Size and Shape Effect of Gold Nanoparticles in “Far‐Field” Surface Plasmon Resonance

The “far‐field” surface plasmon resonance (FSPR) of metal nanoparticles, which have built a facile way to emission enhancement of red, green, blue, and white with nice reproducibility, has big potential application in solution‐processed organic light‐emitting diodes (OLEDs). According to the theory of the “far‐field” effect, the reflectivity of the metal surface and the phase shift at the reflection play an important role in enhancing ratio, which strongly relate to the size and shape of nanoparticles. In this work, gold nanospheres with different sizes and nanorods are synthesized in order to determine the size and shape effect of FSPR. The results demonstrate that the one with higher reflectivity in a certain range induces a better emission enhancement in the luminous efficiency and the maximum brightness. The nanoparticles with bigger sizes and shape of rods have higher reflectivity, which is consistent with the simulation based on FSPR effect. The phase shifts of different nanoparticles are optimized by the distance between gold nanoparticles and emitters. The metal NPs with a high reflectivity and the applicable phase shift will have big potential for the emission enhancement in OLEDs.     

Quantum phase transitions in electronic systems

Quantum phase transitions occur at zero temperature when some non‐thermal control‐parameter like pressure or chemical composition is changed. They are driven by quantum rather than thermal fluctuations. In this review we first give a pedagogical introduction to quantum phase transitions and quantum critical behavior emphasizing similarities with and differences to classical thermal phase transitions. We then illustrate the general concepts by discussing a few examples of quantum phase transitions occurring in electronic systems. The ferromagnetic transition of itinerant electrons shows a very rich behavior since the magnetization couples to additional electronic soft modes which generates an effective long‐range interaction between the spin fluctuations. We then consider the influence of rare regions on quantum phase transitions in systems with quenched disorder, taking the antiferromagnetic transitions of itinerant electrons as a primary example. Finally we discuss some aspects of the metal‐insulator transition in the presence of quenched disorder and interactions.     

Controlling magnetic dipole transition with magnetic plasmonic structures

A plasmonic structure with double gold patches is proposed for enhancing the spontaneous emission of a magnetic dipole transition through a magnetic hot area. A Purcell factor of nearly 2000 can be obtained at optical frequencies together with a low sensitivity in spatial and spectral mismatches between the light emitter and the resonance mode. The associated resonance can be tuned from the visible to the IR frequencies, enabling efficient control of forbidden transitions using plasmonic structures.     

Tunable and High Photoluminescence Quantum Yield from Self‐Decorated TiO2 Quantum Dots on Fluorine Doped Mesoporous TiO2 Flowers by Rapid Thermal Annealing

Herein a novel approach is reported to achieve tunable and high photoluminescence (PL) quantum yield (QY) from the self‐grown spherical TiO₂ quantum dots (QDs) on fluorine doped TiO₂ (F‐TiO₂) flowers, mesoporous in nature, synthesized by a simple solvothermal process. The strong PL emission from F‐TiO₂ QDs centered at ≈485 nm is associated with shallow and deep traps, and a record high PL QY of ≈5.76% is measured at room temperature. Size distribution and doping of F‐TiO₂ nanocrystals (NCs) are successfully tuned by simply varying the HF concentration during synthesis. During the post‐growth rapid thermal annealing (RTA) under vacuum, the arbitrary shaped F‐TiO₂ NCs transform into spherical QDs with smaller sizes and it shows dramatic enhancement (≈163 times) in the PL intensity. Electron spin resonance (ESR) and X‐ray photoelectron spectroscopy (XPS) confirm the high density of oxygen vacancy defects on the surface of TiO₂ NCs. Confocal fluorescence microscopy imaging shows bright whitish emission from the F‐TiO₂ QDs. Low temperature and time resolved PL studies reveal that the ultrafast radiative recombination in the TiO₂ QDs results in highly efficient PL emission. A highly stable, biologically inert, and highly fluorescent TiO₂ QDs/flowers without any capping agent demonstrated here is significant for emerging applications in bioimaging, energy, and environmental cleaning.     

Spray Forming: Controlling the Atomization Result with Regard to Particle Properties

Spray forming is a new production process for manufacturing semi‐finished metal products. The procedure combines the liquid metal atomization with the compaction event of the generated metal droplets on a substrate. During spray forming, the heat emission of the molten metal particles is one of the most important transfer operations defining the thermal conditions in the spray and deposit. Definite thermal conditions throughout the manufacturing process lead to fine equi‐axed grain structures and therewith to characteristic and desired material properties. Thus, in particular, the disintegration of the molten metal occurring during spray forming is an essential step.     

Iron Precursor Decomposition in the Magnesium Combustion Flame: A New Approach for the Synthesis of Particulate Metal Oxide Nanocomposites

Powders of Fe–Mg–O nanocomposite particles have been grown using a novel chemical vapor synthesis approach that employs the decomposition of a metalorganic precursor inside the metal combustion flame. After annealing in controlled gas atmospheres composition distribution functions, structure and phase stability of the obtained magnesiowüstite nanoparticles are measured with a combination of techniques such as inductively coupled plasma‐optical emission spectroscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction, and scanning and transmission electron microscopy. Complementary Mössbauer spectroscopy measurements reveal that depending on Fe loading and temperature of annealing either metastable and superparamagnetic solid solutions of Fe³⁺ ions in periclase (MgO) or phase separated mixtures of MgO and ferrimagnetic magnesioferrite (MgFe₂O₄) nanoparticles can be obtained. The described combustion technique represents a novel concept for the production of mixed metal oxide nanoparticles. Adressing the impact of selected annealing protocols, this study underlines the great potential of vapor phase grown non‐equilibrium solids, where thermal processing provides means to trigger phase separation and, concomitantly, the emergence of new magnetic properties.     

A Surface Study of Ultrathin Ceria Nanoparticles Decorated with Transition‐Metal Ions

A wide range of nanoparticle properties can be tuned by changing their surface characteristics, especially when dealing with ultrathin nanomaterials. Surface modification with transition‐metal ions may affect a variety of the nanoparticles' properties including the surface charge, the electronic structure, and the electrical and optical characteristics. In this work, a surface study of ceria nanoparticles modified by attachment of various transition‐metal ions to their surface is conducted. Characterization of the decorated particles as well as of the modifying transition‐metal ion is carried out using zeta potential in organic solution, UV–Vis absorption, and electron paramagnetic resonance measurements, together with isothermal titration calorimetry, X‐ray photoelectron spectroscopy, and energy dispersive X‐ray spectroscopy. All measurements confirm the attachment of the cation to the surface of ceria, both in solid state and in colloidal suspension. It is suggested that the modifying ion‐complex attaches to ceria both via chemical or strong physical interactions and weak physical interactions, demonstrated by a case‐study modification of ceria using a copper‐oleylamine complex. The metalization has a significant effect on the surface charge of the nanoparticles by shifting the zeta potential to more positive values and on the optical properties of the modifying transition‐metal ions by red‐shifting their absorption peak.     

Theory of a proton spin maser with two emission coils

A nuclear maser oscillator with two emission coils, coupled solely by a stream of a prepolarized liquid which is initially at negative spin temperature, is investigated theoretically. The second emission coil is assumed to be tuned by a condenser to the proton spin resonance, while the first emission coil can be detuned. If the spin-spin interaction time is sufficiently long, then the voltage amplitude available from the terminals of the second coil can go through two maxima as the first coil is detuned. For maximum detuning of the first coil, a self-modulation effect can arise in the second resonance circuit.     

Atmospheric Pressure Plasma Application for Pollution Control in Industrial Processes

Economic application of atmospheric pressure plasma technology for industrial pollution control requires fulfilling two propositions: First application of pollution control technologies needs to result in clear environmental, health, or safety benefits motivating political measures. Second plasma technology needs to be competitive as compared to other available pollution control technologies. Thus in this article methods for the evaluation of atmospheric plasma application for industrial pollution control are reviewed: Examples of emission regulations and emission control technologies are given. Requirements of industrial scale emission control and of thermal and non‐thermal exhaust gas treatment technologies are described. The potential of various non‐thermal plasma reactor concepts for cost effective treatment of industrial scale gas flows is analyzed, and methods for the evaluation of plasma energy balance and plasma chemical kinetics are given for them. How to deal with shortcomings of atmospheric pressure plasmas such as lack of plasma‐chemical selectivity is addressed in a section about plasma‐catalytic hybrid processes. Further the progress made recently in electrostatic precipitation is reviewed, and the importance of electro‐hydrodynamic effects for the reactor design both for electrostatic precipitation and for plasma chemical pollution control is considered. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Composite‐Assisted Phase‐Matching: Efficient Wavelength Conversion in Nonlinear Optical Composite Materials Containing Metal Nanoparticles

A novel phase‐matching scheme which is based on the dispersion compensation in the nonlinear optical composite materials containing metal nanoparticles is proposed. Anomalous dispersion originating from the plasmon resonance in metal nanoparticles compensates the dispersion of the host nonlinear material, leading to the perfect phase‐matching and high efficiency of nonlinear optical wavelength conversion. The effectiveness of this approach is theoretically demonstrated, taking third‐order nonlinear processes such as the direct third‐harmonic generation and four‐wave mixing in ZnO composites containing silica‐core–silver‐shell nanoparticles as examples. The results show that with the proposed phase‐matching scheme, unprecedentedly high conversion efficiency can be obtained compared with preceding results in third‐order nonlinear optical solid‐state materials.     

Gold‐Cluster‐Based Dual‐Emission Nanocomposite Film as Ratiometric Fluorescent Sensing Paper for Specific Metal Ion

A dual‐emission ratiometric fluorescent sensing film for metal ion detection is designed. This dual‐emission film is successfully prepared from chitosan, graphitic carbon nitride (g‐C₃N₄), and gold nanoclusters (Au NCs). Here, it is shown that the g‐C₃N₄ not only serves as the fluorescence emission source, but also enhances the mechanical and thermal stability of the film. Meanwhile, the Au NCs are adsorbed on the surface of chitosan film by the electrostatic interaction. The as‐prepared dual‐emission film can selectively detect Cu²⁺, leading to the quench of red fluorescence of Au NCs, whereas the blue fluorescence from g‐C₃N₄ persists. The ratio of the two fluorescence intensities depends on the Cu²⁺ concentration and the fluorescence color changes from orange red to yellow, cyan, and finally to blue with increasing Cu²⁺ concentration. Thus, the as‐prepared dual‐emission film can be worked as ratiometric sensing paper for Cu²⁺ detection. Furthermore, the film shows high sensitivity and selectivity, with low limit of detection (LOD) (10 ppb). It is observed that this novel gold‐cluster‐based dual‐emission ratiometric fluorescent sensing paper is an easy and convenient way for detecting metal ions. It is believed that this research work have created another avenue for the detection of metal ions in the environment.     

Enhanced photoluminescence of conjugated polymer thin films on nanostructured silver

Photoluminescence of a conjugated polymer in the presence of surface plasmons on metallic nanoparticles is studied. A layered device structure was constructed that enabled control over nanoparticle diameter and separation between the polymer and nanoparticles layers. The dependence of the surface plasmon evanescent field and energy transfer has been investigated with the largest enhancement in photoluminescence observed at a 40 nm distance separation between the fluorophore and the surface plasmon. A spectrum of surface plasmon resonances ranging from the emission to the absorption energies of the conjugated polymer revealed largest enhancements when the resonance was tuned to the conjugated polymer emission energy. At peak photoluminescence the maximum photoluminescent enhancement was found to be 5.6 times of the photoluminescence of the control structure and the total integrated enhancement was 5.9 times.     

Tunable Infrared Luminescence and Optical Amplification in PbS Doped Glasses

PbS-doped glasses are prepared. Absorption and luminescence spectra show that both the absorption and infrared emission can be tuned widely by thermal treatment conditions. Optical amplification at 1300 nm is observed, and amplified spontaneous emission （ASE） spectrum is also measured to confirm the optical gain from PbS quantum dots.     

An alternative tuning approach to enhance NMR signals

By using spin-noise type measurement we show that the resonance frequency of the reception circuit of classical NMR spectrometers does not match the Larmor frequency even if, in emission, the electronic circuit is perfectly tuned at the Larmor frequency and matches the amplifier impedance. We also show that this spin-noise method can be used to ensure a match between the Larmor frequency and the reception circuit resonance frequency. In these conditions, (i) the radiation damping field is in perfect quadrature to the magnetization and (ii) the NMR signal level and potentially the signal-to-noise ratio, are enhanced. This choice induces a change of the probe resonance frequency by several hundreds of kHz for 500 or 700 MHz spectrometer. We show that the resulting mismatch condition for emission can be removed by adding other tuning and matching degrees of freedom located on the excitation line (or by symmetry on the reception line) decoupled to the probe resonance circuit by the crossed diodes.     

金属表面粗糙度对热红外偏振特性影响研究

根据热红外偏振的原理和探测方法,利用一种热红外偏振探测系统分别研究了铝质和钢质金属板热红外偏振度和其表面粗糙度之间的关系.金属板的表面粗糙度通过喷砂和刨床加工控制.实验结果分析表明:在观测角较小时,喷砂方式处理的金属目标板,粗糙度对它们的热红外偏振度影响较小;而刨床加工的金属目标板,粗糙度对它们的热红外偏振度影响较大.在观测角较大时,无论经过何种加工方式处理表面的金属目标板,都遵循表面越是光滑其热红外偏振度越大的规律.     

Broadband Terahertz Polarization Converter and Asymmetric Transmission Based on Coupled Dielectric‐Metal Grating

Coupled dielectric‐metal gratings are investigated for broadband terahertz (THz) wave polarization conversion and asymmetric transmission by the experiments and numerical simulations, which are composed of the subwavelength Si grating and metallic wire grating layers. The dielectric grating layer with a large artificial birefringence and low dispersion is employed as a phase engineered waveplate, and the metal wire grating arranged with a 45° angle to the dielectric grating is utilized as a high‐efficiency polarizer. Due to the subwavelength integration, this coupled grating presents a local resonance coupling mechanism between dielectric and metal gratings, which greatly enhances the polarization rotation and expands the bandwidth, not a simple combination with dielectric and metallic gratings. The results demonstrate that a broadband asymmetric transmission with an extinction ratio of 30dB from 0.2 to 1.2 THz is achieved and the highest transmission of 90% can be obtained. It provides a simple way towards practical applications for THz artificial dispersion materials, polarization control and asymmetric transmission.     

Red/Near‐Infrared Emissive Metalloporphyrin‐Based Nanodots for Magnetic Resonance Imaging‐Guided Photodynamic Therapy In Vivo

Near‐infrared emissive (NIR) porphyrin‐implanted carbon nanodots (PCNDs or MPCNDs) are prepared by selectively carbonization of free base or metal complexes [M = Zn(II) or Mn(III)] of tetra‐(meso‐aminophenyl)porphyrin in the presence of citric acid. The as‐prepared nanodots exhibit spontaneously NIR emission, small size, good aqueous dispersibility, and favorable biocompatibility characteristic of both porphyrins and pristine carbon nanodots. The subcellular localization experiment of nanodots indicates a lysosome‐targeting feature. And the in vitro photodynamic therapy (PDT) results on HeLa cells indicate the nanodots alone have no adverse effect on tumor cells, but display remarkable photodynamic efficacy upon irradiation. Moreover, MnPCNDs containing paramagnetic Mn(III) ions, which possesses good biocompatibility, NIR luminescence, and magnetic resonance imaging and efficient singlet oxygen production, are further studied in magnetic resonance imaging‐guided photodynamic therapy in vivo.     

Continuously tunable sub-half-wavelength localization via coherent control of spontaneous emission

We propose a continuously tunable method of sub-half-wavelength localization via the coherent control of the spontaneous emission of a four-level Y-type atomic system,which is coupled to three strong coupling fields including a standing-wave field together with a weak probe field.It is shown that the sub-half-wavelength atomic localization is realized for both resonance and off-resonance cases.Furthermore,by varying the probe detuning in succession,the positions of the two localization peaks are tuned continuously within a wide range of probe field frequencies,which provides convenience for the realization of sub-half-wavelength atomic localization experimentally.     

Theory of thermionic emission

A comprehensive theory of thermionic emission from clean metal surfaces is presented. The theory takes into account the energy band structure of the metal, inelastic scattering due to electron-electron collisions and the thermal vibration of the atoms. We applied the theory to thermionic emission from Cu(100). We calculated the thermally emitted current from this plane as a function of applied field. We find an almost periodic deviation from the Schottky line, similar in nature with that which is observed in emission from polycrystalline emitters [1]. We believe that accurate measurements of the amplitude and phase of these deviations from the Schottky line can, when analysed in the manner described here, provide valuable information on the surface optical potential. We have also calculated the total energy distribution of the emitted electrons for a typical value of the applied field. The dependence of the above measurable quantities on the parameters which enter the theory is analysed and demonstrated by explicit numerical calculations.