Absorption Band Edge Research Articles

Green‐synthesis of Ni‐Co nanoferrites using aloe vera extract: Structural, optical, magnetic, and antimicrobial studies

Nickel‐doped cobalt nanoferrites (NixCo1‐xFe2O4, where x = 0.0 to 1.0 with step size 0.2) were prepared using the auto combustion method in which aloe vera extract was taken as a fuel. Further, characterization for antimicrobial, structural, optical, and magnetic studies was performed for the prepared ferrite nanoparticles. Antimicrobial activity was assessed against a prevalent human fungal pathogen, Candida albicans. The X‐ray diffraction (XRD) pattern confirmed the spinel cubic phase with an average crystallite size of 28 nm. The Fourier transform infrared spectroscopy (FTIR) confirmed the stretching mode of vibration at the tetrahedral and the octahedral sites. Further, the analysis of magnetic properties was done using vibrating sample magnetometer (VSM), and the magnetic parameters, specific magnetization (67.69 emu/g) as well as squareness ratio σR/σS (0.47) were observed. From the UV–Visible absorbance spectra, the absorbance band edge was observed between 700 and 800 nm, and band gap values were observed at 2.84 eV for x = 1.0. Furthermore, the antimicrobial studies of the obtained ferrite nanoparticles were inspected against the C. albicans fungi, and it was observed that nickel‐doped cobalt ferrite shows an inhibitory nature. Maximum inhibition of 0.43 (67% growth) was observed for the composition x = 1.0. Therefore, these ferrite nanoparticles can be used as a drug against fungus infection.

Thermoluminescence properties of TiO2/Cu/TiO2 multilayer thin films fabricated by (RF/DC) sputtering for radiation dosimetry

The most popular TLDs are composed of phosphors, ceramics, and crystals. Despite having a high light output per unit of absorbed dose, they suffer from rapid signal fading, light scattering, saturation at higher doses, and difficulties annealing for re-use. Here, we report the characteristics of a novel TiO2/Cu/TiO2 multilayer thin film dosimeter fabricated using radio-frequency (RF) and direct current (DC) sputtering methods with a faster deposition rate, high purity, and uniformity. The multilayer sequence was set to TiO2 (150 nm)/Cu (x)/TiO2 (50 nm), at varying Cu thicknesses (x = 5, 10, 25, 40, and 50 nm). The structure, morphology, elemental composition, and optical properties of the films were characterized by the XRD, FESEM, EDX, and UV–Vis, respectively. Next, the best TiO2 multilayer films with 5 nm Cu were tested for morphological, structural, and optical properties at 600 and 1200 mGy of x-ray radiation. The dosimetric properties of samples irradiated with X-ray doses ranging from 100 to 1500 mGy were then investigated. The best annealing time, reproducibility, fading, low minimum detectable dose as well as the effect of different heating rates on the TL glow curve have all been studied. Our results indicate that the films are amorphous, porous with spherically shaped nanoparticles, have a uniform distribution of elements, and are transparent in the visible region. The optimum TL intensity was found at TiO2 (445 nm)/14.2 nm Cu/TiO2 (130 nm) sequence. The dose-response has a good linear correlation to x-ray radiation with a sensitivity that is 0.444 times less than that of TLD-100 sensitivity within the dose range 100–1500 mGy. Upon irradiation, the band gap decreases, crystallinity increases, pores increase, films become rougher, and the absorption band edge extends to higher wavelengths. The single and multilayer TiO2 films have high-intensity peaks at 270 and 274 ∘C, respectively, which is typical of TL glow curve peaks used in TLD applications. There were no significant changes in the TL reading after six times of reuse, and the fading was observed at 49.57% after 15 days of irradiation. The findings indicate that TiO2/Cu/TiO2 multilayer films are appropriate for thermoluminescence dosimetric applications.

FeSe2/TiO2 heterostructure as an efficient photocatalyst and their electrochemical energy storage applications

This paper reported the facile synthesis of FeSe2 and TiO2 and their different wt.% composites (75 and 50% of TiO2, here after FT-1 and FT-2) via solvothermal in/ex-situ sol-gel method for the first time efficient photocatalytic degradation of Rhodamine removal and supercapacitor applications. Small bandgap energy was obtained for FT-1 samples from the optical analysis, with a more negligible band edge absorption. The result shows that the composite of FeSe2 and TiO2 increases the absorption, which collectively enhances the separation of the charge carriers and redox activities. The photocatalytic activities analysis demonstrated that the FT-1 sample reveals the fastest removal of the RB dye in just 60 min (FT-2, FeSe2, and TiO2 = 90, 100, and 180 min) with good stability (98%) after several cycles. As supercapacitor electrode materials, all electrodes showed well-defined peaks in their CV loops and voltage plateaus in their charge/discharge profile, illustrating the pseudocapacitive charge storage mechanism. No voltage decay was observed during many discharge currents from the charge/discharge investigation, demonstrating the chosen potential frame is a suitable window for the FeSe2 and TiO2 nanomaterials. The higher capacity of 295 (FT-1) than other electrodes (FeSe2, TiO2, and FT-2 = 220, 115, and 240 C/g) at 1 A/g was obtained to reach 180 at 10 A/g, resulting in an enhanced rate capability of 82%. The high rate capability is the cause of its more minor charge transfer resistance, resulting in higher conductivity and supporting rapid charge transport kinetics. These outstanding properties open a new avenue for other FeSe2 and TiO2 nanomaterials for efficient energy storage technologies.

Efficient Zn2+ doping into CsBr nanocrystals using benzoyl bromide

The potential route to induce effective metal doping into the colloidal nanocrystal (NC) lattice is still limited due to the unfavorable energy cost and needs further investigation for colloidal chemistry involved in the optical properties and device development with optimized NC design. In this study, we reports a bright blue emitting Zn2+-doped CsBr NCs (6.7 at.%) by introducing reactive benzoyl bromide to promote a preferential reaction with metal cations that are not favorably incorporated into the CsBr lattice. In particular, the acyl group (R-C = O-) of benzoyl bromide is more effective to adopt additional metal cations into the crystal lattice during the nucleation and growth process of colloidal CsBr NCs compared to alkylammonium bromides with long hydrocarbon chains, providing a new synthetic route for metal doping into the metal halide perovskites NCs. Zn2+-doped CsBr NCs exhibit a blue PL emission at 425 nm with a Stokes shift of 113 nm for the weak absorption band edge.

Large wafer-level two-dimensional h-BN with unintentional carbon doping grown by metalorganic chemical vapor deposition

Large wafer-level hexagonal boron nitride (h-BN) was grown on sapphire by MOCVD in a pulse epitaxy mode. Comprehensive materials characterizations were performed on these samples including Fourier infrared spectroscopy, X-ray diffraction, Transmission Electron Microscope (TEM), and X-ray photoelectron spectroscopy. It is indicated that the BN film is hexagonal crystal phase with sp2 B–N bond and the content of B and N elements is about 1:1. The growth model of the h-BN on sapphire by MOCVD was proposed. A small amount of unintentionally doped carbon element was characterized in the h-BN film through XPS and optical absorption spectrometer analysis. The content of carbon was positively correlated with the flow rate of Triethyl-borane (TEB). The absorption band edge of h-BN doped carbon is about 219 nm and the band gap is 5.65 eV. According to first-principles calculations, C replacing the positions of N atoms in h-BN causes the absorption peak of the impurity level at 295 nm. Meanwhile, two-dimensional interlayer Van der Waals (vdW) characteristics of h-BN were observed, on account of the h-BN self-separation phenomenon that occurred on the sapphire, the upper AlN layer on the h-BN layer could be peeled from the sapphire.

Syntheses and characterization of dithienyl-blocked hexapyrrin and its mononuclear complexes

With the purpose to develop long chain-conjugated oligopyrrin-like compounds and their metal complexes, and thus achieve tunable near-infrared absorption, a dithienyl-blocked hexapyrrane [Formula: see text] was synthesized by acid-catalyzed [2+4+2] condensation, followed by oxidation with DDQ to afford dithiaoctapyrrin 1, and its mononuclear metal complexes 1-Cu and 1-Zn were synthesized by treating 1 with Cu(II) and Zn(II) acetates. All the compounds were systematically characterized by NMR/EPR, and HRMS. The crystal structures revealed that 1 adopts a double hook-like conformation. Whereas, both complexes 1-Cu and 1-Zn adopt spiral-hook hybrid conformations, showing smaller interplanar angles between the rings within the spiral part, compared with those in the hook-like counterpart of molecule 1, which is favorable for red-shifting the absorption. As expected, the absorption band edges for complexes 1-Cu and 1-Zn are red-shifted to ca. 1560 nm, compared with that of 1260 nm observed for 1.

Coupling the Piezoelectric Effect and the Plasmonic Effect to Enhance the Photocatalytic Degradation of Ciprofloxacin in Au-Ferroelectric Bi4Ti3O12 Nanofibers

In this study, ferroelectric Bi4Ti3O12 and Au-Bi4Ti3O12 nanofibers were synthesized by electrospinning and ion sputtering. The piezoelectric effect of Bi4Ti3O12 and the surface plasmon effect of Au were used to improve the photogenerated electron–hole separation and optical absorption. The results of the characterization showed successful preparation of the orthorhombic Bi4Ti3O12 nanofibers, in which the absorption band edge was 426 nm with a 2.91 eV band gap. The piezo-photocatalytic activity of the Bi4Ti3O12 was tested through the degradation of the antibiotic ciprofloxacin under three different experimental conditions: light, vibration, and light plus vibration. All of the ciprofloxacin was degraded after 80 min in piezo-photocatalytic conditions, with a piezo-photocatalytic degradation rate of 0.03141 min−1, which is 1.56 and 3.88 times, respectively, that of photocatalysis and piezo-catalysis. After loading Au on the Bi4Ti3O12, the degradation efficiency was improved under all three conditions, and the piezoelectric photocatalytic efficiency of Au-Bi4Ti3O12 for ciprofloxacin degradation was able to reach 100% in 60 min with a piezo-photocatalytic degradation rate of 0.06157 min−1. The results of the photocurrent and impedance tests indicated that the photocurrent density of Bi4Ti3O12 nanofibers loaded with Au is increased from 5.08 × 10−7 A/cm2 to 8.17 × 10−6 A/cm2, which is 16.08 times higher than without loading the Au. This work provides an effective way to improve the conversion efficiency of photocatalysis to degrade organic pollutants by combining the plasmon effect and the piezoelectric effect.

Smart Reversible Transformations between Chiral Superstructures of Copper Clusters for Optical and Chiroptical Switching.

Superstructures made from nanoscale clusters with new collective properties are promising in high-tech applications; however, chiral superstructures remain elusive, and the limited intercluster coupling effect at room temperature hampers the tailoring of collective properties. Here, we show that from chiral monomeric copper clusters to two enantiomeric pairs of supercrystals with distinct phases, the absorption band edge red-shifts by over 1.3 eV, with photoluminescence and circularly polarized phosphorescence from visible (572 nm) to near-infrared (NIR, 858 nm). These supercrystals with high NIR quantum yields of up to 45% at room temperature are prototyped for night-vision imaging. In response to solvent and temperature stimuli, chiral supercrystal-to-supercrystal transformations occurred, concomitant with high-contrast optical/chiroptical switching. In situ single-crystal X-ray diffraction (SCXRD), steady-state and time-resolved optical spectroscopy, and response experiments combined with theoretical calculations demonstrate that distance-sensitive intercluster orbital interactions contribute to the exceptional collective optical responses. Such chiral supercrystals built from subnanoscale metal clusters with novel collective chiroptical responses would be useful in the fields of information storage and NIR optical devices.

Spontaneously enhanced visible-light-driven photocatalytic water splitting of type II PG/AlAs5 van der Waal heterostructure: A first-principles study

To solve the problem of energy scarcity and widespread environmental contamination, it is necessary to design green and low-cost photocatalysts for water splitting. In this paper, a new penta-graphene/AlAs5 (PG/AlAs5) van der Waals (vdW) heterostructure is proposed and its performance for photocatalytic hydrolysis is calculated using the first-principles method. The findings suggest that the PG/AlAs5 heterostructure belong to type-II indirect semiconductor, and the edge position and band gap width of this heterostructure satisfy the requests of redox reaction. Furthermore, the oxidation reaction (OER) on the AlAs5 side and the hydrogen evolution reaction (HER) on the PG side are thermodynamically spontaneous under different conditions. Surprisingly, the introduction of strain engineering has changed the position of the band edge and light absorption performance of PG/AlAs5 heterostructure, which is powerful for the performance of photocatalytic water splitting. The PG/AlAs5 vdW heterostructure exhibits well visible light absorption intensity without applying strain and biaxial strain of 2%. In conclusion, the findings suggest that the PG/AlAs5 vdW heterostructure is a prospecting catalyst for visible-light hydrolysis.

Two Birds, One Stone: Coupling Hydrogen Production with Herbicide Degradation over Metal–Organic Framework-Derived Titanium Dioxide

Consumption of contaminated water can have detrimental effects on the health of every living organism on earth. There is, thus, a need to develop novel materials and technologies to purify water. Water is also a source of hydrogen, a clean renewable fuel that can be generated through the action of a photoactive catalyst and the earth’s abundant solar energy. Using photocatalysis, we can purify water by removing organic pollutants through the photodegradation reaction (oxidation) and produce hydrogen (H2) through the hydrogen evolution reaction (reduction). However, we can combine these two reactions in a single process to achieve an efficient photocatalytic system. Herein, we report the dual-functional photocatalysis (DFP) on herbicide-contaminated water using TiO2 polymorphs derived from the amino-functionalized metal–organic framework (MOF), MIL-125-NH2. Heteroatom TiO2 doping led to the generation of N- and N,S-doped TiO2. Of all the pristine and doped TiO2 phases synthesized, the N,S-doped anatase (NSTA) was the best dual-functional photocatalyst in degrading glyphosate (PMG) with simultaneous H2 production at a rate of 660 μmol g–1 h–1. Nuclear Magnetic Resonance studies indicate the preferential cleaving of PMG’s C–N bonds, here referred to as α and β C–N bonds, leading to the formation of glycine, formic acid, and phosphoric acid as the major degradation products. Density functional theory calculations indicate PMG’s activation through the carboxy and phosphoric acid groups on the surface of NSTA and through the phosphoric acid group on the surface of TiO2-rutile. Our results suggest that the catalytic activity of NSTA can be attributed to the templated impact of the parent MOF, owing to its porosity, redshifting of the band absorption edge toward the visible region, reduced energy bandgap, surface defects, and the presence of oxygen vacancies. The binding mode of PMG to NSTA and its degradation allowed us to test the photodegradation of other herbicides, such as glufosinate ammonium and 2,4-dichlorophenoxyacetic acid. Interestingly, our MOF-derived NSTA proved to be active in purifying water when all three herbicides were combined and produced H2 with a rate of 329 μmol g–1 h–1 simultaneously.

Suzuki-Miyaura Coupling Polymerization: Synthesis, Characterization and Optical Properties

The new thiazole-based polymer was synthesized by the Suzuki-Miyaura crossing-coupling reaction of 5-bromo-N-(3-bromophenyl)thiazol-2-amine and 9,9-dioctyl-9H-fluorene-2,7-diboronic acid bis(pinacol) ester. The synthesized monomer and poly[N,N'(1,3-phenylene)bis(thiazol-2-amine)-co9,9’dioctylfluorene] (Poly[Tm]) were characterized by the Elemental analysis, Fourier Transform Infrared spectroscopy, Nuclear Magnetic Resonance spectroscopy, Thermogravimetric analysis and Gel Permission chromatography. Furthermore, the optical properties of the Poly[Tm] were studied at three concentrations of 0.625, 1.25 and 2.5 mM in solution. The absorption band edge values of Poly[Tm] decreased with the increasing concentration of the solutions. When the concentration of the Poly[Tm] solution was increased, transmittance values of the Poly[Tm] were increased, and its molar extinction coefficient was resulted in higher absorbance values. Synthesized Poly[Tm] could provide a novel concept for the design of transistors and photovoltaics.

Oxygenated carbon functionalized TiO2 aerogel surface: Facile synthesis, surface, structural and photovoltaic investigations

The present study reports the synthesis of in-situ surface functionalized TiO2 aerogel through microwave-assisted sol-gel method. Glucose was used as a carbon source, and different amounts of oxygenated carbon were inserted on the surface of TiO2 aerogel. The presence of oxygenated carbon on the surface of TiO2 is confirmed by Raman analysis. The microstructural analysis of the materials was performed by Field Emission Scanning Electron Microscope (FESEM) and transmission Electron Microscope (TEM). After doping with COx, the retained porous surfaces were achieved. X-ray Photoelectron Spectroscopy (XPS) indicates an increase in the amount of carbon and oxygen compared to the titanium and oxygen ratio of TiO2. The increase in the peak area of O1s spectra indicates the insertion of different forms of oxygenated carbon. The C1s spectra confirm that various forms of oxygenated carbon, such as –COH, –COOH, CO–C and OC=O, are on the surface of TiO2 aerogel. Due to surface-adsorbed COx, the TACOx samples had extended absorption band edges and reduced band gaps in optical studies. As a result of that, the energy for the electron injection (0.52 eV) was significantly reduced in the TACOx-20% sample. In addition, the BET surface area analysis reveals a high surface area of 144 m2/g for the TACOx-20% sample. Dye adsorption studies also reveal the high dye loading of 0.65 μmol/mg found in the TACOx-20% sample due to more surface hydroxyl groups on the surfaces. The porous network structure, altered optical properties, and the insertion of hydrophilic groups on the surface of COx-doped titania aerogel are beneficial for adsorbing more dye molecules, which are crucial for improving the photovoltaic efficiency of the materials.

Preparation of nanosheets embedded ZnSe/Bi2Se3 core/shell quantum dots for the study of optical properties and antibacterial activity

Cation exchange reaction is a well-known ion exchange method that is very much feasible for easy synthesis procedure and greater tunability in size and shape of nanomaterials. Here, we have synthesized different water dispersed ZnSe/Bi2Se3 core/shell quantum dots by using the cation exchange method with varying Bi content. The variation in Bi concentration allows the change in shell thickness which ultimately affects the structural and optical behaviors. The ZnSe/Bi2Se3 quantum dots exhibited type II band alignment. The as-prepared quantum dots embedded nanosheets exhibit broad, amorphous XRD pattern of the ZnSe phase. A shift in the peak position of the XRD pattern as well as Raman vibrational bands with varying Bi content suggests the formation of the Bi2Se3 shell. Also, the shifting among the XPS peaks confirms the change in the chemical environment of both Zn-Se and Bi-Se bonds in the hybrid system. This ensures the Se ions on the surface of ZnSe coordinated the bismuth complex. The increase in shell thickness enhances the band edge absorption and reduces the optical bandgap which is due to the increase in the particle size of the sample. A broad photoluminescence emission is observed for all the cases with 514 and 325 nm excitation. Each broad spectrum is comprised of different component peaks corresponding to excitonic and defects (vacancies and interstitials) related emission. The core/shell materials are most suitable for different biomedical applications. Hence, the ZnSe/Bi2Se3 quantum dots are analyzed for antibacterial activity, which showed a good antibacterial response against Staphylococcus aureus (ATCC 25,923).

Facile low temperature development of Ag-doped PbS nanoparticles for optoelectronic applications

The present article is based on Silver (Ag) doped Lead sulfide (PbS) nanoparticles for optoelectronic applications. Structural and morphological properties of pristine PbS and 0.5, 1.0, 2.5 and 5.0 wt% Ag doped PbS nanoparticles (NPs) were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. X-ray diffraction (XRD) patterns of pure PbS, 0.5, 1.0, and 2.5 wt% Ag: PbS NPs were marginally shifted towards a lower diffraction angle and XRD profile of 5.0 wt% Ag: PbS NPs was shifted to the right side with respect to JCPDS card. The crystallite sizes of pristine PbS and Ag: PbS NPs were obtained in the range of 17–18.7 nm. The phase and substitution of Ag into the PbS lattice were confirmed by the Fourier transform (FT) Raman spectra of Ag:PbS NPs. Scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy was employed to observe the morphology and to confirm the homogeneous doping of pristine PbS and Ag-doped PbS NPs. The optical band gaps were determined in the range of 3.011–3.378 eV and 1.201–1.286 eV, respectively from diffused reflectance spectra of pristine PbS and Ag: PbS NPs. Urbach energies were evaluated as 1.5687, 1.8879, 2.8020, 1.6425, and 1.2799 eV from the slopes of the fitted straight lines near the absorption band edge region of pure, 0.5, 1.0, 2.5, and 5.0 wt %, respectively. Current (I)-voltage (V) characteristics of the prepared NPs were carried out in the presence of an applied voltage (±4 V). The enhancement in I–V characteristics of 2.5 and 5.0 wt % was caused by the increment in the injected charge density. The optical transition states were examined by the second-order derivative of the absorbance spectra. The high carrier density in Ag: PbS has been attributed to the bottleneck effect, which is confirmed by the BM shift and I–V characteristics. It was found that Ag: PbS NPs exhibited an increase in electrical properties compared to the pristine PbS NPs.

Optical properties of ZnFe2O4 nanoparticles and Fe-decorated inversion domain boundaries in ZnO.

The maximum efficiency of solar cells utilizing a single layer for photovoltaic conversion is given by the single junction Shockley-Queisser limit. In tandem solar cells, a stack of materials with different band gaps contribute to the conversion, enabling tandem cells to exceed the single junction Shockley-Queisser limit. An intriguing variant of this approach is to embed semiconducting nanoparticles in a transparent conducting oxide (TCO) solar cell front contact. This alternative route would enhance the functionality of the TCO layer, allowing it to participate directly in photovoltaic conversion via photon absorption and charge carrier generation in the nanoparticles. Here, we demonstrate the functionalization of ZnO through incorporation of either ZnFe2O4 spinel nanoparticles (NPs) or inversion domain boundaries (IDBs) decorated by Fe. Diffuse reflectance spectroscopy and electron energy loss spectroscopy show that samples containing spinel particles and samples containing IDBs decorated by Fe both display enhanced absorption in the visible range at around 2.0 and 2.6 eV. This striking functional similarity was attributed to the local structural similarity around Fe-ions in spinel ZnFe2O4 and at Fe-decorated basal IDBs. Hence, functional properties of the ZnFe2O4 arise already for the two-dimensional basal IDBs, from which these planar defects behave like two-dimensional spinel-like inclusions in ZnO. Cathodoluminescence spectra reveal an increased luminescence around the band edge of spinel ZnFe2O4 when measuring on the spinel ZnFe2O4 NPs embedded in ZnO, whereas spectra from Fe-decorated IDBs could be deconvoluted into luminescence contributions from bulk ZnO and bulk ZnFe2O4.

Optical properties of Ga-Ge-Sb-Se chalcogenide glasses doped with terbium and dysprosium ions, near the fundamental absorption band edge

In the paper, results of measurements of the optical response of chalcogenide glasses of the Ga5Ge20Sb10Se65 composition doped with rare-earth ions Tb3+ or Dy3+, in the wavelength range of 0.7-1.5 μm by the method of IR spectroscopy are presented. Parameters characterizing the fundamental absorption band edge of the glasses --- optical bandgap energy, Urbach tail parameter and weak absorption tail parameter --- have been evaluated. It has been found that doping in low concentrations (up to 0.3 wt%) does not influence the optical bandgap energy and optical properties of the glasses in the range of the Urbach tail, but in the range of the weak absorption tail, optical response of the glasses depends on the activator concentration. Crystallization of the glasses produced by the direct melting method also depends on the activator concentration. In the glasses doped with Dy3+, absorption bands of the ion are located in the range of the weak absorption tail of the glass that makes possible energy transfer between the ions and the gap states of the charge carriers. Keywords: rear earth elements, chalcogenide glasses, bandgap energy, Urbach tail, weak absorption tail, gap states.

Invesigation of the electronic structure and Optoelectronic properties of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> using GGA+U method based on first-principle

In this work, the formation energy, band structure, state density, differential charge density and optoelectronic properties of undoped and Si doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> are calculated using GGA+U method based on density functional theory. The results show that the Si-substituted tetrahedron Ga(1) is more easily synthesized in experiments, and the obtained <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> band gap and Ga 3d state peak are in good agreement with the experimental results, and the effective doping is more likely to be obtained under oxygen-poor conditions. After Si doping, the total energy band moves to the low-energy end, and Fermi level enters the conduction band, showing n-type conductive characterastic. Si 3s orbital electrons occupy the bottom of the conduction band, the degree of electronic coocupy is strengthened, and the conductivity is improved. The dielectric function ε2(ω) results show that with the increase of Si doping concentration, the ability to stimulate conductive electrons first increases and then decreases, which is in good agreement with the quantitative analysis results of conductivity. The optical band gap increases and the absorption band edge rises slowly with the increase of Si doping concentration. The results of absorption spectra show that Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> has strong deep ultraviolet photoelectric detection ability. The calculated results provide a theoretical reference for the further experimental investigation and the optimization innovation of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> and relative device design.

Оптические свойства халькогенидных стекол системы Ga-Ge-Sb-Se, легированных ионами тербия и диспрозия, вблизи края полосы фундаментального поглощения

In the paper, results of measurements of the optical response of chalcogenide glasses of the Ga5Ge20Sb10Se65 composition doped with rare-earth ions Tb3+ or Dy3+, in the wavelength range of 0.7 – 1.5 μm by the method of IR spectroscopy are presented. Parameters characterizing the fundamental absorption band edge of the glasses - optical bandgap energy, Urbach tail parameter and weak absorption tail parameter - have been evaluated. It has been found that doping in low concentrations (up to 0.3 mass%) does not influence the optical bandgap energy and optical properties of the glasses in the range of the Urbach tail, but in the range of the weak absorption tail, optical response of the glasses depends on the activator concentration. Crystallization of the glasses produced by the direct melting method also depends on the activator concentration. In the glasses doped with Dy3+, absorption bands of the ion are located in the range of the weak absorption tail of the glass that makes possible energy transfer between the ions and the gap states of the charge carriers.

Investigation of electronic structure and optoelectronic properties of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>using GGA+<i>U</i> method based on first-principle

In this work, the formation energy, band structure, state density, differential charge density and optoelectronic properties of undoped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> and Si doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> are calculated by using GGA+<i>U</i> method based on density functional theory. The results show that the Si-substituted tetrahedron Ga(1) is more easily synthesized experimentally, and the obtained <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> band gap and Ga-3d state peak are in good agreement with the experimental results, and the effective doping is more likely to be obtained under oxygen-poor conditions. After Si doping, the total energy band moves toward the low-energy end, and Fermi level enters the conduction band, showing n-type conductive characteristic. The Si-3s orbital electrons occupy the bottom of the conduction band, the degree of electronic occupancy is strengthened, and the conductivity is improved. The results from dielectric function <i>ε</i><sub>2</sub>(<i>ω</i>) show that with the increase of Si doping concentration, the ability to stimulate conductive electrons first increases and then decreases, which is in good agreement with the quantitative analysis results of conductivity. The optical band gap increases and the absorption band edge rises slowly with the increase of Si doping concentration. The results of absorption spectra show that Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> has the ability to realize the strong deep ultraviolet photoelectric detection. The calculated results provide a theoretical reference for further implementing the experimental investigation and the optimization innovation of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> and relative device design.

Manganese and Nitrogen co-doped TiO2 for the photocatalytic degradation of anionic dyes and phenol under sunlight

ABSTRACT Different compositions of manganese (x = 1 & 3 wt. %) and nitrogen (y = 1 wt. %) co-doped TiO2 (MnxNyT) photocatalysts are prepared by the conventional sol-gel method. The crystallinity, optical properties, phase purity and surface morphology of prepared nano-photocatalysts were characterised in detail. The structural analyses show that the simultaneous doping with manganese and nitrogen controls the growth of TiO2 crystal structure having an average crystallite size in the range of 14.6 to 24.5 nm. The optical analysis also demonstrated that due to the synergistic effect of Mn and N, co-doped TiO2 represents the red-shift in the absorption band edge from 3.33 eV to 2.39 eV, which improved the response of TiO2 structure towards the visible region and enhanced electron-hole separation. Among all, Mn3N1T represented the better photocatalytic efficiency against anionic dyes (Blue KBR and Red GD) and phenol under optimised conditions (such as initial substrate’s concentration = 20 ppm, photocatalyst dose = 0.5 g and solution pH of 3 and 7, respectively) due to its low bandgap, low crystallite size and high absorptivity towards the visible region. The kinetics study also showed that the degradation of dyes and phenol over Mn3N1T followed pseudo-first-order kinetics.