Increase In Band Gap Energy Research Articles

Characterizations of pure and eu-doped ZnO aerogels nanostructures elaborated by a modified sol gel process

Herein we report on the structural and optical properties of pure and Eu-doped (3% at.) ZnO aerogels nanostructures (ZnO-ans) synthesized by sol-gel associated with drying at supercritical conditions of isopropanol (254 °C, 54 bars). The samples were investigated using X-ray diffraction (XRD), SEM, UV-visible spectroscopy, FTIR and photoluminescence (PL). XRD studies exhibit the formation of a high crystal quality ZnO wurtzite hexagonal structure. The UV-visible measurements point out that the absorption intensity and the band gap energy increase after Eu-doping. FTIR analysis confirms the formation of ZnO phase and reveals a shift toward longer wavenumber of the Zn-O absorption band after Eu -doping. SEM images show that Eu3+ ions lead to change the morphology of ZnO crystalline from pastille to sphere. PL measurements reveal a decrease of UV luminescence intensity and an increase of the visible one due to Eu-doping.

Enhancing photocatalysis through annealing: Unveiling the role of physical properties in photocatalytic behavior

Using spray pyrolysis, silver-doped In2S3 thin films were deposited on pre-heated glass substrates, with varying doping concentrations. Subsequently, these films underwent vacuum annealing at 400 °C for a duration of 2 h. A comprehensive study of their structural, morphological, and optical properties was conducted, revealing homogeneous, compact, crack-free films with polycrystalline tetragonal-phase of In2S3. Among the set of the analyzed films the best parameter values, including crystallite size, dislocation density, micro-strain, grain size, and root mean square (RMS) roughness, were achieved when maintaining a Silver-to-indium (|Ag|/|In|) ratio of 4 % in the precursors for both as-deposited and annealed samples. The annealing process had a discernible impact on the grain size distribution, resulting in a significant increase in crystallite and grain size, along with RMS roughness, for most doped films. The optical analysis of these films unveiled their transparency in the visible and near-infrared regions, coupled with substantial absorption in the UV region. Higher Ag concentration in the as-deposited films led to an increased band gap energy in the annealed samples. The roughness peaked at |Ag|/|In| = 4 %, resulting in a noteworthy enhancement of photocatalytic activity, achieving 95 % photodegradation of a methylene blue aqueous solution. This underscores the critical role of surface properties in determining performance. Future research intends to explore other applications for these thin films, including potential usage in gas sensors, capitalizing these films' promising characteristics.

High-energy storage capacity of cellulose nanofiber supercapacitors using bound water

The performance of electric double-layer capacitors and lithium-ion batteries deteriorates with increasing humidity. The desirable effect of bound water on the energy-storage properties of physically dry cellulose nanofiber (Na-ACF) supercapacitors with sodium (Na) carboxylate radicals was investigated using infrared and near-infrared spectroscopy, and nuclear magnetic resonance spectroscopy, alternating current impedance analyses, and first-principles calculations. The storage capacity decreased gradually upon heating to 423 K and reached zero upon exceeding 483 K, accompanied by increasing electrical resistance, forming a distorted semicircle in Nyquist diagram and drawing the phase angle to zero in Bode diagram. This is attributed to the water in the hydration gel bound to the Na+-ions that cross-link the cellulose chains, evaporating as the temperature increases, and finally becoming Na2O. The increased band-gap energy from the increase in bound water prevents leakage from the supercapacitor. In contrast to ordinary batteries, bound water is necessary for developing Na-ACF supercapacitors.

Impact of silver substitution on the structural, magnetic, optical, and antibacterial properties of cobalt ferrite

Silver-doped Cobalt Ferrite nanoparticles AgxCo1−xFe2O4 with concentrations (x = 0, 0.05, 0.1, 0.15) have been prepared using a hydrothermal technique. The XRD pattern confirms the formation of the spinel phase of CoFe2O4 and the presence of Ag ions in the spinel structure. The spinel phase AgxCo1−xFe2O4 nanoparticles are confirmed by FTIR analysis by the major bands formed at 874 and 651 cm−1, which represent the tetrahedral and octahedral sites. The analysis of optical properties reveals an increase in band gap energy with increasing concentration of the dopant. The energy band gap values depicted for prepared nanoparticles with concentrations x = 0, 0.05, 0.1, 0.15 are 3.58 eV, 3.08 eV, 2.93 eV, and 2.84 eV respectively. Replacement of the Co2+ ion with the nonmagnetic Ag2+ ion causes a change in saturation magnetization, with Ms values of 48.36, 29.06, 40.69, and 45.85 emu/g being recorded. The CoFe2O4 and Ag2+ CoFe2O4 nanoparticles were found to be effective against the Acinetobacter Lwoffii and Moraxella species, with a high inhibition zone value of x = 0.15 and 8 × 8 cm against bacteria. It is suggested that, by the above results, the synthesized material is suitable for memory storage devices and antibacterial activity.

2-Deoxy-d-glucose functionalized zinc oxide nanodrug for kidney cancer treatment

For the first time, zinc oxide (ZnO) nanoparticles (NPs) are synthesized by the green combustion method using apple peel extract as a reducing agent. Further, ZnO-Deoxy-d-Glucose (2DG) nanohybrids were synthesized by the sputtering method. These synthesized biomolecule-coated NPs and nanohybrids are characterized with different techniques. The Bragg reflections confirm the hexagonal Wurtzite structure for ZnO. A decrease in crystallite size and an increase in energy band gap were observed for ZnO and ZnO-2DG. The tuning of the band gap plays a vital role in cytotoxicity, arbitrated by intracellular reactive oxygen species. The cytotoxic properties, such as the percentage of inhibition and the percentage of the proliferation of ZnO and ZnO-2DG nanohybrid, are examined against the Kidney cancer Vero cell line and also compared with the standard drugs Levofloxacin and Doxorubicin. Compared to ZnO, ZnO-2DG shows excellent cytotoxic properties, even better than the standard drug against the Vero cell line. Thus, the present ZnO-2DG nanohybrid might be used as a nanodrug and go on to replace Levofloxacin and Doxorubicin as standard drugs in kidney cancer cell therapy.

Green synthesis of NiO doped CuO Nanoparticles: Potential for Environmental Remediation

The presented study reports the green synthesis of pure and Ni-doped CuO nanoparticles by Allium staivum (Garlic) extract. Cupric nitrate (Cu (NO3)2) and Nickel nitrate (Ni (NO3)2) as intermediate precursors in Allium staivum (Garlic) extract were used to synthesize Pure and Ni-doped CuO nanoparticles. XRD patterns confirmed the absence of any impurity peaks suggesting the monoclinic phase of CuO and successful doping of Ni into the CuO matrix. Tauc’s plots showed an increase in optical band gap energy with the introduction of Ni dopant. The photocatalytic activity of prepared samples was investigated against Methylene blue (MB) dye and Ciprofloxacin (CIP) under the UV light spectrum. The photocatalytic activity results depicted an enhanced photodegradation efficiency of Ni-doped samples against both MB and CIP organic pollutants. The experimental results reveal that the degradation of MB and CIP can reach 70% and 67% respectively. The synthesized samples thus possess a potential for the treatment of antibiotic-contaminated waters for eliminating or reducing antibiotic residues from the environment. Both CuO and CuN nanoparticles at concentrations of 5, 10, 20 and 30 mg/ml were used to investigate bacterial activity against E. coli. CuN refers to nickel doped CuO nanoparticles. Zones of inhibition of the synthesized nanoparticles (derived from green synthesis) against E. coli for CuO and CuN were 11 mm and 28 mm at 30 mg/ml respectively. The large zone of inhibition values reported in this work reveals that the synthesized nanoparticles give better antibacterial activity.

Catalytic degradation of methylene blue and bactericidal action by silver and CS-doped iron oxide nanostructures: Experimental and DFT approaches

In this research, Ag (3 and 6 wt %) and carbon sphere (CS) (3 wt. %) were successfully incorporated into Fe2O3 using a co-precipitation approach. This study aimed to degrade the methylene blue (MB) dye and investigate the bactericidal effect of doping-dependent Fe2O3. The pristine sample has good stability and is less toxic however showed poor degradation potency. To enhance the catalytic activity (CA), CS was introduced as it increases Fe2O3 adsorption capacity and improves metal oxide properties. Ag was incorporated into CS-Fe2O3, which created additional active sites and might generate reactive oxygen species (ROS). XRD patterns revealed the tetragonal and monoclinic structure of Fe2O3, and crystallinity was enhanced with dopants (Ag and CS). FTIR was performed to identify vibrational and rotational modes and functional groups of samples. SAED pattern represented the polycrystalline structure of Fe2O3 and (3 & 6 wt%) Ag/CS-Fe2O3. UV–vis spectroscopy depicted that absorption decreased with the increasing amount of Ag/CS and increased band gap energy (Eg). PL spectra of doped Fe2O3 represent the reduction in recombination rate resulting in enhanced CA. EDS spectra exhibited the presence of Fe, O, Na, Au, and C, which confirmed the elemental composition of pristine and doped samples. TEM images indicate nanorods (NRs) of Fe2O3, and HRTEM provides interlayer d-spacing increased upon doping. The nanostructures exhibited excellent CA for the degradation of MB dye in an acidic medium, around 99.44%. Ag/CS-Fe2O3 (6 wt %) nanostructures have shown a significant increase in the inhibition zone (3.65 mm) against Escherichia coli (E. coli) at high-level doses. This study suggests that (3 & 6 wt%) Ag/CS-Fe2O3 nanostructures revealed superior catalytic and antibacterial activity for wastewater treatment. First-principles calculations indicate that the adsorption energies show a relatively strong interaction between MB and (3 & 6 wt%) Ag/CS-Fe2O3.

Improved Photocatalytic and Antibacterial Activity of Mg0.33Ni0.33Co0.33GdxFe2‐xO4 Nanoparticles Synthesized via the Co‐precipitation Method

AbstractThis study reports the synthesis of Mg0.33Ni0.33Co0.33GdxFe2‐xO4 nanoparticles (NPs) with 0.00≤x≤0.08 by the co‐precipitation method. The structural and optical properties of NPs are investigated. As Gd content increases, the lattice parameter and the bandgap energy increase whereas the particle size decreases. The photocatalytic performance of NPs is evaluated in the degradation of methyl violet (MV) dye under sunlight irradiation. The best activity is exhibited by Mg0.33Ni0.33Co0.33GdxFe2‐xO4 where x=0.04. The rate of the photodegradation reaction is boosted by increasing the pH and temperature. 95.4 % of MV is degraded after 240 min upon the addition of 5 wt. % carbon dot. The NPs are tested against Gram‐positive (Staphylococcus aureus and Enterococcus faecium) and Gram‐negative bacteria (Escherichia coli and Leclercia adecarboxylata) isolated from wastewater. The antibacterial activity was tested by the minimum inhibitory concentration and minimum bactericidal concentration broth microdilution assay, agar well diffusion assay and time‐kill test. The results show that the NPs exhibit inhibitory activity against Gram‐positive bacteria. Furthermore, NPs show bacteriostatic activity after 3 hours of incubation. The antibiofilm activity of the NPs is tested by the inhibition of biofilm formation and the destruction of pre‐formed biofilm assays. The results show an inhibitory activity of the NPs against Gram‐positive biofilms.

Optimizing energy storage properties under moderate electric fields in Na0.5Bi0.5TiO3-based ceramics via configuration entropy modulation

Lead-free ceramic capacitors with large energy storage density and efficiency synchronously under moderate electric fields is a challenging. In this work, a pathway of configuration entropy modulation (ΔSconfig) overcomes this challenge. The (1-x)(Na0.5Bi0.47La0.03)0.94Ba0.06TiO3-xSr(Sn0.2Ti0.2Al0.2Ta0.2Hf0.2)O3 ceramics were successfully synthesized. With the system ΔSconfig increases from 0.98 R to 1.79 R. The 0.85 NBLBT-0.15 SSTATH ceramic obtains a large recoverable energy density (Wrec = 4.28J/cm3) and ultra-high efficiency (η = 92.6%) under 260 kV/cm. The implementation of prominent energy storage performance can be attributed to the refinement of grain and domain size, and the increase of band gap and activation energy, which caused by the increase in ΔSconfig. More critically, the same composition also possesses great frequency (1–100 Hz) and thermal (20–140 °C) stability of energy storage performance as well as the high power density of PD ∼ 36.19 MW/cm3 and transient discharge rate of t0.9–44 ns at 120 kV/cm. This work shows that the regulation of ΔSconfig is an effective strategy to achieve outstanding energy storage properties under moderate electric fields.

Optical response of green synthesized thin Cr2O3 films prepared via drop and spin coatings

This study investigated the impact of optical bandgap energy on the optical constants of Cr2O3 thin films, which were prepared via green synthesis method and deposited using drop and spin-coatings at 600, 800, 1000, and 1200 rpm onto Cu substrates. The deposited Cr2O3 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and UV–VIS-NIR spectroscopy. XRD revealed that the prepared nanocoating surfaces are pure eskolaite Cr2O3 phase. The grain size of the prepared Cr2O3 films decreased from 15 nm to 12 nm for the drop and spin coatings, respectively. The morphology of the drop and spin coated samples showed nanorods, mesospherical, and quasi-spherical shaped nanoparticles, respectively, along with the presence of O and Cr. The bandgap energy increased from 2.35 eV to 2.50 eV, with increasing Spin Coater rotational speeds (RS) from drop to 1200 rpm, respectively. As bandgap energy increase, the carriers' spatial dimension shrinks, resulting in grains smaller than or equal to the exciton's Bohr radius. Thicker film materials tend to have lower bandgap energies due to strain effects, whereas smaller grain sizes tend to have higher bandgap energies. The determined refractive index and extinction coefficient values vary as the bandgap energy varies for all prepared samples. These findings confirmed that differences in bandgap energy affect the refractive index (n) and extinction coefficient (k) of Cr2O3 thin films. These are attributed to quantum confinement, internal scattering, and interference effects of Cr2O3 thin film surfaces.

Judd-Ofelt analysis, optical and structural features of borate glass doped with erbium oxide

This article presents a description of the structural-optical relationship in amorphous borate glass, with a decent investigation of Judd-Ofelt parameters to understand the effect of structural changes on optical properties due to the erbium oxide addition. Using density measurements, the effect of heavy molecular weight and larger ionic radius of erbium oxide was demonstrated. FT-IR analysis revealed the BO3 to BO4 conversion, confirming the network polymerization and connectivity. Astonishingly, the effect of erbium oxide on the increased band gap energy and the mitigated Urbach energy was demonstrated. Interestingly, Judd-Ofelt analysis was utilized to demonstrate the impact of the composition changes on the relation between the structural changes and optical properties. The influence of excited configurations of Er3+ ions was measured from the line strengths. The hypersensitive transitions from I15/24toH11/24 and G9/24 were observed at 375 nm and 519 nm, which have relatively higher intensities compared to other ones. Thus, they are attractive transitions for light emitting devices, LEDs, and solid lasers. The decreased values of Ω2 parameter is related to the increase in symmetry and high polarization around Er3+ ions. Consequently, the decrement in Ω2 suggests that the bond nature between Er3+ and O2− ions tends to be more ionic. Calculations of radiative parameters such as spontaneous radiative transition probability, radiative lifetime, and branching ratio were presented. The hypersensitive transitions have the highest values of the spontaneous radiative transition probability, predicting their high luminescence efficiency in glass host, besides the effectiveness of their usability in designing photonic devices. The obtained high branching ratio confirmed the lasing action of Er3+ ions in the glass host, especially the hypersensitive transitions of Er3+ ions.

Preparation and characterization of lanthanum-based perovskite oxides LaMO3 (M=Fe, Cr, Mn) thin films by electrophoretic deposition

In this study, we report the fabrication and characterization of perovskite thin films deposited on FTO substrates via electrophoretic deposition (EPD). The x-ray diffraction (XRD) patterns showed the formation of the orthorhombic structure for and films and the trigonal structure for the film. The field-emission scanning electron microscopy (FE-SEM) micrographs revealed nano-spherical particles with an average grain size of about 50 nm covering the surface with fewer porosities compared to the other films. Moreover, the film exhibited a higher transparency in the visible region (∼84%). The estimated bandgaps of and perovskite films were found to be 2.17, 3.18, and 2.92 eV, respectively. In addition, the refractive indices of all deposited films were calculated using five empirical models that relate the refractive index to the bandgap, which consistently revealed a decrease in refractive index with an increase of bandgap energy This study holds significant implications for the field of perovskite thin films as we contribute new insights into the fabrication of lanthanum-based perovskite thin films using the EPD technique. The comprehensive characterization of microstructural, morphological, and optical properties provides valuable information for understanding the structure-property relationship in these materials. Furthermore, the determination of bandgaps and refractive indices enhances our understanding of the optical properties of perovskite films. The findings from this study pave the way for potential applications in optoelectronic devices, where fine-tuning of material properties is critical for optimal device performance.

Photocatalytic and photovoltaic applications of green synthesized titanium oxide (TiO2) nanoparticles by Calotropis gigantea extract

Titanium di oxide (TiO2) nanoparticles were prepared by green synthesis method using leaves, seeds, and flower solvent extract of Calotropis gigantean medicinal plant. The X-ray diffraction (XRD) analysis of the prepared TiO2 nanoparticles shows tetragonal structure of anatase phase TiO2. The quantum confinement of the TiO2 particles by the inclusion of active biomolecules was confirmed by optical studies. The polycrystalline nature of the prepared nanoparticles was confirmed by XRD and SAED analysis. The particle size reduction and increase of band gap energy are noted with Calotropis gigantean leaf assisted TiO2, while it increases with flower and seed assisted TiO2. The prepared nanoparticles exhibit the size dependent photocatalytic activity and solar cell fabrication. Calotropis gigantean leaf assisted TiO2 NPs had the highest photocatalytic activity, completely degrading methylene blue in 60 min with an 96 % of degradation, due to a low recombination rate of photo-generated electrons and holes. The prepared Calotropis gigantean plant assisted TiO2 nanoparticles boosted the concentration of OH• and O2• radicals in the solution, which is beneficial for enhancing the photodegradation rate of organic compounds. Plant derivative based TiO2 nanoparticles are the best candidates due to simplicity and cost-effectiveness leading to economical and operational advantages in the large-scale synthesis of nanoparticles.

Influence of Lanthanum Doping on the Photocatalytic and Antibacterial Capacities of Mg0.33Ni0.33Co0.33Fe2O4 Nanoparticles

The increase in environmental pollution, especially water pollution, has intensified the requirement for new strategies for the treatment of water sources. Furthermore, the improved properties of nano-ferrites permit their usage in wastewater treatment. In this regard, novel Mg0.33Ni0.33Co0.33LaxFe2−xO4 nanoparticles (NPs), where 0.00≤x≤0.08, were synthesized to test their photocatalytic, antibacterial and antibiofilm activities. The structural and optical properties of the prepared NPs were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-Vis spectroscopy and photoluminescence (PL) analysis. As La content increases, the bandgap energy increases, whereas the particle size decreases. The photocatalytic activity of the prepared NPs is evaluated by the degradation of methylene blue (MB) dye under sunlight irradiation. Superior activity is exhibited by Mg0.33Ni0.33Co0.33La0.01Fe1.99O4 NPs. The influence of catalyst dosage, pH, temperature and addition of graphene (Gr) on the photodegradation reaction was studied. Increasing the pH and temperature improved the rate of the photodegradation reaction. The antibacterial and antibiofilm activities of the NPs were assessed against Escherichia coli, Leclercia adecarboxylata, Staphylococcus aureus and Enterococcus faecium. Mg0.33Ni0.33Co0.33Fe2O4 NPs inhibited bacterial growth. They had bacteriostatic activity on all isolates, with a greater effect on Gram-positive bacteria. All tested nano-ferrites had significant antibiofilm activities against some biofilms.

Effects of Fe, Co, or Ni substitution for Mn on [formula omitted] perovskite: Structural, morphological, and optical analyses

In this work, lanthanum strontium-based perovskites La0.7Sr0.3BO3 (B = Mn, Fe, Co, or Ni) samples are successfully synthesized. Hexagonal and Rhombohedral phases in the LSMO sample are observed using the XRD results. From reflectance data, the band gap energies are found to be 2.95 eV, 3.19 eV, 3.03 eV, and 3.14 eV for LSMO, LSFO, LSCO, and LSNO, respectively leading to a blue shift after the replacement. Linear optical evaluations exhibit increased band gap energy and decreased Urbach energy with the replacement of the Fe, Co, or Ni at the Mn site indicating presence of the localized defect states. The calculated extinction coefficient and refractive index parameters, using the Kramers-Kronig method, represent maximum values at the same wavelength for the LSFO. The nonlinear optical parameters are calculated using the obtained data from Diffuse reflectance spectroscopy. The connection of nonlinear optical absorption (β) with localized defect states has been discussed.

Design of a KNN-BZT Ceramic with High Energy Storage Properties and Transmittance under Low Electric Fields.

With the advancement of science and technology, single-function ceramics have been difficult to meet the rapid development of electronic components. It is of great significance to find and develop multifunctional ceramics with excellent performance and environmental friendliness (such as good energy storage and transparency). Especially, the realization of its excellent performance under low electric fields has more reference and practical value. In this study, by Bi(Zn0.5Ti0.5)O3 (BZT) modification in (K0.5Na0.5)NbO3 (KNN), reducing grain size, and increasing band gap energy, the purpose of improving energy storage performance and transparency has been achieved under low electric field. The results show that the submicron average grain size decreased to 0.9 μm and the band gap energy (E g) increased to 2.97 eV for 0.90KNN-0.10BZT ceramics. The transparency is up to 69.27% in the near-infrared region (1344 nm) and the energy storage density is 2.16 J/cm3 under 170 kV/cm. Moreover, the 0.90KNN-0.10BZT ceramic exhibits a power density (P D) of 17.50 MW/cm3 and the stored energy can be discharged in 1.60 μs at 140 kV/cm. This revealed a potential application of KNN-BZT ceramic as an energy storage and transparent capacitor in the electronics industry.

Influence of Donated Pair of Electrons by a Nitrito-Group Ligand on the Solid-State Properties of Lead Sulfide Thick Films

In general, thick and thin films are developed to provide special properties that range from electrical properties, optical, mechanical and chemical properties that can satisfy the needs for specific applications in technology. Lead sulfide (PbS) is an example of such films. Lead sulfide thin films have been synthesized on glass substrates. Some of the advantages of PbS thin film in olar cell applications include low material consumption, shorter energy payback period, large area modules, monolithic integration, tuneable material properties, low-temperature processes, and transparent modules. PbS thin films help also help in preventing corrosion of metallic parts of many devices. They are also used to offer protection against wear in moving parts. Materials such as jewelry, wrist watches, and knives are often coated to avoid corrosion. For deposition of PbS thin films, lead acetate is used as lead precursor and for sulfur source thiourea, has been was used in many studies.in this study, three samples of lead sulphide thick films were deposited on microscope glass slides at varying nitrito-group ligand concentrations at room temperature using solution method. The nitrito group ligand has a capacity to coordinate a central metal {Pb) atom using two different sites. First, it can use the nitrogen (N) atom as donor atom (nitrito group) and the oxygen (O) as donor atom (nitrito group). Secondly, it can use a sulphur (S) atom as donor atom ( in a thiocyanate group) and nitrogen (N) atom as donor atom ( as in a isothiocyanate). The influence of nitrito-group ligand on the solid-State properties of PbS thin films deposited by chemical bath technique were investigated and characterized using UV-VIS spectrophotometer and Four-Point Probe (FPP) technique. They were analyzed graphically, and the results show that, the donated pair of electrons from the nitrito group ligand caused absorption edge to decreases towards longer wavelength region while band gap energy increase from 1.61eV to 3.71eV with increase concentration. On the sampled films, there was a consistent increase in the sheet resistance and electrical conductivity as the concentration of Nitrito-group ligand increases.

Band gap structure - Lewis acid/base feature correlation for potassium/sodium polyniobates and polytitanates

Polyniobates and Polytitanates are extensively studied because of their characteristic structure, electronic and acid/alkali feature as perovskite oxide based materials. Based on the experimental data from references and theoretical results calculated by density functional theory (DFT), respectively, the qualitative correlation between band gap structure and Lewis acid/base feature is investigated in the present paper. When it comes to band gap structure, the bond angle θ and bond length are considered as the quite influential factors. As the M-O-M bond angle deviates from 180° and the bond length elongates, the band gap energy increases. The conduction band potential and valence band potential are associated with Sanderson charge fraction δi. It can be drawn from this study that the conduction band potential is positively correlated with Lewis acid (Nbδ+ or Tiδ+) strength and valence band potential is negatively correlated with Lewis base (Oδ−) strength for potassium polyniobates and polytitanates with different phase structure. The conduction band potential and valence band potential are positively correlated with Lewis acid (Nbδ+ or Tiδ+) strength and Lewis base (Oδ−) strength for sodium polyniobates and polytitanates with same phase structure. Sanderson electronegativity and the charge for the O 1s confirm the correlation between band gap structure and Lewis acid and base. In addition, the phase structures of polyniobates and polytitanates affect the Lewis acid feature of the conduction band and Lewis base feature of valence band respectively, resulting in changes in their band gap structure.

Thickness-dependent terahertz emission from Bi2S3 films under excitation below and above the band gap

Two-dimensional (2D) materials demonstrate fascinating thickness-dependent optical properties due to their van der Waals interaction and quantum confinement in the linear optical regime. However, the thickness-dependent nonlinear optical response is more complicated as virtual carriers (dipoles) and real carriers can be generated by below- and above-band-gap excitation, which calls for a more comprehensive understanding of these carriers in 2D materials. Herein, a direct band gap ${\mathrm{Bi}}_{2}{\mathrm{S}}_{3}$ is utilized to investigate the thickness-dependent nonlinear optical response by a terahertz (THz) emission spectroscopy. The results suggest that the THz emission intensity decreases with the increase of band gap energy under an 800-nm femtosecond laser excitation, which can be described by an empirical exponential equation. Under below-band-gap excitation, the optical rectification effect induced by instantaneous polarization (virtual carriers) dominates the THz emission mechanism in thin ${\mathrm{Bi}}_{2}{\mathrm{S}}_{3}$ films. In contrast, under above-band-gap excitation, real carriers are controlled by both resonant optical rectification and surface depletion electric field effects, resulting in shift and drift currents in thick ${\mathrm{Bi}}_{2}{\mathrm{S}}_{3}$ films. The contribution ratio of the shift and drift currents is $\ensuremath{\sim}1:1$ at ${45}^{\ensuremath{\circ}}$ oblique incidence. This competition between shift and drift currents results in the elliptically polarized THz wave generation, and the major axis orientation and ellipticity of the ellipse could be manipulated by changing the polarization of the pump light. In this paper, we imply the potential for designing tunable on-chip THz sources and nonlinear optoelectronic devices based on thickness-dependent 2D materials.

Physical properties of thin films of (α-Fe2O3) aluminum doped by spray pyrolysis methods

This work aims to study the effect of doping on α-Fe2O3 properties. For this, we elaborated thin layers of pure α-Fe2O3, and aluminum doped with spray pyrolysis method. The structural, morphological, and optical properties of the prepared films form different percentages: 2%, 4%, 6%, 8%and 10% were examined using X-ray diffraction (XRD), FTIR, and UV-Vis, respectively. Structural characterization from X-ray diffractograms confirmed the formation of α-Fe2O3, it has a rhombohedral structure with strong orientation preferential according to a plane (110) and displacement of the diffraction angles towards large values when the doping rate increases. Studies of transmittance spectra in UV-visible range 550-850 nm, showed high transparency of thin layers elaborated and the increase in direct band-gap energy from 2.59 to 2.78 eV. These characteristics are considered important in all applications