Ultraviolet Region Research Articles

Facile synthesis of hierarchical W18O49 microspheres by solvothermal method and their optical absorption properties

In this study, a simple route for the synthesis of hierarchical W18O49 assembled by nanowires is reported. The morphologies and formation of W18O49 single-crystal could be controlled by changing the concentration of WCl6-ethanol solution. This synthesis strategy has the advantages that the hierarchical W18O49 microspheres could be economic synthesized at 180 °C without adding additives. Furthermore, efficient optical absorption properties in ultraviolet, visible and near-infrared region were obtained for the hierarchical W18O49 microspheres comparing with nanowires. These results will further promote the research of tungsten-based oxide nanomaterials.Graphical abstract

Ab initio calculation of electronic and optical properties of vdWHs HfX2/BSb(X = Se,S) using density functional theory

Recently, another series of two-dimensional (2D) materials called van der Waals heterostructures (vdWhs) have attracted a lot of attention due to their outstanding properties and wide application in electronic and optical devices. Based on density functional theory (DFT) calculations, the properties of heterostructures were investigated with two different vertical arrangements, formed by two isolated sheets of HfX2(X = Se,S) and Boron antimonide(BSb) monolayer. In particular, vdW interactions are present in all these heterostructures rather than covalent bonding. All thevdWHsare semiconductor with indirect k-M band gap, for which the HSE06 functional exhibit a larger gap, but the electronic gap of all heterostructures is smaller than the electronic gap of their constituent sheets. In addition, all vdWHs show excellent optical absorption in the visible, near-infrared, and ultraviolet regions in the x direction, while the absorption peaks for all vdWHs are higher in the z direction. By fabricating heterostructures from isolated plates, their absorption power increases. The present review demonstrates an effective method for the design of novel vdWHs, and it explores their applications for photocatalytic, photovoltaic, and optical devices.

Forecasting optical response in lieu of electronic properties of TlCaF3 via halogen substitution for UV filtration: a DFT perspective

ABSTRACT It is demonstrated that the substitution of Cl, B, and I at different concentrations in TlCaF3 significantly alters the phase, electronic band structure and optical, elastic, mechanical and anisotropic properties of the material. At 2.81% and 5.63% concentrations of all substituted elements, the cubic phase of TlCaF3 transforms into a pseudo-cubic tetragonal phase. With the addition of substitutional atoms, a systematic considerable narrowing of the bandgap is seen, and it can be either direct or indirect depending on the symmetrical positions. The bandgap shrinking can be addressed, in part, via the total/partial/elemental density of states (DOS) in line with structural variations. From the optical response, the refractive index rises with substitution atoms. According to the mechanical stability requirements for each substitution, the determined elastic constants for cubic and tetragonal structures match. Additionally, using elastic parameters, it is possible to estimate the unique mechanical features to evaluate the ductility and brittleness of pure and substituted compounds. Furthernore, Cl, Br and I-atoms’ substitution would make them a suitable choice for improved optimisation in ultraviolet filters (UVF) due to the existence of their absorption spectra in the ultra-violet region and the modification in structural, electrical, optical, elastic and mechanical properties.

Properties of the chalcogenide-based double perovskites Ba2NbBiS6 and Ba2TaSbS6 with respect to structural, electronic and optical aspects

In this work, we delve into the investigation of the structural, electronic, and optical properties of Ba2NbBiS6 and Ba2TaSbS6 chalcogenide-based double perovskites, which are structured in the cubic space group [Formula: see text] form. We have performed first-principles calculations using density functional theory (DFT) to study the above properties. The electronic band structure and density of states of this compound have been investigated, and their results show that Ba2NbBiS6 and Ba2TaSbS6 exhibit a semiconducting nature with an indirect energy gap of 1.680[Formula: see text]eV and 1.529[Formula: see text]eV, respectively. Furthermore, an investigation was conducted on the optical properties of the compounds throughout the energy range spanning from 0[Formula: see text]eV to 55[Formula: see text]eV. This investigation focused on many parameters, including dielectric functions, optical reflectivity, refractive index, extinction coefficient, optical conductivity, and electron energy loss. The optical data obtained from the calculations reveals that all compounds demonstrate isotropy in optical polarization. Furthermore, it has been noted that our compounds exhibit absorption properties inside the ultraviolet (UV) region. Consequently, these materials hold promise as potential candidates for various applications, such as UV photodetectors, UV light emitters, and power electronics. This is primarily attributed to their inherent absorption limits and the presence of prominent absorption peaks in this spectral range. In brief, chemical mutation techniques have been employed to manipulate the characteristics of double-sulfide perovskites to develop durable and environmentally friendly perovskite materials suitable for solar purposes.

Pressure action on ductility and optoelectronic properties of non-toxic AGeBr[formula omitted] (A = Cs, K, Na, Rb) perovskites

We performed first-principles calculations base on generalized gradient approximation(GGA) in the framework of density functional theory (DFT) to examine the effect of pressure on the structural, mechanical, electronic and optical properties of non-toxic AGeBr3 perovskites (A = Cs, K, Na, Rb) for applications in photovoltaic and optoelectronic devices. The dependence of physical properties is evaluated for several pressure values ranging from 0 GPa to 10 GPa. The determined lattice parameters show agreement with previous values and decrease with the applied pressure. All considered materials show semiconductor behavior with direct bandgap (R ⟶ R) at atmospheric pressure. The hybrid functionals HSE and PBE0 have been used to determine accurate values for bandgaps. A very good agreement was found with available experimental values. The calculated bandgap values were found to be 2.129 [2.608] for CsGeBr3, 2.065 [2.481] for KGeBr3, 2.032 [2.397] for NaGeBr3 and 2.089 [2.530] for RbGeBr3, at the HSE [PBE0] level of theory. However, as the applied pressure increases, a reduction in the bandgap is observed, leading to semiconductor to metallic transition. The materials similarly show improved optical properties under pressure with high absorption coefficients in the visible and ultraviolet regions. In addition, the ductility and stability of the considered materials were found also to improve under hydrostatic pressure, which makes them suitable for incorporation into thin films for high performance optoelectronic devices application.

Structural, vibrational and optical characterisations of Li2Ba3(P2O7)2:Cr3+ by solid-state reaction method

ABSTRACT Cr3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowder was successfully synthesised by solid-state reaction technique. The nanopowder was characterised by several techniques. X-ray diffraction analysis reveals orthorhombic crystal structureand average crystallite size values 34.21 and 28.41 nm are determined by Debye Scherrer’s formula and Williamson-Hall (W-H) method. The morphology displayed both SEM and HR-TEM images are irregular stone-like shapes. EDS analysis confirms the constituted elements. The SAED patterns of HR-TEM with well matched with XRD data. FT-IR and Raman spectra analysis confirmed incorporation of Cr3+ in the Li2Ba3(P2O7)2 pyrophosphate nanopowder. The EPR spectrum exhibited signal at g = 1.968 which is attributed to interaction between Cr3+ and Cr3+ exchange pair. The site symmetry of Cr3+ ions occupy a distorted octahedral. Photoluminescence spectrum exhibited bands correspond to ultraviolet, blue and green regions. The evaluated CCT of 6517 K indicates yellowish-green emission near cold light which reveals that the present prepared sample is useful for LEDs applications.

Tunable electronic, transport, and optical properties of fluorine- and hydrogen-passivated two-dimensional Ga2O3 by uniaxial strain

Two-dimensional (2D) semiconductors have shown great prospects for future-oriented optoelectronic applications, whereas the applications of conventional 2D materials are significantly impeded by their low electron mobility (⩽200 cm2 V−1 s−1). In this work, strain-mediated fluorine- and hydrogen-passivated 2D Ga2O3 systems (FGa2O3H) have been explored via using first-principles calculations with the Heyd–Scuseria–Ernzerh and Perdew–Burke–Ernzerhof functionals. Our results reveal a considerable high electron mobility of FGa2O3H up to 4863.05 cm2 V−1 s−1 as the uniaxial tensile strain reaches 6%, which can be attributed to the enhanced overlapping of wave functions and bonding features. Overall, when applying uniaxial strain monotonously along the a(b) direction from compressive to tensile cases, the bandgaps of 2D FGa2O3H increase initially and then decrease, which originates from the changes of σ* anti-bonding in the conduction band minimum and π bonding states in the valence band maximum accompanying the lengthening Ga–O bonds. Additionally, when the tensile strain is larger than 8%, the stronger π bonding at the G point leads to an indirect-to-direct transition. Besides the highest electron mobility observed in n-type doped 2D FGa2O3H with 6% tensile strain, the electrical conductivity is enhanced and further elevated as the temperature increases from 300 K to 800 K. The variations of the absorption coefficient in the ultraviolet region are negligible with increasing tensile strain from 0% to 6%, which sheds light on its applications in high-power optoelectronic devices.

A comprehensive computational investigation on the physical properties of the chalcogenide ternary Y2ZnX4 (Y = In, Ga; X = S, Se) compounds

In this study, the structural, elastic, vibrational, electronic, optical, thermodynamic, and thermoelectric properties of the chalcogenide ternary Y2ZnX4 (Y = In, Ga; X = S, Se) compounds are comprehensively investigated using the pseudopotential plane-wave (PP-PW) and full-potential linearized augmented plane wave (FP-LAPW) methods. The analysis of elastic and vibrational properties reveals the dynamic and mechanical stability of these compounds. The calculated energy band gaps, ranging from 1.47 eV (Ga2ZnSe4) to 2.55 eV (In2ZnS4) in the visible spectrum, decrease as X atoms are substituted with S to Se. All examined compounds demonstrate favorable optical absorption (α > 105 cm−1) in the ultraviolet region. Notably, Ga2ZnSe4 exhibits absorption red-shift towards the visible region at hν = 2.76 eV due to its lower energy band gap, making it a promising candidate for solar cells. The three-dimensional representation of Young's modulus indicates significant deviation from sphericity, revealing anisotropic behavior in all compounds. Pugh's ratio, Poisson's ratio, and Cauchy's pressure analysis suggest ductile behavior in all four chalcogenide ternary compounds. Additionally, all compounds, except In2ZnS4, display auxetic properties. Finally, the calculated thermoelectric properties identify Ga2ZnS4 and In2ZnS4 as promising candidates for high-performance thermoelectric applications, with high Seebeck coefficients of 1848 and 1936 μV/K, respectively, and ZT values approaching unit.

High-harmonic spin-shearing interferometry for spatially resolved EUV magneto-optical spectroscopy

We present a method for achieving hyperspectral magnetic imaging in the extreme ultraviolet (EUV) region based on high-harmonic generation (HHG). By interfering two mutually coherent orthogonally-polarized and laterally-sheared HHG sources, we create an EUV illumination beam with spatially-dependent ellipticity. By placing a magnetic sample in the beamline and sweeping the relative time delay between the two sources, we record a spatially resolved interferogram that is sensitive to the EUV magnetic circular dichroism of the sample. This image contains the spatially-resolved magneto-optical response of the sample at each harmonic order, and can be used to measure the magnetic properties of spatially inhomogeneous magnetic samples.

First-principles screening of optoelectronics and thermoelectric response of XAcTe2 (X=K, Rb) full Heusler alloys: mBJ+SOC effect

Structural geometry, Electronic, optical, and thermoelectric attributes of XAcTe2 (X=K,Rb) full Heuser alloys were investigated theoretically via density functional theory (DFT). Structural optimization yielded optimized lattice parameters along with obtained negative formation energies (Ef) revealed the thermodynamically stable cubic geometries of alloys under investigation. For both alloys, the computed electronic band dispersions exhibit semiconductor behavior with a direct band gap. The band gap value of KAcTe2 is 1.59 eV, and 1.66 eV for RbAcTe2. The analysis of optical response shows maximum absorption α (ω) in the ultraviolet (UV) region, validating their quality for photovoltaic devices. The investigation of thermoelectric characteristics showed that both alloys display higher electrical conductivities and lower thermal conductivities.

First-principles study of the effect of strain on the structural and optoelectronic properties of flexible photovoltaic material Cs2AgInBr6

The lead-free double-perovskite halide materials are promising materials for photovoltaics. Recently, Cs2AgInBr6 (CAIB) has been synthesized with the estimated direct nature of a band gap value of 1.57 eV. To cover the wide solar spectrum for photo-conversion, the applied strain is one of the promising approaches to achieve it through band gap tuning. The density functional theory is used to investigate the effect of compressive strain on the structural, electronic, and optical properties of CAIB. The elastic constants follow the Born–Huang stability criterion and show the mechanical stability of the composition even under compressive strain. The Poisson’s ratio in the range of 0.23–0.26 and B/G > 1.75 indicate the ductile and soft nature of the material. The band gap increases monotonically without changing the direct nature of the band gap by increasing the compressive strain. However, the larger value of strain reproduces more dispersive conduction band minima and valence band maxima, resulting in lower effective masses and consequently larger carrier mobilities. The variations in the optical properties of CAIB are explored under compressive strain. The structural, electronic, and good photo response of the material in the visible and ultraviolet regions indicate the suitability of the material for flexible photovoltaics.

Strain modulated optical properties of MoSi2P4 monolayer – insights from DFT

Strain plays a very important role in tuning the properties of the materials for the desired applications. In the present work, we have investigated the variation of strain on the electronic and optical properties of a recently synthesized class of compound MoSi2P4 monolayer using the first principle methods. The MoSi2P4 monolayer is found to be dynamically and thermally stable at room temperature. The electronic structure of studied monolayer indicates a direct bandgap (at K-point) of 0.685 eV and 1.177 eV using the PBE and HSE06 hybrid functionals, respectively. To tune the electronic bandgap and optical properties, mechanical strain was applied (up to ±10%). A high optical absorption coefficient of the order of 105 cm−1 is observed. The absorption starts in the infrared and visible region covering a large part in the ultraviolet region. The absorption coefficient is found to decrease (increase) under tensile (compressive) strain. Our study indicates the potential application of MoSi2P4 monolayer in flexible optoelectronic devices for absorption and detection in the infrared, visible and ultraviolet region.

Emission Spectra of Uranium Particulates at High Temperature.

The emission spectrum of micron-scale uranium particulates at high temperatures in the ultraviolet, visible, and near-infrared spectral regions is investigated using a heterogeneous shock tube. Temperatures from 3000 to 9000 K are characterized in an inert argon environment and with incremental amounts of added oxygen. Atomic line spectra do not emerge above the continuum emission spectrum until between 4500 and 5000 K in pure argon, and 6100 and 6600 K in 1% oxygen. For 5% oxygen, however, the threshold for atomic emission drops below 3800 K. Uranium monoxide molecular emission in the strongest visible band at 595.4 nm is not observed at any condition. Uncertainties in particle temperature determination in high-temperature shock tube environments are discussed, and limitations to such measurements are presented, such as those from experimental factors such as the powder loading method and expected detection limits of uranium species in relevant conditions.

Spatial shaping of low- and high-order harmonics generated using vortex beams

We demonstrate the generation of the low- and high-order harmonic vortex beams from a single spiral phase plate illuminated by different laser wavelengths. The second harmonic (532 nm) originates from the application of the wavefront-structured 1064 nm femtosecond pulses with fractional orbital angular momentum (OAM) during propagation through a lithium triborate crystal, while the third harmonic (500 nm) originates from the application of the wavefront-structured near-IR (1500 nm) femtosecond pulses with integer OAM during propagation through a 150 μm thick fused silica plate. The topological charges (TCs) of the second and third harmonics are measured and compared. The increase in TC and the peculiarities in OAM variations during modification of the polarisation of the incident radiation are analysed and discussed. The two-colour-pump-driven second-harmonic vortex radiation interacted with an Ar gas jet to generate vortex harmonics up to the 14th order with double-lobe complex spatial profiles in the extreme ultraviolet region.

Bidirectional π − π stacking for near-infrared photothermal effects and photo-thermo-electric conversion in a semiconductive hydroxamate coordination polymer

Photo-thermo-electric conversion is an emerging technology for utilizing solar energy. As the main component, photothermal materials play a significant role in achieving high conversion efficiency from sunlight to electrical energy. Organic photothermal materials have attracted intense attention recently due to their excellent photothermal efficiency and recycling capabilities. However, broad sunlight absorption in organics heavily relies on the realization of intramolecular or intermolecular charge transfer. Exploring more versatile and efficient methods to construct materials with broad sunlight absorption remains a great challenge. Herein, we report a novel photothermal compound from the perspective of modulating molecular assembly structure. By combining two distinct metal ions, Ba2+ and Mn2+, with the planar ligand H2ONDI, a new coordination polymer, {[BaMn(ONDI)2(H2O)3]⋅H2O}n (1), can be obtained. This coordination polymer exhibits rare bidirectional π−π stacking columns along both the a and b axis. The tightly bidirectional arrangement of ligands in 1 results in a broad optical absorption from the ultraviolet region to the near-infrared area, leading to intriguing near-infrared photothermal effects under irradiation of a laser of 808 nm with a efficiency of 42.3 %. By integrating with thermoelectric devices, 1 shows good application potential in the field of photo-thermo-electric conversion, with the maximum open circuit voltage reaching 313 mV under the irradiation of 1 sun. Furthermore, 1 displays semiconducting behavior because the presence of bidirectional π−π stacking columns facilitates charge transport along two directions, including hopping and band-like charge transport.

Effective photoabsorption and band-structural engineering in CuxO/NiO interfacial photosensor for improved ultraviolet response

Energy bands modulations in thin films heterostructure has offered exceptional leads towards the development of photosensing material. In this work, nanostructured metal oxides interfacial electrode structure has been employed to fabricate a highly sensitive ultraviolet (UV) sensor with high responsivity and detectivity. A unique, simple and cost-effective electrodeposition approach was adopted for the growth of the film samples. The interfacial structural effect and optical energy band modulations on the photo-electronic structure and UV detector performance of the structure have been examined. The films had fair transmissions of the visible light spectrum with CuxO dominance in the resulting bilayer structure and a high absorption peak in the ultraviolet (UV) region. The energy band gap redshifted towards the bilayer structure from 3.74 to 2.67 eV. Charge carriers trapping through surface recombination has been found to reduce from the assistance of ohmic contact formation of the heterostructure. The bilayer film-based photodetector demonstrated enhanced performance with photodetectivity (1.6⨯1011 Jones at 0.068 mWcm−2 power density), attributable to the existence of lower recombination state in the structure, according to the UV sensing study. The study showed that tailoring dissimilar metal oxide semiconducting films to the bilayer (CuxO/NiO) structure can provide excellent UV photodetector performance over single-layer of NiO and CuxO.

Study of structural, dynamical stability, electronic magnetic and optical properties of RbSnO3 oxide perovskite compound using the density functional theory approach

This study investigates the structural, phonon, elastic, electronic, magnetic and optical properties of cubic perovskite RbSnO3. The calculations are based on the linearized augmented plane wave method with total potential (FP-LAPW), implemented in the Wien2k code; two approximations are used for calculate properties, PBE-GGA and TB-mBJ . The values of the tolerance factor and the formation energy of this material indicate that it is stable in the cubic structure of Pm3̅m symmetry. The Born criteria for the compound under study confirm its mechanical stability, while its phonon dispersion curves confirm its dynamic stability. The results of the electronic and magnetic properties show that the compound is ferromagnetic (FM) semi-metallic (DM) with semiconductor behavior in the majority spin channel and with an indirect gap in the M → Γ direction and having a total magnetic moment equal to 1 μB and a Curie temperature equal to 527 K. Optical spectra of the compound show high optical conductivity in the infrared region and towards the end of the spectrum at around 6 eV, high reflection in the infrared region with a maximum at 0.25 eV, and high absorption in the ultraviolet region at 6 eV. In view of these results, the RbSnO3 perovskite can be a promising candidate for spintronics applications as it can be used in optical devices working in the ultraviolet (UV) light region.

Improved stability of aluminum surface plasmon resonance sensor by protective gold layer

The surface plasmon resonance (SPR) sensing in the ultraviolet (UV) region, achieved through the optimization of aluminum (Al) film conditions, has attracted attention due to its heightened energy levels and more plentiful molecular electronic transitions compared to the visible region. In this research, the stability of the UV-SPR sensor is improved by applying a protective thin layer of gold (Au) onto the Al film. This reduces spectral alterations observed when the Al film was uncoated in water pre and post flow system measurements. This exploration presents the initial experimental confirmation of the reliability of Al-Au bilayer coatings as SPR sensors in the UV region, highlighting advancements in UV-SPR sensor technology.

Photocatalytic activity and magnetic properties of Ba2FeMoO6 ferromagnetic double perovskite

Ba2FeMoO6 samples were prepared using the sol-gel method without and using Cetyltrimethylammonium bromide (CTAB) to study their photocatalytic properties. The structural and morphological properties of the samples were characterized systematically. The Rietveld refinement described a cubic structure with space group Fm-3m and a single phase with no detectable impurity for either. FESEM images showed that the sample's morphology changed significantly with the addition of the CTAB. The BET analysis of the sample containing CTAB (BFMOC) showed that the special surface area of the pores increased ten times compared to parent sample and its pore size decreased. The UV–Vis spectrum of the BFMOC sample showed two absorption peaks at 223 nm and 705 nm in the ultraviolet and visible regions, respectively. Diffuse reflectance spectroscopy (DRS) spectra of the samples showed direct band gaps (∼2eV) for both. Photocatalytic and absorbent properties were observed in both samples. The photocatalytic properties of the samples revealed that they effectively degraded the dye triphenylmethane MG. By adding CTAB, the Curie temperature of the BFMO sample increased from 304 K to 310 K, while saturation magnetization decreased from ∼1.43 μB/f.u to ∼0.89 μB/f.u. The low coercive field value indicates that the both samples possess soft magnetic and ferromagnetic properties.

Crystal structures and photoluminescence properties of undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders

Undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders were produced by a solid-state reaction process. The prepared samples underwent characterizations using XRD, SEM with EDS, HR-TEM with SAED, FTIR, Raman, UV-Vis, EPR and PL techniques. The XRD analysis confirms the orthorhombic crystal structure of the prepared samples and unit cell parameters were evaluated. The samples exhibited stone-like structures with low aggregation based on the micrographs obtained from SEM and HR-TEM images. Additionally, the grain and particle sizes of the powder samples were evaluated. The elements Li, O, P, Ba and Fe were confirmed to be present in the produced samples by EDS spectra. FT-IR and Raman spectral investigation revealed the fundamental vibrational and bending modes of various phosphate groups. The energy bands, identified as characteristic bands of Fe3+ ions, were produced in the UV–visible region of the optical absorption spectrum for the doped sample. The crystal field and inter-electronic parameters (Dq = 915, B = 700 and C = 2715 cm−1) were also evaluated. Furthermore, the refractive index and metallization criteria properties were calculated using energy bandgap values of 4.46 and 4.38 eV of the produced samples. The doping of Fe3+ ions led to a reduction in the bandgap energy, resulting in a red-shift. A resonance signal was observed in the EPR spectrum at g = 2.05, which can be ascribed to iron ions entering the host lattice at a distorted octahedral symmetry sites and this was also supported by optical absorption studies. The produced sample showed emission peaks at 354, 440 and 530 nm in the ultraviolet, blue and green regions of its photoluminescence spectrum. Photometric parameters, such as CCT, CRI and CIE chromatic coordinates, reveal that the prepared samples could bee used in LEDs applications. This work offers novel visions into diphosphate compounds doped with transition metal ions.