Transparent Region Research Articles

TeO[formula omitted]–BaO–Bi[formula omitted]O[formula omitted] tellurite optical glasses I. - Glass formation, structural, thermal and optical properties

The present study investigates the glass-forming ability (GFA), structural, thermal, and optical properties of the TeO2–BaO–Bi2O3 (TeBaBi) glass system, focusing on the mutual substitution trends of its constituent compounds. Prepared glasses were synthesized by the melt-quenching method at 900 °C and the GFA was extended by chemical compositions with lower TeO2 (55–85 mol.%) and higher Bi2O3 (5–15 mol.%) content via optimization of the synthesis process. The introduction of BaO and/or Bi2O3 results in the increase of the glass transition temperature (Tg≈327–384°C), molar volume (Vg≈28.9–33.1cm3mol−1) and optical basicity (OB≈0.97–1.03). Prepared TeBaBi glasses exhibit satisfactory thermal stability and wide spectral region of optical transparency from 0.4–6.5 μm with observed narrowing of optical window with higher TeO2 content. Compositional evolution of Tg may be described for the TeBaBi glasses using multilinear regression analysis with high correlation (r≥0.995) across the whole GFA region. The structure of studied TeBaBi glasses was investigated by Raman scattering and directly compared to the TeO2–ZnO–BaO (TZB) glass system prepared and characterized under identical conditions. Structural analysis revealed a similar degree of internal glass structure transformation regardless of whether a divalent zinc cation or trivalent bismuth cation is present.

Weld seam object detection system based on the fusion of 2D images and 3D point clouds using interpretable neural networks

This study introduces a novel approach that addresses the limitations of existing methods by integrating 2D image processing with 3D point cloud analysis, enhanced by interpretable neural networks. Unlike traditional methods that rely on either 2D or 3D data alone, our approach leverages the complementary strengths of both data types to improve detection accuracy in environments adversely affected by welding spatter and smoke. Our system employs an improved Faster R-CNN model with a ResNet50 backbone for 2D image analysis, coupled with an innovative orthogonal plane intersection line extraction algorithm for 3D point cloud processing. By incorporating explainable components such as visualizable feature maps and a transparent region proposal network, we address the “black box” issue common in deep learning models.This architecture enables a more transparent decision-making process, providing technicians with necessary insights to understand and trust the system’s outputs. The Faster-RCNN structure is designed to break down the object detection process into distinct, understandable steps, from initial feature extraction to final bounding box refinement. This fusion of 2D-3D data analysis and interpretability not only improves detection performance but also sets a new standard for transparency and reliability in automated welding systems, facilitating wider adoption in industrial applications.

Aggregation in Deep Eutectic Solvents (DESs): Formation of Polar DES-in-Nonpolar DES Microemulsions.

The versatility of environmentally benign and inexpensive deep eutectic solvents (DESs) lies in their widely varying physicochemical properties. Depending on its constituents, a DES may be highly polar or nonpolar in nature. This offers an enticing possibility of formation of novel nonaqueous microemulsions (MEs). Evidence of the presence of polar DES-in-nonpolar DES MEs is presented with reline (formed by mixing choline chloride and urea in 1 : 2 mol ratio) as the polar DES forming the ME pools, Thy : DA [formed by mixing thymol (Thy) and n-decanoic acid (DA) in 1 : 1 mol ratio] nonpolar DES as the bulk oil phase and nonionic surfactant Brij-35 as the emulsifying agent. While only sparingly miscible in Thy : DA, as high as 2.5 M reline can be solubilized in this DES in the presence of 100 mM Brij-35; reline loading (w Rel = [reline]/[Brij-35]) as high as 25 can be achieved. The ternary phase diagram of the Thy : DA/Brij-35/reline system reveals a clear and transparent single-phase region where MEs may be forming. Dynamic light scattering confirms the presence of MEs of 2-10 nm size. Even as up to 2.5 M (ca. 0.35 mole fraction) reline, whose dynamic viscosity (η) and electrical conductivity (κ) are very high, is added to 100 mM Brij-35 solution of Thy : DA, the η and κ values of the solution increase insignificantly, thus conforming to the formation of MEs in the solution. Fourier transform infrared (FTIR) absorbance spectra and fluorescence probe responses further indicate that reline is not dispersed in the medium but rather forms polar pools of the MEs. These novel nonaqueous polar DES-in-nonpolar DES MEs will not only expand the application potential of DESs but also offer a new class of organized media with widespread potential.

Effect of substrate temperature and position on properties of Cu3N thin films deposited by reactive radio frequency magnetron sputtering

Copper nitride (Cu3N) thin films were deposited on soda lime glass (SLG) substrates by reactive radio frequency (RF) magnetron sputtering using a pure Cu target in the presence of argon and nitrogen. The structural, optical, and electrical properties of the Cu3N films were investigated systematically on substrate temperature and position, demonstrating that both parameters strongly influence the properties of Cu3N thin films. XRD patterns revealed the formation of the Cu3N phase at all substrate temperatures and positions. The transmittance of the Cu3N thin films was over 80 % in the transparent region and the band gap for Cu3N was determined to 1.7–1.9 eV with a very high absorption coefficient above 104 cm−1. The n-type conductivity was observed in every Cu3N film but the resistivity varied considerably with both substrate temperature and position. The promising physical properties of Cu3N thin films suggest their potential application in optoelectronic devices such as thin film solar cells.

Three-periodic 1D photonic crystals based on dielectric oxides SiO2, Al2O3, TiO2, ZrO2: an emerging class of structures with wide possibilities for applied photonics

One-dimensional three-periodic photonic-crystal (PC) structures based on dielectric nonmagnetic materials (SiO2, Al2O3, TiO2, ZrO2) that form [(ab)N(cd)M]K supercells including “internal” subcells of the (ab)N and (cd)M types are considered. The classification of this class of structures makes it possible to distinguish three large groups of subcells that differ in optical contrast values (low-, medium-, and high-contrast). Using the transfer matrix method, frequency-angle spectra and energy characteristics of the PC structures are studied and optimal combinations of layers (and contrast) are found, enabling obtaining controllable photonic band gaps (PBGs). A generalization of the obtained results shows that in the transparent region, the optical and energy properties of structures with high and medium optical contrast are of the greatest practical interest. It is found that the group of medium-contrast structures has a greater flexibility in the formation and rearrangement of the PBG due to a practically equivalent effect of the optical properties of both cells on the transmission spectrum. An analysis of the spatial-angular distribution of the transverse component of the Umov-Poynting vector and variation in the number of subcells (internal periods) shows that the structure of this group can provide a controlled radiation pattern (at a telecommunication wavelength of 1.55 μm) on the lateral surface of the PC. The findings may give a competitive advantage in the development of polarization-sensitive couplers, highly sensitive angle sensors for fiber-optic systems, and optical filters operating in the infrared range.

PbBeB2O5: A High-Performance Ultraviolet Nonlinear-Optical Crystal with Functional [BeB2O8]8- Group.

High-performance nonlinear-optical (NLO) crystals need to simultaneously meet multiple basic and conflicting performance requirements. Here, by using a partial chemical substitution strategy, the first noncentrosymmetric (NCS) PbBeB2O5 crystal with a BeB2O8 group was synthesized, exhibiting a two-dimensional [BeB2O5]∞ layer constructed by interconnecting BeB2O8 groups and bridged PbO4 with an active lone pair. The crystal shows a promising UV NLO functional feature, including a strong SHG effect of 3.5 × KDP (KH2PO4), large birefringence realizing phase matchability in the whole transparency region from 246 to 2500 nm, a short UV absorption edge of 246 nm, and single-crystal easy growth. Remarkably, theoretical studies reveal that the BeB2O8 group has high nonlinear activity, which could stimulate the discovery of a series of excellent NLO beryllium borates.

Superalkalides based on stacked janus molecule with improved optical nonlinearity

Research is actively being carried out to design new materials with exceptional nonlinear optical (NLO) responses. In this context, a systematic investigation of designing novel hypothetical materials e.g., superalkalides based on stacked Janus dimer, all-cis-1,2,3,4,5,6-hexafluorocyclohexane (C6H6F6)2 has been reported using high-level density functional simulations. The superalkalides are designed here by doping alkali metals on the fluorine face and superalkalis on the hydrogen face of Janus dimer. The thermodynamic stability of newly designed complexes is demonstrated by the interaction energies (Eint), ranging between −13.64 and −33.12 kcal/mol. Moreover, the superalkalide nature of these complexes is proved by negative charge and HOMO on superalkalis in natural bond orbitals (NBO) and frontier molecular orbitals (FMO) analyses, respectively. Energy gaps (Eg) between HOMO and LUMO orbitals of the designed complexes lie in the range of 0.63–0.83 eV. UV–Vis analysis is performed to gain idea about the transparent region of electromagnetic spectrum for nonlinear activity. The nonlinear activity of the designed superalkalide(s) is studied by static first hyperpolarizability β0, dynamic first hyperpolarizability β(ω) and dynamic second hyperpolarizability γ(2- ω; ω, ω). The highest β0, β(ω), and γ(2- ω; ω, ω) ranges up to 1.1 × 107, 2.9 × 106 and 2.9 × 1012 au, respectively for designed complexes. A comprehensive examination of these superalkalides based on stacked Janus dimers with exceptionally high NLO response highlights their potential for use in nonlinear optical materials.

Luminescence and Electron–Hole-Trapping Centers in α-Ca2P2O7−Mn

The mechanisms of formation of induced intrinsic and impurity radiative states, which consist of intrinsic and impurity electron–hole-trapping center states in irradiated Ca2P2O7−Mn and Ca2P2O7 phosphates, were investigated using thermoactivation and vacuum-ultraviolet spectroscopy methods. These centers are excited at photon energies of 4.0 eV and 4.5 eV, which are within the matrix’s transparency region. New radiative-induced states at 3.06 eV and 2.92 eV are demonstrated to be generated upon the excitation of anions by photons with energies of 5.0 and 5.64 eV. This process is due to charge transfer from the ion to the impurities, specifically Mn2+(O2−−Mn2+) and the neighboring ion O 2−−(P2O7)4−. Furthermore, upon the excitation of matrix anions with photon energies exceeding the band gap (8.0–8.25 eV), electron-trapping by impurities such as Mn2+ and (P2O7)4− ions results.

Design of High-Performance Inorganic-Organic Hybrid Nonlinear Optical Materials Using Superhalogen Al13 and Dianhydrides.

Novel inorganic-organic hybrid complexes Al13-X (X represents the dianhydrides PMDA, NTCDA, and PTCDA) are theoretically designed and studied using density functional theory (DFT) and time-dependent DFT. These conjugated dianhydrides containing four acceptor carbonyl groups are commonly used as electron acceptor materials. These compounds possess large binding energies, reflecting the sufficient binding of Al13 to the dianhydride molecule. The binding nature of the complexes is of charge transfer type, i.e., electrons are transferred from the aluminum cluster to the dianhydride. All of the aimed complexes have large mean polarizability (α0) and first hyperpolarizability (β0). The β0 values are explained on the basis of electronic transitions in crucial excited states using the TD-DFT method. Additionally, the hole-electron distribution was analyzed, revealing the nature of electronic excitation. Absorption spectra analysis shows that these complexes have an excellent infrared (IR) transparent region (1000-5000 nm). Therefore, these inorganic-organic hybrid complexes with high stability can be considered as potential candidates for new IR nonlinear optical molecules.

Temperature-dependent index of refraction Sellmeier model for crystalline and polycrystalline materials.

The temperature dependence of optical window materials remains an important issue for a variety of applications from spacecraft, laser components, to high-speed aircraft. Concerning the refractive index in regions of transparency, current models are empirically based polynomial fits for the Sellmeier model strength and mode location parameters. These polynomial fit functions limit the ability to accurately extrapolate beyond the experimental range used to develop the fit functions. Thus, the development of a physics-based model as a function of temperature is an important goal for these critical materials. Such a model will allow extrapolation to higher and lower temperatures as long as the physical mechanisms do not change. For vibrational modes, a thermal average of the anharmonically shifted energy levels is investigated and compared to experimental data. The first anharmonic term can be estimated using the Morse potential based on a multiphonon absorption model. Experimentally, these modes redshift, and this is consistent with the developed temperature-dependent index of refraction Sellmeier model. This redshifting phenomena can also be applied to electronic transition shifts. In addition, the temperature-dependent oscillator number density can be obtained from known expansion coefficient models and experimental data. Other model parameters, in particular the electronic and vibrational mode polarizability, still need experimental grounding for a given material. The method is incorporated into a modified Sellmeier model format.

Preparation and characterizations of glasses in the TeO2–Ga2O3–M2O (M═Li, Na, K) systems

AbstractGlasses in the TeO2–Ga2O3–M2O (M═Li, Na, or K) systems were synthesized by a melt‐quenching technique. The glass forming areas were delimited for each system. Systematic analyses were performed on two series of samples—the first one with a constant TeO2/Ga2O3 ratio of 85/15, that is, [(TeO2)0.85(Ga2O3)0.15]100−x[M2O]x with 0 ≤ x ≤ 25 (with a step of 5 mol%), the second one with a constant alkaline oxide concentration of 10 mol%, that is, [TeO2]90‐y[Ga2O3]y[M2O]10 with 5 ≤ y ≤ 15 (with step of 2.5 mol%). The values of the glass transition temperature, density, and optical transmission parameters (the positions of short‐ and long‐wavelength absorption edge and the maximum transmittance value) were determined. The changes in these parameters were studied for varying glass compositions. In addition, the values of refractive index were measured at various wavelengths across the whole transparency region reaching from the visible up to the mid‐infrared range.

Crystal-Like Atomic Arrangement and Optical Properties of 25La2O3-75MoO3 Binary Glasses Composed of Isolated MoO42.

Transparent and brown La2O3-MoO3 binary glasses were prepared in bulk form using a levitation technique. The glass-forming range was limited, with the primary composition being approximately 25 mol % La2O3. The 25La2O3-75MoO3 glass exhibited a clear crystallization at 546 °C, while determining its glass transition temperature was difficult. Notably, despite its amorphous nature, the glass possessed a density and packing density comparable to those of crystalline La2Mo3O12. X-ray absorption fine structure and Raman scattering analyses revealed that the glass structure closely resembles La2Mo3O12 due to the presence of isolated MoO42- units, whereas disordered atomic arrangement around La atoms was confirmed. The glass demonstrated transparency ranging from 378 to 5500 nm, and the refractive index at 1.0 μm was estimated to be 2.0. The optical bandgap energy was 3.46 eV, which was slightly smaller than that of La2Mo3O12. Additionally, the glass displayed a transparent region ranging from 6.5 to 8.0 μm. This occurrence results from the decreased diversity of MoOn units and connectivity of Mo-O-Mo, which resulted in the reduced overlap of multiphonon absorption. This glass formation, with its departure from conventional glass-forming rules, resulted in distinctive glasses with crystal-like atomic arrangements.

Recent advances on applications of single-walled carbon nanotubes as cutting-edge optical nanosensors for biosensing technologies.

Single-walled carbon nanotubes (SWCNTs) possess outstanding photophysical properties which has garnered interest towards utilizing these materials for biosensing and imaging applications. The near-infrared (NIR) fluorescence within the tissue transparent region along with their photostability and sizes in the nanoscale make SWCNTs valued candidates for the development of optical sensors. In this review, we discuss recent advances in the development and the applications of SWCNT-based nano-biosensors. An overview of SWCNT's structural and photophysical properties, sensor development, and sensing mechanisms are described. Examples of SWCNT-based optical nanosensors for detection of disease biomarkers, pathogens (bacteria and viruses), plant stressors, and environmental contaminants including heavy metals and disinfectants are provided. Molecular detection in biofluids, in vitro, and in vivo (small animal models and plants) are highlighted, and sensor integration into portable substrates for implantable and wearable sensing devices has been discussed. Recent advancements, which include high throughput assays and the use of machine learning models to predict more sensitive and robust sensing outcomes are discussed. Current limitations and future perspectives on translation of SWCNT optical probes into clinical practices have been provided.

The flow characteristics for gas jet in liquid crossflow with special emphasis on the vortex-cavity interaction

The objective of this paper is to investigate the complex three-dimensional vortex structures created by the interaction of gas jet with liquid crossflow. A high-speed camera technique is used to record the evolution patterns of the jet cavity. High-precision numerical methods with the Chorin projection method and volume of fluid method (VOF) are employed to understand the complex flow features associated with jet–freestream interaction. The results present that three distinct regions of the jet cavity could be observed, referred to as the transparent cavity region (TCR), the transition region (TR), and the foam cavity region (FCR). The interaction between the flow of gas jet and liquid crossflow creates multiscale vortex structures, including the counter-rotating vortex pair (CVP), the upper-deck counter-rotating vortex pair (up-CVP), the horseshoe vortices, the shear layer vortices, and the fine-scale vortices, respectively. The relationship between multiscale vortex structures and the pulsation of the gas-liquid interface is analyzed in detail by analyzing the spatial distribution of different vortex structures and the fluctuations of the gas-liquid interface. In addition, the effect of the gas entrainment coefficient on cavity flow patterns and vortex structures is compared and analyzed.

Chiral and Polar Duality Design of Heteroanionic Compounds: Sr18 Ge9 O5 S31 Based on [Sr3 OGeS3 ]2+ and [Sr3 SGeS3 ]2+ Groups.

Chirality and polarity are the two most important and representative symmetry-dependent properties. For polar structures, all the twofold axes perpendicular to the principal axis of symmetry should be removed. For chiral structures, all the mirror-related symmetries and inversion axes should be removed. Especially for duality (polarity and chirality), all of the above symmetries should be broken and that also represents the highest-level challenge. Herein, a new symmetry-breaking strategy that employsheteroanionic groups to construct hourglass-like [Sr3 OGeS3 ]2+ and [Sr3 SGeS3 ]2+ groups to design and synthesize a new oxychalcogenide Sr18 Ge9 O5 S31 with chiral-polar duality is proposed. The presence of two enantiomers of Sr18 Ge9 O5 S31 is confirmed by the single-crystal X-ray diffraction. Its optical activity and ferroelectricity are also studied by solid-state circular dichroism spectroscopy and piezoresponse force microscopy, respectively. Further property measurements show that Sr18 Ge9 O5 S31 possesses excellent nonlinear optical properties, including the strong second harmonic generation efficiency (≈2.5 × AGS), large bandgap (3.61eV), and wide mid-infrared transparent region (≈15.3µm). These indicate that the unique microstructure groups of heteroanionic materials are conducive to realizing symmetry-breaking and are able to provide some inspiration for exploring the chiral-polar duality materials.

Na2CeF6: A Highly Laser Damage-Tolerant Double Perovskite Type Ce(IV) Fluoride Exhibiting Strong Second-Harmonic Generation Effect.

Perovskite structure compounds are significant candidates for designing new optical function materials due to their structural variability. Here, an inorganic tetravalent cerium fluoride, Na2CeF6, is derived from the perovskite structure through double-site cation co-substitution. Na2CeF6 crystalizes in the non-centrosymmetric space group . Edge-sharing connected NaF9 and CeF9 polyhedra build the whole 3D structure of Na2CeF6. Importantly, it represents the first Ce(IV) fluoride nonlinear optical (NLO) crystal and can produce a strong and phase-matchable second-harmonic generation (SHG) effect of ≈2.1 times that of KH2PO4 (KDP), making it the strongest among non-lone pair electron metal fluoride system. Further, it exhibits a high laser-induced damage threshold (LIDT) of 74.65-76.25MWcm-2, which is over 20 times that of AgGaS2. It also exhibits a wide transparent region (0.5-14.3µm). This work provides a facile route for exploring high-performance halide NLO materials.

Influence of spatial dispersion in metal on optical characteristics of a magnetoplasmonic layered nanoparticle cluster

In the current work, the diffraction problem of a plane electromagnetic wave on a cluster of two layered nanocylinders consisting of a magnetoplasmonic core and a gold shell is considered. The arising effects of spatial dispersion in the gold shell are taken into account within the framework of the generalized nonlocal optical response theory. Based on the discrete source method scheme, an analysis of the influence of the mutual arrangement of particles, their deformation, and the effect of spatial dispersion on the behaviour of the absorption cross-section and the near-field enhancement factor is conducted. It is shown that the position of the plasmon resonance can be shifted to the transparency region of biological tissues by varying the distance between particles and the core material. It has been established that taking into account spatial dispersion in the gold shell leads to a decrease in intensity and a slight shift of the plasmon resonance position to the shortwave region, without going beyond the tissue transparency region.

Observations on the embryonic development of the mud crab, Scylla paramamosain

To investigate the embryonic development of the mud crab Scylla paramamosain, we analyzed three critical parameters: egg color of, embryo morphology (through conventional and laser scanning confocal microscopy), and the distribution of cell divisions. During embryonic development, the egg color exhibited a progressive transition, shifting from orange to reddish-orange, then to brown, before ultimately darkening to black. Each embryo displayed a spherical shape, measuring approximately 280 μm in diameter, characterized by a smooth surface devoid of any depressions. The embryonic cell division was in the form of mixed oogenesis, comprised of complete division in the early stage, spiral oogenesis in the middle stage and surface division in the late stage. It is noteworthy that the blastopore appeared at the position where the transparent area and cell aggregation just appeared under the microscope, and the blastomere was a characteristic of the embryo entering the gastrulation stage. After entering the gastrulation stage, the cells aggregated towards the blastopore and formed two symmetrical cell clusters, which formed a V-shape with the void of the classic blastopore. When the transparent region occupied approximately 1/5 of the embryo’s volume, the embryo entered the nauplius stage, and the thoracic and abdominal armor, as well as the optic lobe and abdominal limb primordia, could be clearly distinguished. The appearance of the compound eye pigment band indicated the stage of compound eye pigment formation. At this time, the transparent area accounted for 1/4 of the embryo and a large number of ganglia appeared. The change of the compound eye pigment band from red to black was also one of the reasons for the blackening of the egg color of the crabs. The data obtained through this study have potential applications in the determination of embryonic development status and obtaining of high-quality seeds for S. paramamosain culture.

Optical Absorption, Photocarrier Recombination Dynamics and Terahertz Dielectric Properties of Electron-Irradiated GaSe Crystals

Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals were studied. Two absorption bands with the low-photon-energy threshold at 1.35 and 1.73 eV (T = 300 K) appeared in the transparency region of GaSe after the high-energy-electron irradiation. The observed absorption bands were attributed to the defect states induced by Ga vacancies in two charge states, having the energy positions at 0.23 and 0.61 eV above the valence band maximum at T = 300 K. The optical pump-terahertz probe technique (OPTP) was employed to study the dark and photoexcited terahertz conductivity and charge carrier recombination dynamics at two-photon excitation of as-grown and 9 MeV electron-irradiated GaSe crystals. The measured values of the differential terahertz transmission at a specified photoexcitation condition were used to extract the terahertz charge carrier mobilities. The determined terahertz charge carrier mobility values were ~46 cm2/V·s and ~14 cm2/V·s for as-grown and heavily electron-irradiated GaSe crystals, respectively. These are quite close to the values determined from the Lorentz–Drude–Smith fitting of the measured dielectric constant spectra. The photo-injection-level-dependent charge carrier lifetimes were determined from the measured OPTP data, bearing in mind the model injection-level dependencies of the recombination rates governed by interband and trap-assisted Auger recombination, bulk and surface Shockley–Read–Hall (SRH) recombination and interband radiative transitions in the limit of a high injection level. It was found that GaSe possesses a long charge carrier lifetime (a~1.9 × 10−6 ps−1, b~2.7 × 10−21 cm3ps−1 and c~1.3 × 10−37 cm6ps−1), i.e., τ~0.53 μs in the limit of a relatively low injection, when the contribution from SRH recombination is dominant. The electron irradiation of as-grown GaSe crystals reduced the charge carrier lifetime at a high injection level due to Auger recombination through radiation-induced defects. It was found that the terahertz spectra of the dielectric constants of as-grown and electron-irradiated GaSe crystals can be fitted with acceptable accuracy using the Lorentz model with the Drude–Smith term accounting for the free-carrier conductivity.

Precession of magnetic moments with change of their orientations

In the work the precession of the magnetization vector in nano-sized magnets is induced by a femtosecond laser pulse, the frequency of which lies in the transparency region of the magnet material. It is shown that an alternating magnetic field applied to the XOY plane generates the magnetic equilibrium position vectors and elliptical precession occurs if a constant magnetic field acts along the Z axis. In this case the precession angle changes periodically in time and the precession frequency is determined by the amplitude of the total magnetic field.