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We report the investigation on the lateral shifts that linearly-polarized (LP) and radially-polarized (RP) Bessel beams experience during the Mie scattering by a nanosphere. A numerical procedure based on the angular spectrum theory is developed to solve the scattered electromagnetic field and subsequent lateral shifts with a high computational efficiency, which can be easily applied to an arbitrary shaped polarized beam. The influences of different factors, including conical angle, nanosphere radius and position, on the lateral shifts are systematically investigated. The results demonstrate that for on-axis scattering, a LP Bessel beam can be regarded as a plane wave with the same polarization state but an equivalent longer wavelength, while a RP Bessel beam can be regarded as a plane wave with a polarization state along the propagation direction exhibiting independence on the conical angle. The findings help deepen our understandings of lateral shifts in light scattering of vectorial non-diffractive beams.

Fast quantitative characterization of a rectangular groove with sizes from sub-micrometers to micrometers on a surface has been demanding in quality control of optical elements. We report a numerical procedure for retrieval of the geometrical parameters of a rectangular groove, including width and depth, from the angular distribution of the scattered light generated by launching plane waves on the groove on a metallic surface from different propagation directions. The far-field intensity of scattering light is first obtained by numerically solving the electromagnetic problem with the modal theory. Then, a two-stage inverse modeling approach is developed to retrieve the groove parameters based on the lookup table and repulsive particle swarm optimization from multi-angle scattering light distribution that is highly sensitive to the groove parameters. Noise influences are considered in the simulation. Results suggest that our method can precisely obtain the groove parameters for noisy signals. As the measurement of light scattering can be conducted with high efficiency, it should be a powerful tool to characterize rectangle grooves on metallic surfaces.

Light scattering has been proven to be an effective tool to characterize and classify particles of different properties. However, inverse modeling to quantitatively retrieve the particle property from light scattering is still a tough task in most applications. In this paper, a hybrid approach using machine learning and genetic algorithm is developed to obtain the geometrical and optical parameters of a sphere from its angular scattering pattern in a light sheet. Scattering patterns related to different parameters are first generated by numerically solving Mie scattering based on angular spectrum theory. Multilayer perception neural network (NN) is then employed to roughly estimate the parameter, while genetic algorithm is adopted to retrieve the precise value. Influences of intensity noise on the inverse modeling are finally examined. Results suggest that the proposed hybrid approach can retrieve the parameters of the sphere from its scattering pattern with high precision in a time-effective manner, which could be widely applied in various scattering-based instruments.

Ag doped ZnO thin films have potential applications in many electronic and optoelectronic devices. Effective control of the chemical state of Ag is important for adjusting the electrical and optical properties of Ag-doped ZnO materials. So far, the influence of annealing temperature on the physical properties of Ag-doped ZnO thin films prepared by sol-gel method has rarely been reported. In this work, Ag-doped ZnO thin films were prepared by spin-coating technique and the evolution of microstructure, optical properties and conduction type with the rise of annealing temperature were investigated. The experimental results show that with the increase of annealing temperature, the crystalline quality of Ag-doped ZnO thin film is gradually improved and the grains gradually grow up. The ultraviolet emission has been also enhanced step by step. When the annealing temperature exceeds 450 °C, the surface segregation of Ag is directly observed by a field emission scanning electron microscope. In addition, the diffraction peak of metallic Ag is also perceived on the XRD patterns. The X-ray photoelectron spectroscopy shows that the chemical valence of Ag has been changed from +1 to 0. The surface segregation of Ag leads to the conduction type of the ZnO thin film to change from P type to N type. The surface segregation of Ag is caused by the high annealing temperature combined with a rapid cooling treatment.

In this work, Sn-doped ZnO thin films were deposited by sol-gel method. The structural, morphological and optical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, fluorescence spectroscopy, respectively. The composition of the films was examined by energy dispersive X-ray spectroscopy (EDX). The photocatalytic performance was tested using methylene blue (MB) as a simulated organic pollutant. The results showed that all the ZnO thin films were preferentially oriented along the c-axis direction. The Sn-doping led the grains of the ZnO films to decrease. However, a kind of truncated-cone shaped nanostructures occurred on the surface of ZnO thin films when Sn-doping concentration was above 2 at.%, and both the number and the size of the ZnO truncated-cones increased with the further rise of the Sn-doping concentration. As a result, the surface roughness of the films was largely enhanced and the optical absorption was also improved. The wettability of the films was investigated by the water droplet spreading on the ZnO thin film surfaces. It showed that Sn-doping resulted in a smaller contact angle. The photocatalytic test on MB dyes showed that Sn-doping enhanced photodegradation efficiency of ZnO thin films. The improvement of the degradation efficiency was attributed to three main factors: (1) the formation of truncated-cone nanostructures on the surface of ZnO thin films increased the surface roughness and optical absorption; (2) the recombination of photogenerated electrons and hole was suppressed; (3) Sn-doping enhanced the surface energy of the ZnO thin films.

In this letter, the room-temperature ferromagnetic behavior in the ZnO/CuO nanocomposites has been reported. The composites composed of ZnO and CuO with different ratios were prepared by hydrothermal method. X-ray diffraction (XRD) and selected area electron diffraction (SAED) confirmed that these composites were made up by wurtzite ZnO and monoclinic CuO. X-ray photoelectron spectroscopy (XPS) indicated that Cu ions on the surface of the materials were in a divalent state. Magnetic measurements showed that all ZnO/CuO composites possessed room-temperature ferromagnetism, while pure ZnO was diamagnetic. With the increase of CuO content in the composites, ZnO/CuO composites displayed the coexistence of ferromagnetism and paramagnetism, and paramagnetism was gradually enhanced and dominated later.

We systematically explore the effects of Raman scattering (RS) on modulation instabilities (MIs) in nonlinear two-core optical fibers (TCFs) with the symmetric and antisymmetric continuous wave (CW) states. The main contribution of this paper is that the analytical gain spectra with RS effects are given explicitly for both anomalous and normal dispersion regimes. Our results show that the MI spectra with RS effects can be significantly changed. First of all, MI arises for any total power in both normal and anomalous dispersion regimes. Secondly, MI gain can be significantly enhanced especially at large values of perturbation frequencies. In addition, the modulation frequency generating MI expands from the finite frequency domain without RS effects to the infinite frequency domain. The MI analysis is finally verified numerically with wave propagation method.

Rigorous solution of plane-wave scattering by a groove based on electromagnetic theory will be time-consuming if the groove width is much larger than the illumination wavelength. To accelerate the computation, an approach based on geometrical optics approximation is developed here. The incident beam is split into several parts during reflection and refraction. Contribution of every part is superposed to obtain the electric field at the interface between the groove and air, with which diffraction theory is utilized to calculate the far-field scattered light. Results demonstrate that the approach is capable of accurately calculating plane-wave scattering by rectangular grooves with large widths in a time-efficient manner, which can be beneficial for further inverse scattering problems.

It is a recent hot topic of widespread interest to control the optical properties of metal oxide by noble metal nanoparticles. In this work, ZnO/Ag nanocomposite thin films were prepared by one-step sol-gel method. The crystal phase, morphology of the samples was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The presence of silver nanoparticles was confirmed by transmission electron microscopy (TEM). The distribution and chemical valence state of Ag in the samples was analyzed by elemental mapping images and X-ray photoelectron spectroscopy (XPS), respectively. The optical properties of the samples were studied by UV–visible spectroscopy and photoluminescence. It is found that the thermal treatment temperature has an important effect on the chemical state of silver in ZnO, and the change of chemical state of silver in turn affects the ultraviolet (UV) emission of ZnO. Under an appropriate heating temperature, the doped silver in the ZnO thin film can form silver nanoparticles, and the photoemission transfer of electrons from the silver nanoparticles to ZnO can effectively enhance the UV emission of ZnO thin film. The results show that under the experimental conditions applied in this study, 250°C is an optimum heating temperature, since the ZnO/Ag composite film heated at 250 °C has the strongest UV emission performance.

In recent years, Cu-doped ZnO materials have attracted wide attention due to some unique properties, such as p-type conduction, room-temperature ferromagnetism and plentiful luminescence behavior. In this work, Cu-doped ZnO thin films with different doping levels were prepared by sol–gel method. The structural, morphological features and the composition of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX), respectively. The optical properties were analyzed by the UV–visible transmittance spectra and fluorescence spectra. The Cu-doping in a low concentration does not influence the crystal phase of wurtzite ZnO and has a very small impact on c-axis preferred orientation of ZnO thin films. With the increase of Cu-doping concentration, the Cu ions are gradually changed from dominant Cu+ ions to dominant Cu2+ ions. Cu-doping in a low concentration caused strong blue-violet emissions in ZnO thin films. The violet emission is attributed to the transition of electrons from the conduction band to Cu+ acceptor levels, and the blue emission is ascribed to the transition of electrons from Cu2+ donor levels to Cu+ acceptor levels.

An ultra-broadband and angle-insensitive absorber is proposed and demonstrated in the mid-infrared (MIR) atmospheric window. The structure is coated with periodically arranged metal grating on top of a metal-insulator-metal (MIM) plate. The average absorption is up to 96.6% in the range of 8–14 µm. Due to the structural characteristics, the absorption properties are polarization-dependent, and the perfect absorption can be realized for a TM-polarized wave when the incident angle is smaller than 50°, bandwidth of 90% absorption reaches approximately 6 µm. The absorption characteristics can be feasibly manipulated via tuning the geometrical parameters. The electrical field intensity distributions are studied to disclose the broadband absorption mechanism. The proposed broadband absorber has many potential applications, including polarization detectors, heat radiators, infrared sensors and so on.

Gallium oxide (Ga2O3) thin films were deposited on c-plane sapphire substrates at low temperature (RT) by magnetron sputtering method using Ga2O3 ceramic target and were post annealed at various temperatures ranging from 500 to 900 ℃ . The effect of annealing temperature on the surface morphology, crystalline structure, chemical composition and optical properties of Ga2O3 thin films were investigated. A phase separation is observed at 800 ℃ and α -phase Ga2O3 thin films is obtained at low annealing temperature while β -Ga2O3 at high temperature. With annealing temperature increases, the optical bandgap decreases from 5.47 to 5.00 eV and the surface morphology become more and more smooth. A broad emission band centered at 550 nm is observed for all samples which can be attributed to the donor acceptor pair (DAP) recombination related to the oxygen vacancies.

Characterization of a rectangular groove with a width of several micrometers on a metallic surface has been demanding for surface quality evaluation in the fabrication of high-quality optics. In this paper, a numerically study on Gaussian light sheet scattering by a groove is performed based on angular spectrum and modal theories in accordance with requirements of a practical experiment setup. Plane wave scattering is first solved by the modal theory and then superposed to obtain Gaussian light sheet scattering. Influences of illumination and groove parameters are finally investigated. Results show that the groove information is encoded in the scattering signal, which gives indications to the establishment of metrology systems.

In order to achieve the enhancement and manipulation of light absorption in graphene monolayer within the visible (Vis) and near infrared (NIR) regions, a design of absorber inspired by contact coupled gratings with an absentee layer is demonstrated. It is proved that the absorptance of monolayer graphene can be greatly enhanced to near unity through rigorous coupled-wave analysis (RCWA) numerical calculation. The thickness of grating and homogeneous absentee layers can significantly change the linewidth and resonant mode position in absorption spectrum. Furthermore, the lateral shift of the contact coupled gratings changes the magnetic field distributions in the grating cavity and the surface-confined mode at the cover/grating interface, thus facilitating the dynamic control of the spectral bandwidth of the graphene absorber. The proposed devices could be efficiently exploited as tunable and selective absorbers, allowing to realize other two-dimensional (2D) materials-based selective photo-detectors.

Pattern assisted ZnO nanorods (NRs) growth are performed using electron beam lithography (EBL) and hydrothermal method. The patterns of lines, circles and squares are prepared on polycrystalline ZnO seed layer using PMMA as photoresist. It is found that the ZnO NRs can only grow on the area with ZnO seed layer, not on the PMMA surface. The TEM results show that the ZnO NRs have single crystal structures with good orientation along the c-axis. The excitation power dependence of photoluminescence (PL) spectra of ZnO NRs shows that with excitation power increasing, the near band edge emission increases rapidly than the defects related visible emissions. The temperature dependence of PL spectra was measured in the temperature range of 13–300 K. The dependence of peak position and peak energy of exciton bound (D0X) emission of ZnO NRs on temperature were analyzed. Two non-radiative recombination channels for the D0X emission are discussed in detail.

We report on a novel method of generating light sheet with extended depth of field based on one-dimensional Airy beam by the use of single cylindrical lens. In the method, coma is intentionally introduced into the system by oblique illumination to approximate a cubic phase mask. Experimental studies were presented to validate this method. This technique can be easily applied to current light sheet generators where cylindrical lens is used, as only tilt of the cylindrical lens is needed.

Color coding has been experimentally demonstrated to be able to extend the depth of field (DoF) of an imaging system in single snapshot. A numerical model is adopted in this paper to quantitatively characterize its imaging properties (strehl ratio, point spread function and modulation transfer function). To improve the system’s performance under nonuniform spectrum, we proposed to introduce wavefront coding into the system. Numerical results show that wavefront coding acts as an average filter of the spectrum, so that it is able to get an almost invariant MTF across the focal line even under nonuniform spectrum, which is desirable in many applications.

In this study, nanocrystalline TiO 2 modified ZnO thin films were prepared by electron beam evaporation. The structural, morphological and optical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV-visible spectroscopy, fluorescence spectroscopy, respectively. The composition of the films was examined by energy dispersive X-ray spectroscopy (EDX). The photoluminescent spectrum shows that the pure ZnO thin film exhibits an ultraviolet (UV) emission peak and a strong green emission band. Surface analysis indicates that the ZnO thin film contains many oxygen vacancy defects on the surface. After the ZnO thin film is modified by the nanocrystalline TiO 2 layer, the UV emission of ZnO is largely enhanced and the green emission is greatly suppressed, which suggests that the surface defects such as oxygen vacancies are passivated by the TiO 2 capping layer. As for the UV emission enhancement of the ZnO thin film, the optimized thickness of the TiO 2 capping layer is ∼16 nm. When the thickness is larger than 16 nm, the UV emission of the ZnO thin film will decrease because the TiO 2 capping layer absorbs most of the excitation energy. The UV emission enhancement in the nanocrystalline TiO 2 modified ZnO thin film can be attributed to surface passivation and flat band effect.

In this work, the multilayered thin films composed of ZnO nanoparticles and SiO x layers were prepared by electron beam evaporation. The evolution behavior of photoluminescent properties of the samples with the increase of ZnO nanolayer thickness and annealing temperature was investigated. The morphology, crystal structures and luminescent properties of the samples were analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and photoluminescence (PL), respectively. The SEM images revealed that the thin films were multilayer-structured with ZnO nanoparticles sandwiched in SiO x layers. The HRTEM disclosed that the SiO x was amorphous and ZnO was crystalline. The componential analyses showed that ZnO nanoparticles contained many oxygen vacancies and the x for SiO x was 1.96. The pure ZnO thin film showed three strong emission bands (namely, near ultraviolet, green and red emission bands) with nearly identical intensity. However, as for the ZnO nanoparticles sandwiched in SiO x layers, their green emission efficiency was greatly improved and the red emission was suppressed. Annealing treatments at 300 and 400 °C further enhanced the green emission. The largely enhanced green emission was attributed to the strong interaction between ZnO and SiO x .

Narrow band mid-infrared (MIR) absorption is highly desired in thermal emitter and sensing applications. We theoretically demonstrate that the perfect absorption at infrared frequencies can be achieved and controlled around the surface phonon resonance frequency of silicon carbide (SiC). The photonic heterostructure is composed of a distributed Bragg reflector (DBR)/germanium (Ge) cavity/SiC on top of a Ge substrate. Full-wave simulation results illustrate that the Tamm phonon-polaritons electric field can locally concentrate between the Ge cavity and the SiC film, contributed to the improved light-phonon interactions with an enhancement of light absorption. The structure has planar geometry and does not require nano-patterning to achieve perfect absorption of both polarizations of the incident light in a wide range of incident angles. Their absorption lines are tunable via engineering of the photon band-structure of the dielectric photonic nanostructures to achieve reversal of the geometrical phase across the interface with the plasmonic absorber.

A multispectral absorber based on Bloch surface wave (BSW) resonance with distributed Bragg reflectors (DBRs) coated with monolayer graphene is proposed. The guided Bloch surface wave resonance (GBSWR) is realized by coupling the diffraction of a subwavelength grating with the BSW at the interface between a 1D-PhC and graphene layer. Strong absorption phenomenon occurs induced by the coupling of the incident light and GBSWR. The highly efficient absorption and spectral selectivity with designing structural parameters in the visible range are verified through the rigorous coupled-wave analysis (RCWA) method. It is found that the number of absorption peaks is strongly related with the stacked period number of two dielectric materials in DBR. Compared with previous studies, not only the complete absorption of single-atomic-layer graphene can be achieved, but also the above 90 % absorption for all of resonance positions is maintained. These characteristics open up new methods of enhancing the light-graphene interaction, which may find potential application in high-performance modulators and sensors.

As an important optoelectronic material, ZnO thin film has been used in lots of fields such as antireflection optical coatings, photoluminescence-based sensors, photocatalysts, etc. Many studies have demonstrated that the characteristics of the surface layer of ZnO thin film (such as crystalline state, point defect types, number of point defects, roughness, etc.) dominate its physical properties and thus determine the performance of the optoelectronic or microelectronic device prepared from it, so how to effectively control the characteristics of the surface layer is worthy of in-depth study. In this investigation, we prepared ferric chloride doped ZnO thin films and explored the effect of heat-treatment temperature on the crystalline state and luminescence behavior of the surface layer. The results show that all samples possess a double-layer structure: the bottom layer is a conventional ZnO layer composed of polycrystalline particles, while the top layer is made up of dense pyramid-like nanostructures. These pyramid-like nanostructures have good crystalline quality and high c-axis orientation. The increase of the heat-treatment temperature accelerates the formation of a high-quality optical surface layer in the ZnO thin film, and the formation of this high-quality surface layer in turn greatly improves the ultraviolet emission efficiency of the ZnO thin film.

In this work, ZnO thin films were prepared by electron beam evaporation and rapidly annealed at different temperatures. The analysis of X-ray diffraction (XRD) showed that all the ZnO thin films were preferentially oriented along the c-axis. With the increase of annealing temperature, the degree of preferred orientation along the c-axis was enhanced and ZnO crystals also increased gradually. However, the transmittance and optical bandgap of the samples were almost not affected by the rapid annealing treatment. The photoluminescence spectra showed that all the samples exhibited strong UV and visible emissions (mainly green and red emissions). Although the strong UV emission along with strong green emission was often reported previously, the strong co-emission of UV, green and red light was rarely reported. If, as many researchers suggested, the green emission of ZnO was mainly related with oxygen vacancy defects and the red emission was associated with oxygen interstitial defects, thus the strong co-emission of green and red light was hard to happen in theory. The strong co-emission of green and red light or green/red emissions with different wavelengths at the same time implies that there are probably several sources for green or red emissions. Deeply and extensively investigating the luminescence behavior of ZnO materials is favorable for revealing visible emission mechanisms and developing ZnO-based light-emitting devices as possible as soon.

In this work, ZnO and CuO were first prepared by thermal evaporation and direct precipitation, respectively, and then CuO/ZnO composites were obtained by mechanical grinding the mixtures of CuO and ZnO. Scanning electron microscopy, Raman spectroscopy, Raman imaging, UV–vis absorption spectroscopy, and photoluminescence spectroscopy were used to analyze the morphology, structure, and optical properties of CuO/ZnO composites. Raman spectra suggest that the prepared ZnO has a high crystalline quality, while the CuO/ZnO composites have an internal stress. Compared with ZnO, the absorption edge of CuO/ZnO composites shows a red-shift, and the absorption intensity in the visible region is increased greatly. Pure ZnO shows a strong ultraviolet (UV) emission and a weak green emission. As for the CuO/ZnO composites, with the increase of CuO content, the intensity of the UV emission is gradually reduced and the UV peak is gradually moving towards the longer wavelength direction. The decrease in the UV emission intensity should be attributed to interface effects, and the red-shift of UV emission peaks may be caused by unintentional Cu-doping.

ZnO thin film is an important optical material. Therefore, using simple methods or techniques to improve its optical quality is an important research topic. In this study, a sol-gel spin-coating method was used to deposit ZnO thin films co-doped with Fe and Cl on glass substrates and the effect of annealing temperature on their microstructure and optical properties was explored. Field emission scanning electron microscope observes that all samples have a double-layer structure: the upper layer is composed of single-crystal nanocolumns and the lower layer is made up of polycrystalline nanoparticles. The increase of annealing temperature leads to some important changes: (1) the UV emission is gradually enhanced; (2) the absorption edge is gradually red-shifted; (3) cavities are formed in the lower layer of ZnO thin films. As far as we know, there are few reports on cavities in the lower layer of ZnO thin films. The appearance of these cavities, we speculate, is due to the mass transport from the lower layer to the upper layer, that is, the formation of single crystal nanocolumns is the result of sacrificing the polycrystalline nanoparticles in the lower layer of ZnO thin films.

The Zn-Sn-(OH)x thin film was prepared by sol-gel method at low temperature, and its structure, morphology, and photoluminescence properties were studied as a function of annealing temperature. X-ray diffraction patterns showed that the as-grown film contained highly crystalline zinc hydroxystannate. When it was annealed at 300 °C, zinc hydroxystannate was decomposed, and wurtzite-structured ZnO was formed. High-resolution TEM images and selected electron diffraction patterns further confirmed the formation of wurtzite-structured ZnO after annealing. The scanning electron microscope observed that the as-grown Zn-Sn-(OH)x film contained two layers: the upper layer was a crystalline ZnSn(OH)6 thin film, and the underlying layer was an amorphous Zn-Sn-O ternary composite. After it was annealed at 300 °C, some pyramid-like nanostructures appeared on the film surface. As the annealing temperature was further increased, the areal density of the pyramid-shaped nanostructures decreased, but the diameter and height increased. The photoluminescence spectra showed that the ZnSn(OH)6 film exhibited strong violet and blue-green co-emission. After annealing, the visible emission intensity was obviously reduced, while an ultraviolet emission from ZnO was being appeared. We proposed that the violet emission of ZnSn(OH)6 thin film might be related to the zinc interstitials, and the blue-green emission should come from the electronic transitions related to oxygen vacancy levels.

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.

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.

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.

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 b s t r a c t Pure 2% and 4% Ag-doped ZnO thin films have been synthesized on glass substrates by sol–gel method. The structure, morphology and optical properties of the samples have been studied by X-ray diffractometer (XRD), scanning probe microscope, UV–vis spectrophotometer, respectively. The XRD result shows that the pure ZnO has a wurtzite hexagonal structure, no phase segregation is observed. The surface morphology of pure ZnO thin film shows that the grains are growing preferentially along the c-axis orientation perpendicular to the substrates. The transmittance spectra reveal that all samples have high transmittance above 90% in visible region. With Ag doping content increase, a red shift is observed. The performance of Ag-doped ZnO films using in thin film solar cells are simulated. The results show that 4% Ag-doped ZnO thin film can greatly improve the absorption of the cells. Compare to pure ZnO, solar cell’s energy conversion efficiency improvement of 2.47% is obtained with 4% Ag doped ZnO thin film.

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.

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 thin films with various Nd doping levels (0%, 1%, 3% and 5%, respectively) have been synthesized by the sol–gel method on glass substrates. X-ray diffraction (XRD) spectra and atom force microscope (AFM) studies reveal that all samples possess hexagonal wurtzite structure without any second phase. 1% Nd doped ZnO thin film has the best crystalline quality. With Nd concentration increases, the grain size reduces gradually. The optical measurements show that with Nd concentration increases, the absorption peak shifts to short wavelength, which indicates that the optical band gap of Nd-doped ZnO thin films increases. All samples have ultraviolet emission centered at 377 nm and strong green emission at 511 nm. The intensity of green emission gradually increases with Nd concentration increases. The emission mechanism is discussed in detail.

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.

ZnO thin films with various Co doping levels (0%, 1%, 3%, 5%, 8%, respectively) have been synthesized by sol gel spin coating method on glass substrates. XRD and XPS studies of the films reveal that cobalt ions are successfully doped into ZnO crystal lattice without changing the hexagonal wurtzite structure. The morphologies are studied by SEM and AFM and show wrinkle network structures with uniform size distribution. With Co doping concentration increasing, the wrinkle network width decreases gradually. The transmittance spectra indicate that Co doping can effectively reduce the optical bandgap of ZnO thin films. Photoluminescence show that all samples have ultraviolet, violet and green emission. When Co doping concentration increases up to 5%, the intensity of violet emission is greatly increased and a strong deep blue emission centered at 439 nm appears. The ferromagnetism of all samples was observed at room temperature. The emission mechanisms and ferromagnetism origination are discussed in detail. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate subwavelength grating-coupled distributed Bragg reflector (DBR) in order to achieve total absorption at preselected wavelengths in a graphene monolayer. Multispectral and near-unity absorption (approximately 99.44% of the incident light at normal incidence) can be achieved in the proposed photonic structure at near-infrared (NIR) regimes. When the system meets the condition of critical coupling, the excited guided mode resonance (GMR) occurs at the resonance wavelength, and the corresponding electric field intensity around the graphene sheet can be greatly enhanced due to the reinforced light-graphene interaction. Multiple absorption peaks can be tuned within the wavelength region of 1.3 μm to 1.6 μm by varying the structural parameters. Our findings also indicate that the near-total-absorption peaks are highly dependent on the number and thickness of unit cells in DBR. These features make the proposed structure have great potential in applications of scalable perfect absorbers (PAs).

The surface modification plays an important role on both physical and chemical properties of zinc oxide (ZnO) materials. In this review paper, efforts are made to summarize and analyze reported results regarding surface modification method, surface modification effect on the luminescence and superhydrophobic properties of ZnO thin films and nanostructures. Furthermore, the photocatalytic activity and gas sensor property of modified ZnO using both organic and inorganic species are also involved.

A planar graphene-coated multilayer configuration for the excitation of multiple optical Tamm states and significant improvement of the light absorption has been demonstrated. Significantly, unity absorption can be realized in graphene for which the total thickness of the absorbing layer is as small as 1/220 of the incident wavelength. The designed graphene absorber has excellent optical performance for sensing applications, along with the advantage of an all-dielectric form. Additionally, our proposed methodology is applicable to other two-dimensional materials with deep sub-wavelength thicknesses and paves the way for efficient energy-harvesting devices with simple planar structures.

Modulation instabilities in the randomly birefringent two-mode optical fibers (RB-TMFs) are analyzed in detail by accounting the effects of the differential mode group delay (DMGD) and group velocity dispersion (GVD) ratio between the two modes, both of which are absent in the randomly birefringent single-mode optical fibers (RB-SMFs). New MI characteristics are found in both normal and anomalous dispersion regimes. For the normal dispersion, without DMGD, no MI exists. With DMGD, a completely new MI band is generated as long as the total power is smaller than a critical total power value, named by Pcr, which increases significantly with the increment of DMGD, and reduces dramatically as GVD ratio and power ratio between the two modes increases. For the anomalous dispersion, there is one MI band without DMGD. In the presence of DMGD, the MI gain is reduced generally. On the other hand, there also exists a critical total power (Pcr), which increases (decreases) distinctly with the increment of DMGD (GVD ratio of the two modes) but varies complicatedly with the power ratio between the two modes. Two MI bands are present for total power smaller than Pcr, and the dominant band can be switched between the low and high frequency bands by adjusting the power ratio between the two modes. The MI analysis in this paper is verified by numerical simulation.