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ZnO thin films and ZnO nanostructures have good UV emission properties, which are ideal materials for preparing short-wavelength light-emitting devices. In this study, Fe-doped ZnO thin films were prepared by sol-gel method using ferric chloride as the doping source. Compared with undoped ZnO thin films, the UV emission of low-concentration Fe-doped ZnO thin films did not show significant changes. However, the UV emission of high-concentration Fe-doped (≥4 at.%) ZnO thin films was significantly enhanced and the refractive index had also increased largely. It is observed by a scanning electron microscope (SEM) that the high-concentration Fe-doped ZnO thin film has a two-layer structure: the upper layer is composed of the frustum of hexagonal pyramid (FHP) shaped nanostructures, and the bottom layer in contact with the substrate is composed of polycrystalline spherical grains. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) show that the upper FHP-shaped nanostructure is a single crystal with high crystalline quality, while the bottom layer is polycrystalline. Therefore, the formation of single crystal ZnO nanostructures greatly improves the optical quality of ZnO thin films. At present, as far as we know, the experimental results of partially converting polycrystalline ZnO into single crystal ZnO to greatly improve the UV emission performance of ZnO thin films have rarely been reported. The ZnO thin film with a two-layer structure prepared here is a candidate material for preparing UV light-emitting devices.

The growth of high quality ZnO thin films is a hot research topic in the field of optoelectronic materials. In this study, high quality ZnO thin films with a double-layer structure were obtained by sol-gel method. Al-doping induced transition from polycrystals to single crystals in the ZnO thin films was found. The results show that Al-doping improves the c-axis orientation of ZnO thin films. When the Al-doping concentration is higher than 4at%, the frustum of hexagonal pyramid (FHP) shaped ZnO nanostructures are formed on the polycrystalline ZnO thin films surface. As the Al-doping concentration further rises, the areal density of the FHP-shaped nanostructures also gradually increases and the size becomes more uniform. Both SAED patterns and high-resolution TEM images indicate that the FHP-shaped ZnO nanostructures are single crystals. It is of great scientific significance to transform polycrystalline ZnO into single crystal ZnO by Al-doping combined with a simple heat-treatment process. Compared with pure ZnO thin films, the FHP-shaped nanostructures on the surface show better UV emission performance, suggesting these materials are ideal ones for the preparation of ZnO-based UV emitters. The authors propose that the growth mechanism of FHP-shaped ZnO nanostructure is a multi-step solid-solid reaction dominated by surface diffusion of zinc atoms.

A tunable resonant doubled-sided dielectric grating (DSDG) structure has been designed for operating in the near-infrared (NIR) wavelength range under transverse electric (TE) polarization. The rigorous coupled-wave analysis (RCWA) is applied to determine the optical characteristics, and the reflection resonance of the grating structure is analyzed by varying their geometrical parameters. The excited sharp Fano resonance (FR) is demonstrated numerically that does not occur in single layer grating. The maximal magnitude of electric field in the spacing layer sandwiched by the gratings is 35 times enhanced compared with incident filed, that dues to the waveguide resonance, which can be excited by a normally incident plane wave in the proposed design. The relationship between structure parameters of DSG and the reflectance spectrum in order to guarantee the appearance of FR in the designed structure is fully investigated. An optical refractive index (RI) sensor with a potential sensitivity of 602.15 nm/RIU is designed based on the proposed structure. The method demonstrated may lead to potential applications for the design of tunable filter or modulator with narrow-band with a wide range of potential applications including telecommunications, optical information processing, and optical sensors.

A novel type of plasmonic filter consisting of metal–insulator–metal bus waveguides coupled with a T-shaped side-coupled cavities and stub waveguides. By finite-difference time-domain (FDTD) simulations, it is found that the resonant wavelength can be controlled by adjusting the length and height of the resonator. The effect of the asymmetry on the transmission property has also been examined. The result demonstrates that the asymmetrical plasmonic waveguide-resonator system performs a plasmonic analogue of electromagnetically induced transparency (EIT) in atomic systems, as confirmed by numerical experiments. The EIT-like transparency window exhibits a distinct resonance shift with respect to a small fluctuation in the refractive index of the surrounding medium, which can be used to increase the sensitivity of the plasmonic sensors. The proposed plasmonic filter and sensor have compact size that may find significant applications in highly-integrated dense wavelength division demultiplexing systems, nanoscale optical switching, and slow-light devices in highly integrated optical circuits and networks.

Tunable filter based on two metal–insulator–metal (MIM) waveguides coupled to each other by a ring resonator with double narrow gaps is designed and numerically investigated by finite-difference time-domain (FDTD) simulations. The propagating modes of surface plasmon polaritons (SPPs) are studied. By introducing narrow gaps in ring resonators, the transmission in different resonance modes can be effectively adjusted by changing the gap width (g), and the transmitted peak wavelength has a nonlinear relationship with g. Another structure consisting two cascading ring resonators and regular MIM waveguide have also been proposed. The mechanism based on circular ring resonators with narrow gaps may provide a novel method for designing all-optical integrated components in optical communication and computing.

ZnO thin films are prepared by sol–gel method. Their surface and sectional morphologies have been observed by scanning electron microscopy (SEM). It is found that the Sr-doping leads to a porous structure in ZnO thin films and this kind of porous structure distributes throughout the whole film rather than only distribute on the film surface. Furthermore, the variation of Sr-doping concentration can tailor the pore density in the films. The formation of the porous structure probably results from the lattice distortion due to the large difference between the ion radiuses of Sr2+ and Zn2+. The mapping of the samples shows that the Sr element is uniformly distributed in the whole thin films. The photocatalytic experiments show that the photocatalytic activity of Sr-doped ZnO thin films has been enhanced compared with that of undoped ZnO thin films. This enhancement should be attributed to the increase of specific surface area deriving from the porous structure.

We theoretically show that bright three-color tripartite continuous-variable entanglement can be generated directly by the process of triply resonant sum-frequency generation using a periodically poled supperlattice. It is demonstrated that two reflected pump beams and the output sum frequency beam are all entangled with each other according to the sufficient inseparability criterion for multipartite continuous variable (CV) entanglement. The dependence of the steady state region and the entanglement on system parameters are discussed. By utilizing the up-conversion process, the generated three entanglement fields have macroscopic intensities as soon as the pump fields are turned on.

To obtain safety working before long-term early warning, we proposed a process for the preparation of luminescent films on metal substrate to detect the wear life. ZnO films were prepared on aluminum (Al) foils by the magnetron sputtering technique. The microstructure, tribological properties and photoluminescence (PL) spectra of ZnO films before and after the friction test were investigated. The microstructure of ZnO films grown on Al foils exhibited a closely packed hexagonal cone shape. ZnO films were grown along the orientation perpendicular to the substrate. The tribometric tests revealed that the average friction coefficient of ZnO films was lower and more stable than that of the substrate. The results of PL spectra indicated that the effect of Al element on ZnO films led to shifts of the defect related visible band. The luminescent center of ZnO films shifted from the emission peak at 510 nm before the friction to 647 nm after the friction, indicating that the green light shifted into the red light as the friction occurred. The visible light was helpful to understanding the failure characteristics during the friction and wear, and provide an early indicator of the impending failure.

A polarization-insensitive and angle-independent graphene absorber (GA) with periodically patterned grating is demonstrated. A periodic nanocavity composed of multilayer subwavelength grating and metal substrate supports a strongly localized mode inside the cavity, where the mode helps to absorb more electromagnetic waves. The proposed GA exhibits polarization-insensitive behavior and maintains the high absorption above 90% within a wide range of incident angle (more than 80°). We attribute the high absorption to the excitation of the cavity mode resonance and magnetic resonance for the transverse electric and transverse magnetic polarizations, respectively. The proposed GA has potential applications in the design of various devices, such as optical modulators or tunable absorption filters because of its remarkable angle-insensitive absorption performance.

Ag-doped ZnO thin films were prepared by a sol–gel method. The structural, morphological and optical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis and photoluminescence spectra. The results show that the Ag in the ZnO thin films annealed at 500 °C for 1 h substitutes for Zn and exists in the form of Ag+ ion (AgZn) while the Ag in the ZnO thin films without a post-annealing mainly exists in the form of simple substance (Ag0). The incorporation of Ag indeed can improve the ultraviolet emission of ZnO thin films and suppress the visible emissions at the same time. However, the mechanisms on the ultraviolet emission enhancement in the annealed and unannealed Ag-doped ZnO thin films are very different. As for the post-annealed Ag-doped ZnO thin films, the UV emission enhancement maybe mainly results from more electron–hole pairs (excitons) due to Ag-doping while for the unannealed Ag-doped ZnO thin films; the UV emission enhancement is attributed to the resonant coupling between exciton emission in ZnO and localized surface plasmon in Ag nanoparticles.

A multiline absorber based on the excitation of guided-mode resonance of one-dimensional photonic crystals (1D-PhCs), including a surface graphene monolayer under the attenuated-total-reflection configuration, is proposed and demonstrated. By carefully designing the structure parameters of the 1D-PhCs, the guided mode can be modulated by the periodic distribution of the refractive index. Our results reveal that the critical coupling of the guided resonance in periodical PhCs to graphene produces the perfect absorption. The number of absorption peaks within the photonic band corresponds to the number of unit cells. An ultrahigh Q-factor value of 4.75×106 is obtained at resonance with unity absorption, which could serve as a promising replacement of metallic thin film as a sensor probe for future biosensing applications.

Whispering gallery mode (WGM) microresonators have been intensively studied in many areas such as sensing, lasing, and fundamental study. WGM microresonators are always coupled by a tapered fiber, and the coupling is controlled by a 3D nanotranslation stage. We always suffer from the instability of coupling condition, which means it is difficult to put microresonators in practical applications. Hence, we present an efficient way to package on-chip ultrahigh-Q microresonators. Stimulated Raman Scattering is achieved in this packaged microresonator, which means we have a portable, narrow linewidth laser and it can be used to expand the working wavelength of a laser. In addition, by coupling two whispering-gallery modes (WGM), which is simultaneously excited in the packaged microtoroid resonator, we can observe an electromagnetically induced transparency (EIT) effect for the first time in a portable WGM structure. This packaged microresonator can be used for real quantum communication applications. Furthermore, highly sensitive sensing can benefit from the high Q-factor and its stability.

As a multifunctional optoelectronic material, ZnO nanorod array has attracted wide attention. In this work, transparent and highly c-axis oriented ZnO nanorod arrays were grown by a simple chemical solution method using zinc acetate and urea as raw materials. Compared with widely used zinc nitrate and hexamethyltetramine, zinc acetate and urea are safer and cheaper. The relationship between crystallization quality, surface defects, optical properties and growth time of ZnO nanorods was investigated. The results show that with the rise of growth time, the length of ZnO nanorods gradually increases, and the crystalline quality gradually improves. The transmittance in the visible range is gradually enhanced, and the absorption edge near 375 nm becomes steeper. The photoluminescence spectra show that as the growth time increases, the intrinsic emission of the ZnO nanorods, i.e., the ultraviolet emission, is gradually enhanced, and the visible emissions related to the defects are gradually weakened. X-ray photoelectron spectroscopy (XPS) analysis show that the oxygen-related defects on the surface of ZnO nanorods gradually decrease with the increase of growth time, which is consistent with the results of the photoluminescence spectra.

In this work, a sol-gel method was used to deposit Al-doped ZnO coatings on stainless steel wire meshes. The effect of coating thickness on the morphology evolution and the photoluminescence, photocatalytic properties were investigated. Field emission scanning electron microscope (FE-SEM) observed that when the Al-doped ZnO coating was thin, it was composed of many nanoparticles. However, with the increase of the coating thickness, some sparse nanorods appeared on the ZnO coating surface. When the coating thickness was increased to six layers, the areal density of nanorods was largely increased. X-ray diffraction (XRD) patterns revealed that the ZnO coatings crystallized into a wurtzite structure, and the nanorods were preferentially oriented along the c-axis direction. Photoluminescence spectra showed that after ZnO nanorods were formed, the UV emission of ZnO coatings was significantly enhanced, which meant that the nanorods had better crystal quality than the nanoparticles. The photocatalytic performance tests for these samples showed that the sample formed by six layers of ZnO sol had the best photocatalytic activity due to its high crystalline quality and the large specific surface area. These ZnO coatings loaded on stainless steel wire meshes exhibited good photocatalytic stability.

Polycrystalline Cr,Nd:GSAG powders were synthesized by co-precipitation method using NH4OH as the precipitant. XRD, TG/DTA, FT-IR and Raman spectroscopy were used to characterize the structural properties of the precursor and the powders sintered at different temperatures. It was found that pure GSAG polycrystalline phase was obtained by sintering the precursor at 900 °C. The structure of the Cr,Nd:GSAG powder sintered at 1000 °C was refined using the Rietveld method. The lattice parameters are a = b = c = 12.4370(4) A, with α = β = γ = 90°. The highest photoluminescence intensity was achieved for the powder sintered at 1100 °C and optical properties of powders of different Cr3+ ions concentration were characterized by using photoluminescence spectroscopy.

ZnO thin film is a widely studied optoelectronic material at present. Doping is an important method to adjust its structural, optical, electrical and magnetic properties. A lot of doped ZnO thin films especially those doped with Al, Ga, Co have been extensively investigated. However, the Sr-doped ZnO thin films are still few reported up to now. In this work, the Sr-doped ZnO thin films have been deposited by sol–gel method. Their structural and optical properties have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectrophotometry and photoluminescence (PL), respectively. The results show that the appropriate Sr-doping levels can improve the crystalline quality and ultraviolet emission performance of ZnO thin films and suppress their visible emissions. This probably results from the decrease of point defects such as oxygen vacancy etc. due to the Sr-doping. What is more, it is also found that there exists a saturation value of Sr-doping concentration in ZnO thin films deposited using our prepared sol system, which is because the dopant Strontium chloride is slightly soluble in ethanol.

A single-layer broadband polarizer has been designed for operating in the telecommunication wavelength band. The rigorous coupled-wave analysis (RCWA) is applied to study the optical spectrum for the optimized structure. High polarization efficiency, high extinction ratio with a broad wavelength range (1.45–1.75 μm) are obtained. Both of the transmission efficiencies of TM-polarization and reflection efficiencies of TE-polarization are over 95%. The extinction ratio of transmission is over 30 dB in the 1.45–1.75 μm wavelength range, and the value is 114 dB for the central wavelength. The designed polarizer may lead to potential application in optical communication and infrared imaging polarimetry.

We present finite difference time domain (FDTD) and rigorous coupled-wave analysis (RCWA) simulations to analyze the optical absorption enhancement of thin film solar cells (TFSCs) employing front double dielectric and back plasmonic grating structures. Simulation results show that the combination of a subwavelength aperture and a double nano-structured dielectric grating with back triangle metallic grating results in an enhancement in total optical absorption. The absorption of the planar structure is enhanced thanks to an increase of the optical path length of the red and near-infrared photons, causing a proportional enhancement of the absorption in this spectral range. 90.85% Average harvesting (on TE and TM) can be achieved by the optimized structure in the spectrum range from 300 to 1100 nm. The designed SC has high integrated absorption and is weakly dependent on incident angle, which should be useful for application in film photovoltaics, photodetectors and infrared imaging.

Surface plasmon polaritons (SPPs) beam filter (BF) and beam splitter (BS) constructed using metal heterostructures are proposed and demonstrated numerically. Both structures have a ring metal heterowaveguide, which is constructed by a metal cylinder and a ring dielectric cladding. The two-dimensional finite-difference time-domain (2D-FDTD) method is employed to study the properties of the proposed BF and BS, and the results show that SPPs can effectively propagate on bended plasmonic waveguides with dielectric claddings. By introducing dielectric and plasmonic waveguides on both sides of the resonant ring, SPPs can be efficiently excited at the output of the waveguide ring resonator (WRR) through mode coupling. The planar metal heterostructures provide a way for constructing various nanoscale counterparts of conventional planar integrated devices such as filters, splitters, resonators, sensors, optical switches, and so on.

We provide an analytical model for the enhancement of optical absorption of active molecules when they are placed in the vicinity of metal nanoparticles of subwavelength dimensions. Through Mie theory, in the context of plane wave expansion (PWE) of a single sphere, we have shown that for a fully random molecular orientation, the absorption enhancement factor is equal to the local field intensity enhancement factor and depends strongly on the nanoparticle size-enabling optimization and separation between the object and metal sphere. With this understanding to the modified absorption, we call for further efforts in the engineering of the perfect absorber.

A high reflectivity (>99%) subwavelength grating mirror (SWGM), yields a very broad reflection spectrum (1.3–2.1 μm), has been designed for parallel polarized ( p -polarized) incident light and evaluated by rigorous electromagnetic simulations. Design-sensitive analysis was made by varying one parameter at one time while keeping the other constant. The operating region of the grating mirror can be adjusted by varying the parameters of grating. The results show that the broadband reflection is unaffected by the refractive index and the thickness of the low index material, which is different from the previous conclusions. Because of its ease of fabrication, the mirror can be integrated with any photonic component with a flat surface, which has potential applications for active and passive photonic devices.

Gold nanorods (AuNRs) are prepared through seeded growth approach. Synthesis parameters of the amount of cetyltrimethylammonium bromide (CTAB), and concentration of ascorbic acid (AA) were studied. We were aiming for an aspect ratio of 3 which could be achieved by a nanorod feature in the range of 45 nm length and 15 nm width. The absorption spectra are observed with an UV–visible NIR spectrophotometer and analysed theoretically. It is known that there are two plasmon resonance peaks for gold nanorod corresponding to transverse surface plasmon resonance (TSPR) and longitudinal surface plasmon resonance (LSPR), respectively. It is found that as the concentration of CTAB increases, the yield of NRs increases. As the concentration of AA increased from 0.05 to 0.2 M, LSP shifts to longer wavelength but upon further increasing the concentration, LSP shifts back to shorter wavelength. A linear relationship between LSPR wavelength and surrounding medium dielectric constant is obtained, which is in good agreement with the theoretical results.

In this study, uniformly distributed leaf-like ZnO nanostructure on glass substrates had been prepared by a simple two-step method. The structural properties were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activity of the leaf-like ZnO nanostructure had been investigated through the degradation of Rhodamine B under UV illumination and using a ZnO thin film and ZnO nanorods as the references. The results show that the photocatalytic activity of leaf-like ZnO nanostructure is higher than that of the ZnO thin film or ZnO nanorods. This is mainly because the leaf-like ZnO nanostructure has a larger surface area than ZnO thin films or ZnO nanorods. What is more, the leaf-like ZnO nanostructure is very firm on the substrate and its photocatalytic activity can be recycled and is stable.

Bandgap engineering of gallium zinc oxynitride (GaZnON) thin films has been performed by the GaN/ZnO pseudobinary alloying in a periodical superlattice order through the pulsed laser deposition technique. By tuning the growth temperature, the combined engineering of anions and cations in GaZnON quaternary alloys leads to a large tunability of the optical bandgap from 1.80 to 4.34 eV. In terms of the enthalpy of formation and kinetic dynamics of reactant species, nitrogen incorporation is effective to form Zn3N2-rich GaZnON quaternary alloys at low-temperature (

In recent years, heterogeneous photocatalysis has been paid much attention in the world as an important technique for treating wastewater. In this study, ZnO-decorated SnO2 nanopowders were prepared by hydrothermal method, and the effect of ZnO addition on the photocatalytic activity of SnO2 powder was investigated. The structure and morphology of the samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composition was determined by X-ray photoelectron spectroscopy (XPS). The recombination behavior of photogenerated electrons and holes was studied by photoluminescence. The photocatalytic activity of the samples was tested by degradation of methylene blue (MB) which was used as a simulated organic pollutant. The experimental results show that compared with pure ZnO and SnO2 powders, the particle size of ZnO-SnO2 composites is reduced, photoluminescence is weakened, but the photocatalytic activity is improved. The enhancement in photocatalytic activity is attributed to the increased specific surface area due to the decrease of particle size and the formation of ZnO-SnO2 heterojunction which inhibits the recombination of photogenerated electrons and holes.

Improving the response of ZnO photocatalyst to visible light is a hot topic. In this work, the porous ZnO thin films were first prepared by sol-gel method, and then CuO nanoparticles were deposited on the porous ZnO thin films to form CuO-ZnO heterojunction; the effect of CuO content on the photocatalytic activity of ZnO thin films were investigated. The results show that the formation of CuO-ZnO heterojunction effectively separates the photogenerated electron-hole pairs, leading to significant decrease of ZnO ultraviolet emission. In addition, the ZnO thin films with CuO nanoparticles modified on the surface increase the absorptive capacity in the visible range. Photocatalytic degradation of methylene blue shows that the photocatalytic activity of all CuO/ZnO thin films is greatly improved. The improvement of photocatalytic performance should be attributed to the enhanced separation efficiency of photogenerated electron-hole pairs by the CuO-ZnO heterojunction and the increased light absorption in the visible range by CuO nanoparticles. This kind of CuO/ZnO thin films also shows good photocatalytic reusability.

To provide a more practical, easy-to-implement method to achieve directional modulation with a plasmonic lens, beam manipulation method via compound metallic gratings with two subwavelength slits filled with different dielectrics inside each period is proposed and numerically investigated by finite-difference time-domain (FDTD) method. Compared with conventional metal-grating based structures, phase retardation is tuned by the Fabry-Perot (FP) resonant condition and light bending is achieved by constructing a carefully designed, curved phase front for the plasmonic lenses. Our designs have advantages in ease of fabrication and capability to perform in the far field. With these advantages, the designs are expected to be valuable in applications such as plasmonic circuits and photonic communication.

In this work, ZnO thin films were prepared by sol–gel method on Ag substrates. The structural and optical properties of the films annealed at different temperatures were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence, respectively. The results of XRD showed that all the ZnO thin films had a wurtzite phase and were preferentially oriented along the c -axis direction. The sample annealed at 400 °C exhibited better crystalline quality than the ZnO thin film directly deposited on a Si substrate annealed at the same temperature. The photoluminescence spectra showed that ZnO thin films had an ultraviolet emission band and three visible emission bands including green, yellow and red band. The sample annealed at 400 °C exhibited a stronger green emission and a weaker ultraviolet emission compared with the ZnO thin film deposited on a Si substrate annealed at the same temperature. The difference of the luminescence properties was thought to be originated from different substrates. As for the ZnO films on Ag substrates, the increase of annealing temperature led to different changes of visible emissions; namely, the green emission was enhanced rapidly, the yellow emission was increased slowly and the red emission was slowly increased first and then decreased. These changes of visible emissions under different annealing temperatures were attributed to the variations of defects density in ZnO.

Co-doped ZnO nanorods (ZnO: Co NRs)/p-Si heterojunction has been synthesized by a simple chemical route combine with sol–gel and hydrothermal methods. The structure analysis shows that the ZnO: Co NRs have wurtzite structures without any second phase, the Co ions successfully substitute Zn site in ZnO lattices. Room temperature ferromagnetism of ZnO: Co NRs is observed. The ZnO: Co NRs/p-Si heterojunction shows good nonlinear rectifying behavior with a turn on voltage of 4 V. Room-temperature electroluminescence (EL) spectra shows strong near band edge emission and defect related broad visible emission. With inject current increases, the dominant emission peak changes from visible to ultraviolet (UV). A red shift in visible emission is observed, this is ascribed to the doping effect of Co ions.

A new approach that incorporates two-dimensional photonic crystals (2D-PhCs) and distributed Bragg reflector (DBR) for light trapping to improve the performance of thin film solar cells (TFSCs) was theoretically demonstrated. With careful design optimization, the presented light-trapping structure can lead to a remarkable efficiency enhancement for the cells with very thin silicon active layers due to the significantly enhanced absorption. Rigorous coupled wave analysis (RCWA) simulations reveal that the absorption enhancement could be tuned by tailoring the parameters of the PhC structure. In the longer wavelength range (800 nm–1100 nm), enhanced light absorption can also occur, which is very important for improving absorption in TFSC. The designed back textured structures on the electrode lead to high scattering and diffraction of light when the hybrid structures provide a phase difference of π which helps to increase the effective thickness of TFSC and results in a higher short circuit current. Besides, the potential solar cell quantum efficiency (QE) was estimated.

A high performance sub-wavelength metallic grating coupled surface plasmon resonance (SWMGCSPR) sensor with metal and porous composite layer is proposed. Rigorous coupled-wave analysis (RCWA) is conducted to prove the design feasibility, characterize the sensor's performance and determine geometric parameters of the structure, which is also employed to compute the electromagnetic (EM) field distributions at the resonant wavelengths. Parameters of sensing platform are optimized to achieve the best performance of the SPR sensor. Obtained results reveal that the proposed structure can excite SPR with negative diffraction order of SWMG. Both wavelength and angular sensitivities are greatly enhanced because surface plasmon wave (SPW) exhibits a large penetration depth which will enlarge the distance of interactions between SP and analytes. The detection sensitivities and quality parameters are estimated to be 700 nm/RIU and 509°/RIU with full width at half maximum (FWHM) less than 2.5 nm using the same optimized structure.

ZnO nanorods have been synthesized by hydrothermal method on sol–gel derived ZnO seeds/p-Si substrates. The effect of annealing temperature of seed layers on the morphological, structural and optical properties of ZnO nanorods is systematically investigated. It is found that the diameters of nanorods is controllable ranging from 30 to 200 nm via seed layers annealing and the morphologies of ZnO nanorods change from tapered needle- to hexagonal-like structures. X-ray diffraction measurement shows that all nanorods possess a strong diffraction peak at 34.78° corresponding to ZnO (002) plane and no impurity phase is observed. Photoluminescence (PL) spectrum study shows that all samples exhibit strong near band edge emissions at 392 nm and defect related broad visible emissions centered at 550 nm. With increasing ZnO seeds anneal temperature, the visible emission intensity decreases gradually, which is attributed to the decreases of oxygen vacancies at high annealing temperature.

Tunable band-pass filter based on metal–insulator–metal (MIM) plasmonic circular ring resonators filled with Kerr nonlinear material is designed and numerically investigated by finite-difference time-domain (FDTD) simulations. Indium tin oxide (ITO) thin film with χ (3) =2×10 −10 esu is chosen to fill in the circular ring resonator. The designed filter has one stopband within the spectra range of 800 nm to 1100 nm and the bandwidth of a resonance is 32 nm. It is found that the transmitted-peak can be tuned by changing the intensity of incident light. Due to the Kerr nonlinear effect, the resonant wavelength of the cavity exhibits a red-shift with the increasing of the incident intensity. Narrow band filtering function at desired wavelength can be realized through tuning of peak resonance wavelength by changing the intensities of incident light. The designed plasmonic filter can find important potential applications in highly integrated optical circuits.

A trace gases detection system based on integrated cavity output spectroscopy (ICOS) was developed, where a NIR tunable diode laser (TDL) was used as light source, an optical cavity composed by two plan-concave mirrors with reflection near 99.7% was used as the absorption cell. Trace water vapour (H2O), carbon dioxide (CO2), methane (CH4), carbon monoxide (CO) and mixture of CO2 and CO were tested by ICOS based on the characteristics absorption. The wavelength calibration, cavity transmission characteristics, quantitative measurement ability and sensitivity of the TDL-ICOS were also studied, and a evaluated minimum detectable sensitivity of 1.15 × 10−7 cm−1 was obtained when the system was used to CH4 detection. The experiment results show that TDL-ICOS is expected to be a reliable and promising system for the detection of trace gases since it has some advantages such as real-time monitoring, simple device, easy operation, high sensitivity, good stability and quantitative ability.

ZnO/TiO2 multilayer thin films were prepared by electron beam evaporation and the influence of annealing temperature on their structural and optical properties was investigated. The analyses of X-ray diffraction (XRD) show that TiO2 in the as-deposited ZnO/TiO2 multilayer thin film as well as in that one annealed at 300 °C is amorphous. When the annealing temperature is increased up to 400 °C, the TiO2 is transformed into a brookite phase. Eventually, the TiO2 is transformed into an anatase phase with the annealing temperature rising up to 500 °C. However, ZnO in these composite films all crystallizes in a wurtzite structure and has a preferred orientation along the (0 0 2) direction whether the ZnO/TiO2 multilayer thin film is annealed or not. The photoluminescence spectra show that all the samples have two strong emission peaks including an ultraviolet (UV) peak and a violet peak. The strong UV and violet co-emissions in ZnO materials is seldom reported previously. With the increase of annealing temperature, both the UV and violet emissions are enhanced. However, the intensity of UV emission is increased faster than that of the violet emission under the same annealing temperature. The mechanism of the violet emission and the reason for the variations of the UV and violet emissions with the different annealing temperatures are analyzed.

ZnO/SiO 2 nanocomposite films with periodic structure were prepared by electron beam evaporation technique. Regulating effect of SiO 2 interlayer with various thicknesses on the optical properties of ZnO/SiO 2 thin films was investigated deeply. The analyses of X-ray diffraction show that the ZnO layers in ZnO/SiO 2 nanocomposite films have a wurtzite structure and are preferentially oriented along the c -axis while the SiO 2 layers are amorphous. The scanning electron microscope images display that the ZnO layers are composed of columnar grains and the thicknesses of ZnO and SiO 2 layers are all very uniform. The SiO 2 interlayer presents a significant modulation effect on the optical properties of ZnO thin films, which is reflected in the following two aspects: (1) the transmittance of ZnO/SiO 2 nanocomposite films is increased; (2) the photoluminescence (PL) of ZnO/SiO 2 nanocomposite films is largely enhanced compared with that of pure ZnO thin films. The ZnO/SiO 2 nanocomposite films have potential applications in light-emitting devices and flat panel displays.

International audience; Multisubstituted isoquinolines have been prepared by Rh(III)-catalyzed cyclization of benzylamines with diazo compounds via aryl C-H bond activation using molecular oxygen from air as an oxidant. This method features mild reaction conditions, simple catalytic system, tolerance of a broad range of substrates, high efficiency and regioselectivity.

In this study, pure ZnO thin film, Mg-doped ZnO (ZnMgO) thin film, ZnO/ZnMgO and ZnMgO/ZnO composite thin films were prepared by sol–gel technique. The structural and optical properties of the samples were analyzed by X-ray diffraction, scanning electron microscopy, UV–visible spectrophotometer, ellipsometer and photoluminescence spectra, respectively. The results showed that the incorporation of Mg increased the strain, broadened the optical bandgap, and improved the intensity of ultraviolet emission of ZnO thin film. The full width at half maximum (FWHM) of the ultraviolet emission peak was also increased due to Mg-doping at the same time. Compared with pure ZnO and ZnMgO thin films, the ZnO/ZnMgO thin film showed better crystalline quality and ultraviolet emission performance, smaller strains and higher transmittance in the visible range.

Frequency comb generation in microresonators at visible wavelengths has found applications in a variety of areas such as metrology, sensing, and imaging. To achieve Kerr combs based on four-wave mixing in a microresonator, dispersion must be in the anomalous regime. In this work, we demonstrate dispersion engineering in a microbubble resonator (MBR) fabricated by a two-CO$_2$ laser beam technique. By decreasing the wall thickness of the MBR down to 1.4 $\mu$m, the zero dispersion wavelength shifts to values shorter than 764 nm, making phase matching possible around 765 nm. With the optical \textit{Q}-factor of the MBR modes being greater than $10^7$, four-wave mixing is observed at 765 nm for a pump power of 3 mW. By increasing the pump power, parametric oscillation is achieved, and a frequency comb with 14 comb lines is generated at visible wavelengths.

A conventional VMI (velocity map imaging)-TOF (time-of-flight) spectrometer is modified by adding an extra electrode. By this small modification, the longitudinal focus can be realized for TOF mass resolution while maintaining the lateral focus for optimal VMI energy resolution simultaneously. The mass-resolving power by four-electrode ion optics is greatly enhanced. Our design is especially useful in experiment with a non-focused laser beam.

We have experimentally demonstrated an on-chip all-silk fibroin whispering gallery mode microresonator by using a simple molding and solution-casting technique. The quality factors of the fabricated silk protein microresonators are up to 10^5. A high-sensitivity thermal sensor was realized in this silk fibroin microtoroid with sensitivity of 1.17 nm/K, 8 times higher than previous WGM resonator based thermal sensors. This opens the way to fabricate biodegradable and biocompatible protein based microresonators on a flexible chip for biophotonics applications., 6 pages, 4 figures

A waveguide-coupled surface phonon resonance (SPhR) sensor with super-resolution based on Fano resonance (FR) by using a multilayer system within the Kretschmann configuration in the mid-infrared wavelength region is proposed. Due to the coherent interference of the waveguide and the surface phonon polariton modes, the calculated reflectivity spectrum possesses sharp asymmetric FR dips. An ultra-small linewidth is formed because of the Fano coupling, and the physical features contribute to a highly efficient nano-sensor for refractive index sensing. The bulk and surface sensitivity by intensities are greatly enhanced relative to those of conventional SPhR sensors.

One method for enhancement and manipulation of light absorption with monolayer graphene covered on a single-layer guided mode resonant Brewster filter surface is demonstrated. By means of the rigorous coupled-wave analysis method, the effect of geometrical parameters on the optical response of the structure is investigated. It is possible to achieve a maximum absorption of 60% at the Brewster angle; dual-band optical absorption can also be realized when the depth of the grating is increased. The situation of oblique incidence for TM polarization is studied as well; the absorption property can be controlled by adjusting the incident angle without changing the structural parameters. The proposed structure has the advantage of more free geometry parameters compared to the graphene disk and ribbon, so the absorption could be tuned more flexibly.

Under specific illumination conditions, periodic arrays of metal–dielectric–metal (MDM) waveguides act as uniform optical phased-array antenna where the phase of the radiating optical wave can be controlled by modifying the refractive index distribution of the dielectric material. Based on this property, we propose a planar gradient index MDM-based lens which can transform spherical waves of the transverse-magnetic surface plasmon polariton waves to plane waves with specific beam deflections by adjusting the refractive index configurations. Using numerical simulations based on two-dimensional finite-difference time-domain method, it is confirmed that beam focusing and splitting with multiple dflection angles can also be achieved.

In this work, ZnO thin films were prepared by sol–gel method and the dependence of structural and optical properties of these films on sol concentrations was deeply investigated. Unlike the previous studies, the ZnO thin films deposited in this study have approximately equal thickness, which excludes the influence of film thickness on the physical properties. The results show that low sol concentration is favorable for obtaining high c-axis oriented ZnO thin films with good crystalline quality. When the sol concentration is above 0.7 mol/L, the degree of c-axis orientation of ZnO thin films decreases and the optical quality is also degraded. Photoluminescence spectra indicate that the defect-related blue emission is increased with the enhancement of sol concentration. The mechanism of the blue emission is analyzed. The reason why high sol concentration is unfavorable for formation of high c-axis oriented ZnO thin films and obtaining high optical quality is also discussed.

Nd 3+ -doped gadolinium scandium aluminum garnet (Nd:GSAG) precursor was synthesized by a gel combustion method using metal nitrates and citric acid as raw materials. The structure and morphology of the precursor and the sintered powders were studied by means of X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). The results showed that the precursor transformed into pure GSAG polycrystalline phase at about 800 °C, and the powders sintered at 800–1000 °C were well-dispersed with average particle sizes in the range of 30–80 nm. Optical properties of Nd:GSAG nano-powders were characterized by using photoluminescence spectroscopy. The highest photoluminescence intensity was achieved for the powder sintered at 900 °C.

In this paper, we demonstrate an amorphous silicon (a-Si) thin film solar cell (TFSC) with a homogeneous layer of a-Si to absorb short wavelength photons and periodical a-Si nanorod structures for light trapping enhancement for longer wavelength photons. In such a design, the total absorption can be greatly improved. The periodicity and duty ratio of the nanorods were optimized to enhance the total optical absorption within 500 nanometer (nm) to 1000 nm in the hybrid TFSC structure. The best overall absorption can be achieved when period of nanorods is about 500 nm. When the duty ratio of nanorods is 0.6, the average absorption can reach 80% which represents an improvement by 40% compared to the conventional thin film a-Si solar cell without nanorod structures.

The insulin receptor (IR) recruits adaptor proteins, so-called insulin receptor substrates (IRS), to connect with downstream signalling pathways. A family of IRS proteins was defined based on three major common structural elements: Amino-terminal PH and PTB domains that mediate protein-lipid or protein-protein interactions, mostly carboxy-terminal multiple tyrosine residues that serve as binding sites for proteins that contain one or more SH2 domains and serine/threonine-rich regions which may be recognized by negative regulators of insulin action. The current model for the role of IRS proteins therefore combines an adaptor function with the integration of mostly negative input from other signal transduction cascades allowing for modulation of signalling amplitude. In this review we propose an extended version of the adaptor model that can explain how signalling specificity could be implemented at the level of IRS proteins.