Extinction Spectra Research Articles

Complex refractive index of crystalline quartz particles from UV to thermal infrared

Crystalline quartz is an important element of many materials and one of the major compounds of mineral dust. Thus, knowledge of its optical properties is essential for many applications, in particular for remote sensing techniques. However, despite the fact that crystalline quartz has been an object of study for many years using various experimental approaches, its optical properties and in particular its complex refractive indices (CRI) remain uncertain. The focus of this investigation is the determination of a new set of CRI of crystalline quartz particles retrieved from a methodology which has already demonstrated its efficiency on pure amorphous materials and volcanic ashes. The experimental set-up allows recording simultaneously size distribution (from 15 nm to 20 µm) of airborne particles and extinction spectra over a wide continuous spectral range from thermal infrared (650 cm−1) to UV (40,000 cm−1) with high spectral resolution (up to 0.5 cm−1). By associating these measurements and a numerical procedure coupling scattering theories, the single subtractive Kramers-Kronig relation, and an optimal estimation method in an iterative process, we precisely determine the real and imaginary parts of the CRI of crystalline SiO2 with mean values of the uncertainties of 2.5% and 1.7%, respectively. Moreover, the use of these CRIs allows to simulate an extinction spectrum of another quartz sample very well, which shows their suitability as well as the good reproducibility of the whole process.

Space-resolved chemical information from infrared extinction spectra

A new method is presented for the extraction of the complex index of refraction from the extinction efficiency, Q_{ext} {({tilde{nu }})}, of homogeneous and layered dielectric spheres that simultaneously removes scattering effects and corrects measured extinction spectra for systematic experimental errors such as baseline shifts, tilts, curvature, and scaling. No reference spectrum is required and fit functions may be used that automatically satisfy the Kramers–Kronig relations. Thus, the method yields the complex refractive index of a sample for unambiguous interpretation of the chemical information of the sample. In the case of homogeneous spheres, the method also determines the radius of the sphere. In the case of layered spheres, the method determines the substances within each layer. Only a single-element detector is required. Using numerically computed Q_{ext}({tilde{nu }}) data of polymethyl-methacrylate and polystyrene homogeneous and layered spheres, we show that the new reconstruction algorithm is accurate and reliable. Reconstructing the complex refractive index from a published, experimentally measured raw absorbance spectrum shows that the new method simultaneously corrects spectra for scattering effects and, given shape information, corrects raw spectra for systematic errors that result in spectral distortions such as baseline shifts, tilts, curvature, and scaling.

Extending Ag Nanoparticles as Colorimetric Sensor to Industrial Zinc Electrolyte for Cobalt Ion Detection

The direct and rapid determination of trace cobalt ion (Co2+) in the electrolyte of zinc smelting plants is urgently needed but is impeded by the severe interference of extremely high-concentration zinc ions in the solution. Herein, colorimetric detection of Co2+ by the polyvinylpyrrolidone functionalized silver nanoparticles (PVP-AgNPs) is realized in solutions with the Zn/Co ratio being high, up to (0.8-5) × 104, which is located within the ratio range in industrial solution. The high concentration of Zn2+ induces a strong attenuation of Co2+-related signals in ultraviolet-visible (UV-vis) extinction spectra; nevertheless, a good linear range for detecting 1-6 mg/L Co2+ in 50 g/L Zn2+ solution is still acquired. The strong anti-interference toward other metal ions and the mechanism understanding for trace Co2+ detection in such a high-concentration Zn2+ solution are also revealed by systematic analysis techniques. The results extend the AgNPs as colorimetric sensors to industrial solutions, providing a new strategy for detecting trace-metal ions in industrial plants.

Plasmonic Ag@Cu2O core-shell nanostructures exhibiting near-infrared photothermal effect.

This work was devoted to the investigation of the optical properties, structural characterization, and photothermal conversion performance of Ag@Cu2O nanostructures. The selection of anisotropic silver core, specifically Ag nanocubes, was driven by the possibility to tune LSPR across a broader range of the electromagnetic spectrum. The thickness of the Cu2O shell was intentionally changed through the variation in the Cu salt to the metal core nanoparticles ratios. The LSPRs of Ag(nanocube)@Cu2O core-shell nanoparticles can be fine-tuned to the spectral region to become resonant with the excitation wavelengths of 808 nm NIR laser. Due to the high refractive index of the deposited Cu2O, the redshifts of the plasmon band wavelength in the extinction spectra were observed. Consequently, the photothermal activities of the Ag(nanocube)@Cu2O core-shell NPs have been controlled by the shell thickness at the nanoscale. Ag@Cu2O nanoparticles with thickest shell (∼70 nm) exhibit the most efficient NIR photothermal effect under the irradiation of 808 nm laser at ambient conditions. Results of this work demonstrate that Ag@Cu2O hetero-nanostructures may be optimized and used for the efficient transformation of light into other forms of energy, specifically heat.

Numerical simulations of plasmonic properties of spherical gold nanodisks using T-matrix method: impact of geometry parameters on the sensitivity to the dielectric environment and the field enhancement

Simulations using the transition matrix approach are implemented for spherical gold nanodisks (AuNDs) to obtain insights into their plasmonic properties. We systematically follow the correlation between the optical response of these nanostructures with their geometry parameters and the refractive index of the surrounding medium. Plasmon wavelengths linearly redshift with the diameter-to-height aspect ratio, which is consistent with measured data available in the literature, thereby ensuring calculation accuracy. The relative plasmon resonance shift to the relative increment of the medium refractive index is geometry-dependent and exhibits a linear correlation in which the estimated slope represents the plasmon resonance sensitivity. We confirm the strong dependence of the field enhancement factor on the geometry parameters of nanodisks. The relative contributions of scattering and absorption in the extinction spectra are determined. Simulations show that circular AuNDs have well-controlled optical characteristics that will provide great opportunities to achieve various plasmon-derived applications.

Lattice relaxation effects on the collective resonance spectra of a finite dipole array.

Dielectric/plasmonic lattice relaxation spectroscopy is theoretically discussed in this work. A lattice relaxation effect generally occurs in nanocrystals, which means that from the bulk phase to the crystal surface, lattice parameters show a gradual shift. Here, lattice relaxation is introduced into finite polarizable point arrays or rod arrays as an adjusting tool, and its effect on lattice resonance extinction spectrum peaks is calculated. DDA (discrete dipole approximation) and FDTD (finite difference time domain) methods are applied. Different from an ideal infinite array, a finite array exhibits a broad, rippled extinction spectral peak. The application of an expanded/contracted lattice relaxation to the finite array can compress the ripple on one shoulder of the peak, as a cost, and the other shoulder of the peak gets more rippled, showing a "ripple transfer" effect. The strategy introduced in this work can contribute to the micro/nano optical measurement, on-chip adjustable optical cavity for OPOs (optical parameter oscillators)/lasers and controlling of fluorescence or hot-electron chemistry.

Fermi level shifts of gold nanospheres on ZnO film upon UV irradiation.

Here, Fermi level shifts of gold nanospheres on zinc oxide (ZnO) film upon UV irradiation are studied. These Fermi level shifts are obtained by recording extinction spectra of gold nanospheres characterized by their plasmon resonance and are due to the presence of additional electrons stored in gold nanospheres and coming from ZnO film upon UV irradiation. It is demonstrated that the blueshift of the plasmon resonance of the Au nanospheres upon UV irradiation points out the transfer of electrons from ZnO film to Au nanospheres. Moreover, it is reported that the Fermi level shifts vary with UV irradiation time by approaching the conduction band of ZnO, and are estimated by an analogous model to the electronic structure of a semiconductor, which can be expressed as a function of the plasmon resonance blueshift of the Au nanospheres. Henceforward, these stored electrons and these Fermi level shifts can allow the improvement of the properties of photocatalytic reduction for the gold-semiconductor structures and can also be used for photo-induced enhanced Raman spectroscopy.

Transition metal dichalcogenide coated gold nanoshells for highly effective photothermal therapy.

Transition metal dichalcogenides (TMD) coated gold nanoshells (GNSs), in addition to having low cytotoxicity and a biocompatibility value greater than graphene, exhibit strong light absorption in the near-infrared (NIR) region and high photothermal conversion efficiency. Using a quasi-static approach and bioheat equations, the optical and photothermal properties of GNSs coated with various TMDs are studied for treatment of skin cancer. Our findings show that the intensity of localized surface plasmon resonance (LSPR) peaks and their position in the extinction spectrum of nanoparticles (NPs) can be easily tuned within biological windows by varying the core radius, the gold shell thickness and the number of coating layers of the different TMDs. In order to engineer heat production at designated spatial locations of NPs, near electric field (NEF) enhancement is investigated. Moreover, the effect of laser intensity and the number of TMD layers on the temperature rise and the amount of thermal damage in skin tumor tissue and its surroundings are studied. Our results introduce GNSs with various TMD coatings as superlative nanoagents for photothermal therapy (PTT) applications.

A review of applications of plasmonic and conventional nanofluids in solar heat collection

• The research progress of plasmonic nanofluids in recent ten years is reviewed. • Comparison of plasmonic nanofluids with conventional nanofluids. • The LSPR effect of plasmonic nanofluids enhances the light absorption. • Many factors affect the light absorption and photothermal conversion characteristics. • How to improve the light absorption properties of plasmonic nanofluids needs further discussion. With the development of solar energy utilization and nanotechnology, nanofluid heat collection has attracted significant attention. The solar plasmonic nanofluids with significant local surface plasmon resonance (LSPR) effect have exhibited superior behaviors in thermophysical properties, optical properties, and photothermal conversion efficiency. This paper reviews the research progress of plasmonic nanofluids in solar collectors and PV/T systems and compares them with conventional nanofluids for the first time. The plasmonic nanofluids exhibit excellent light absorption capacity and controllable light intensity and resonance frequency. Due to the existence of the LSPR effect, plasmonic nanofluids show significant absorption peak, which can meet the requirements of broadband solar energy absorption and have better usage value than conventional nanofluids in solar heat collection. Many factors affect the photothermal conversion efficiency of plasmonic nanofluids, such as particle size, concentration and flow rate. Using hybrid nanofluids can significantly broaden the extinction spectrum and further enhance light absorption. To clarify the specific mechanism of plasmonic nanofluids, improve their stability and make them more suitable for different types of solar heat collection, more experimental exploration is needed.

Microstructure building and thermal stability of cermet-based photothermal conversion coatings with layered structures

To enhance the thermal stability of cermet-based photothermal conversion coatings, the present paper proposes a novel strategy to replace the randomly distributed nanoparticles with layered structure. This kind of structure can not only suppress the agglomeration and rapid growth of nanoparticles, but also enhance the interaction between the absorber and sunlight. Thus, the thermal stability and selectivity can be simultaneously improved by this unique kind of structure. Then, a Cr/AlCrN/AlCrON/AlCrO multilayer cermet-based photothermal conversion coating is designed and fabricated by multi-arc ion plating. The microstructure, optical properties and thermal stability of the multilayer coating are studied in detail. The optical properties tests show that the absorptance and emittance of the as-deposited coating achieve 0.903 and 0.183, respectively. More importantly, after being annealed at 500 ℃ in air for 1000 h, the absorptance reaches 0.913 and the emittance arrives at 0.199, implying the enhanced selectivity and thermal stability, which are ascribed to the formation of nanolaminates, in which a series of alternating sublayers is observed in the AlCrON absorber. The nanolaminate is a two-phase composite structure composed of layered AlN and Cr<sub>2</sub>N nanoparticles distributed in amorphous dielectric matrix. According to the finite difference time domain (FDTD) simulations, this unique kind of microstructure can trap photons in the coating, which is beneficial to enhancing the interaction intensity and time between the sunlight and absorbing sublayer, and thus improving the absorption of sunlight. In addition, the reduction of particle spacing during annealing will lead to the red shift of extinction spectrum, which will better match the solar radiation spectrum. At the same time, this kind of structure can avoid the agglomeration of nanoparticles, which can simultaneously tune the optical properties and thermal stability.

Оптическая анизотропия пленок из поливилового спирта с металлическими наностержнями при одноосном растяжении

The possibility of obtaining macroscale anisotropic thin films from polyvinyl alcohol with included metal nanorods under uniaxial tension under conditions that do not lead to a change in the morphology of metal nanoparticles is shown. Silver and gold nanorods were obtained by directed growth from nuclei and then embedded in a polymer matrix based on polyvinyl alcohol. Initially isotropic films with absorption independent of the polarization of the probing light became anisotropic after stretching, which manifested itself in the dependence of the extinction spectra on the polarization of the probing radiation. The weakening of the longitudinal dipole plasmon resonance mode with the simultaneous enhancement of the transverse dipole plasmon resonance when the light polarization is rotated from 0 to 90 degree indicates the orientation of the nanorods in the film along the direction of its stretching. In addition to the change in absorption in the bands of dipole modes, a strong orientational dependence of absorption in the band of the quadrupole mode of the plasmon resonance of metal nanorods was found.

Utilizing inner filter effect in resonance Rayleigh scattering technique: a case study with silver nanocubes as RRS probe and several analytes as absorbers

It was demonstrated that the mechanism of the inner filter effect (IFE) can emerge well in the resonance Rayleigh scattering (RRS) technique and be utilized as a new analytical method in the design of innovative IFE-based sensors. To prove this process, silver nanocubes (Ag NCs) with tunable extinction spectra were selected as RRS probes, and three analytes, doxorubicin (DOX), sunitinib (SUN), and Alizarin Red S (ARS), were considered as the typical absorbers. In addition, in the presence of SUN as a typical analyte, the quenching of the RRS signal of Ag NCs, with λmax of 419nm, was linear in the range 0.01 to 2.5µM of SUN. The limit of detection (LOD) was 0.0025µM. The introduced method was then used to develop a dual-signal assay for the ratiometric determination of Al3+ ions. The suggested dual-signal assay was based on the color changes of ARS caused by Al3+ and the IFE between ARS and Ag NCs. The obtained results showed that the two characteristics of response sensitivity and linear dynamic range are very satisfactory for sensing Al3+ ions. The findings of this study demonstrate that the newly developed IFE mechanism can be employed as an attractive and highly efficient analytical technique for measuring different analytes.

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Optoelectronic Transitions in Gold Spherical Nanoparticles - A Simulation Study

This study examined extinction spectra, electric field intensity, and their variations due to various semiconductor medium, for gold nanoparticles, using Nanosphere Optics Lab Field Simulator which is based on Mie’s theory of scattering by sphere. The peak extinction wavelength and bandwidth are found to get varied with size of the gold nanoparticle, in four different regimes. Asymmetric distributions of electric fields are observed in particles typically larger than 25nm. The significant differences are found in the results due to changes in the embedding medium. The gold nanoparticles' unique tunable electro-optical properties may therefore be useful for medical, health care, industrial catalysts, and other consumer products. The study shows improved results may be obtained in the medium size range i.e. 25-75nm. In addition, the selectivity can be improved linearly as the refractive index of the host material increases.

In situ monitoring the productivity of ultra-small gold nanoparticles generated by pulsed-laser ablation of a high-speed rotating gold target in pure water

We investigate the productivity of ultra-small gold nanoparticles generated by pulsed-laser ablation in liquid of a high-speed rotating gold target as functions of laser ablation time and rotation speed of the target in the range 90–3000 rpm. These experiments were performed by in situ monitoring the extinction spectra of the gold colloidal suspension. The time evolution of the gold volume fraction in the colloidal suspension of the target was determined by modeling the extinction spectra using the shape distribution effective medium theory. The time dependence of the ablation rate, deduced from that of the volume fraction, shows an initial exponential decay followed by a steady-state value at longer ablation time. The influence of the laser-induced roughening of the target surface on the time evolution of the ablation rate is clearly demonstrated. The experimental results also reveal the dependence of the time evolution of the ablation rate of the target on its rotation speed. The effect of the liquid flow on the ablation rate of the target is analyzed and discussed.

SIZE EFFECT IN PLASMON RESONANCE OF GOLD-COPPER SULFIDE CORE-SHELL NANOPARTICLES

This paper studies the nature of changes in extinction spectra when changing the core/shell size ratio in spherical and ellipsoidal (prolate and oblate) gold-copper sulfide (Au-CuS) core-shell nanoparticles. The obtained results are analyzed to establish the regularity of changes in the nanoshells extinction spectra, which can be used to develop devices based on them for different applications. The plasmon properties of spherical and ellipsoidal Au -CuS nanoparticles with different sizes were determined. It is established that the intensity of the extinction cross-section of spherical nanoshells strongly depends on the ratio between the thickness of the core and the shell. It is possible to configure the plasmon properties of oblate and prolate ellipsoidal core-shell nanoparticles by changing the core and shell thickness in both directions. Thus, the results of the study suggest that Au-CuS nanoparticles can be used as potential elements of various sensitive sensors.

DFT calculations of the main optical constants of the Cu<sub>2</sub>ZnSnSe<sub>x</sub>S<sub>4-x</sub> system as high-efficiency potential candidates for solar cells

<span lang="EN-US">In the present work, using quantum-chemical calculations in the framework of density functional theory (DFT), we study the optical properties of semiconductor nanocrystals of kesterite Cu<sub>2</sub>ZnSnS<sub>4</sub> doped with Se. Using the WIEN2k package, the concentration dependences of the optical characteristics of nanocrystals of the Cu<sub>2</sub>ZnSnSe<sub>x</sub>S<sub>4-x</sub><strong> </strong>system (x = 0, 1, 2, 3, 4) were calculated. It is shown that doping with Se at the S position leads to a noticeable improvement in the photo absorbing properties of these nanocrystals, as well as their photoconductivity in the IR range. The calculated absorption and extinction spectra of the materials under study, are compared with experimental data known from the literature. The data obtained will significantly enrich the existing knowledge about the materials under study and will help expand the scope of these compounds in optoelectronic devices, especially in solar cells and other devices that convert solar energy into electricity.</span>

Gold Nanostar Characterization by Nanoparticle Tracking Analysis.

We demonstrate the application of nanoparticle tracking analysis (NTA) for the quantitative characterization of gold nanostars (GNSs). GNSs were synthesized by the seed-mediated growth method using triblock copolymer (TBP) gold nanoparticles (GNPs). These GNPs (≈ 10 nm) were synthesized from Au3+ (≈ 1 mM) in aqueous F127 (w/v 5%) containing the co-reductant ascorbic acid (≈ 2 mM). The GNS tip-to-core aspect ratio (AR) decreased when higher concentrations of GNPs were added to the growth solution. The AR dependency of GNSs on Au3+/Au(seed) concentration ratio implies that growth is partly under kinetic control. NTA measured GNS sizes, concentrations, and relative scattering intensities. Molar absorption coefficients ∼ 109-1010 M-1 cm-1 (ε400nm) for each batch of GNSs were determined using the combination of extinction spectra and NTA concentrations for heterogeneous samples. NTA in combination with UV-vis was used to derive the linear relationships: (1) hydrodynamic size versus localized surface plasmon peak maxima; (2) ε400nm versus localized surface plasmon peak maxima; (3) ε400nm versus hydrodynamic size. NTA for quantitative characterization of anisotropic nanoparticles could lead to future applications, including heterogeneous colloidal catalysis.

On the Optical Properties of the Cu2ZnSn[S1−xSex]4 System in the IR Range

Following the recent classification by the European Commission of some elements as critical raw materials (CRM), there is an increasing interest in the development of CRM-free thin film photovoltaic (PV) technologies, including kesterite materials. Moreover, starting with the performance breakthrough reported by IBM in 2010, the efficiency of kesterite-based solar cells steadily progressed in the following years achieving. Therefore, in recent years, there has been a significant research effort to develop kesterite-based devices. However, despite the large number of theoretical and experimental works, many aspects of the problem have not yet been fully studied. Therefore, the issues considered in the article, especially the behavior of the absorption and photoconductivity spectra of the Cu2ZnSn[S1−xSex]4 system, depending on the S/Se ratio, are extremely important and, at the same time, one of the topical and poorly studied problems. In this work, using quantum-chemical calculations in the framework of density functional theory (DFT), we study the optical properties of semiconductor nanocrystals of kesterite Cu2ZnSnS4 doped with Se. Using the WIEN2k package, the concentration dependences of the optical characteristics of nanocrystals of the Cu2ZnSn[S1−xSex]4 system (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were calculated. It is shown that doping with Se at the S position leads to a noticeable improvement in the photoabsorbing properties of these nanocrystals, as well as their photoconductivity in the IR range. The calculated absorption and extinction spectra, as well as the refractive indices and permittivity of the materials under study, are compared with experimental data known from the literature. The data obtained will significantly enrich the existing knowledge about the materials under study and will contribute to the expansion of the field of application of these compounds in optoelectronic devices. HIGHLIGHTS With an increase in the Se concentration, the absorbing properties and photoconductivity of the nanocrystals of the Cu2ZnSn[S1−xSex]4 system increase The optical band gap narrows with increasing Se/S ratio Curves k(ω) and α (ω) correspond to the maxima of e2 (w) Pure Cu2ZnSnSe4 has the maximum absorption in the IR range GRAPHICAL ABSTRACT

Investigation of the Changes in Extinction Spectrum of Modern Chlorine-Containing Photosensitizing Drugs under the Visible Light Action

The paper presents the results of a study of the extinction spectra (350–900 nm) of aqueous solutions of modern chlorine-containing photosensitizing drugs for photodynamic therapy “Chloderm" (Chloderm, Russia) and "Chloderm with hyaluronic acid" (Chloderm, Russia) before and after irradiation by visible light with wavelengths of 405 nm, 450 nm, and 656±10 nm, with exposure time 0–20 min and intensity 0–200 mW/cm 2 . It is demonstrated that the addition of hyaluronic acid does not deform the shape of the extinction spectrum of the photosensitizing drug but reduces its absorption in proportion to the drop in the concentration of the photosensitizer in the drug. Photodynamic light action in the investigated range of parameters leads to a slight decrease in the extinction coefficient of both drugs at the wavelengths of the exposure, but significantly reduces extinction and deforms the Qy 00 absorption band (600–700 nm), thereby changing the ratio of monomers and tetramers in the drugs. This band is most significantly deformed after exposure to light with a wavelength of 656±10 nm, the least – with a wavelength of 450 nm .