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Synthesis and Optical Properties of Iodinated Multi-walled Carbon Nanotubes
摘要： This paper reports synthesis and optical properties of iodinated multi-walled carbon nanotubes (MWCNT). Multi-walled carbon nanotubes were synthesized by aerosol – assisted chemical vapor deposition method and iodinated by crystalline iodine under increased pressure (approximately ~20 bar) at 400°C. X-ray diffraction analysis, Raman and Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy were applied to characterize the iodinated MWCNTs.The results proved the presence of iodine atoms in iodinated MWCNTs. UV-VIS absorption and photoluminescence properties have been studied in pristine MWCNTs and iodinated MWCNTs suspensions in ethanol. Firstly, photoluminescence intensity of the iodinated MWCNTs remarkably enhanced with the appearance of C–I bonds on the surface of MWCNTs, due to the high concentration of intercalated iodine atoms (approximately 30 wt %). The photoluminescence intensity enhancement of peaks at 430 and 520 nm is highly dependent on defects formed by C–I bonds.
关键词： C–I bonds,photoluminescence,iodinated multi-walled carbon nanotubes,optical properties
更新于2025-11-19 16:56:42
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Band gap engineered zinc oxide nanostructures <i>via</i> a sol–gel synthesis of solvent driven shape-controlled crystal growth
摘要： A reliable sol–gel approach, which combines the formation of ZnO nanocrystals and a solvent driven, low shape-controlled, crystal-growth process to form well-organized ZnO nanostructures at temperature is presented. The sol of ZnO nanocrystals showed shape-controlled crystal growth with respect to the solvent type, resulting in either nanorods, nanoparticles, or nanoslates. The solvothermal process, along with the solvent polarity facilitate the shape-controlled crystal growth process, augmenting the concept of a selective adhesion of solvents onto crystal facets and controlling the final shape of the nanostructures. The XRD traces and XPS spectra support the concept of selective adhesion of solvents onto crystal facets that leads to yield different ZnO morphologies. The shift in optical absorption maxima from 332 nm in initial precursor solution, to 347 nm for ZnO nanocrystals sol, and finally to 375 nm for ZnO nanorods, evidenced the gradual growth and ripening of nanocrystals to dimensional nanostructures. The engineered optical band gaps of ZnO nanostructures are found to be ranged from 3.10 eV to 3.37 eV with respect to the ZnO nanostructures formed in different solvent systems. The theoretical band gaps computed from the experimental XRD spectral traces lie within the range of the optical band gaps obtained from UV-visible spectra of ZnO nanostructures. The spin-casted thin film of ZnO nanorods prepared in DMF exhibits the electrical conductivity of 1.14 × 10?3 S cm?1, which is nearly one order of magnitude higher than the electrical conductivity of ZnO nanoparticles formed in hydroquinone and ZnO sols. The possibility of engineering the band gap and electrical properties of ZnO at nanoscale utilizing an aqueous-based wet chemical synthesis process presented here is simple, versatile, and environmentally friendly, and thus may applicable for making other types of band-gap engineered metal oxide nanostructures with shape-controlled morphologies and optoelectrical properties.
关键词： electrical conductivity,ZnO nanostructures,optical band gap,shape-controlled crystal growth,sol–gel synthesis
更新于2025-11-19 16:56:42
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Crosslink network and phenyl content on the optical, hardness, and thermal aging of PDMS LED encapsulant
摘要： This work aims to synthesize new series of polysiloxane copolymer through hydrosilylation reaction based on different level of crosslink densities and phenyl content. The results revealed that polysiloxanes resins with phenyl rings increased viscosity up to 3800 cps while displaying a relatively high refractive index of 1.531. The asymmetric phenyl substitution onto chain backbone led to formation of densely packed structure resulting in reduced water absorption and gas permeability of PDMS resins. High level of crosslinking contributed to a high shore A hardness and adhesion strength. It displayed transparency of 97% whose percentage reduction was 1.6% under thermal and 0.6% UV aging. No obvious discoloration was observed during accelerated thermal aging up to 210 min at 80 (cid:1)C. These results are key attributes that make the synthesized polysiloxane series as ideal candidate for high brightness LED encapsulant. ? 2019 Wiley Periodicals, Inc. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47895.
关键词： copolymers,thermal properties,ring-opening polymerization,optical properties,synthesis and processing techniques
更新于2025-11-19 16:56:42
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Optical Properties of Quantum Dots with a Core–Multishell Structure
摘要： In the last decade, colloidal semiconductor nanocrystals (quantum dots) have been not only studied fundamentally but also applied in photovoltaics, optoelectronics, and biomedicine. Beginning with simple approaches to the deposition of protective shells, e.g., ZnS on CdSe cores, searches for ways to increase the quantum yield of photoluminescence of quantum dots have resulted now in the development of new types of quantum dots characterized not only by record high extinction coefficients but also by high photoluminescence quantum yields. In this work, the optical properties of core–multishell quantum dots have been analyzed. These quantum dots have been specially designed to reach the maximum possible localization of excited charge carriers inside luminescent cores, which makes it possible to reach a photoluminescence quantum yield close to 100%. Core–multishell quantum dot samples with a shell thickness of 3–7 monolayers have been fabricated. Changes in the characteristics of optical transitions in such quantum dots with an increase in the number of layers of the shell have been studied. The effect of the thickness of the shell on the optical properties of prepared quantum dots has been analyzed. In particular, analysis of photoluminescence lifetimes of such quantum dots has revealed a possible alternative mechanism of radiation of core–multishell quantum dots based on the slow charge carrier transfer from the excited outer layer of the CdS shell to the CdSe core.
关键词： quantum dots,optical properties,core–multishell structure,photoluminescence
更新于2025-11-19 16:56:42
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Tailoring optical cross sections of gold nanorods at a target plasmonic resonance wavelength using bromosalicylic acid
摘要： In many applications, the optical cross sections of gold nanorods (AuNRs) are required to be tailored at a fixed target longitudinal surface plasmon resonance (LSPR) wavelength depending on the excitation source and the photodetector. In this work, we demonstrate the fine tailoring of optical cross sections of AuNRs at a fixed target resonance wavelength, on the basis of AuNR overgrowth using a binary surfactant mixture consisting of 5-bromosalicylic acid (BSA) and cetyltrimethylammonium bromide (CTAB). A systematic study was performed on the sum effects of the BSA concentration and the volume of the growth solution, which gives a formula for quantitative instructions. Based on the formula, we gave examples for the successful synthesis of AuNRs with different optical cross sections at target LSPR wavelengths. From simulation, a nonlinear relationship was further derived to understand the relationship between the aspect ratio and the width of the AuNRs at a target LSPR wavelength for the dimension design of AuNRs. The ratio of optical against physical cross sections was calculated and plotted as a function of the width. The results clearly indicate that AuNRs with a width of 30 nm possess the highest efficiency in terms of optical per physical cross section. Our study provides reliable methods for the synthesis, as well as guidelines for the dimension design of AuNRs, for use in a variety of applications.
关键词： 5-bromosalicylic acid,gold nanorods,optical cross sections,cetyltrimethylammonium bromide,surface plasmon resonance
更新于2025-11-19 16:56:42
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Non-radiation creation of complex centers in wide-gap oxide crystals
摘要： It is shown that complex aggregate centers of oxygen divacancy type (F2 centers) and interstitial aluminum type near the anion vacancy (Ali+) are formed in anion-deficient crystals of corundum (α-Al2O3-δ) and beryllium oxide (BeO1-δ) under thermo-optical treatment (TOT). These centers are similar to those created in stoichiometric α-Al2O3 and BeO crystals under neutron irradiation. It is important to note that thermal stability of the TOT-created complex centers is higher than that of similar neutron-induced centers. It is also established that the probability of their formation is related to the temperature of the TOT, the wavelength of the stimulating light, and the initial anionic deficiency manifested as F+ and F centers (anion vacancies with one and two electrons, respectively).
关键词： Formation of complex defects,Wide-gap anion-deficient oxide crystals,Thermoluminescence,Optical absorption,Thermostability of complex defects,Thermo-optical treatment
更新于2025-11-19 16:56:35
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ZnGa2Se4, a nonlinear material with wide mid infrared transparency and good thermomechanical properties
摘要： During the last decades, mid-infrared (3–12 μm) laser sources using crystals with nonlinear optical properties have attracted a particular attention due to their potential applications in different fields such as optical counter-measures and remote chemical sensing. As transparency of common oxide crystals is limited to about 4 μm, many researches have been focused on chalcopyrite compounds because of their wide transparency in the mid-IR range and their strong nonlinear optical coefficients. There is a need of such crystals able to convert efficiently the near infrared wavelengths from commercially available lasers into wavelengths higher than 5 μm through Optical Parametric Oscillators (OPO) systems. This paper presents a new compound: ZnGa2Se4 (ZGSe). Measurements made on dense polycrystals show a high thermal conductivity value in comparison with other selenides (2.9 W m?1 K?1), a wide transparency from visible to beyond the band III of the mid IR (0.6 μm–17 μm) and a coefficient of thermal expansion inferior to 10?5 K?1. These results are very encouraging and improvements of the growth process are now undertaken to obtain single crystals with the required optical quality.
关键词： Optical materials and properties,ZnGa2Se4,Crystal growth,Thermomechanical properties
更新于2025-11-19 16:56:35
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Complex Optical and Thermal Studies on As-Synthesized Conducting Polythiophene
摘要： A series of conducting polythiophene (PTh) samples have been synthesized using an in situ chemical oxidative polymerization technique in aqueous solution. The characterization of the as-synthesized optimized sample has been carried out by Fourier transform infrared spectroscopy, x-ray diffraction and thermogravimetric–differential thermal analysis techniques. Also, the complex optical parameters of all the as-synthesized polymeric samples have been investigated by using ultraviolet–visible spectroscopy. The as-synthesized polymeric samples exhibited absorption around 220–280 nm. The optical band gap was found to ranges from 5.06 eV to 5.24 eV. The maximum optical conductivity for the sample with a stoichiometric ratio of thiophene to FeCl3 of 70:30 wt.% was found to be 5.973 9 108 S cm?1 at 280 nm. The experimental results reveal that the thermal and optical performance of conducting PTh can be dramatically enhanced for the sample with a stoichiometric ratio of thiophene to FeCl3 of 70:30 wt.%. The improved complex optical properties of as-synthesized samples of conducting PTh validate their potential utilization in optoelectronic devices.
关键词： thermal analysis,complex optical properties,Polythiophene
更新于2025-11-19 16:56:35
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LSPR Biosensing Approach for the Detection of Microtubule Nucleation
摘要： Microtubules are dynamic protein ?laments that are involved in a number of cellular processes. Here, we report the development of a novel localized surface plasmon resonance (LSPR) biosensing approach for investigating one aspect of microtubule dynamics that is not well understood, namely, nucleation. Using a modi?ed Mie theory with radially variable refractive index, we construct a theoretical model to describe the optical response of gold nanoparticles when microtubules form around them. The model predicts that the extinction maximum wavelength is sensitive to a change in the local refractive index induced by microtubule nucleation within a few tens of nanometers from the nanoparticle surface, but insensitive to a change in the refractive index outside this region caused by microtubule elongation. As a proof of concept to demonstrate that LSPR can be used for detecting microtubule nucleation experimentally, we induce spontaneous microtubule formation around gold nanoparticles by immobilizing tubulin subunits on the nanoparticles. We ?nd that, consistent with the theoretical model, there is a redshift in the extinction maximum wavelength upon the formation of short microtubules around the nanoparticles, but no signi?cant change in maximum wavelength when the microtubules are elongated. We also perform kinetic experiments and demonstrate that the maximum wavelength is sensitive to the microtubule nuclei assembly even when microtubules are too small to be detected from an optical density measurement.
关键词： localized surface plasmon resonance,optical biosensors,gold nanoparticles,microtubule nucleation
更新于2025-11-19 16:56:35
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BaHgGeSe4 and SrHgGeSe4: Two New Hg-based Infrared Nonlinear Optical Materials
摘要： New practically usable IR nonlinear optical (NLO) crystals, especially those suitable for high-efficient pumping of the commercial 1 μm laser, are in urgent demand. However, only a few new IR NLO materials have been grown into bulk crystals and realized IR laser output during the past twenty years due to the extreme difficulty in achieving the coexistence of various strongly-correlated properties. In the manuscript, based on the bonding characteristics of the Hg element and an efficient screening strategy for high-performance new crystals, we identified two new Hg-based IR nonlinear (NLO) materials, BaHgGeSe4 and SrHgGeSe4. They crystallize in the polar space group Ama2 with the distorted HgSe4 and GeSe4 tetrahedra aligned parallelly. They exhibit exceptional balance among all the preferred properties for practical applications, especially for high-efficient pumping of the commercial 1 μm laser: Their large band gap (~2.5 eV) can avoid the two-photon absorption of 1 μm laser and increase the laser damage threshold; They are phase matchable with very strong NLO response (5×AgGaS2); They can cover both the 3-5 μm and 8-12 μm atmospheric windows. Moreover, they melt congruently, which indicate that bulk crystals can be obtained by the Bridgman method. Their overall properties outperform the traditional materials AgGaQ2 (Q = S, Se) in a large degree. Detailed structural analysis and calculations elucidate the crucial role of cations in regulating the packing of the anionic groups and that of the highly-polarizable HgSe4 in balancing optical properties.
关键词： phase matchability,second harmonic generation,BaHgGeSe4,IR nonlinear optical materials,SrHgGeSe4,congruent-melting,Hg-based chalcogenides
更新于2025-11-19 16:56:35