Tailoring titanium dioxide by silver particles for photocatalysis

Titanium dioxide-silver (TiO₂–Ag) composites are synthesized by using the hydrothermal method with different weight ratios for photocatalyst applications. With the introduction of Ag, the composites exhibited absorbance in visible region, and the bandgap also decreased by 0.45 eV. The TiO₂–Ag composite with 5:7 ratio shows the best photocatalytic degradation of methylene blue, the highest photocurrent response, and the lowest electrochemical impedance, thus exhibiting the best photocatalytic performance. The introduction of Ag into TiO₂ retards the recombination time of the photo-generated electrons and holes as well as increases the charge transfer rate at interfaces of the composites.     

光子晶体光纤带隙特性的研究

应用平面波展开法数值模拟得到了光子晶体光纤带隙特性,为光子晶体光纤器件的开发提供了理论依据。     

Evaluation of bandgap energy and carrier density of InN nanocolumns

We have measured the optical properties of wurtzite InN nanocolumns and film by photoluminescence (PL) measurements at temperatures from 5 to 300 K and analyzed the PL spectra by fitting with the free-electron recombination bound (FERB) model. For the top-linked InN nanocolumns, we observed strong PL intensity compared to the InN film sample. The PL spectra were asymmetrical with low-energy tails and a red-shift of the PL peak energy position was observed with increasing temperature. However, for the separated InN nanocolumns, we observed weak PL intensity and symmetrical PL spectra. Analyzing the spectra shape of the top-linked InN nanocolumns at 5 K using the FERB model, we evaluated the intrinsic bandgap energy and carrier density of InN nanocolumns to be 0.69 eV and 2.5×10¹⁷ cm⁻³, respectively.     

Synthesis,optical, electrochemical and electroluminescent properties of novel fluorene-alt-bithiophene copolymers bearing phenylvinyl bridged accepting side chains

Two-dimensional poly[fluorene-alt-bithiophene] backboned copolymers were prepared by introducing phenylvinyl bridged accepting side chain containing malononitrile, 1,3-indanedione, or 4-nitrophenyl acetonitrile accepting moiety. The structural, optical, electroluminescent, electrochemical properties of these polymers were studied in details. These polymers possess good thermal stability and low highest occupied molecular orbital (HOMO) level (−5.59 to 5.67 eV). Results show that the introduction of π-conjugated accepting side chains can effectively adjust the optical and electrochemical properties of the resulting polymers. These new alternating copolymers may be promising electroluminescent materials.     

无机卤化物钙钛矿纳米结构的带隙可调制备及光电应用研究

在半导体领域,通过合金化集成两种以上半导体的单纳米结构近年来相继问世,随着纳米材料的成分变化,可以灵活实现半导体的带隙调控,在光通信以及集成光电器件领域有着广泛的应用。然而,传统半导体纳米结构因不同成分之间存在晶格失配,其带隙调节的范围受到了很大限制。因此,钙钛矿作为对晶格失配具有高容忍度的半导体材料,在半导体带隙调控及器件研究领域显示出了巨大的潜力。本文综述了无机卤化物钙钛矿一维合金纳米材料的合成方法以及近年来的研究进展,总结了可调带隙钙钛矿一维合金纳米材料在光电子器件领域中的应用,包括波长可调谐纳米激光器、光电探测器、白光发光二极管、全光开关、太阳能电池等。实现单纳米结构带隙工程将对未来集成器件的发展产生深远的影响。     

Insight into the Multistate Emissive N,P-doped Carbon Nano-Onions: Emerging Visible-Light Absorption for Photocatalysis

Carbon dots (CDs) have become one of the most emerging materials as an alternative solar light-induced photocatalyst in contrast to traditional metal-based systems. However, one of the major challenges is the lack of visible light absorption. Herein, we have fabricated unique N, P-co-doped CDs with a self-assembled onion-like layered structure by using a bottom-up facile synthesis technique from chitosan gel and phosphoric acid as molecular precursors. This typical layered structure of N, P-co-doped carbon nano onions (N, P-CNOs), with an average size of 25–50 nm, displays an enhanced visible light absorption. Detailed structural and elemental characterizations confirm the extensive aromatic domain with P-containing surface functionalities, while electrochemical study clarifies the lowering of band gaps as well as the creation of new electronic states in comparison to the pristine N-CDs. Furthermore, the intrinsic structural features are correlated with the underpinning photophysical processes by steady-state and time-resolved fluorescence spectroscopy. In addition, steady-state polarized emission and thermo-responsive PL properties have been carried out to unveil further the structure-property correlation of N, P-CNOs, and their comparative study with pristine N-CDs at the different excitation wavelengths. Finally, N, P-CNOs exhibit efficient visible-light-induced photocatalysis, and the detailed mechanistic study is carried out by trapping the photogenerated species in an aqueous medium. The prepared N, P-CNOs displayed an excellent visible-light photocatalytic performance over MB dye with a degradation efficiency of 75.8% within 120 min along with a degradation rate constant of ∼0.0109 min⁻¹. It is concluded that the easy to synthesize and low-cost N, P-CNOs with a unique morphology hold great potential for application in visible-light photocatalysis.     

Modeling and Testing of Uniform Fiber Bragg Gratings Using 1-D Photonic Bandgap Structures in Microstrip Technology

A way to model and test fiber gratings and fiber grating-based systems in the microwave range is proposed. The method rests on the equivalence relationship found between a fiber grating and a one-dimensional microstrip photonic bandgap structure that consists of a periodic pattern of circles etched in its ground plane. The equivalence assures that the frequency-response of the fiber grating is an upshifted replica of the corresponding frequency to its equivalent microstrip device. Both apodized and nonapodized uniform fiber gratings have been considered and the feasibility of the proposed method has been shown in simulation and measurement.     

Bragg Reflectors and Resonators in Microstrip Technology Based on Electromagnetic Crystal Structures

Recently, new promising two-dimensional (2-D) Photonic Bandgap Structures (PBG), or more properly Electromagnetic Crystal Structures, for microstrip lines have been proposed. In this paper, we analyze these structures in a manner like a Bragg reflector in optical wavelengths. Joining two of such Bragg like reflectors by means of a conventional microstrip transmission line allows one to design Bragg Resonators. The 2-D periodic pattern of the electromagnetic crystal structure is implemented with circles etched in the ground plane of the microstrip line by means of a numerical milling machine. Simulations have been performed by using HP ^TM Momentum and MDS software, and in accordance with the measurements give, for the Electromagnetic Crystal Structures, new promising potential applications both in microwave and millimeter wave integrated circuits, and also in the experimentation of expensive short wavelength (including photonic) devices by using simpler and cheaper microwave down scaling.     

Effect of impurity concentration on optical and magnetic properties in ZnS:Cu nanoparticles

To obtain enhanced room temperature ferromagnetism (RTFM) along with the increase in optical bandgap in the compound semiconductors has been an interesting topic. Here, we report RTFM along with increase in energy bandgap in chemically synthesized Zn_1−xCu_xS (0 ≤ x ≤ 0.04) DMS nanoparticles. Structural properties of the synthesized samples studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show the formation of cubic phase Cu doped ZnS nanoparticles of ~3–5 nm size. An intrinsic weak ferromagnetic behavior was observed in pure ZnS sample (at 300 K) which got increased in Cu doped samples and was understood due to defect induced ferromagnetism. UV–vis measurement showed increase in the energy bandgap with the increase in Cu doping. The PL study suggested the presence of sulfur and zinc vacancies and surface defects which were understood contributing to the intrinsic FM behavior.