Variation Of Band Gap Research Articles

Phosphoborane nanosheets as a sensing element for liquefied petroleum gas – A first-principles study

Nowadays, elemental monolayer materials are focused by the research communities due to their excellent selectivity, sensitivity, and stability toward air pollutants. In the present work, we deployed stable phosphoborane as a sensor to detect Liquefied Petroleum Gas (LPG) gases, namely isobutane and n-propane. Initially, the structural stability of pure phosphoborane is verified by cohesive energy. Further, the electronic characteristics of phosphoborane are studied with the support of band structure and projected density of states (PDOS) spectrum. The band gap of phosphoborane is calculated to be 2.734 eV (hybrid-GGA/B3LYP) which shows a semiconducting nature. Significantly, the adsorption properties of isobutane and n-propane molecules on phosphoborane are studied by ascertaining adsorption energy, relative band gap variation, and Mulliken charge transfer. In particular, the computed adsorption energy is noticed in the physisorption regime (−0.225 eV to −0.774 eV) and the Mulliken charge transfer is found in the range of 0.027 e to 0.223 e that infers the proposed phosphoborane is a promising sensor to detect the LPG molecules.

First-principles investigation of the ultra-wide band gap halides perovskite XBeF3 (X = Na, K) with pressure effects

Based on the first-principles and quasi-harmonic Debye model, the structure, electronic, optical and thermodynamic properties of XBeF3 (X = Na, K) crystals at 0 ∼ 30 GPa are systematically investigated for the first time. The lattice constant, elastic constants, and bulk modulus of NaBeF3 and KBeF3 crystals are calculated under zero temperature and zero pressure, which are consistent with the literature values. The studies of electronic properties show that the ultra-wide band gaps of NaBeF3 and KBeF3 crystals at 0 GPa are 7.096 eV and 7.720 eV, respectively. Their band gaps increase with increasing pressure, while their type is indirect without the influence of pressure. Besides, the band structure of XBeF3 crystals at 0 ∼ 30 GPa is calculated by HSE06 functional. The variation of the XBeF3 band gap calculated by the HSE06 function with pressure is consistent with the trend of GGA functional. Additionally, the optical properties including reflectivity, absorption coefficient, complex refractive index, dielectric function and conductivity of NaBeF3 and KBeF3 crystals from 0 to 30 GPa have been comprehensively investigated. Using the quasi-harmonic Debye model, the relative volume, expansion coefficient, Debye temperature and heat capacity effect with pressures and temperatures of NaBeF3 and KBeF3 at 0 ∼ 30 GPa are also researched. The Debye temperatures of NaBeF3 and KBeF3 at 300 K are calculated to be 656.38 K and 602.6 K respectively. At relatively high temperature, the heat capacity at constant volume gradually approaches the Dulong-Petit limit. The results in this paper show that NaBeF3 and KBeF3 crystals may be used in the fields of lens materials and window materials in the deep ultraviolet range. Additionally, the ultra-wide band gap characteristics of NaBeF3 and KBeF3 enable them to be useful as highly insulating layers and high-voltage capacitors.

Experimental analysis of methylammonium and Formamidinium-based halide perovskite properties for optoelectronic applications

Nowadays, the toxicity of lead in metal-halide perovskites is the most precarious obstruction in the commercialization of perovskite-based optoelectronic devices. However, Pb-free metal halide perovskites as environment-friendly materials because of their exceptional properties, such as band-gap tunability, narrow emission spectra, low toxicity and easy solution-processability, are potential candidates for optoelectronic applications. Recently, literature reported the poor structural stability and low-emission intensity of Bi-based perovskite NCs. Still, this paper focuses on the fabrication of Formamidinium (FA)-based Bi mixed halide and Methylammonium(MA)-based Bi-pure halide perovskites using Ligand-Assisted Reprecipitation Technique (LARP) technique. XRD diffraction patterns of FA-based perovskites were slightly broad, signifying the nanocrystalline form and limited size of perovskite nanocrystals. While the XRD diffraction patterns of MA3Bi2X9 (X = Cl/Br/I) perovskites were narrow, signifying the amorphous nature and larger size of perovskite nanocrystals. The peak positions were varied in MA-based bismuth halide perovskites with respect to the halide variation from Br to Cl to I ions. The optical study shows the variation in band gap and average lifetime with respect to halide variation leading to enhanced optical properties for device applications. The band-gap of FA3Bi2BrxCl1-x & FA3Bi2IxCl1-x perovskites was calculated to be around 3.7 & 3.8 eV, respectively, while in MA-halide perovskites the band-gap was calculated to be 2.8 eV, 3.1 eV & 3.4 eV with respect to halide variation from I to Cl to Br in perovskite samples using Tauc's plot respectively. Moreover, simulation is carried out using the SCAPS-1D software to study the various parameters in MA & FA-based Bi-pure or mixed halide perovskites. Here, we discussed the variation in efficiency with respect to the thickness variation from 100 to 500 nm for MA3Bi2I9 halide perovskites. These MA3Bi2I9 halide perovskites show minimum efficiency of 4.65 % at 100 nm thickness, while the perovskite sample exhibits maximum efficiency of 10.32 % at 500 nm thickness. Thus, the results stated that the thickness of absorber layers directly affects the device characteristics for optoelectronic applications.

The effect of pH adjustments on the structural and optical properties of CIAS thin films

CIAS, ‘Cu (In Al) Se2’ thin films are prepared on the glass substrates using economical chemical bath deposition ‘CBD’ technique. The effect of pH adjustments before or after preheating the reaction mixture has been discussed in this paper in a detail. Due to pH adjustment the change in the preferential orientation on the structural properties and the band gap variation with respect to thickness on the optical properties, has also been discussed.

A numerical approach to study the effect of bandgap and electron affinity in HTL-free perovskite solar cells and design of two-terminal silicon/perovskite tandem solar cell

The hole-transport layer (HTL) free perovskite solar cells with carbon electrode (c-PSCs) have garnered significant attention owing to their simple design, cost-effectiveness, and good stability. However, the power conversion efficiency (PCE) of these cells is still very low in comparison to conventional PSCs that utilize HTLs and metal electrodes. Tandem solar cells (TSCs) based on perovskite and crystalline silicon (c-Si) solar cells are considered possible contenders for surpassing the theoretical maximum limit and addressing the efficiency constraints encountered in single junction PSCs. The current research work assesses the design and optimization of a c-Si/c-PSC-based two-terminal (2-T) monolithically coupled TSC utilizing a one-dimensional solar cell capacitance simulator (SCAPS-1D) software. Initially, a detailed examination of standalone c-PSC has been conducted to evaluate bandgap and electron affinity variation. Then, the optimized c-PSC was integrated with the bottom c-Si cell by adopting a widely employed current matching technique. An investigation was undertaken to identify a current matching condition between two subcells that yielded optimal performance for the device. Under optimum conditions, a Voc of 2.138 V, Jsc of 15.60 mA/cm2, FF of 85.79%, and PCE of 28.62% were achieved in a 2-T monolithically connected tandem cell. We believe the results acquired in this study would be of significant importance in advancing highly efficient 2-T tandem cells based on HTL-free c-PSCs.

High-performance normally off AlGaN/GaN high electron mobility transistor with p-type h-BN cap layer

Normally off AlGaN/GaN high electron mobility transistors (HEMTs) with p-type gates are attracting increasing attention due to their high safety and low power loss in the field of power switching. In this work, to solve the Mg difficult activating problem of the conventional p-GaN gate AlGaN/GaN HEMTs, we propose an advanced design for the normally off AlGaN/GaN HEMT with a p-type hexagonal boron nitride (h-BN) gate cap layer to effectively manipulate the channel transport of the device. The simulation results demonstrate that the p-hBN gate cap HEMTs yield superior performance over conventional p-GaN gate HEMTs in terms of output current and breakdown voltage, which can be attributed to the deeper potential well formation at the AlGaN/GaN interface and more accumulation of holes located at the p-hBN/AlGaN interface. Moreover, we investigate the effect of bandgap variation on device performance, taking into account that the exact bandgap of h-BN remains under debate. Herein, valuable insights into h-BN cap-gate E-mode AlGaN/GaN HEMT devices are provided, which could serve as a useful reference for the future development of robust III-nitride material power electronic devices.

Synthesis of Na0.02Bi0.98FeO3-δ through the standardized preparation of BiFeO3

This research describes the synthesis of the ferroelectric perovskite Na0.02Bi0.98FeO3-δ using a low-cost solid-state method starting from a bismuth ferrite BiFeO3 structure in order to obtain a material with improved properties for photovoltaic applications. The synthesized materials were characterized by X-ray Diffraction (XRD) technique to determine the effective synthesis conditions for six undoped BiFeO3 samples obtained at different calcination temperatures and quantified by Rietveld® refinement of diffraction patterns, finding homogeneous phase formation at 810 °C under laboratory conditions. The effective synthesis temperature allowed obtaining a stable perovskite-type material, doped with Na+ and its structural characterization by XRD showed a structural modification in the unit cell with respect to BiFeO3 due to the incorporation of sodium cation. The binding energies determined by X-ray photoelectron spectroscopy (XPS) confirmed the formation of the main crystalline phase and the insertion of Na+ cations inside perovskite structure. The morphological characterization by scanning electron microscopy (SEM) of the synthesized material showed the formation of two stable morphologies: Bi2Fe4O9 and Na0.02Bi0.98FeO3-δ as the predominant phase. The optical characterization by Raman spectroscopy allowed identifying variations in the vibration modes of the perovskite doped with respect to undoped bismuth ferrite. The variation of the optical bandgap was determined using the Tauc’s equation and the electrical characterization by solid state electrochemical impedance spectroscopy (SS-EIS) demonstrated an increase in electrical conductivity, at room temperature, by the Na+ doped perovskite, proving an optimal behavior for its potential uses as a semiconductor. The results indicate that the current methodology is promising for the low-cost production of Na0.02Bi0.98FeO3-δ type perovskites for photovoltaic applications.

Effects of time-delayed vibration absorber on bandwidth of beam for low broadband vibration suppression

The effects of time-delayed vibration absorber (TDVA) on the dynamic characteristics of a flexible beam are investigated. First, the vibration suppression effect of a single TDVA on a continuous beam is studied. The first optimization criterion is given, and the results show that the introduction of time-delayed feedback control (TDFC) is beneficial to improving the vibration suppression at the anti-resonance band. When a single TDVA is used, the anti-resonance is located at a specific frequency by the optimum design of TDFC parameters. Then, in order to obtain low-frequency and broad bands for vibration suppression, multiple TDVAs are uniformly distributed on a continuous beam, and the relationship between the dynamic responses and the TDFC parameters is investigated. The obtained relationship shows that the TDVA has a significant regulatory effect on the vibration behavior of the continuous beam. The effects of the number of TDVAs and the nonlinearity on the bandgap variation are discussed. As the multiple TDVAs are applied, according to the different requirements on the location and bandwidth of the effective vibration suppression band, the optimization criteria for the TDFC parameters are given, which provides guidance for the applications of TDVAs in practical projects such as bridge and aerospace.

Growth kinetics of crumb-like structure formation on SnO2 nanowires during direct oxidation

A facile AAO (anodic aluminum oxide) template-assisted vacuum die-casting technique was used to create Sn nanowires and convert them into SnO2 without degrading the wires nanostructure. As a function of time and temperature, the controlled oxidation on the Sn nanowires of two different spatial configurations (100 and 250 nm in diameter) revealed distinct oxidation mechanisms. The 250-SnO2 nanowires exhibits a peculiar crumb-like structure formation over the surface due to the higher level of Sn atom dislocation. Conversely, the sub-100 nm SnO2 nanowires shows a highly crystalline, homogenous, and defect-free surfaces. The optical properties of the sub-100 nm SnO2 nanowires were characterized using UV–Vis spectroscopy. The heat-treated tin oxides nanowires samples at temperatures of 300, 500, and 700 °C for 7 h exhibited optical energy bandgaps of 1.8, 2.6, and 3.3 eV, respectively. The observed variation in bandgap is attributed to the unique phase compositions achieved in each of the heat-treated samples. Moreover, the obtained results showed exceptional structural integrity and optical properties that are inherently interconnected with the diverse phases achieved under precise heat treatment conditions.

Effects of structure parameters on kink states of two-dimensional valley photonic crystals

We construct graphene-like valley photonic crystals (VPCs) by breaking spatial inversion symmetry in two-dimensional (2D) all-dielectric photonic crystals with honeycomb lattice. By tuning sizes of two scattering rods in unit cell, variations of topological band gaps of VPCs are investigated in detail. Further, valley-locked kink states and their unidirectional propagations are numerically studied by constructing two kinds of zigzag waveguide interfaces between two VPCs with opposite valley Chern number. Our results show that changing structure parameters of VPCs can effectively tune topological band gaps, adjust configurations of valley kink states, and control their unidirectional propagations, and particularly in some cases, resonant structures along waveguide interface can even destroy the valley-locked unidirectional propagations of kink states. We also investigate transverse localizations of kink states and reveal their robustness as they propagate along the interfaces. Our research gives further understandings on properties of VPCs, provides detailed regulation of kink states with change of structure parameters and paves the way for design of photonic devices based on VPCs.

Structural, dielectric and electronic properties of Ba1-xSrxZr0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.24, 0.27, 0.3) ceramics: Combined experimental and ab-initio study

Ba1-xSrxZr0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.24, 0.27 and 0.3) materials were synthesized using conventional solid state reaction route. Structural properties were investigated using X-ray diffraction analysis. All the samples reveal single phase structure. The dielectric properties of all the samples were investigated at different temperatures of 100 K to 300 K, and at different frequencies of 1 kHz to 500 kHz. The diffusivity rises with increase in Sr divalent cation concentration. It is seemed that with increase in Sr2+ concentration the transition temperature reduces for all compositions. This may because of the introduction of Sr2+ by replacing Ba2+ since Sr+2 has smaller ionic radius than Ba+2. Moreover, the dielectric constant maxima for Ba1-xSrxTi0.7Zr0.3O3 increases up to x = 0.24 and then further increment in Sr content up to x = 0.3, the maxima of dielectric constant shows decrease. Moreover, charge conduction mechanism and optical response of Ba1-xSrxZe0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.3) has been calculated theoretically by using CASTEP. Herein, the calculated density of states (DOS) and three dimensional integrated charge density reveal that concentration of Sr in Ba1-xSrxZe0.3Ti0.7O3 (x = 0.1, 0.2, 0.3) causes variation in energy band gap. As regards optical response of Ba1-xSrxTi0.7Zr0.3O3, with x = 0.3 the high frequency absorption decreases to minimal value in accordance to experimental findings.

Doped CeO2/water nanofluids analyzed the performance of thermal conductivity and heat transfer: An experimental and theoretical investigations

A combined experimental and theoretical study on thermal conductivity, heat transfer specific heat, and electronic properties has been done for doped CeO2/water nanofluid. First, the sol-gel method was implemented for the synthesis of doped CeO2 nanoparticles and then a mixture of nanoparticles with different concentrations of nanofluid. X-ray diffraction and SEM analysis confirm the structural phase purity and homogeneous mixing of nanofluids. Experimental thermal conductivity and specific heat of pure and 4f-doped CeO2 were estimated and found very close to our theoretical calculations. Experimental investigations have been carried out for the measurement of heat transfer using pure and doped CeO2/water nanofluid as the coolant. The experiments were aimed at determining the heat transfer and other thermal properties with different concentrations and with various fluid with Reynolds number 2500 and 3500. The heat transfer coefficient of nanofluids increases not only with an increase in the volume flow rate of the hot water but also increases with increase in the atomic number of dopant elements in CeO2. Electronic states show variation in band gap with doping which may also play an important role in the improvement of solar collectors. It is clear from experimental and theoretical findings that the thermal and electronic properties depend on number of valance electrons. Hence doping of 4f-element in CeO2 plays a vital role to increase the thermal conductivity and tuning of electronic properties leads to many applications in thermal sensors and solar cell-based industries.

Structural, Optical, Magnetic and Dielectric Properties of Ce-Doped MgFe2O4 Prepared by Microwave Hydrothermal Method

The microwave hydrothermal method has been used to synthesize MgFe2-x Ce x O4 (x = 0.0 – 0.10) nanoparticles, which have been characterized using X-ray diffraction (XRD), fourier transform Infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectrometer, vibrating sample magnetometer (VSM) and dielectric properties. XRD investigation confirms the cubic spinel structure, and the Debye–Scherrer formula was used to determine the crystallite size, showing values of 19 – 108 nm. FTIR confirms the presence of all functional groups and FE-SEM displays particle-like morphology. The UV-visible analysis was used to explain the variation of the optical bandgap as Ce3+ doping increased. VSM analysis of MgFe2-x Ce x O4 showed ferromagnetic behaviour. The samples exhibit low magnetization values ranging from 8.83 emu g−1 to 18.91 emu g−1. The values of the dielectric constant (ε′) and the dielectric loss (tanδ) decreased with frequency due to the influence of space-charge polarization and showed a dispersive behaviour at higher frequencies.

Role of nanoscale compositional inhomogeneities in limiting the open circuit voltage in Cu(In,Ga)S2 solar cells

As Si-based solar cell technologies approach their theoretical efficiency limits, alternative photovoltaic systems, such as tandem solar cells, are gathering increased attention due to their potential to reach higher efficiencies by better use of the solar spectrum. Cu(In,Ga)S2 (CIGS) is a promising material for the top cell due to its large, tunable bandgap energy (Eg), stability, and already established high efficiencies. However, the deficit in open circuit voltage is still large; therefore, an improved understanding of the efficiency losses is required. Scanning electron microscopy cathodoluminescence was used to study the role of the polycrystalline nature for radiative recombination in CIGS samples of varying Cu-content. Considerable differences between neighboring grains were observed in the emission energy and the emission intensity, with significant drops in emission energy at the grain boundaries. Lateral homogeneity in the near band edge (NBE) energy was found to reduce for samples with Cu-poor compositions, with its standard deviation halving (σNBE ∼ 20 meV) compared to the more stoichiometric films (σNBE ∼ 50 meV), which corresponds to an open circuit voltage loss contribution that is nearly an order of magnitude lower. Such inhomogeneities can be attributed mainly to local variations of the Ga concentration. Hence, the differences between the samples could be explained by the different deposition times at elevated temperature allowing for different extents of homogeneity. Thus, Cu-poor films are not only favorable because of lower concentrations of deep defects but also because of reduced bandgap variations.

Structural phase transition driven dielectric and optical properties with reduction in band gap in Sr2+ modified BaTiO3 ceramics

Ferroelectric materials with crystal symmetry transition from single phase to multiphase coexistence exhibit anomalous photosensitive properties. The optical properties (optical band gap and photosensitive) found on non-centrosymmetric and centrosymmetric systems achieved research interest because of their interesting behavior. In this regard, the lead-free polycrystalline Ba1−x Sr x TiO3 (BSTO, 0 ) has been synthesized to explore its crystal structure, dielectric, light absorption, and photocurrent sensing properties for various applications. Both experimental and theoretical studies on BSTO (0 ceramics confirm the crystal symmetry transition with the reduction of band gap as compared to pristine BaTiO3. This crystal symmetry transition plays an important role in varying the various physical properties as it involves the transition from the polar phase to the non-polar phase. The optical band gap has been estimated experimentally by the Tauc plot method and found that there is a small variation of energy band gap from 3.615 eV to 3.212 eV with Sr substitution. The highest dielectric constant was found to be 5327 at lower frequency on Ba0.76Sr0.24TiO3 after that for further increase in Sr concentration the dielectric constant decreases because of the introduction of the non-polar phase. A strong correlation between crystal structure and physical properties (dielectric, optical, etc.) has been observed. The photocurrent of the samples is significant which reveals that the sample is influenced by the photons. In a nutshell, the present study deepens the understanding of the correlation between crystal structure and various physical properties of BSTO and, hence provides an idea of required design parameters to construct a ferroelectric system for better photosensitive nature suitable for device applications.

Adsorption Analysis at Critical Temperature of PM2.5 Contaminants

Increasing levels of PM2.5 (Particulate Matter having a diameter less than 2.5 µm) offer the highest risk, leading to a multitude of serious health complications, and hence the high-performance monitoring of these tiny pollutants may help to safeguard people's health. The sensitivity of PM2.5 pollutants to bulk gold as an application of sensors is investigated using the industry standard virtual nanolab. Within the framework of linear combination of atomic orbital (LCAO) computation, the density functional theory (DFT) is implemented using the Kohn–Sham formulation to analyze the electronic properties of bulk gold Au (111) substrate for specific PM2.5 pollutants (sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon dioxide (CO2), nitric oxide (NO), and carbon monoxide (CO)) sensing. The results demonstrate that different gases are adsorbed differently on Au (111), depending on their critical temperature (TC ). Consequently, NO is observed to be highly sensitive to Au (111) substrate due to its large band gap variation of −31% to −57%, considerable adsorption energy of −1.05 eV, and an improved charge transfer of 0.02 eV.

Comparative analysis of photovoltaic thermoelectric systems using different photovoltaic cells

The photovoltaic-thermoelectric (PV-TE) system has emerged as a focal point in research endeavors aimed at harnessing the full spectrum of solar energy and enhancing the efficacy of solar power generation. Owing to the variations in bandgap and inherent material properties across diverse photovoltaic cells, the capacity to utilize the solar spectrum of PV-TE systems can be significantly affected when using different photovoltaic cells. Historically, investigations into the influence of photovoltaic cells on PV-TE systems have been predominantly rooted in theoretical simulations. These examinations have primarily concentrated on the holistic system efficiency under varying temperature conditions. In this study, we integrated three distinct types of photovoltaic cells into PV-TE systems. Both simulation and experimental methodologies were employed to evaluate the impact of these photovoltaic cell types on the PV-TE systems' performance. Additionally, we compared the back temperatures of standard PV systems with those of PV-TE systems. The average photovoltaic conversion efficiencies of PV-TE systems equipped with CIGS, CdTe, and a-Si photovoltaic cells were 21.9%, 19.7%, and 12.7%, respectively. Meanwhile, the average efficiencies of TEG were 0.256%, 0.102%, and 0.083% respectively, with average backplate temperatures of 39.3 °C, 44.0 °C, and 40.5 °C. The temperature disparities between the back of standard photovoltaic systems and PV-TEG-PCM systems stood at 4.70 °C, 2.32 °C, and 3.43 °C, respectively. Notably, CIGS photovoltaic cells, which harness a specific range of the solar spectrum more effectively, showcased superior performance. Furthermore, a broader usable solar spectrum band for a PV cell doesn't always translate to enhanced performance. These findings offer valuable insights for optimizing the power generation capabilities of photovoltaic-thermoelectric systems leveraging full-spectrum solar energy.

Modeling Size and Shape Dependence of Electro-Optical Properties of Semiconductor Nanosolids

Based on cohesive energy, the size and shape effect on Bandgap, Dielectric constant and Phonon frequency of low-dimension semiconductor nanomaterials are predicted with structural miniaturization down to the nanoscale. It is projected that nanomaterial’s optical and electrical properties no longer remain constant but become tunable. The model reports that the bandgap increases while the dielectric constant and phonon frequency drop on decreasing size to the nanoscale. The bandgap variation, dielectric constant and phonon frequency are reported for spherical, thin film, nanowire, regular tetrahedral and regular octahedral shapes of semiconductor nanosolids. The shape effect becomes prominent as the form changes from spherical to regular tetrahedral shape up to the size limit of 20 nm. A good agreement between our model predictions and the available experimental and simulation data justifies the theory’s validity.

Effect of precursors on ZnO nanoparticles to enhance the level-III ridge details of LFPs and anti-counterfeiting applications

Comparative analysis for the combustion-based synthesis of zinc oxide nanoparticles (NPs) utilizing various precursors of zinc was reported. l-ascorbic acid extraction was used as a fuel for the combustion process. The sizes, morphologies, structural details and purity of samples were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffractometry (XRD). XRD pattern matches with the standard JCPDS card of ZnO with good crystallite size. The average crystallite size of the NPs was confirmed the nano-regime. Variations in morphological structures and the energy band gap variation with the change in precursors was reported. Using a powder-dusting technique, on separate surfaces, level-III features of the fingerprints produced by these NPs without any background noise. The suggested powder composition was easy to make and effective for producing latent finger prints on a variety of dry and wet surfaces. In the area of counterfeit prevention, the fluorescent ink has several potential applications. Invisible security ink was developed for anti-counterfeiting applications based on the UV fluorescence feature of ZnO NPs. The fluorescent invisible security ink for screen printing was evaluated and proved to be stable on a variety of microporous papers. The new strategy adopted here lowers the cost of ink by using rare earth free ZnO NPs.

Optical characteristics of Mg-based (Mg/Co & Mg/Mn) TF for hydrogen storage applications

This study has proposed and analyzed the role of hydrogen gas on optical characteristics of Mg-based Mg/Co and Mg/Mn bilayer structures. Thermal evaporation at a pressure of 10-5 torr was used to prepare these Thin Films (TF), which were then effectively deposited onto glass substrates. To obtain homogenous structure, prepared TF were vacuum annealed at 573 K. Hydrogen gas was injected into the chamber at various pressures (10, 20 & 30 psi) to observe how hydrogenation influenced TF. Using a Hitachi-330 spectrophotometer, the UV–Vis transmission spectra were recorded in visible range of wavelength (300–800 nm). TF' optical transmission was reduced, and it was revealed that the energy band gap increased as hydrogen pressure increased. It implies that hydrogen absorption in TF can be used to tailor the energy band gap. An optical micrograph of a hydrogenated TF that has been annealed reveals a dark black state. The variation in energy band gap due to hydrogen and increasing value of the film resistance are evidence for the phase shifts caused on by hydrogenation from metal to semiconductor.