Peak Absorption Wavelength Research Articles

Silver nanoplates-based colorimetric iodide recognition and sensing using sodium thiosulfate as a sensitizer

A colorimetric method for the recognition and sensing of iodide ions (I−) has been developed by utilizing the reactions between triangular silver nanoplates (TAg-NPs) and I− in the presence of sodium thiosulfate (Na2S2O3). Specifically, I− together with Na2S2O3 can induce protection of TAg-NPs owing to the formation of insoluble AgI, as confirmed by the high-resolution transmission electron microscopy (HRTEM). In the absence of Na2S2O3, the etching reactions on TAg-NPs were observed not only by I− but also other halides ions. The Na2S2O3 plays as a sensitizer in this system, which improved the selectivity and sensitivity. The desired colorimetric detection can be achieved by measuring the change of the absorption peak wavelength corresponding to localized surface plasmon resonance (LSPR) with UV–vis spectrophotometer or recognized by naked eye observation. The results show that the shift of the maximum absorption wavelength (Δλ) of the TAg-NPs/Na2S2O3/I− mixture was proportional to the concentration of I− in the range 1.0×10−9–1.0×10−6molL−1. Moreover, no other ions besides I− can induce an eye discernible color change as low as 1.0×10−7molL−1. Finally, this method was successfully applied for I− determination in kelp samples.

A Method to Improve Mineral Identification Accuracy Based on Hyperspectral Data

To improve the mineral identification accuracy of the rapid quantificational identification model, the noise was filtered in fragment based on the wavelength of altered mineral absorption peak and the regional spectral library that fitted for the study area was established. The filtered spectra were analyzed by the method with regional spectral library. Compared with the originally mineral identification result, the average efficiency rate was improved by 5.1%; the average accuracy rate was improved by 17.7%. The results were optimized by the method based on the position of the altered mineral absorption peak. The average efficiency rate would be improved in the future to identify more accurate minerals.

A Through-hole Array on Optical Fibers Fabricated by 1-kHz/400-nm Femtosecond Laser Pulses for an in-line/pico-Litter Spectrometer Design

Abstract Femtosecond laser machining has successfully been applied to develop for a spectroscopic sensing in multi-mode optical fibers by embedding through holes penetrating the fiber core, which could work to be a sample cell for spectroscopic measurements. In this report, the spectroscopic measurement using the pico-litter sample cell will be shown for liquid dye of Rhodamine 6G (R6G). Even with a single cell volume of 20 pL, the absorption spectra are appeared in the visible range centered at a wavelength of 530 nm corresponding to the peak absorption wavelength of R6G solutions.

一种差分吸收式光纤瓦斯传感系统

Optical fiber methane gas sensing system based on differential absorption was investigated. Two distributed feedback laser diodes were used in the system.The wavelength of the reference light source was 1551nm and the wavelength of the measurement light source was 1653nm,which was located around the absorption peak wavelength of methane.The methane absorption peak was detected by scanning the wavelength of the measurement light source,and then the concentration of methane was measured by comparing the output power at the absorption peak with that not at the absorption band. The system possesses the properties of high resolution,good stability and a measurement resolution of 0. 038%is achieved for methane detection.

Interstellar Dust Models Towards Some IUE Stars

We study the extinction properties of composite dust grains, consisting of host silicate spheroids and graphite as inclusions, using discrete dipole approximation (DDA). We calculate the extinction cross sections of the composite grains in the ultraviolet spectral region, 1200–3200 Å, and study the variation in extinction as a function of the volume fraction of the inclusions. We compare the model extinction curves with the observed interstellar extinction curves obtained from the data given by the International Ultraviolet Explorer (IUE) satellite. Our results for the composite grains show a distinct variation in the extinction efficiencies with the variation in the volume fraction of the inclusions. In particular, it is found that the wavelength of peak absorption at 2175 Å shifts towards the longer wavelength with the variation in the volume fraction of inclusions. We find that the composite grain models with the axial ratios viz. 1.33 and 2.0 fit the observed extinction reasonably well with a grain size distribution, a = 0.005–0.250 μm. Moreover, our results on the composite grains clearly indicate that the inhomogeneity in the grain structure, composition, and the surrounding media modify the extinction properties of the grains.

Quantitative structure-property relationship modeling of Grätzel solar cell dyes

With fossil fuel reserves on the decline, there is increasing focus on the design and development of low-cost organic photovoltaic devices, in particular, dye-sensitized solar cells (DSSCs). The power conversion efficiency (PCE) of a DSSC is heavily influenced by the chemical structure of the dye. However, as far as we know, no predictive quantitative structure-property relationship models for DSSCs with PCE as one of the response variables have been reported. Thus, we report for the first time the successful application of comparative molecular field analysis (CoMFA) and vibrational frequency-based eigenvalue (EVA) descriptors to model molecular structure-photovoltaic performance relationships for a set of 40 coumarin derivatives. The results show that the models obtained provide statistically robust predictions of important photovoltaic parameters such as PCE, the open-circuit voltage (V(OC)), short-circuit current (J(SC)) and the peak absorption wavelength λ(max). Some of our findings based on the analysis of the models are in accordance with those reported in the literature. These structure-property relationships can be applied to the rational structural design and evaluation of new photovoltaic materials.

Absorption Cross Section Simulation: a Preliminary Study of Ultraviolet Absorption Spectroscopy for Ozone Gas Measurement

Preliminary study to measure gaseous ozone concentration using ultraviolet absorption spectroscopy is presented. Firstly, background of ozone is introduced. Next, fundamental theory behind ultraviolet absorption spectroscopy is discussed based on Beer-Lambert’s Law and absorption spectrum of ozone. After that, absorption cross section of ozone is simulated via spectralcalc.com. Temperature of system is varied. Peak absorption cross section and peak absorption wavelength are found to be 1.166 ´ 10-21 m2 molecule-1 and 255.376 nm respectively at 300 K and 0 torr. Absorption cross section in ultraviolet region shows slight variation of at most 1.286 per cent when temperature is changed from 200 K to 300 K. Around room temperature, peak absorption cross section simulated in current work is consistent with previous work, because relative error is found to be small in between 1.630 per cent and 3.087 per cent. Unlike previous work, absorption of light by ozone is detected in ultraviolet region only due to weak absorption in visible region.

Photonic spectral modulation in bacteriorhodopsin molecules and optimization of signal wavelength

In general, in excited-state absorption (ESA) based all-optical light modulator, maximum signal intensity modulation is achieved at the wavelength corresponding to maximum excited to ground state absorption cross-section ratio. However, theoretical analysis of photonic spectral modulation of broadband signal beam based on ESA in bacteriorhodopsin (BR) provides counterintuitive interesting results in the signal wavelength region 460–700nm. It is shown that the signal modulation is enhanced significantly at some particular wavelength values (optimum signal wavelength). Optimum signal wavelength in the region 450–700nm, varies with modulating intensity, and does not correspond to the peak absorption wavelength of the longer lived intermediate states. Present analysis is very useful in designing ESA based power efficient photonic devices.

Molecular Origins of Optoelectronic Properties in Coumarins 343, 314T, 445, and 522B

The relationships between the structure and laser dye properties of four coumarin derivatives are investigated to assist in knowledge-based molecular design of coumarins for various optoelectronic applications. Four new crystal structures of coumarins 343, 314T, 445, and 522B are determined at 120 K and analyzed via the empirical harmonic–oscillator–stabilization–energy and bond-length–alternation models, based on resonance theory. Results from these analyses are used to rationalize the optoelectronic properties of these coumarins, such as their UV–vis peak absorption wavelength, molar extinction coefficient, and fluorescence quantum efficiency. The specific molecular structural features of these four coumarins and the effects on their optoelectronic properties are further examined via a comparison with other similar coumarin derivatives, including coumarins 314, 500, and 522. These findings are corroborated by density functional theory (DFT) and time-dependent DFT calculations. The structure–property cor...

Phospholipid micelle-based magneto-plasmonic nanoformulation for magnetic field-directed, imaging-guided photo-induced cancer therapy

We present a magnetoplasmonic nanoplatform combining gold nanorods (GNR) and iron-oxide nanoparticles within phospholipid-based polymeric nanomicelles (PGRFe). The gold nanorods exhibit plasmon resonance absorbance at near infrared wavelengths to enable photoacoustic imaging and photothermal therapy, while the Fe3O4 nanoparticles enable magnetophoretic control of the nanoformulation. The fabricated nanoformulation can be directed and concentrated by an external magnetic field, which provides enhancement of a photoacoustic signal. Application of an external field also leads to enhanced uptake of the magnetoplasmonic formulation by cancer cells in vitro. Under laser irradiation at the wavelength of the GNR absorption peak, the PGRFe formulation efficiently generates plasmonic nanobubbles within cancer cells, as visualized by confocal microscopy, causing cell destruction. The combined magnetic and plasmonic functionalities of the nanoplatform enable magnetic field-directed, imaging-guided, enhanced photo-induced cancer therapy. From the Clinical EditorIn this study, a nano-formulation of gold nanorods and iron oxide nanoparticles is presented using a phospholipid micelle-based delivery system for magnetic field-directed and imaging-guided photo-induced cancer therapy. The gold nanorods enable photoacoustic imaging and photothermal therapy, while the Fe3O4 nanoparticles enable magnetophoretic control of the formulation. This and similar systems could enable more precise and efficient cancer therapy, hopefully in the near future, after additional testing.

Synthesis and Properties of Au Nanoparticles with Various Sizes

Properties of Au nanoparticles (NPs) caused by various sizes (5-12 nm) were studied in this article. Au NPs capped with citrate of various sizes were synthesized by two methods including trisodium citrate dihydrate reduction of chloroauric acid tetrahydrate and sodium borohydride reducion of chloroauric acid tetrahydrate. Au NPs were characterized and measured by using transmission electron microscope (TEM), UV-vis-NIR absorption spectroscopy, and surface Raman scattering. The results of experiment indicated that the size of Au NPs was related to the type of reducing agent and molar ratio of reducing agent and chloroauric acid. The weaker the reducing capacity of the reducing agent or the lower the molar ratio, the bigger the size of Au NPs is. The max wavelength of absorption peak for the citrate-capped Au NPs is red-shifted with the increase of particle diameter. Raman scattering observed from Au NPs of various sizes is found to be NP size-dependent. It is clear that the bigger Au NPs are more apparent in the Raman scattering determination. Size-tunable Au NPs should be crucial for biosensors, particularly as Raman-tag particles.

Effect of polarization on intersubband transition in AlGaN/GaN multiple quantum wells

Intersubband transitions (ISBT) of AlGaN/GaN multiple quantum wells (MQWs) with wavelength towards atmospheric window (3–5 μm) have been investigated. A Ga-excess epitaxial method is used in the molecular beam epitaxy leading to ultra-sharp interface and negligible elements inter-diffusion. The absorption peak wavelength of the ISBT was successfully tuned in the range of 3–4 μm by modifying the GaN well thickness from 2.8 to 5.5 nm. It was further found that the polarization charge density of the AlGaN/GaN MQWs was about −0.034 C/m2 which gave rise to blueshift of the ISBT wavelength and thus partially compensated its redshift with increasing well thickness.

Molecular Origins of the High-Performance Nonlinear Optical Susceptibility in a Phenolic Polyene Chromophore: Electron Density Distributions, Hydrogen Bonding, and ab Initio Calculations

The molecular and supramolecular origins of the superior nonlinear optical (NLO) properties observed in the organic phenolic triene material, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile), are presented. The molecular charge-transfer distribution is topographically mapped, demonstrating that a uniformly delocalized passive electronic medium facilitates the charge-transfer between the phenolic electron donor and the cyano electron acceptors which lie at opposite ends of the molecule. Its ability to act as a “push–pull” π-conjugated molecule is quantified, relative to similar materials, by supporting empirical calculations; these include bond-length alternation and harmonic-oscillator stabilization energy (HOSE) tests. Such tests, together with frontier molecular orbital considerations, reveal that OH1 can exist readily in its aromatic (neutral) or quinoidal (charge-separated) state, thereby overcoming the “nonlinearity-thermal stability trade-off”. The HOSE calculation also reveals a correlation between the quinoidal resonance contribution to the overall structure of OH1 and the UV–vis absorption peak wavelength in the wider family of configurationally locked polyene framework materials. Solid-state tensorial coefficients of the molecular dipole, polarizability, and the first hyperpolarizability for OH1 are derived from the first-, second-, and third-order electronic moments of the experimental charge-density distribution. The overall solid-state molecular dipole moment is compared with those from gas-phase calculations, revealing that crystal field effects are very significant in OH1. The solid-state hyperpolarizability derived from this charge-density study affords good agreement with gas-phase calculations as well as optical measurements based on hyper-Rayleigh scattering (HRS) and electric-field-induced second harmonic (EFISH) generation. This lends support to the further use of charge-density studies to calculate solid-state hyperpolarizability coefficients in other organic NLO materials. Finally, this charge-density study is also employed to provide an advanced classification of hydrogen bonds in OH1, which requires more stringent criteria than those from conventional structure analysis. As a result, only the strongest OH···NC interaction is so classified as a true hydrogen bond. Indeed, it is this electrostatic interaction that influences the molecular charge transfer: the other four, weaker, nonbonded contacts nonetheless affect the crystal packing. Overall, the establishment of these structure–property relationships lays a blueprint for designing further, more NLO efficient, materials in this industrially leading organic family of compounds.

Multispectral near-perfect metamaterial absorbers using spatially multiplexed plasmon resonance metal square structures

Near perfect infrared light absorption at multi-spectral wavelengths has been experimentally demonstrated by using multiplexed metal square plasmon resonance structures. Optical power absorption over 95% has been observed in dual-band metamaterial absorbers at two separate wavelengths and optical power absorption over 92.5% has been observed in triple-band metamaterial absorbers at three separate wavelengths. The peak absorption wavelengths are primarily determined by the sizes of the metal squares in the multiplexed structures. Electrical field distributions in the middle of the dielectric spacer layer were calculated at the peak absorption wavelengths. It is shown that strong light absorption corresponds to the local quadrupole plasmon resonance modes in the metamaterial structures.

Microwave-Assisted Synthesis of Cadmium Sulfide Nanoparticles: Effect of Hydroxide Ion Concentration

ABSTRACTCadmium sulfide nanoparticles were synthesized by a microwave-assisted route in aqueous dispersion. The cadmium sulfide nanoparticles showed an average diameter around 5 nm and a cubic phase corresponding to hawleyite. The aqueous dispersions of the nanoparticles were characterized by UV-Vis spectroscopy, luminescence analysis, transmission electron microscopy and X-ray diffraction. The addition of sodium hydroxide solutions at different concentrations causes a red-shift in the wavelength of the first excitonic absorption peak of the cadmium sulfide nanoparticles, indicating a reduction of the band gap energy. Besides, the intensity of the luminescence of the nanoparticle dispersions was increased. However, there is a threshold concentration of the hydroxide ion above which the precipitation of the cadmium sulfide nanoparticles occurs.

Thermal Behavior and UV Properties of Organomodified Kaolin Oleochemically Derived from Rubber Seed Oils (<i>Hevea brasiliensis</i>) and Tea Seed Oils (<i>Camellia sinensis</i>)

Kaolin was modified using a chemical complex of hydrazine hydrate and oleochemical sodium salts derived from rubber seed oil (SRSO) and tea seed oil (STSO) respectively. Characterization of the pristine kaolin and the modified kaolins were performed using Scanning Electron Microscopy (SEM), Simultaneous Thermogravimetric/Differential Thermal Analysis (TG/DTA) and UV Spectrophotometry. TG/DTA revealed that the incorporation of the oleochemical salts enhanced thermal decomposition of kaolin into metakaolin. Ultraviolet spectrophotometric studies conducted on the modified kaolin show for the first time that the SRSO-modified kaolin and STSO-modified kaolin have a peak absorbance wavelengths of 312.72 nm and 314.26 nm respectively. This shows that the modified kaolin is a promising candidate for sunscreen applications.

Influence of Reaction Temperature on Crystal Structure and Band Gap of ZnO Nanoparticles

Zinc oxide nanoparticles have been synthesized at room temperature and at 50°C via precipitation method for the present study. The effect of synthesis temperature on the crystalline size, microstructure, optical properties, and energy gap of the synthesized zinc oxide nanoparticles has been investigated. The particle size was found to reduce from 26 nm to 17 nm when the reaction temperature was increased from room temperature to 50°C. Energy gap of the prepared samples has been theoretically determined using effective mass model equation and compared with the experimental value. It depicts that the energy gap of the smaller nanoparticles is higher than the bigger one. The recorded blue shift confirmed the quantum confinement effect. Compositional quality and functional group of the zinc oxide nanoparticles have been studied, and the frequency of zinc oxide nanoparticles has been observed at two different regions, 566 cm−1 and 432 cm−1. The recorded ultraviolet-visible spectrum shows absorption peaks at 361 nm and 328 nm, which are less than the absorption peak of bulk zinc oxide (388 nm). Peak absorption wavelength measurement shows the average size of the prepared zinc oxide nanoparticles is as small as 1.55 nm.

Photosystem trap energies and spectrally-dependent energy-storage efficiencies in the Chl d-utilizing cyanobacterium, Acaryochloris marina

Acaryochloris marina is the only species known to utilize chlorophyll (Chl) d as a principal photopigment. The peak absorption wavelength of Chl d is redshifted ≈40nm in vivo relative to Chl a, enabling this cyanobacterium to perform oxygenic phototrophy in niche environments enhanced in far-red light. We present measurements of the in vivo energy-storage (E-S) efficiency of photosynthesis in A. marina, obtained using pulsed photoacoustics (PA) over a 90-nm range of excitation wavelengths in the red and far-red. Together with modeling results, these measurements provide the first direct observation of the trap energies of PSI and PSII, and also the photosystem-specific contributions to the total E-S efficiency. We find the maximum observed efficiency in A. marina (40±1% at 735nm) is higher than in the Chl a cyanobacterium Synechococcus leopoliensis (35±1% at 690nm). The efficiency at peak absorption wavelength is also higher in A. marina (36±1% at 710nm vs. 31±1% at 670nm). In both species, the trap efficiencies are ≈40% (PSI) and ≈30% (PSII). The PSI trap in A. marina is found to lie at 740±5nm, in agreement with the value inferred from spectroscopic methods. The best fit of the model to the PA data identifies the PSII trap at 723±3nm, supporting the view that the primary electron-donor is Chl d, probably at the accessory (ChlD1) site. A decrease in efficiency beyond the trap wavelength, consistent with uphill energy transfer, is clearly observed and fit by the model. These results demonstrate that the E-S efficiency in A. marina is not thermodynamically limited, suggesting that oxygenic photosynthesis is viable in even redder light environments.

Broadband continuous-wave technique to measure baseline values and changes in the tissue chromophore concentrations

We present a broad-band, continuous-wave spectral approach to quantify the baseline optical properties of tissue and changes in the concentration of a chromophore, which can assist to quantify the regional blood flow from dynamic contrast-enhanced near-infrared spectroscopy data. Experiments were conducted on phantoms and piglets. The baseline optical properties of tissue were determined by a multi-parameter wavelength-dependent data fit of a photon diffusion equation solution for a homogeneous medium. These baseline optical properties were used to find the changes in Indocyanine green concentration time course in the tissue. The changes were obtained by fitting the dynamic data at the peak wavelength of the chromophore absorption, which were used later to estimate the cerebral blood flow using a bolus tracking method.

Optical properties and irradiation effects of Cu+ and Eu2+ doped alkali halide single crystals grown from melt using Czochralski technique

Copper (Cu) and europium (Eu) doped potassium chloride, potassium bromide and sodium chloride single crystals were grown using Czochoralski technique. Optical absorption (OA) studies were carried out to find the peak absorption wavelength in these crystals. Photoluminescence (PL) and thermoluminescence (TL) studies were carried out in these crystals both before and after irradiating with 60Co gamma rays. The photoluminescence emission was found by exciting the crystals using light of wavelength where maximum absorption was obtained. In the case of Cu doped samples the photoluminescence emission intensity was found to decrease after irradiation. The Eu2+ emission intensity was also found to decrease in all samples. The TL emission studies showed the characteristic emission of the dopants in these crystals except in bromide. The TL emission spectra in these samples showed emission in the range 420–450nm.