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Amorphous thin films of SnO2, prepared by a vacuum evaporation technique under a pressure of 10− 5 mbar, are employed as electro-optical filters suitable for microwave, infrared, and visible light communication technologies. The filters perform as optical layers, exhibiting optical transitions within an energy band gap of 3.62 eV, with the band gap containing energy band tails of widths of 0.63 eV. In addition, dielectric dispersion analyses on the optical filters show their ideality for high k-gate dielectric applications. Wide tunability in the dielectric response is observed in these films. Moreover, analyses of the optical conductivity and terahertz cutoff frequency spectra have shown that SnO2 films exhibit resonance of optical signals suitable for infrared and visible light communication technology as well. When excited with infrared light of energy of 1.38 eV, the drift mobility and free hole concentration in these films reach 11.72 cm2/Vs and 2 × 1017 cm− 3, respectively. Furthermore, the device exhibits a negative resistance effect in the microwave range of 0.1–1.80 GHz, and terahertz cutoff frequency values in the range of 10 GHz − 48 THz. The features of the SnO2 electro-optical band filter make them attractive for communication technology extending from 5G/6G to IR and reaching visible light communications. [ABSTRACT FROM AUTHOR]

The density functional theory with generalized gradient approximation is used to investigate the structural, electronic, and optical properties of Cu0.125As2S3 and Cu0.25As2S3 configurations with copper impurity at c‐face center interstitial site. The AsS bond lengths remain nearly the same but CuS bond lengths decrease with the increase in copper concentration. Both the configurations show n‐type conductivity and strong p–d hybridization in valence and conduction bands. The density of copper d states in the valence band increases with the increase in Cu content. The calculated optical constants are strongly anisotropic up to 10 eV; however, at higher energies the anisotropy diminishes. The broad peaks in the optical constants along E→$\overset{\rightarrow}{E}$||b→$\overset{\rightarrow}{b}$ and c→$\overset{\rightarrow}{c}$ axes are found in the vicinity of 2 eV. However, the peak heights increase and shift toward lower energy with the increase in copper content. Further, the static dielectric constant, refractive index, and reflectivity increase and the optical bandgap decreases with the increase in copper concentration. The comparison of optical constants shows that Cu0.25As2S3 may be as good choice as Ag0.25As2S3 for optical applications. [ABSTRACT FROM AUTHOR]

Two pyrazoline core fluorescent materials were designed, synthesized and characterized by various approaches. The synthesized materials were confirmed by standard 1 H NMR and FT-IR techniques. Porous like morphologies were found from SEM analysis and the thermal stability of the materials analyzed with TGA–DSC analysis. Emission properties, quantum yield, lifetime and bandgap energy of the materials have also been studied. Solvent effect of absorption and emission spectral results indicated that the wavelength was red-shifted to increase the solvent polarity. The semiconducting nature was studied by UV–visible spectra, cyclic voltammetry analysis and theoretical calculation. I–V characteristic analysis was used to determine turn-on voltage of the materials for optoelectronics. [ABSTRACT FROM AUTHOR]

In this study, a novel algorithm to solve the position of a nematic liquid crystal molecular director inside a device has been proposed. The formulation for minimizing the Gibbs free energy, composed by the free energy deformation (Frank-Oseen equations) minus the electrical energy, has been established using a vectorial representation of the director. The three liquid crystal elastic constants have been considered. The differential equations involved have been solved by applying numerical methods, using an algorithm developed by the authors. It has been compared with other techniques and the main advantages are that the new algorithm is faster and more accurate than other previous methods such as finite difference method (FDT) or a boundary value problem solver of MATLAB (bvp4c). Simulation program is also a powerful tool for analyzing other liquid crystal properties such as refractive index and permittivity as a function of voltage. To validate the simulation results, they have been compared with some measurements of a nematic liquid crystal device manufactured for that purpose. The comparison of birefringences simulated and measured show results that are fairly in agreement. This work also aims to provide a software simulation tool easy to reprogram for more complex devices. [ABSTRACT FROM AUTHOR]

In this paper, we present radio-frequency electro-magnetic field characterization of an electrooptic (EO) probe. This probe is able to simultaneously measure temperature and one component of the electric field (e-field) in a continuous wave (CW) or in a pulsed regime. For this purpose, linearity, selectivity, and sensitivity measurements are performed in air and in a cuvette filled with a water solution. The media are exposed to 1800-MHz CW electromagnetic wave through a transverse electromagnetic cell. Numerical characterization is also performed using finite-difference time-domain simulations. The EO probe presents a dynamic range exceeding 70 dB. Selectivity up to 25 dB is measured, demonstrating the ability of the EO probe to measure one unique component of the e-field. The EO probe sensitivity is equal to 0.77 and to 0.18 V · m-1Hz-½, in the air and in the water solution, respectively. This millimeter-sized EO probe is particularly suited for the measurement of ultrawide bandwidth and high-voltage e-fields up to a few megavolts per meter. [ABSTRACT FROM AUTHOR]

Abstract: Blends consisting of doped silicon nanocrystals (Si-ncs) and two conjugated polymers (poly(3-hexylthiophene) (P3HT) and poly(methoxy ethylexyloxy phenylenevinilene) (MEH PPV)) with improved photostability were fabricated. We show that a top-down approach by electrochemical etching is suitable for preparing doped (boron and phosphorus) freestanding and surfactant-free Si-ncs. The doping of Si-ncs was confirmed by low temperature photoluminescence and electron spin resonance analysis. It is demonstrated that such Si-ncs can be successfully used for the fabrication of room temperature photoluminescent and photosensitive blends. We argue that the luminescence and transport properties of the blends are controlled by the Si-ncs properties and could be assigned to quantum confinement of excitons in nanocrystalites with an energy band gap of ∼2eV. Furthermore, the blending of doped Si-ncs in both conjugated polymers led to the establishment of a bulk heterojunction between the Si-ncs and polymer. The difference in electron affinity and ionization potential between nanocrystals and polymer dissociated the excitons. Those blends showed increased carrier transport and photoconductivity under ambient conditions. It was found that introduction of less defective p-type doped Si-ncs significantly improved overall photostability of the blend. The Si-ncs non-toxicity and easy integration into well-established silicon technologies might bring considerable benefit for hybrid optoelectronic and photovoltaic device development. [Copyright &y& Elsevier]

Abstract: Copolymer of 2,5-di(4-methylthiophen-2-yl)-1-(4-nitrophenyl)-1H-pyrrole (MTNP) with 3,4-ethylene dioxythiophene (EDOT) was electrochemically synthesized and characterized via cyclic voltammetry, Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy, conductivity measurements. Spectroelectrochemical investigations showed that resulting copolymer film has distinct electrochromic properties. It has five different colors (dark purple, red, light grey, green, blue). At the neutral state λ max due to the π-π⁎ transition was found to be 500 nm and Eg was calculated as 1.71 eV. Double potential step chronoamperometry experiment shows that copolymer film has good stability, fast switching time (1.1 s) and high optical contrast (30%). Electrochromic device based on P(MTNP-co-EDOT) and PEDOT was constructed and characterized. Oxidized state of the device shows dark purple color with a blue color reduced state. At interval potentials device has good transparency and colors of the device are yellow and grey. Maximum contrast and switching time of the device were measured as 23% and 1.1 s at 650 nm. [Copyright &y& Elsevier]

The magnetic penetration depth of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films has been determined as a function of temperature by using picosecond optoelectronic sampling techniques. Electrical pulses of 8 ps full width at half maximum were generated on photoconductive switches by a mode-locked Nd:YAG pumped dye laser and propagated on superconducting delay lines which were 250 mm in length. The measured behavior at low temperature (T

Very large lattice strain and strain-induced polarization are achieved in KNbO3 using epitaxial growth of a thin KNbO3 film onto a (001)-oriented SrTiO3 single-crystal substrate. We demonstrate experimentally that epitaxy produces dramatic changes of interband transitions in the film compared to those of a reference KNbO3 crystal: the energies of transitions change, some transitions are substantially suppressed and new ones appear in the film. A comparison of the experimental observations with theoretical calculations points to yet unexplored phenomena. Our results indicate that optical refraction and electro-optical coefficients of ferroelectric films can be controlled by epitaxial growth, which is of importance for emerging photonic and optoelectronic applications. [ABSTRACT FROM AUTHOR]