Optical Characteristics Of Materials Research Articles

Zinc vanadium Oxide/g-C3N4 nanosheets as potential material for ascorbic acid sensing and photocatalytic reduction of CO2

Two-dimensional mixed metal oxides have attracted attention because of their unique characteristics and diverse crystal structure. In this work, we have synthesized zinc vanadium oxide and its nanocomposite with graphitic-carbon nitride via wet-chemical and hydrothermal methods. XRD analysis unsheathe the ZnV2O6/g-C3N4 for wet-chemically synthesized composite while Zn2V2O7/g-C3N4 for hydrothermally prepared composite. The sample synthesized using the wet-chemical process, has an agglomerated structure in the FESEM micrographs while hydrothermally synthesized sample reveal porous nanosheets of the composite material. Zn2V2O7/g-C3N4 is further characterized with XPS and HRTEM. UV–visible spectroscopy was used to describe the material's optical characteristics and the Tauc relation was used to compute the associated optical bandgap. The as-synthesized composites were assessed as an electrochemical sensing material for ascorbic acid sensing in a neutral pH analyte (PBS). Furthermore, Zn2V2O7/g-C3N4 shows exceptional photocatalytic CO2 reduction and yielded CH4 as a result. As-prepared nanocomposites can be used in commercial applications for electrochemical diagnostics and photocatalytic applications.

Quantum mechanical analysis of halogen-based ionic liquid crystal [C12MIM.X(where X = Cl, Br)] molecules

ABSTRACT The electrical and non-linear optical characteristics of 1-dodecyl 3-methyl-imidazolium chloride (C12MIM.Cl or DDMIM.Cl) and 1-dodecyl 3-methyl-imidazolium bromide (C12MIM.Br or DDMIM.Br) ionic liquid crystals for optoelectronic devices were investigated in this study utilising B3LYP method and 6-311++G(d,p) basis set with Gaussian09 software. The majority of ionic liquid crystal research to date has been experiment-driven, with very few theoretical studies on the material's optical characteristics. Additional understanding of the behaviour of ionic liquid crystals is revealed through molecular spectroscopic research. The electronic properties (molecular energy band gap, electrostatic potential map and HOMO–LUMO orbitals) and spectroscopic (IR, UV) characteristics were assessed with the aid of a theoretical/computational model at B3LYP/6-311++G(d,p), whereas a nonlinear optical (NLO) study was carried out using the B3LYP and M06-2X methods with 6-31G(d) and 6-311++G(d,p) basis sets. Results demonstrate reasonable nonlinear optical characteristics in these molecules.

Study of optical properties of DM–DM planar interface by incorporating non-linearity and NID space

Study of the optical characteristics of materials, objects and geometries has wider role and applications in science and engineering. Reflection and transmission coefficients are used to study the optical properties of planar geometries. Primary aim of the presented work is to study the reflection and transmission of second harmonic generation in non-integer dimensional environment. Nonlinear medium in our considered geometry is of second harmonic generation type hence we only studied the second order reflection and transmission characteristics. Solution of the nonlinear wave equation is obtained by using slowly varying amplitude approximation and method of separation of variables in NID space is used to study how the presence of NID medium alter the electromagnetic waves. As a special case of the original geometry we also studied the changes in the behavior of the coefficients when an epsilon negative and a mu negative NID mediums are used as a reflected half space. In all the cases impact of the non-linearity and the noninteger dimensions on the unknown coefficients are studied separately. It is studied that higher amplitude of the reflection coefficient can be achieved by using a dielectric magnetic NID medium compared to epsilon negative NID medium. On the other hand it is also noted that for epsilon near zero medium, amplitude of the reflection coefficient reaches zero for specific values of the nonlinear permeability and incident angle whereas, for mu negative NID medium amplitude of both the coefficients increases (decreases) by increasing the values of ϵic(ϵrc). It is also noted that dimensions of the NID mediums can be used as a controlling factor for the amplitude of the coefficients by keeping the same shape. For the verification of the analytical results nonlinear power law is used.

Emerging 2D Materials with Nonparabolic Bands for Ultrafast Photonics

In recent years, 2D materials have been widely used in optical and photonic applications such as mode lockers, optical switches, polarizers, and optical modulators. As is known, many 2D optical materials are parabolic semiconductors. The electronic states determines the material's optical characteristics. The energy band structure with a bandgap dominates the electron dynamics process associated with intrinsic light absorption. Particularly, the Dirac cone and flat band (FB) are special nonparabolic energy band structures in materials. Dirac materials are characterized by a zero bandgap, and FB materials have a completely flat dispersionless band in the Brillouin zone. These materials are used as emergent and promising 2D materials for saturable absorbers (SAs) due to their excellent nonlinear optical response, and they become potential candidates for ultrafast photonics applications. Herein, the focus is on the characteristics of the energy band structure; the carrier dynamics are reviewed, and application in ultrafast photonics are summarized.

Terahertz conductivity of iron oxide-graphene oxide composite pellet

Electrical and optical characteristics of materials are the most used physical properties that serve as tools to identify and analyze certain dynamics of matter being studied. In this paper, the optical parameters of iron oxide-graphene oxide composite mixed with polyethylene were characterized using terahertz time domain spectroscopy (THz-TDS) and impedance spectroscopy. The real and imaginary conductivities were obtained from impedance measurements in the low frequency range. The complex refractive index and absorption coefficient were also determined using THz-TDS. From these quantities, the complex conductivity of the sample was determined and was fitted using the combined Drude-Smith Lorentz model.

Characterization of Zn-Doped CdO Nanoparticles Thin Films Synthesized by Pulsed Laser Deposition

In this investigation, thin films of CdO:Zn were synthesized by using the technology of pulsed lasers. Additionally, the effect of different concentrations of Zn doping on the material's physical properties was investigated. According to XRD research, the films have a polycrystalline structure, and it was discovered that the size of the crystallites changes depending on the amount of Zn doping. The morphology of the produced films reveals that there are spherical nanoparticles distributed evenly all over the surface of the films and ranging in size from nanometer to nanometer. The increase in Zn doping concentrations resulted in an improvement of the material's optical characteristics. The results of the Hall effect observations show that each of the films possesses n-type conductivity. This property, combined with the films' low resistivity, enables them to be utilized in a wide variety of contexts. In addition to this, each of the films has a large concentration of carrier molecules.

Enhancement of Photocatalytic Activity and Microstructural Growth of Cobalt-Substituted Ba1−xCoxTiO3 {x = 0, …, 1} Heterostructure

The photocatalytic degradation process and absorption kinetics of the aqueous solution of the Cibacron Brilliant Yellow 3G-P dye (Y) were investigated under UV-Vis light. Pure barium titanate BaTiO3 (BT) and cobalt ion-substituted barium Ba1−xCoxTiO3 (x = 0, …, 1) nano-compound powders (BCT) were synthesized using the sol–gel method and colloidal solution destabilization, and utilized as photocatalysts. The powder X-ray diffraction (PXRD) crystal structure analysis of the BT nanoparticles (NPs) revealed a prominent reflection corresponding to the perovskite structure. However, impurities and secondary phase distributions were qualitatively identified in the PXRD patterns for x ≥ 0.2 of cobalt substitution rate. Rietveld refinements of the PXRD data showed that the BCT nano-compound series undergoes a transition from perovskite structure to isomorphous ilmenite-type rhombohedral CoTiO3 (CT) ceramic. The nanoparticles produced displayed robust chemical interactions, according to a Fourier transform infrared spectroscopy (FTIR) analysis. The BT and BCT nanoparticles had secondary hexagonal phases that matched the PXRD results and small aggregated, more spherically shaped particles with sizes ranging from 30 to 114 nm, according to transmission electron microscopy (TEM). Following a thorough evaluation of BCT nano-compounds with (x = 0.6), energy-dispersive X-ray (EDX) compositional elemental analysis revealed random distributions of cobalt ions. Through optical analysis of the photoluminescence spectra (PL), the electronic structure, charge carriers, defects, and energy transfer mechanisms of the compounds were examined. Due to the cobalt ions being present in the BT lattice, the UV-visible absorption spectra of BCT showed a little red-shift in the absorption curves when compared to pure BT samples. The electrical and optical characteristics of materials, such as their photon absorption coefficient, can be gathered from their UV-visible spectra. The photocatalytic reaction is brought about by the electron–hole pairs produced by this absorption. The estimated band gap energies of the examined compounds, which are in the range of 3.79 to 2.89 eV, are intriguing and require more investigation into their potential as UV photocatalysts. These nano-ceramics might be able to handle issues with pollution and impurities, such as the breakdown of organic contaminants and the production of hydrogen from water.

Optical multicoating using low-refractive-index SiO2 optical thin films deposited by sputtering and electron beam evaporation

Controlling the refractive index of optical thin-films can improve the optical characteristics of materials. We have developed a combination deposition system that can perform sputtering and electron beam evaporation either separately or simultaneously. The combination deposition system can produce silicon dioxide (SiO2) optical films with refractive indices ranging from 1.26 to 1.47. Using the developed system, we fabricated a monomaterial multilayer coating with 51 layers of SiO2 on a SiO2 substrate, i.e., same material. The wavelength of the as-prepared bandstop was consistent with the designed wavelength. In addition, the light-scattering intensity ratio of the fabricated optical filter was similar to that of conventional filters.

Inertia of the oscillatory mechanisms of giant nonlinearities of optical materials in the terahertz spectral range

Subject of study. The inertia of the oscillatory mechanisms of the nonlinearities of isotropic dielectric media in the field of the terahertz-frequency electromagnetic waves was investigated for resonant and nonresonant interactions between radiation and matter. The purpose of this work was to construct a dynamic model of the nonlinear polarization responses of optical media with oscillatory nature in the field of terahertz pulses and to estimate the time constants characterizing the inertia of such responses during resonant and nonresonant interactions between radiation and media molecular vibrations. Method. The model of anharmonic vibrations of the atoms of each molecule as an oscillator in the general case for an isotropic medium, with both quadratic and cubic nonlinearities, was reduced for a macroscopic optical characteristic—its polarization—to a model as a system of parametrically coupled equations with only cubic nonlinearities. The system parameters were determined from well-known characteristics of a medium, such as its thermal expansion coefficient, stretching molecular vibration frequency, and refractive index. Main results. Expressions were obtained for the inertial time constants of the cubic susceptibilities of optical media with nonlinear vibrations in two- and one-photon resonant interactions with quasi-monochromatic terahertz pulses as well as in nonresonant interactions with broadband terahertz pulsed radiation through the thermal, spectral, and optical characteristics of materials known in the literature. Numerical estimates were obtained for the inertial time constants of the nonlinear susceptibilities of media with particularly high vibrational nonlinearities in the refractive indices, namely, α-pinene and water, as well as silicon dioxide. For these materials, the inertial time constants of the resonant oscillatory mechanisms of the nonlinearities for radiation in the terahertz spectral range were shown to be of the order of hundreds of femtoseconds; for the nonresonant interactions, the time constants decreased to ten femtoseconds or less. Practical significance. The obtained inertial time constant estimations of the polarization responses of materials indicate that their giant nonlinearities in the far infrared spectral range could be used to develop ultrafast photonic devices for pulsed terahertz radiation parameter control.

Optical Transitions and Magnetism in Mn-Implanted Gallium Nitride for Three-Level Magnetooptic Devices

A method of preparing passive materials suitable for magnetooptic interactions is shown using manganese implantation into gallium nitride (GaN) epitaxial layers, which establishes both dilute ferromagnetism and a three-level optical system with persistence to over 300 K. A sweep of thermal anneal parameters for a high implant dose into Mg-doped p-type GaN films is presented, and the materials are tested for both their magnetization and photoluminescence (PL). The optimal anneal process at 825 °C for 5 min maintains ferromagnetism with $T_{C}$ > 305 K, confirming magnetic alignment at room temperature with a coercivity of ~100 Oe. PL and spectrophotometry of the optimally prepared materials show the effects of the mid-gap defect state on the material's optical characteristics. The anneal process returns the real part index to its baseline dispersion while retaining an onset of absorption starting at the defect level $E_{A}$ = 1.8 eV, signifying a stable mid-gap energy transition with a measured state lifetime of $τ _{PL}$ = 2.7 ns. The scalability of this process for producing three-level transition magnetic materials suggests passive optical or magnetooptic devices can be constructed that interconnect photonic and spintronic effects for emerging system designs and potential applications in quantum information.

Theoretical probe of absorption and fluorescence emission characteristics of highly luminescent ReL(CO)3X (L = 12H-indazolo[5,6-f][1,10]phenanthroline and X = F, Cl, Br, I): a DFT/TD-DFT study

Four novel rhenium (Re) tricarbonyl complexes (ReL(CO)3X; X = F, Cl, Br, I and L = 12H-indazolo[5,6-f][1,10]phenanthroline) with promising luminescent properties were investigated using a DFT/TD-DFT approach at the ωB97X-D3/6-31 + G(d,p)//LANL2DZ level of theory. The effects of halogen co-ligands (F, Cl, Br and I) and solvents (acetonitrile (ACN), dichloromethane (DCM) and dimethylsulfoxide (DMSO)) on luminescent properties of the complexes were examined. The studied Re(I) tricarbonyl complexes assumed distorted octahedral geometry with an N–Re–N bite angle of ca. 75°, and showed possible p–π interactions between the halogen (X) atom and the N-donor ligand (L) ring. Prominent electronic excitations (with high oscillator strengths) are S0→S3, attributed to the hole–electron orbital transition based on the natural transition orbitals analyses, and characterised as MLCT/LMCT. The complexes exhibited prominent Stokes fluorescence with Stokes shifts ranging from 9204 to 19490 cm−1. ReL(CO)3Cl in ACN showed the largest Stokes shift, whereas ReL(CO)3I in ACN displayed the smallest Stokes shift. Fluorescence emission wavelengths varied with X and solvent, though the four complexes emit in the cyan/blue range in DCM. ReL(CO)3F (in ACN) exhibited the highest fluorescence lifetime and quantum yield. The study demonstrates the tunability of photophysical properties and promotes the theoretical probe of optical characteristics of materials as corroborative efforts to experimental findings.

Light emission of Lu2Sn2O7 pyrochlore driven by oxygen vacancy and local site engineering

This work manifested the crucial role played by defect and dopant ion local structure in maneuvering light emission characteristics of optical materials. We have harnessed the full gamut of visible light emission from green to yellow to orange-red endowed by oxygen vacancies (OVs) in undoped Lu2Sn2O7 (LSO) pyrochlore and Sm3+/Dy3+ doping in LSO pyrochlore. The energy required to create a OVs at 48f position is lowered with respect to VO8b, hence VO48f defects are expected to present at a larger fraction and are responsible for green emission in the LSO. Though Dy3+ ion is distributed at both Lu3+ and Sn4+ site, the contribution of asymmetric Dy@Sn ion is more than that of symmetric Dy@Lu in PL process of Lu2Sn2O7:Dy3+ leading to intense yellow light compared to blue light and is consistent with the DFT calculations. On the other hand, Sm3+ substitution at the Sn lattice site is thermodynamically more favorable in Lu2Sn2O7:Sm3+ (LSOS) by 1.38 eV with respect to Lu lattice site. Based on time-resolved photoluminescence spectroscopy, it is postulated that Sm@Sn with far-off OVs leads to magnetic dipole (MDT) and the one with nearby OVs leads to electric dipole transition (EDT) in LSOS. This concept of defect induced emission and role of defect and dopant local structure can be applicable to various luminescent phosphors which provides a unique approach for tuning other properties of optically multifunctional crystals that are highly sensitive to defect and dopants local site engineering.

A stokes polarimetric light microscopy view of liquid crystal droplets

The optical characteristics of materials, such as their magnetooptical effects, birefringence, optical activities, linear and circular dichroism, are probed via the polarisation states of light transmitted through or reflected from the specimens. As such, the measurements of the polarisation states play an important role in many research disciplines. Experimentally, Stokes parameters provide a full description of the polarisation states of light. We report the implementation of a dual- photoelastic modulator based polarimeter in a light microscope, enabling the determination of Stokes parameters at each pixel. As a case study, polarimetric images of liquid crystal droplets of different internal structures are obtained, showing their distinct polarisation characteristics. We demonstrate that the prototype Stokes polarimetric microscope allows the quantitative determination of the polarisation characteristics of light at the object plane and enables the access of the information of full polarisation states as compared to a conventional cross polariser microscope. This work shows that Stokes polarimetric microscopy may find potential applications in a wide range of research fields.

High-Efficiency Spatial-Wave Frequency Multiplication Using Strongly Nonlinear Metasurface.

In the past decades, metasurfaces have opened up a promising venue for manipulating lights and electromagnetic (EM) waves. In the field of nonlinearity, second‐harmonic generation (SHG) is a research focus due to its diverse applications. There have been many researches for realizing SHG in optical regime using nonlinear characteristics of optical materials, but its efficiency is low. In microwave frequencies, SHGs are basically studied in the guided‐wave systems. Here, high‐efficiency SHGs of spatial waves are presented in the microwave frequency using nonlinear metasurface loaded with active chips at the subwavelength scale. The nonlinear meta‐atom is composed of receiving antenna, transmitting antenna, and active circuit of frequency multiplier, which can realize strongly nonlinear response and link the EM signals from the receiving to transmitting antennas. Correspondingly, to achieve the function of spatial‐wave frequency multiplication, the working frequency of the transmitting antenna in the meta‐atom should be twice as that of the receiving antenna, and hence the active chip is well matched to obtain the signal transforming with high efficiency. Good performance of the spatial‐wave frequency multiplication is demonstrated in the proof‐of‐concept experiments with the best transform efficiency of 85.11% under normal incidence, validating the proposed method.

Investigation of structural, optical and dispersion parameters of [formula omitted] (A = Bi, Ce, and Y, with [formula omitted] = 0.0 and 0.1) compounds

Lanthanum titanate nanoparticles of La2−xAxTi2O7 (the undoped is denoted by LTO and the monodoped with Bi, Ce, and Y is denoted by LBTO, LCTO and LYTO, respectively) were prepared by sol-gel route. X-ray diffraction (XRD) reveals that these compounds crystallize as a monoclinic perovskite structure with a space group P21. Optical transmittance and reflectance made it possible to obtain more optical and optoelectronic of studied nanoparticles. The data collected reveal that the samples have a wide band gap (Eg) that varies between 3.50 and 3.88 eV. The dispersion parameters have been studied in terms of a single oscillator by the Wemple and Di-Domenico (WDD) model. The dispersion energy Ed, the excitation energy Eo have a crucial role in identifying the characteristics of optical materials and allow the calculations of the factors required for the design of spectral dispersion and optical communication devices.

Photo-Induced Charge Transfer Enhancement for SERS in a SiO2-Ag-Reduced Graphene Oxide System.

Understanding and controlling the disorder in materials, especially the disorder caused by structural composition and doping effects, are important keys to studying the optical characteristics of materials. In this study, a SiO2-Ag-reduced graphene oxide (rGO) composite structure was prepared by a simple wet chemical method, in which Ag nanoparticles (NPs) and SiO2 were decorated onto the surface of rGO. The introduction of Si atoms can control not only the plasmon effect of Ag NPs but also, more importantly, the defect concentration of rGO. The formation of defects causes the rGO structure to enter a metastable state, which facilitates charge separation and transfer in the system. It is worth noting that changes in defect concentration can affect the energy band position of rGO; therefore, controlling the defect concentration can be used to achieve charge transfer resonance coupling. This study not only revealed the ultrahigh surface-enhanced Raman scattering activity of the substrate structure but also elucidated in detail the effect of the crystallinity of this rGO-based composite system on its optical properties.

Solving the inverse problem for determining the optical characteristics of materials

The paper describes a methodology for determining the optical and physical properties of anisotropic thin film materials. This approach allows in the future designing multilayer thin-film coatings with specified properties. An inverse problem of determining the permittivity tensor and the thickness of a thin film deposited on a glass substrate is formulated. Preliminary information on the belonging of a thin-film coating to a certain class can significantly reduce the computing time and increase the accuracy of determining the permittivity tensor over the entire investigated range of wavelengths and film thickness at the point of reflection and transmission measurement Depending on the goals, it is possible to formulate and, therefore, solve various inverse problems: o determination of the permittivity tensor and specification of the thickness of a thick (up to 1 cm) substrate, often isotropic; o determination of the permittivity tensor of a thin isotropic or anisotropic film deposited on a substrate with known optical properties. The complexity of solving each of the problems is very different and each problem requires its own specific set of measured input data. The ultimate results of solving the inverse problem are verified by comparing the calculated transmission and reflection with those measured for arbitrary angles of incidence and reflection.

Multilayer optical thin film design with deep Q learning

Multilayer optical film plays a significant role in broad fields of optical application. Due to the nonlinear relationship between the dispersion characteristics of optical materials and the actual performance parameters of optical thin films, it is challenging to optimize optical thin film structure with the traditional models. In this paper, we present an implementation of Deep Q-learning, which suited for the most part for optical thin film. As a set of concrete demonstrations, we optimize solar absorber. The optimal program could optimal this solar absorber in 500 epoch (about 200 steps per-epoch) without any human intervention. Search results perform better than researchers’ manual searches.

Dip Coated Indium Oxide Films and Their Optical Constants

Metal oxide play very important role in the field of semiconductors. Metals have high reflectivity for the light radiation in the range of infrared and visible range and low reflectivity in the ultraviolet and higher frequency range. Indium oxide thin films were successfully deposited by the sol gel dip coating method. The envelope method was used to evaluate the optical parameters and thickness. Resistivity, mobility and carrier concentration were obtained from Hall measurements. The dispersion energy was obtained from the single effective oscillator model. The energy band gap values estimated from Tauc’s plot and the static refractive index estimated from the Cauchy’s curve fitting agree well with single effective oscillator model. Optical characteristics of materials are determined by the interaction of the electromagnetic radiation with the valence electron of the materials which lies within or near visible range of electromagnetic spectrum. The other optical parameters like optical conductivity and the dielectric constants were also evaluated.

Electronic Structure and Optical Properties of the FeAl2 Compound

The electronic structure and optical properties of the binary intermetallic compound FeAl2 have been studied. Spin-polarized calculations of the electronic structure have been performed and the magnetic moments of atoms have been determined. Using the method of ellipsometry, the optical characteristics of material have been measured in a spectral range of 0.22–15 μm. It is shown that the experimental interband optical conductivity of the compound is satisfactorily interpreted based on the calculated density of electronic states.