Band Gap Energy Of ZnO Research Articles

Low temperatures improved transport properties of [formula omitted] nanoparticles using co-precipitation technique

Pure ZnO and Mn-doped ZnO nanoparticles with the formula Zn(1−X)Mn(X)O (x = 0 %, 3 %, 6 %, and 9 %) were synthesized through a co-precipitation method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the phase and morphology of the nanoparticles. The x-ray diffraction results confirmed all the prepared samples have a wurtzite crystal structure. The morphological valuations of the produced nanoparticles show that the particles are spherical within a nanometer range. Impedance spectroscopy was used to characterize the impedance in the frequency range of 20 Hz to 2 MHz at temperatures from 140 K to 280 K. Results showed that Mn-doping enhances ac conductivity and decreases the bandgap energy of ZnO. This Mn variation in ZnO at low temperatures and high frequencies has potential applications in optoelectronic devices.

High sensitivity of nitrobenzene on the ZnO monolayer and the role of strain engineering

Volatile organic compounds (VOCs) emissions have been a recurring problem that has challenged research centers to find new ways to monitor them. From this perspective, this work investigates nitrobenzene sensing through computational simulations, a well-known toxic compound, using the strained and strain-free two-dimensional (2D) ZnO monolayer, a traditional metal oxide semiconductor (MOS). The results indicate that nitrobenzene is adsorbed via strong physisorption on the 2D ZnO and maintains interaction with the sensor under thermal stimulus (500 K), as demonstrated via ab initio molecular dynamics (AIMD) simulations. The nitrobenzene also changes the ZnO band gap energy from 4.59 to 1.85 eV and shifts 0.35 eV the work function value. Under biaxial strain, the nitrobenzene becomes chemisorbed on the ZnO monolayer. Also, remarkable conductivity changes are observed with the nitrobenzene adsorption on the strained ZnO. Excellent values of sensitivity are found, 2.29 × 1023, 8.11 × 1022 and 2.80 × 1016 for strain-free ZnO and the maximum compressed and stretched ZnO monolayer, respectively. Short recovery times of 1.16 × 10−4 s (T = 300 K) and 6.89 × 10−8 s (T = 500 K) are also found for strain-free ZnO monolayer, indicating a great reusability for nitrobenzene. Consequently, the ZnO monolayer can be used to detect nitrobenzene.

Photocatalytic Degradation of Toxic Rhodamine B Dye by Green‐Synthesised Activated Carbon‐Supported Cobalt Doped ZnO With Further Assessment of ZnO Nanoparticles in Antimicrobial Applications

AbstractThis work investigates the synthesis of ZnO nanoparticles, cobalt (Co)‐doped ZnO, and Activated Carbon (AC) ‐Co doped ZnO via green precipitation technique. AC developed from lotus stems and precipitated by lotus leaf extract. Comprehensive structural, optical, and morphological investigations by FT‐IR, XRD, FE‐SEM, EDX, HR‐TEM, UV‐DRS, PL, and XPS studies are used to characterize the photocatalysts. The ZnO nanoparticles are shown to have a hexagonal phase by XRD examination. The results of the FT‐IR analysis proved that specific chemical bonds exist in the ZnO, Co−ZnO, and AC−Co‐doped ZnO nanocomposites. FE‐SEM images revealed spherical morphology with aggregated, randomly distributed particles with an average size range of ZnO, Co−ZnO and AC−Co−ZnO are 59.55, 42.55, 41.16 nm. The band gap energies of ZnO, Co ‐ZnO, and AC−Co‐ ZnO, are found to be 3.10, 2.57, and 1.94 eV, respectively. Rhodamine B is used as a model contaminant to assess the samples under UV‐light driven photocatalytic effectiveness. The photocatalytic degradation efficiency (%) of the pristine ZnO, Co‐doped ZnO, and AC−Co‐doped ZnO catalysts are increased to 61.76, 74.86, and 91.46 % after 140 minutes of under UV‐light irradiation. Degradation rate constant (k) of the AC−Co−ZnO photocatalyst is found to be greater than that of pristine ZnO and Co−ZnO. Due to the synergistic effect of the AC and Co metal dopants and the spherical morphology of the AC−Co−ZnO sample, which boosted UV‐visible light absorption with reduced charge carrier recombination, resulting in outstanding photocatalytic activity. The study also investigated the bioactive effect of the samples on six bacterial species, revealing that the AC−Co‐doped ZnO nanocomposite has the most enhanced inhibitory effects against gram‐positive and gram‐negative bacteria. Consequently, medical wound dressing materials which helps to promote early healing by preventing microbial contamination.

Aqueous synthesis of bare and Ag incorporated ZnO, CuO and ZnO–CuO nanomaterials with enhanced catalytic potential

The present work demonstrates a low-cost, single-step route for synthesizing ZnO, CuO, and ZnO–CuO nanomaterials using oxalic acid as a precipitating agent, avoiding using other surfactants. The current research also demonstrates the chemical reduction method for incorporating Ag nanoparticles onto the surface of the synthesized metal oxide nanostructures using sodium borohydride as the reductant. X-ray diffraction studies reveal the phase purity and crystallinity of the nanoparticles, while X-ray Photoelectron Spectroscopy characterizes the chemical states of surface elements. UV–vis spectra of the samples disclose the modifications shaped by Ag nanoparticles in the absorption characteristics and energy band gap of ZnO, CuO, and ZnO–CuO nanomaterials. The catalytic potentials of the synthesized materials are tested by monitoring degradation reactions of hazardous organic pollutants, including methylene blue and methyl orange, within a few minutes. The significant finding of the present study emphasizes the incorporation of Ag nanoparticles to ZnO–CuO nanocomposite and the use of sodium borohydride in photocatalysis effectively to enhance the rates of degradation of pollutant dyes without the use of intense radiation or unique lamps by initiating a three-stage electron transfer mechanism.

Hysteresis loops on voltage-current characteristics and optical responses of PEDOT:PSS/ZnO nanorods/ZnO:Ga heterostructure

Volage (V)-current (I) curves of the poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/ZnO nanorods (NRs)/ZnO:Ga (GZO) heterostructure exhibited a rectification behavior with hysteresis loops both in forward voltage (VF) and reverse voltage (VR) regions. The ultraviolet (UV) light irradiation of 360 nm led to the increase in the reverse current (IR), i.e. generation of photocurrent (PC), and the decrease in the hysteresis loop area in the VF region. In dark, the 1/V vs. ln (I/V2) plot revealed that the dominant carrier transport mechanisms in the low- and the high-VF regions are the direct tunneling and the Fowler-Nordheim (F-N) tunneling through the dipole layer formed at the interface between the PEDOT:PSS and ZnO NRs layers, respectively. On the contrary, the carrier transport in the middle-VF region in dark was dominated by the bulk-limited mechanisms, such as the space-charge-limited (SCL) conduction controlled by the single shallow traps, the trap-free SCL conduction, and the trap-filled-limit conduction controlled by the traps with Gaussian distribution. The UV light irradiation changed the carrier transport mechanism in the middle-VF region to the trap-free SCL conduction. The resistive switching related to the hysteresis loop was found to be caused by the trapping and detrapping of the injected carriers at the traps. In dark, the maximum forward current was increased by the repetition of the VF sweep of 0 V → 5 V → 0 V, but decreased by the repetition of the VR sweep of 0 V → -5V → 0 V, indicating the possibility of the resistive memory. At the low VRs, PC spectra showed a main peak at 350 nm, which is corresponding to slightly higher photon energy than the bandgap energy of ZnO. Moreover, the existence of the tail extending into the bandgap was also observed on the PC spectra. From the time response of PC, the depth of the trap state was estimated to be 0.64–0.77 eV.

Characteristics of the incorporation of Yb defect states in CuO:ZnO nanocomposite

Exploring magnetic order in nonferromagnetic substances, such as CuO:ZnO, becomes especially attractive when introducing defect states through nonmagnetic ion doping. In this study, we delved into the impact of Yb doping on the structural, morphological, optical, and magnetic properties of CuO:ZnO. The Yb doped CuO:ZnO was prepared with different Yb concentrations (x = 0.00–20 %) via the temperature-assisted co-precipitation method. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, and vibrating sample magnetometer (VSM) were used to investigate the structural, morphological, optical, and magnetic properties of Yb doped CuO:ZnO nanocomposites.The incorporation of Yb in CuO:ZnO nanocomposites leads to a notable shift of the characteristic XRD peaks of CuO and ZnO to lower angles, accompanied by an increase in the lattice parameters. UV–visible absorption spectroscopy shows an overall decrease in the optical band gap energy of ZnO as the Yb defect level increases. FE-SEM studies revealed the transformation of spherical structures into agglomerated non-spherical structures upon the introduction of Yb ions into CuO:ZnO nanocomposites. According to XPS data, the predominant valences of Yb-doped CuO:ZnO nanocomposites are Zn2+, Cu2+, and Yb3+. One noteworthy observation from the XPS results is that, in comparison to the intensity of OL or Oad peaks, the intensity of OV (Oxygen vacancy) defect peak increases when the Yb impurity concentration increases. Magnetic measurements demonstrated a diamagnetic order in pure ZnO, which converts to a ferromagnetic order with the incorporation of Yb defect states. The ferromagnetic properties of the Yb-doped CuO:ZnO nanocomposite can be ascribed to the exchange interaction of Yb3+ ions with defect states (Oxygen Vacancy) in ZnO and CuO.

Characterization and evaluation of the anti-bacterial activity of facile biosynthesis Zinc oxide nanorods using Spirulina platensis

ABSTRACT ZnO nanorods (NRs) were synthesized with Zn(NO3)2, citric acid, and NaOH as precursors and Spirulina platensis as a capping agent. The sol-gel-hydrothermal method was used to synthesize ZnO-NRs with pH adjustment of the reaction to modify its morphology. Furthermore, the products of ZnO-NRs were characterized by FT-IR, UV-Vis UV-DRS, XRD, SEM, and EDS instruments. The characterization result shows crystal and particle size differences when the biosynthetic pH ranges from 7 to 13. The ZnO bandgap energy changed at a certain pH ranging from 3.13 to 3.17 eV. FTIR analysis shows that the stretching of Zn-O occurs at wave number 436 cm−1. The morphological patterns of SEM-EDX showed that the ZnO-NPs were spherical, cube, and nanorods. However, the dominant morphology is nanorods form, where the particle sizes ranged from 120 to 180 nm. The result of the antimicrobial activity test against Staphylococcus epidermidis shows that the maximum inhibition of ZnO-pH 9 was 6–16 mm. The antioxidant test also shows that ZnO-pH 9 had the highest antioxidant content, accounting for 72.1%.

Effects of thermal treatment on the complex structure of luminescence emission of Li-doped ZnO screen-printed films

The ZnO–Li films were synthesized and investigated in an attempt to explore and develop RE-free phosphor materials capable of emitting intense visible light in a wide spectral range. The effects of both heterovalent doping with lithium and high-temperature annealing on the optical properties of ZnO films were studied. The films were deposited on the Al2O3 substrate using the screen-printing method and annealed at 800–1,000°C in air for 0.5–3 h. Both doping and annealing result in the transformation of the shape of reflectance spectra in the range of 300–400 nm and the shift of absorption edge to the long-wavelength region. At the same time, the bandgap value estimated taking into account the exciton peak position and its binding energy is independent of Li-doping. The feature at 300–400 nm and the shift of absorption edge are ascribed to the appearance of the absorption band that excited the yellow photoluminescence band. The photoluminescence spectra of undoped and Li-doped films show the emission bands in the ultraviolet and visible spectral ranges. The ultraviolet emission is due to ZnO exciton recombination. The visible emission band comprises several components peaked at 430, 482, 540, 575, and 640 nm. Their relative intensities depend on Li-doping, annealing temperature, and annealing duration. The 430- and 482-nm luminescence bands were observed in Li-doped films only. Their excitation spectra show the peak located at 330–340 nm, indicating that the energy significantly exceeds the ZnO bandgap energy. Consequently, the 430- and 482-nm luminescence bands are attributed to an additional crystal phase formed under annealing. Other components of visible emission bands are ascribed to the defect-related emission of ZnO. The possible nature of these bands is further discussed. Li-doping and annealing at intermediate temperatures result in blue emission and an enhancement of other visible bands, which makes ZnO–Li films a perspective material in photonic applications.

One-pot synthesis of In2O3/ZnO nanocomposite photocatalysts and their enhanced photocatalytic activity against cationic and anionic dye pollutants

An In2O3/ZnO nanocomposite was synthesized by co-precipitation and applied in the photocatalytic degradation of cationic and anionic dyes. The nanocomposite was characterized by X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectrometry (EDS), surface area analysis and UV–visible diffuse reflectance spectrometry (UV–Vis DRS). The XRD, Raman and XPS analyses revealed that the nanocomposite was composed of two phases (In2O3 and ZnO). SEM images showed agglomerations of In2O3 and ZnO, and TEM images confirmed the adhesion of In2O3 nanoparticles to the surface of ZnO. The specific surface area of the nanocomposite increased from 5.86 to 8.41 m2/g with increments of In2O3 content. The optical bandgap energies of ZnO and In2O3 powders were 3.12 and 2.90 eV, respectively. The best photocatalyst was 2%In2O3/ZnO nanocomposite and the optimal dosage was 150 mg. Under UV irradiation, 92.17, 55.54 and 38.61% of MB, RhB and MO, respectively, were degraded over the 2%In2O3/ZnO nanocomposite. Since the point of zero charge of 2%In2O3/ZnO was about 6.6, MB and RhB were more completely degraded under basic conditions while MO was more completely degraded under acidic conditions. The possible charge transfer mechanism for photocatalytic degradation over the 2%In2O3/ZnO nanocomposite was proposed based on an active species test. The results showed that h+, •OH and •O2- species were the reactive species responsible for the photocatalytic degradation of MB, RhB and MO. The In2O3/ZnO nanocomposite could remove the cationic dyes from water in a neutral condition and exhibited good stability.

Synthesis of ZnO Crystal with Micro‐Nano Structures by a Continuous Co‐Precipitation Method: Morphological Evolution and Mechanism Analysis

AbstractZnO crystals are employed in numerous industries, but precisely controlling their morphologies is still challenging. In this work, a continuous flow process for synthesizing ZnO crystals is developed based on the co‐precipitation method. ZnO crystals at different morphologies, including needle‐like, rod‐like, flower‐like, spindle‐like, and nanospheres, are successfully prepared at low temperature. The influence of reaction temperature, pH value, ZnCl2 feeding concentration, and reaction time on the morphology, size, and purity of ZnO crystals is systematically investigated. The results of X‐ray diffraction show that the high‐purity ZnO can only be produced when the reaction temperature is above 75 °C. The band gap energies of ZnO evaluated by UV–vis diffuse reflectance spectroscopy increase with the synthesis temperature. According to scanning electron microscope (SEM) findings, the size of ZnO crystals is regulated by controlling the reaction time. Interestingly, the morphology of ZnO crystals is changed from 1D to 3D structure by controlling the feeding concentration of ZnCl2. Moreover, a concentration difference mechanism of ZnO crystal morphology evolution is proposed by monitoring the real‐time concentration of free Zn2+ ions.

Fabrication, characterization, and application of PSf/Ni@ZnO amalgamated membrane for photocatalytic degradation of dyeing wastewater from batik industry

The ultraviolet-light-driven composite membrane incorporated with nickel@zinc oxide (Ni@ZnO) photocatalyst for batik wastewater treatment is demonstrated in this study. Co-precipitation and non-solvent-induced phase separation techniques were directed to fabricate the nanocomposite membranes. Based on characterization results, the scanning electron microscope and energy dispersive X-ray analyses showed a large surface pore of the polysulfone (PSf)/Ni@ZnO membrane with a well-arranged loose-spongy structure and a predominant presence of elemental O, compared to the pristine membrane. The improved photocatalytic activity was observed by a decreased ZnO band-gap energy from 3.31 to 3.07 eV after nickel doping. Based on the atomic force microscope results, the addition of Ni@ZnO promoted a rougher surface membrane, while also increasing the porosity, hydrophilicity, water uptake ability, and mechanical strength of PSf membrane. Furthermore, PSf/Ni@ZnO 1% (w/w) showed the best performance in photodegradation-filtration systems with 10 times higher permeability than pristine PSf; total dissolved solid, chemical oxygen demand, and dye removal were 26.4%, 33.5%, 92.2%, respectively; with photodegradation efficiency reaches 53.26%. The photodegradation stability test for five consecutive cycles also revealed that PSf/Ni@ZnO 1% (w/w) was 62.5% more reactive than PSf/ZnO, which was established by its fresh and recycled crystal structure membranes. Thus, the PSf/Ni@ZnO 1% (w/w) membrane was out to be the most outstanding ultraviolet-light-driven photocatalytic membrane for efficient batik wastewater treatment.

Effect of Annealing on the Structural and Optical Properties of ZnO/ITO and AZO/ITO Thin Films Prepared by Sol-Gel Spin Coating

This paper aims to investigate the effect of annealing on the structural and optical properties of ZnO/ITO and AZO/ITO thin films. In the preparation of ZnO and AZO films, zinc acetate dehydrate (Zn(CH3COO)2.2H2O), ethanol, diethanolamine (DEA), and AlCl3 were used as a starting material, solvent, stabilizer, and dopant sources, respectively. Both ZnO and AZO films were fabricated on ITO (indium tin oxide) substrates using the spin coating technique at room temperature with a rotating speed of 3,000 rpm in 30 s. The films were heated at various temperatures in the temperature range of 400 - 600 °C for 60 min. The crystallite size of the film is calculated using Debye-Scherrer and Williamson-Hall Methods. Based on the UDM results, the crystallite size of ZnO/ITO and AZO/ITO films increases after annealing in comparison with the films before annealing. From the optical UV-Vis measurements, there was an increase in the transmittance value of the samples after annealing. The transmittance value of ZnO/ITO and AZO/ITO films increases from 40 % before annealing to approximately 80 and 90 %, respectively after annealing. The increase in the transmittance valued in both ZnO/ITO and AZO/ITO after annealing is mainly due to an improvement in the crystalline phase of these films. The band gap energy of ZnO and AZO films is reduced with increasing annealing temperatures, from 3.26 eV before annealing to 3.19 eV for ZnO and 3.23 eV for AZO films after annealing at 600 °C.
 HIGHLIGHTS
 
 The sol-gel spin coating method was used to study the effect of annealing on the structural and optical properties of ZnO/ITO and AZO/ITO films
 The transmittance valued in both ZnO/ITO and AZO/ITO after annealing increase as a result of an improvement in the crystalline phase of these films
 Reducing the amorphous phase and the increase of the crystallite size of the films are the main reason for narrowing the band gap energy of the ZnO/ITO and AZO/ITO films

Preparation and photocatalytic H2 production property of graphene oxide/CdS/single crystal ZnO nanorod ternary hybrids

In order to further improve the photocatalytic H2 production ability of CdS/single crystal ZnO nanorod heterostructure (CZ), graphene oxide/CdS/single crystal ZnO nanorod hybrid (GCZ) were synthesized by microwave-assisted co-precipitation method, and the influence of graphene oxide (GO) content on the properties of ternary materials was tested. Experimental results exhibit that GO further enhance the photocatalytic H2 production capacity of CZ material. When GO wt% is 2.91%, the as-prepared products have the best photocatalytic H2 production capacity, which its average H2 production rate is 6.511 mmol g−1 h−1. The enhancement for H2 production capacity benefits from increasing specific surface area, reducing bandgap energy of ZnO and accelerating the migration rate of photo-induced carriers due to the superior property of GO and building efficient heterojunction between ZnO and CdS.

Structural, electrical and optical properties of hetrostructured MoS2/ZnO thin films for potential perovskite solar cells application

ZnO, MoS2, MoS2/ZnO/glass, and ZnO/MoS2/glass thin films have been deposited on glass substrates by chemical bath deposition techniques (CBD). XRD results confirmed the formation of MoS2, ZnO, MoS2/ZnO/glass, and ZnO/MoS2/glass films. All the films have a hexagonal structure. The grain size of heterostructured (MoS2/ZnO/glass and ZnO/MoS2/glass) films is larger than pure (ZnO and MoS2) films. The band gap energy of ZnO, MoS2, MoS2/ZnO/glass and ZnO/MoS2/glass is 3.14 eV, 1.52 eV, 1.62 eV and 2.67 eV, respectively. Photoluminescence (PL) emission peaks of ZnO are observed in the visible region. When ZnO film is deposited on MoS2 film, PL peaks are shifted to smaller wavelengths. A very high PL intensity peak of MoS2 is observed. When MoS2 film was deposited on ZnO film the peak intensity was reduced. The average sheet resistivity of glass/MoS2, glass/ZnO, MoS2/ZnO/glass and ZnO/MoS2/glass films is 6.44 × 104, 7.89 × 103, 5.65 × 104, and 2.45 × 103 (ohm-m), respectively. These materials have potential applications in perovskite solar cells.

Synergetic effect of oxygen vacancies and morphology of ZnO photocatalyst prepared by non-hydrolytic sol-gel route for the photo-oxidation of 2-propanol in a gas-solid system

The effects of the nature of some carboxylic acids (oxalic, malic, citric, and tartaric acid) and of the annealing temperature in the preparation of the ZnO photocatalyst by a non-hydrolytic sol-gel route (using zinc acetate as the precursor) have been studied for oxidation of 2-propanol in air as probe reaction in a gas-solid regime. The physico-chemical characterization by XRD, SEM/EDX and UV–vis-DRS revealed a synergetic effect of the presence of oxygen vacancies and morphology of ZnO on the reaction performance. Oxygen vacancies were found to increase with decreasing annealing temperature, and this result indicates the possibility of their production in situ without the addition of a doping agent.XRD results showed that ZnO samples present a pure wurtzite structure with an average crystal size ranging from 21 nm to 42 nm. The specific surface area of samples ranged from 3.0 m2·g–1 to 18 m2·g–1and SEM observation indicated the presence of different agglomeration of both faceted and non-faceted particles. The lowest band gap energy of ZnO was 3.2 eV. The photocatalytic oxidation of 2-propanol in gas-solid regime was carried out in oxygen atmosphere. An increase of acid concentration during the ZnO preparation caused a decrease on the activity of the photocatalyts. An increasing amount of zinc acetate with respect to acid during the preparation of the photocatalysts enhanced the oxygen vacancies in the solid, which induced an increase of the 2-propanol oxidation rate constant. The increasing of the annealing temperature decreased the oxygen vacancies and hence the photocatalytic activity of ZnO. The highest 2-propanol oxidation rate (kapp = 4.00·10–2 min–1) was obtained by using the ZnO sample prepared with a 1:2 molar ratio of zinc acetate:oxalic acid, and annealed at 400 °C. This photocatalyst showed an oxidation rate 80 times higher than that of the least active photocatalyst (kapp = 5.00·10–4 min–1) obtained using zinc acetate:tartaric acid at 1:1 molar ratio and annealed at 500 °C.

Zn0.97-xCu0.03VxO (x = 0, 0.02, 0.04) hexagonal tube and microrods structures: Optical, refractive index, electrical and solar photocatalytic properties

The optical, refractive index, electrical, dielectric and solar photocatalytic properties of pure and Zn0.97-xCu0.03VxO (x = 0, 0.02, 0.04) compositions synthesized by coprecipitation method have been studied. Pure single phase of hexagonal wurtzite structure of ZnO was confirmed by XRD and Rietveld refinement analysis. The SEM obviously illustrated that Cu doping and Cu/V codoping have great impacts on morphology of ZnO particles. Remarkably, incorporation of Cu ions converts the spherical shape of the pure ZnO particles to open hexagonal tube and microrods structures while Cu/V ions lead to formation of mixed particles possess microrods and very fine spherical shapes. Optically, lowering in the optical band gap energy of ZnO with formation of long tails extend to visible light wavelengths (460 nm) were detected due to insertion of Cu and Cu/V ions. Based on Ravindra, Moss, Hervé, Reddy, and Kumar models, hexagonal Zn0.97Cu0.03O exhibits the highest refractive index values of 2.1558, 2.3509, 2.2961, 2.7368 and 2.3355, respectively. At different frequencies, 3 wt% Cu doping enhanced the room temperature electrical conductivity values of ZnO and further improvements were seen due to insertion of V3+/4+ ions plus Cu2+ dopant. Zn0.95Cu0.03V0.02O composition revealed a colossal dielectric constant of 1947 at 50 Hz and at nearly all frequency it possesses the highest values. The low cost solar photocatalytic test showed that both Zn0.97Cu·03O and Zn0.93Cu0.03V0.04O catalysts have high efficiencies of 81% and 82% to degrade the organic Congo red pollutant in 90 min.

The role of size-controlled CeO2 nanoparticles in enhancing the stability and photocatalytic performance of ZnO in natural sunlight exposure

In order to enhance the photocatalytic performance and stability, the various proportions of the size controlled cerium oxide (CeO2) nanoparticles were dispersed at the pre-synthesized ZnO. Although, the expected dual absorption onsets, probably due to the diminutive difference between the bandgaps of CeO2 (∼2.9 eV) and ZnO (∼3.1 eV), were not observed however, a blue shift in the bandgap energy of ZnO was witnessed with the increasing surface density of CeO2 particles. The delayed excitons recombination process with the increasing concentration of CeO2 nanoparticles was verified by the PL spectra. The structural investigation by Raman and XRD analysis revealed the surface attachment of CeO2 particles without altering the rock-salt lattice of ZnO. The morphological and fine microstructural analysis established the uniform distribution of evenly sized CeO2 particles at the surface of ZnO with the discrete fringe patterns of both the entities whereas the XPS analysis confirmed the majority of Ce4+ in dispersed CeO2. In comparison to pure ZnO, cyclic voltammetric (CV) analysis, under illumination, exposed the supportive role of surface residing CeO2 particles in eradicating the photo-corrosion of ZnO whereas the chronopotentiometry (CP) predicted the prolonged life-span of the excitons. Compared to pure ZnO, an appreciably high activity was revealed for 10% CeO2 loading as compared to pure ZnO for the removal of mono and di-nitrophenol derivatives and their mixtures under natural sunlight exposure. The variations in the removal rates in the mixture as compared to individual nitrophenol exposed the structure-based priority of ROS for the respective phenol. The significantly enhanced photocatalytic activity of the composite catalysts revealed the incremental role of surface-mounted CeO2 entities in boosting the generation of ROS under sunlight irradiation. The experimental observations were correlated and compiled to establish the mechanism of the removal process.

Dynamic regulating of lasing mode in a whispering-gallery microresonator by thermo-optic effect

Realizing dynamic regulation of specific optical components while being easy to integrate with photonic circuits will have a revolutionary impact on tunable laser sources, active filters, and all-optical switching/integration. Here, we demonstrate a temperature tunable Ga-doped ZnO microresonator with a conductivity of ∼1.75 S/cm controlled by the injection current and realize point-to-point heating. The shift in the resonant wavelength with a tuning range of 2 nm for TE66 mode is achieved by the effect of current-induced temperature rising on the refractive index of the microresonator crystal, namely, the thermo-optic effect. Meanwhile, the thermo-optic coefficient of 16.7 × 10−4/K around the bandgap energy of ZnO is also obtained. This operating mode of electronically controlled temperature establishes a solid foundation for the practicality and integration of tunable lasers.

Influence of the calcination temperature on the formation of precipitated ZnO:Ce nanocrystal by employing ultrasound irradiation

Cerium doped Zinc Oxide (ZnO:Ce) nanocrystals were synthesized through precipitation of nitrate solution by employing ultrasound irradiation. The precipitate products were calcinated at various temperature. The calcination temperature is an important key on the formation and properties of nanocrystal. This paper studied influence of calcination temperature on the formation and optical properties of ZnO:Ce nanocrystal. ZnO:Ce nanocrystals were characterized by x-ray diffractometer and UV-Vis spectrophotometer. The x-ray diffraction patterns revealed the formation of hexagonal wurtzite crystal structure for ZnO:Ce nanocrystals. The increase in calcination temperature improved crystallinity and reduced the band gap energy of ZnO:Ce. The result showed that the calcination temperature strongly influenced ZnO:Ce nanocrystals formation. The optical properties of ZnO:Ce nanocrystal can be modified by varying calcination temperature.

Optical Properties of ZnO, TiO<sub>2</sub> and ZnO:TiO<sub>2</sub> Composite Films

We report a fabrication and characterization of ZnO, TiO2 and ZnO:TiO2 composite thin films. The films were prepared on glass substrates by using the dip coating sol-gel method. ZnO was synthesized by using Zinc acetate dehydrated, glacial acetic acid and ethanol. Meanwhile, TiO2 was prepared by using titanium isopropoxide, acetic acid, isopropyl alcohol and methanol. The single sols were mixed with fixed molarity of 0.2 mol to obtain ZnO:TiO2 composite films. The optical properties of metal oxide, such as transmittance, absorbance and band gap were determined using UV-Vis spectrometer. FTIR was used to determine the chemical bonds of the materials. ZnO has the highest transmittance spectra (91%), followed by TiO2 (70%) and ZnO:TiO2 (35%) composite films. The absorbance edge shifted to the longer wavelength for ZnO:TiO2 composite film. The energy band gap of ZnO, TiO2 and ZnO: TiO2 composite were 3.8 eV, 3.6 eV and 3.5 eV, respectively.