Optical Properties Of ZnO Nanostructures Research Articles

Substantial effect of Cr doping on the third-order nonlinear optical properties of ZnO nanostructures

Here in, the present work we report the influence of Cr doping on the nonlinear properties of hydrothermally prepared ZnO nanoparticles. Structure has been confirmed from XRD analysis and exhibit a hexagonal wurtzite structure. Observed peak shift and decrease in crystallite size observed from XRD analysis confirms the successful Cr doping. FE-SEM images show distorted rod-like morphology and the doping percentages are confirmed from the EDAX spectra. The XPS spectrum confirms the existence of oxygen vacancies, which validates the existence of divalent oxidation states of zinc and the trivalent state of chromium. The calculated bandgap values validate thatZn0.98Cr0.02O nanoparticles exhibit the lowest bandgap energy due to the presence of optically active sub-levels within the bandgap region. Variation in peak intensity was observed from the Raman spectra, which validates the addition of Cr into lattice sites of ZnO. Under continuous wave (CW) laser regime, the Z-scan method was used to determine the third order nonlinearity and demonstrate, Zn0.96Cr0.04O nanoparticle show a combined effect of saturable absorption (SA) and reverse saturation absorption (RSA) under open aperture measurements with an increase in nonlinear absorption coefficient (βeff), and third-order NLO susceptibility (χ(3)) values on increasing Cr3+ doping concentration.

Hydrophilic ionic liquid assisted hydrothermal synthesis of ZnO nanostructures with controllable morphology.

Nanostructured ZnO with controllable morphology was prepared by a hydrothermal method in the presence of three different hydrophilic ionic liquids (ILs), 1-ethyl-3-methylimidazolium methylsulfate, ([C2mim]CH3SO4), 1-butyl-3-methylimidazolium methylsulfate, ([C4mim]CH3SO4) and 1-ethyl-3-methylimidazolium ethylsulfate, ([C2mim]C2H5SO4) as soft templates. The formation of ZnO nanoparticles (NPs) with and without IL was verified using FT-IR and UV-visible spectroscopy. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns indicated the formation of pure crystalline ZnO with a hexagonal wurtzite phase. Field emission scanning electron microscopic (FESEM) and high-resolution transmission electron microscopic (HRTEM) images confirmed the formation of rod-shaped ZnO nanostructures without using IL, whereas the morphology varied widely following addition of ILs. With increasing concentrations of [C2mim]CH3SO4, the rod-shaped ZnO nanostructures transformed into flower-shaped nanostructures whereas with rising concentrations of [C4mim]CH3SO4 and [C2mim]C2H5SO4 the morphology changed into petal- and flake-like nanostructures, respectively. The selective adsorption effect of the ILs could protect certain facets during the formation of ZnO rods and promote the growth in directions other than [0001] to yield petal- or flake-like architectures. The morphology of ZnO nanostructures was, therefore, tunable by the controlled addition of hydrophilic ILs of different structures. The size of the nanostructures was widely distributed and the Z-average diameter, evaluated from dynamic light scattering measurements, increased as the concentration of the IL increased and passed through a maximum before decreasing again. The optical band gap energy of the ZnO nanostructures decreased when IL was added during the synthesis which is consistent with the morphology of the ZnO nanostructures. Thus, the hydrophilic ILs serve as self-directing agents and soft templates for the synthesis of ZnO nanostructures and the morphology and optical properties of ZnO nanostructures are tunable by changing the structure of the ILs as well as systematic variation of the concentration of ILs during synthesis.

The Effect of Al-Cu Co-Dopants on Morphology, Structure, and Optical Properties of ZnO Nanostructures

The Effect of Al-Cu Co-Dopants on Morphology, Structure, and Optical Properties of ZnO Nanostructures

Structure-correlated excitation wavelength-dependent optical properties of ZnO nanostructures for multifunctional applications

Excitation wavelength-dependent visible emissions from ZnO nanostructures demonstrate that defect states are insufficient to explain their optical properties.

Synthesis, characterization, and the influence of energy of irradiation on optical properties of ZnO nanostructures

Zinc oxide nanoparticles (NPs) are synthesized by the sol–gel method for optoelectronics, photonic, and medical applications. The as-synthesized NPs are irradiated with lasers with wavelengths of 1064 nm and 532 nm in an attempt to improve the particles' structural and functional properties. The NPs are characterized by means of X-ray diffraction, scanning and transmission electron microscopy techniques, atomic force microscopy, and ultraviolet–visible spectroscopy. The structural analysis shows that the particles have a polycrystalline hexagonal structure of the space group (P63mc). The average crystallite size of nanoparticles varies in the range of 13–15 nm after and before irradiation by a laser beam. The morphological characterization revealed the formation of agglomerates of NPs in the range of 42–46 nm A shift is observed in the absorption spectra after irradiation with a laser beam. This shift is due to the effect of irradiation on the sample’s electronic structure. This effect is confirmed by a decrease in the bandgap energy. The optical parameters are also deduced and discussed. The irradiation of ZnO nanoparticles by laser beams of wavelength 1064 nm and 532 nm decreases the size of the crystallites which increases their antibacterial activity. The biological activity of the NPS and in improving the efficacy of antibiotics are tested and analyzed. Results emphasized the positive role of ZnO-NPs in the above-mentioned application.

Study of the Optical Properties of Zno Nano-structure at Different Ti Content

Study of the Optical Properties of Zno Nano-structure at Different Ti Content

Structural and Optical Properties of ZnO Nanostructures Synthesized by Hydrothermal Method at Different Conditions

ZnO nanostructures were synthesized by hydrothermal method at different temperatures and growth times. The effect of increasing the temperature on structural and optical properties of ZnO were analyzed and discussed. The prepared ZnO nanostructures were characterized by X-ray diffraction (XRD), UV–Vis. absorption spectroscopy (UV–Vis.), Photoluminescence (PL), and scanning electron microscopy (SEM). In this work, hexagonal crystal structure prepared ZnO nanostructures was observed using X-ray diffraction (XRD) and the average crystallite size equal 14.7 and 23.8 nm for samples synthesized at growth time 7 and 8 hours respectively. A nanotubes-shaped surface morphology was found using scanning electron microscopy (SEM). The optical properties showed that the samples had good absorbance in the UV-Vis. region and wide band gap. The PL spectrum displayed that the intensity of ultraviolet (UV), band gap and defect bands depend on the growth temperature of the ZnO nanostructure. The largest band gap was 3.351 eV for ZnO nanostructure synthesized at 100 °C and growth time 8h.

Optimization of the luminescence and structural properties of Er-doped ZnO nanostructures: effect of dopant concentration and excitation wavelength

The present study reports the effect of Er doping on the structural, morphological, and optical properties of ZnO nanostructures. ZnO: Er nanorods with different doping concentrations were successfully synthesized via a hydrothermal method. X-ray diffraction and Energy-dispersive X-ray spectroscopy analyses suggest the successful incorporation of Er into the wurtzite structure of ZnO; A secondary phase of Er2O3 appears when the Er concentration exceeds 2.5 wt%. The optical band-gap of ZnO was determined from the analysis of ultraviolet–visible spectra, and a decrease of the band gap is emphasized with increasing Er concentration. Photoluminescence spectra display a strong and broad deep-level emission band, which intensified with increasing Er concentration. The current work provides more details about the excitation wavelength effect on the luminescence of pure and Er-doped ZnO materials, finding that the visible photoluminescence emission intensity could be controlled by adjusting the Er concentration as well as the excitation wavelength; better luminescence was obtained with high Er concentration and high excitation wavelength. Moreover, the DFT calculations support the experimental results and confirm that the presence of oxygen vacancies has an effect on the structural and electronic properties of ZnO. Hence, the research findings of this work could provide an experimental and theoretical reference that may motivate future research on the study of ZnO-based optoelectronic applications.

Correction to: Influence of precursor ions on the structural morphological and optical properties of ZnO nanostructure and cytotoxicity on murine NIH 3T3 cells

Correction to: Influence of precursor ions on the structural morphological and optical properties of ZnO nanostructure and cytotoxicity on murine NIH 3T3 cells

Impact of Radio Frequency Plasma Power on the Structure, Crystallinity, Dislocation Density, and the Energy Band Gap of ZnO Nanostructure

The aim of this study is to investigate the effect of radio frequency (RF) plasma power on the morphology, crystal structure, elemental chemical composition, and optical properties of ZnO nanostructure using a direct current magnetron sputtering technique. This study emphasized that the growth rate and surface morphology of the polycrystalline ZnO were enhanced as the radio frequency (RF) plasma power increased. This can be observed by fixing other parameters such as the growth time, substrate temperature, and chamber partial pressure. The RF plasma power alteration from 150 to 300 W can produce uniform nanograin, spheroid, and nanorods. Additionally, the RF plasma power alteration leads to the alteration in the ZnO nanorod diameter from 14 to 202 nm. It was observed that the XRD intensities are increased at higher plasma powers. This, perhaps, can be inferred from the transformation of the granular microcrystals to the needlelike or platelike large crystals, as already examined using SEM images. This also has an impact on the average crystalline size, which increased from 10 to 40 nm on increasing the RF plasma power. Moreover, the increase of the RF plasma power has an obvious impact upon the optical band-gap energy, which was accordingly decreased from 3.26 to 3.22 eV. Finally, the absorption band edge was shifted to a lower-energy region due to the quantum size effect at the nanorange.

Fe doped ZnO nanostructures prepared via sol-gel dip-coating technique for iso-butane (i-C4H10) sensing

Fe doped ZnO (FZO) nanostructures with varying Fe concentrations say 0, 1, 3, 5, 7, and 9 wt.% were prepared on the glass substrates via the sol-gel dip-coating technique. Effects of Fe-doping concentration on the structural, morphological, optical properties and the response to iso-butane (i-C4H10) gas of ZnO nanostructures were studied. The X-ray diffraction (XRD) analysis showed that Fe doping has a significant effect on particle size, strain, and crystalline quality in the prepared films. Scanning Electron Microscopy (SEM) images of the prepared samples revealed nanoparticles and nanorods formation, with content Fe variation. The Energy Dispersive Spectroscopy (EDS) results confirmed the presence of Zn, O, and Fe elements. UV-Vis absorption measurements showed that the deposited films have a transmittance between 69% and 89%, and the differential optical transmittance plot indicated that the band gap energy decreases with increasing Fe doping ratio. The sensitivity characteristics to iso-butane gas were evaluated as a function of the film composition, operating temperature in the range from 150 to 300 °C, and volume gas concentration from 0.8 to 6.4 Vol.%. The obtained results showed that the iso-butane response, as well as the structural, morphological, and optical properties of ZnO nanostructures, changed with the Fe doping. Also, the iso-butane sensing results evidently showed that the 3 wt.% Fe doped ZnO nanostructure offered a remarkable response of ~ 76.3% with a quick response time of ~ 67 s to 0.8 Vol.% of i-C4H10 at the optimum operating temperature of 250 °C. Therefore, FZO nanostructures produced can be used as a sensor for the detection of iso-butane gas in various industrial and domestic branches.

The influence of Mn doping on the structural and optical properties of ZnO nanostructures

We report the hydrothermal synthesis of Zn1-xMnxO (x = 0.00, 0.02, 0.04, 0.06) nanostructures and their structural, morphological and optical properties. The X-ray diffraction analysis confirmed the wurtzite phase and successful incorporation of Mn in ZnO matrix. Field emission scanning electron microscopy (FE-SEM) images revealed the suppression of growth rate and change in morphology of ZnO from nanoplates to nanorods at higher Mn concentration. Furthermore, a red shift is observed in the Fourier transform infra-red (FTIR) spectra, which is attributed to the variation of bond length and Zn–O–Zn structural perturbation. UV–visible absorption measurements indicated a blue shift in the bandgap from 3.28 eV (pure ZnO) to 3.42 eV (x = 0.06), which is assigned to the Burstein-Moss effect. The photoluminescence spectra exhibited UV excitonic and yellow-green defective emissions. The intensity of broad visible emission peak is decreased which is ascribed to the surface defect quenching due to the presence of Mn as a dopant.

Influence of ZnO nanostructure configuration on tailoring the optical bandgap: Theory and experiment

Exploiting the link between form and function of semiconductor nanostructure provides a new prospect for tailoring the features of nanoscale materials. However, achieving this remains a challenge in the fabrication of optoelectronic devices. Therefore, this research systematically presents theoretical and experimental investigations of shape dependent structural and optical properties of ZnO nanostructures (nanoparticles, vertically oriented nanorods and compact ZnO) synthesized using the electroless deposition technique to understand the principles of bandgap modification. FESEM, XRD, Photoluminescence (PL) and UV–Vis spectroscopic characterizations were employed. The characterizations show increase in lattice parameters, bandgap and density of dislocations from 0.3236 nm to 0.3258 nm, ~3.14 eV to ~3.51 eV and ~17 × 10-4 to ~39 × 10-4, respectively as the ZnO nanostructures are transformed from compact ZnO to ZnO nanoparticles. The expansion in lattice parameter is attributed to lower compressive stress that exists in ZnO nanoparticles compared to compact ZnO. The blue shift (0.06 eV) in bandgap is ascribed to overlapping of the orbitals and energy level in ZnO nanoparticles which causes a substantial increase in energy gap between valence and conduction bands. The small size-induced hardening in ZnO nanoparticles accounts for their comparatively higher dislocation density. Theoretically, conversion from compact ZnO to ZnO nanoparticles extends the bandgap from 3.38 eV to 3.44 eV, which is consistent with the experimental results. This study confirms the shape dependency of the structure and bandgap of ZnO nanostructures, which may provide a new insight into future integrated optoelectronic device applications.

ZnO Nanostructures Synthesized by Vapor Transport and Liquid Phase Synthesis Techniques: Growth and Properties

In this review, we briefly describe work devoted in recent years towards the effective control of morphology, structure and optical properties of ZnO nanostructures, with particular focus on cost effective and simple methods for ZnO nanowires (NWs) fabrication. For the vapor transport technique, we describe in detail mechanisms for growth precursors generation, their transport in inert and forming gas, as well as their reactions on different pretreated substrates and corresponding growth mechanisms. As for low temperature synthesis methods, three techniques are outlined: sol-gel, solvothermal and electrophoretic deposition, with emphasis on effective morphology, structure and optical properties control. In this context, we discuss recent attempts to understand the role of solvent and alkaline agents used during solvothermal synthesis of ZnO nanostructures on their morphology and photoluminescence properties. Recent success of electrophoretic deposition of ZnO nanoparticles on pre-patterned silicon substrates in the form of NWs and NW bunches is highlighted over many previous attempts to fabricate ZnO NWs with inconvenient sacrificial templates. Finally, we present a critical discussion on the current understanding of passivation mechanisms of ZnO NW surfaces by MgO shells.

Surface plasmons enhanced band-edge emission in Ni nanoparticles decorated ZnO nanorods arrays architecture

We report nickel (Ni) nanoparticles (NPs) surface plasmons assisted enhanced photoluminescence behaviour in Ni-decorated ZnO NRs arrays architecture. ZnO NRs arrays architecture was grown on the Si substrate by a conventional hydrothermal route, followed by Ni NPs were decorated on the surface of ZnO NRs arrays architecture by pulsed laser deposition technique. The XRD and Raman analyses confirm the grown nanostructure is in hexagonal wurtzite structure. On Ni NPs decoration, a more than 14-fold enhancement in the band-edge emission with simultaneous suppression in the visible emission is observed. The improved PL emission can be attributed to the resonant coupling between the exciton emission of ZnO NRs arrays and the surface plasmons of Ni NPs. The energy band diagram demonstrates the interfacial charge transfer that takes place from the trapping states of ZnO NRs arrays architecture to Ni NPs, then surface plasmons bands of Ni NPs to the conduction band of ZnO NRs arrays architecture. Our experimental results reveal the decoration of Ni NPs on ZnO NRs arrays architecture is an effective means to tailor the optical properties of ZnO nanostructures.

Tailoring of crystal phase, morphology, and optical properties of ZnO nanostructures by starch-assisted co-precipitation synthesis and annealing

ZnO nanostructures have been synthesized by simple co-precipitation method in the presence or absence of surfactant (starch) and subsequent annealing at 500 and 800 °C for 5 h. The XRD results show ZnO and Zn5(OH)8Cl2·H2O phases in the absence, but only ZnO phase in the presence, of starch. The secondary phase diminishes upon annealing and only pure ZnO phase with improved crystallinity is realized at 800 °C. FTIR endorses different phases along with the starch surfactant by the representative modes. Diverse morphologies: hexagonal; tubular; spherical; and cluster morphologies are observed for different synthesis and annealing conditions. The direct band gap is found to be ~ 3.2 eV and experienced a red shift on annealing. The PL spectra consists of characteristic near band edge (NBE) emission in UV region and a broad emission in visible region corresponding to direct excitonic transitions and oxygen defect transitions, respectively. Samples having rod-like morphology as predominant exhibit strong UV and weak defect emissions, while those with spherical morphology as dominant display weak UV and broad defect emissions in PL. The quenching of NBE emission takes place on annealing, which is indicative of increase in non-radiative transitions or deformation of crystallinity or change in morphology. The PL emissions are strongly influenced by surfactant and annealing temperature. Such results offer new prospects for tuning and optimizing the properties of ZnO semiconductor for applications where the optical properties are decisive.

Studying the Effect of Annealing on Optical and Structure Properties of Zno Nanostructure Prepared by Laser Induced Plasma

In this paper, Zinc oxide were deposited on a glass substrate at room temperature (RT) and two annealing temperatures 350ºC and 500ºC using laser induced plasma technique. ZnO nanofilms of 200nm thickness have been deposited on glass substrate. X-RAY diffraction (XRD), atomic force microscopy and UV-visible spectrophotometer were used to analyze the results. XRD forms of ZnO nanostructure display hexagonal structure with three recognized peaks (100), (002), and (101) orientations at 500ºC annealing temperature. The optical properties of ZnO nanostructure were determined spectra. The energy gap was 3.1 eV at 300 oC and 3.25eV at 500ºC annealing temperature.

Refluxed sol–gel synthesized ZnO nanopowder with variable zinc precursor concentrations

ZnO nanoparticles were synthesized using refluxed sol–gel method with variable zinc precursor concentration ranging from 0.1 to 0.2 M. The structural, morphology and optical properties of ZnO nanostructures were investigated using different characterization techniques. Concentration of zinc precursor significantly affects the morphology, structural and optical properties. All ZnO samples prepared are pure hexagonal wurtzite in structure and the crystallite sizes increases from 24 to 35 nm. The average lattice parameters were calculated as a = 0.3267 nm and c = 0.5232 nm. The average bond length of ZnO nanocrystalline was calculated to be around 0.1988 nm. The photoluminescence measurement result shows that both UV (at 380 nm) and visible (between 428 and 636 nm centered at 540 nm) emissions are displayed with the excitation wavelength of 248.6 nm from NeCu laser source. The room temperature photoluminescence measurement shows that the emission wavelength shifted towards the higher wavelength as zinc precursor concentration increases. The intensity ratio of the near-band-edge emission to deep-level emission increases as zinc precursor concentration increases. With low temperature photoluminescence (from 84 to 300 K) measurement, the emission energy increases from 3.28 to 3.35 eV. The deep-level emission of the ZnO was displayed in the green and yellow regions of the visible spectrum. The reflectance spectra from UV–Vis spectroscopy show that the concentration of zinc precursor has a significant effect on the band gaps of the material which decreased from 3.26 to 3.24 eV as the zinc precursor concentration increased from 0.1 to 0.2 M.

Effect of Sr2+ doping on the linear and nonlinear optical properties of ZnO nanostructures

We present the structural and third order nonlinear optical properties of Sr2+-doped ZnO nanostructures synthesized by chemical precipitation technique. The prepared nanoparticles are systematically investigated by UV–vis absorption, X-ray diffraction (XRD), Photoluminescence spectroscopy and Field emission scanning electronic microscopy (FESEM), respectively. UV–vis absorption spectra show that the particles have a higher absorption in UV region and possess a large optical transparency in visible region. XRD patterns show that all the prepared nanoparticles are well crystallized with hexagonal wurtzite structure. The incorporation of Sr in ZnO was also confirmed by fluorescence quenching. FESEM images showed the formation of nanostructures with sheet-like structure. Third-order nonlinear optical properties of the nanostructures have been studied by Z-scan technique using diode pumped continuous wave (cw) laser system at a wavelength of 532 nm. Experimental results reveal that the materials exhibit saturable absorption (SA) and self-defocusing nature.

Size-tunable ZnO nanotapes as an efficient catalyst for oxidative chemoselective C[sbnd]B bond cleavage of arylboronic acids

Herein, we report a simple but effective chemical approach for the synthesis of size-tunable ZnO nanotapes by precipitation method in the presence of phytochemicals present in the flower extract of Lantana camara plant. The electron microscopic study confirmed that the size of ZnO nanotapes can be systematically controlled by varying the concentration of either flower extract or metal ions and the flower extract played the key role in controlling the growth of ZnO nanotapes. The phase and crystalline analysis was carried out by X-ray diffraction method which indicated that ZnO nanostructures are highly crystalline in nature and are free from any impurities. The synthesized ZnO nanostructures exhibited interesting optical properties as investigated by UV–vis absorption and photoluminescence spectroscopy. Further the surface functionalities affect the optical properties of ZnO nanostructures which possess relatively strong UV emissions; a blue emission and a green emission. The synthesized ZnO nanostructures showed excellent catalytic properties in the ipso-hydroxylation of different aryl/ hetero-arylboronic acid to phenol in a relatively greener reaction conditions. These catalysts are highly stable and are re-usable upto six cycles of ipso-hydroxylation without losing its catalytic properties.