Indirect Energy Band Gap Research Articles

Influence of Polyaniline on the Structural, Linear/Nonlinear Optical, and Dielectric Characteristics of Poly(Vinyl Chloride/Poly (Ethylene Oxide) Blends

Polyvinyl chloride (PVC)/polyethylene oxide (PEO)/x wt % polyaniline (PANI) polymer blends were produced using a solvent casting method. X-ray diffraction was used to investigate the formed blends. The effect of adding different amounts of PANI on the light absorbance, transmittance, reflectance, extinction coefficient, refractive index, optical dielectric properties, nonlinear optical parameters and relaxation time characteristics of the PVC/PEO blends were explored. The direct and indirect optical band gap energies of the undoped PVC/PEO were 4.25 and (4.06, 2.76) eV, respectively. The direct and indirect optical band gap energies were reduced to their lowest values (4.02, 3.1) and (3.68, 2.14, 1.12) eV as the amounts of PANI were increased to 0.2 wt %. The effect of alloying between PVC and PEO and adding PANI on the emitted fluorescence spectra under various excitation wavelengths were investigated. All samples displayed varying degrees of blue-violet, blue, or blue-green colors depending on the concentrations of PANI.

First-principles study on the structural and electronic properties of β-(AlxGa1-x)2O3 alloy

The generalized gradient approximation plus U parameter method is adopted to study the structural and electronic properties of β-(AlxGa1-x)2O3. The results show that the bond length, volume and lattice parameters of β-(AlxGa1-x)2O3 monotonically decrease with increasing Al component. β-Ga2O3 has a direct band gap of 4.703 eV while β-Al2O3 possesses an indirect band gap of 7.278 eV. After fitting the predicted theoretical band gap data in this work, the acquired bowing parameters for the direct and indirect band gap energies are 2.17eV and 1.92eV, respectively. Besides, the transition from the direct to indirect band gap of β-(AlxGa1-x)2O3 occurs when the Al component is 0.33. As the Al component increases, the conduction band minimum (CBM) shifts toward the higher energy and the valence band maximum (VBM) moves to the lower energy, resulting in the enlargement of the band gap energy of β-(AlxGa1-x)2O3. The decline of the VBM is on account of the enhanced total p−p coupling interaction and the weakened pO−2p−dGa−3d coupling interaction. However, the rise of the CBM is owing to the enhanced total s−s coupling interaction.

Impact of PbO on structural, thermal, optical and gamma ray shielding behaviour of TeO2-CdO based glasses

A study was conducted to investigate the effect of an increase in the concentration of PbO on the structural, thermal, optical, and gamma ray shielding behavior of TeO2-CdO based glasses. The glasses were found to contain TeO4 and TeO3 units, as well as CdO metal oxide clusters, as indicated by the Raman spectrum. The glasses displayed minor weight loss (approximately 3%), suggesting high resistance to thermal degradation. With an increase in the concentration of PbO, the glass transition temperature (Tg), onset temperature (To), and crystallization temperature (Tc) all decreased. Additionally, the indirect band gap energy decreased from 3.497–3.337 eV as the lead oxide concentration increased. Moreover, the effects of PbO concentration on the linear attenuation coefficient (LAC) were investigated. The LAC values were found to be highest at 39.5 keV and decreased with increasing energy. As the PbO concentration increased, LAC values also increase. The Zeff displayed an inverse relationship with energy, except for an abrupt increase at 121.8 keV. The half value layer was found to be positively correlated with energy and varied with changes in PbO and CdO concentrations. The glasses demonstrated effective gamma radiation shielding properties, with the HVL remaining small even at higher energies, suggesting potential applications in industries such as medical imaging where thin shielding materials are preferred.

Insights from Experiment and Theory on Peculiarities of the Electronic Structure and Optical Properties of the Tl2HgGeSe4 Crystal.

Tl2HgGeSe4 crystal was successfully, for the first time, synthesized by the Bridgman-Stockbarger technology, and its electronic structure and peculiarities of optical constants were investigated using both experimental and theoretical techniques. The present X-ray photoelectron spectroscopy measurements show that the Tl2HgGeSe4 crystal reveals small moisture sensitivity at ambient conditions and that the essential covalent constituent of the chemical bonding characterizes it. The latter suggestion was supported theoretically by ab initio calculations. The present experiments feature that the Tl2HgGeSe4 crystal is a high-resistance semiconductor with a specific electrical conductivity of σ ∼ 10-8 Ω-1 cm-1 (at 300 K). The crystal is characterized by p-type electroconductivity with an indirect energy band gap of 1.28 eV at room temperature. It was established that a good agreement with the experiments could be obtained when performing first-principles calculations using the modified Becke-Johnson functional as refined by Tran-Blaha with additional involvement in the calculating procedure of the Hubbard amendment parameter U and the impact of spin-orbit coupling (TB-mBJ + U + SO model). Under such a theoretical model, we have determined that the energy band gap of the Tl2HgGeSe4 crystal is equal to 1.114 eV, and this band gap is indirect in nature. The optical constants of Tl2HgGeSe4 are calculated based on the TB-mBJ + U + SO model.

Effect of two-step cubic GaN buffer layer on the radio-frequency plasma-assisted molecular beam epitaxy growth of cubic AlN films grown on MgO (001) substrates

Cubic AlN (c-AlN) films were grown on MgO (001) substrates through the use of a two-step cubic GaN (c-GaN) buffer layer using radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) technique. The two-step c-GaN buffer layer was found to be crucial for the epitaxial growth of c-AlN, as it showed a specific epitaxial relationship between c-AlN and c-GaN along the MgO [100] zone axis. On the other hand, the c-AlN films grown with the one-step and nonGaN buffer layers showed columnar grain structure. The optical study found that the c-AlN films grown with the two-step c-GaN buffer layer had an indirect bandgap energy of 4.99 ± 0.02 eV, which is consistent with previous experimental data and theoretical calculations. The c-AlN films grown with the one-step and nonGaN buffer layers had indirect bandgap energies of 5.00 ± 0.02 eV and 5.18 ± 0.02 eV, respectively. These results highlight the importance of the two-step c-GaN buffer layer in enhancing the MBE growth of c-AlN on MgO (001) substrate.

Soda-lime-silica glass structure with MoO3 doping: An optical approach

MoO3 incorporated sodium-lime-silicate glasses of composition 55SiO2 - 25Na2O - 5CaO - 10ZnO - 5MgO(1-x): MoO3 (x) (x = 0, 0.1, 0.3, 0.5, and 1) were prepared using the melt-quench technique. The transmittance and absorbance spectrum of the glasses were detected by UV–VIS spectroscopy between the wavelength range of 250–900 nm. The optical transmittance of the doped glasses was significantly enhanced by adding MoO3 to the base glass structure. The indirect band gap (Eg) and Urbach energy (EU) values have been evaluated with the help of absorption spectra. Band gaps range from 3.478 to 3.752 eV, and Urbach energies range from 0.223 to 0.709 eV. Advanced optical characterization of glasses was obtained using standard equations by analyzing important optical parameters such as molar volume, refractive index, optical dielectric constant, molar refraction, electronic polarizability, and metallization criterion. All the data has been discussed in accordance with the MoO3 contributions. The glass structure with 0.1 % MoO3 doped, coded as M-01, showed a different change in the measurements and calculations than the other glasses. The glass structure under consideration exhibits superior characteristics in terms of light transmittance, band gap value, and metallization criterion, while displaying comparatively lower values for Urbach energy, refractive index, optical dielectric constant, and electronic polarizability.

Optical properties of chromium-selenide films designed for terahertz applications

Herein the effects of indium substrates on the properties of chromium selenide thin films are reported. Chromium selenide thin films and indium substrates are prepared by the thermal evaporation technique under a vacuum pressure of 10−5 mbar. It is observed that indium sublayers alters the atomic stoichiometry of chromium selenide. It induces the formation of Cr2Se3 phase instead of CrSe2 phase which grow onto glass substrates. Both of the glass/CrSe2 and In/Cr2Se3 films displayed direct and indirect energy band gaps. The respective gaps are 2.60 eV and 3.19 eV and 2.25 eV and 2.83 eV. The Urbach tails states exhibited a width of 2.24 eV in glass/CrSe2 and showed value of 0.85 eV in In/Cr2Se3. In addition a light absorbability enhancement of more than 45% is reached at the In/Cr2Se3 interfaces in the visible range of light. Moreover, as terahertz resonators, In/Cr2Se3 films showed larger optical conductivity. It also displayed a spectral terahertz cutoff frequency in the range of 3.0–35 THz. Furthermore, when utilized as terahertz resonators, In/Cr2Se3 films demonstrate heightened optical conductivity and a spectral terahertz cutoff frequency ranging from 3.0 to 35 THz. Analyzing these terahertz oscillators using Drude-Lorentz models reveals that the density of free charge carriers increases with higher oscillator energy, while the drift mobility of these carriers within the terahertz resonators varies between 1.10 and 3.09 cm²/Vs. The array of features showcased by In/Cr2Se3 thin films, including their performance as terahertz resonators, positions them as strong contenders for applications in optical and terahertz technologies.

A study of the UV photodetectors properties based on the effect of TiO2 on ZnO nanorods grown via the chemical bath deposition method on p-type Si (100) substrates

In this study, a heating composition process was used to construct Ti-doped ZnO (Ti/ZnO) nanocomposites to serve as an active layer in UV detection devices. Prior to synthesis, a ZnO seed layer was deposited on p-type Si (100) substrates (p-Si substrates) using radio frequency (RF) sputtering. Afterward, Ti/ZnO thin films (TFs) were successfully grown using the chemical bath deposition method (CBD) by combining different amounts of TiO2 nanofluid with ZnO precursor solutions. The volume of the TiO2 nanofluid ranged from 12.5% to 50% with respect to the total volume. FE-SEM, EDX, and AFM were employed to examine the morphological, elemental, and topographical characteristics of the formed nanocomposites. Thermo-evaporation was used to print Ag interdigitated electrodes (IDE) on the nanocomposites to fabricate UV photodetectors. The (002) Ti/ZnO peak along the z-axis on the substrate, which increases with increasing amounts of TiO2, provides evidence of the crystallinity and the hexagonal wurtzite structure of the samples. UV–Vis spectroscopy showed high diffuse reflectance curves with indirect energy bandgaps from 3.1969 eV to 3.2203 eV. The TiO2 nanofluid used in the growth impacted the synthesized Ti/ZnO, which affected the performance of the photodetectors. A responsivity, photosensitivity, gain, detectivity, rise time, and decay time of 0.107495 AW−1, 3833.67%, 39.34, 6.75 × 108 jones, 0.19 s, and 0.24 s were recorded when 50% of the TiO2 was used during the synthesis process of the ZnO nanorods. Based on the findings, the nanocomposites grown on p-Si substrates are suitable for use as thin films in optoelectronics, especially UV detection devices.

Computational insight into the fundamental physical properties of ternary ABCl3 chloroperovskites compounds using the DFT approach

In this research, the ternary non-centrosymmetric chloroperovskites compounds of the form ABCl3 (A = Rb and B = Be, Mg) are investigated extensively to predict the structural, mechanical, and optoelectronic properties with DFT incorporated in WIEN2K code. The crystalline structure of interested chloroperovskites is identified to be cubic, non-centrosymmetric, and stable. The elastic constants Cij, bulk modulus, criteria of Pugh ratio, and the Born criteria confirm the ductility and mechanical stability of ternary RbBeCl3 and RbMgCl3 materials. Electronic properties such as the band structures and density of states are examined with the most widely recognized TB-mBJ potential approximation. RbBeCl3 shows semiconducting behaviour with an indirect wide band gap energy of 3.74 eV from R-Γ symmetries points, while RbMgCl3 is assumed to be an insulator that possesses indirect wide band gap energy of 6.28 eV from R-Γ. It is identified that the ABCl3 (A = Rb and B = Be, Mg) non-centrosymmetric compounds change the behavior from wide band gap semiconductors to perfect insulators when the ‘B’ site in ABCl3 varies from ‘Be’ to ‘Mg’ element. In the electromagnetic range from 0 eV to 40 eV of incident photons energy, several parameters in optical properties that includes the dielectric function, refractive index, absorption coefficient, optical conductivity, extinction coefficient, and energy loss function are investigated for the quest of potential applications of interested non-centrosymmetric cubic systems in modern photovoltaic technologies. These outcomes may add inclusive understanding within ultraviolet ranges for photovoltaic applications.

The Synthesis, Structure, and Luminescent Properties of TmMgB5O10 Crystals.

TmMgB5O10 spontaneous crystals were synthesized via the flux-growth technique from a K2Mo3O10-based solvent. The crystal structure of the compound was solved and refined within the space group P21/n. The first principles calculations of the electronic structure reveal that TmMg-pentaborate with an ideal not defected crystal structure is an insulator with an indirect energy band gap of approximately 6.37 eV. Differential scanning calorimetry measurements and powder X-ray diffraction studies of heat-treated solids show that TmMgB5O10 is an incongruent melting compound. A characteristic band of the Tm3+ cation corresponding to the 3H6 → 1D2 transition is observed in the photoluminescence excitation spectra of TmMg-borate. The as-obtained crystals exhibit intense blue emission with the emission peaks centered at 455, 479, 667, and 753 nm. The most intensive band corresponds to the 1D2 → 3F4 transition. TmMgB5O10 solids demonstrate the thermal stability of photoluminescence.

Orange and yellow emissions through Sm3+ and Tb3+/Sm3+ doped potassium-zinc phosphate glasses for WLED applications

A spectroscopic analysis of potassium-zinc phosphate glasses activated with Sm3+ and Tb3+/Sm3+ is presented. Both glasses showed high transparency in the visible region with direct and indirect band gap energy values of 3.70 and 3.96 eV, and 3.85 and 4.22 eV for the Sm3+ doped and Tb3+/Sm3+ co-doped glasses, respectively. The Urbach energies estimated for the single doped and codoped glasses resulted to be 0.26 and 0.24 eV, respectively. Upon 408 nm excitation, the Sm3+ singly doped glass exhibited a 592 nm orange emission with correlated color temperature (CCT) and color purity (CP) of 1677 K and 99%, respectively. The Judd-Ofelt (JO) theory was applied to value the radiative parameters of the Sm3+ doped glass. It was found JO parameter values of Ω2 = 1.93 × 10−20 cm2, Ω4 = 3.72 × 10−20 cm2 and Ω6 = 2.85 × 10−20 cm2, which lead to peak stimulated emission cross-section (σpeak), gain bandwidth (σpeak× Δλeff) and optical gain (σpeak× τR) values of 4.49 × 10−22 cm2, 9.70 × 10−28 cm3 and 14.14 × 10−25 cm2s for the main samarium 4G5/2 → 6H7/2 emission. Such values resulted to be comparable or higher than those reported for sodium-tellurite and borate-silicate-based glasses. The emission in the Tb3+/Sm3+ co-doped glass under Tb3+ and Sm3+ co-excitation displayed yellow (λex = 304, 318 and 377 nm) and orange (λex = 344 and 360 nm) emission tonalities with CP values up to 88 and 97%, respectively. The overlapping of Tb3+ emission bands with those of Sm3+ excitation suggested the existence of energy transfer from terbium to samarium, which according to the Tb3+ emission decay behavior is non-radiative. Such a process arises from the Tb3+: 5D4 energy level with an efficiency of 0.41 within Tb3+-Sm3+ clusters.

Improving the optical, photoluminescence, and electrical properties of PEO/NaAlg-WO3 nanocomposites for optoelectronic and nanodielectric applications

Nanocomposites based on polyethylene oxide (PEO)/Sodium Alginate (NaAlg) with varying content of tungsten trioxide nanoparticles (WO3 NPs) have been synthesized by using a green solvent casting method. Through the use of X-ray diffraction (XRD), Fourier transforms infrared (FTIR), and Ultraviolet–visible spectroscopy (UV–Vis.), the interaction of mixed components has been evaluated. Studies using spectroscopy have shown that WO3 nanoparticles and the blend's component parts interact strongly at their interfaces. XRD confirms the increasing amorphous propensity of the PEO/NaAlg film with increasing nanofiller loading. FTIR implies the development of molecular complex of the polymer with the nanofiller. From UV–Vis analysis, Tauc's relation was used to specify the direct and indirect bandgap energy. The Eg (direct) of pure PEO/NaAlg was considerably decreased from 4.23 to 3.04 eV by adding 2.0 wt% of WO3 NPs. The fluorescence for various WO3 NPs concentrations in PEO/NaAlg blend films was analyzed. The PEO/NaAlg blend's fluorescence intensity decreased with increased doped with WO3 NPs. The films made of nanocomposites also had their dielectric behavior and electrical conductivity examined. In contrast to the electrical conductivity (AC), the dielectric constant and dielectric loss of PEO/NaAlg-WO3 nanocomposites drop as the frequency of the electric field rises. The investigation revealed that an increase in WO3 concentration led to a corresponding rise in the nanocomposites' dielectric loss and dielectric constant values. The fabricated system of PEO/NaAlg-WO3 NPs nanocomposites films showing improved in AC conductivity and dielectric characteristics and could be suggested in optoelectronic and nanodielectric devices.

Novel cobalt lead ferrite (CPFO)/Ps nanocomposites with enhanced structure, optical and dielectric properties

Hexa-spinel ferrite nanoparticles of Cobalt Lead Ferrite (CPFO) were prepared by a flash auto combustion method, while xCPFO/PS (x = 0, 2.5, 5, and 7.5 wt%) nanocomposite films were synthesized by casting method. The diffraction pattern and Rietveld refinement of CPFO nanoparticles proved that they have a face-centred cubic spinel and a hexagonal structure. HRTEM micrographs of cobalt lead ferrite (CPFO) nanoparticles show an average particle size of around 30 nm. FESEM cross-section images of CPFO/PS nanocomposite films showed CPFO nanoparticles dispersed in the PS matrix. All optical characteristics of the synthesized nanocomposite films, including absorbance, transmittance, direct and indirect energy band gap, Urbach energy, excitation coefficient, and refractive index, were investigated using a UV-visible spectrophotometer examination. The direct optical energy band gap lowered from 4.533 eV to 4.368 eV, and the indirect energy optical bandgap lowered from 4.337 eV to 4.146 eV, while the Urbach energy increased from 0.103 eV to 0.209 eV with increasing the nanofillers from 0 to 7.5 wt%. Broadband dielectric spectroscopy was used over a wide frequency range (0.1 Hz–1 MHz). The dielectric real permittivity (ε′), the dissipation factor tan (δ) and the electric modulus (M′&M′′) measurements were studied. CPFO nanoparticles’ addition significantly enhanced the dielectric real permittivity (ε′), the dissipation factor tan (δ), and the ac conductivity of all nanocomposites.

Reacting Mn3O4 powders with quaternary ammonium hydroxides to form two-dimensional birnessite flakes

There is a current interest in synthesis of two-dimensional (2D) materials that would be cost-efficient to scale to industry production. In this study, we report on a bottom-up approach to convert a manganese oxide (Mn3O4) powder into crystalline, 2D layered birnessite flakes. The Mn3O4 precursor powder, is reacted with aqueous solutions of, tetramethyl-, tetraethyl- or tetrabutylammonium hydroxide in a shaker oven at 80 °C for 4 days. X-ray diffraction confirmed that in all cases, upon filtration of colloidal suspensions, well-stacked, crystalline, 2D MnO2 birnessite layers formed, that upon characterization were found to be quite similar. The major differences were the spacings between the flakes that depended on cation size. Selected area diffraction patterns in a transmission electron microscope confirmed both the structure and the polycrystallinity of the flakes. Raman spectroscopy confirmed the structure. The zeta-potentials of the 2D flakes were measured to be ≈−35 ± 2 mV. When UV–Vis spectra were converted to Tauc plots, direct and indirect band gap energies of ≈2.15 and ≈2.60 eV were obtained, respectively. Additionally, the oxygen evolution reactivity of our birnessite flakes significantly are better than those found for Pt/C, demonstrating a high degree of catalytic reversibility. The facile conversion of a relatively inexpensive, earth-abundant oxide, Mn3O4, into a highly value-added 2D birnessite using a one-pot, simple hugely scalable, protocol at near ambient temperatures and pressures with various quats can be considered a breakthrough in the production of these nanomaterials.

A novel and simple approach of rare earth ions (Y3+ and La3+) decorated nano calcium carbonate/ polyethylene glycol for photocatalytic degradation of organic pollutants in wastewater

Pristine and rare earth ions (Y3+ and La3+) decorated rhombohedral nano CaCO3/PEG were extracted from natural dolomite rock using a novel green route biomimetic synthesis. XRD analysis confirmed the crystal phase and doping of Y3+ and La3+ in the CaCO3/PEG. The FTIR analysis confirmed the presence of various functional groups in the synthesized nanoparticles. The obtained products exhibited good thermal stability at the temperatures up to 844 °C. The absorption and emission peaks were blue-shifted due to the impact of the doping ion concentration. The surface chemical compositions were analyzed using XPS. The direct and indirect bandgap energies of nCY1 (0.02 M Y3+: CaCO3/PEG) and nCL1 (0.02 M La3+: CaCO3/PEG) were 3.95, 3.27 eV (direct bandgap) and 2.52, 2.09 eV (indirect bandgap) respectively. The measured fluorescence quantum yields of nCY1 and nCL1 were 22% and 26%, respectively. FESEM with EDX mapping and HR-TEM with SAED analysis was used to determine the morphology, elemental mapping, and crystalline behavior. The photocatalytic activity of prepared samples were performed against methylene blue under UV irradiation. Based on photocatalytic results, nCL1 showed extremely high photocatalytic activity (92%). The effects of the scavenging agents were investigated using superoxide radicals, photogenerated holes, electrons, and OH radicals. Hence, the prepared samples could be an effective catalysts for significant environmental issues. This is the first study for preparing Y3+ and La3+ doped CaCO3/PEG nanoparticles from natural dolomite rock using a low-cost and nontoxic biomimetic method to get enhanced photodegradation efficiency.

Structural, mechanical, electronic and optical properties of MgZnO3 perovskite: First-principles study

This study examines the structural, mechanical, electronic, and optical properties of MgZnO3 perovskite using the first-principles calculation based on density functional theory (DFT). We perform the comparative study using four different exchange–correlation functionals–LDA:CA, GGA:PBE, GGA:PBEsol and mGGA:SCAN, and incorporate a Hubbard U-potential of 4.0 eV to address the electron-correlation effect of Zn-3d orbital. Further, we implement a hybrid functional–HSE06 for the band correction. From the assessment of structural optimization, tolerance factor, and formation and cohesive energies, we predict the stability of our system. The investigation of its structural properties shows that it exists in a cubic phase with 3.71-3.81 Å of lattice constant. An analysis of its mechanical properties predicts that it is a stable, rigid, ductile, and crystalline material with a metal-ionic bond. Based on the band structure analysis, MgZnO3 perovskite has an indirect band gap energy in the range of 0.92-1.77 eV along R-Γ high symmetric points, indicating a suitable material for photovoltaic and photocatalytic devices. We observe the dominant contribution of O-2p orbitals around the Fermi level from DOS/PDOS calculations. Moreover, the optical characterization of this perovskite has been found to indicate high values of refractive index, optical conductivity, and reflection coefficient in the infrared region, and absorption of radiation in the ultraviolet region, which suggests it as a potential material for optoelectronic devices.

Influence of Pr[formula omitted] ions on the structural properties of Er[formula omitted]-doped tellurite-tungsten glasses

An understanding of the optical, thermal and structural properties of tellurite glasses is necessary for the development of new technological applications. Previous works have already been published studying the properties mentioned above, however, the mechanism of modification of the glassy structure due to the addition of rare earth ions is still an open topic in materials science. In this paper, we report the mechanisms of structural modification of the Er3+ and Pr3+-doped glass tellurite-tungsten system through a systematic study. TeO2–ZnO–WO3–GeO2 glasses codoped with Er2O3 and varying the content of Pr2O3, was prepared by the conventional melt-quenching technique and studies of its structural, thermal and spectroscopic properties were carried out. The direct and indirect bandgap energies and the Urbach energy evidence an increase in the structural disorder of the glassy matrix due to the deformation of the TeO linkages by the insertion of Pr3+ ions in the sample can be suggested. Raman spectroscopy results showed an increase in TeO3+1 and TeO3 compared to TeO4 when the Pr2O3 doping was increased, modifying the structural coordination in TeO2, generating non-bridging oxygens. Raman spectroscopy in low-frequencies shows the Boson peak changed with the increase in the concentration of Pr3+. Furthermore, was obtained that transverse modes predominate in low Raman frequencies. This work suggests that the presence of Pr3+ ions influences the optical and thermal properties, in addition to altering the local glassy structure, generating a change in the coordination of network formers such as TeO2.

Chitosan – TiO2 Nanocomposite Films for Efficient Decolourisation of Sulphur Black Dye under Dark Conditions

ABSTRACT Sulphur dyes are a class of dyes known for their low cost and excellent fastness to light and wash. But, excess amounts of unused dyes, electrolytes and sulphide contents were found to cause serious hazards to health and environment. This work reports the synthesis of cost-effective, non-toxic, environment-friendly chitosan (CS) and chitosan-TiO2 (5 wt% (CST-5), 10 wt% (CST-10) and 15 wt% (CST-15)) polymer nanocomposite films by the facile solution casting method. CS and CST polymer nanocomposite films were tested for the decolourisation of sulphur black dye. The structural analysis of the synthesised films using X-ray Diffraction (XRD) displayed the semi-crystalline peaks of chitosan and the anatase phase of TiO2 with tetragonal-bcc structure. The morphological analysis using Atomic Force Microscopy (AFM) revealed that TiO2 had dispersed uniformly into the polymer matrix. UV–Vis DRS and PL revealed the wide indirect band gap energy and charge transfer characteristics, respectively, of the polymer nanocomposite films. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) studies revealed the various bonds, functional groups and elemental properties of CS and TiO2-loaded CS films. Sulphur black dye decolourisation studies conducted under dark conditions at room temperature and atmospheric pressure revealed that CST-5 nanocomposite film exhibited an excellent decolourisation efficiency of 87.6% within 12 min of contact with the sulphur black dye solution. This swift and enhanced decolourisation was due to the synergistic effects of adsorption by chitosan and catalytic wet air oxidation (CWAO) by the catalyst TiO2. These nanocomposite films are potential materials for the treatment of wastewater and decolourisation of various toxic dyes.

Effect of Ge concentration on optical properties of films synthesized by vacuum-thermal evaporation of glassy Ge–Se alloys

Four non-crystalline GexSe100−x (x = 15−25 at. %) films were obtained by vacuum-thermal deposition of glassy Ge–Se alloys. With the use of spectroscopic ellipsometry, it was determined that the films are semiconductors with indirect band gap energy Eg = 2.0−2.07 eV. An anomalous dispersion of the refractive index n (λ) with nmax at λmax depending on x was revealed in the films at λ = 240−500 nm. It was established that as the concentration of Ge decreases, nmax increases, and λmax red shifts. Based on the Wemple-DiDomenico model, the nonlinear coefficients χ(3) and n2 characterizing the synthesized films were calculated as a function of x. The highest χ(3) and n2 values are achieved in the films at x = 15 at. %. The results obtained can be used for the development and creation of Ge–Se optical filters with an adjustable blue absorption band edge.

Sensitivity estimation of indium oxide thin film for gamma sensing

This article aims to study the modification in the structural, optical and electrical properties of indium oxide thin film after gamma irradiation and estimation of sensitivity for gamma sensing applications. The thin film of indium oxide was deposited on a 450 °C preheated glass substrate using the spray pyrolysis technique. The deposited thin film of molar concentration 0.15 M and thickness of around 600 nm was irradiated with different gamma doses (100 Gy, 200 Gy, 300 Gy and 400 Gy). The optical properties of the irradiated film are studied using UV–Visible spectroscopy. Transmittance increased after irradiation up to 200 Gy and beyond that, it decreased. Indium oxide is an n-type semiconductor which exhibits both direct and indirect transitions. Both direct and indirect bandgap energy are calculated using Tauc’s plot. Extinction coefficient and refractive index variation with irradiation were also estimated. Photoluminescence study confirmed the gamma-induced defect formation and annihilation for an irradiation dose of 400 Gy and 200 Gy, respectively. Resistivity also decreased up to 200 Gy and beyond that, it increased. The sensitivity of the deposited film was estimated from the electrical measurements, and it lies between 10.7 and 53.4 mA/cm2/Gy.Graphical abstract