Band Gap Of Crystal Research Articles

Electro-optical and thermal characterization of copper tartrate crystals grown in silica gel

Copper Tartrate crystals were grown by Gel Growth technique by single diffusion method. Silica gel of Optimum specific gravity was set with tartaric acid at optimum pH and aging period. Band gap of copper tartrate crystal is determined using to be 5.24 eV. In PL spectra broad peak is observed at nearly 367.44186 nm in the range 287 nm to 458 nm along with the sharp, intense transmission maxima peak at wavelength nearly 505.03876 nm which is characteristic of a material composition and electronic band structure. This shows the transparency of it in UV-Visible region and it as a filter in this range TGA analysis concludes that Copper tartrate has loss of one-half water molecule as crystalline water and is stable up to 85.02 ℃DSC analysis assigns the temperature value 314.5 ℃ as melting point and apparent enthalpy of fusion determined is 10.18 mW.

Crystal structure, bandgap, photoluminescence and resistivity properties of double perovskite Cs2AgBiCl6 single crystal and its thin film.

Lead-free Cs2AgBiCl6 double perovskite (Cs2AgBiCl6-DP) material, as a substitute for lead halide perovskite materials, has the advantages of environmental friendliness and high stability and has attracted much attention. However, the photoluminescence and conductive properties of Cs2AgBiCl6-DP have not been well studied. In this study, we prepared Cs2AgBiCl6-DP single crystals (SCs) by coordination-dissolution and coordination-precipitation method. Single- and powder-XRD, SEM, EDS, XPS, and EPR characterization were performed to confirm the structural characteristics of Cs2AgBiCl6-DP SCs. The Tauc diagram based on UV-visible (UV-vis) absorption spectroscopy reveals that the optical bandgap of Cs2AgBiCl6-DP SCs is extrapolated to 2.51 eV. Steady-state fluorescence spectra and time-resolved fluorescence spectra show that Cs2AgBiCl6-DP SCs has four fluorescence peaks entered at 443, 615, 650 and 723 nm and a fluorescence lifetime of about 4.16 ns. Cs2AgBiCl6/PMMA thin films were prepared by spin coating suspension (Cs2AgBiCl6 DP and PMMA in acetone solvent). The intensity of emission peak increases with the increase of light intensity at 369 nm. The intensity of emission peak located at 576 nm decreases with increasing incidence wavelength (from 369 to 454 nm) at 10 W m-2. The emission intensity remains basically unchanged under continuous illumination for 9 hours at 369 nm at 5 W m-2, which indicates that the Cs2AgBiCl6-DP thin film has good stability. In addition, the resistivity and block resistance show a negative exponential change with increasing temperature. These results provide some interesting ideas for the fields of photoluminescence and thermistors.

Expanding momentum bandgaps in photonic time crystals through resonances

Expanding momentum bandgaps in photonic time crystals through resonances

Adjusting the opening and closing of the bandgaps of plasma photonic crystals

Closing or opening the first two photonic bandgaps (PBGs) of plasma photonic crystals (PPCs) by adjusting the plasma parameters are studied. We first calculated the impedance of the band structure of one-dimensional PPCs and found that in the presence of plasma, the impedance under two certain frequencies can match that of the air. We have verified through simulation that when the two PBG frequencies and two impedance-matched frequencies are equal to each other, the two PBGs can be closed simultaneously under the same plasma density. On the other hand, a more common situation is that we need two plasma densities to, respectively, close the two PBGs located near different impedance-matched frequencies. At this point, by adjusting the plasma density, the PBGs can be closed in segments, that is, we can choose to close or open the corresponding PBGs at different plasma densities.

Electro-optical and thermal characterization of copper tartrate crystals grown in silica gel

Copper Tartrate crystals were grown by Gel Growth technique by single diffusion. Silica gel of Optimum specific gravity was set with tartaric acid at optimum pH and aging period. Band gap of copper tartrate crystal is determined using UV-Visible spectroscopy to be 5.24 eV. In PL spectra broad peak is observed at nearly 367.44186 nm in the range 287 nm to 458 nm along with the sharp, intense transmission maxima peak at wavelength nearly 505.03876 nm which is characteristic of a material composition and electronic band structure. This shows the transparency in UV-visible region and material is a filter in this range .TGA analysis concluded that Copper tartrate has one half water molecule as crystalline water and is stable up to 85.02 0 C.DSC analysis assigns the temperature value 314.5 0C as melting point and apparent enthalpy of fusion determined is 10.18 mW.

A semi-definite optimization method for maximizing the shared band gap of topological photonic crystals

Topological photonic crystals (PCs) can support robust edge modes to transport electromagnetic energy in an efficient manner. Such edge modes are the eigenmodes of the PDE operator for a joint optical structure formed by connecting together two photonic crystals with distinct topological invariants, and the corresponding eigenfrequencies are located in the shared band gap of two individual photonic crystals. This work is concerned with maximizing the shared band gap of two photonic crystals with different topological features in order to increase the bandwidth of the edge modes. We develop a semi-definite optimization framework for the underlying optimal design problem, which enables efficient update of dielectric functions at each time step while respecting symmetry constraints and, when necessary, the constraints on topological invariants. At each iteration, we perform sensitivity analysis of the band gap function and the topological invariant constraint function to linearize the optimization problem and solve a convex semi-definite programming (SDP) problem efficiently. Numerical examples show that the proposed algorithm is superior in generating optimized optical structures with robust edge modes.

Exploiting the Bragg Mirror Effect of TiO2 Nanotube Photonic Crystals for Promoting Photoelectrochemical Water Splitting.

Exploiting the Bragg mirror effect of photonic crystal photoelectrode is desperately desired for photoelectrochemical water splitting. Herein, a novel TiO2 nanotube photonic crystal bi-layer structure consisting of a top nanotube layer and a bottom nanotube photonic crystal layer is presented. In this architecture, the photonic bandgap of bottom TiO2 nanotube photonic crystals can be precisely adjusted by modulating the anodization parameters. When the photonic bandgap of bottom TiO2 nanotube photonic crystals overlaps with the electronic bandgap of TiO2, the bottom TiO2 nanotube photonic crystal layer will act as a Bragg mirror, leading to the boosted ultraviolet light absorption of the top TiO2 nanotube layer. Benefiting from the promoted UV light absorption, the TiO2 NT-115-NTPC yields a photocurrent density of 1.4 mA/cm2 at 0.22 V vs. Ag/AgCl with a Faradic efficiency of 100%, nearly two times higher than that of conventional TiO2 nanotube arrays. Furthermore, incident photon-to-current conversion efficiency is also promoted within ultraviolet light region. This research offers an effective strategy for improving the performance of photoelectrochemical water splitting through intensifying the light-matter interaction.

The Crystal Structure, Band Gap, and Optoelectronic Performance of Lead‐free Cs2PdBr4 Metal Halide Single Crystal and its Thin Film

AbstractPd‐based halide materials play an important role in organic synthesis, catalysis, and optoelectronic areas. As a typical metal halide, Pb‐based perovskite materials have the potential to become a newcomer in the field of photodetectors due to their excellent optoelectronic properties. However, the toxicity of lead has led to its unfriendliness to the environment. Herein, we synthesized the lead‐free Cs2PdBr4 metal halide single crystal (SC). The crystal structure of needle‐like Cs2PdBr4 SC is resolved and identified to monoclinic crystal system and C2 space group by X‐ray diffraction. The band gap of Cs2PdBr4 SC is extrapolated to 1.54 eV by absorption and reflection spectra. Cs2PdBr4 thin films (TFs) on ITO Interdigitated electrodes (IEs) were prepared by methods of vacuum evaporation. The photodetectors based on Cs2PdBr4‐ITO IEs exhibit regular responses under 397–564 nm monochromatic light, stable operation at weak light intensity of 1 mW/cm2 (397 nm), a responsivity of 0.27 mA/W and a detectivity of 1.13×106 Jones. This study can arouse interest in catalysis and photodetector.

On the lowest-frequency bandgap of 1D phononic crystals

This manuscript puts forward and verifies an analytical approach for the design of phononic crystals that feature a bandgap at the lowest possible frequencies, in the sense of finding the optimal layer thicknesses for a given set of materials in a prescribed layering order. The mathematical formulation rests upon the exact form of the half-trace function (half of the trace of the global transfer matrix) of the layered medium, which is directly connected to its bandgap structure. After showing that there is a tight relation between the frequency at which the first bandgap opens up and the curvature of the half-trace function at zero frequency, a new optimization strategy is proposed, based on the minimization of this curvature. Notably, the optimal solution is expressed as a closed-form equation and remains valid for any number of layers within the unit cell. We validate this analytical result by comparison with a numerically optimized design, finding remarkably good agreement between both solutions.

Improving photoelectrochemical performance of transferred TiO2 nanotubes onto FTO substrate with Mo2C and NiS as Co-catalyst

The photoelectrochemical (PEC) performance of titanium dioxide nanotube (TiO2 NT) photoelectrodes for sustainable hydrogen production has garnered significant research interest. Despite the advantages of TiO2 NT fabricated via anodization of titanium metal, such as their well-ordered vertical structure, challenges persist including the thick oxide barrier layer, limited optical transparancy, and the wide energy band gap (∼3.0 eV), which constrain their practical efficiency in PEC applications. This study addresses these limitations by introducing a novel approch to transfer TiO2 NT onto a fluorine-doped tin oxide (FTO) substrate. TiO2 NTs were synthesized with varying anodization times and steps to achieve optimal free-standing structures. To further enhance PEC performance, co-catalyst including molybdenum carbide (Mo2C) and nickel sulfide (NiS) were incorporated using immersion and successive ionic layer adsorption reaction (SILAR) methods, respectively. Comprehensive characterization using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), ultraviolet–visible–near infrared (UV–Vis–NIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) provided insights into the crystal phase, morphological structure, band gap, and elemental composition of the photoelectrodes. Photoelectrochemical and photostability evaluations were conducted through linear scan voltammetry (LSV) and chronoamperometry under dark and light conditions. Results indicate that transferring TiO2 NTs onto FTO significantly enhanced photocurrent density, achieving a 2.5-fold increase at 0.7 V versus a TiO2 NT/Ti substrate. The incorporating of co-catalysts Mo2C, NiS and the combined NiS/Mo2C further enhanced the photocurrent density to 2.20, 3.00 and 8.00 mA cm−2 respectively, with a remarkable 31-fold enhancement compared to the TiO2 NT/Ti substrate. This findings underscore the potential of the TiO₂ NT/FTO photoelectrode with optimized co-catalyst integration for advanced photoelectrochemical applications.

Infrared Stealth Coating with Tunable Structural Color Based on ZnO Spheres.

It is important to develop low infrared (IR) emissive coating with tunable structure color to improve the infrared-visible stealth performance of military equipment. In this work, uniform ZnO spheres are used as building units to construct photonic structures with both bright adjustable structure color and low IR emissivity due to the relatively high refractive index and low IR emissivity of ZnO. The vivid tunable structural colors are provided by the photonic bandgap of ZnO photonic crystals (PCs) or the quasi-bandgap of amorphous photonic crystals (APCs), respectively. Both ZnO PCs and APCs exhibited low IR emissivity in 3-5µm. The IR emissivity of 255nm ZnO PCis 0.483 and the IR emissivity of 255nm ZnO APC is 0.492 at 25°C. With the increase of temperature, the IR emissivity offurther decreased to 0.295 and 0.312 at 300°C. These structures can be applied to a variety of surfaces, and all these structures have good thermal and light stability as well. This work may open a simple and effective way to fabricate materials with good infrared-visible stealth performance, expanding the application of ZnO PCs and APCs coatings in the camouflage area.

Synthesis and Upconversion Luminescence Fine-tuning of Yb3+/Ho3+-Doped Indium and Gallium Oxide Nanoparticles.

Rare earth (RE) dopants can modulate the bandgap of oxides of indium and gallium and provide extra upconversion luminescence (UCL) abilities. However, relevant UCL fine-tuning strategies and energy mechanisms have been less studied. In this research, InGaO, Ho3+ monodoped and Yb3+/Ho3+ codoped In2O3, and Ho3+ monodoped Yb3Ga5O12 nanoparticles (NPs) were synthesized by a solvothermal method. The effects of Yb3+ and Ho3+ dopants on the crystal structures, UCL properties, and optical bandgaps of the oxides were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UCL spectroscopy, and measurements of decay times, pump power dependence, and transmittance spectra. The crystal structures of oxide products of indium and gallium were significantly modified with RE dopants. In2O3 and Yb3Ga5O12 were selected as the host materials. For Yb3+/Ho3+ codoped In2O3 NPs, there existed energy transfers from the defect states of In2O3 to Ho3+ and from Yb3+ to Ho3+. With a fixed Ho3+ concentration, In2O3:0%Yb3+,2%Ho3+ NPs showed the optimal UCL properties mainly due to In2O3-Ho3+ energy transfer and Ho3+-Yb3+ energy-back-transfer, while with a fixed Yb3+ concentration, In2O3:5%Yb3+,3%Ho3+ NPs with a slight Yb2O3 impurity and Yb3Ga5O12:2%Ho3+ NPs did mainly due to Ho3+-Ho3+ cross-relaxation. Besides, the optical bandgaps of In2O3 and Yb3Ga5O12 were noticeably broadened with RE dopants. These findings can offer feasible directions for the synthesis and UCL fine-tuning of RE-doped oxides of indium and gallium and improve their multifunction application prospects in the fields of semiconductor and UCL nanomaterials.

Isogeometric topology optimization for maximizing band gap of two-dimensional phononic crystal structures

A smooth and efficient isogeometric topology optimization (ITO) method for maximizing band gaps in two-dimensional phononic crystals is developed in the paper. The band gaps of phononic crystals are computed by the NURBS-based isogeometric analysis, and the material distributions of two-dimensional phononic crystals are represented by the smooth, high-order continuity of the NURBS surface. The densities defined at each control point of the NURBS surface are employed as optimized design variables. The isogeometric analysis optimization using the same spline technique for both geometry and numerical analysis can benefit the optimization procedure and obtain smooth optimized structures, which can be easily used in 3D printing. The maximizing band gaps of phononic crystals for both out-of-plane and in-plane wave modes are obtained here using the present ITO approach. Numerical examples validated the effectiveness and reliability of the ITO method in broadening the band gaps and finding the optimal phononic crystals. And the numerical results show that the smooth optimized structures are obtained with fewer iterations.

Synthesis of MoS2@MoO3/(Cu+/g-C3N4) ternary composites with double S-scheme heterojunction for peroxymonosulfate activation exposing to visible light

The construction of semiconductor heterojunction is an effective way for charge separation in photocatalytic degradation of pollutants. In this study, a novel MoS2@MoO3/(Cu+/g-C3N4) ternary composites (MMCCN) was prepared via a simple calcination method. The as-prepared composites exhibited exceptional performance in activating peroxymonosulfate (PMS) for the degradation of rhodamine B (RhB). The activity testing results indicated that 99.41 % of RhB (10 mg·L−1, 10 mL) was effectively removed by the synergistic effect of composites photocatalyst (0.1 g·L−1) and PMS (0.1 g·L−1) under visible light irradiation for 40 min. Its reaction rate constant exceeded that of Cu+/g-C3N4, MoO3 and MoS2 by a factor of 3.56, 17.30 and 11.73 times, respectively. The crystal structure, band gap and density of states (DOS) of the semiconductors were calculated according to the density functional theory (DFT). Free radical trapping tests and electron spin resonance spectroscopy validated that 1O2, O2− and h+ are primary reactive species participating in the decomposition of RhB. The ternary composites demonstrated good stability and maintained excellent degradation efficiency even across four reaction cycles. Furthermore, the activation mechanism and the intermediates produced during the decomposition course of RhB by MMCCN/PMS/vis system were analyzed and elucidated. A double S-scheme heterojunctions was responsible for efficient separation of photo-induced electron-hole pairs. This work presents a novel method in the construction of double S-scheme heterojunctions for PMS activation which is expected to find wide applications in wastewater treatment and environmental remediation.

Printing of 3D photonic crystals in titania with complete bandgap across the visible spectrum.

A photonic bandgap is a range of wavelengths wherein light is forbidden from entering a photonic crystal, similar to the electronic bandgap in semiconductors. Fabricating photonic crystals with a complete photonic bandgap in the visible spectrum presents at least two important challenges: achieving a material refractive index > ~2 and a three-dimensional patterning resolution better than ~280 nm (lattice constant of 400 nm). Here we show an approach to overcome such limitations using additive manufacturing, thus realizing high-quality, high-refractive index photonic crystals with size-tunable bandgaps across the visible spectrum. We develop a titanium ion-doped resin (Ti-Nano) for high-resolution printing by two-photon polymerization lithography. After printing, the structures are heat-treated in air to induce lattice shrinkage and produce titania nanostructures. We attain three-dimensional photonic crystals with patterning resolution as high as 180 nm and refractive index of 2.4-2.6. Optical characterization reveals ~100% reflectance within the photonic crystal bandgap in the visible range. Finally, we show capabilities in defining local defects and demonstrate proof-of-principle applications in spectrally selective perfect reflectors and chiral light discriminators.

Anisotropic ferroelectric-shaped hysteresis loop and colossal permittivity in thermally treated rutile TiO2 single crystals

Space charge polarization is an unavoidable phenomenon in electronic components that leads to deterioration of electrical response. Hence manipulation and utilization of space charge polarization to improve electrical properties is a phenomenal task. In the present study, heating treatment produces oxygen vacancies, resulting in the crystal structures (i.e., modulated structure and intergrowth structure) and band gap are anisotropic, which in turn leads to anisotropic nonlinear polarization behavior and colossal permittivity. Quantitative analysis of the atomic-scale structure confirms the modulated structure and intergrowth structure are anisotropic. A modulated structure along a axis of rutile TiO2 with a width of six times that of a rutile crystal cell a is constructed through an intergrowth structure between rutile and srilankite TiO2 phases in rutile TiO2 single crystals, wherein space charges at the intergrowth structure give rise to ferroelectric-shaped hysteresis in heated TiO2 single crystals along [001] direction. Impedance spectra display three kinds of space charge polarizations (modulated structure, intergrowth structure, and electrode non-ohmic contact) contribute to the colossal permittivity along [001] direction. The space charge polarizations contribute to a colossal permittivity (∼45,000), high resistivity (∼1010 Ω cm), and ferroelectric-shaped P-E loop (remanent polarization: ∼17.1 μC/cm2, coercive field: ∼4.3 kV/cm) in the heated TiO2 single crystal along [001] direction, while a linear polarization behavior and permittivity value of 120 are obtained along [100] direction. The findings provide guidance for the utilization of space charge polarization in dielectric materials.

Solar-blind ultraviolet photodetector derived from direct carrier transition beyond the bandgap of CdPS3 single crystals

Solar-blind ultraviolet photodetector derived from direct carrier transition beyond the bandgap of CdPS3 single crystals

Origin and tuning of bandgap in chiral phononic crystals

The wave equation revealing the wave propagation in chiral phononic crystals, established through force equilibrium law, conceals the underlying physical information, such as the essence of the motion coupling and the inertial amplification effect. This has led to a controversy over the bandgap mechanism. In this article, we theoretically unveil the reason for this controversy, and put forward an alternative approach from wave behavior to formulate the wave equation, offering an alternative pathway to articulate the bandgap physics directly. Based on the physics revealed by our theory method, we identify the obstacles in coupled acoustic and optic branches to widen and lower the bandgap. Then we introduce an approach based on spherical hinges to decrease the barriers, for customizing the bandgap frequency and width. Finally, we validate our proposal through numerical simulation and experimental demonstration.

Ultrasensitive Detection of Cancer Biomarkers Using Photonic-Crystal-Enhanced Single-Molecule Imaging.

The rapid and sensitive quantification of low-abundance protein markers holds immense significance in early disease diagnosis and treatment. Single-molecule fluorescence imaging exhibits very high detection sensitivity and thus has great application potential in this area. The single-molecule signal, however, is often susceptible to interference from background noise due to its inherently weak intensity. A variety of signal amplification techniques based on cascading reactions have been developed to improve the signal-to-noise ratio of single-molecule imaging. Nevertheless, the operation of these methods is typically complicated and time-consuming, which limits the clinical application. Herein, we introduce an enzyme-free, photonic-crystal-based single-molecule (PC-SM) biochip for cost-effective, time-efficient, and ultrasensitive detection of disease markers. The PC-SM biochip can enhance the signal-to-noise ratio of single molecules by nearly 3-fold compared with unamplified samples, through coupling of the single-molecule photon energy with the optical band gap of the photonic crystal. We used the PC-SM biochip to detect the low-abundance leukemia inhibitory factor in the blood of pancreatic cancer patients and healthy people and achieved a detection limit of 2.0 pg/L and an AUC of 0.9067. The method exhibits exceptional sensitivity and specificity, showing great application potential in various clinical settings.

Heteroepitaxial α‐Ga2O3 Thin Film‐Based X‐Ray Detector with Metal–Semiconductor–Metal Structure

This study explores the potential of 700‐nm‐thick heteroepitaxial α‐Ga2O3 thin films on c‐plane sapphire substrates for X‐ray detector applications. The crystal quality and optical bandgap of the heteroepitaxial α‐Ga2O3 thin films are comparable to those of high‐quality α‐Ga2O3 thin films. The α‐Ga2O3 thin film X‐ray detector with a metal–semiconductor–metal structure exhibits a charge neutral point shift, resulting in a short‐circuit current density of 9.07 nA cm−2 and an open‐circuit voltage of –1.2 V. The detector achieves the highest signal‐to‐noise ratio of 973 at 0 V, while the maximum sensitivity (14.7 μC Gyair−1 cm−2) occurs at 10 V. The proposed X‐ray detector demonstrates a reliable transient response and long‐term robustness, suggesting the promise of heteroepitaxial α‐Ga2O3 for low‐cost, high‐quality, large‐area X‐ray detectors.