Absorption Peak Position Research Articles

Preparation and characterization of graphene nanosheet doped with silver nanoparticles

Simple process (exploding wire technique) was used to Prepared sliver nanoparticles (AgNPs). The graphene sheet was added to AgNPs with different concentrations (0.002g/ml and 0.01g/ml). well dispersion of AgNPs are achieved by simple chemistry process. The samples were characterized by ultraviolet-visible spectroscopy (UV-Vis), x-ray diffraction (XRD), atomic force microscopy (AFM) and Field emission scanning electron microscope (FESEM). The results showed a wide band absorption of AgNPs-graphene (AgNPs-GN) extended from VU to IR region, surface plasmon resonance (SPR) absorption peak position for the AgNPs at (350-600) nm, XRD confirmed the clear distribution of the peaks attributed to polycrystalline for AgNPs appeared at 20=38.14°, 44.27°, 64.33, and 77.37° respectively and AgNPs-GN at 2θ=26.51° and 54.65°. The AFM showed that AgNPs have uniformly distribution on the surface of graphene sheet. The average size of AgNPs was confirmed by around (50-80) nm by FESEM and the AgNPs-GN have average particle size (20-40) nm. The AgNPs-GN could become prominent candidate for optoelectronic applications.

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

DFT study for the absorption spectra evolution of CdS magic-size clusters

Absorption spectroscopy is important and necessary for the study of magic-size clusters (MSCs). However, researches regarding the relationship between the structural change and absorption spectra variation are quite limited. Herein, we compared the structural variation and absorption evolution of MSCs by first-principles calculations in this paper. Firstly, we simplified the single crystal structure In37P20(OOCCH2Ph)51 of InP MSC to In37P20H68 and calculated its absorption spectrum using three different functionals (PBE, B3LYP, HSE06). By comparing the absorption spectra calculated from the In37P20H68 structure with those measured from the InP MSC sample, we evaluated the difference in absorption spectra calculated by different functionals and the rationality of this kind of method for structure simplification. Secondly, we validated the structural model Cd37S20 proposed for CdS MSC-311 by calculating the absorption spectrum of Cd37S20H68 and comparing the similarity between the absorption spectrum calculated and the experimental measured. Finally, we expanded structures based on the principal characteristics of Cd37S20 and calculated the corresponding absorption spectra of them. By comparing the difference among the absorption spectra of the expanded structures, we demonstrate that the absorption peak position shifts of MSCs are more sensitive to their anisotropy, instead of the number of atoms added and local structure change. These findings provide an in-depth understanding of the structure-absorption relationship.

Dynamically tunable perfect THz absorption in graphene-based metamaterial structures

We investigate THz absorption properties of a graphene-based metamaterial structure composed of a graphene/SiC defect layer placed on one side of the periodic array of Si and SiO2 layers. We demonstrate that the proposed structure can lead to perfect THz absorption because of strong photon localization in the defect layer of the structure. The maximal absorption value and corresponding frequency can be tuned by controlling the Fermi energy through a gate voltage. Moreover, the absorption peak value is insensitive to the incident angle and period number. The position of the THz absorption peak can be tailored by adjusting the thickness spacer layer SiC. By applying an external magnetic field, one can dynamically manipulate the left-handed circularly polarized (LCP) or right-handed circularly polarized (RCP) absorption. Our proposal may have potentially important applications in optoelectronic devices such as circular polarized wave sensors, photodetectors and absorbers.

Infrared spectroscopic imaging study of BV-2 microglia altering tumor cell biological activity and cellular fraction

Tumor brain metastasis is a severe threat to patients’ neurological function, in which microglia may be involved in the process of tumor cell metastasis among nerve cells. Our study focused on the interaction between microglia and breast and lung cancer cells. Changes in the proliferation and migration ability of cocultured tumor cells were examined; synchrotron radiation-based fourier transform infrared microspectroscopy (SR-FTIR) was used to detect changes in the structures and contents of biomolecules within the tumor cells. The experimental results showed that the proliferation and migration ability of tumor cells increased after coculture, and the structures and contents of biological macromolecules in tumor cells changed. The absorption peak positions of the amide Ⅱ and amide Ⅰ bands observed for the four kinds of tumor cells changed, and the absorption intensities were significantly enhanced, indicating changes in the secondary structures and contents of proteins in tumor cells, which may be the root cause of the change in tumor cell characteristics. Therefore, the metabolites of microglia may be involved in the progression of tumor cells in the nervous system. In this study, we focused on the interaction between microglia and tumor cells by using SR-FTIR and provided a new understanding of the mechanism of brain metastasis.

A novel “off-on-off” fluorescent sensor based on inner filter effect for ultrasensitive detection of protamine/trypsin and subcellular colocalization

Protease is an important physiological enzyme that can catalyze the hydrolysis of peptide bonds at specific sites and trypsin is a proteolytic enzyme present in the pancreas, the fluctuation of whom reflect dysfunction of body. Thus, it is necessary to develop sensitivity detections for protamine and trypsin. Herein, an "off-on-off" fluorescent sensor based on the inner filter effect was established for individually quantification of protamine and trypsin by using silicon quantum dots (SiQDs) and triangular silver nanoprisms (TSNPRs) based on the inner filter effect (IFE). The maximum absorption peak position of TSNPRs is 550 nm, which completely overlaps the emission peak (536 nm) of SiQDs and considerably improves sensitivity of the sensor. The proposed IFE-based sensor proved a good linearity from 0–30 ng/mL for protamine determination with detection limit of 5 ng/mL. For trypsin detection, the constructed sensor displayed a liner detection range from 0 to 40 ng/mL with a detection limit of 8 ng/mL. Besides, the SiQDs have equipped with the excellent capability for subcellular colocalization, providing a promising potential for practical applications.

Perturbative approach to the polaron shift of excitons in transition metal dichalcogenides

In this paper we study the phonon's effect on the position of the 1s excitonic resonance of the fundamental absorption transition line in two-dimensional transition metal dichalcogenides. We apply our theory to WS$_{2}$a two-dimensional material where the shift in absorption peak position has been measured as a function of temperature. The theory is composed of two ingredients only: i) the effect of longitudinal optical phonons on the absorption peak position, which we describe with second order perturbation theory; ii) the effect of phonons on the value of the single particle energy gap, which we describe with the Huang Rhys model. Our results show an excellent agreement with the experimentally measured shift of the absorption peak with the temperature.

Efficiency of Tri-n-octylamine for the liquid-liquid extraction of Co (II) from acidic chloride medium

Cobalt criticality is increasing as a function of time and this concern has impelled researchers to ascertain efficient recovery schemes of cobalt. In this paper, an extraction strategy for cobalt utilizing tri-n-octyl amine (TOA) in kerosene from acidic chloride media has been developed. The extraction percentage was found to be 76.7 using 1.5M TOA. The extracted species has been formulated as (R3NH) CoCl3 based on the findings of slope analysis. Influence of various salting out agents like NH4Cl, KCl, and NaCl on the percentage extraction has been analysed and KCl emerged as beneficial for extraction. The estimated values of enthalpy change and entropy change shows that the extraction process is enthalpy driven with formation of Co (II)-TOA inner sphere complex. Kerosene as diluent was proved to be efficient in comparison to other aromatic hydrocarbons for the extraction of Co under the present experimental conditions. In order to examine the interaction between cobalt and TOA, FTIR analysis has been carried out. The changes in absorption peak position of functional groups confirmed binding of TOA with Co (II).

Deep Learning Optical Spectroscopy Based on Experimental Database: Potential Applications to Molecular Design.

Accurate and reliable prediction of the optical and photophysical properties of organic compounds is important in various research fields. Here, we developed deep learning (DL) optical spectroscopy using a DL model and experimental database to predict seven optical and photophysical properties of organic compounds, namely, the absorption peak position and bandwidth, extinction coefficient, emission peak position and bandwidth, photoluminescence quantum yield (PLQY), and emission lifetime. Our DL model included the chromophore–solvent interaction to account for the effect of local environments on the optical and photophysical properties of organic compounds and was trained using an experimental database of 30 094 chromophore/solvent combinations. Our DL optical spectroscopy made it possible to reliably and quickly predict the aforementioned properties of organic compounds in solution, gas phase, film, and powder with the root mean squared errors of 26.6 and 28.0 nm for absorption and emission peak positions, 603 and 532 cm–1 for absorption and emission bandwidths, and 0.209, 0.371, and 0.262 for the logarithm of the extinction coefficient, PLQY, and emission lifetime, respectively. Finally, we demonstrated how a blue emitter with desired optical and photophysical properties could be efficiently virtually screened and developed by DL optical spectroscopy. DL optical spectroscopy can be efficiently used for developing chromophores and fluorophores in various research areas.

Study on Optical Properties and Biological Activity of Proanthocyanidins at Different pH and Alkalinit

The UV-Vis absorption and fluorescence spectra of proanthocyanidins at different pH values were studied, and the change of absorption peak position was analyzed. The intermediate stable states of proanthocyanidins in different pH conditions, the electron transition modes and emission spectra of these steady states were analyzed. Eight parts of proanthocyanidins, each with mass of 1.00 mg, were added to acetic acid buffer solution with different pH in turn. The absorption of samples at the same pH concentration was measured by UV-visible spectrophotometer and fluorescence spectrophotometer, spectrogram analysis was carried out. The absorption peak wavelength of proanthocyanidins did not change obviously in acid condition, the quantum yield of proanthocyanidins was low in different pH solutions, and the excited molecules returned to the ground state mainly by non-radiative transition. Under the same temperature conditions, the stability of proanthocyanidins decreased with the increase of pH, and the color of the solution ranged from orange to red. The charge distribution of hydroxyl groups analyzed the ability of combining free radicals at different sites of proanthocyanidins with hydroxyl groups, which suggested that proanthocyanidins may have better antioxidant activity.

Impact of amino acid substitutions on the behavior of a photoactivatable near infrared fluorescent protein PAiRFP1

A photoactivatable near-infrared fluorescent protein (NIR-FP) PAiRFP1 has been developed by 15 amino acid substitutions in its nonfluorescent template Agp2. In our previous communication, we investigated the role of three amino acids in PHY domain distal from BV molecule. The impact of the twelve amino acids in GAF domain, especially five residues near BV-binding pocket is unclear. In this paper, PCR based reverse mutagenesis, spectroscopic methods, molecular modelling and simulations have been employed to explore the roles of these substitutions during the molecular evolution of PAiRFP1. It was found that the residue L163 is important for protein folding in PAiRFP1. The residues F244 and C280 exerted remarkable effects on molar extinction coefficient, NIR fluorescence quantum yield, molecular brightness, fluorescence fold, and dark recovery rate. The residues F244 and V276 modulate the maximum absorption and emission peak position. The reverse mutant L168M exhibited a higher fluorescence fold than PAiRFP1. Additionally, the reverse mutants V203A, V294E, S218G and D127G possessed better spectral properties than PAiRFP1. This study is important for the rational design of a better BphP-based photoactivatable NIR-FPs.

Modeling of plasmon resonance in periodic multilayer structures based on chromium with a surface island layer

The optical properties of Cr/Si/Cr and Cr/CrSi2 /Cr structures with periodically located chromium islands are modeled using the finite-difference time domain method. These structures are characterized by the phenomenon of plasmon resonance. The dependences of the intensity and position of the plasmon absorption peak on the thickness and radius of the islands are determined. It was observed that when the island thickness increases to 120 nm, the intensity of the absorption peak increases to 69 % for the Cr/Si/Cr structure and to 55 % for the Cr/CrSi2 /Cr structure. It was found that the peak of plasmon absorption in the spectrum of the Cr/Si/Cr structure is at a shorter wavelength (8.4 µm for Cr/Si/Cr, 11.1 µm for Cr/CrSi2/Cr), and also has a higher intensity (the share of absorbed radiation is 14 % higher compared to the peak of plasmon absorption in the spectrum of the Cr/CrSi2 /Cr structure). The obtained dependences indicate that the Cr/Si/Cr and Cr/CrSi2 /Cr structures can be used as IR detectors.

Transformations Among Colloidal Semiconductor Magic-Size Clusters.

A knowledge of colloidal semiconductor magic-size clusters (MSCs) is essential for understanding how fundamental properties evolve during transformations from individual molecules to semiconductor quantum dots (QDs). Compared to QDs, MSCs display much narrower optical absorption bands; the higher cluster stability gives rise to a narrower size distribution. During the production of binary QDs such as II-VI metal (M) chalcogenide (E) ones, binary ME MSCs observed were interpreted as side products and/or the nuclei of QDs. Prior to the current development of our two-step approach followed by our two-pathway model, it had been extremely challenging to synthesize MSCs as a unique product without the nucleation and growth of QDs. With the two-step approach, we have demonstrated that MSCs can be readily engineered as a sole product at room temperature from a prenucleation stage sample, also called an induction period (IP) sample. It is important that we were able to discover that the evolution of the MSCs follows first-order reaction kinetics behavior. Accordingly, we proposed that a new type of compound, termed as "precursor compounds" (PCs) of MSCs, was produced in an IP sample. Such PCs are optically transparent at the absorption peak positions of their MSC counterparts as well as to longer wavelengths. It is thought that quasi isomerization of a single PC results in the development of one MSC.In this Account, we provide an overview of our latest advances regarding the transformations among binary CdE MSCs as well as from binary CdTe to ternary CdTeSe MSCs. Optical absorption spectroscopy has been employed to study these transformations, all of which display well-defined isosbestic points. We have proposed that these MSC to MSC transformations occur via their corresponding PCs, also called immediate PCs. It is reasonable that the as-synthesized PC (in an IP sample) and the immediate PC (in an incubated and/or diluted sample) probably have different configurations. A transformation between two PCs may involve an intermolecular reaction, with either first-order reaction kinetics or a more complicated time profile. A transformation between one immediate PC and its counterpart MSC may contain an intramolecular reaction. The present Account, which addresses the PC-enabled MSC transformations with isosbestic points probed by optical absorption spectroscopy, calls for more experimental and theoretical attention to understand these magic species and their transformation processes more precisely.

Density functional theory study on optical and electronic properties of co-doped graphene quantum dots based on different nitrogen doping patterns

Heteroatom doping, especially co-doping, is an effective way to tailor electronic structures of graphene quantum dots (GQDs) with synergistic effects and desirable properties. However, due to different synthesis methods, the widespread use of GQDs co-doped with heteroatoms is hindered by the poor understanding of their optical properties and mechanisms. In this work, co-doped GQDs based on three N-doping configurations are chosen to reveal underlying mechanisms of optical properties using density functional theory and time-dependent density functional theory calculations. Based on different N-doping patterns, B, P and S atoms can endow GQDs with a wide spectrum of new optical properties and electronic structures. The HOMO–LUMO gaps of N-doped GQDs with graphitic N, pyrrolic N, and pyridinic N are 0.77, 0.25 and 2.69 eV, respectively. In the co-doped GQDs, B, P and S containing functional groups cause low absorptions in the range of 400 to 800 nm and multiple absorption peaks at about 400 and 600 nm, while the N atom affects the position and intensity of prominent absorption peak according to three different N-doping patterns. The B atom forms sp2 hybridization in the graphene lattice, while the P and S atoms transform the sp2 hybridized carbon into the sp3 state. It is anticipated that this work will provide valuable insights for understanding absorption mechanisms and electronic properties of heteroatom co-doped GQDs as well as achieving new applications with well-defined and desired properties.

3D fluorescence confocal microscopy of InGaN/GaN multiple quantum well nanorods from a light absorption perspective.

A nanostructure of In0.18Ga0.82N/GaN multiple quantum well (MQW) nanorods (NRs) was fabricated using top-down etching with self-organized nickel (Ni) nanoparticles as masks on the wafer. The optical properties of In0.18Ga0.82N/GaN MQW NRs were discussed by experiment and theory from a light absorption perspective. Three-dimensional (3D) optical images of NRs were successfully obtained by confocal laser scanning microscopy (CLSM) for physical observation of the optical phenomenon of InGaN/GaN MQW NRs. Moreover, optical simulations were performed by COMSOL Multiphysics via the three-dimensional finite-element method to explore the influences of NR geometrical parameters on optical absorption. The simulated results demonstrate that the absorption of NRs is higher than that of the film due to the waveguide properties of NRs resulting from their higher refractive index than embedding medium and higher aspect ratio than bulk. In addition, an increase in the diameter results in a red-shift of the absorption peak position of In0.18Ga0.82N/GaN MQW NRs. The smaller pitch enhances the near-field coupling of the nanorods and broadens the absorption peak. These results clearly illustrate the optical properties of In0.18Ga0.82N/GaN MQW NRs from the perspective of 3D confocal laser scanning microscopy. This work is promising for the applications of III–V optoelectronic devices.

Novel Terahertz Spectroscopy Technology for Crystallinity and Crystal Structure Analysis of Cellulose.

Crystallinity is an essential indicator for evaluating the quality of fiber materials. Terahertz spectroscopy technology has excellent penetrability, no harmful substances, and commendable detection capability of absorption characteristics. The terahertz spectroscopy technology has great application potential in the field of fiber material research, especially for the characterization of the crystallinity of cellulose. In this work, the absorption peak of wood cellulose, microcrystalline cellulose, wood nano cellulose, and cotton nano cellulose were probed in the terahertz band to calculate the crystallinity, and the result compared with XRD and FT-IR analysis. The vibration model of cellulose molecular motion was obtained by density functional theory. The results showed that the average length of wood cellulose (WC) single fiber was 300 μm. The microcrystalline cellulose (MCC) was bar-like, and the average length was 20 μm. The cotton cellulose nanofiber (C-CNF) was a single fibrous substance with a length of 50 μm, while the wood cellulose nanofiber (W-CNF) was with a length of 250 μm. The crystallinity of cellulose samples in THz was calculated as follows: 73% for WC, 78% for MCC, 85% for W-CNF, and 90% for C-CNF. The crystallinity values were obtained by the three methods which were different to some extent. The absorption peak of the terahertz spectra was most obvious when the samples thickness was 1 mm and mixed mass ratio of the polyethylene and cellulose was 1:1. The degree of crystallinity was proportional to the terahertz absorption coefficients of cellulose, the five-movement models of cellulose molecules corresponded to the five absorption peak positions of cellulose.

Plasmonic-Enhanced Light Absorption in Periodic Silicon Structures: The Effect of Inter-Island Distance

Absorption spectra of Si/SiO2/Si structure with highly doped silicon layers are simulated with Finite Difference Time Domain (FDTD) as a function of periodicity of surface islands. The effect of multiple resonance is studied for different inter-island distances. A wide band (>12 µm) of high light absorption (>70%) is registered for a structure with a period of 8 μm and an inter-island distance of 3 μm. It is revealed for the spectral range of 10–20 μm that the reduction of the inter-islands distance shifts the absorption peak position to the region of longer waves and results in the growth of the absorption level.

Investigation of acoustic plasmons in vertically stacked metal/dielectric/graphene heterostructures for multiband coherent perfect absorption.

Coherent absorption, as the time-reversed counterpart to laser, has been widely proposed recently to flexibly modulate light-matter interactions in two-dimensional materials. However, the multiband coherent perfect absorption (CPA) in atomically thin materials still has been elusive. We exploit the multiband CPA in vertically stacked metal/dielectric/graphene heterostructures via ultraconfined acoustic plasmons which can reduce the photon wavelength by a factor of about 70 and thus enable multiple-order resonances on a graphene ribbon of finite width. Under the illumination of two counter-propagating coherent beams, the two-stage coupling scheme is used for exciting multispectral acoustic plasmon resonances on the heterostructure simultaneously, thereby contributing to the ultimate multiband CPA in the mid-infrared region. The strong dependence of the nearly linear dispersion of acoustic plasmons on the chemical potential in graphene and the separation between the metal and the graphene allows the tunability in spectral positions of absorption peaks. Intriguingly, the absorption of each resonant peak is continuously tuned by varying the relative amplitude of two counter-propagating beams, and even their phase difference, respectively. The maximum modulation depth of 4.46*105 is observed. The scattering matrix is employed to demonstrate the principle of CPA and the finite-difference time-domain (FDTD) simulations are used for elucidating the flexible tunability. More importantly, the multiband coherent absorber is robust to the incident angle, and thus undoubtedly benefits extensive applications on optoelectronic and engineering technology areas for modulators and optical switches.

Oxygen vacancies mediated cooperative magnetism in ZnO nanocrystals: A d0 ferromagnetic case study

This article reports on the oxygen vacancies and defects induced cooperative magnetism of 28nm (as prepared) and 74nm (annealed) sized nanocrystals of ZnO synthesized through sol- gel auto-combustion route. UV–Vis–NIR optical absorption and photoluminescence (PL) spectroscopic measurements showed marginal red shifting in the band gap energy and characteristic blue shift in the UV absorption peak position with the size reduction of ZnO nanocrystallites. PL analysis revealed that 28nm sized ZnO nanocrystals have higher number of oxygen vacancies and lower interstitial defects in comparison to 74nm (annealed) nanocrystals of ZnO. Both the sample display oxygen vacancy and defect mediated ferromagnetic behaviour at 300K but 28nm ZnO nanocrystals are better ferromagnetic in comparison to annealed ZnO nanocrystals. The annealed ZnO nanocrystals also showed considerable diamagnetic character. High field (±7 Tesla) magnetization measurements down to 5K and PL analysis establish presence, inter-conversion of oxygen vacancies and valence fluctuations in neutral, mono and divalent oxygen vacancies. The monovalent oxygen and zinc vacancies play important role in the mediation of d0 type cooperative magnetism in the ZnO nanocrystals.

Tuning the optical and magneto-optical properties in core-shell structured Fe@Ag nanoparticles

Magnetic nanoparticles (NPs) have attracted a great deal of attention due to their possible uses in many biomedical applications, such as targeted drug delivery, sensing, and ultra-sensitive disease detection. In this work, theoretical calculations based on optical absorption and magneto-optical (MO) properties in core–shell structured Fe@Ag NPs embedded in a polymethyl methacrylate (PMMA) host were investigated as a function of incident light wavelength. First, the optical absorption property of pure Ag NPs was investigated. For pure single spherical Ag nanoparticle with diameters in the range of 5–50 nm, the resonance absorption peak shows a slight redshift as the particle size increases. In terms of the optical absorption property for the two basic two-particle geometries of Ag NPs with varying Ag NPs interparticle distances ranging from 8–100 nm, when the particles were perpendicular to the direction propagation and parallel to the polarisation direction of an incident electric field, a blueshift of the absorption peak position was observed with increasing interparticle distance. On the other hand, a redshift of the absorption peak position with increasing interparticle distance was observed when the polarisation direction of the incident light was perpendicular to the particle axis. After coating plasmonic Ag on the Fe core called Fe@Ag core–shell NPs, the shifting and enhancement of the absorption and MO properties of Fe nanoparticles due to localised surface plasmon resonance excitation were observed to greatly exceed the calculated values for pure Fe NPs. The calculated results suggest that both interparticle distance and Ag shell thickness in a core–shell structured Fe@Ag NPs influence the tuning and enhancement of the spectra. These findings can be utilised as basic knowledge for the development of synthesis methods to obtain suitable Fe@Ag core–shell NPs for future applications.