Peak Absorption Wavelength Research Articles

Hybrid Metamaterials Perfect Absorber and Sensitive Sensor in Optical Communication Band

A subwavelength metamaterial perfect absorber (MPA) in optical communication band was proposed and tested using the finite-difference time-domain method. The absorber is periodic and comprises a top layer of diamond silicon surrounded by L-shaped silicon and a gold layer on the substrate. It can achieve dual-band perfect absorption, and one of the peaks is in the optical communication band. By changing the gap (g) between two adjacent pieces of L-shaped silicon, and the thickness (h) of the silicon layer, the resonance wavelength of absorption peak can be tuned. When the incident electromagnetic wave entered the absorber, the metamaterial absorber could almost completely consume the incident electromagnetic waves, thereby achieving more than 99% perfect absorption. The absorption peak reaches 99.986% at 1310 nm and 99.421% at 1550 nm. Moreover, the MPA exposed to different ambient refraction indexes can be applied as plasma sensors, and can achieve multi-channel absorption with high figure of merit (FOM*) value and refractive index (RI) sensitivity. The FOM* values at 1310 nm and 1550 nm are 6615 and 168, respectively, and both resonance peaks have highly RI sensitivity. The results confirm that the MPA is a dual-band, polarization-independent, wide-angle absorber and insensitive to incident angle. Thence it can be applied in the fields of optical communication, used as a light-wave filter and plasma sensor, and so on.

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.

Hybridized Defects in Solid-State Materials as Artificial Molecules.

Two-dimensional materials can be crafted with structural precision approaching the atomic scale, enabling quantum defects-by-design. These defects are frequently described as "artificial atoms" and are emerging optically addressable spin qubits. However, interactions and coupling of such artificial atoms with each other, in the presence of the lattice, warrants further investigation. Here we present the formation of "artificial molecules" in solids, introducing a chemical degree of freedom in control of quantum optoelectronic materials. Specifically, in monolayer hexagonal boron nitride as our model system, we observe configuration- and distance-dependent dissociation curves and hybridization of defect orbitals within the bandgap into bonding and antibonding orbitals, with splitting energies ranging from ∼10 meV to nearly 1 eV. We calculate the energetics of cis and trans out-of-plane defect pairs CHB-CHB against an in-plane defect pair CB-CB and find that in-plane defect pair interacts more strongly than out-of-plane pairs. We demonstrate an application of this chemical degree of freedom by varying the distance between CB and VN of CBVN and observe changes in the predicted peak absorption wavelength from the visible to the near-infrared spectral band. We envision leveraging this chemical degree of freedom of defect complexes to precisely control and tune defect properties toward engineering robust quantum memories and quantum emitters for quantum information science.

A Fire Warning Method Using Tunable Diode Laser Absorption Spectroscopy

Tunable diode laser absorption spectroscopy (TDLAS) technology is adopted herein to detect fire gas produced in the early stage of the fire. Based on this technology, a fire warning detection system with multiple lasers and detectors is proposed. Multiple drivers input laser’s temperature and injected current data, making its output wavelength consistent with the measured gas’ absorption peak wavelengths in absorption spectroscopy. Multiple light beams are coupled to the same optical fiber. After the light beams pass through the long optical path absorption cell filled with fire gas, the beams are separated by a converter. The signals are demodulated by different detectors and further analyzed for fire warnings. After the fire warning system’s design, the system’s various hardware modules are designed, including the light source module, TDLAS controller, gas chamber module, photoelectric detector, and data collection. When the temperature remains unchanged, the output wavelength is linearly related to the injected current. When the injected current remains unchanged, the output wavelength is linearly related to the operating temperature. With a semiconductor laser’s injected current of 40 mA, the initial temperature of 38.6 °C, and the output wavelength of 1578.16 nm, the output wavelength increases continuously as the temperature increases. The harmonic signal amplitude after gas absorption is positively correlated with the measured gas concentration, indicating that the second harmonic signals can estimate the fire gas concentration.

The pH and Ammonia Sensitivity and Antioxidant Activity of Anthocyanins from Lycium ruthenicum

In this paper,the anthocyanin extracted from dried Chinese wolfberry was extracted with ethanol as the extraction liquid,and its pH sensitivity,response to volatile ammonia and meat putrid gas,and antioxidant activity were studied. The results showed that the anthocyanin content in the anthocyanin concentrate was 291.93 mg/L. The anthocyanins of Lycium ruthenicum had good pH sensitivity,and the color of anthocyanin solution changed significantly between pH1 and pH13. As the pH value increased,the solution changed from purple pink to light green,yellow-green,brown-yellow and bright yellow,and the corresponding wavelength of the maximum absorption peak shifted from 522 nm to 619 nm. Black fruit of Chinese wolfberry anthocyanins on volatile ammonia and corruption for meat gas response effect was good,when the ammonia concentration increased,anthocyanins solution maximum absorption peak decreased,and its corresponding wavelength was obviously red shifted,and the higher the concentration of ammonia,the faster the reaction rate,the lower the freshness of meat food and the faster the volatilization of volatile base nitrogen gas. The full band scanning pattern of the meat products was similar to that in ammonia water.Anthocyanin solution and vitamin C(VC)solution were both with strong hydroxyl radical scavenging rate and anthocyanin solution had stronger scavenging capacity than VC,and the IC50 of the two was 5.54 and 10.19 mg/L,respectively. The results can provide a reference for the development and utilization of Lycium barbarum anthocyanins.

The effect of rare earth on color conversion properties of Cd–S–Se quantum dot embedded silicate glasses for white LED

Abstract Various rare earth (RE) oxides such as Pr2O3, Dy2O3, Ho2O3, and Er2O3 were introduced into Cd–S–Se quantum dot embedded glasses (QDEGs) to investigate their effect on the color conversion properties of the Cd–S–Se QDEGs. The absorption and emission peak wavelengths due to the excitonic transition of the Cd–S–Se QDs were modified by the introduction of RE oxides, implying their influence on QD formation. The photoluminescence of the various QDEGs RE oxides under 450 nm excitation were monitored and compared with the un-doped QDEGs. White LEDs (wLEDs) were also fabricated with the RE-doped QDEGs and their color conversion properties, such as quantum yield (QY), luminous efficacy, correlated color temperature (CCT) and color rendering index (CRI) were examined. Transmission electron microscope (TEM) revealed that the size and spatial distribution of the QDs were improved by the RE-oxides. Their effect on QD formation within the silicate glass was discussed using Raman spectroscopy.

Triple-band black-phosphorus-based absorption using critical coupling

Black phosphorus (BP) is an important two-dimensional material that plays a key role in new photoelectric devices. In this work, a triple-band BP-based absorber was proposed, in which a monolayer BP is coupled with the missing angle rectangular structure. Due to the critical coupling of the guided resonance, the BP absorber achieves a triple-band absorption. The results showed that the absorption spectra at 2901.76 nm, 3810.71 nm, and 4676.97 nm under TM polarization achieve a high absorption of 95.45%, 98.68%, and 98.06%, respectively. In addition, the absorption peak and resonance wavelength can be flexibly adjusted by the electron doping of BP, the geometrical parameters of the structure, and the refractive index of the dielectric substrate. Because of the anisotropy properties of BP, the structure exhibits polarization-dependent absorption characteristics. Thus, the missing angle rectangular structure will provide a potential to design mid-infrared absorbers and shows a significant practical application in many photoelectric devices such as photodetectors, modulators, and optical switches.

Cobalt (III)-EDTA dissociates and chromium (III)-EDTA is slightly more stable under in vitro reducing conditions comparable to those in the rumen

Ideal digesta markers used for feeding studies are inert, unabsorbable, and move with the digesta they are intended to mark. Both chromium (III) and cobalt (III) salts of EDTA (CrEDTA and CoEDTA, respectively) are used as markers of liquid digesta in dairy cattle research. A small portion is absorbed and excreted in urine, but the markers are assumed to remain unreactive and as inert salts in the digesta and animal. The degree to which these colored salts remain bound in solution can be estimated through spectrophotometric measurement at their wavelength (λ) of peak absorbance. The objective of this in vitro study was to evaluate whether CrEDTA and CoEDTA dissociate under reducing conditions that could be experienced in the rumen. In a completely randomized design with 2 replicate analytical runs and samples in duplicate within run, approximately 26 mg/L Cr from CrEDTA or Co from CoEDTA was incubated in a 26-mL reaction volume containing 20 mL of Goering and Van Soest medium without tryptone, 3 mL of CoEDTA or CrEDTA solutions, or water (reagent blanks), and 3.0 mL of a combination of distilled water with 0, 0.25, 0.50, 0.75, or 1.00 mL of reducing solution (RedSol). After incubation for 0.5 h at 39°C, absorbance was read at λ = 535, 465, and 560 nm, the peak λ for EDTA salts of Co(III), Co(II), and Cr(III), respectively. Mean reagent blank values were subtracted from CoEDTA and CrEDTA data. The absorbance data at peak λ were analyzed by marker in models that included RedSol with analytical run as a random variable. Contrasts were used to detect linear through quartic effects of RedSol. Samples with RedSol had redox potentials of -250 to -328 mV, which are within the range of reported ruminal measures. As RedSol increased, CoEDTA showed a linear decline of 75% in ABS at 535 nm and a quadratic 4-fold increase followed by a 60% decline at 465 nm. These responses indicate a reduction of Co(III) to Co(II) and subsequent dissociation of Co(II)EDTA. The absorbance of CrEDTA at 560 nm showed a tendency for an 8% linear decrease as RedSol increased. Wavescans from λ = 330 to 700 nm showed CrEDTA retaining its characteristic 2-peak pattern as RedSol increased, whereas CoEDTA curves deformed entirely. We conclude that CoEDTA is not a stable, inert digesta marker under reducing conditions achievable in the rumen and is therefore unsuitable for use in studies with ruminants. Reexamination of the suitability of available liquid digesta markers is advised.

Control of optical absorption of silica glass by Ag ion implantation and subsequent heavy ion irradiation

Silica glass samples were implanted with 50–380 keV Ag ions. After ion implantation, some samples were subsequently irradiated with 16 MeV Au ions. The effects of the implantation and the subsequent Au ion irradiation on the optical absorption spectra and morphologies of the Ag nanoparticles produced in the samples were studied by using an ultraviolet–visible scanning spectrophotometer and a transmission electron microscope, respectively. For the samples implanted with 200 keV or 380 keV Ag ions to high fluence, optical absorption peaks appeared around 600 nm, as well as the well-known surface plasmon resonance peaks around 400 nm, and Ag spherical nanoparticles with a high spatial density were observed. The absorption peaks around 600 nm are explained as being due to interactions between the Ag nanoparticles (inter-particle interaction). Under the subsequent irradiation with 16 MeV Au ions, the optical absorption around 400 and 600 nm showed a blue shift and the peak intensity markedly decreased. Transmission electron microscopy observation revealed an elongation of the Ag nanoparticles along the direction of the 16 MeV Au irradiation, and a resulting enlargement of the distances between the nanoparticles. The change in the peak wavelength and peak intensity of the optical absorption by the 16 MeV Au irradiation can, therefore, be explained as originating from a decrease in inter-particle interaction.

Coscinodiscus diatom inspired bi-layered photonic structures with near-perfect absorptance accompanied by tunable absorption characteristics.

Inspired by the morphology of Coscinodiscus species diatom, bi-layered photonic structures comprised of dielectric-filled nano-holes of varying diameters have been designed and analyzed to enhance and tune absorption characteristics of GaAs-based thin-film photonic devices. Finite difference time domain-based numerical analysis and effective medium approximation based theoretical calculations show that by adjusting diameter and areal density of the nano-holes of the two layers, the peak absorption wavelength can be tuned over a wide spectral range, while attaining a maximum peak-absorptance value of about 97% and a maximum absorption bandwidth of ∼ 190 nm. The maximum enhancement factor of the bi-layered structure is about 11% higher than the value obtained for its equivalent single-layered counterpart over the near-ultraviolet to visible regime of the spectra. High absorptance over a wide-angle for TM polarization and tunable angle-dependent absorption characteristics for TE polarization are also obtained for the proposed ultra-thin absorbers. It has been shown that instead of having misaligned pore-centers as in Coscinodiscus species diatoms, a bi-layered structure designed with layers of identical lattice constant offers significant flexibility in terms of design and practical realization of thin-film photonic devices.

Crystallites and Electric Fields in Solid Ammonia.

Absorption spectra of vacuum‐deposited films of ammonia have been obtained in the range 115 nm to 310 nm for a set of 15 deposition temperatures, Td, between 20 K and 80 K. Results focus upon the region 115 nm to 130 nm in overlapping D, E, F and G←X Rydberg transitions involving Wannier‐Mott excitons. We identify two phases of ammonia, showing the solid to be polymorphic. Peak absorption wavelengths in the region of interest are found to shift to the red by 299 cm−1, for Td between 20 K to 50 K, and 1380 cm−1 for Td between 55 K to 80 K. Shifts provide evidence for the presence of spontaneously generated electric fields in these films, of values in excess of 108 V m−1 for Td of 20 K to 50 K to a few times 107 V m−1 for 55 K to 80 K. Results enable us to place a lower limit of 1.58 nm on the size of crystallites in the low temperature regime. This dimension represents 16 unit cells or 64 species, giving a more quantitative description than the nebulous term amorphous, as applied to solid ammonia. We also determine that crystallites formed in the high temperature regime contain, within ±20 %, 1688, 756 and 236 molecules of ammonia, respectively at Td of 65 K, 60 K and 55 K.

Expanding the Vocabulary of a Protein: Application of Subword Algorithms to Protein Sequence Modelling.

Deep learning has proven to be a useful tool for modelling protein properties. However, given the variability in the length of proteins, it can be difficult to summarise the sequence of amino acids effectively. In many cases, as a result of using fixed-length representations, information about long proteins can be lost through truncation, or model training can be slow due to the use of excessive padding. In this work, we aim to overcome these problems by expanding upon the original vocabulary used to represent the protein sequence. To this end, we utilise two prominent subword algorithms that have been previously used to reach state-of-the-art results in various Natural Language Processing tasks. The algorithms are used to encode the original protein sequence into a set of subsequences before they are analysed by a Doc2Vec model. The pre-trained encodings produced by each algorithm are tested on a variety of downstream tasks: four protein property prediction tasks (plasma membrane localization, thermostability, peak absorption wavelength, enantioselectivity) as well as drug-target affinity prediction tasks over two datasets. Our results significantly improve on the state-of-the-art for these tasks, demonstrating the benefits of using subword compression algorithms for modelling proteins.

Synthesis of Nano ZnO: A Catalyst for N-formylation of Aromatic Amines and Biodiesel Application

Background: Zinc oxide nanoparticles prepared from an easy, eco-friendly and cost-effective green combustion technique using an extract of turmeric root has been an immense attractive nanomaterial that is used widely in light emitting display systems, piezoeletricity, electric conductivity, and biological applications. The prepared samples were characterized for their structural and morphological study using various analytical techniques. Results: Crystallite size was calculated by both XRD as well as UV-visible absorption measurements and Crystallite size was found to be 14-36 nm. An equation was developed with the aid of an effective mass model (Brus 1986) to calculate the size of the particle as a function of the peak absorbance wavelength. The energy bandgap of the synthesized sample calculated to be in the range of 4.74 - 5.0 eV by UV-Vis spectra confirms the quantum confinement. ZnO nanocatalyst is used for the synthesis of biodiesel from garcinia gummigutta seed oil has been studied. The environmental friendly procedure was carried for the formylation of amines under solvent-free reaction condition and simple work-up giving pure products with prompt recyclability behavior are the main features of the reaction. Conclusion: In this work, ZnO NPs were synthesised using turmeric root extract as a fuel via green combustion method. It is an environmentally friendly, easy as well as cost-effective method for the synthesis of nanoparticles. ZnO NPs were examined through various equipments such as PXRD, UV-Vis, FTIR, and SEM studies. XRD study show the hexagonal wurtzite structure. it is a good catalyst for the synthesis of biodiesel from the pongamiapinnata oil. It also serves as a catalyst for the Nformylation reactions, which involves the clean procedure under milder reaction conditions with an excellent yield of the desired products

Laser-ablated core-shell nanostructures of MWCNT@Ta2O5 as plasmonic framework for implementation of highly sensitive refractive index sensor

Refractive index is a crucial physical parameter to be estimated in myriad analytical procedures, biological and physico-chemical processes, and a variety of industrial operations. This work describes a nanomaterial-assisted strategy for highly sensitive investigation of refractive index variations utilizing core-shell nanostructures having multi-walled carbon nanotubes as core surrounded by tantalum (v) oxide shell (MWCNT@Ta2O5). Pulsed laser ablation technique using Q-switched Nd:YAG laser is used to synthesize MWCNT@Ta2O5 core-shell nanostructures in liquid phase. Their refractive index sensing attributes are probed by measuring absorption spectra corresponding to core-shell nanostructures prepared using glucose solutions of varying refractive index values spanned in range 1.33–1.39 as solvent. A red shift equaling ∼8 nm in peak absorption wavelength is attained with an increase in solvent refractive index. The operating parameters including the laser fluence and ablation duration are optimized to fine tune the sensing performance. Morphologically characterized by SEM, TEM and EDS, MWCNT@Ta2O5 core-shell nanostructures exhibit sensitivity and limit of detection of 240 nm/RIU (at refractive index 1.33) and 1.62×10−3 RIU, respectively. Further, the sensitivity follows a linear declining trend in the considered refractive index range of 1.33–1.39. The distinguished analytical features furnished by the nanostructured material in a wide refractive index range project it as an efficient scaffold for refractive index measurements for various applications in different disciplines.

Complete optical absorption in hybrid halide perovskites based on critical coupling in the communication band.

In order to remarkably enhance the absorption capability of (CH3NH3)PbI3, a tunable narrow-band (CH3NH3)PbI3-based perfect absorber based on the critical coupling with guided resonance is proposed. By using the finite-difference time-domain (FDTD) simulations, a complete absorption peak is achieved at the wavelength of 1310 nm. Moreover, we have compared the simulation results with theoretical calculations, which agree well with each other. By changing related structural parameters, the wavelength of absorption peak can be tuned effectively. Furthermore, the proposed absorber can tolerate a relatively wide range of incident angles and demonstrate polarization-independence. In addition to (CH3NH3)PbI3, the complete optical absorption in the other halide perovskites can be realized by the same mechanism.

A Si-based InP/InGaAs nanowire array photodetector operating at telecommunication wavelength

A Si-based vertical nanowire heterostructure array photodetector is designed and studied by a coupled three-dimensional optoelectronic simulation. Each nanowire is composed of an InP/In0.53Ga0.47As/InP axial p-i-n junction, which is designed to operate at telecommunication wavelengths. The results show that the absorption of the nanowire array strongly depends on the D/P ratio and nanowire diameter. By tuning the D/P ratio and diameter simultaneously, the peak absorption wavelength could be fixed at 1550 nm. Due to the light-trapping and light-concentrating properties, the nanowire array photodetector exhibits a remarkable responsivity beyond 0.8 A/W, several times higher than its thin film counterpart with the equivalent thickness. This work suggests that the III–V nanowire array is promising for high-performance Si-based photodetectors applied in optical telecommunication systems.

Simple gold nanoparticles production method by ablated laser: Diameter modification

Recently, an improved interest in gold nanoparticles (AuNPs) with an interesting phenomenology such as plasmon resonance, has been aroused. There are many methods to synthesized AuNPs. We have successfully fabricated AuNPs base on laser ablation method. The pulsed Nd:YAG laser ablated at 1064 wavelength to a pure gold plate. The frequency was adjusted in low range to produce low energy density laser beam. Three different solution (aqueous, polyvinyl alcohol and polyethylene glycol) was applied to modify AuNPs diameter. The modified nanoparticles diameter was observed by mean UV-Vis spectroscopy exhibit different absorption peak wavelength. For comprehensive discussion, the spectrum was compared to simulation tool on MATLAB. Interestingly, AuNPs diameters have been modified by using different solution.

Influence of annealing temperature of ZnS-coated TiO2 films on the performance of dye-sensitized solar cells

This work deals with ZnS-coated TiO2 films prepared via liquid phase deposition and immersion techniques and then applied as photoanode of dye-sensitized solar cells. The samples underwent annealing treatment at various annealing temperatures. The morphology of TiO2 is nanograss and covered by agglomerate and hexagonal ZnS layer. The anatase crystallite size, absorption peak wavelength and optical reflectance increase with annealing temperature. However, the energy gap decreases with the temperature. The device utilizing the sample annealed at 400 °C performed the highest η of 0.24 % due to this device owns the lowest leak current and the longest carrier lifetime.

Reshaping enhancement of gold nanorods by femtosecond double-pulse laser.

Gold nanorod (Au NR) is an attractive material due to its superior physical and chemical properties. Various applications in diagnostics and biomedicine have been demonstrated. The single-pulse laser is commonly used to reshape nanoparticles in a solvent; however, the laser-material reaction mechanisms underlying nanoparticle reshaping remain unclear. Here, we report the reshaping of Au NRs by ultrafast pump-probe-like double-pulse laser irradiation to understand the reaction dynamics. We demonstrate the enhancement of double-pulse-induced reshaping, which provides an opportunity to design new Au NR structures. It shows that the reshaping enhancement is dependent on the delay time (${\tau _s}$τs) between a pair of separated pulses. The absorption peak wavelength of Au NRs exposed to the shaped double pulse was lower than that of using a single pulse of the same total fluence when ${\tau _s}$τs was less than the electron-phonon relaxation time. This phenomenon was mainly attributed to changes in electronic heat transport and electron-phonon coupling, which affected the pulse delay-dependent nanorod (NR) temperature.

Length dependent optical characteristics analysis for semiconductor nanowires

Resonant optical mode excitations in semiconductor nanowires result in enhanced absorptions. Nominally, only the diameter dependent radial mode excitations have been considered for the increased absorption. In this paper, we try to understand how the length of the nanowires affects the resonant wavelength and peak absorption wavelengths. We answer two questions viz (1) at what minimum length are radial optical modes stabilized and dominate the absorption characteristics and (2) do longitudinal modes play a role in absorption characteristics especially in determining the resonant wavelength. Two different semiconductors are studied viz silicon and gallium arsenide. We find that even nanowires as short as 200 nm exhibit absorption characteristics dominated by the radial mode excitation. However, for lengths smaller than 200 nm, the optical characteristics are dominated by scattering. Further, we observe that longitudinal modes are excited in low absorption semiconductor materials like silicon for lengths up to 700 nm and the absorption peak depends both on the diameter and the wavelength. Further, shorter length nanowires may have higher absorption than the longer ones in this regime. We also observed that scattering from the nanowires is less than 2% of the incident light. For higher absorption semiconductor like GaAs, absorption characteristics are mainly determined by the radial mode excitations even for shorter lengths. The results provide further insight into the radial mode excitations in semiconductor nanowires.