Absorption Peak Position Research Articles

INFLUENCE OF POLYMER MOLECULAR WEIGHT ON LIGHT HARVESTING AND PERFORMANCE PARAMETERS OF THE ORGANIC SOLAR CELL

In the present article, we try to illustrate the behavior of the most common organic solar cell under the influence of polymermolecular weight (in the range of 21,100-128,800 g/mol) on light harvesting and device performance parameters. The presentwork demonstrates that, the molecular weight of donor polymer plays an important role in the light harvesting and performanceof a common-bulk heterojunction organic solar cell based on poly(3-hexylthiophene) (P3HT), as a donor polymer, and[6,6]-phenyl-C61-butyric acid methyl ester (PCBM), as an acceptor. Through this study it is found that, the optical absorptionof P3HT:PCBM solar cell active layer is increased by increasing P3HT molecular weight. This may be as a result of increasingactive layer thickness and/or increasing backbone chain length of the polymer. In the same time, the absorption wavelengthrange is narrowed and the absorption peak position is shifted towards lower wavelengths due to the entanglement in polymerchains and reduction in polymer crystallinity at higher P3HT molecular weights. The external quantum efficiency (EQE) of theinvestigated solar cells is increased by increasing P3HT molecular weight until the molecular weight that entangles the P3HTchins and, therefore, restricts the charge carrier transfer and, then, reduces the EQE of the P3HT:PCBM solar cell. The performanceparameters of the P3HT:PCBM solar cell are improved by increasing P3HT molecular weights around 25,300 g/moland, after that, deteriorated at higher P3HT molecular weights up to 128,800 g/mol as a result of polymer chain entanglementand reduction of the P3HT crystallinity. The present study shows that the best P3HT molecular weight is 25,300 g/mol, whichproduces power conversion efficiency around 2.5 %.

Nonlinear optical absorption of a two electron GaN/AlN constant total effective radius multi-shells quantum rings

In this paper, we have investigated the effect of the well number and quantum ring thickness on subband energies, intersubband transition energy and linear and nonlinear optical properties of a two electron GaN / AlN constant total effective radius multi-shells quantum rings (CTER-MSQRs). Effect of well number increase on linear and third order absorption coefficients and refractive index changes is not monotonic, while if inner ring radius R0 increases absorption coefficient monotonically decreases. Absorption peak positions have no red/blueshifts when well number or inner quantum ring radius R0 increase. When well number increases, the amount of nonlinearity monotonically decreases. Finally, six-wells CTER-MSQR has minimum nonlinearity.

Tunable THz absorption in graphene-based heterostructures.

We investigate THz absorption properties of graphene-based heterostructures by using characteristics matrix method based on conductivity. We demonstrate that the proposed structure can lead to perfect THz absorption because of strong photon localization in the defect layer of the heterostructure. The THz absorption may be tuned continuously from 0 to 100% by controlling the chemical potential through a gate voltage. By adjusting the incident angle or the period number of the two PCs with respect to the graphene layer, one can tailor the maximum THz absorption value. The position of the THz absorption peaks can be tuned by changing either the center wavelength or the thicknesses ratio of the layers constituting the heterostructure. Our proposal may have potentially important applications in optoelectronic devices.

Optical properties of GaN/AlN constant total effective radius multi-wells quantum rings

In this study, we have investigated the effect of the number of wells and quantum ring thickness on subband energy levels, intersubband transition energies and optical properties of a constant total effective radius multi-wells quantum rings. By increasing of the number of wells from 1 to 2, we have red shift in the absorption peak positions while by more increasing of the number of wells from 2 to 10 a blue shift is visible. By increasing of the number of wells for system with \(\hbox {R}_{0}=40\,\hbox {nm}\) (large inner radius), we only see a blue shift. Increasing of the \(\hbox {R}_{0}\) values at a constant well numbers or increasing of the well numbers at constant \(\hbox {R}_{0}\) values lead the increase of the absorption coefficient amplitude. In the later case, single quantum well system is an exception.

Temperature-dependent infrared dielectric functions of MgO crystal: an ellipsometry and first-principles molecular dynamics study.

In this work, the state-of-the-art infrared variable angle spectroscopic ellipsometry (IR-VASE) and first-principles molecular dynamics (FPMD) method were combined to obtain the infrared dielectric functions of MgO crystal in the spectral range 300-1000 cm(-1) and for temperatures up to 1950 K. The IR-VASE can measure the infrared dielectric functions of MgO crystal at temperatures ranging from 300 to 573 K and reproduce previous infrared-reflectivity experiments. As temperature increases, it demonstrates that the amplitude of dominant absorption peak centered around 400 cm(-1) reduces, the width broadens, and the position shifts to longer wavelength. Besides ellipsometry study, the FPMD method was implemented, seeking to theoretically predict the infrared spectra of MgO crystal at elevated temperatures. Comparing with experimental measurements, the FPMD method can reproduce the essential feature of ellipsometry and previous infrared-reflectivity experiments even at elevated temperatures, though with some deviations in predicting the exact position and amplitude of dominant absorption peak. On the other hand, the FPMD method can predict the temperature effect on the infrared dielectric functions of MgO crystal, e.g., redshift and broadened absorption peak with increasing temperature.

THz Spectroscopy of Food, Industrial and Pharmaceutical Paraffin Wax

The absorption coefficient spectra and refractive index spectra of food grade, industrial grade and pharmaceutical grade paraffin wax, the three different types of paraffin wax within the terahertz frequency range from 0.2 to 2.2 THz are measured using transmission-type terahertz time-domain spectroscopy. The average refractive indexes of food grade, industrial grade and pharmaceutical grade paraffin wax in the frequency range are respectively 1.50, 1.49 and1.46. The three different types of paraffin wax all have weak absorption for terahertz waves and each paraffin wax have several obvious absorption peaks. However, all found absorption peak positions of the three different types of paraffin wax are so close that the three are relatively difficult to be identified using transmission-type terahertz technique in present experimental conditions.

A theoretical study on the stability and intramolecular interaction in 5-nitrotetrazolates with the DFT and DFT-D methods

Two new salts 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate and 1-methyl-3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate were designed based on the structures of experimentally synthesized 3-azido-1,2,4-triazolium 5-nitro-tetrazolate and 1-methyl-3-azido-1,2,4-triazolium 5-nitro-tetrazolate, to explore new promising candidates for energetic materials and to investigate the influences of the substituents (- CH 3 and - N 3) and solvent (water) on the intramolecular interactions and properties. The intramolecular hydrogen bonding interactions were investigated by the natural bond orbital (NBO) and the quantum theory of atoms in molecules (QTAIM) analyses using the density functional theory (DFT) and the dispersion correction DFT (DFT-D) methods. The low-lying singlet electronic transitions were estimated using the time-dependent DFT. All four examined salts exist as ionic structures in aqueous solution while acid–base molecular complexes form in gas phase. The hydrogen bond energy (E H ) obtained with the DFT-D method is larger than that obtained with the DFT method, but the trend is consistent, i.e. - N 3 increases while - CH 3 decreases E H . In addition, the position of the strongest electronic absorption peak has a little correlation with the number of - N 3 and - CH 3 groups. 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate is a valuable energetic salt with the highest nitrogen content, oxygen coefficient and density and the second highest heat of formation and chemical stability.

New biocide guanidine-containing nanocomposites

New water-soluble nanocomposites based on Ag and copolymers of 2,2-diallyl-1,1,3,3-tetraethylguanidiniumchloride with N-vinylpyrrolidone [poly(AGC-VP)] and vinylacetate [poly(AGC-VA)] have been developed. The average silver particle size ranged from 52 to 62 nm for poly(AGC-VA) and from 28 to 30 nm for poly(AGC-VP), with the corresponding UV–vis absorption peak position at 405–410 nm. The using of copolymers resulted in improvement in bactericide properties of composites. Following these results, the newly developed nanocomposite scaffold may be considered for new water-soluble medicines and biocides.

Synthesis of l-glutathione-capped-ZnSe quantum dots for the sensitive and selective determination of copper ion in aqueous solutions

l-Glutathione capped (GSH) ZnSe quantum dots (QDs) have been synthesized as a fluorescence ions probes for ultrasensitive Cu (II) detection. These QDs surface decoration with glutathione shells can be directly applied without previous treatment. The fluorescence quenching of the GSH-capped-ZnSe QDs depends on the concentration, pH values and reaction time of the Cu2+ solution. Based on the effective electron transfer from GSH to Cu2+ and the surface ligand stripping occurs onto the surface of ZnSe QDs, it results in the reduction of Cu2+ to Cu+ and increment of surface defection on the surface of the QDs. Under the optimum conditions, the detection limit of Cu2+ is 2×10−10molL−1. Meanwhile, the effect of foreign ions displays a low interference response in the detecting of Cu2+ ions. Moreover, based on the invariable absorption peak position and curtate luminescence lifetime of ZnSe QDs, the quenching process has also been confirmed to be a dynamic quenching procedure. With regard to the practical feasibility test of the fluorescent probe, a relative lower standard deviation (RSD) (≤3%) and a high recovery rate demonstrate that the proposed simple method is sensitive, accurate and reliable.

Synthesis of Au nanorods in a low pH solution via seed-media method

The gold (Au) nanorods with various aspect ratios are obtained by a seed-media method in low pH growth solution. Transmission electron microscopy (TEM) and UV-visible spectrophotometry are utilized to characterize the Au nanorods, and the longitudinal absorption peak positions of Au nanorods show different shifting trends of the growth evolutions in various low pH (1∼3) solutions. Other influential factors on the shape of Au nanorod are also systematically studied under low pH reaction condition. The positions of longitudinal peak shift between 600 nm and 900 nm, with the aspect ratios of Au nanorods varying from 2 to 5 both in the simulation and experimental results. The simulation results are in agreement with experimental ones.

Synthesis and solvatochromic behavior of branched oligophenylenes with hydroxy groups

Investigation of the solvatochromic behavior in branched oligophenylenes (OPs) will lead to a better understanding of intramolecular charge transfer behavior in the aromatic compounds and toward the development of new functional materials. However, there is no report on solvatochromism of branched OP. In this study, branched OPs with phenolic hydroxy groups were synthesized by using reactions with transition metal complexes. The treatment of these compounds with a base produced corresponding deprotonated species, whose absorption and photoluminescence peak positions in solution shifted towards longer wavelengths with an increase in the donor numbers of the solvents. These results will be useful in providing information for the development of new solvatochromic and energy trapping materials based on branched aromatic compounds. Copyright © 2014 John Wiley & Sons, Ltd.

Laser-assisted generation of gold nanoparticles and nanostructures in liquid and their plasmonic luminescence

Nanoparticles (NPs) and surface nanostructures (NS) are produced via laser ablation of a bulk gold target in liquid using second harmonics of 10 ps Nd:YAG laser (532 nm) with repetition rate of 50 kHz. The morphology and plasmon photoluminescence (PL) properties of obtained nanoscale objects are described. Transmission electron microscopy and field emission scanning electron microscopy are used for morphology characterization of NPs and NS, respectively. Plasmon PL of both gold NPs and NS is experimentally studied using the third harmonics of the Nd:YAG picosecond laser (355 nm) as a pump. The wavelength of intensity maximum of PL of Au NPs colloidal solution virtually coincides with the position of Au NPs plasmon absorption peak. Real-time excitation of both plasmon PL and Raman scattering of surrounding liquid by picosecond laser pulses in aqueous colloidal solution is also investigated. The efficient cross section of plasmon PL of Au NPs colloid is evaluated using Raman scattering of water as a comparative parameter. The results are in good agreement with values obtained in previous works. Plasmon PL from self-organized NS on the Au surface produced via laser ablation is observed for the first time. Its spectrum is compared to PL spectra of both aqueous colloidal solutions of NPs and of NPs deposited on a Si wafer. The obtained experimental data are discussed with reference to the band structure of bulk Au.

Influence of Coulomb-induced band couplings on linear excitonic absorption spectra of semiconducting carbon nanotubes

Starting from the extended Su-Schrieffer-Heeger model, multiband semiconductor Bloch equations are formulated in momentum space and applied to the analysis of the linear optical response of semiconducting carbon nanotubes (SCNTs). This formalism includes the coupling of electron-hole pair excitations between different valence and conduction bands, originating from the electron-hole Coulomb attraction. The influence of these couplings, which are referred to as nondiagonal interband Coulomb interaction (NDI-CI), on the linear excitonic absorption spectra is investigated and discussed for light fields polarized parallel to the tube direction. The results show that the intervalley NDI-CI leads to a significant increase of the band gap and a decrease of the exciton binding energy that results in a blueshift of the lowest-frequency excitonic absorption peak. The strength of these effects depends on the symmetry of the SCNT. Furthermore, for zigzag SCNTs with higher symmetry other nonintervalley NDI-CI terms also affect the spectral positions of excitonic absorption peaks.

Synthesis of Ag nanoparticles with tunable sizes using N,N-dimethyl formamide.

Ag nanoparticles (NPs) were fabricated using N,N-Dimethyl formamide (DMF) as a solvent and reducing agent together with polyvinyl pyrrolidone (PVP) through a solvothermal method. The position of surface plasmon resonance (SPR) band of as-prepared Ag NPs changed with the chain length of PVP and red shifted with increasing the molecular weight of PVP. The concentration of PVP and reaction time affected the position of absorption peaks. The selective adsorption of PVP on the {100} and {111} facets of Ag depended on the kinds of solvents, which determined the driving force of the growth process of nanostructures. For comparison, ethylene glycol, water, and ethanol was added serving as solvents in the presence of PVP. The result indicates that DMF is a vital factor to kinetically control the formation of Ag NPs. Therefore the favorable facets of Ag nanostructures are {111} facets in a DMF solution. Ag nanoplates together with nanowires were observed in the system of ethanol and water, respectively.

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.

ESR properties of polyaniline in a wide pH range

In this paper, polyaniline was synthesized using cyclic voltammetry in a potential range between −0.20 and 1.10V (vs. SCE), in a solution consisting of 0.20M aniline and 0.60M H2SO4. The electron spin resonance (ESR) measurements of the emeraldine salt of polyaniline were done in a wide pH range of 0.7 (0.20M H2SO4 solution) to 12.0 of 0.30M Na2SO4 solution. It was found that the ESR signal of polyaniline was still very strong at pH 10.0 and then its ESR signal disappeared at pH>10.0. This result is unexpected because polyaniline was electrochemically inactive and its conductivity vanished at pH>5.0 based on the previous reports. The visible spectra of polyaniline showed no change in the absorption peak position in a pH range of 0.7–7.0, indicating no occurrence of deprotonation; while its absorption peak shifted markedly towards the short wavelength direction from pH 8.0 to 12.0, as a result polyaniline film become purple, indicating occurrence of deprotonation. The ESR signal disappearance and deprotonation of polyaniline are strongly related to pKb values of pH functional group in polyaniline chains. The entire deprotonation process of polyaniline is suggested to include the conventional deprotonation step, i.e.; without charge transfer and the reduction step of polyaniline that was confirmed with electrochemical measurements.

Transient Absorption of Gold Nanorods Induced by Femtosecond Laser Irradiation

The action of femtosecond laser irradiation on the optical absorption of gold nanorods has been measured by the pump-probe technique in spectral regions of the longitudinal and transverse modes of surface plasmons. The evolution of the parameters of plasmon absorption bands, namely, peak positions and band widths, after the impact of a pump pulse on a water suspension of nanorods has been revealed by the advanced data processing, accounting for a chirp of the “white continuum” of a probe pulse. The observed kinetics fits the hot electron relaxation theory. In addition, a significant increase of the cross-phase modulation in the spectral range of the surface plasmon absorption band has been found. The irreversible nanorod shape transformation (a change of the aspect ratio) has been observed after long-term irradiation. Pump-probe measurements were performed at the Center for collective use of equipment “Femtosecond Laser Complex” of National Academy of Sciences of Ukraine.

Electron-electron and electron-phonon correlation effects on the finite-temperature electronic and optical properties of zinc-blende GaN

We combine the effect of the electron-electron and electron-phonon interactions to study the electronic and optical properties of zb-GaN. We show that only by treating the two effects at the same time it is possible to obtain an unprecedented agreement of the zero and finite-temperature electronic gaps and absorption spectra with the experimental results. Compared to the state-of-the-art results our calculations predict a large effect on the main absorption peak position and width as well as on the overall absorption lineshape. These important modifications are traced back to the combined electron-phonon damping mechanism and non uniform GW level corrections. Our results demonstrate the importance of treating on equal footing the electron and phonon mediated correlation effects to obtain an accurate description of the III-nitrides group physical properties.

Photosensitive surfactants: micellization and interaction with DNA.

Recently, photosensitive surfactants have re-attracted considerable attention. It has been shown that their association with oppositely charged biologically important polyelectrolytes, such as DNA or microgels, can be efficiently manipulated simply by light exposure. In this article, we investigate the self-assembly of photosensitive surfactants as well as their interactions with DNA by calorimetric and spectroscopic methods. Critical micelle concentration (CMC), standard micellization enthalpy, entropy, and Gibbs energy were determined in different conditions (ionic strengths and temperatures) for a series of cationic surfactants with an azobenzene group in their tail. It is shown, that aggregation forces of photosensitive units play an important role in the micellization giving the major contribution to the micellization enthalpy. The onset of the aggregation can be traced from shift of the absorption peak position in the UV-visible spectrum. Titration UV-visible spectroscopy is used as an alternative, simple, and sensitive approach to estimate CMC. The titration UV-visible spectroscopy was also employed to investigate interactions (CAC: critical aggregation concentration, precipitation, and colloidal stabilization) in the DNA-surfactant complex.

The Impact of λ/4 Type Absorber Protective Layer 's Thickness on Absorbing Properties

Abstract .Electromagnetic radiation affects normal operation of electronic devices and causes harm to human health, the use of electromagnetic radiation protective material, especially the electromagnetic wave absorption material, is an effective method for interference control and radiation protection, λ / 4 type dielectric absorber with a simple and practical nature, the protective layer should be added to ensure its durability in practice, this article discusses the gypsum board as the substrate, the thickness of conventional protective layer's material impacts on the absorbing properties. Studies show that: the position of absorption peak moves to lower frequency with increase of the protective layer's thickness by the theory and experiment, this paper puts forward the protective layer's thickness criterion's impact on the absorption characteristics, the thickness less than 0.05 cm has little effect on absorption characteristics in S band , which can simplify theoretical calculation and be convenient to select a material; when the thickness of the protective layer has a significant effect on absorption, the relationship among the parameters of absorber can be found according to theoretical simulation, thereby reducing or eliminating the impact of protective layer thickness on absorption characteristics.