Dependent Absorption Research Articles

Two photon absorption induced optical limiting action of L-Aspartic acid monohydrate

The organic l-Aspartate Monohydrate (L-AspMH) crystal is grown by slow evaporation technique. Single crystal XRD analysis reveals that L-AspMH belongs to an orthorhombic system with P 21 21 21 space group. The inter-contacts in the crystal structure are analyzed using the Hirshfeld surface analysis. To support the experimental results, quantum chemical calculations using the density functional theory (DFT) are done. The molecular structure of L-AspMH crystal is optimized by DFT/B3LYP functional, 6–311G++(d,p) basis set. The FT-IR and FT-Raman spectra are also stimulated and validated experimentally. The blue-shift in the O–H stretching wavenumbers is due to the presence of O–H⋯O hydrogen bonding. The highest occupied molecular orbital (HOMO: −7.409 eV) energy, lowest unoccupied molecular orbital (LUMO: −0.927 eV) energy and energy gap (6.483 eV) of the AspMH crystal is calculated. The hyper conjugative and inter/intra molecular interactions have been investigated through the Natural Bond Orbital (NBO) analysis. UV–vis absorption studies shows the material exhibit absorbance maxima in the UV (204 nm) region and high transmittance in the Visible-NIR (340–900 nm) region. The predicted first order hyperpolarizability is found to be 13 times greater than that of urea. Third-order nonlinear optical property of the crystal is studied using Z-scan technique under nanopulsed Nd:YAG laser. L-AspMH exhibit intensity dependent nonlinear absorption behaviour was witnessed with M-type (2.46 × 1012 W/m2) at lower on-axis input intensity and reverse saturable absorption (4.98 × 1012 W/m2) at higher on-axis input intensity. The material demonstrates sequential two absorption induced optical limiting action. Higher two-photon absorption coefficient (0.56 × 10−10 m/W) and lower onset optical limiting threshold (5.41 × 1012 W/m2) makes AspMH a potential candidate for optical limiting devices.

Linear and nonlinear optical properties of Bi12GeO20 single crystal for optoelectronic applications

The present paper aims at presenting linear and nonlinear optical properties of Bi12GeO20 single crystals grown by Czochralski method. Transmission and reflection measurements were performed in the 400–1000 nm region. The recorded spectra were analyzed considering well-known optical models. Spectral dependencies of absorption coefficient, skin depth, refractive index, real and imaginary components of dielectric function were presented. The analyses performed on absorption coefficient showed direct bandgap and Urbach energies as 2.56 and 0.22 eV, respectively. The first- and third-order nonlinear susceptibilities and nonlinear refractive index of the crystal were also reported in the present work. The results of the present paper would provide valuable information for optoelectronic device applications of Bi12GeO20.

The "Tethered Solvent" Effect - H-Bonding-Controlled Thermo-Halochromism of a Push-Pull Azo Chromophore via Its Secondary Amidoalkyl Acrylamide Side Chain.

The fascinating field of thermo-halochromism of azo chromophores still astounds with unexplored facets nourished by the intricate relationship between molecular structure variations and their spectroscopic signatures. In this respect, we investigated the thermally dependent absorption behaviour of acrylamide derivatives of o-methyl red, characterised by two secondary amide linkages with hydrogen bonding-active protons in the pendant alkyl substituent. The systems were studied by a combination of UV-vis, derivative, and difference, as well as 2D-NMR (Nuclear Overhauser Effect Spectroscopy, NOESY) spectroscopy. These experiments show that the thermo-halochromism is specifically influenced by hydrogen bonding interaction of the secondary amidoalkyl acrylamide side chain with the azobenzene core in dependence of the spacer length. Apparently, the substituent acts like a solvent, which is directly tethered to the chromophore and where the tether length determines the interaction by conformational freedom. We refer to this novel phenomenon as "H-bonding-controlled thermo-halochromism".

Highly efficient hexagonal-phase Nd3+ doped KLaF4 nanoparticles colloidal suspension for liquid lasers

Innovative approach in the exploration of high-power liquid laser media, utilizing hexagonal KLaF4: x% Nd3+ (x = 1–30 mol%) nanoparticle colloidal solutions synthesized from one-step chemical route is hereby presented. The phase purity and nano size distributions of the nanoparticles are confirmed from X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The concentration dependent absorption and steady-state and dynamic infrared emission (at 1058 nm, 4F3/2 → 4I11/2) features of Nd3+ ion of KLaF4: x% Nd3+ liquid media are closely examined. The estimated stimulated emission cross-sections, branching ratios and quantum efficiencies establishes the potentiality of these hexagonal nanoparticle colloidal solutions for high power liquid laser applications. Inokuti-Hirayama (I–H) and diffusion dominated Yokota-Tanimoto (Y-T) models are employed to examine the dynamic emission evolution of KLaF4: x% Nd3+ (x ≥ 5–30 mol%). The proposed study substantiate that the colloidal solution can serve as a new laser media for low-cost and high-energy liquid lasers and amplifiers.

Investigation of Intensity Dependent Nonlinear Absorption in Cerium Phosphate Nanorods

Cerium Phosphate (CePO4) is a material that has attracted attention because of its unique properties, redox capabilities, and a wide variety of applications. Cerium Phosphate nanoparticles with a nanorod structure were successfully synthesized by a hydrothermal synthesis procedure using Cerium Nitrate Hexahydrate (Ce (NO3)3.6H2O) and Diammonium Hydrogen Phosphate ((NH4)2HPO4) as the precursors without adding any surfactants. The synthesized CePO4 nanorods were characterized using X-ray Powder Diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis which showed pure monoclinic nanorod structures. The linear absorption was analyzed by UV-visible absorption spectrometry. The nonlinear absorption was measured by the open aperture Z-scan technique using a Q switched Nd-YAG laser at 532nm. The Z-scan curve exhibited reverse saturable absorption. In this study, the dependence of nonlinear absorption of CePO4 on the intensity of incident light was investigated. The non-linear absorption coefficient was measured and it was found that the non-linear absorption decreased with the increasing intensity.

Investigation of linear and nonlinear optical properties of PbWO4 single crystal

In this manuscript, PbWO4 single crystals having great importance for device applications were studied in terms of linear and nonlinear optical properties. For this purpose, transmission and reflection experiments were performed in the wavelength range of 350–1000 nm. X-ray diffraction analysis presented crystalline structure as scheelite type tetragonal. Spectral dependencies of absorption coefficient, skin depth, refractive index, dielectric function were reported. Optical band gap of the crystal was estimated as 3.25 eV from the Tauc and derivative spectral methods. Urbach, critical point, single oscillator and dispersion energies, static refractive index and dielectric constant were revealed for PbWO4 single crystal. First- and third-order nonlinear susceptibilities, and nonlinear refractive index were also computed for the studied crystal.

Study of birefringence inside nanocrystalline Zinc Oxide thin films using terahertz spectroscopy

We present experimental characterizations of nanocrystalline Zinc Oxide (ZnO) thin films in far-infrared (terahertz) frequency region using terahertz time-domain spectroscopy. A time dependent profile, frequency dependent transmission coefficient, refractive index, absorption coefficient and optical density of ZnO thin films are measured in the terahertz regime. A birefringence is observed as a result of TO–LO phonon splitting took place in the ZnO deposited at 400 °C substrate temperature, while at low substrate temperature of 200 °C there is no sign of birefringence. Thus, it can be clearly evidenced that the presence of birefringence in ZnO is correlated with crystallinity exists inside of the thin films. Absorption behaviour of ZnO nano-crystalline thin films shows the potential use of it for future THz photonics devices. RF magnetron sputtering is the key for the deposition of nanocrystalline ZnO thin films on Si (100) substrate at different temperatures. The X-ray diffraction pattern of ZnO thin films were confirmed the formation of wurtzite hexagonal structure and nanocrystalline nature of the deposited ZnO thin films.

Vibrational and structural properties of the RFe4Sb12 (R=Na, K, Ca, Sr, Ba) filled skutterudites

Vibrational and elastic properties of the $R$Fe$_{4}$Sb$_{12}$ skutterudites are investigated by, respectively, temperature $(T)$ dependent extended X-ray absorption fine structure (EXAFS) and pressure $(P)$ dependent x-ray diffraction (XRD) experiments. The Fe $K$-edge EXAFS experiments of the $R=$ K, Ca and Ba materials were performed in the $T$-interval $6<T<300$ K and XRD experiments of the $R=$ Na, K, Ca, Sr and Ba materials were performed in the $P$-interval $1\text{ atm }<P<16$ GPa. From EXAFS, we obtained the correlated Debye-Waller parameters that were thus analyzed to extract effective spring constants connected with the Fe-$Y$ (where $Y=$ either $R$, Fe or Sb) scattering paths. Our findings suggest that in the case of the light cations, $R=$ K or Ca, the $R$ atoms are relatively weakly coupled to the cage, in a scenario reminiscent to the Einstein oscillators. From the XRD experiments, we obtained the bulk modulus $B_{0}$ for all $R=$Na, K, Ca, Sr and Ba materials, with values ranging from $77$ GPa ($R=$ K) to $R=99$ GPa ($R=$ Ba) as well as the compressibility $\beta$ as a function of $P$. The trend in $\beta$ as a function of the $R$ filler is discussed and it is shown that it does not correlate with simple geometrical considerations but rather with the filler-cage bonding properties.

Vilazodone-phospholipid mixed micelles for enhancing oral bioavailability and reducing pharmacokinetic variability between fed and fasted states

Despite the effectiveness and high tolerability of vilazodone (VLZ) as an antidepressant, its use is still limited due to its poor solubility and food dependent absorption. This study aims to load VLZ-phospholipid complex into self-assembled micelles forming VLZ-PL mixed micelles (VLZ-PL-MM), that can enhance VLZ solubility, improve its bioavailability and reduce the pharmacokinetic variability between the fed and fasting conditions. The effect of surfactant type and concentration was assessed using four different non-ionic surfactants (Brij 58, Tween 80, Labrasol and Pluronic F127) in four different weight ratios between the drug-complex and surfactant (1:0.5, 1:1, 1:2 and 1:3 w/w). Two VLZ-PL-MM formulae prepared using Brij 58 and Labrasol in 1:3 w/w ratio were selected as optimised ones since they have the highest encapsulation efficiency (100.83 and 93.87%, respectively), a particle size below 250 nm (206.73 and 221.33 nm, respectively) and negative zeta potential values (−29.63, −17.20 mV, respectively). Lyophilisation of these formulations using 3% sucrose was successful with no statistical changes in particle size and zeta potential upon rehydration. Both formulations elicited faster and higher in-vitro drug release profiles compared to the pure drug and the marketed tablet. In addition, both selected formulae improved ex-vivo permeation across rabbit intestinal membrane compared to the pure drug and the marketed tablet, with marked superiority of the one prepared using Brij 58. The results of the in-vivo study in male albino rabbits revealed similar AUC0-24 values after the oral administration of the best achieved VLZ-PL-MM system under fed and fasted conditions (769.89 and 741.55 ng.h mL−1, respectively). On the other hand, the marketed product showed significantly lower values of the AUC0-24 relative to the VLZ-PL-MM system and there was a marked enhancement of absorption of drug from the marketed product in presence of food (244.24 and 174.96 ng.h mL−1 under fed and fasted conditions, respectively). In addition, VLZ concentrations in the brain after 24 h obtained from the selected VLZ-PL-MM were significantly higher than those obtained from marketed tablet under fed and fasted conditions. Thus, the phospholipid mixed micelles formulation enhances the oral bioavailability of the poorly soluble drug and reduces the pharmacokinetic variability between fasting and fed conditions.

Two-year-long high-time-resolution apportionment of primary and secondary carbonaceous aerosols in the Los Angeles Basin using an advanced total carbon–black carbon (TC-BC(λ)) method

In recent years, carbonaceous aerosols (CA) have been recognized as a significant contributor to the concentration of particles smaller than 2.5 μm (i.e., PM2.5), with a negative impact on public health and Earth's radiative balance. In this study, we present a method for CA apportionment based on high-time-resolution measurements of total carbon (TC), black carbon (BC), and spectral dependence of absorption coefficient using a recently developed Carbonaceous Aerosol Speciation System (CASS). Two-year-long CA measurements at two different locations within California's Los Angeles Basin are presented. CA was apportioned based on its optical absorption properties, organic or elemental carbon composition, and primary or secondary origin. We found that the secondary organic aerosols (SOA), on average, represent >50 % of CA in the study area, presumably resulting from the oxidation of anthropogenic and biogenic volatile organic components. Remarkable peaks of SOA in summer afternoons were observed, with a fractional contribution of up to 90 %. On the other hand, the peak of primary emitted CA, consisting of BC and primary organic aerosol (POA), contributed >80 % to the CA during morning rush hours on winter working days. The light absorption of BC dominated over the brown carbon (BrC), which contributed to 20 % and 10 % of optical absorption at the lower wavelength of 370 nm during winter nights and summer afternoons, respectively. The highest contribution of BrC, up to 50 %, was observed during the wildfire periods. Although the uncertainty levels can be high for some CA components (such as split between primary emitted and secondary formed BrC during winter nights), further research focused on the optical properties of CA at different locations may help to better constrain the parameters used in CA apportionment studies. We believe that the CASS system combined with the apportionment method presented in this study can offer simplified and cost-effective insights into the composition of carbonaceous aerosols.

Linear and nonlinear optical characteristics of Bi12SiO20 single crystals

Bi12SiO20 single crystals grown by Czochralski method were optically investigated in detail in the present paper. Transmission and reflection measurements were performed at room temperature in the 400–800 nm spectral range on the (111) plane. Linear and nonlinear optical characteristics of the Bi12SiO20 crystal were determined analyzing the transmission and reflection spectra. The spectral dependencies of absorption coefficient, skin depth, refractive index, optical and electrical conductivities, real and imaginary parts of dielectric function were plotted. Analyses of optical parameters presented the direct band gap and Urbach energies as 2.55 and 0.33 eV, respectively. Static refractive index and dielectric constant, oscillator strength, dispersion and single oscillator energies, nonlinear refractive index, first- and third-order nonlinear susceptibilities were revealed. Structural properties of the Bi12SiO20 crystal were investigated by x-ray diffraction and scanning electron microscopy measurements.

Thiazolo[5, 4-d]thiazole based dye modified microspheres as metal nanoparticle reactor template and hybrid catalyst

2,5-di(pyridin-4-yl)thiazolo[5,4-d]thiazole (Py2TTz) molecule was synthesized and used to modify poly(4-vinyl benzylchloride) microparticles (PVBC-MPs) thanks to its superior interaction with 4-vinyl benzyl chloride monomer containing active –Cl atom. PVBC spherical microparticles were successfully synthesized by suspension polymerization method and they were modified via two different approaches as in-situ and post-modification. Monodispersity of particles via in-situ modification is a challenging approach due to the low solubility of Py2TTz. Therefore, post-modification of PVBC microparticles with Py2TTz dye was carried out. The particles act as metal nanoreactor in the absence of any reducing agent both at room temperature and 50 °C. The particle morphology was determined with electron microscopies before and after reduction process. Metal nanoparticles (MNP) on MPs were characterized via XRD analysis. Gold, silver and platinum nanoparticles (AuNP, AgNP and PtNP) decorated microparticles were successfully synthesized. According to the ICP-MS results, 25.6% Ag, 24.7% Pt and 0.33% Au were found in the microparticles treated with metal cations. These MNP decorated MPs were used as hybrid heterogeneous catalyst for 4-nitrophenol reduction into 4-aminophenol. The highest catalytic efficiency was obtained with AgNPs decorated MPs as also consistent with the ICP-MS data. The catalytic activities of the MNP decorated MPs were determined with time dependent absorption measurents via UV–Vis spectrophotometer.

Narrowband Near-Infrared Photodetectors Based on Perovskite Waveguide Devices.

Organic-inorganic perovskites have attracted great interest for developing wavelength-selective photodetectors. Currently, the spectral response range of narrowband photodetectors is mainly concentrated within the visible light region, lacking near-infrared photodetectors. Here, we present perovskite narrowband near-infrared photodetectors achieved by transverse propagation of light in perovskite waveguide devices for the first time. The response spectra of photodetectors are continuously tuned from 750 to 1000 nm by changing the perovskite component and the position of the incident light with the full width at half-maximum of 25-80 nm. The theoretical and experimental results reveal that the typical perovskite photodetectors serve as an optical waveguide to confine and propagate the light, in which the long wavelength light propagates a longer distance; oppositely, the short wavelength light with the higher loss in devices fails to produce a photoresponse, owing to the wavelength dependent absorption of perovskite. This provides a new concept for designing narrowband photodetectors and will simulate new applications.

Evaluation of an Ussing Chamber System Equipped with Rat Intestinal Tissues to Predict Intestinal Absorption and Metabolism in Humans.

Oral bioavailability (F) is one of the key factors that need to be determined in drug discovery. This factor is determined by the permeability and solubility of new molecule entities (NMEs) according to the biopharmaceutics classification system (BCS). In the present study, we evaluated the permeability of 22 drugs in rat intestinal tissues using an Ussing chamber system and correlated the permeability with data on human intestinal absorption (Fa) and intestinal availability (Fa×Fg) reported in the literature. The rat intestinal permeability data were better correlated with the combined effect of the absorbed fraction (Fa) and the fraction escaping intestinal metabolism (Fg) than Fa itself. Clear regional dependent absorption was observed for most of the test drugs, and ileal Papp was generally higher than that in other segments. Finally, the function of the efflux transporter P-glycoprotein (P-gp) with regard to oral absorption of substrates was evaluated with an Ussing chamber. We also demonstrated that the rat intestinal stability of the three cytochrome P450 (CYP) substrates was consistent with the human data. An Ussing chamber system incorporating rat intestinal tissue would be a valuable tool to predict human intestinal absorption and metabolism for molecules with various physicochemical properties.

Angle-tunable two-photon absorption in twisted graphene systems

We theoretically study the two-photon absorption of twisted bilayer, trilayer and double bilayer graphene with Bernal stacking and demonstrate the layer and twist angle dependent two-photon absorption properties based on both the density functional theory calculations and our developed continuum model for small angle range. The expressions of two-photon absorption for above mentioned three twisted graphene layers around Dirac points are obtained. For small rotation angles which are less than 15 ° , the rotation angle well tunes the two-photon absorption coefficient in terms of the angle-dependent renormalized Fermi velocity. • Energy bands of twisted graphene systems around K point were investigated using DFT calculation. • Two-photon absorption spectra in twisted graphene systems were simulated on the basis of the second-order perturbation theory. • Twist angle effectively tuned the two-photon absorption coefficient within the small angle range ( θ < 15 ° ).

Thermally and magnetically controlled dual-band terahertz metamaterial absorber based on InSb

A thermally and magnetically controlled dual-band terahertz metamaterial absorber with a simple structure consisting of a patterned InSb film, a Teflon dielectric layer, and a metal board is designed and investigated. Numerical simulation results demonstrate that the absorption peak can reach 94% at 0.434 THz and 0.692 THz at 300 K, in the absence of an applied magnetic field. The absorber has the features of polarization insensitivity due to the symmetry of the structure and wide incidence angle absorption. The physical absorption mechanism can be analyzed by the impedance matching theory, the electric field distribution, the current distribution, and the excitation of LC resonance theory. Furthermore, the metamaterial absorber enables temperature-tunable characteristics due to the temperature-dependent variation of the permittivity of InSb in the terahertz region. By varying temperature from 295 to 320 K, the first resonance frequency gradually shifts from 0.413 to 0.529 THz with the second peak shifting from 0.654 to 0.863 THz. In addition, frequency dependent absorption of the InSb-based metamaterial absorber under a series of applied magnetic fields is discussed. When the magnetic field B is changed from 0.2 T to 1T, the dual resonant frequencies gradually shift from 0.4816 THz to 0.423 THz and 0.7804 THz to 0.716 THz. The InSb pattern film behaves as a resonant unit, thus providing an alternative method for designing independent bi-tunable absorbers in the terahertz band. The proposed absorber has the advantages of good tunability, simple structure, and high sensitivity, which has great potential in terahertz sensors. This work provides an effective method for implementing thermally and magnetically dual-controlled terahertz metamaterial absorbers.

The effect of absorption ratio on meltpool features in laser-based powder bed fusion of IN718

The purpose of this research is to develop a hybrid experimental and computational model to estimate the absorption of the laser for Laser-Based Powder Bed Fusion (LB-PBF) of IN718. The research also aims to find an underlying knowledge on the effect of absorption ratio on meltpool morphology. This model helps to improve the accuracy of the prediction of the meltpool morphology and the rheology of the melt tracks as well as the temperature-related phenomena in the process. In this paper, two test sets for the initial test with constant and dynamic/(process parameters dependent) absorption ratios were simulated. Melt tracks with different process parameters are printed and simulated from low to high energy density. Then, the Absorption Ratio (AR) is changed for each simulation until the same meltpool depth as the experimental results is obtained. In the next step, the temperature of the meltpool in the interaction area of the laser and material is measured from the performed simulations. Based on the obtained temperature and process parameters, a mathematical model is developed to estimate the absorption ratio in different conditions. The model is validated in hybrid computational and experimental conditions. The investigation provides the first model to calculate the absorption ratio in LB-PBF based on the temperature of the meltpool and process parameters. Results show that the developed model significantly enhances the accuracy of estimating meltpool features such as temperature, rheological and thermophysical properties of the material in the melting state.

Specific features of Stokes photoluminescence of the La2S3–Ga2S3–Er2S3 glasses

Series glasses with compositions (100–х-y) Ga2S3 – х La2S3 – y Er2S3 (х = 30, 35, 40; y = 0, 1, 3 mol.%) were synthesized and their optical properties were examined. Glass-forming region for the novel La2S3–Ga2S3 system was determined. Composition−dependent optical absorption spectra within the spectral range 480–1020 nm and photoluminescence (PL) under excitation by laser radiation with 532 nm wavelength were measured. The PL maxima were found at 660, 810, 860, 980 and 1540 nm. The origin of the excited states in Er3+ ions was analyzed using an energy diagram. PL decay kinetics processes were analyzed in detail, within the frame of the two exponents model. This one indicates that the Erbium ions emitting in both red and IR spectral ranges are embedded in the glass matrices a like as separate ions or form clusters of erbium ions. The presented research results along with literature data indicate a wide opportunity for potential applications like thermal and radiation sensors, non-linear optical triggers, up-converters, contactless thermometers or active media for IR lasers.

Origin and manifestation of semiconductor facet effects

AbstractSemiconductor crystals generally exhibit notable facet‐dependent electrical conductivity and photocatalytic activity properties. If semiconductor nanocrystals of different shapes are available, their light absorption and emission bands can also display facet dependence, although bulk plus surface absorption combines to give the recorded spectra. All these physical phenomena can be understood, assuming a thin surface layer exists with slight structural deviations as predicted by density functional theory (DFT) calculations to give dissimilar band structures and hence different degrees of band bending and barriers to charge transport across a particular crystal face. This layer thereby tunes light absorption. Recent X‐ray diffraction (XRD) and high‐resolution transmission electron microscopy (HR‐TEM) analyses begin to suggest the presence of the proposed surface layer.

Novel Spinifex littoreus fibre and sugarcane biosilica on mechanical, wear, time dependent and water absorption behaviour of epoxy structural composite

Novel Spinifex littoreus fibre and sugarcane biosilica on mechanical, wear, time dependent and water absorption behaviour of epoxy structural composite