Shift In Optical Band Gap Research Articles

Magnetic, Optical, Electrical and Antimicrobial Properties of MnCuZnFe2O4 Nanoparticles

AbstractThe Mn0.92Cu0.08‐yZnyFe2O4 (y=0.02, 0.04, 0.06 and 0.08) nanoparticles (MCZF NPs) were synthesized via the hydrothermal process at low operating temperature. The MCZF system generated a cubic spinel structure as seen by the X‐ray diffraction patterns. The average crystallite size was observed to be increasing from 25 to 30 nm. The broad (γ1) and narrow (γ2) absorption bands were seen in FTIR spectra and the cation distributions at tetrahedral (A) and octahedral (B) sites, respectively, was indicated. The surface morphology was analyzed using electron microscopy. Clarification was provided for the dependence of the optical bandgap shift (Eg~1.96–2.15 eV) on the concentration of substituent. The superparamagnetic nature of MCZF can be advantageous for biomedical applications and it was demonstrated by the magnetization versus applied magnetic field (M−H) loops. Small values of remanence magnetization (Mr) and coercivity (Hc) were found using magnetization versus magnetic field (M−H) curves at y=0.02, 0.04, 0.06, and 0.08. This proved that MCZF NPs exhibited the superparamagnetic behavior. The cation distribution at two sublattices was also estimated using a two‐sublattice model. The greatest zone of inhibition in an antibacterial study of MCZF (produced by the green method) was 10.8 mm for Pseudomonosa aeruginosa and 9.4 mm for Staphylococcus aureus.

Asymmetric optical properties and bandgap shift of pre-strained flexible ZnO films

Strain engineering has been extensively explored to modulate the various intrinsic properties of flexible inorganic semiconductor films. However, experimental characterization of tensile and compressive strain-induced modulation of optoelectronic properties and their differences has not been easily implemented in flexible inorganic semiconductor films. Herein, the strain-dependent structural, optical, and optoelectronic properties of flexible ZnO films under pre-tensile and pre-compressive strains are systemically investigated by a Mueller matrix ellipsometry-based quantitative characterization method combined with x-ray diffraction and first-principle calculation. With extended prestress-driven deposition processing under bi-direction bending modes, pre-tensile and pre-compressive strains with symmetric magnitudes can be achieved in flexible ZnO films, which allows precise observation of the strain-driven asymmetric modulation of optoelectronic properties. When the applied prestrain varies approximately equally from 0% (baseline) to −0.99% (compression) and 1.07% (tensility), respectively, the relative changes for the c-axis lattice constant are 0.0133 and 0.0104 Å, respectively. Meanwhile, the dependence factors of the bandgap energy on the pre-compression and pre-tensile strains were determined as −0.0099 and −0.0156 eV/%, respectively, and the complex refractive index also presents an asymmetric varying trend. With the help of the strain–stress analysis and the first-principle calculation, the intriguing asymmetric strain-optical modulation effect could be attributed to the biaxial strain mechanism and the difference in the deformation potential between the two prestrain modes. These systematic investigation consequences are thus promising as a basis for the booming applications of the flexible inorganic semiconductor ensemble.

Growth of MAPbI3 perovskite films on MWCNT-modified TiO2 thin films for solar cell applications

In this work, we have modified titanium dioxide (TiO2) films by incorporating multi-walled carbon nanotubes (MWCNTs) in TiO2-sol. TiO2 and MWCNT-modified TiO2 thin films have been prepared via solution processing spin coating route. Further, the structural, optical, and surface morphology of methyl ammonium lead iodide (MAPbI3) films have been studied onto pristine TiO2 and MWCNT-modified TiO2 films. We extensively analyze how different MWCNT concentrations impact the TiO2 and perovskite film structure, optoelectronic properties, and surface characteristics. The findings highlight that the MAPbI3 films maintain a tetragonal structure with enhanced crystallinity compact and smooth surface morphology in MWCNT-modified TiO2/MAPbI3 films. Besides this, enhanced optical absorbance in MAPbI3 films have also been observed on perovskite films fabricated onto MWCNT-modified TiO2 films with enlarged grains and a red shift in optical band gap has been observed for MWCNT-modified TiO2 films and MWCNT-modified TiO2/ MAPbI3 films. Further, various critical electrical parameters such as charge carrier concentration, Hall mobility, sheet resistance, and resistivity have been investigated to understand the effects of the incorporation of MWCNT on TiO2 films. The value of carrier concentration enhances from 3.76 × 1024 cm−3 to 6.39 × 1024 cm−3 on incorporation of MWCNT in TiO2 films. Furthermore, an enhancement in crystallinity, optical absorbance, and grain size has been observed in perovskite films fabricated onto TiO2/MWCNT films. Thus, TiO2 modification with MWCNT can tune the optical and charge transport properties of charge-transporting layer TiO2 films for perovskite photovoltaics and other optoelectronic devices.

Impact of high LET radiation on various properties of CR-39 detector

Since polyallyl diglycol carbonate (PADC), viz. CR-39 has been widely used for radiation detection and measurement in various complex radiation fields, therefore, a systematic study has been carried out in this work to demonstrate the significant effect of linear energy transfer (LET) of heavy ions on the optical, structural and chemical (etching) properties of the detector. The PADC samples were exposed to heavy ions (7Li, 12C, 16O and 19F) of different energies to study the effect of LET from 76 to 1002 keV/μm. Samples were chemically processed to develop the latent tracks induced by heavy ions. Image analysis showed an increase in the damaged track size with the LET as well as the etching time. Having same energy, the track sizes of two different ions were found to be different because of the differences in their LET values. Similarly, for one particular ion, the track sizes were found to be smaller for higher energy due to low LET than that of the lower energy corresponding to high LET. Hence, this criterion is successfully demonstrated for particle identification by using PADC. Furthermore, spectrophotometric studies (UV–vis, FTIR) have been carried out to determine the changes in opacity, Urbach's energy, optical bandgap, molecular vibrations and red shift of the cut off wavelength with the increase in LET values.

Excitation wavelength altered PL study of Co doped ZnO nanoparticles suitable for white LED application

Abstract ZnO nanoparticles doped with Co at different concentration (Zn1−x Co x O) were synthesized by sol–gel auto combustion method and are characterized by using various characterization tools. Structural study using X-ray diffraction technique (XRD) analysis showed the crystalline nature with hexagonal wurtzite geometry and the composition analysis using energy dispersive X-ray spectroscopy (EDX) confirmed the incorporation of Co in the ZnO lattice in the case of doped nanoparticles. Scanning electron-microscopy (SEM) and transmission electron microscopy (TEM) analysis showed the prepared nanoparticles as spherical, loosely agglomerated and having dimension of nanoscale. UV–vis DRS studies indicated a red shift in optical band gap with Co doping. PL spectra exhibits emission in the UV and visible region and the analysis revealed information about the presence of various types of defects in the ZnO lattice. An increase in the excitation wavelength gives intense emission in the high wavelength region for doped nanoparticles confirming the presence of divalent and monovalent oxygen as main defects. The Zn0.93Co0.07O nanoparticles records CIE coordinates lying in the white region of CIE color space at 350 nm with CCT of 5561.4 K suggesting their suitability in fabrication of white light emitting diodes.

High sensitivity detection of different pH ranges with rGO-nanocomposite coated eFBG sensor.

In the proposed work, a highly sensitive reduced graphene oxide (rGO) coated etched fiber Bragg grating (eFBG) pH sensor is developed and characterized. To create the sensing probe, a nanocomposite layer of rGO is coated over the unclad area of the eFBG. The analysis of rGO material has been done using different characterization tools such as UV-VIS-NIR spectroscopy, x-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Experiments are performed using pH samples ranging from pH 2 to pH 12 to validate the operational sensing range of the proposed sensor. The effectiveness of the proposed sensor is evaluated with various pH values by monitoring the shift in the resonance peak of the sensor's reflection spectrum in a real-time interrogation system. The sensor performs well in both low and high pH ranges, with a maximum sensitivity of 0.232nm/pH at pH 12. Due to a shift in the rGO's optical band-gap at both low and high pH values in the samples, the sensor can detect minimal changes in concentration. In the reflected spectrum, the Bragg wavelength (λ B) shifts as a result of the change in the refractive index. The λ B is observed to change as the pH of the aqueous solution is changed experimentally. Its performance is shown to be minimally affected by the ambient temperature (in the range of 19-21∘ C). The sensor also has the capacity for remote sensing, a quick response time, a small size, a low cost, a miniaturized probe, and the ability to reuse the probe.

Structural and Optical Characterisation of Size-Selected Glutathione-Capped Colloidal Cu–In–S Quantum Dots

Size-selected series of copper-deficient colloidal Cu–In–S quantum dots (QDs) stabilized with glutathione are obtained by the exchange reaction in aqueous solutions under mild synthesis conditions. The optical bandgap and photoluminescence maximum position shift toward higher energies with decreasing QD size. Based on X-ray diffraction data, the QDs are assigned to a tetragonal chalcopyrite-type structure. The average size of QDs, estimated from the Scherrer formula and from the comparison with the absorption edge-based sizing curves, exhibits a fair agreement, being in the interval of 1.2–2.9 nm. The Raman spectra of Cu–In–S QDs are analyzed with the account for the QD structure, confinement-related effects, non-stoichiometry, and possible existence of secondary phases.

Ultraviolet photodetector based on RbCu2I3 microwire

Copper-based halide perovskites have shown great potential in lighting and photodetection due to their excellent photoelectric properties, good stability and lead-free nature. However, as an important piece of copper-based perovskites, the synthesis and application of RbCu2I3 have never been reported. Here, we demonstrate the synthesis of high-quality RbCu2I3 microwires (MWs) by a fast-cooling hot saturated solution method. The prepared MWs exhibit an orthorhombic structure with a smooth surface. Optical measurements show the RbCu2I3 MWs have a sharp ultraviolet absorption edge with 3.63 eV optical band gap and ultra-large stokes shift (300 nm) in photoluminescence. The subsequent photodetector based on a single RbCu2I3 MW shows excellent ultraviolet detection performance. Under the 340 nm illumination, the device shows a specific detectivity of 5.0 × 109 Jones and a responsivity of 380 mA·W−1. The synthesis method and physical properties of RbCu2I3 could be a guide to the future optoelectronic application of the new material.

Photoluminescence of wurtzite-type Ce-doped ZnS nanocrystals processed by a low-temperature aqueous solution approach

Undoped and Ce-doped ZnS nanocrystals with hexagonal wurtzite structure were synthesized by a low-temperature aqueous solution method that uses l-cysteine as complexing and capping agent. The morphology analysis revealed the formation of polydisperse nanocrystals with sizes in the range of 2–4 nm, while the energy dispersive X-ray spectroscopy showed that all the samples were sulfur deficient. The presence of Ce3+ species in the Ce-doped samples was confirmed by the X-ray photoelectron spectroscopy technique. UV–vis spectroscopy indicated that all samples had a blue shift of optical bandgap compared to bulk ZnS. According to the room-temperature photoluminescence studies, the spectra of Ce-doped ZnS nanocrystals exhibited a broad band emission consisting of UV and blue components, associated with ZnS defects, and a green component due to the 5d-4f transition of Ce3+.

Tuning the Photocatalytic Performance of Ni-Zn Ferrite Catalyst Using Nd Doping for Solar Light-Driven Catalytic Degradation of Methylene Blue

In this paper, we describe the creation of a moderate band gap Nd-substituted Ni-Zn ferrite as a nano photo catalyst via a simple and cost-effective process of solution combustion. Nd substitution alters the crystallite size, shape, band gap, and magnetic characteristics of Ni-Zn ferrite significantly. Investigations using X-ray diffraction revealed that all samples display a pure phase. The average crystallite size was determined to be between 31.34 and 38.67 nm. On Nd doping, morphology investigations indicated that the shape of nanoparticles changed from approximately spherical to stacked grains. Band gap experiments confirmed the red shift in optical band gap on Nd doping. The synthesized catalysts Ni0.5Zn0.5Fe2O4 (Nd0), Ni0.5Zn0.45Nd0.05Fe2O4 (Nd1), and Ni0.5Zn0.5Nd0.05Fe1.95O4 (Nd2) have been effectively used for the degradation of methylene blue dye under the solar light irradiation. The sample with Nd substitution on Fe sites had the highest methylene blue degradation efficiency. Nd2 photo catalyst degrades the methylene blue dye with a degradation efficiency of 98% in 90 min of solar light irradiation. The photocatalytic activity is triggered by the existence of oxygen vacancies and a mixed valence state of Ni, Fe, and Nd, as confirmed by the XPS investigation. In addition, the investigations on scavenging reveal that the hydroxyl radical is a reactive component in the degradation process. The degradation route has been investigated in relation to the many potential reactions and discovered reactive substances.

Structural phase transition and charge carrier dynamics in Dy containing La6MoO12 ionic conductor

The solution combustion method was adopted to prepare a single-phase La6MoO12 compound by doping 10% Dy in the La site and sintered at 800 °C, 1000 °C, and 1200 °C temperatures. The X-ray diffraction patterns confirmed a phase transition of the samples from the cubic fluorite phase (Fm3‾m) to a complex rhombohedral structure (R3‾m) with increasing sintering temperature. The microstrain and particle size show the opposite behaviour in the case of 800 °C and 1200 °C sintered samples. The FE-SEM and XRD results corroborated the increment of particle size with sintering temperature. Elemental mapping confirmed the uniform distribution of elements in the compositions. Red and blue shifts in optical bandgap were observed with sintering temperature. All samples show a negative temperature coefficient of resistance (NTCR) behaviour. The sample sintered at 1200 °C has the highest ionic conductivity of 1.03×10−4Ω−1cm−1 at 540 °C. The reciprocal temperature dependence of conductivity followed the VTF equation. The dielectric loss tangent indicated that all samples have a single relaxation process. The time-temperature superposition principle has been verified from the scaling of the dielectric loss tangent.

Influence of deposition power and annealing on the performance of RF-sputtered SnS for infrared photodetection

Tin sulfide has shown their great potential in electronic and photonic systems due to its unique optoelectronic properties, less toxic nature, cost-effective and economically earth-abundant elements. The multivalence of Sn and stereochemical activity endow it with rich phase spaces and susceptible internal structures, which in turn directly affect its properties. In this paper, optimization studies towards the influence of RF power and post-deposition annealing temperature on the micro structure and photodetection performance of SnS are achieved by RF magnetron sputtering method. The structural characterizations confirm the significance of RF power for phase formation and photoelectric conversion ability. The optical band gap shifts from 1.41 eV to 1.30 eV as RF power increasing from 30 W to 50 W, in the meantime, the optoelectronic performances such as responsivity and specific detectivity are subsequently improved to be 226.55 mA/W and 1.76 × 1010 Jones. Further, the variations in infrared photodetection performance correlated with the annealing temperature exhibite a more well-behaved photoresponse at 300 °C. The results pave the way to discern the growth − structure − property relationships and then guide potencial applications of tin sulfide family.

Robust Stability of Optical and Electronic Properties of Gallium‐Doped Zinc Oxide Thin Films to Gamma Ray Irradiation

Through combined measurements of broadband optical spectroscopy (10 meV to 6 eV), electrical resistivity, and Hall effect, the effects of gamma ray irradiation on electronic and optical properties of gallium-doped ZnO (GZO) thin films, deposited by ion plating direct-current arc discharge, are investigated. A significant number of films, deposited at various discharge currents (I D = 100–200 A) and oxygen gas flow rates (OFR = 0–25 sccm), exposed to doses of 15 and 30 kGy of gamma rays, are studied. The results indicate strong resilience of films to irradiation: visible range transparency is reduced by 10–12% and the optical bandgap shifts to lower energies by less than 3%, while electrical resistivity, carrier concentration, and electron mobility remain nearly unchanged.

Effects of ambient high-temperature annealing on microstructure, elemental composition, optical and electrical properties of indium tin oxide films

500 nm-thickness indium tin oxide (ITO) films were deposited onto quartz glass substrates and annealed at 700–1000 °C for 1 h. Microstructure, elemental composition, optical and electrical properties of ITO films were systematically studied. It is found that the crystalline is cubic bixbyite, and preferred orientation changes from mainly (222) to (400) with the increasing temperature. Obvious changes are also observed in morphology of ITO films during the ambient high-temperature annealing. ITO film annealed up to 1000 °C is still stable Sn doped In2O3, oxygen defects decreases and adsorbed oxygen increases. The resistivity of ITO films after annealed at 700 and 800 °C firstly increases slightly and then increases sharply, when annealing temperature is increased to 900 and 1000 °C. Average transmittance of these films was 70%–80% and their optical band gap shifts to lower energy with the increase of the annealing temperature.

Investigation on the optical and electrical properties of undoped and Sb-doped SnO2 nanowires obtained by the VLS method

In this work, we report the effects of Sb doping on the optical and electrical properties of the SnO2 nanowires obtained by the vapor-liquid-solid (VLS) method. The absorption edges were found to be 3.30 eV and 3.66 eV for undoped SnO2 and Sb-doped SnO2 (ATO) nanowires, respectively. The energy shift was related to the Burstein-Moss effect taking place in the doped nanowires. We studied the ATO optical bandgap (ΔE = 0.36 eV) shift as a function of carrier concentration. The incorporation of Sb caused the resistivity to decrease three orders of magnitude for single-nanowire ATO devices. In addition, it was found that undoped SnO2 nanowires exhibit semiconductor characteristics while a metal-insulator transition (MIT), around 170 K, was observed in the ATO nanowires.

Synthesis, characterization and antibacterial performance of transparent c-axis oriented Al doped ZnO thin films

Highly c-axis oriented ZnO thin films with wurtzite structure were grown onto preheated glass using spray pyrolysis technique with varying Al/Zn ratios. The transmittance of visible photons through these films was more than 90% and the color bands seen at an off angle was a clear indication of good quality surface. There was an abrubt change in the surface morphology from mixed nanorods and hexagonal stacks to pyramid like structure on increase in Al/Zn ratios. The shift in optical band gap towards high photon energy on introducing Al in ZnO lattice was regarded as Burstein-Moss effect. Photoluminisce spectroscopy revealed the presence of oxygen vacancies and defects related to Zn. The films were tested for their antibacterial activity against Escherichia Coli bacteria; their efficacy was enhanced on increasing Al/Zn ratio. These antimicrobial coatings with excellent optical properties have potential capability to be used in surgical instruments, protective hospital apparels, medical implants, storage containers, textile, and food packs.

Stimulating photodiode characteristics of hybrid ZnPc-MWCNTs

The ability to functionalize multi-wall carbon nanotubes (MWCNTs) with organic semiconductors is a promising methodology to promote their use in multiple optoelectronic applications, especially at the visible region of the optical spectra. In this article, we investigate the structural, optical, and electrical properties of chemically synthesized MWCNTs hybridized with zinc phthalocyanine (ZnPc) molecules. Interestingly, the hybrid ZnPc-MWCNTs optical bandgap shifts towards the visible light at 2.6 eV instead of the near-infrared bandgap of the pristine sample at 1.2 eV. Besides, the ZnPc-MWCNTs hybrid exhibits enhanced p-n heterojunction photodiode characteristics that are significantly improved with temperature increase. Moreover, the I-V curves of the hybrid ZnPc-MWCNTs sample under visible illumination conditions express a current intensity three times higher than the pristine MWCNTs sample. This promotes the use of the ZnPc-MWCNTs hybrid in various optoelectronic applications working in the visible region of optical spectra.

Efficient hydrogen evolution by liquid phase plasma irradiation over Sn doped ZnO/CNTs photocatalyst

In this study, the liquid phase plasma (LPP) was irradiated over pure zinc oxide (ZnO), strontium (Sn) doped ZnO, and Sn doped ZnO/CNTs photocatalysts for hydrogen evolution from pure water and from aqueous solution of water-methanol. The possible relationship between hydrogen evolution and optical emissions from LPP for activation of ZnO based photocatalysts was revealed. The role of carbon nanotubes (CNTs) as a support material for improved photocatalytic hydrogen evolution was also investigated in this study. The photocatalytic hydrogen evolution from water mixed methanol under LPP irradiation was compared with pure water splitting. The photolysis produced negligible amount of hydrogen due to minimal photodecomposition of water molecules under LPP irradiation. The plasma born reactive species also played crucial role in photolysis. However, the hydrogen evolution rate increased significantly in the presence of ZnO photocatalyst. Further improvement in hydrogen evolution rate was noticed on Sn doping of ZnO and compositing with CNTs. The highest hydrogen evolution rate of 11.46 mmh−1g−1 from water mixed methanol was achieved with Sn doped ZnO/CNTs photocatalyst. This hydrogen evolution rate from water-methanol solution was 9 times higher than from the splitting of pure water. This hydrogen evolution rate is attributed to excessive production of hydroxyl radicals, red shift in optical band gap of Sn doped ZnO/CNTs photocatalyst, slow electron-hole recombination and fast decomposition of methanol as sacrificial reagent.

Graphene oxide deposition on neodymium doped zinc borotellurite glass surface: Optical and polarizability study for future fiber optics

Neodymium oxide doped tellurite-based glass has been widely documented for potential uses in optoelectronics, but graphene oxide (GO)-coated tellurite-based glass has rarely been reported. In this work, we compare two sets of glass series which were GO-coated and uncoated tellurite-based glass series denoted as ZBTNd-GO and ZBTNd, respectively. The two sets of glasses were fabricated via melt-quenched process. A set of glass was coated with GO using low-cost spray coating method. The structural and morphological properties of the glass samples were investigated to confirm the type of structure in glass and formation of graphene oxide on glass surface. The X-ray diffraction (XRD) pattern confirmed the amorphous structural arrangement in both sets of glass series. The morphological study proved the existence of GO layers on top of the ZBTNd-GO surface. The optical bandgap energy of ZBTNd-GO glass was found in the range of 3.253 eV–3.381 eV which was higher than ZBTNd glass. Meanwhile, the refractive index of ZBTNd-GO glass varies from 2.301 to 2.332 which was higher than ZBTNd glass due to the presence of functionalized oxygenated groups in GO structure. The oxide ion polarizability of ZBTNd-GO glass was found decreased due to the shift of optical band gap when coated with GO. This work offers a new form of glass that could be used as a new strategy to upgrade the current photonic materials.

Structural and optical modifications of CdS properties in CdS-Au thin films prepared by CBD

In this work highlights the modifications of the crystalline structure and properties of the nanostructured cadmium sulphide (CdS) thin films, including gold quantum dots grown to form a hybrid metal-semiconductor system. By means of chemical bath deposition (CBD) good quality thin films are obtained, with the advantage of doping in-synthesis with no required additional steps. Film thicknesses around 100 nm were determined by ellipsometry. The binding energies of elements in the CdS and CdS-Au samples were measured by X-ray photoelectronic spectroscopy (XPS). The materials crystalline structure was studied by X-ray diffraction (XRD). A change from disperse like-single-crystalline (highly oriented) CdS NP’s films to monodisperse CdS NP’s–Au QD’s like-single-crystalline samples was observed. This behaviour was confirmed by TEM micrographs. The samples properties pass from an intermediate quantum confinement regime (IQCR) in CdS to a strong one (SQCR) in CdS-Au. The Raman vibrational spectra allowed the analysis of the phonon emissions in CdS, where the Raman shift gives structural information and confirms the effects of IQCR in CdS and the SQCR in CdS-Au. The optical UV–Vis characterization describes the effect of the structural modifications, with an optical band gap shift at higher energy in the CdS-Au sample related to the SQCR. Photoluminescence (PL) measured at room-temperature shows a decrease of PL intensity in CdS-Au film due to via defects-recombination, with respect to that in CdS. This fact is interpreted as an effect of a decreasing of surface defects due to passivation by the Au presence.