Violet Emission Peak Research Articles

Investigation of diodic behavior in p-NiO/n-SnO2 bilayer heterojunctions fabricated via DC magnetron reactive sputtering

Tin oxide (SnOx) thin films at varying oxygen flow rates and Nickel oxide (NiO) thin films were deposited by reactive dc magnetron sputtering on glass substrates. Structural, chemical, morphological, optical and electrical properties of the deposited films were studied. XRD studies confirmed that the deposited films were polycrystalline in nature. SnOx thin films have shown two phases such as SnO and SnO2. AFM and SEM were used to analyse the morphology of the films and EDS confirmed the presence of Sn and Ni in the respective films. The examination of the x-ray photoelectron spectrum showed that the sputtered SnOx films contain both Sn2+ and Sn4+ oxidation states and NiO films contain Ni+2 and Ni+3 oxidation states. Photoluminescence study shows strong violet and weak red emission peaks for SnOx films and NiO showed strong emission peaks in the orange-red region. The optical results demonstrate that the films were transparent. The bandgap of SnOx and NiO samples were ∼3.3 eV and − 3.42 eV, respectively. Further we constructed a p-NiO/n-SnO2 heterojunction diode and its electrical characteristics were thoroughly assessed. Using dark current–voltage measurements, electrical characteristics such saturation current, ideality factor and barrier height were determined. The increase in oxygen flow rate led to reduction in the rectification of the devices. Our findings support the creation of high-performance metal oxide heterojunction for optoelectronic devices.

Investigation of Electronic and Optical Properties of Al/Ag and Al/N Co-Implanted ZnO Thin Films

Either metal/metal or metal/non-metal co-doping is one of the most effective methods to modulate the visible emission of ZnO. In this paper, ZnO, aluminum-doped ZnO (Al-ZnO), aluminum and silver co-doped ZnO (Al/Ag-ZnO), and aluminum and nitrogen co-doped ZnO (Al/N-ZnO) are deposited. Combining the substitution of zinc ions using Al and/or Ag doping and the substitution of oxygen ions using N doping is expected to introduce more interstitial zinc and oxygen vacancy defects related to visible light emission in ZnO films. The results indicate that the PL spectrum of ZnO shows a violet emission peak at 406 nm and other weak visible emission peaks. After Al doping, we observe a strong blue emission at 421 nm, and its intensity is further enhanced and attains the maximum for Al/N-ZnO. However, for Al/Ag-ZnO, the blue emission shifts toward a longer wavelength, and the intensity of the blue emission conversely decreases. Then, the band structures, the density of states (DOS), the partial density of states (PDOS), and the optical constant of doped ZnO are calculated using density functional theory (DFT). Based on the experimental and theoretical results, the enhancement mechanism of visible light is discussed.

Antimicrobial and anticancer properties of calcium doped zinc oxide nanocomposites prepared using precipitation method

A precipitation method is used to synthesise calcium doped zinc oxide (CaZnO) nanocomposites (NCs). Xray diffraction (XRD) analysis validated the hexagonal wurtzite structure of the synthesised CaZnO NCs. Transmission electron microscopy (TEM) images illustrate that the fabricated CaZnO NCs are spherical in shape. Energy dispersive X-ray (EDAX) spectroscopy is used to determine the elemental composition. The Fourier transform infrared (FTIR) spectrum of CaZnO NCs exhibited a peak of Zn-O vibration at 434 cm-1. Violet, blue and green emission peaks are noticed for CaZnO NCs in the photoluminescence (PL) spectra. The ZnO, CaO, CaZnO NCs are assessed using the well diffusion method for antimicrobial efficacy against Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Candida albicans (C. albicans). In comparison to ZnO and CaO nanomaterials (NMs), CaZnO NCs showed highest antimicrobial activity. MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetra zolium bromide) assay is used to ascertain cytotoxicity against human breast cancer cell line (MDA-MB-231). CaZnO NCs reduce cell viability as their concentration increases which emphasise their potent anticancer activity against MDA-MB-237 cells.

Enhanced photocatalytic activity of ZnO hexagonal tube/r-GO composite on degradation of organic aqueous pollutant and study of charge transport properties

ZnO hexagonal tube and ZnO/r-GO nanocomposites were synthesized by hydrothermal method and the nanostructures were characterized by XRD, UV-DRS, PL, FTIR, FESEM, and TEM techniques. The main violet emission peak of the synthesized nanostructures is due to the transition between interstitial zinc and hole (valence band) of ZnO. The potential of ZnO/r-GO nanocomposite was evaluated using methyl orange (MO) and rhodamine-B (RhB), and the results were compared with the activity of synthesized ZnO nanostructures. More than 95% of MO and RhB were by ZnO/r-GO nanocomposite and it was found to be higher than that of ZnO hexagonal tube. The degradation MO and RhB were found to follow first-order kinetics and it has a rate constant of 7.68 × 10−2and 7.83 × 10−2 min−1, respectively. These results are mainly due to the enhanced charge transport property. Trapping experiments show that superoxide radical anion and hydroxide radicals are chief species responsible for the degradation of MO and RhB. The chemical stability of the nanocomposite was evaluated by cycle test experiments and it reveals that the catalyst can be reused up to few cycles without considerable loss of photocatalytic activity. This work affords a simple stratagem to integrate ZnO hexagonal tubes and r-GO nanosheets to construct effective catalysts for the degradation of organic compounds.

Structural, morphological and opto-electrical properties of transparent conducting SnO2 thin films: Influence of Sb doping

ABSTRACT Pure and antimony doped tin oxide (Sb:SnO2) thin solid films were synthesised through a simple and low-cost nebulised spray pyrolysis (NSP) route. The influence of Sb doping on the different physical properties of these films was systematically investigated. The results of X-ray diffraction (XRD) study exhibited polycrystalline in nature of all films with tetragonal cassiterite structure of single phase SnO2. XRD analysis also revealed the reduction in crystallite size as well as the grain size observed in scanning electron microscopy (SEM) with Sb doping concentration. The average transmittance of all the films was greater than 73% at the visible wavelength region and the transparency was reduced by Sb inclusion. The direct optical band gap value was the lowest of 3.94 eV for pure SnO2 and enhanced by Sb doping level. The effects of Sb doping concentration on extinction coefficient, refractive index, dielectric constant, optical conductivity and optical density of the films were examined. Photoluminescence spectrum revealed a broad violet emission peak near 390 nm and Sb doping intensified the peak. Both the resistivity and sheet resistance were found to vary in the range of 1.61 × 10−3 Ω.cm to 3.92 × 10−4 Ω.cm and 32.73 Ω/□ to 134.41 Ω/□, respectively with the variation of Sb doping concentration. The highest mobility and carrier concentration were 54.74 cm2/Vs and 7.02 × 1021 cm−3 for undoped and 10% Sb doped films, respectively. However, the figure of merit was found to be maximum of 1.38 × 10−3 (Ω/cm2)−1 for 5% Sb doping concentration among the films.

Red-orange photoluminescence emission of sol-gel dip-coated prepared ZnO and ZnO:Al nano-crystalline films

Zinc oxide films doped with 0–5 % wt. Aluminum (AZO) were prepared by sol-gel method and coated on glass substrate via dip-coating process. The sol was obtained with 0.5 M ethanolic solution of zinc acetate deposited into glass substrate with 200 mm/min withdrawing speed for 3 times. The deposited films were transformed into nanocrystalline undoped or Aluminum-doped ZnO after heat treatment at 400 ̊C for 2 h. Processing conditions and the effects of Al doping on crystallinity, morphology, and optical properties of ZnO films were characterized by X-ray diffraction (XRD), FESEM analysis, UV-VIS and photoluminescence spectroscopy. XRD analysis confirmed that all nano structured thin films have a hexagonal wurtzite structure. Results showed that Al doping has considerable effect on particle size, absorbance, transmittance and photoluminescence emission of samples. Depending on the Al concentration film transparency significantly increased, the highest transparency greater than 80% for 3 wt % AZO prepared films has been acquired. Accordingly the calculated optical band gap energy was varying from 3.2 to 3.7 eV related to Al doping level. The photoluminescence studies of undoped ZnO and AZO films have revealed very interesting features. Correspondingly photoluminescence spectra indicated that elaborated undoped ZnO and AZO films could emit luminescence emission over the entire visible region included violet emission peak at 413 nm, blue emission peak at 487 nm, green emission peak at 531 nm and orange-red emission peak at 630 nm that later is not very common in ZnO which is mainly attributed to Oi-related transitions.

Physical properties of rare earth metal (Gd3+) doped SnO2 thin films prepared by simplified spray pyrolysis technique using nebulizer

Pristine and rare earth (i.e) gadolinium doped SnO2 thin films have been coated on micro-glass substrates with different Gd doping concentration at constant temperature 450 °C by simplified spray pyrolysis technique using nebulizer unit. The variation of doping concentration from 0 to 6 wt.% in the steps of 2 wt.%. Structural, optical, electrical, morphological and photoluminescence properties had been examined as a function of gadolinium doping level. The X-ray diffraction study exposed that all the prepared pristine and Gd doped SnO2 thin films are (110) preferred orientation with tetragonal crystal structure. The observed transmittance of Gd:SnO2 thin film varies between 91–80% in the visible regions. The estimated optical band gap value was initially decreased from 3.79 to 3.74 eV and then it was slightly increased as 3.77 eV with respect to the increase of Gd doping concentrations. Homogeneous surface morphology with polyhedrons like grains without cracks for all the prepared samples was illustrated by SEM studies. EDS spectra confirms that the existence of Sn, O and Gd elements in the 4% Gd doped SnO2 thin film surface. PL results indicates that three emission bands such as ultra violet, blue and green emission peaks at the wavelength of 360, 493 and 519 nm respectively, for all the prepared Gd:SnO2 films. Minimum resistivity (ρ) 7.14 × 10−4 Ω-cm with activation energy (Ea) 0.05 eV, maximum carrier concentration (n) 2.36 × 1020 cm−3 and figure of merit (ϕ) 52.96 × 10−3 (Ω/sq)−1 were obtained for 4% Gd doped SnO2 thin film using Hall effect measurements.

Laser stimulated second and third harmonic optical effects in F: SnO2 nanostructures grown via chemical synthetic route

Laser stimulated second and third harmonic generation effects in Fluorine doped tin oxide (F:SnO2) nanostructures versus the fluorine content is presented. The F:SnO2 nanostructures have been fabricated at various fluorine doping concentrations by spray pyrolysis technique. The films exhibit polycrystalline nature with a preferential growth orientation along (1 1 0) diffraction plane as evident from x-ray diffraction studies. The optical transmittance of the F:SnO2 films has increased from 68% to 80%. Photoluminescence studies revealed that strong violet emission peak corresponds to ∼400 nm and relatively weak red emission peak at about ∼675 nm was observed for all the F:SnO2 films. Increase in theβeff value upon fluorine incorporation supports the applicability of the deposited films in passive optical limiting applications. The principal origin of second harmonic generation signals (SHG) for this type of nanostructures is played by the space charge density acentricity due to the F doping. The enhanced second and third harmonic generation signals observed on F:SnO2 nanostructures endorses the credibility of these materials in various nonlinear optical trigger device applications.

Effect of Precursors on Key Opto-electrical Properties of Successive Ion Layer Adsorption and Reaction-Prepared Al:ZnO Thin Films

Aluminum-doped zinc oxide (Al:ZnO) thin films were deposited on glass substrates by successive ion layer adsorption and reaction (SILAR) method using different precursors. This inexpensive SILAR method involves dipping of substrate sequentially in zinc solution, de-ionized water and ethylene glycol in multiple cycles. Prepared films were investigated by x-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), optical absorption, photoluminescence (PL), Raman spectroscopy and electrical studies. XRD study confirmed incorporation of aluminum in ZnO lattice with a polycrystalline hexagonal wurtzite structure of the films. The crystallite size determined by the Scherrer equation showed an increase from 28 nm to 35 nm for samples S1 to S4, respectively. SEM study showed smooth morphology with homogeneous distribution of particles. From the AFM images, the surface roughness was found to change according to precursors. For the optical analysis, the zinc chloride precursor showed high optical transmittance of about 90% in the visible range with a band gap value 3.15 eV. The room-temperature PL spectra exhibited a stronger violet emission peak at 420 nm for all the prepared samples. The Raman spectra showed a peak around 435 cm−1 which could be assigned to non-polar optical phonons (E2-high) mode AZO films of a ZnO wurtzite structure. Hall effect measurements showed n-type conductivity with low resistivity (ρ) and high carrier concentrations (n) of 2.39 × 10−3 Ω-cm and 8.96 × 1020 cm−3, respectively, for the film deposited using zinc chloride as precursor. The above properties make the prepared AZO film to be regarded as a very promising electrode material for fabrication of optoelectronic devices.

Hydrothermal synthesis of Ga-doped In2O3 nanostructure and its structural, optical and photocatalytic properties

In this work, pure and Ga-doped In2O3 nanostructures have been synthesized by facile template-free hydrothermal method. The structural, morphological and optical properties are characterized by using XRD, FT-IR, HR-SEM and TEM, EDS, XPS, UV-DRS, and PL techniques. X-ray diffraction analysis indicates a pure cubic phase while crystallite size decreases with Ga doping. HR-SEM and TEM observations reveal irregular-shaped and spindle-like nanostructures with enhanced crystallinity and reduction in particle size with Ga doping. XPS spectra reveal the oxidation state of Ga is +3. The energy band gap estimated by UV–vis DRS spectroscopy is found to increase slightly from 3.40 to 3.45eV with Ga doping. Photoluminescence spectra display violet, blue and green emission peaks are observed during Ga doping concentrations. Photodegradation of Methylene blue dye under ultra violet light radiation is found to double with Ga doping; i.e. 48% for Ga- In2O3 compared to 22% for pure In2O3.

Influence of cerium dopant on magnetic and dielectric properties of ZnO nanoparticles

Ce-doped ZnO nanoparticles (NPs) with different Ce doping concentrations (0, 0.96, 1.96, 2.52 and 3.12 at.% of Ce) were prepared by the chemical co-precipitation method. Energy-dispersive analysis of X-rays confirms the presence of Ce in Ce-doped ZnO nanoparticles. Raman spectra revealed the hexagonal wurtzite structure of pure and Ce-doped ZnO nanoparticles and presence of various defects. The photoluminescence spectra exhibited enhanced violet and blue emission peak intensities for 0.96 at.% of Ce, while broad band green emissions decreased with Ce content. Electron paramagnetic resonance (EPR) studies revealed the presence of oxygen vacancies (V O), zinc vacancies (V Zn) and Ce3+ ions in the prepared ZnO nanoparticles. VSM studies showed room temperature ferromagnetism (RTFM) in the Ce-doped ZnO NPs. The substituted Ce3+ions found to induce RTFM along with V O, V Zn in correlation with the results obtained from the EPR, PL and Raman studies. The variation of dielectric constants (e r), dielectric loss (e″) and ac conductivity (σ ac) as a function of frequency and Ce concentration is studied using ‘Maxwell–Wagner Model.’

Fabrication and characterisation of flower‐like ZnO nanostructures grown chemically on flexible PEN substrate

Flower-like ZnO nanostructures were successfully produced on a polyethylene naphthalate (PEN) substrate through a chemical bath deposition method. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible were utilised to investigate the structural and optical properties of grown flower-like ZnO nanostructures. FESEM image indicates that fabricated ZnO nanostructures formed from the ZnO nanoflowers with different shape and the petals of the ZnO nanoflower grow symmetrically and radially from the centre. XRD pattern of the ZnO nanoflowers indicate that the ZnO nanorods of the nanoflowers were preferentially grown along the c-axis. The PL results of the ZnO nanoflowers exhibited a strong violet and indigo emission peaks are centred approximately at 413 and 425 nm, respectively.

Synthesis of TiO2 nanowires via thermal oxidation process in air

TiO2 nanowires were synthesised by thermal oxidation of TiO powder in air at atmospheric pressure. No catalysts and substrates were used for the formation of TiO2 nanowires. These nanowires were fabricated at 1000°C. Nanowires could not be synthesised at temperatures lower than or higher than 1000°C. X-ray diffraction data revealed that the nanowires were of TiO2 with rutile crystallographic structure. Scanning electron microscopy study revealed that the diameters of the nanowires were in the range of 50–120 nm and the lengths were in the range of 3.2–8.0 μm. A strong violet emission peak at 410 nm was observed in the cathodoluminescence (CL) spectrum taken at room temperature, which is the signature of the high crystalline quality of the TiO2 nanowires.

Microstructure and Optical Properties of Yttrium-doped Zinc Oxide (YZO) Nanobolts Synthesized by Hydrothermal Method

In this work, yttrium-doped zinc oxide (YZO) nanopowder was synthesized via hydrothermal precipitation-method. The microstructure and optical properties of yttrium-doped zinc oxide nanopowder were characterized, which confirmed the well-crystalline wurtzite hexagonal phase of ZnO. The yttrium-doped zinc oxide nanopowder grains formed the nanobolts of ~400 nm in length and ~900 nm in width. High resolution-transmission electron microscopy (HR-TEM) of the nanobolts revealed uniform lattice fringes and no visible faults and/or distortions. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of yttrium in the zinc oxide lattice, proving the contribution of yttrium on the microstructural and optical properties of the material. A strong ultra violet (UV) emission peak of the YZO exhibited a red shift compared to pure zinc oxide, which was ascribed to the defects and the formation of a shallow energy level caused by the incorporation of yttrium.

Red luminescence from ZnO : Cr3+ nanophosphors under visible excitation

ZnO : Cr3+ (1 mol%) nanophosphor is synthesized by the wet chemical solution combustion method at the temperature of 400∘C. Powder X-ray diffraction results confirmed that Cr3+-doped and undoped ZnO nanophosphors exhibit hexagonal wurtzite structure. The average crystallite size calculated from Scherrer’s method is 25 nm for undoped and 14 nm for Cr3+-doped ZnO. The UV–visible absorption spectra shows red shift in Cr3+-doped ZnO. Photoluminescence studies of undoped ZnO show violet emission peak at 400 nm and blue emission peak at 447 nm. Cr3+-doped ZnO shows red emission peaks at 642, 694 and 746 nm, which are mainly attributed to spin forbidden transitions of 2Eg →\(^{4}\textit {A}_{2g}\) of Cr3+ ion in ZnO : Cr 3+ nanophosphor. Thermoluminescence (TL) studies recorded at a heating rate of 6∘C s −1 show two well-resolved glow peaks at 124 and 284∘C. It is found that the TL intensity increases with the gamma irradiation dose (500 Gy– 10 kGy).

Study on influences of Sb doping content on the defects of ZnO film by photoluminescence (PL) spectrum and raman scattering spectrum

Sb-doped ZnO thin films with different values of Sb concentrations are deposited on glass substrate by using spin-coating technique. The influences of Sb doping content on the microstructural, photoluminescence and Raman properties of ZnO film are systematically investigated by X-ray diffraction (XRD), transmission spectrum, photoluminescence (PL) spectrum and Raman scattering spectrum. The results indicate that ZnO thin film doped with Sb exhibits a hexagonal wurtzite structure with preferred c-axis orientation. The strong violet emission peak located at 3.11 eV is observed in the Sb-doped ZnO thin film by photoluminescence. Conbining the Raman scattering spectrum with photoluminescence, it is concluded that the strong violet emission peak related to SbZn-O complex defect in ZnO:Sb film.

Fe-doping induced tailoring in the microstructure and optical properties of ZnO nanoparticles synthesized via sol–gel route

Effects of Fe doping on the structural, photoluminescence and optical properties of sol–gel derived Zn100−xFexO (0 ≤ x ≤ 5) nanoparticles have been investigated. X-ray diffraction and HRTEM studies reveal a single phase wurtzite crystal structure without any secondary phase. The nanocrystalline nature of samples and their crystallinity have been confirmed by transmission electron microscopy measurements. Raman spectroscopy has been employed to study the crystalline quality and the structural disorder. The photoluminescence spectra display that all the samples have an violet emission peak centered at 416 nm, and 5 at. wt% Fe-doped ZnO nanoparticles have the strongest violet emission peak. These results suggest that 5 at. wt% Fe-incorporation can improve the crystalline quality and enhance the ultraviolet emission of ZnO nanoparticles. The optical band gap has been determined from optical absorption spectra. The optical band gap depends on Fe-doping level and on the microstructure of the samples, and is in the range of 3.20–3.47 eV.

Self-assembled growth of tandem nanostructures based on TiO2 mesoporous/ZnO nanowire arrays and their optoelectronic and photoluminescence properties

Growth of ZnO nanowires within TiO2 mesoporous structures is carried out by hydrothermal method. Structural, optical and thermal characterizations have been carried out by SEM, XRD, EDAX, DTG, TG, PL and UV–Vis spectroscopy. XRD characterization shows that the all diffraction peaks of the tandem nanostructures films can be well indexed to a mixture of hexagonal wurtzite ZnO and anatase TiO2 structures. The UV–Visible absorbance spectrum indicates that the tandem nanostructures based on TiO2 mesoporous/ZnO nanowire arrays have 3.13 eV band gap energy while pure ZnO nanowire and bare TiO2 mesoporous show 3.37 and 3.22 eV band gap energy, respectively. The PL spectra of tandem nanostructures show that the UV, violet and yellow emission peaks appeared at 3.1, 2.6 and 2.3 eV, respectively. It has been shown that from the PL spectra, the enhanced ultraviolet emission of TiO2/ZnO tandem structures is related to the fluorescence resonance energy transfer between TiO2 mesoporous and ZnO nanowires. Thermogravimetric analysis from room temperature to 800 °C has been performed to identify the thermal stability and the amount of tandem TiO2/ZnO structures.

Influence of deposition rate on PL spectrum and surface morphology of ZnO nanolayers deposited on Si (100) substrate

Zinc oxide (ZnO) thin films were deposited on Si (100) substrate through sputtering of zinc by DC magnetron, followed by thermal oxidation. Different deposition rates were used in coating films with 100 nm thickness (0·6–4·5 nm/s). Photoluminescence spectra of the produced samples were obtained and it was found that the violet emission peak intensity increases with deposition rate. Scanning electron microscopy (SEM) micrograph and atomic force microscopy (AFM) images for the zinc oxide films were obtained. Morphological changes due to various deposition rate are discussed in the light of changes observed in the ZnO crystals. Low coating rates produced smooth surface with small grains while higher deposition rates increased the surface roughness and larger grain size. AFM and SEM results are in good agreement and support the PL results.

Photoconductive UV detectors based heterostructures of Cd and Mg doped ZnO sol gel thin films

The photoconductive properties of single (CdZnO/MgZnO, Li:CdZnO/MgZnO) and double (MgZnO/ZnO/MgZnO, CdZnO/ZnO/MgZnO) heterostructures were studied by sol gel method at different annealing temperatures. These structures were analysed by X-ray diffraction (XRD) and photoluminescence (PL). The photoconductive measurements were carried out by semiconductor parametric analyzer. The hexagonal wurtzite structure was retained with good crystalline nature. The UV related strong near band edge (NBE) emission, ultra violet and blue green emission peaks were observed from PL spectra. Photocurrent was observed to have enhanced as a result of annealing temperature and Li substitution in the doped ZnO lattice. The increase of responsivity at ten orders of magnitude was found. Meanwhile, the dark current was found to have increased slightly due to the adsorption of O2 and H2O molecule on the surface of the film. Sub-linear behaviour of photocurrent was also observed.