Photon Absorption Effects Research Articles

Tunable Nonlinear Optical Properties Based on Metal–Organic Framework Single Crystals

AbstractSolid‐state hybrid materials with designability in topology and tunable photo‐responsiveness hold great promise for multitudinous applications from optoelectronics to information storage/communication. However, the judicious design and synthesis of metal–organic frameworks (MOFs) with intrinsically custom‐made nonlinear optical (NLO) properties including multiple photon absorption and harmonic generation effects suitable for miniaturized devices remain highly challenging. Herein, the design and synthesis of a novel pillared framework named after Zn‐TCPE‐DPNI MOF coordinated by zinc ions (Zn2+), aggregation induced emission (AIE) featured [1,1′‐biphenyl]‐4‐carboxylic acid (H4TCPE), and N,N′‐di(4‐pyridyl)‐1,4,5,8‐naphthalenetetracarboxydiimide (DPNI) are reported. The highly ordered Zn‐TCPE‐DPNI MOF single crystal exhibits tunable NLO responses by switching incident excitation wavelengths of a femtosecond laser from 900 to 1500 nm. The noticeable transformation from two‐ or three‐photon excited photoluminescence (2PL or 3PL) to the concurrent occurrence of 3PL and third harmonic generation (THG), and eventually to the mere emergence of THG with a high effective susceptibility χ(3) (3ω) of 2.9 × 10−12 esu is observed. This study paves a novel avenue for the design and synthesis of photoluminescent MOF crystals with tunable NLO responses toward the fabrication of multifunctional NLO devices targeted for optoelectronics and information communication.

Degradation of typical environmental pollutants (ciprofloxacin, carbamazepine and 17-β estradiol) on supported TiO2 photocatalysts: Identification of degradation products and in silico toxicity assessment

The study describes a few significant aspects of photocatalytic studies: (i) the methodology for finding optimal support for TiO2 photocatalytic films with possible environmental application and (ii) degradation of pollutants of widespread concern including detailed kinetic study and identification of degradation products with respective in silico toxicity assessment. Different cotton textiles and glass fiber mesh were studied as flexible supports for TiO2. Preliminary experiments were done with an aqueous solution of 2-HBA in a rectangular open channel reactor under UVA light, due to known kinetics and photocatalytic degradation pathway of 2-HBA. Further environmental application of the photocatalytic film on the most appropriate support was studied in the same reactor using ciprofloxacin (CIPRO), carbamazepine (CARBA) and 17β-estradiol (E2) as model environmental pollutants under UVA and artificial solar irradiation. A detailed kinetic study, including photon absorption effects, was performed using recently published models. Degradation products were identified by means of high-resolution mass spectrometry (UHPLC-QTOF MS system) with electrospray ionization analysis of the water samples. The environmental impact of photocatalytic oxidation of CIPRO, CARBA and E2 was addressed via in silico toxicity assessment of initial pollutants and respective degradation products.

Degradation of binary mixtures of water pollutants in a photocatalytic microreactor: Competitive kinetics with explicit radiation absorption effects

The photocatalytic degradation of 17-α-ethinylestradiol (EE2) and phenol in aqueous solutions was studied using a continuous flow, planar microreactor under simulated sunlight. A TiO2 thin film was employed as photocatalyst. The degradation rates of single compounds and binary mixtures were well described by the Langmuir-Hinshelwood equation, including competitive terms for the companion pollutant and the intermediate products, and the effect of photon absorption by the photocatalyst. The absorbed radiation in the microreactor was calculated from the optical properties of the TiO2 film and the application of the Net Radiation method. The estimation of the kinetic parameters was carried out by numerical integration of coupled mass balance equations for EE2 and phenol employing the Runge-Kutta method, and adjusting the kinetics parameters with a nonlinear least-squares solver. The objective of this routine was to minimize the sum of the squares of the differences between the simulated and experimental outlet concentrations of EE2 and phenol under different operating conditions. Using this approach, intrinsic kinetic parameters were obtained. The model was able to predict the degradation of both organic pollutants under different inlet concentrations, irradiation levels, and fluid flow rates. This methodology can be extended to assess the simultaneous degradation of multi-component systems.

Studying the Spectral Energy Distributions Emanating from Regular Galactic XRBs

X-ray binary systems (XRBs) exhibit similar dynamics and multimessenger emission mechanisms to active galactic nuclei (AGNs) with the benefit of shorter time scaling. Those systems produce rich spectral energy distributions (SEDs) ranging from the radio band to the very high energy gamma rays. The emission origin varies between the system’s accretion disk (X-rays) to the corona and, most notably, to the two twin plasma ejections (jets) that often meet the interstellar medium forming highly observable radio lobes. Modeling of the jets offers an excellent opportunity to understand the intrinsic mechanisms and the jet particles, such as electrons, positrons, and protons. In this work, we employ a lepto-hadronic jet model that assumes particle acceleration through shock waves over separate zonal regions of the jet. The hadronic models consider proton–proton collisions that end up in gamma-ray photons through neutral pion decays. The main leptonic mechanisms involve synchrotron radiation (from both electrons and protons) and inverse Compton scattering of ambient photons (coming from the disk, the corona, and the companion star) on jet electrons. The emissions from the disk, the corona, and the donor star are also included in the SED calculations, along with the photon absorption effects due to their interaction with higher-energy jet photons. We apply the model on a 10M⊙ black hole accreting at the Eddington rate out of a 20M⊙ companion star. One of our goals is to investigate and determine an optimal frame concerning the values for the free parameters that enter our calculations to produce higher integral fluxes.

Enhanced electro-optical properties of nematic liquid crystal doped with Nitrogen doped graphene quantum dots

The first step of this study was to prepare mixtures that contained different concentrations of N doped graphene quantum dots (NGQDs) into nematic liquid crystals (NLCs). Then, through the Z-scan technology, the optical measurements in the nonlinear regime were conducted with a continuous wave (CW) at 632 nm wavelength and a low power laser beam. The nonlinear absorption (NLA) coefficient, nonlinear refractive (NLR) index, and third-order nonlinear susceptibility of NLCs doped with different concentrations of the NGQDs at distinctive laser powers and diverse applied voltages of external electric field was experimentally measured. The Z-scan results demonstrate that prepared cells have two photon absorption (2PA) and self-focusing effects. As the result, the concentration of the NGQDs in E7 and power of laser were optimum at 1% wt. and 11 mW, respectively. The effect of a DC electric field on optical nonlinearity was also investigated in the mixtures of NLCs and NGQDs at the concentration of 1% wt. Based on these findings, this sample can be used in both nonlinear optics and ultrafast broadband photonics.

Prediction of gamma-ray emission from Cygnus X-1, SS 433, and GRS 1915+105 after absorption

Context. Stellar black hole X-ray binary stars (BHXRBs) are among the most luminous and powerful systems located in our Milky Way and in other galaxies of the Universe. Their jets are prominent sources of particles (e.g., neutrinos) and radiation emissions in energy ranges detectable by terrestrial and space telescopes, even from galaxies deep in the space. A significant factor, however, would be the photon absorption effect that occur due to scattering on the lower end of the energy radiation of the system’s surroundings. Aims. We aim to study in detail and extract predictions for the emitted gamma-ray intensities and integral fluxes of the jets emanating from BHXRB systems Cygnus X-1, GRS 1915+105, and SS 433. Toward this end, we also investigate the severe effects of gamma-ray absorption that eradicate part of the produced intensity spectra. Furthermore, we explore the jet regions that are most likely to emit unabsorbed gamma-rays capable of reaching detectors on Earth. Our goal is to calculate the integral fluxes before and after absorption for the abovementioned systems and compare the results with the very-high-energy gamma-ray observations of sensitive telescopes such as the MAGIC, H.E.S.S., Fermi-LAT, and so on. Methods. The implemented gamma-ray emission mechanisms initiate from the p − p scattering process inside the hadron-dominated jets following the well-known shock-wave particle acceleration. In addition, we estimate the optical depths of three absorption processes between gamma-ray photons and (i) accretion disk X-ray emission, (ii) black hole corona photons, and (iii) donor star thermal emission. We also examine the dependence of the absorption optical depths on various parameters, such as the disk’s temperature, coronal radius and, donor star luminosity. Results. We find that disk absorption is dominant for distances of z < 1010 cm from the black hole, while the donor star absorption dominates for 1010 < z < 1012 cm. Beyond that jet point, the absorption effects become significantly weaker. Cygnus X-1 presents the highest gamma-ray integral flux across the jet length, while GRS 1915+105 emits the least due to its weakly collimated jets. The jets of SS 433 emit gamma-rays only for z > 1010 cm due to severe disk absorption fueled by the system’s super-Eddington accretion limit.

Constructing trinary heterostructure of TiO2/CoCr2O4/SrTiO3 to enhance photocatalytic activity toward degradation of yellow 28 dye

Today, the design of efficient visible light-driven photocatalytic systems for the degradation of organic dyes is of great interest in human health and environmental protection. Constructing heterostructured nanocomposites using coupling metal oxide semiconductors with visible-light-responsive photocatalytic materials is an effective strategy to improve the photocatalytic potential. For this purpose, a trinary TiO2/CoCr2O4/SrTiO3 heterostructured photocatalyst with enhanced visible-light photocatalytic activity was fabricated using the intimate interfacial contact of TiO2/SrTiO3 nanotubes with CoCr2O4 nanoparticles. Compared with single or binary photocatalysts, trinary TiO2/CoCr2O4/SrTiO3 nanocomposite demonstrated enhanced photocatalytic activity and cycling stability in the degradation of basic yellow 28 (BY28) dye under visible-light irradiation. The optimal TiO2/CoCr2O4/SrTiO3 nanocomposite degraded almost 99% of BY28 under visible light in 2 h, compared to approximately 37%, 66%, and 71% for the SrTiO3 nanorods, CoCr2O4 nanoparticles, and TiO2 nanotubes, respectively. This superior photocatalytic performance can be ascribed to the synergistic effects of elevated photon absorption, charge transfer, and efficient charge separation. In addition, the probable mechanism for the degradation of BY28 dye over TiO2/CoCr2O4/SrTiO3 nanocomposite is also elucidated using PL and active species scavenger studies.

Evaluation of a helicoidal flux photoreactor applied in the dicloxacillin degradation by UV-C/H2O2 and UV-A/photo-Fenton including the effect of photon absorption

The efficiency of a helical flow photoreactor in the oxidation of the antibiotic Dicloxacillin as a function of the recirculation flow, the local volumetric rate of photon absorption (LVRPA) and photonic efficiency using oxidation processes based on UV-C/H2O2 and UV-A/photo-Fenton were evaluated in this work. Mathematical modeling of the degradation process and experiments in lab-scale helicoidal reactor were done. Mathematical evaluation was supported in function of photon flux, mass balance and reaction rate law. The LVRPA was calculated by modified Beer-Lambert Equation. The effect of the concentration of hydrogen peroxide and iron (II) on the efficiency of the oxidation of the antibiotic Dicloxacillin was evaluated by means of the photo-Fenton. In 45 min, 100% degradation of dicloxacillin was achieved using 1.5 mM H2O2 and 7.32 μM ferrous ion in the photo-Fenton experiments with the helical flow photoreactor. The optical thickness of the reaction and distribution of energy absorption confirmed the kinetic and photonic efficiency performance. The prediction of the model presented a global error less to 2.4% between experimental and simulated data.

Correcting for the hemoglobin absorption artifact in fiber photometry data

Fiber photometry is a widely used fluorescence approach for measuring neuronal activity in freely behaving animals; however, these signals can be contaminated by hemoglobin absorption artifacts. Zhang et al. propose a computational method to quantify and correct hemoglobin photon absorption effects using spectral fiber photometry, resulting in more accurate neuronal activity measurements.

Spectral fiber photometry derives hemoglobin concentration changes for accurate measurement of fluorescent sensor activity

SummaryFiber photometry is an emerging technique for recording fluorescent sensor activity in the brain. However, significant hemoglobin absorption artifacts in fiber photometry data may be misinterpreted as sensor activity changes. Because hemoglobin exists widely in the brain, and its concentration varies temporally, such artifacts could impede the accuracy of photometry recordings. Here we present use of spectral photometry and computational methods to quantify photon absorption effects by using activity-independent fluorescence signals, which can be used to derive oxy- and deoxy-hemoglobin concentration changes. Although these changes are often temporally delayed compared with the fast-responding fluorescence spikes, we found that erroneous interpretation may occur when examining pharmacology-induced sustained changes and that sometimes hemoglobin absorption could flip the GCaMP signal polarity. We provide hemoglobin-based correction methods to restore fluorescence signals and compare our results with other commonly used approaches. We also demonstrated the utility of spectral fiber photometry for delineating regional differences in hemodynamic response functions.

Design and Numerical Simulation of Color Tunable Laterally Arranged Quantum well Light Emitting Diode with Double Anode Single Cathode

In this paper, a color-tunable light emitting diode LED with two laterally arranged single quantum wells (SQWs) is designed, and simulated. In this work, III-nitride materials are used. The structure has been numerically investigated using the ATLAS simulation software. The proposed structure has three electrodes. This gives the opportunity to emit violet (420 nm) or green (560 nm) light individually. Furthermore, it can emit simultaneously a mixture of both colors, and at a certain mixture ratio the white light is obtained with chromaticity coordinates ( x = 0.3113, y = 0.3973). The lateral arrangement of the two SQWs reduces the negative effect of photon absorption; which will give good external quantum efficiency (EQE). The structure has a big importance in the application of the solid-state lighting, especially in the white light generation.

The effect of nitrogen-doped carbon nano-onions on the third order nonlinear optical responses of CoWO4-MnO2 nanocomposites

CoWO4, CoWO4-MnO2, and CoWO4-MnO2-NCNO nanostructures were prepared via precipitation method followed by calcination at 450 °C. The nitrogen-doped carbon nano-onions (NCNOs) were synthesized by annealing the ultra-dispersed aminated-nanodiamond solution under He gas at 1150 °C followed by calcination at 400 °C. The morphological, structural, and optoelectronic responses of the samples were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Z-scan methods. The order of the nonlinear absorption (NLA) and nonlinear refraction (NLR) of samples are 10−3 (cm/W) and 10−8 (cm2/W), respectively. In different incident intensity of laser, all synthesized samples showed positive and negative sign of NLA and NLR indices, respectively. The NLA coefficient originates from two photon absorption effect and NLR indices indicate the self-defocusing effect. The lowest nonlinear optical response belonged to CoWO4 nanoparticles. CoWO4-MnO2-NCNO nanocomposite showed the higher nonlinear optical responses than CoWO4 and CoWO4-MnO2 nanocomposites. The large ratio of the surface area of NCNO and oxygen reduction activity of NCNO due to high incident intensity are the main reasons for increasing nonlinearity. The nonlinearity results are promising candidate for using in optical and photonic devices.

Spectral Fiber-Photometry Derives Hemoglobin-Absorption Changes for Accurate Measurement of Fluorescent Sensor Activity

Fiber-photometry is an emerging technique for recording fluorescent sensor activity in the brain. Here we demonstrate significant hemoglobin-absorption artifacts that may be misinterpreted as sensor activity changes. Because hemoglobin exists in nearly every location in the brain and its concentration varies over time, such artifacts could significantly impede the accuracy of photometry recording results. We present a novel use of spectral photometry technique and propose a computational method to quantify photon absorption effect from an activity-independent fluorescent protein, which can be used to derive oxy- and deoxy-hemoglobin concentration changes and correct target sensor activities across spectra. We further demonstrate the utility of this method for delineating brain regional differences in neurovascular transfer functions and shed light on the interpretation of hemodynamic-based neuroimaging data.

AC-gate controlled transport sideband spectroscopy in GaAs quantum channels

A modeling investigation is conducted on the quantum transport in an n-type split-gate structure controlled by either an AC finger gate or an AC top gate. The quantum conductance is numerically computed for three different sideband approximations. The results show that various quasi-bound states (QBSs) are formed under the competing effects of photon emission and absorption at different sidebands. Additionally, it is shown that the structure of the QBSs depends on the relative proportion of an electron resonance transmission and an electron resonance reflectance induced by a sideband. Furthermore, the number of QBSs formed increases with the number of sidebands considered in the analysis.

Contribution of temperature and photon absorption on solar photo-Fenton mediated by Fe3+-NTA for CEC removal in municipal wastewater

Solar photo-Fenton process with ferric nitrilotriacetate has great potential for contaminant of emerging concern (CEC) removal from municipal effluents. To scale-up the process, gaining know-how about the effect of temperature and photon absorption is fundamental. This work presents for the first time an in-depth study about the effect of both variables on the reaction mechanism. To this end, imidacloprid (IMD) was selected as a surrogate CEC (100 μg/L). The experimental plan comprised two steps: (i) lab-scale experiments in simulated effluents, and (ii) experiments at pilot-scale in raceway pond reactors with actual effluents. Despite the process being photo-limited in the volumetric rate of photon absorption range of 103–413 μE/m3·s, the increase in the liquid depth from 5 to 15 cm allowed improving the treatment capacity, achieving more than 80 % of IMD removal with reaction times around 30 min. These results provide the necessary knowledge for photoreactor design and continuous flow operation.

Nonlinear coupling of two nonlinear coupled plasmonic nanowires in the ‎presence of Kerr and two-photon absorption in the modes of TM00 and TM10‎

The nonlinear interactions of coupled nanowires are important phenomena in data processing of integrated photonic circuits. In this paper, we investigate the nonlinear coupling of two silver nonlinear coupled plasmonic nanowires for TM00 and TM10 modes under different amplitudes in the presence of Kerr effect, and the other case that the medium has Kerr and two photon absorption (TPA) effect too. The results show that in the presence of TPA effect the nonlinear optical effects appear in lower input amplitudes than Kerr effect. The Kerr effect occurs in upper intensities than the TPA effect and nonlinear optical effect leads to decrease the exchange of plasmonic waves between two nanowires. Also, the coupling length (Lc), that it means the characteristic length of the structure has a lower coupling distance that through propagating in the medium the transfer of the wave is completely, in TM00 mode is lower than TM10 mode. Also, the results show that for different values of initial amplitudes of field in a fixed value of Lc, the coupling efficiency increases with increasing the value of intensity.

Cu-doped ZnO synthesis by ionothermal method: Morphology and optical properties

Zinc oxide (ZnO) and Cu-doped ZnO nanostructures having different morphologies such as nanorod, nanosheet and flower like have been synthesized via a one-step, eco-friendly ionothermal synthetic method at ambient pressure using [OMIM]Br and [C8DABCO]Br ionic liquids in terms of solvent and template. The dopant contents in the samples were 3%. The synthesized nanomaterials were examined by using scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Visible absorption spectroscopy, and Z-scan technique. The results show that ILs and Cu2+ play on significant role on morphology of nanostructures. The average crystal size of ZnO was found to be in the range of 15.5–17 nm. Also doped in different ILs are effect on bandgap of products. The third order nonlinear absorption coefficient and refractive index were calculated and increased due to the enhancement of polarizability by the doping ions (Cu2+). Open and closed aperture of Z-scan method revealed two photon absorption and self-focusing (n2 > 0) effect in the samples. Third order nonlinear susceptibility of samples is in order of 10−7(cm2/W). As a result, Cu dopant of ZnO samples are more effective than their morphology in nonlinear coefficient results. The synthesized samples are proposed as a new-type nonlinear optical materials for optical applications.

Ammonia and methane oxidation on TiO2 supported on glass fiber mesh under artificial solar irradiation.

In this work, we present the application of solar photocatalysis for air purification including toxic substances such as ammonia and methane normally related to emissions from agriculture (e.g., poultry and cattle farms), landfills, etc. The study was done in three different laboratory and semi-pilot scale reactors: annular reactor (AR), mini-photocatalytic wind tunnel (MPWT), and photocatalytic wind tunnel (PWT). Reactors present a physical model for estimation of air-borne pollutant degradation over TiO2-based photocatalytic layer in respect to optimal operating conditions (relative humidity, air/gas flow, and feed concentration). All studies were performed under artificial solar irradiation with different portions of UVB and UVA light. The application of solar photocatalysis for air purification was evaluated based on thorough monitoring of pollutants in inlet and outlet streams. The kinetic study resulted with intrinsic reaction rate constants: kp,int,NH3 = (3.05 ± 0.04) × 10-3 cm4.5 mW-0.5 g-1 min-1 and kp,int,CH4 = (1.81 ± 0.02) × 10-2 cm4.5 mW-0.5 g-1 min-1, calculated using axial dispersion model including mass transfer considerations and first-order reaction rate kinetics with photon absorption effects. The results of photocatalytic oxidation of NH3 and CH4 confirmed continuous reduction of pollutant content in the air stream due to the oxidation of NH3 to N2 and CH4 to CO and CO2, respectively. The application of solar photocatalysis in outdoor air protection is still a pioneering work in the field, and the results obtained in this work represent a good basis for sizing large-scale devices and applying them to prevent further environmental pollution. In the current study, a TiO2 P25 supported on a glass fiber mesh was prepared from commercially available materials. The system designed in this way is easy to perform, operate, and relatively inexpensive.

STOCHASTIC PERTURBATION OF OPTICAL SOLITONS WITH QUADRATIC–CUBIC NONLINEAR REFRACTIVE INDEX

This work obtains mean free velocity of bright optical solitons in optical fibers that are studied with quadratic–cubic form of nonlinear refractive index. The perturbation terms are from multi–photon absorption, filters and stochastic effect. The Langevin equation is derived from soliton perturbation which lead to the mean free velocity of the soliton.

Quantitative analysis of the intertube coupling effect on the photoluminescence characteristics of distinct (n, m) carbon nanotubes dispersed in solution

In this work, we quantitatively studied the intertube coupling of different (n, m)-sorted semiconducting single-wall carbon nanotubes (SWCNTs) on their photoluminescence (PL) efficiencies by precisely tuning the ratio of (9, 4) and (6, 5) SWCNTs in the mixture. A significant decrease in the PL intensity of (9, 4) SWCNTs was observed after mixing with (6, 5) species when fixing the (9, 4) concentration, which was confirmed to be caused by the absorption of incident photons and reabsorption of the emitted photons by the added (6, 5) species. By contrast, a similar decrease in the PL intensity of (6, 5) SWCNTs was also observed after mixing with the larger-diameter (9, 4) species. Different from that of (9, 4) SWCNTs, the PL decrease of (6, 5) SWCNTs was found to originate not only from photon absorption and reabsorption by the (9, 4) species but also from one-way exciton energy transfer (EET) from the (6, 5) SWCNTs to the larger-diameter (9, 4) SWCNTs. Both the experimental results and numerical simulations further demonstrated that increasing the concentration of mixed (9, 4) SWCNTs would enhance the effects of photon absorption and reabsorption and EET on the PL intensity of (6, 5) SWCNTs quantified by the decrease ratio of the (6, 5) PL intensity. Meanwhile, the influence of EET was found to be always weaker than that of photon absorption and reabsorption. We proposed that the observed EET between isolated SWCNTs in a surfactant solution is derived from their proximity due to Brownian motion.