Optical Properties Of Materials Research Articles

Gradient Luminescence Enhancement in Organic Metal Halide Perovskites via the Suppression of [SbCln]3-n Unit Distortion.

Intrinsic stereochemical activity of the 5s2 electron configuration in Sb3+ leads to structural distortion within [SbCln]3-n units, which, while stabilizing the material, paradoxically diminishes luminescence intensity due to induced asymmetry. To address this issue, a strategy, which encompasses increasing the structural dimensions and introducing In3+ doping, was developed to mitigate the geometrical distortion in the [SbCln]3-n units within the metal-organic perovskite (DABCO)2Sb2Cl10·H2O and (DABCO)2SbCdCl9·2H2O (DABCO = triethylenediamine). This dimensional augmentation confines lattice distortion effectively, and the In3+ doping modifies the 5s2 electron configuration of Sb3+, thereby reducing the distortion at its origin. The unique suitability of indium-based halides as a matrix for Sb3+ doping is underscored by our approach, which capitalizes on their ability to regulate the electron configuration of Sb3+. This strategy has been validated through crystallographic data from single-crystal X-ray diffraction. By effectively reducing the adverse effects of geometric distortion, several hundred-fold enhancements in the luminescent intensity of the material have been achieved by our methodology, leading to potential applications in white-light LEDs. This advancement not only highlights the pivotal role of structural symmetry in the optical properties of materials but also exemplifies the power of material engineering to optimize the optical performance.

Aligning and Observing the Liquid Crystal Director in 3D Using Small Magnetic Fields and a Wedge‐Cell

AbstractThe mechanical and optical properties of liquid crystalline materials are largely dependent on the director profile. More complex soft robotic functions and programmed optical properties require spatially varying director profiles, ideally in 3D. However, it is challenging to achieve arbitrary director orientation with most established alignment techniques, as one needs to overcome surface interactions, use high electric or magnetic field strengths and temperatures. Another experimental difficulty is that there is a lack of suitable techniques that can be used to characterize the director in 3D. Here, this study first shows that the addition of 5CB to reactive mesogens permits cross‐linked liquid crystalline materials to be fabricated with a spatially varying 3D director profile using weak magnetic fields (0.13 T). This study also shows, how these can be characterized with an optical technique that uses a wedge cell to visualize the programmed 3D director profile. Interestingly, the method also permits the real‐time observation of the director. This work shows that it is possible to precisely control the director in 3D with low magnetic fields and that the dynamics can be directly observed, which facilitates potential applications of soft liquid crystalline (LC) gels and potentially also elastomers.

Recent advances in machine learning and deep learning-enabled studies on transition metal dichalcogenides

Abstract The machine learning and deep learning (ML/DL) techniques have significantly advanced the understanding and utilization of TMDs by enabling efficient analysis, prediction, and optimization of their properties. ML/DL methods permit rapid screening, optimization and analysis of two-dimensional (2D) material candidates, potentially accelerating the discovery and development of TMDs with desired electronic, optoelectronic, and energy storage properties. This review provides a comprehensive review of machine learning and deep learning (ML/DL) methods to enhance 2D materials research via the optimization of synthesis conditions, interpretation of complex data sets, and the use of generative adversarial networks and variational autoencoders for innovative material design and image processing tasks. Furthermore, it highlights the potential of ML/DL techniques in predicting and tailoring the electronic, optical, and mechanical properties of 2D materials to meet specific application requirements.

Spectroscopic ellipsometry utilizing frequency division multiplexed lasers

Spectroscopic ellipsometry (SE), which measures the thickness of thin films in a non-contact way with an accuracy of angstroms, has been widely used for optical metrology. Several types of SE are available both commercially and in research, although they require specific implementations depending on the application. Here, we theoretically and experimentally demonstrate the Frequency Division Multiplexing Spectroscopic Ellipsometry (FDM-SE) technique. With respect to conventional rotating polarizing element ellipsometry, our variant uses discrete-wavelength intensity-modulated laser diodes. This modification enables the measurement of optical properties of materials at multiple wavelengths simultaneously. We further compare the performance of the FDM-SE to a commercial instrument by measuring the thickness of SiO2 films on a Si wafer, obtaining a difference between the measured thicknesses with both methods of less than 5 Å. The proposed FDM-SE technique therefore provides a more efficient alternative to conventional SE with a high accuracy for thickness measurements.

Ion‐Beam‐Induced Biaxial Tensile Strain Engineering in Nanoscale Zinc Oxide Films on Silicon Dioxide

AbstractStrain engineering is a powerful tool for adjusting the electrical and optical properties of materials, particularly in 2D materials on flexible polymer substrates. However, current strain‐engineering techniques are primarily utilized for thin 2D materials on flexible substrates, with limited research on thicker materials on traditional substrates. In this study, the enhancement in electrical properties resulting from strain effects in 30‐nm‐thick ZnO films deposited on SiO2 wafers through N2 ion beam irradiation is proposed. The N2 ion beam, at an optimal energy level, induces strain in the underlying SiO2 layer, leading to a 2.5‐fold increase in the saturation mobility and charge‐carrier density of the overlying ZnO film. Density functional theory calculations reveal that the introduction of N2 molecules into the SiO2 crystal induces biaxial lattice expansion, which, in turn, strains the overlying ZnO film. These findings demonstrate the effective application of strain engineering in films of relatively large thickness, even on traditional substrates. It is anticipated that this strain engineering approach using ion‐beam irradiation will significantly broaden the range of applications for strain engineering technology.

Polar-Twisted, Nano-Modulated Nematics: Form Chirality and Physical Properties

Recently, two new polymorphs have been added to the nematic class: the polar-twisted nematic (NPT) in 2016 and the ferroelectric nematic (NF) in 2020. Comprised of achiral molecules, both exhibit local polar ordering and adopt modulated structures, right- and left-handed helical organizations—form chirality—albeit on vastly different dimensional scales; modulations have a ~10 nanometer pitch in the NPT and ~500 nm in the NF. Here, we focus on the structure and symmetries of the NPT phase and the ensuing physical properties. Based on an array of order parameters that fully describe the molecular ordering and the nano-modulations thereof, we present a consistent formulation of the dielectric, optical, surface anchoring, and elasticity properties of the NPT materials. We show that these properties are distinctly different from those associated with an elastically modulated, locally uniaxial, nematic.

Engineering the third-order nonlinear optical absorption properties of two-dimensional layered materials

Engineering the third-order nonlinear optical absorption properties of two-dimensional layered materials

Sulfur-Rich Norbornadiene-Derived Infrared Transparent Polymers by Inverse Vulcanization.

Infrared (IR) transparent polymer materials prepared by inverse vulcanization, as a promising candidate to replace inorganic materials, are new materials for constructing key devices in IR optics. However, it is difficult to achieve a balance between infrared optical and thermal properties in polymers due to the intrinsic infrared absorption of organic materials. Herein, our strategy is to construct a high boiling point symmetrical molecular norbornadiene derivative cross-linking agent (DMMD) which can be inverse vulcanized with molten sulfur, and obtain Poly (S-r-DMMD) with different sulfur content by controlling the feed ratio of sulfur. With the rigid core and low IR activity in DMMD, the prepared polymers exhibit tunable thermal properties (Tg: 98.3-119.8 °C) and high IR transmittance (medium-wave infrared region (MWIR): 42.9-52.6 %; long-wave infrared region (LWIR): 1.5-5.29 %). In addition, Poly (S-r-DMMD) can be used to prepare large-size free-standing Fresnel lenses for IR imaging by simple hot-pressing, which provides flexibility in the design and production of IR fine lenses. This study provides a novel strategy for balancing the thermal and optical properties of IR transparent polymer materials, while providing relevant references for balancing the IR optical and thermal properties of polymer materials.

Sulfur‐Rich Norbornadiene‐Derived Infrared Transparent Polymers by Inverse Vulcanization

AbstractInfrared (IR) transparent polymer materials prepared by inverse vulcanization, as a promising candidate to replace inorganic materials, are new materials for constructing key devices in IR optics. However, it is difficult to achieve a balance between infrared optical and thermal properties in polymers due to the intrinsic infrared absorption of organic materials. Herein, our strategy is to construct a high boiling point symmetrical molecular norbornadiene derivative cross‐linking agent (DMMD) which can be inverse vulcanized with molten sulfur, and obtain Poly (S‐r‐DMMD) with different sulfur content by controlling the feed ratio of sulfur. With the rigid core and low IR activity in DMMD, the prepared polymers exhibit tunable thermal properties (Tg: 98.3–119.8 °C) and high IR transmittance (medium‐wave infrared region (MWIR): 42.9–52.6 %; long‐wave infrared region (LWIR): 1.5–5.29 %). In addition, Poly (S‐r‐DMMD) can be used to prepare large‐size free‐standing Fresnel lenses for IR imaging by simple hot‐pressing, which provides flexibility in the design and production of IR fine lenses. This study provides a novel strategy for balancing the thermal and optical properties of IR transparent polymer materials, while providing relevant references for balancing the IR optical and thermal properties of polymer materials.

Laser pretreatment enhances the laser-induced damage threshold of MgAl2O4 transparent ceramics

The demand for transparent ceramics as essential optical components in high-energy laser systems is escalating. Given the continuous surge in laser output power, there is an urgent need to enhance their laser-induced damage threshold (LIDT). This research systematically investigates the influence of variables such as laser energy density, number of scan repetitions, and stepwise scanning on the LIDT of MgAl2O4 transparent ceramics by modulating the process parameters of laser pretreatment. Through this method, oxygen vacancy defects on the material surface were effectively minimized, achieving surface purification of transparent ceramics and reducing residual stress. Under a consistent laser energy density of 8.96 J/cm2, the transparent ceramics were subjected to 1 to 9 scanning passes. The LIDT showed a progressive increase with the number of scans, reaching a maximum value of 15.0 J/cm2 after seven scans, which corresponds to a 34% improvement compared to untreated samples. Additionally, laser pretreatment facilitated the expansion of the material's bandgap and increased transmittance in the 200-300 nm band, further substantiating the intimate relationship between the reduction of oxygen vacancy defects and the improvement of optical properties. The findings indicate that laser pretreatment, as an effective post-processing technique, can substantially augment its resistance to laser damage by optimizing the microstructure and surface characteristics of the material. Moreover, judicious control of laser energy density and number of scan repetitions is crucial for optimally improving LIDT. In conclusion, this study offers what we believe to be a new theoretical foundation and technical support for the performance optimization of transparent ceramics in high-power laser systems, underscoring the significant potential of laser pretreatment as an effective post-processing technology in enhancing material optical properties and durability.

Autonomous Vibrationless Temperature-Controlled Cryosystem for Optical Studies with a Spectroscopic Ellipsometer

Introduction. Ellipsometry is a highly sensitive, non-destructive optical method used to study the optical and structural properties of materials and thin films.Problem Statement. At the Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, the first in Ukraine serial spectroscopic ellipsometer SE-2000 (manufactured by SEMILAB Ltd., Hungary) has been employed for research, but its measurement capabilities are currently limited to room temperature.Purpose. This research aims to expand the functionality of the SE-2000 by creating a temperature-controlled cryosystem that operates within a temperature range from –195 оC to +80 оC (approximately 80—353 K).Materials and Methods. An autonomous, precision, vibrationless, cryosystem has been designed and manufactured for low-temperature optical investigations in reflection mode, based on a gas-flow cryostat. The cryosystem includes a cryostat, a microprocessor temperature controller, and an adjustment table.Results. The cryostat operates on a gas-flow principle. A laminar gas flow is generated by excess pressure achieved through the heating of cryogenic liquid by a heater-evaporator in the feeder tank. The flow intensity is regulated by adjusting the power supplied to the heating element, eliminating vibrations in the cryostat and sample. The heat exchange chamber is positioned at the top of the nitrogen tank, with the test sample mounted in horizontal plane. Incident and reflected light beams interact with the sample from the upper hemisphere. Sample positioning is adjustable via translational motion along three Cartesian coordinates and by tilting the cryostat with the help of the adjustment table.Conclusions. This system is suitable for use in optical devices that operate in specular reflection mode, with access to the sample surface from the upper hemisphere.

Transient Optical Modulation in Vanadium and Selenium Doped MoS2 by Carrier–Carrier and Carrier–Phonon Interactions

AbstractDoping and alloying induce defect states in atomically thin transition metal dichalcogenides (TMDCs), leading to strong carrier–phonon interactions. The robust excitonic behavior of these layered materials can be modified by injecting a high density of charge carriers. However, comprehending the influence of carrier–phonon and carrier–carrier interactions on the optical properties of 2D materials is crucial for their optoelectronic and photonic applications. Here, transient absorption (TA) spectroscopy is employed to demonstrate the modulation of the transient optical behavior of TMDCs through doping and excitation near Mott density. The TA spectra reveal broadening attributed to carrier–carrier and carrier–phonon interactions, with the broadening being particularly pronounced in vanadium (V) doped TMDCs due to the hybridization of defect and exciton transitions. Analysis of TA kinetics suggests the involvement of various carrier species in the carrier dynamics of TMDCs, with the influence of mid‐gap carriers dominating at higher excitation densities. Nonetheless, the presence of strong carrier–phonon coupling in V‐doped TMDCs is demonstrated by temperature‐dependent Raman and photoluminescence spectroscopy. The results reveal that the enhanced coupling between acoustic phonons and carriers can lead to multiphonon emission. The findings of this study hold promise for controlling the optical response of TMDCs in ultrafast optoelectronic applications.

Terahertz refractive index control of 3D printing materials by UV exposure

Recently, significant progress has been made in the development of THz optics based on metamaterials to overcome the limited availability of suitable materials for conventional optics. Although 3D printing technology is a promising method for rapidly fabricating these subwavelength structures, the structural degree of freedom for 3D printed metamaterials is still limited by the optical properties of printing materials. In this study, we controlled the THz refractive index and extinction coefficient of the 3D printing resin by UV exposure doses during the printing process. Samples were fabricated as uniform plates under different curing conditions in printing, and their optical properties were measured in the range between 0.3 THz and 2.0 THz using THz time-domain spectroscopy (THz-TDS). The refractive index and extinction coefficient were changed from 1.65 to 1.80, and from 0.04 to 0.12, respectively, with increasing UV doses from 1 mJ/cm2, which allows resin to solidify and become printable, to 100 mJ/cm2, where the optical changes become almost saturated. The results provide insights into optimizing the fabrication process of THz devices, even those with a gradient and complex refractive index profile, by utilizing 3D printing technology for a broad range of applications.

Effects of ferrous ion doping on the structural, optical, and electronic properties of tin tungstate materials

Metal oxide materials have widespread applications in multiple application fields. On doping Fe3+ ions into α – SnWO4, structural, optical, and electronic properties varied noticeably leading the material into energy storage device applications. Pure and doped SnWO4 materials were prepared using the solid-state reaction method. Two different phases were observed on doping Fe ions into the host observed through X-ray diffraction. Different functional groups and their vibrations were found using FTIR spectroscopy which deliberately led to the confirmation of the prepared sample's structure. Raman spectroscopy identified different intra and inter-molecular vibrations. Optical energy bandgap was found to be 3.26 eV and 2.78 eV for Pure SnWO4 and SnWO4: Fe3+ ions respectively. The results obtained from Diffuse reflectance spectra were validated using Density Functional Theory calculations. The theoretical band gap values were found to be close to the experimental value. The optical spectra were also obtained through DFT calculations which were reliable to experimental findings and exciton binding energies were discussed.

Laser-induced reconfigurable wavefront control with a structured Ge2Sb2Te5-based metasurface

Phase change materials have been widely exploited in active metasurfaces due to their large index contrast. Despite recent advances in phase-change metasurfaces, it remains a challenge to integrate diverse reconfigurable optical functionalities into a single metasurface. Here, we demonstrate an effective strategy to realize reconfigurable wavefront control by combining a Ge2Sb2Te5-rod array with laser writing technology. Through arbitrarily modifying the position and power of laser source, the laser writing process helps to realize site-selective and multi-level phase change of Ge2Sb2Te5 rods. Due to multi-level switching for optical properties of Ge2Sb2Te5 material, the Ge2Sb2Te5-rod array offers complete phase control and high amplitude modulation. Subsequently, various optical devices are designed in numerical simulation, including a phase-only hologram, dynamic meta-deflectors, a grayscale image and a perfect absorber. The structured Ge2Sb2Te5-based metasurface with the combination of laser writing technology offers an effective way to explore various types of optical functionalities in the same device.

Strain effect on the electronic and optical characteristics of FAGeX3 (X=Cl, Br, and I) perovskite materials: DFT analysis

This study investigates the electronic and optical properties of a perovskite material known as Formamidinium Germanium Halide (FAGeX3), where X represents the elements Chlorine (Cl), Bromine (Br), and Iodine (I). We explore the bandgap, density of state (DOS), and partial density of state (PDOS) to understand their electronic properties. We use two methods, PBE and HSE-06, to determine the bandgap. Further, we investigate the optical properties by investigating the real and imaginary functions of the dielectric constant, refractive index, electron energy loss function, and absorption coefficient. Our research extends to the impact of biaxial strain, both tensile and compressive, in the −6% to +6 % range. Without strain, the materials exhibit direct bandgaps at the R point, with FAGeCl3 showing the highest bandgap (2.1359 eV), followed by FAGeBr3 (1.7325 eV), and FAGeI3 with the lowest (1.2581 eV). Our results reveal that applying tensile strain increases the bandgap and induces a blueshift, shifting the optical responses to shorter wavelengths, while compressive strain reduces the bandgap and causes a redshift, enhancing longer wavelength responses. Our findings demonstrate that FAGeX3 perovskites exhibit highly tunable electronic and optical properties under strain, making them exceptional candidates for advanced optoelectronic applications.

The DFT prediction of comprehensive properties of antiperovskites Mg6CX4 (X = S, Se, Te) and effects of defects and surface adsorption

It is important to search potential materials to meet ever-increasing demand in various fields. In order to understand the new hexagonal antiperovskites material Mg6CX4 (X=S, Se, Te), their mechanical, electronic and optical properties were studied based on density functional theory (DFT). The structural stability has been confirmed by the elastic constant criteria, formation energy, phonon dispersion spectra and ab-initio molecular dynamics (AIMD) simulation performed at 300 K. Besides, the Poisson's ratios over 0.26 demonstrate the ductility of the studied materials. They all have direct electronic band structures with bandgaps of 0.977 eV for Mg6CS4, 0.809 eV for Mg6CSe4 and 1.274 eV for Mg6CTe4, respectively. The calculated melting temperatures are all around 1000 K, which indicates the potential for high-temperature application. Therefore, Mg6CTe4 fits most for absorber in solar cells due to its proper bandgap and dispersive band edge. The antiperovskites exhibit high and broad light absorption in visible and near ultraviolet region with absorption coefficient greater than 104 cm−1, which inidcates a broad applicable prospect in optoelectronic field. Mg6CTe4 is also a candidate for efficient solid-state refrigeration due to its lowest thermal conductivity as 0.0046 W/(K•m). The defect analysis suggests that oxygen defects are the most favorable and have complex effects on bandgaps. The high bandgap sensitivity to surface adsorbates implies potential application in gas detector.

High-Resolution Infrared Reflectance Distribution Measurement Under Variable Temperature Conditions.

The bidirectional reflectance distribution function (BRDF) can effectively characterize the reflectance properties of a target, which can be used to correct infrared remote sensing data and improve the accuracy of remote sensing measurements. When the surface temperature changes, the reflectance characteristics of the target usually change, and it is necessary to carry out BRDF measurements under variable temperature conditions. In this paper, a variable-temperature infrared BRDF measurement system based on a robotic arm is developed to realize high-resolution wide-temperature region measurement of BRDF. To improve the measurement accuracy, the shaping optical path was used to expand the laser beam, combined with the laser level to accurately adjust the three-dimensional coordinates of the robotic arm, and the dichotomy method is used to calibrate the detector nonlinearly. A portable heater suitable for the mechanical arm corner mechanism is developed, and fast and high-precision temperature control is realized by proportional integral derivative (PID) control. The specular and diffuse BRDF distributions were measured at room temperature to verify the effectiveness of the system. The BRDF distribution of SUS314 stainless steel samples with different roughness is measured during two temperature increases from 20 °C to 1000 °C, and the changing rule of BRDF under variable temperature environment is summarized, which provides technical support for evaluating the optical properties of high-temperature materials and improving the measurement accuracy of remote sensing data.

Evaluation of optical and mechanical properties of crown materials produced by 3D printing.

The various advantages of crown materials produced using three-dimensional (3D) printers have increased their use in restorative and prosthetic dentistry in recent years. Accordingly, their optical and mechanical properties have become more important. To evaluate the mechanical, surface and optical properties of crown materials produced with 3D printing and computer-aided design (CAD)/computer-aided manufacturing (CAM), which has recently been used frequently in the clinic. The 3-point bending test was used to evaluate the mechanical properties of 2 different crown materials produced with 3D printing (Permanent Crown and VarseoSmile Crown Plus) and a crown material produced using CAD/CAM (Vita Enamic). After the initial color and surface roughness measurements were made, the specimens were immersed in 4 different solutions. The most translucent material was VarseoSmile Crown Plus (p < 0.05). In all specimens, coffee caused the most discoloration (p < 0.05). The effects of the solutions on the roughness were mostly observed in Permanent Crown specimens (p < 0.05). Vita Enamic showed the highest statistically significant values in terms of flexural strength (p < 0.05). The stereolithographic technique among the materials produced by 3D printing can be recommended for use in restorations due to its higher flexural strength.

Dual-Modal Illumination System for Defect Detection of Aircraft Glass Canopies.

Defect detection in transparent materials typically relies on specific lighting conditions. However, through our work on defect detection for aircraft glass canopies, we found that using a single lighting condition often led to missed or false detections. This limitation arises from the optical properties of transparent materials, where certain defects only become sufficiently visible under specific lighting angles. To address this issue, we developed a dual-modal illumination system that integrates both forward and backward lighting to capture defect images. Additionally, we introduced the first dual-modal dataset for defect detection in aircraft glass canopies. Furthermore, we proposed an attention-based dual-branch modal fusion network (ADMF-Net) to enhance the detection process. Experimental results show that our system and model significantly improve the detection performance, with the dual-modal approach increasing the mAP by 5.6% over the single-modal baseline, achieving a mAP of 98.4%. Our research also provides valuable insights for defect detection in other transparent materials.