcyn, Piotr Samol, Tomasz Wojciechowski, Roman Minikayev, Wojciech Paszkowicz, Wojciech Zaleszczyk, Maciej Szewczyk, Anna Konopka, Grzegorz Gruzeł, Mirosława Pawlyta, Mikołaj Donten, Kamil Ciszak, Karolina Zajdel, Małgorzata Baniewicz, Piotr Stępień, Mariusz Łapiński, Grzegorz Wilczyński, Krzysztof Fronc
Nanostructures as color-tunable luminescent markers have become major, promising tools for bioimaging and biosensing. The separated molybdate/Gd2O3 doped rare earth ions (erbium, Er(3+) and ytterbium, Yb(3+)) core-shell nanoparticles (NPs), were fabricated by a one step homogeneous precipitation process. Emission properties were studied by cathodo- and photoluminescence. The scanning electron and transmission electron microscopes were used to visualize and to determine the size and shape of the NPs. The spherical NPs were obtained...
November 13, 2017: Nanotechnology
Yasuhiro Yamada, Mizuki Hoyano, Ryo Akashi, Kenichi Oto, Yoshihiko Kanemitsu
We studied the optical responses of organic-inorganic halide perovskite CH3NH3PbBr3 single crystals doped with heterovalent Bi(3+) ions (electron densities up to 2.3 × 10(12) cm(-3)). The Bi doping causes no significant changes in the band gap energy but leads to an enhanced Urbach tail and photoluminescence blue shift. On the basis of the time-resolved photoluminescence measurements, we attribute the PL response to a shorter carrier lifetime induced by Bi doping, which results in a reduced photon recycling effect (i...
November 15, 2017: Journal of Physical Chemistry Letters
Shoma Aki, Kenji Sueyoshi, Hideaki Hisamoto, Tatsuro Endo
We investigated the origin of the optical responses of a two-dimensional photonic crystal (2D-PhC) optode membrane ion sensor based on plasticized poly(vinyl chloride) (PVC) containing lipophilic dye. We previously developed a highly sensitive potassium ion sensor. However, the contributions of various factors to the sensor's optical response could not be distinguished. Here, we synthesized a lipophilic dye with spectral changes that do not overlap with those of propagated light in the PhC. Using this synthesized dye excluded the contribution of light absorption by the dye to the peak intensity change of the ion sensor...
2017: Analytical Sciences: the International Journal of the Japan Society for Analytical Chemistry
Ya-Nan Zhang, Yong Zhao, Tianmin Zhou, Qilu Wu
Photonic crystal (PC) cavities, which possess the advantages of compactness, flexible design, and suitability for integration in a lab-on-a-chip system, are able to distinguish slight variations in refractive index with only a small amount of analyte. Combined with the newly proposed optofluidic technology, PC-cavity devices stimulate an emerging class of miniaturized and label-free biochemical sensors. In this review, an overview of optofluidic PC cavities based biochemical sensors is presented. First, the basic properties of the PC, as well as the sensing principle of the PC cavity, are discussed...
November 10, 2017: Lab on a Chip
H Olof Jönsson, Carl Caleman, Jakob Andreasson, Nicuşor Tîmneanu
Serial femtosecond crystallography is an emerging and promising method for determining protein structures, making use of the ultrafast and bright X-ray pulses from X-ray free-electron lasers. The upcoming X-ray laser sources will produce well above 1000 pulses per second and will pose a new challenge: how to quickly determine successful crystal hits and avoid a high-rate data deluge. Proposed here is a hit-finding scheme based on detecting photons from plasma emission after the sample has been intercepted by the X-ray laser...
November 1, 2017: IUCrJ
Xin Su, Yu Jiang, Xiaoqian Sun, Suli Wu, Bingtao Tang, Wenbin Niu, Shufen Zhang
Patterned photonic crystals (PCs) have attracted considerable attention due to their great potential in practical applications. Direct writing is an important and convenient method to fabricate patterned PCs. However, due to the limited interaction among spheres and the evaporation of ink, the obtained patterns usually suffer from poor structure strength, and non-uniform and unstable structural colors. In this work, an in situ embedding and locking strategy for fabricating tough PC patterns in one step was demonstrated...
November 9, 2017: Nanoscale
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