Mn-doped ZnO Samples Research Articles

Structural investigations of ZnO nanostructure

Undoped and Mn-doped ZnO samples with different percentages of Mn content (1, 5 and 10 at%) were synthesized by a dip coating sol–gel method. We have studied the structural, chemical and optical properties of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. We note that doping favors c-axis orientation along (002) planes. Up to 5 at% of Mn doping level, the c- axis lattice parameter shifts towards higher values with the increase of manganese content in the films. The expansion of the lattice constant of ZnO–Mn indicates that Mn is really doped into the ZnO. The SEM investigations of all samples revealed that the crystallites are of nanometer size. The sur- face quality of the ZnO–Mn film increases with Mn doping but no significant change of the grain size is observed from SEM images. The transmittance spectra show that the trans parency of all the samples is greater than 85 %. We note, also, that a small doping (1 %) lowered the refractive index while the thickness of the layers and the gap increase. However, on raising the proportion of Mn beyond 5 %, practically the same values of index and gap as pure ZnO are found.

Effect of microwave processing on Mn doped ZnO diluted magnetic semiconductor characteristics

5 and 7.5 at% Mn doped ZnO samples were prepared by microwave treatment following thermal curing. The XRD phase analysis reveals the Mn may be present in the unreacted Mn3O4 form or bonded with wurtzite ZnO forming substitutional solid solution (Zn0.99Mn0.01O and Zn0.95Mn0.05O) or spinel (ZnMn2O4). The Fourier transform infra-red (FTIR) band shift to higher wavenumber for the microwave treated samples appearing at 538 and 619 cm−1 indicates formation of ZnMn2O4 spinel structure. Identification of tiny particles in the wall of ZnO lamellae and decrease in Zn2p binding energy signifies vigorous chemical changes taken place on microwave treatment. The structural evolution was depicted by 3d modelling. Quantitative estimation of Mn in the samples was performed by microwave plasma atomic emission spectroscopy (MPAES) and the result matches with the calculated value. Raman spectroscopy shows clear peaks of ZnO, Mn3O4 and MnO2 compounds for all the samples prepared. Whereas, shoulder peak of ZnMn2O4 is observed for 7.5 at% Mn doped microwave pre-treated sample. The optical absorption spectra show major peak near to 360 nm signifying bandgap of ZnO in the visible range. The cation substitution in the host lattice by dopant creates oxygen vacancy (VO) in excess, responsible for increasing bound magnetic polaron, which is clearly evidenced by the presence of broad PL peak near to 535 nm and 548 nm for microwave treated samples. The microwave treatment assists the incorporation of Mn into ZnO lattice as evidenced by reduction of photoluminescence (PL) peak intensity. The magnetic hysteresis loop (B-H curve) of the samples clearly shows increase in saturation magnetisation by ~16.1 and ~24.7 % on microwave treatment of 5 and 7.5 at% Mn doped ZnO respectively.

Structural investigations of ZnO nanostructure

Undoped and Mn-doped ZnO samples with different percentages of Mn content (1, 5 and 10 at%) were synthesized by a dip coating sol–gel method. We have studied the structural, chemical and optical properties of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. We note that doping favors c-axis orientation along (002) planes. Up to 5 at% of Mn doping level, the c- axis lattice parameter shifts towards higher values with the increase of manganese content in the films. The expansion of the lattice constant of ZnO–Mn indicates that Mn is really doped into the ZnO. The SEM investigations of all samples revealed that the crystallites are of nanometer size. The sur- face quality of the ZnO–Mn film increases with Mn doping but no significant change of the grain size is observed from SEM images. The transmittance spectra show that the trans parency of all the samples is greater than 85 %. We note, also, that a small doping (1 %) lowered the refractive index while the thickness of the layers and the gap increase. However, on raising the proportion of Mn beyond 5 %, practically the same values of index and gap as pure ZnO are found.

An Eco-approach synthesis of undoped and Mn doped ZnO nano-photocatalyst for prompt decoloration of methylene blue dye

The present work reports the synthesis of nano pure ZnO and Mn-doped ZnO in an Eco-approach using seed extract of Cassia angustifolia for the removal of methylene blue. The aqueous Phyto-molecules helps in the reduction of metal precursor to nano-photocatalyst zinc oxide and the changes in absorbance was noted in UV-DRS for varying the parameters to get optimized. Different concentrated dopant material manganese sulphate (0.001 M, 0.003 M, and 0.005 M) was introduced on ZnO to enhance the optical absorption and to generate a new Fermi level. The XRD data exhibit the same wurtzite pattern for pure ZnO and Mn-doped ZnO samples. The slight shift in peak positions was noted in Mn-doped ZnO samples compared to pure ZnO without additional peaks determines the incorporation of Mn2+ ions in the lattice of ZnO NPs. The peak appearance in FT-IR denotes the bond formation among functional groups and metal oxide. The structural morphology of ZnO and Mn-doped ZnO was observed in Field Emission Scanning Electron microscopy. The elemental composition of Mn in ZnO was predicted in the EDAX. The High-resolution transmission electron microscopy (HRTEM) denotes the reduced size and altered the crystallinity of ZnO when Mn was introduced as the dopant in the green route. The effective photocatalytic activity of nano ZnO, Mn-doped ZnO achieves 84 and 95% decoloration of water pollutant Methylene blue (MB) dye with H2O2 and UV radiation by changing parameters like dye concentration, amount of catalyst, and pH. Results from this study suggest that the nano- Mn-doped ZnO photocatalyst can be advantageous for dye removal compared to pure ZnO. The green synthesized Mn-doped ZnO using Cassia angustifolia seed might considerable for treating dye contaminated water and supports in water remediation.

The Enhancement of Visible Photodetector Performance based on Mn doped ZnO Nanorods by Substrate Architecting

ZnO is one of the most fascinating and cost-effective materials for numerous applications, especially optoelectronics. To improve its properties and performance, many techniques have been developed, in which doping and surface engineering are usually of interest. Recently, combining techniques for further enhancement has got significant attention but not fully explored. In this study, a new combination to widen the light absorbance of ZnO nanorods (NRs) is introduced. This combination is based on (i) doping of Mn and (ii) substrate architecting. Patterned substrates are formed with master molds as digital video disc (DVD) and lotus leaf through polydimethylsiloxane (PDMS) molding. Mn-doped ZnO NRs were then hydrothermally grown on them at low temperatures. For investigate their morphology, structure and optical properties, scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet-visible spectroscopy (UV-Vis) were employed. The obtained results show that the Mn-doped ZnO samples with the patterned substrates own a remarkable increase (> 40%) in the visible light absorbance as compared to that with the flat substrate due to an increment of light scattering. Besides, a photodetector is fabricated based on the optimized patterning PDMS substrate with the active material of Mn doped ZnO NRs. The results show that the photocurrent of patterning device is 3.8 time higher than that of flat substrate. Overall, our approach for growing Mn-doped ZnO NRs on 3D patterned structures at low temperature is promising for optical applications such as flexible and stretchable optoelectronic devices.

Effect on the structural, optical and electrical properties of Mn-doped ZnO nanobelts synthesized via the hydrothermal method

The structural, optical and electrical properties of Mn-doped ZnO samples with different percentages of Mn synthesized using the hydrothermal method were studied. The structural properties were studied using X-ray diffraction (XRD). The XRD patterns analyzed via the Rietveld structure refinement method showed a typical wurtzite structure and no other impurity phases. The lattice parameters calculated for the Mn-doped ZnO from the XRD pattern were found to be slightly larger than those of the ZnO, which indicates the substitution of Mn into the ZnO lattice. Transmission electron microscopy (TEM) revealed the synthesis of ZnO nanobelts. The incorporation of Mn ions into the ZnO lattice was also confirmed by Fourier transform infrared spectroscopy and UV-spectroscopy. Results show that the increase in Mn concentration increases the gap energy. The study of the electrical properties shows two conduction phenomena. The variation of impedance, dielectric constant and dielectric loss tangent is also discussed.

Synthesis, Characterization, Photocatalytic and Sensing Properties of Mn-Doped ZnO Nanoparticles.

In this paper, Mn-doped ZnO nanoparticles (0 to 10 mol% Mn) were synthesized by facile low-temperature aqueous solution process and characterized by several techniques such as field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible and Raman-scattering spectroscopy. The SEM studies confirmed that the synthesized nanoparticles are grown in high density and increase in Mn content was found to have a significant effect on the morphologies of ZnO nanoparticles. The XPS studies established the structural variation of the samples with the change in dopant concentration and its oxidation state. XPS probe the existence of impurity phases in the as-synthesized samples. The results indicate further that hexagonal wurtzite structure of ZnO undergoes distortion with the increase in the dopant concentration. Also, with the increase in the dopant concentration, the blue-shift was observed in the UV-vis. spectra. Photocatalytic and chemicals sensing performances of these nanomaterials have been investigated by subjecting them to photocatalytic degradation of methyl orange (MO) under UV irradiation and for the detection of picric acid (PA) in aqueous solutions. Mn doped ZnO samples were found to be more efficient in catalyzing the MO degradation than pure ZnO. 5 mol% Mn doped ZnO nanomaterials were studied to use as fluorescence sensor for the detection of PA and the observed detection limit was found to be 2.5 μM.

One step synthesis of vertically grown Mn-doped ZnO nanorods for photocatalytic application

Pure and Mn-doped ZnO nanorods thin films on glass substrates were successfully synthesized by a one-step hydrothermal route. It was confirmed from XRD data that pure and Mn-doped ZnO samples show hexagonal (wurtzite) structures and the particle size was found to be in the range 27–31 nm. From XRD data it was clearly found that vertical growth along (002) plane after Mn-doping into ZnO lattice. Functional groups and chemical species were detected using FT-IR spectra. Diameter and length of ZnO nanorods were determined by TEM which is in the range 350 nm, 1–4 μm respectively. UV–Vis results exhibit red shift with increasing Mn concentration in ZnO lattice. The 5% Mn-doped ZnO sample exhibits higher fluorescence intensity in visible region with surface defects. The electrical resistance of pure and Mn-doped ZnO nanorods was demonstrated by I–V characteristics. It was explicitly outlined from Raman spectra E 2 high mode was shifted towards the higher wavenumber from 439 to 440 cm−1 owing to Mn doping in ZnO lattice. The average surface area, pore volume, and pore diameter were measured by using the BET isotherm. The photocatalytic activity of pure and Mn-doped ZnO was evaluated by the degradation of methylene blue (MB) under UV–Vis light irradiation which indicates that 5% Mn-doped ZnO nanorods have better photocatalytic activity than other samples.

Electron Paramagnetic Resonance Study of Al-incorporated ZnO:Mn Diluted Magnetic Semiconductors

We have employed electron paramagnetic resonance spectroscopy and magnetization measurements in order to study the effect of Al-incorporation on the magnetic interactions in ZnO:Mn diluted magnetic semiconductors. Al-doping is shown to decrease the antiferromagnetic correlation and to increase the ferromagnetic interaction, which is attributed to the hydrogen-mediated ferromagnetic Mn complexes in our Mn-doped ZnO samples.

Investigations on structural, optical and dielectric properties of Mn doped ZnO nanoparticles synthesized by co-precipitation method

Mn doped ZnO (ZnO:Mn) nanopowders with Mn:ZnO ratio from 0 to 3% were successfully synthesized by co-precipitation method. Their structural, optical, dielectric and conducting properties were investigated. All samples crystallize in the hexagonal wurtzite structure. The change in lattice parameters, bond length and preferential crystalline orientation for Mn doped ZnO samples indicates Mn2+ ions incorporation in ZnO lattice. Both micro-strain and dislocation density decrease due to doping whereas the average crystallite size increases suggesting the improvement of crystalline quality. The optical transmission in the visible region was improved as a result of doping. The observed decrease in ac conductivity (σac) with increasing Mn content is associated with the increase of defects amount. Cole-Cole plots of all samples were fitted to a circuit consisting in a parallel combination of a resistance and a constant phase element (CPE).

Structural, Optical, and Photocatalytic Activities of Ag-Doped and Mn-Doped ZnO Nanoparticles

We report the photocatalytic activities of ZnO, Ag-doped ZnO, and Mn-doped ZnO nanoparticles (NPs). Ag-doped and Mn-doped ZnO samples were synthesized using a coprecipitation method and calcined at 600°C. XRD, SEM, EDX, and UV-vis spectroscopy techniques were employed for characterization of the synthesized samples. The photocatalytic activities of the samples were evaluated by measuring the photocatalytic decolorization of methyl violet with sunlight being the source of energy. XRD patterns of the samples confirmed the wurtzite structure without change which was indicative of the absence of Mn- and Ag-related secondary phases for the doped ZnO. The UV-vis spectra indicated the band gap energy of ZnO, Ag-doped ZnO, and Mn-doped ZnO to be 2.98, 2.80, and 2.64 eV, respectively. Photocatalytic decolorization of methyl violet for the synthesized samples was found to be favorable at a pH of 9.0, catalyst dose of 1 g/L, and initial dye concentration of 4.5 × 10−4 g/L. Mn-doped ZnO and Ag-doped ZnO photocatalytic decolorization efficiency was significantly higher than undoped ZnO. Incorporation of Mn and Ag enhanced the visible-light photocatalytic activity of ZnO; this could be due to the ability of these metals to increase the surface defects of ZnO which in turn shift their optical absorption towards the visible region.

Investigations on the physical properties of Mn-modified ZnO samples prepared by sol–gel route

In this report, we have synthesized successfully sol–gel derived Zn1−xMnxO (x = 0.02, 0.04 and 0.06) nanoparticles to see the effect of Mn doping on structural, optical and magnetic properties of ZnO. The phase purity and structural analysis of all the samples have been made by the X-ray diffraction (XRD) technique with Rietveld refinement using the FullProf software. This study clearly revealed that Mn-doped ZnO nanoparticles exhibit hexagonal wurtzite structure with P63mc symmetry. Lattice parameters found to be increased with Mn doping, this shows that Mn2+ is successfully substituted on Zn2+ sites. The morphology of the nanoparticles was examined by FE-SEM. UV–Vis, FTIR, PL and VSM techniques have been used to see the optical and magnetic response of all the samples. UV–Vis spectra clearly indicate the sharp increment in the band gap energy with Mn doping up to 3.22 eV might be due to the Burstein–Moss effect. FT-IR studies have been utilized to find out the different phonon modes present in the prepared samples. Photoluminescence study revealed a blue shift of the near band emission (NBE) and an increase in the intrinsic defects (viz. VO and OZn) density with increasing Mn concentration up to a certain extent of doping (6%). Magnetic measurement of the Mn doped ZnO samples shows bound magnetic polaron (BMP) induced room temperature ferromagnetism (RTFM) behavior, however, there is suppression of ferromagnetic behavior due to the existence of antiferromagnetic ordering also present in the samples, supported by the Curie–Weiss Law.

Low temperature ammonia gas sensor based on Mn-doped ZnO nanoparticle decorated microspheres

Ammonia is a kind of colorless, pungent gas which is highly toxic to human health when inhaled above the moderate level. Detection of ammonia at low temperature is one of the most challenging tasks. In this work, low-temperature ammonia gas sensor using manganese-doped ZnO sphere as sensing material was successfully developed. Undoped ZnO nanorods and Mn-doped ZnO microsphere were successfully synthesized by the simple hydrothermal method and the structural, surface morphological, optical and gas sensing properties were investigated. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) revealed that the Mn-doped ZnO has sphere like-morphology decorated with nanoparticles. X-ray photoelectron spectroscopy (XPS) analysis indicated that the Mn-doped ZnO sample is in the Mn2+ valence state. Mn-doped ZnO sphere showed enhanced selectivity towards ammonia compared to other gases at low temperature. Mn-doped ZnO (8 wt%) showed the higher response of 28.58. The response and the recovery time of the fabricated sensor towards 20 ppm ammonia are 4 and 10 s (s).

Sonochemical synthesis, characterization, and magnetic properties of Mn-doped ZnO nanostructures

Mn-doped ZnO samples, Zn1–x Mn x O (x = 0, 0.01, 0.03 and 0.05; mole fraction), were successfully synthesized by sonochemical method. The undoped and Mn-doped ZnO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. XRD patterns of all products are identified to hexagonal wurtzite ZnO structure and their three main peaks shift toward lower diffraction angles due to the incorporation of Mn2+ into ZnO crystal lattice. The morphologies of Zn1–x Mn x O (x = 0, 0.01, 0.03 and 0.05) were examined by SEM and TEM. The undoped ZnO sample shows large-scale uniform microflowers which are broken into nanorods and nanoparticles by Mn dopant. Their magnetic properties were investigated by a vibrating sample magnetometer at room temperature. The magnetization-applied field behavior of undoped ZnO defines its weak ferromagnetic behavior. The 3 mol% Mn-doped ZnO shows the highest saturation magnetization of 51.73 × 10−3 mA·m2·g−1, and the 5 mol% Mn-doped ZnO has suppressed ferromagnetic property due to the formation of Mn clusters inside.

Structural, optical, and magnetic properties of Mn-doped ZnO samples

This study investigated the microstructure, optical, and magnetic properties of Zn1−xMnxO powder samples with x=0.02–0.08 synthesized by a solid-state reaction route. X-ray diffraction revealed that the cell parameters, a and c, increased with the increase in Mn content, which indicated that Mn ions substitute into the lattice of ZnO. UV–vis measurements revealed that the band gap decreased due to the incorporation of Mn. Photoluminescence studies confirmed the formation of oxygen vacancies (VO) in all samples. Magnetic measurements revealed that all samples exhibited room temperature ferromagnetism (RTFM), and the average magnetic moment per Mn atom decreased as the Mn content, and annealing temperature (TA) increased. However, our results indicate that the ferromagnetic property is an intrinsic property of the ZnO:Mn samples due to VO and/or defects, and it does not originate from any secondary magnetic phase.

Influence of different precursors and Mn doping concentrations on the structural, optical properties and photocatalytic activity of single-crystal manganese-doped ZnO

Mn-doped ZnO single-crystal micronuts were synthesized via hydrothermal method in an hexamethylenetetramine aqueous solution. These micronuts are of wurtzite crystal structure. The effects of Mn doping amount and precursor concentration on the structural, optical properties and photocatalytic activity have been investigated. The synthesized Mn-doped ZnO was characterized by X-ray powder diffraction, field emission scanning electron microscopy (FESEM), UV–Vis absorption and photoluminescence spectroscopy. The structural analyses based on X-ray diffraction revealed the absence of Mn-related secondary phases. According to FESEM results, the length of ZnO micronuts was in the range of 5–8 μm. The band gap energy increased on increasing Mn doping concentration. The photocatalytic activity was studied by degradation of methyl orange aqueous solution, which showed that the Mn-doped ZnO micronuts prepared in precursor concentration of 0.1 M and 4% Mn doping had the highest photocatalytic activity. The effects of crystal defect and band gap energy on photocatalytic activity of Mn-doped ZnO samples were studied in different precursors and Mn doping amounts.

Effect of pressure and doping on lattice structure of zinc oxide

The semiconductor ZnO belongs to the IIb-VI binary compound. It has a high exciton binding energy of 60meV. The bonding in these materials is covalent with some ionic character. Induced changes on the physical properties of Mn doped ZnO samples due to different dopant concentrations and pressure were evaluated. The results obtained showed higher solubility limit for Mn doped ZnO due to pressure. The trend of XRD results for higher Mn concentration (9at%) as pressure increases, was towards doping improvement. The XRD, SEM and UV–vis study of the samples also revealed that there were variations in the lattice parameters, nanoparticle size and bandgap energy of the doped and pressurized doped samples. Further, the directions of variation of bandgap energy values and calculated particle size, as well as SEM values of the doped samples due to pressure variation were found to be the same i.e. all of them together either increase or decrease as pressure varies. However, these variations were found to be opposite to that of lattice constants (all a and most c values) variation for both Mn dopant concentrations (3at% and 9at%). These physical variations of unpressurized doped samples can be attributed to the change in the polar bonding of the elemental constitutions in the lattice. While for the pressurized doped samples, the variations attributed to repulsion of lone pairs as well as change in the electronegativity of the system.

Magnetic properties of Mn doped ZnO: the role of synthesis route

Structural, morphological, optical, magnetic properties and chemical state of the constituent elements of 2 at% Mn doped ZnO samples synthesized by solid state reaction and sol–gel techniques were analyzed. The role of chemical or valency state in tuning the magnetic properties has been investigated. X-ray diffractometer, scanning electron microscope, UV–visible and X-ray photoelectron spectroscopes and superconducting quantum interference device vibrating sample magnetometer (SQUID VSM) were employed for investigation. Mn incorporation in ZnO lattice has been shown by single phase wurtzite structured samples. The presence of defects particularly zinc vacancy (VZn) has been evidenced from band tailing. Solid state reaction technique derived sample exhibit strong intrinsic ferromagnetism but sol–gel sample didn’t show strong ferromagnetic (FM) ordering. Antiferromagnetic (AFM) interaction is present in both samples. The chemical state of Mn is +2 for solid state reaction technique derived sample whereas for sol–gel technique derived sample it is a mixed chemical state (exists in both +2 and +3 states). Finally, the peculiar magnetic behavior has been interpreted from the interaction between VZn and d-electrons of Mn2+ and Mn3+ states.

Synthesis, Structure, and Room Temperature Ferromagnetism of Mn and/or Co Doped ZnO Nanocrystalline

Nanostructures of pure and (Mn, Co) doped and codoped ZnO have been prepared by chemical coprecipitation method. The crystal structure, morphology, and ferromagnetism of the prepared samples were investigated by using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy, and vibrating sample magnetometer. The X-ray diffraction results demonstrated that all samples having a single phase with hexagonal wurtzite structure of ZnO. FTIR spectra showed the characteristic absorption bands of ZnO in different samples. The TEM images revealed that pure and Co-doped ZnO samples having uniform nanoparticle shapes with an average particle size of 18–20 nm. whereas, Mn-doped ZnO sample has nanorod structure and (Mn, Co) codoped ZnO sample has a mixture of nanoparticle and nanorod structures. The magnetic hysteresis loop of pure ZnO nanoparticles at room temperature revealed a saturation magnetization of 0.22 emu/g and a coercivity of 91.6 Oe. Alternatively, the hysteresis loops of Zn 0.99Mn 0.01O, Zn 0.99Co 0.01O, and Zn 0.98Mn 0.01Co 0.01O samples illustrated more pronounced magnetic properties with saturation magnetization of 0.788, 0514, and 0.918 emu/g and coercivity of 141.9, 452.5, and 185.6 Oe, respectively. The effects of doping ions on the structure and ferromagnetism of the investigated samples are discussed.

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing**Project supported by the National Basic Research Program of China (Grant No. 2013CB934001) and the National Natural Science Foundation of China (Grant Nos. 51072012 and 51272015).

Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H2/Ar atmosphere with different H2/Ar ratios. It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO. Mn ions initially enter into interstitial sites and a Mn3+O6 octahedral coordination is produced in the prepared Mn-doped ZnO sample, in which the nearest neighbor Mn3+ and O2 ions could form a Mn3+–O2−–Mn3+ complex. After H2 annealing, interstitial Mn ions can substitute for Zn to generate the Mn2+O4 tetrahedral coordination in the nanocrystals, in which neighboring Mn2+ ions and H atoms could form a Mn2+–O2−–Mn2+ complex and Mn–H–Mn bridge structure. The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn3+–O2−–Mn3+ complex, while the annealed samples exhibit their ferromagnetism, which originates from the Mn–H–Mn bridge structure and the Mn–Mn exchange interaction in the Mn2+–O2−–Mn2+ complex.