Peak Absorption Wavelength Research Articles

Synergistic modification of end groups in Quinoxaline fused core-based acceptor molecule to enhance its photovoltaic characteristics for superior organic solar cells

The competence of organic solar cells (OSCs) could be enhanced by improving the light absorption capabilities as well as the open-circuit voltage (Voc) of utilized molecules. To upgrade overall functionality of OSCs, seven new molecules were designed in this work using an end-cap alteration technique on Quinoxaline fused core-based non-fullerene acceptor (Qx-2) molecule. This technique is known to be quite advantageous in terms of improvement of the effectiveness and optoelectrical behavior of various OSCs. Critical parameters like the absorption maximum, frontier molecular orbitals, excitation energy, exciton binding energy, Voc, and fill factor of molecules were considered for the molecules thus designed. All newly designed molecules showed outstanding improvement in optoelectronic as well as performance-related properties. Out of all scrutinized molecules, Q1 exhibited highest wavelength of absorption peak (λmax = 779 nm) with the reduced band gap (1.90 eV), least excitation energy (Ex = 1.59 eV), along with the highest dipole moment (17.982950 D). Additionally, the newly designed compounds Q4, Q5, and Q6 exhibited significantly improved Vocs that were 1.55, 1.47, and 1.50 eV accordingly, as compared to the 1.37 eV of Qx-2 molecule. These molecules also showed remarkable improvement in fill factor attributed to direct correspondence of Voc with it. Inclusively, these results support the superiority of these newly developed molecules as prospective constituents of upgraded OSCs.

Increasing Charge Carrier Mobility through Modifications of Terminal Groups of Y6: A Theoretical Study.

The applications of non-fullerene acceptor Y6 with a new type of A1-DA2D-A1 framework and its derivatives have increased the power conversion efficiency (PCE) of organic solar cells (OSCs) up to 19%. Researchers have made various modifications of the donor unit, central/terminal acceptor unit, and side alkyl chains of Y6 to study the influences on the photovoltaic properties of OSCs based on them. However, up to now, the effect of changes of terminal acceptor parts of Y6 on the photovoltaic properties is not very clear. In the present work, we have designed four new acceptors-Y6-NO2, Y6-IN, Y6-ERHD, and Y6-CAO-with different terminal groups, which possess diverse electron-withdrawing ability. Computed results show that with the enhanced electron-withdrawing ability of the terminal group, the fundamental gaps become lower; thus, the wavelengths of the main absorption peaks of UV-Vis spectra red-shifts and total oscillator strength increase. Simultaneously, the electron mobility of Y6-NO2, Y6-IN, and Y6-CAO is about six, four, and four times faster than that of Y6, respectively. Overall, Y6-NO2 could be a potential NFA because of its longer intramolecular charge-transfer distance, stronger dipole moment, higher averaged ESP, enhanced spectrum, and faster electron mobility. This work provides a guideline for the future research on modification of Y6.

A Sensitive Biosensor Based on Plasmonic-Graphene Configuration for Detection of COVID-19 Virus.

In this paper, four individual structures based on graphene-plasmonic nano combinations are proposed for detection of corona viruses and especially COVID-19. The structures are arranged based on arrays in the shapes of half-sphere and one-dimensional photonic crystal formats. The half-sphere and plate shaped layers are made of Al, Au, SiO2 and graphene. The one-dimensional photonic crystals lead the wavelength and peak corresponding to the absorption peak to lower and higher amounts, respectively. In order to improve the functionality of the proposed structures, effects of structural parameters and chemical potentials are considered. A defect layer of GZO is positioned in the middle of one-dimensional photonic crystal layers to shift the absorption's peak wavelength to the appropriate wavelength range for diagnosing corona viruses (~300 nm to 600 nm). The last proposed structure is considered as a refractive bio-sensor for detection of corona viruses. In the final proposed structure (based on different layers of Al, Au, SiO2, GZO and graphene), corona viruses are considered as the biomolecule layer and the results are obtained. The proposed bio-sensor can be a good and functional candidate for detection of corona viruses and especially COVID-19 in photonic integrated circuits with the satisfying sensitivity of ~664.8 nm/RIU (refractive index unit).

Dependence of gold nanoparticle formation on Muntingia calabura and Lagerstroemia speciosa extract amounts

Investigating gold nanoparticle formation using plant extract combinations could pave the way for more green synthesis possibilities involving interactive effects of biochemicals. In this study, varying amounts of combined leaf extracts of Muntingia calabura and Lagerstroemia speciosa provide reducing agents capable of producing quasi-spherical gold nanoparticles with average diameter ranging from 30 to 40 nm. These gold nanoparticles generate visible light absorbance peaks at 550 to 559 nm. Gold nanoparticle formation time and peak absorbance wavelength increase with the combined leaf extract amount up to 2.5 vol parts before an eventual decrease is observed for 3 vol parts of extract. Nanoparticle sizes due to 1.5–2.5 vol parts of extract are comparable with each other and are significantly different as compared with nanoparticles produced using 3 vol parts of extract. Based on comparing absorbance spectra before and after two weeks, all the gold nanoparticles were found to be stable for that time period. In conclusion, the combined extract could be used to vary gold nanoparticle size, absorbance, and formation time depending on its amount.

Vertical photon sorting by stacking silicon and germanium nanopillars for broadband absorbers

Abstract Perfect absorbers based on all-dielectric metasurfaces exhibit great potential in photodetection, photovoltaics, and imaging applications. This study proposes and demonstrates an all-dielectric broadband absorber comprising subwavelength-thick nanopillar Mie resonators in the visible light range. This nanopillar functions as a perfect absorber based on degenerate critical coupling with a characteristic “degenerate critical length.” At this length, the nanopillars are capable of achieving perfect absorption. Beyond this length, the peak of perfect absorption is not affected with further increases in the length of the nanopillars. Hence, this study realizes broadband absorption via the stacking of amorphous silicon and germanium nanopillars with the same width at different peak absorption wavelengths. The absorption spectra are almost independent of the order of the stacked structures; hence, the stacked nanopillars in the specific stacking order can behave as a vertical photon sorter, sorting photons based on the wavelength. This study provides a systematic route to the realization of broadband absorbers with vertical photon sorting capability via the vertical stacking of nanopillars.

Colorimetric-Based Concentration Measurement of Manganese Ions using Spectroscopy Approach

This paper presents the spectroscopy analysis of manganese ions (Mn2+) to investigate the correlation between its concentration and optical absorbance at different wavelength spectra. This work was performed as a preliminary work to establish guidelines and references for future work in developing a monochromatic light-based colorimetric system for concentration measurement of Mn2+. The samples were prepared at the concentration range of 0.2–1.0 ppm using a colorimetric reagent (i.e., 0.1 % PAN solution) that produced an orange-based coloured solution. Qualitative analysis was performed to obtain the absorbance spectra, which are significant in identifying the suitable colour of monochromatic light (e.g., LED), as well as to predict the settling time for steady-state condition before the measurement could be taken. The results showed that for the range of concentration studied, the blue to cyan region gives the best absorbance with peak absorbance wavelength occurred at around 495 nm. Testing at the time interval between 30 and 90 min after sample preparation also gives the indication of the steady-state condition for a complete colorimetric reaction. Then, quantitative analysis was performed to obtain a standard calibration curve that relates optical absorbance and Mn2+ concentration. The curve is significant to serve as a standard reference for the results to be obtained during colorimetric system development. The calibration curve gives a good linearity at R2 = 0.99, thus verifying the sample preparation and measurement procedures, as well as instrumentation setting used in this work.

Absorption peak wavelength and bandwidth control in MoS2-based absorbers on the basis of SPPs and LSPs excitation

The nanometer-sized absorber that we introduced in this paper consists of a monolayer of atomically thin MoS2 on a silica substrate covered by inclined gold gratings. By selecting the period of the gold grating of the order of the incident light wavelength, both surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) can be excited in the structure at the visible spectrum. By selecting different values of the gold ribbon’s widths, we show that the excited modes can be adjusted to SPPs, LSPs, or SPPs and LSPs together. With the excitation of SPPs, the narrowband absorption peak wavelength, and with the excitation of LSPs, the FWHM of the absorption peak can be adjusted by the ribbon’s geometry parameters. In the case of simultaneous excitation of SPPs and LSPs, by increasing the ribbons’ inclination, the LSP peaks will redshift, while the SPP peaks blueshift, which leads to wider absorption peaks. The effect of increasing the ribbons’ height is opposite to that of the ribbons’ inclination, which is accompanied by the SPP peak red shift and LSP peak blue shift. This way, the more the height of the ribbons, the less the absorption peak bandwidth is. This paper’s results are a promising guide for designing plasmonic absorbers with desired bandwidths and peak wavelengths, which are widely demanded in designing photovoltaics and photonic sensors.

Indocyanine green-mediated antimicrobial photodynamic therapy as an adjunct to non-surgical periodontal treatment: a systematic review and meta-analysis.

Indocyanine green-mediated antimicrobial photodynamic therapy as an adjunct to non-surgical periodontal treatment: a systematic review and meta-analysis.

Hybrid acoustic materials through assembly of tubes and microchannels: design and experimental investigation

PurposeThe purpose of this paper is the design and experimental investigation of compact hybrid sound-absorbing materials presenting low-frequency and broadband sound absorption.Design/methodology/approachThe hybrid materials combine microchannels and helical tubes. Microchannels provide broadband sound absorption in the middle frequency range. Helical tubes provide low-frequency absorption. Optimal configurations of microchannels are used and analytical equations are developed to guide the design of the helical tubes. Nine hybrid materials with 30 mm thickness are produced via additive manufacturing. They are combinations of one-, two- and four-layer microchannels and helical tubes with 110, 151 and 250 mm length. The sound absorption coefficient of the hybrid materials is measured using an impedance tube.FindingsThe type of microchannels (i.e. one, two or four layers), the number of rotations and the number of tubes are key parameters affecting the acoustic performance. For instance, in the 500 Hz octave band (α500), sound absorption of a 30 mm thick hybrid material can reach 0.52 which is 5.7 times higher than the α500 of a typical periodic porous material with the same thickness. Moreover, the broadband sound absorption for mid-frequencies is reasonably high with and α1000 > 0.7. The ratio of first absorption peak wavelength to structure thickness λ/T can reach 17, which is characteristic of deep-subwavelength behaviour.Originality/valueThe concept and experimental validation of a compact hybrid material combining a periodic porous structure such as microchannels and long helical tubes are original. The ability to increase low-frequency sound absorption at constant depth is an asset for applications where volume and weight are constraints.

Top-Down Fabrication of Luminescent Graphene Quantum Dots Using Self-Assembled Au Nanoparticles.

A new graphene quantum dot (GQD) fabrication method is presented, which employs a lithographic approach based on self-assembled Au nanoparticles formed by solid-state dewetting. The GQDs are formed by the patterned etching of a graphene layer enabled by Au nanoparticles, and their size is controllable through that of the Au nanoparticles. GQDs are fabricated with four different diameters: 12, 14, 16, and 27 nm. The geometrical features and lattice structures of the GQDs are determined using transmission electron microscopy (TEM). Hexagonal lattice fringes in the TEM image and G- and 2D-band Raman scattering evidence the graphitic characteristics of the GQDs. The oxygen content can be controlled by thermal reduction under a hydrogen atmosphere. In GQDs, the absorption peak wavelengths in the ultraviolet range tend to decrease as the size of the GQDs decreases. They also exhibit apparent photoluminescence (PL). The PL peak wavelength is approximately 600 nm and becomes shorter as the size of the GQDs decreases. The blue shift in the optical absorption and PL of the smaller GQDs is attributed to the quantum confinement effect. The proposed GQD fabrication method can provide a way to control the physical and chemical properties of GQDs via their size and oxygen content.

Precipitation and optical properties of PbSexS1-x quantum dots in glasses

Lead chalcogenide quantum dots have particular optoelectronic properties induced by the quantum confinement effects and have promising potentials towards applications in infrared spectral range. Modulation of the optoelectronic properties of lead chalcogenide quantum dots is mainly based on the thermal treatment. In this work, precipitation and optical properties of alloyed PbSexS1-x quantum dots in glasses are investigated. Composition, size, absorption, and photoluminescence properties of PbSexS1-x quantum dots are modulated by chalcogen elements in glasses and thermal treatment. By adjusting the concentration of ZnSe and ZnS in the glasses, average diameters of the PbSexS1-x quantum dots are tuned in the range of 8.1–16.1 nm, their absorption peak wavelengths are tuned in the range of 724–2497 nm, and photoluminescence bands are tuned in the range of 1016–2165 nm with full width at half maximum in the range of 167–517 nm. Fraction of Se in the PbSexS1-x quantum dots precipitated in glasses is dependent on the concentrations of ZnSe and ZnS in the glass and heat-treatment temperature. Increase in concentration of S in the glasses results in the reduction of relative fraction of Se in the PbSexS1-x quantum dots formed in glasses. More importantly, high heat-treatment temperature promotes the enrichment of Se in PbSexS1-x quantum dots, and Se fraction in PbSexS1-x quantum dots increases from 0.69 to 0.89, from 0.53 to 0.85, from 0.47 to 0.79, and from 0.45 to 0.76 for those precipitated in glasses with ZnSe/(ZnSe+ZnS) molar ratios of 0.545, 0.375, 0.286, and 0.231, respectively. Increase in ZnSe/(ZnSe+ZnS) molar ratios in glasses also leads to reduction in diameter of PbSexS1-x quantum dots formed in glasses. These alloyed PbSexS1-x quantum dots also exhibit improved photoluminescence quantum yields and enhanced resistance to thermal quenching of photoluminescence.

Laser-induced surface plasmon resonance and SERS performance of AgCuAl medium entropy alloy films

AgCuAl films were deposited on glass substrates using a sputtering system. The films were dewetted using a continuous wave (CW) laser with a wavelength of 1070 nm and various settings of the laser power, duty cycle, and speed, respectively. The results showed that nanoparticles were produced for accumulated energies in the range of 0.1 ∼ 2.2 kJ/mm3. At lower unit volume energies (0.1 ∼ 1.3 kJ/mm3), the particles had a size of around 120 ∼ 130 nm. However, as the accumulated energy increased to 1.7 kJ/mm3, the particle size reduced to 95 nm. The AgCuAl films produced using a duty cycle of 30 % showed an optical absorption peak wavelength in the range of 600 ∼ 620 nm. Moreover, a blue shift was observed as the laser power increased as a result of the smaller particle size. AgCuAl nanoparticles (NPs) show a strong Raman scattering effect at 680 cm−1 in the presence of melamine solution. Hence, the feasibility of detecting melamine via surface-enhanced Raman spectroscopy was confirmed.

Effect of the Juglans Regia (Walnut) leaf extract concentration on the biosynthesis of ZnO nanoparticles: Characterisation and antimicrobial activity

ABSTRACT In the present article, we have developed an eco-friendly, phytosynthetic, cost-effective, and straightforward method for the synthesis of ZnO nanoparticles using leaf extracts of Juglans Regia (JR) as green reducing agents. The powder X-ray diffraction pattern revealed the high crystalline nature of synthesised ZnO nanoparticles also rivalled with ICSD no. 98–009-4004. The SEM images of the samples showed the spherical and irregularly distributed rod and plate-like structures. The EDS spectrum filed only Zn and O peaks revealed that the sample has good purity in ZnO nanoparticles. The HRTEM analysis explained the formed ZnO nanoparticles by biogenic reduction were hexagonal shape with definite edges and the average grain size was obtained as 33.18 ± 6.2 nm for the 50JR sample. The d-spacings of fringes and SAED pattern got also rivalled with XRD d-spacings. According to the UV-Visible analysis, the values of peak absorbance wavelength decreased (blue shift) with the increase in the leaf extract concentrations. The bandgap values were calculated in the range of 2.74–3.17 eV. The Fourier Transform Infra-Red study explicated the biomolecules for the reduction of nanoparticles and also ZnO bonding. These results also proved the presence of ZnO nanoparticles synthesised using Juglans Regia extract. Regarding the antimicrobial effects of ZnO NPs, ZnO NP which was using 50 mL JR extracts was detected as highly efficient nanoparticles against test microorganisms. In particular, the highest antimicrobial activity was measured with 15.66 ± 1.15 mm against Candida albicans 10,231 and revealed data compared with fluconazole, as reference antifungal, recorded 69% antimicrobial index. The findings demonstrated that ZnO NPs can be evaluated for use in biomedical applications.

Tunable perfect optical absorption in truncated photonic crystals with lossy defects

We theoretically investigate tunable optical absorption properties of photonic crystals containing lossy materials as defects. It is found that a lossy defect can induce one or multiple perfect absorption peaks in the bandgap of photonic crystals and the number of the peaks mainly depends on the thickness of the defect layer. On the one hand, multiple complete absorption peaks can also emerge in the photonic bandgap when multiple lossy defects are inserted within the photonic crystals, and the resonant wavelengths of absorption peaks can be modulated by changing the distances among the defects. On the other hand, the optical absorption away from resonant wavelengths is nearly zero in the whole visible range. Such nanostructures can be used to engineer novel optical devices such as tunable single-channel and multi-channel perfect optical absorbers.

A three-band perfect absorber based on a parallelogram metamaterial slab with monolayer MoS2

As a two-dimensional (2D) material, monolayer MoS2 which limits its optical applications has a low absorption efficiency. In this paper, we propose a three-band perfect metamaterial absorber in the visible light range based on monolayer MoS2. The peak absorptivity of the structure at each resonance wavelength is nearly perfect, moreover, the light absorption of monolayer MoS2 is obviously enhanced at the three resonant wavelengths. The dielectric–dielectric–metal structure we designed produces the coupling of Fabry–Perot resonance and high-order diffraction guided-mode resonance at different absorption peaks, which has been proved by the slab waveguide theory. In addition, the multi-modal absorption phenomenon is explained by extracting the equivalent impedance. The results show that we can adjust the absorption peak wavelength by regulating the parameters of the structure. This structure not only provides an idea for enhancing the interaction between light and two-dimensional materials but also has potential applications for optical detection devices.

2.5 kW TMI-free co-pump Yb-doped fiber oscillator by 971.5 nm pumping wavelength

Pump wavelength shift from the peak absorption wavelength of 976 nm is one of the strategies for mitigation of transverse mode instability (TMI) in high-power Yb-doped fiber lasers. In the present contribution, 971.5 nm is introduced as an effective pumping wavelength for the increment of TMI threshold. By using this pumping wavelength, a 2580 W co-pumped fiber oscillator is built by 20/400 µm active fiber, with more than a twofold increase in the TMI threshold. Our analytical and experimental investigations indicate that due to the lower heat load of the pumping wavelength of 971.5 nm in the gain medium, it can properly mitigate TMI in fiber oscillators. Power scaling in here presented fiber oscillator is just limited to the occurrence of stimulated Raman scattering (SRS) induced mode instability and to the best of authors’ knowledge, this is the first evidence of SRS-induced mode instability in high-power fiber oscillators and TMI is not the restricting factor in power scaling anymore.

Local control of optical absorption properties of glass using precipitation of gold nanoparticles via gold sphere movement driven by laser

Glass embedded with metal nanoparticles is a promising material necessary for optical devices because of its absorption properties associated with the surface plasmon resonance (SPR) of metal nanoparticles. We demonstrated that continuous-wave laser illumination of the metal sphere in glass migrates the metal sphere and dopes the migration trajectory. In this study, we have attempted to locally control the absorption properties of borosilicate glass via gold nanoparticle precipitation using gold sphere migration. The gold sphere was moved in the glass via laser illumination, and the gold nanoparticles were precipitated in the movement trajectory. The trajectory was colored in red and purple gradations because of the SPR of gold nanoparticles. The particle size of the precipitated gold nanoparticles and the absorption peak wavelength increased with increasing velocity of the gold sphere. The absorption properties of the trajectory depend on the velocity of the gold sphere migration, which enabled local control of the absorption properties of the glass.

Investigating The Effects of The Different Rhodamine 6G Laser Dye Volume Ratios on The Optical Properties of PMMA/PC Films

Rhodamine 6G – polymethylmethacrylate/polycarbonate (Rh6G–PMMA/PC) were prepared by a casting method at room temperature with diverse volume ratios of Rh6G dye solution (5, 10, 15, 20 and 25) ml. The as-prepared films were categorised via UV–Vis spectrophotometer, and the optical properties were investigated in the wavelength range of (200-800) nm. The absorption peaks for pure PMMA/PC film were affected by inserting Rh6G dye solution, the wavelength of absorption peak of pure PMMA/PC film is at 300 nm and 340 nm while there are different behaveior at different concentration of RG6 after mixing with PMMA/PC films; there are red shift for concentrations (10 and 25 ml) of RG6 after mixing with PMMA/PC films by appear another peaks at 530 nm and 535 nm respectively. In addition, there is a blue shift for concentrations (15 and 20 ml) of RG6 after mixing with PMMA/PC films, as evidenced by the appearance of new peaks at wavelength 265 nm. Furthermore, new peaks appeared and were absorbed while the energy band gap was influenced, with values ranging from 4.3 eV for pure PMMA/PC film to 4.18 eV for mixtures 10 and 25 ml concentration of Rh6G/ PMMA/PC belonging to the red shift to 4.9 eV and 4.85 eV for mixtures 15 and 20 ml concentration of Rh6G/ PMMA/PC belonging to the blue shift.

Gold Nanoparticle-Crystalline rubrene hybrid nanocomposite via plasma processing and realization of Plasmon-enhanced organic thin film transistor with high responsivity

High performing and operationally stable thin film transistor device is successfully fabricated with an organic frame-work implemented by synthesis of rubrene crystals with gold nanoparticles (Au NPs). A novel synthesis route for the fabrication of the active material in the form of crystalline rubrene composite (CRC) is adopted via plasma processing approach. This report highlights two important features: a) report of a one-step process to synthesize crystalline rubrene gold nanocomposite in a thin film architecture and b) demonstration of a plasmon transistor for plasmon resonance energy detection. The fabricated device is a low-light responsive device showing the typical p-type characteristics. Excellent p-channel characteristics is shown by the device with a maximum field effect mobility of 0.215 cm2/V.s. At the peak wavelength of plasmonic absorption a very high responsivity of 25 A/W is achieved. Hot carriers are collected by the transistor from the nanostructures of Au NPs that contributes to the increase in drain current by modulating the channel conductivity. Due to the versatile nature of the plasmonic nanostructures in terms of wavelength tunability for the CRC material, this architecture has the potential to offer a wide range of spectrum that can be used in various applications.

Implementation of Micro-EDM Monitoring System to Fabricate Antimicrobial Nanosilver Colloid.

This study implemented a discharge energy and success-rate monitoring system to replace the traditional oscillograph observation method and conducted a microbial control test for a nanosilver colloid prepared by an Electrical Discharge Machine (EDM). The advantage of this system is that the discharge conditions can be instantly and continuously observed, and the optimized discharge parameter settings can be recorded. The monitoring system can use the arcing rate to control the energy consumption of the electrodes to standardize the nanosilver colloid. The results show that the arcing rate, electrode weight loss, and absorption peak wavelength are very accurate. The nanosilver colloid prepared by EDM is free of any chemical additive, and in comparison to other preparation methods, it is more applicable to biotechnology, even to the human body. The microbial control test for the nanosilver colloid included a Bathroom sample, Penicillium, Aspergillus niger, and Aspergillus flavus. In test solution NO.1 (prepared by micro-EDM), the effects of all four samples were inhibited at 14mm in a metal ring experiment, and in the cotton pad experiment, Penicillium was inhibited at 17 mm. In the metal ring experiment, test solution NO. 2 (prepared by EDM) had an effect at 20 mm on the bathroom samples, but at only 15 mm on flavus. In the cotton pad experiment, the inhibited effect was more effective in Penicillium and Aspergillus Niger; both inhibited effects occurred at 25 mm. Test solutions NO.3 (prepared by micro-EDM) and NO.4 (32 ppm Ag+) had a 14–15 mm effect on all samples in the metal ring experiment. In the cotton pad experiment, NO.3 had an effect on Penicillium at 19 mm while the effect on the others occurred at 14 mm, and NO.4 had an effect at 25 mm in Penicillium and Aspergillus Niger, and only at 14 mm in the bathroom and Aspergillus flavus samples.