Optical Properties Of ZnO Nanoparticles Research Articles

Structural and optical properties of ZnO nanoparticles deposited on porous silicon for mc-Si passivation

In this paper, we demonstrate the potential application of ultrathin ZnO film combined with porous Si treatment for multi-crystalline silicon (mc-Si) surface passivation. ZnO films were grown on porous silicon (PS) and glass substrate by spray pyrolysis method using zinc nitrate precursor with different molar concentrations varying from 0.05 to 0.25 M. The effects of molar concentration on the structural, optical and electronic properties of ZnO film were discussed. This method has been successfully used to achieve both antireflection and passivation properties of the mc-Si-treated samples. As a consequence, the effective minority carrier lifetime increases from 1 to 90 μs at a minority carrier density (Δn) of 3 × 1013 cm−3. The proposed treatment demonstrates also a significant decrease in the reflectivity of ZnO/PS-treated mc-Si as compared to untreated one. The reflectivity decreases from 32 % for untreated mc-Si wafers to 9 % for ZnO/PS-treated ones. The prepared cells give relatively high short-circuit currents (I sc) which leads to the recorded high conversion efficiency. An optimum Zn concentration is required to optimise the solar cell efficiency. This simple and cost-effective passivation method leads to an increase of mc-Si solar cells efficiency to 12 %.

Doping effect of Ag+, Mn2+ ions on Structural and Optical Properties of ZnO nanoparticles

Pure ZnO and co-doped (Mn, Ag) ZnO nanoparticles have been successfully prepared by chemical co-precipitation method without using a capping agent. X-ray diffraction (XRD) studies confirms the presence of wurtzite (hexagonal) crystal structure similar to undoped ZnO, suggesting that doped Mn, Ag ions are substituted to the regular Zn sites. The morphology of the samples were studied by scanning electron microscopy (SEM). The chemical composition of pure and co-doped ZnO nanoparticles were characterized by energy dispersive X-ray analysis spectroscopy (EDAX). Optical absorption properties were determined by UV-vis Diffuse Reflectance Spectrophotometer. The incorporation of Ag+, Mn2+ in the place of Zn2+ provoked to decrease the size of nanocrystals as compared to pure ZnO. Optical absorption measurements indicates blue shift in the absorption band edge upon Ag, Mn ions doped ZnO nanoparticles.

The Influence of Hydrothermal Duration on Structures and Optical Properties of ZnO Nanoparticles

ZnO nanoparticles were synthesized by hydrothermal method using ethylene glycol as a stabilizer and as well as a template. This study was aimed to examine the influence of hydrothermal duration (3, 6, and 12 hours) on the structures and optical properties of ZnO nanoparticles. X-ray diffraction results show that all peaks appear in the diffraction pattern indicate the hexagonal wurtzite structure of ZnO. The lattice parameters found just slightly varied with addition of hydrothermal duration. It is found that the particles size decreases whereas the average crystals size increase with hydrothermal duration. The average crystal size found increase with addition of hydrothermal duration. On the other hand, the particle grains were spread evenly distributed with decreasing size with hydrothermal duration increase, as indicated in the SEM images. Optical properties were investigated based on the optical transmission of the ZnO films. It is known that the films strongly absorb the visible region, whereas the absorption edge in the UV region. Bandgap energy of the films found increase with hydrothermal duration, that were 3.18 eV, 3.21 eV and 3.24 eV for 3 hours, 6 hours and 12 hours, respectively.

Influence of Precursors on Morphology and Spectroscopic Properties of ZnO Nanoparticles

ZnO Nanopowders are prepared with three different precursor's viz., NaOH, KOH and Na2CO3 using co-precipitation method. Further samples are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-Vis Optical absorption and Photoluminescence (PL) spectroscopy analyses. Morphology and optical properties of ZnO nanoparticles are investigated for the each precursor. XRD patterns indicate hexagonal phase unit cell structure. ZnO nanoparticles exhibit an absorption band at 355nm and two photoluminescence bands peaking at 397nm & 530nm. From the analyses of results, it is very clear that precursors used in the present study have played a vital role in surface morphology, structural and optical properties of ZnO nanoparticles.

Effect of Synthesis Temperature, Nucleation Time, and Postsynthesis Heat Treatment of ZnO Nanoparticles and Its Sensing Properties

Control in size, crystallinity, and optical properties of ZnO nanoparticles (NPs) synthesized via coprecipitate method were investigated. A systematic change in particle size, crystallinity, and optical properties was observed by increasing synthesis temperature from 65°C to 75°C. A detailed study also suggested that smaller nucleation time is better to control the size distribution but the crystallinity will be compromised accordingly. Postannealing of ZnO NPs at 400°C also improves the crystal quality. Ultraviolet (UV) sensors were successfully synthesized and the results suggested that as‐synthesized ZnO NPs can be used as active material for sensor applications.

Red shift of the band-edge photoluminescence emission and effects of annealing and capping agent on structural and optical properties of ZnO nanoparticles

Use of nontoxic and biodegradable capping agents during the synthesis of nanomaterials has drawn a lot of research attention due to their potential applicability in biophotonic and bio-imaging devices. However, here we have reported the synthesis of an uncapped and biodegradable polyvinyl alcohol (PVA) capped ZnO nanoparticles (NPs), by using a simple chemical precipitation method at room temperature, followed by isochronal annealing of the as-synthesized sample at 200, 400, 500 and 600°C for 2h in air. The effects of using PVA and thermal annealing on the structural and optical properties of synthesized ZnO NPs have been reported. From the X-ray diffraction data analyses it has been observed that the use of PVA caused tensile strain in the annealed samples, whereas the samples synthesized without PVA capping showed compressive strain. For an estimation of strain and sizes of the NPs, three different models namely, uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM) have been used. The photoluminescence (PL) emission characteristics of the samples have been reported and they are found to consist of a strong near band-edge UV emission, which is systematically red shifted due to annealing from 371 to 383nm for the capped and from 372 to 385nm for the uncapped samples. Such biodegradable capped nanoparticles having UV PL emission might find potential applications as biophotonic materials.

Aqueous chemical route synthesis and the effect of calcination temperature on the structural and optical properties of ZnO nanoparticles

This article reports the controlled size of ZnO nanoparticles synthesized via simple aqueous chemical route without the involvement of any capping agent. The effect of different calcination temperatures on the size of the ZnO nanoparticles was investigated. X-ray diffraction (XRD) results indicated that all the samples have crystalline wurtzite phase, and peak broadening analysis was used to evaluate the average crystallite size and lattice strain using Scherrer's equation and Williamson–Hall (W–H) method. Morphology and elemental compositions were investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy. The average crystallite size of ZnO nanoparticles estimated from Scherrer's formula and W–H analysis was found to increase with the increase in calcination temperature. These results were in good agreement with AFM results. Optical properties were investigated using UV–vis spectroscopy in diffused reflectance (DR) mode, with a sharp increase in reflectivity at 375nm and the material has a strong reflective characteristic after 420nm at 500°C calcination temperature. Furthermore, photoluminescence spectroscopic results revealed intensive ultraviolet (UV) emission with reduced defect concentrations and a slight shifting in band gap energies with increased calcination temperature from 200°C to 500°C. This study suggests that the as-prepared ZnO nanoparticles with bandgap tunability might be utilized as window layer in optoelectronic devices.

The Effect of Surfactants and Co-Reagents on the Microstructure, Morphology and Optical Properties of ZnO Nanoparticles Synthesized by Microwave Irradiation

Zinc oxide nanoparticles (ZnO NPs) have been synthesized through microwave irradiation by using different surfactants (Polyvinyl pyrrolidone (PVP), Polyethylene glycol (PEG) and Sodium dodecyl benzene sulphonate SDBS)) and co-reagents (NH3 and NaOH). The synthesized samples were analyzed by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning and transmission electron microscopy (SEM and TEM). Depending on the surfactants and reagents used, various ZnO nanostructures having spherical, rectangle, star-like, needle and rod-like structures with different crystallite size have been obtained. The optical and photoluminescence properties of the samples were investigated and discussed in terms of the different surfactant and reagents used for the synthesis. Keywords: Microwave synthesis, PEG, ZnO, PVP, SDBS, surfactants.

Effects of graphene oxide concentration on optical properties of ZnO/RGO nanocomposites and their application to photocurrent generation

The effects of different concentrations of graphene oxide (GO) on the structure and optical properties of ZnO nanoparticles (NPs) were investigated. The nanocomposites were synthesized via the sol-gel method in a gelatin medium. X-ray diffraction patterns (XRD) and Fourier transform infrared spectroscopy indicated that the GO sheets were reduced and changed to reduced GO (RGO) during the calcination of the nanocomposites at 400 °C. In addition, the XRD patterns of the NPs indicated a hexagonal (wurtzite) structure for all the products. Microscopic studies showed that the NPs were decorated and dispersed on the RGO sheets very well. However, these studies revealed that the RGO concentration had an effect on the crystal growth process for the ZnO NPs. Furthermore, these studies showed that the NPs could be grown with a single crystal quality in an optimum RGO concentration. According to the XRD results that were obtained from pure ZnO NPs, the calcinations temperature was decreased by the RGO. UV–vis and room temperature photoluminescence studies showed that the optical properties of the ZnO/RGO nanocomposite were affected by the RGO concentration. Finally, the obtained ZnO/RGO nanocomposite was used to generate a photocurrent. Observations showed that the photocurrent intensity of the nanocomposite was significantly increased by increasing the RGO, with an optimum RGO concentration.

Structural, Optical and Photocatalytic Properties of ZnO Nanoparticles Prepared by Precipitation Method

ZnO nanoparticles were synthesized from PEG600 diacid modified-Zn (CH3COO)2.2H2O solution by precipitation method and an aqueous NaOH solution was used as precipitating agent. The crystal structure, morphology and optical property of ZnO nanoparticles were characterized by XRD, SEM and UV-Vis spectrophotometer, respectively. The crystallinity increased while the Eg value decreased as a function of PEG600 diacid concentrations. The ZnO nanoparticles that had the highest crystallinity and lowest Eg value exhibited the highest efficiency of photocatalytic degradation of about 90% when irradiating with a UV light for 3 h.

Effect of doping on structural and optical properties of ZnO nanoparticles: study of antibacterial properties

Abstract Sol-gel method was successfully used for synthesis of ZnO nanoparticles doped with 10 % Mg or Cu. The structure, morphology and optical properties of the prepared nanoparticles were studied as a function of doping content. The synthesized ZnO:(Mg/Cu) samples were characterized using XRD, TEM, FTIR and UV-Vis spectroscopy techniques. The samples show hexagonal wurtzite structure, and the phase segregation takes place for Cu doping. Optical studies revealed that Mg doping increases the energy band gap while Cu incorporation results in decrease of the band gap. The antibacterial activities of the nanoparticles were tested against Escherichia coli (Gram negative bacteria) cultures. It was found that both pure and doped ZnO nanosuspensions show good antibacterial activity which increases with copper doping, and slightly decreases with adding Mg.

Influence of Cr incorporation on structural, dielectric and optical properties of ZnO nanoparticles

This study demonstrated the effect of Cr doping on structural, dielectric and optical behavior of ZnO nanoparticles synthesized through sol–gel method. Characteristic investigations have been carried out by X-ray diffraction, Field emission scanning electron microscope, Energy dispersive X-ray spectrometry, and Transmission electron microscope. The results confirmed the formation of nanoparticles in polycrystalline single phase with hexagonal wurtzite structure. The crystallite size has been found to vary around 20nm. Dielectric studies were carried out by Impedance spectroscopy. The decrease effect of dielectric parameters with increase in dopant has been explained on the basis of Maxwell–Wagner model and Koops phenomenological theory. The impedance analysis suggested that the contribution of grain boundaries is dominating over grain contribution. A red shift in UV–vis spectra signified that band gap can be tuned by Cr doping from 3.32 to 3.22eV because of the s–d and p–d exchange interactions.

Room temperature ferromagnetism in finite sized ZnO nanoparticles

We report systematic investigations on the evolution of nanostructured ZnO, room temperature ferromagnetism, and tunable optical properties of ZnO nanoparticles prepared by a mechanical alloying process. It was observed that both un-milled and as-milled powders exhibited a wurtzite structure, but average crystallite size decreased and the effective strain increased for the initial periods of milling. Paramagnetic nature observed in un-milled ZnO gradually unveils room temperature ferromagnetic ordering with modest moment and coercivity. A maximum moment of 0.013µB/f.u. at 12kOe applied field and a coercivity of 172Oe were obtained for 40h milled ZnO powder. Thermo-magnetization data reveal a clear magnetic phase transition from ferromagnetic to paramagnetic state around 500°C, which shifts slightly towards higher temperature with an increasing milling period up to 20h. Annealing of as-milled ZnO powder and UV–vis studies display a drastic reduction in room temperature magnetic moment and blue-shifting of excitonic absorption peak. The observed ferromagnetic properties are intrinsic and discussed on the basis of finite size effect, defect density due to oxygen vacancy. These nanoparticles with tunable magnetic and optical properties are promising to find applications in multifunctional spintronic and photonic devices.

Enhanced visible light photocatalytic performance of ZnO/ZnS/CuS ternary nanocomposites

The ZnO/ZnS/CuS ternary nanocomposites (ZOSCTN) were synthesized via a three-step chemical method with ZnO/ZnS binary nanocomposites (ZOSBN) as the intermediate and ZnO nanoparticles (ZON) as the initial product. The structural, morphological and optical properties of ZON, ZOSBN and ZOSCTN were characterized by X-ray diffraction, field emission scanning electron microscopy and Ultraviolet–visible spectroscopy. ZOSBN can maintain the morphology and size of ZON. However, after the introduction of the third component, ZOSCTN become blades-like with the thickness about 20–50nm. Moreover, ZOSCTN has markedly improved visible light photocatalytic performance than ZON and ZOSBN because of the high solar absorption and heterostructures interfaces.

Fabrication and Characterization of Chitosan/Cellulose-ZnO Nanocomposites for Bactericidal Applications

ABSTRACTThe present work focuses on the fabrication of environmental friendly ZnO nanocrystals and chitosan/cellulose films hosting ZnO nanoparticles (NPs) as an attempt to produce nanocomposites with enhanced bactericidal capacity. The solution casting method was used to fabricate the chitosan/cellulose blend films. Highly monodisperse ZnO nanoparticles were synthesized using Zinc acetate and Triethylene glycol (TEG) via a modified Polyol route. ZnO crystal size was controlled by the heterogeneous nucleation approach. Optical properties of ZnO nanoparticles were studied by UV–vis spectroscopy and Photoluminescence Spectroscopy (PL) techniques. The nanoparticles’ size and morphology were determined by Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD), respectively. Obtained results confirmed the effectiveness of the size-controlled synthesis employed. The chitosan/cellulose/ZnO nanocomposites were characterized by Fourier Transform – Infrared spectroscopy (FTIR) and X-ray diffraction (XRD) methods. The mechanical properties of produced bare and ZnO-bearing composites were determined from stress-strain tests. The Standard Plate Count and the Halo Zone methods were used to evaluate the bactericidal properties of the ZnO nanoparticles, chitosan/cellulose blend films and chitosan/cellulose/ZnO nanocomposites againstEscherichia coli(ATCC 35218).

Effect of Sn doping on microstructural and optical properties of ZnO nanoparticles synthesized by microwave irradiation method

Pure and Sn-doped ZnO nanostructures have been synthesized by the microwave irradiation method. The influence of Sn loading on the morphology and microstructure was evaluated by using field emission scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectrum analysis techniques, X-ray diffraction, and Fourier transform infrared spectroscopy. A change in the growth pattern, from needle-like particles for pure ZnO to agglomerated spherical crystallites for Sn-doped ZnO, has been observed. TEM observations indicated that the average particle size of the pure ZnO nano needles is in the range of 40–60 nm, whereas on addition of Sn spherical nanoassemblies size lies in the range of 10–21 nm. The pure ZnO and Sn-doped ZnO nanostructures were further characterized for their optical properties by UV–Vis reflectance spectra (DRS) and photoluminescence (PL) spectroscopy.

Effect of laser pulse energy and wavelength on the structure, morphology and optical properties of ZnO nanoparticles

In this work, the effects of the laser pulse energy and laser wavelength on the production of ZnO nanoparticles prepared by pulsed laser ablation of Zn metal plate in deionized water are investigated. The beam of a Q-switched Nd:YAG laser of 1064 and 532 nm wavelengths at 6 ns pulse width and different fluences is employed to irradiate the solid target in water. The ZnO nanoparticles were found to be hexagonal. The size distribution of generated ZnO nanoparticles is decreased by increasing the laser pulse energy. The rate of ZnO nanoparticles production is increased with increasing the laser pulse energy and is decreased with increasing the laser photon energy. ZnO nanoparticles were formed with different shapes depending on the laser pulse energy and laser wavelength. The bandgap energy for ZnO nanoparticles generated with 1064 nm laser pulse wavelength is calculated to be 3.59–3.89 eV.

Controlling the size and optical properties of ZnO nanoparticles by capping with SiO2

The size and shape of the ZnO nanoparticles synthesized through sol–gel method were controlled by capping with SiO2. X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) and High Resolution Transmission Electron Microscope (HR-TEM) results demonstrated that the particle growth of the ZnO nanoparticles has been restricted to 5nm with SiO2 capping. As a result, the absorption spectra of ZnO nanoparticles capped with SiO2 got blue shifted (toward lower wavelength side) due to strong quantum confinement effects. BET (Brunauer–Emmet–Teller) surface area pore size analyzer results showed that surface area of samples increased monotonously with increase of SiO2 concentration. It was observed that the absorption spectra of ZnO capped with SiO2 broadened with increase of SiO2 concentration. Absorption and photoluminescence excitation results (PLE) confirmed that this broadening is due to the absorption of non-bridging oxygen hole centers (NBOHC) of SiO2. These results also indicated that ZnO nanoparticles capped with SiO2 are insensitive to Raman scattering. Maximum UV emission intensity was achieved with 353nm excitation wavelength compared to 320nm in ZnO as well as in SiO2 capped ZnO nanoparticles. Furthermore, there is an enhancement in the intensities of emission peaks related to oxygen vacancies and interstitials with SiO2 capping. The enhancement in the UV intensity is attributed to the surface passivation of ZnO nanoparticles and excitation processes in SiO2.

Influence of Mn doping on optical properties of ZnO nanoparticles synthesized by microwave irradiation

In this study, manganese [Mn]-doped zinc oxide [ZnO] nanoparticles are prepared by microwave irradiation method using zinc acetate and manganese acetate as precursors. The optical properties of the samples were investigated by UV-Vis–NIR, photoluminescence (PL) and Fourier transform infrared spectroscopy. Optical absorption analysis of the samples exhibits a red shift in the absorption band edge with increasing dopant concentration, and corresponding defects in ZnO are responsible for broad bands in the visible part of the photoluminescence (PL) spectrum. The room-temperature photoluminescence shows that the intensity of near band energy (NBE) emission depends strongly on the content of Mn in ZnO. We have also discussed in the paper the types of transitions and possible assignments of the PL bands. The chemical groups of the samples were confirmed by FTIR spectra.

ZnO nanoparticles as a luminescent down-shifting layer for photosensitive devices

The optical properties of ZnO nanoparticles (NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting (DS) efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device (photodiode), thereby increasing its efficiency. Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency (EQE) characteristics of the final devices were measured. Through comparison of the photodiode's EQE characteristics before and after the deposition of the ZnO NPs layer, it was concluded that for the photodiode with a low UV sensitivity (about 8%), the ZnO luminescent layer produces a down-shifting effect and the EQE in the UV and blue range improves by 16.6%, while for the photodiodes with a higher initial UV sensitivity (about 50%), the EQE in this range decreases with the ZnO layer thickness, due to the effects competing with DS, like the diminution of the ZnO layer transmittance and an increasing diffusion.