Tailoring the Dopant Distribution in ZnO:Mn Nanocrystals (original) (raw)
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Synthesis and characterization of Mn-doped ZnO nanocrystals
(2004) Journal of Physical Chemistry B, 108 (20), pp. 6303-6310.
We report the synthesis and characterization of several sizes of Mn-doped ZnO nanocrystals, both in the free-standing and the capped particle forms. The sizes of these nanocrystals could be controlled by capping them with polyvinylpyrollidone under different synthesis conditions and were estimated by X-ray diffraction and transmission electron microscopy. The absorption properties of PVP-capped Mn-doped ZnO exhibit an interesting variation of the band gap with the concentration of Mn. Fluorescence emission, electron paramagnetic resonance, and X-ray absorption spectroscopy provide evidence for the presence of Mn in the interior as well as on the surface of the nanocrystals.
Synthesis of Mn doped ZnO nanocrystals by solvothermal route and its characterization
Materials Chemistry and Physics, 2011
Undoped and Manganese doped Zinc Oxide were prepared by solvothermal technique. The structural analysis was carried out using X-ray diffraction. It showed that the undoped Zinc Oxide and Manganese doped Zinc Oxide nanocrystals to exhibit hexagonal wurtzite structure. Grain sizes were estimated from Atomic Force Microscopy and Transmission Electron Microscopy images. The surface morphological studies from Scanning Electron Microscope, Transmission Electron Microscope and Atomic Force Microscope depicted spherical particles with formation of clusters. The magnetic behavior studied by Vibrating Sample Magnetometer indicated paramagnetic behaviour. Hyperfine splitting is observed using Electron Spin Resonance studies.
Role of spectator ions in influencing the properties of dopant-free ZnO nanocrystals
Towards fundamental studies and potential applications, achieving precise control over the generation of defects in pure ZnO nanocrystals has been always intriguing. Herein, we explored the role of spectator ions (Co 2+ and Ni 2+ ) in influencing the functional properties of ZnO nanocrystals. The crystalline quality, phase purity, and composition of as-prepared samples were thoroughly established by powder X-ray diffraction, electron microscopy (TEM and STEM), and by Raman and X-ray photoelectron spectroscopies (XPS). Despite the presence of Co 2+ and Ni 2+ ions in the reaction mixture, STEM-energy dispersive spectroscopy (EDS), XPS analysis, and inductively-coupled plasma mass spectrometry (ICP-MS) revealed that the ZnO nanocrystals formed are dopant-free. Even so, their luminescence and magnetic properties were substantially different from those of pure ZnO nanocrystals synthesized using a similar methodology. We attribute the origin of these properties to the defects associated with ZnO nanocrystals generated under different but optimized conditions.
Structural and magnetic properties of Mn-doped ZnO nanocrystals
Abstract: Mn-doped ZnO nanocrystals were successfully prepared using a novel sol–gel method followed by drying in autoclave under supercritical conditions. The estimated crystallite size is in the range of 30–50 nm, in agreement with TEM analysis. Rietveld refinements confirm the formation of pure Mn-doped ZnO for lower Mn concentration. i.e. less than 5%. The lattice parameters increase with increasing Mn content according to Vegard's law due to the larger ionic radius of Mn2+ compared to that of Zn2+. Magnetic analysis reveals that increasing the doping level of Mn above 2% is not helping the long range ferromagnetic order in the sample but only enhancing the paramagnetic component. The paramagnetic susceptibility is found to increase linearly with increasing Mn concentration which suggests the formation of uncoupled magnetic moment. The estimated values for the magnetic moment per Mn atom are found to be in the range of 2–3.5 µB/Mn. Ab-initio calculations also have been performed which showed that doping diamagnetic bulk ZnO with Mn induces ferromagnetic at room temperature, the total magnetic momentum increases with increasing Mn content whereas the magnetic moment of Mn is predicted to be in the range of 3–3.5 μB/Mn atom which is consistent with the values obtained from magnetic measurements.
Magnetism in Mn-doped ZnO nanoparticles prepared by a co-precipitation method
Nanotechnology, 2006
We report the synthesis of nominal 2 and 5 at.% Mn-doped ZnO nanocrystalline particles by a co-precipitation method. Rietveld refinement of x-ray diffraction data revealed that Mn-doped ZnO crystallizes in the monophasic wurtzite structure and the unit cell volume increases with increasing Mn concentration. DC magnetization measurements showed ferromagnetic ordering above room temperature with H c ∼ 150 Oe for nominal 2 at.% Mn-doped ZnO nanoparticles annealed at 675 K. A distinct ferromagnetic resonance (FMR) signal was observed in the EPR spectra of the 2 at.% Mn-doped ZnO nanoparticles annealed at 675 K. EPR measurements were used to estimate the number of spins participating in ferromagnetic ordering. Of the total Mn present in the 2 at.% Mn ZnO lattice, 25% of the Mn 2+ ions were responsible for ferromagnetic ordering, whereas nearly 5% of the Mn 2+ ions remained uncoupled (isolated spins). A well resolved EPR spectrum of 5% Mn-doped ZnO samples annealed at 875-1275 K (g = 2.007, A = 80 G, D = 210 G and E = 15 G) confirmed that Mn was substitutionally incorporated into the ZnO lattice as Mn 2+. On increasing the temperature of annealing beyond 1075 K an impurity phase emerges in both the 2 and 5 at.% Mn-doped ZnO samples, which has been identified as a variant of (Zn 1−X Mn(II) X)Mn(III) 2 O 4 with T c ∼ 15 K. Our results indicate that the observed room temperature ferromagnetism in Mn-doped ZnO can be attributed to the substitutional incorporation of Mn at Zn-sites rather than due to the formation of any metastable secondary phases.
Materials Sciences and Applications, 2012
Mn-doped nanocrystalline ZnO particles have been successfully synthesized at low temperature (80˚C) by the coprecipitation method using zinc sulfatehepta hydrate and NaOH. The structural and magnetic properties have been characterized using X-ray diffraction (XRD), Energy dispersive x-ray, vibrating sample magnetometer and electron spin resonance. XRD measurements revealed that the sample posses hexagonal wurzite structure. From the Rietveld refined XRD spectra, the lattice parameters, average crystallite size and microstrain values was obtained. In this range of doping concentrations all samples show an expansion of the lattice parameters relative to the bulk samples. From magnetic measurements we observed the presence of room temperature ferromagnetic order in our Mn-doped ZnO samples.
Preparation and Characterization of Mn Doped Zno Nanoparticles
The Mn doped ZnO thin films were deposited on glass substrates by dip coating method. Characterization techniques of XRD, SEM, UV-visible spectra measurements and VSM were performed to investigate the structural, optical and magnetic properties. ZnO thin films were prepared with three different growth time of 3, 4 and 5 hours at 100°C. Manganese (Mn) was doped with the prepared ZnO thin film in three different growth layer concentrations (0.01,0.02 and 0.03mol). In Mn doped ZnO, as the concentration of manganese increases, the ferromagnetic behavior decreases.
Synthesis and characterization of Mn-doped ZnO column arrays
Applied Surface Science, 2010
In the present work undoped and Mn doped ZnO nanoparticles (ZnO:Mn), diluted magnetic semiconductors, were successfully synthesized by sol-gel method at room temperature. The morphology of ZnO nanoparticles constituted by flower-like structures with hexagonal morphologies that changed significantly after the incorporation of Mn. Rietveld refinements results showed that Mn ions are successfully doped into ZnO matrix without altering its wurtzite phase. Meanwhile, Raman spectroscopy analyses confirm the wurtzite structure of undoped ZnO and ZnO:Mn nanoparticles. The lattice parameters increase with increasing Mn content due to the large ionic radius of Mn 2+ compared to that of Zn 2+. Electron spin resonance measurements were performed to gain information about oxidation state and site occupancy of the magnetic Mn ions in the ZnO lattice. Moreover, UV-vis absorption spectra have been utilized to calculate the optical band gap of the undoped ZnO and ZnO:Mn nanoparticles before and after different γirradiation doses. The band gap of ZnO:Mn (2%) is 2.62 eV which is noticeably smaller than the 3.26 eV of undoped ZnO. The thermal decomposition properties of the prepared nanoparticle samples were also studied using simultaneous Thermogravimetric analysis in temperature range from 30 up to 500 o C.
Physica E: Low-dimensional Systems and Nanostructures, 2014
Mn-doped ZnO nanoparticles (NPs) of different compositions have been synthesized by chemical co-precipitation method. The products were sintered at 800 � C. X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), photoluminescence spectroscopy (PL) and UV-Vis spectroscopy have been used to characterize the samples. The XRD studies revealed that Mn-doped ZnO has Wurtzite structure. The SEM images show different morphology for different compositions. Violet, blue and green emissions have been observed for Mn-doped ZnO NPs as evidenced from the photoluminescence spectra. The optical energy band gap of the NPs has no correlation with Mn concentration.
Nanoparticles of ZnO Doped With Mn: Structural and Morphological Characteristics
Materials Research
In this study, the effects of dopant concentrations on the structural and morphological characteristics of Zn 1-x Mn x O powders (x= 0.025, 0.05, 0.075, and 0.1 mole) synthesized by the Pechini method has been investigated. The powder was characterized by X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET) specific surface, energy dispersive X-ray (EDX), scanning electron microscopy (SEM) and Spectroscopy with Fourier transform (FTIR). An XRD analysis of the powder showed the formation of ZnO phase with a typical single phase wurtzite structure. The EDX analysis revealed Mn incorporated in the ZnO structure. The particle size calculated by BET ranged from 24 to 63 nm, confirming the nanometric size of the powder particles. The SEM analysis revealed irregular shaped particle agglomerates and the presence of nanosheets. From FTIR it was confirmed the wurtzite structure in ZnO and ZnO nanoparticles doped with Mn.