Mn Doping Concentration Research Articles

Color-tunable optical properties of cadmium-free transition metal ions doped InP/ZnS quantum dots

Cadmium-free InP quantum dots (QDs) exhibit many unique optical properties, and show great promise as light emitting materials. In this work, a series of high-efficient and color-tunable transition metal ions (Cu, Mn) single- and co-doped InP/ZnS QDs with the average size of 3.2–3.7 nm, were firstly prepared via a nucleation-doping method in an organic synthetic route. These three kinds of doped InP/ZnS QDs all exhibit dual emission with one peak position around green region owing to the intrinsic state and the other peak position around orange-red region resulted from dopant emission, the relative intensity of which can be effectively tuned by varying Cu or Mn dopant concentration. The dopant emission of Cu doped InP/ZnS QDs from 572 to 696 nm can be realized via increasing Cu dopant concertration from 0.25% to 10%, while the peak position of dopant emission in Mn doped InP/ZnS QDs system remains unaltered as Mn dopant concentration increasing. Besides, the interaction mechanism of Cu and Mn dopant in co-doped InP/ZnS QDs system was investigated with steady-state and time-resolved PL spectroscopy measurements. The results reveal that the dopant emission is dominated by Cu doping rather than Mn doping. These unique results in doped InP/ZnS QDs would help to understand the fundamental aspects of doping, and the dual-emissive and color-tunable optical properties of single-phase doped InP/ZnS QDs will endow them with great promise as color-converting materials for use in solid-state lighting.

Enhanced optoelectrical properties of Mn-doped ZnS films deposited by spray pyrolysis for ultraviolet detection applications

In the present study, chalcogenide manganese-doped zinc sulfide (Mn-doped ZnS) films were deposited by spray pyrolysis method at various concentration of Mn2+ ions (0 ≤ Mn2+ ≤ 15 mol%) and the effect of Mn-doping concentration on the photodetection characteristics of the films was investigated. The phase structure, chemical composition and surface morphology of the films were characterized by grazing incidence X-ray diffraction, energy dispersive spectroscopy, and field emission scanning electron microscopy. The results confirmed the stable zinc blende phase, nanocrystalline structure and the nearly stoichiometric ratio of elements, as well as uniform and well adherent of the films to the substrates. The Mn2+ concentration-dependent optical and electrical properties of the films were investigated using ultraviolet-visible spectroscopy, photoluminescence, and current-voltage measurements. The photoluminescence spectra exhibited two emission peaks located at ultraviolet (UV) and orange regions. The optical density, optical band gap energy, and Urbach energy were also evaluated. By increasing Mn2+ content, a slight decrease in the optical band gap energy was observed, while the Urbach energy broadened, gradually. Therefore, a linear relationship between the band gap energy and Urbach energy was found. Moreover, the relevance of the steepness parameter and electron-phonon interaction was studied. The optoelectrical analysis in the dark and under light irradiation with different wavelengths revealed the visible-blind nature of the samples. The electrical characteristics of the fabricated UV detectors featured tremendous photocurrent gain and photo-response switching behavior to UV-A irradiation.

Mn-doping composition dependence of the structures, electrical and magnetic properties, and domain structure/switching of Aurivillius Bi5Ti3FeO15 films

Mn-doped Bi5Ti3FeO15 (BTFO) films were prepared by a chemical solution deposition route. The effect of a series of different Mn-doping concentrations from 0.05 to 0.4 on structures, electrical and magnetic properties, and domain structure/switching was systematically studied. Mn-doping into BTFO can avail the grain growth. Ferroelectric and dielectric properties are improved through Mn-doping, and the optimized Mn-doping content is 0.25 with remnant polarization of 17.2 μC/cm2 and permittivity of 371.2 at 10 kHz. Moreover, similar evolution of the permittivity and loss tangent with frequency to that of parent BTFO films appears in the BTFMO films when Mn-doping content is below 0.25, while obvious dispersion phenomena is demonstrated with further increasing Mn-doping content. A 180° domain structure and local ferroelectric switching are observed in all these Mn-doped BTFO thin films, and the piezo-displacement can reach 416 p.m. in 0.15 Mn-doped BTFO film. Finally, ferromagnetic properties appear in all these Mn-doped BTFO thin films. The coercive field shows weak temperature independence on Mn-doping contents, while the remnant magnetization is raised by Mn-doping.

XANES, EXAFS, EPR, and First-Principles Modeling on Electronic Structure and Ferromagnetism in Mn Doped SnO2 Quantum Dots

The effect of Mn dopant on the electronic structure and magnetic properties of SnO2 quantum dots was investigated using X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), electron paramagnetic resonance, and first-principles modeling. The results demonstrated that dilute Mn atoms substituted for Sn generates numerous oxygen vacancies. Interestingly, lower Mn doping concentration (2%) favored the formation of Mn3+ structures and increase of Mn doping to higher concentration (10% Mn) led to predominance of Mn3+ with a small fraction of Mn2+ configuration. The slight increase in bond length observed for 10% Mn doped SnO2 QDs in EXAFS also corroborates with the XANES results where the absorption edge was shifted to lower energy, giving an indication of a very small presence of Mn in the +2 oxidation state. Electron paramagnetic resonance studies revealed the exchange coupled Mn interactions and also changes in distribution of local magnetic configurations with the ...

Crystal Structure and Multiferroic Behaviors of Solid Solution (1-y)BiFe<sub>(1-x)</sub>Mn<sub>x</sub>O<sub>3</sub>-yBaTiO<sub>3</sub>

It is expected that BiFeO3-based materials will have both ferroelectricity and ferromagnetism. (1-y)BiFe(1-x)MnxO3-yBaTiO3 system was prepared using solid state reaction method. The goal of this study is to uncover the impacts of Mn doping and BaTiO3 content on the crystal structure, magnetism and ferroelectric properties. By forming a solid solution with BaTiO3, stable perovskite BiFeO3 was achieved. The rhombohedrally distorted (1-y)BiFe(1-x)MnxO3-yBaTiO3 showed weak ferromagnetism due to the composition of BaTiO3 and the doping of Mn ion. 0.8BiFe0.9Mn0.1O3-0.2BaTiO3 and 0.7BiFe0.9Mn0.1O3-0.3BaTiO3 ceramics exhibited typical P-E hysteresis loops.

Impact of Mn-dopant concentration in observing narrowing of band-gap, urbach tail and paramagnetism in anatase TiO2 nanocrystals

In addition to the numerous applications of Mn-doped TiO2, it could be a potential candidate as a dilute magnetic semiconductor.

Tunable optical, electronic and magnetic properties of semiconductor nanoparticles induced by magnetic and nonmagnetic dopants: A comparative experimental and theoretical study

While combining semiconductor and magnetic properties at the nanoscale provides dilute magnetic semiconductor (DMS) nanomaterials with a wide range of applications in next-generation electronic devices, tuning DMS properties still presents a challenge. Here, the synthesis of pure ZnO and transition metal (TM)-doped ZnO nanoparticles (NPs) with different magnetic (Fe and Co) and nonmagnetic (Mn) dopant concentrations (ranging from 2% to 10%) is reported using a co-precipitation method. Introducing the TM-dopants into ZnO NPs with 35 nm wurtzite structure causes crystallite and mean NP sizes to decrease, as characterized by X-ray diffraction and field-emission scanning electron microscopic analyses. Room-temperature magnetic measurements indicate coexistence of paramagnetic and ferromagnetic phases with tunability in the resulting TM-doped NPs. The maximum ferromagnetic coercivity and saturation magnetization are found to be 89 Oe and 0.074 emu/g for 10% Fe-doped ZnO NPs. UV–visible spectra showed a blue shift with increasing the dopant concentration, being in agreement with increasing trend in band gap energy calculated from band structure and density of state of TM-doped ZnO nanocrystal systems.

Mn valence state mediated room temperature ferromagnetism in nonpolar Mn doped GaN

In this work, we demonstrate room temperature ferromagnetism in nonpolar, m-plane manganese doped gallium nitride (m-GaN:Mn) epitaxial thin films synthesized using plasma-assisted molecular beam epitaxy on nonpolar, m-plane sapphire (Al2O3) substrates. We observed that Mn doping concentration plays a key role in stabilizing the valence state of Mn ions thereby influencing the magnetic and transport properties. Chemical characterization by X-ray photoelectron spectroscopy, X-ray absorption near edge spectra, and energy dispersive X-ray spectroscopy affirm homogeneous valence state Mn+3 in lightly doped samples, while higher doping levels cause a heterogeneous Mn+0 and Mn+2 mixed valence states. Magnetic measurements indicate that films with low doping levels show the signature of room temperature ferromagnetism, while films with higher doping show antiferromagnetic/spin glass behavior besides the indication of MnGa alloys. Temperature dependent resistivity measurements show that both the samples are semiconducting with deep level defect states. Our findings suggest the possibility of incorporating spin functionality in non-polar optoelectronic devices.

Endogenous Dynamic Nuclear Polarization for Natural Abundance 17O and Lithium NMR in the Bulk of Inorganic Solids.

In recent years magic angle spinning-dynamic nuclear polarization (MAS-DNP) has developed as an excellent approach for boosting the sensitivity of solid-state NMR (ssNMR) spectroscopy, thereby enabling the characterization of challenging systems in biology and chemistry. Most commonly, MAS-DNP is based on the use of nitroxide biradicals as polarizing agents. In materials science, since the use of nitroxides often limits the signal enhancement to the materials' surface and subsurface layers, there is need for hyperpolarization approaches which will provide sensitivity in the bulk of micron sized particles. Recently, an alternative in the form of paramagnetic metal ions has emerged. Here we demonstrate the remarkable efficacy of Mn(II) dopants, used as endogenous polarization agents for MAS-DNP, in enabling the detection of 17O at a natural abundance of only 0.038%. Distinct oxygen sites are identified in the bulk of micron-sized crystals, including battery anode materials Li4Ti5O12 (LTO) and Li2ZnTi3O8, as well as the phosphor materials NaCaPO4 and MgAl2O4, all doped with Mn(II) ions. Density functional theory calculations are used to assign the resonances to specific oxygen environments in these phases. Depending on the Mn(II) dopant concentration, we obtain significant signal enhancement factors, 142 and 24, for 6Li and 7Li nuclei in LTO, respectively. We furthermore follow the changes in the 6,7Li LTO resonances and determine their enhancement factors as a function of Mn(II) concentration. The results presented show that MAS-DNP from paramagnetic metal ion dopants provides an efficient approach for probing informative nuclei such as 17O, despite their low gyromagnetic ratio and negligible abundance, without isotope enrichment.

Effect of Mn Doping on Multilayer PbS Quantum Dots Sensitized Solar Cell

The effect of Mn-ion doping on the device performance of multilayer PbS quantum dot (QD) sensitized solar cells is investigated. Undoped as well as the doped PbS QDs, with different doping concentration, are synthesized using simple chemical methods on poly-vinyl alcohol matrix. QDs are characterized using ultraviolet visible spectroscopy, x-ray diffraction analysis, high-resolution transmission electron microscopy, energy dispersive x-ray, and photoluminescence spectroscopy. The QDs were introduced as sensitizer in ZnO-based solar cells in single as well as multiple layers. The current density vs. voltage characteristics are obtained for different Mn doping concentrations as well as for multiple numbers of QD layers, under artificial illumination. Enhanced photo-conversion efficiency was observed in multiple layered doped PbS QDs sensitized solar cell compared to undoped QDs sensitized solar cell.

Thermal plasma-inspired synthesis of ZnO1−XMnx dilute magnetic semiconductors for enhanced visible light photocatalysis

We report a simple, time-consuming and scalable synthesis of ZnO1−xMnx nanocrystals (Mn-ZnO NCs) using a thermal plasma chemical method. The diffusion of the Mn2+ into the host ZnO lattice causes pronounced change in the structure, morphology, spectroscopy and magnetic properties of ZnO. The Mn-doping in ZnO lattice introduces defects by changing the lattice constant values, vibration mode shift at a particular position, decrease in the band gap energy from 3.23 to 3.08 eV, with more than 90% photoluminescence quenching proficiency which has not only makes it as the efficient photocatalyst in methylene blue dye degradation but also confirms change in the shape and the magnitude of the electron spin resonance spectra, suggesting revelation of the dilute magnetic semiconducting properties in ZnO. The onset of the sharp resonance peak at 0.6% Mn-doping level followed a sharp fall in the intensity when Mn-concentration ≥0.8% has thoroughly been investigated and explored. Moreover, a tunable optical absorption change of Mn-ZnO NCs at various Mn-contents corroborats a proficient visible light photocatalytic performance which has been optimized, exquisitely, on controlling the shape and Mn-doping concentration level. Our results offer a basic understanding of synergetic effect taking place in enhancing the photocatalytic performance, which otherwise could cause by a defect-mediated ferromagnetic coupling and optimal Mn-doping concentration.

Tailoring structural, surface, optical, and dielectric properties of CuO nanosheets for applications in high-frequency devices

In the present study, a simple chemical method for the preparation of CuO nanostructures by varying Mn-doping concentration has been reported. It also provides an extensive investigation of structural, surface, and optical and dielectric properties of Mn-doped CuO nanostructures. Single-phase monoclinic crystal structure of CuO formation for all samples with average crystallite size of 20–24 nm has been observed from X-ray diffraction (XRD) results. A morphological transformation from nanosheets to spherical nanoparticles have been found with Mn doping as depicted by scanning electron microscopy (SEM) images. The successful doping of Mn ions into CuO crystal has also been supported by Fourier transform infrared spectroscopy (FTIR) results. The widening of the optical bandgap of CuO nanostructures has been observed with increasing Mn doping which may be attributed to band-filling effects and exchange interactions. Interestingly, the values of dielectric constant of CuO nanostructures have been observed to increase systematically with Mn doping making it potential material for high-frequency device applications.

Magnetic enhancement and magnetic signal tunability of (Mn, Co) co-doped SnO2 dilute magnetic semiconductor nanoparticles

Co and Mn-Co co-doped SnO2 nanoparticles have been successfully synthesized using a simple technique called as citrate precursor assisted co-precipitation (CPACP). Structural and compositional analyses by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Energy Dispersive X-Ray Fluorescence Spectrometer (EDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed that Co and Mn ions were incorporated into the SnO2 host lattice without changing the inherent rutile structure. The average crystallite size of the prepared samples were estimated to be in the range of 8–12 nm. In a single Co2+-doped SnO2 sample, the magnetization was observed to increase as the Co2+ ions concentration increased. The transition metal Mn can adjust the magnetic signal of the Co2+-doped SnO2 sample, which is subject to the concentration of Mn dopant. Adding a proper amount of Mn to the Co2+-doped SnO2 sample enhanced the magnetization. As the Mn2+ ions concentration increases, the magnetic properties of the (Mn, Co) co-doped SnO2 nanoparticles gradually shift from ferromagnetic behavior to superparamagnetism. However, the sample Sn0.83Mn0.12Co0.05O2 exhibits diamagnetic behavior when the concentration of Mn2+ ions is doped excessively.

Effect of Mn doping on mechanical properties and electronic structure of WCoB ternary boride by first-principles calculations**Project supported by the National Key Research and Development Program, China (Grant No. 2016YFB0700503), the National High Technology Research and Development Program of China (Grant No. 2015AA034201), the Beijing Science and Technology Plan, China (Grant No. D161100002416001), the National Natural Science Foundation of China

The first-principles calculations are performed to investigate the structural, mechanical property, hardness, and electronic structure of WCoB with 0, 8.33, 16.67, 25, and 33.33 at.% Mn doping content and W2CoB2 with 0, 10, and 20 at.% Mn doping content. The cohesive energy and formation energy indicate that all the structures can retain good structural stability. According to the calculated elastic constants, Mn is responsible for the increase of ductility and Poissonʼs ratio and the decrease of Youngʼs modulus, shear modulus, and bulk modulus. By using the population analysis and mechanical properties, the hardness is characterized through using the five hardness models and is found to decrease with the Mn doping content increasing. The calculated electronic structure indicates that the formation of a B–Mn covalent bond and a W–Mn metallic bond contribute to the decreasing of the mechanical properties.

Microstructural, optical, magnetic and photocatalytic properties of Mn doped ZnO nanocrystals of different sizes

The present work explores the differences in the various properties of Mn doped ZnO nanocrystals when the sizes of the doped nanocrystals are significantly different. Mn doped ZnO nanocrystals of sizes ≈20 nm and ≈5 nm were synthesized by the chemical co-precipitation method. The targeted Mn doping concentrations were 2%, 6% and 10% (atomic), however, the observed doping concentrations were low (≈0.5%, ≈1% and ≈2%). The microstructural, morphological, optical and magnetic properties as well as the photocatalytic activities of the nanocrystals were investigated. The variations of the lattice strain and lattice volume with increasing Mn concentrations were found to be correlated. The un-doped and Mn doped ZnO nanocrystals were found to be ferromagnetic at room temperature. Variation of band gap with increasing Mn concentrations was observed. Significant/insignificant quenching of the photoluminescence emissions was observed for sizes ≈20 nm/≈ 5 nm after doping. The saturation magnetization was found to depend on the Mn concentrations as well as on the nanocrystal sizes. Agglomerated Mn2+ resulted in a decrease in saturation magnetization of the ≈2% Mn doped nanocrystals of sizes ≈5 nm. Correlation between the photoluminescence properties and photocatalytic activities was observed.

Tailoring the visible emissions in ZnS:Mn films for white light generation

Abstract This paper reports the effect of manganese incorporation on the structural, optical and luminescence properties of the as-deposited ZnS films prepared by RF magnetron sputtering process. Mn act as a nucleation centre for the growth of highly crystalline defect free ZnS films with mixed cubic and hexagonal phases. The +2 valence state of Mn ions in ZnS lattice is confirmed by the XPS analysis. An absorption band due to d-d transition of Mn2+ ions is visible in the absorption spectra of ZnS film with highest Mn doping concentration. ZnS:Mn films present an intense orange emission along with the host emissions of ZnS. Optimum Mn content for superior orange emission from ZnS:Mn films is found to be 3 wt %. Origin of orange photoluminescence emission due to the incorporation of Mn2+ in Zn2+ host lattice and its quenching due to cross-relaxation mechanism in the films with higher Mn doping concentration is discussed in detail. We report the possibility of one-step generation of white light emission from the as-synthesized ZnS:Mn films by the adequate tailoring of ZnS host emissions in the blue and green regions (445 nm and 530 nm respectively) and Mn related emission in the orange region (585 nm) employing only one excitation wavelength by suitably tuning the Mn doping concentrations. PL decay of the orange emission is monitored to explore the luminescence mechanism and lifetime of the emission.

(Invited) PGM-Free Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions in Reversible Alkaline Fuel Cells

The intrinsic instability of carbon largely limits its use for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as a bifunctional catalyst in reversible fuel cells or water electrolyzers. Herein, we discovered that Mn doping has a promotional role in stabilizing nanocarbon catalysts for the ORR/OER in alkaline media. Stable nanocarbon composites are derived from an inexpensive carbon/nitrogen precursor (i.e., dicyandiamide) and quaternary FeCoNiMn alloy via a template-free carbonization process. In addition to FeCoNiMn metal alloys/oxides, the carbon composites comprise substantial carbon tube forests growing on a thick and dense graphitic substrate. The dense carbon substrate with high degree of graphitization results from Mn doping, while active nitrogen-doped carbon tubes stem from FeCoNi. Catalyst structures and performance are greatly dependent on the doping content of Mn. Various accelerated stress tests (AST) and life tests verify the encouraging ORR/OER stability of the nanocarbon composite catalyst with optimal Mn doping. Extensive characterization before and after ASTs elucidates the mechanism of stability enhancement resulting from Mn doping, which is attributed to (i) hybrid carbon nanostructures with enhanced resistance to oxidation and (ii) the in situ formation of the β-MnO2 and FeCoNi-based oxides capable of preventing carbon corrosion and promoting activity. Note that the improvement in stability due to Mn doping is accompanied by a slight activity loss due to a decrease in surface area. This work provides a strategy to stabilize carbon catalysts by appropriately integrating transition metals and engineering carbon structures.

Temperature-dependent photoluminescence of Mn doped CsPbCl3 perovskite nanocrystals in mesoporous silica

Highly luminescent Mn doped perovskite nanocrystals (NCs) are promising in solid state lighting. The thermal stability of Mn2+ luminescence in Mn: CsPbCl3 NC/mesoporous silica (MPS) composites was studied at temperature ranging from 80 K to 450 K by steady-state and time-resolved photoluminescence (PL) spectroscopy. The Mn: CsPbCl3 NCs with various Mn doping concentrations were synthesized by changing the Mn/Pb molar ratios at 190 °C. It was found that the Mn doped NC films showed a more significant decrease in PL intensities and lifetimes at high temperature above 320 K than the Mn doped NC/MPS films, indicating that the Mn2+ luminescence in doped NC/MPS films exhibited better thermal stability than that of NC films. Further the broadening and shifts of Mn2+ emission bands in doped NC and NC/MPS films were observed at elevated temperature. The temperature-dependent linewidths of Mn2+ emission bands were discussed by electron-phonon coupling.

Electronic Structure and Related Band Parameters of Hexagonal Wurtzite Zn1−xMnxO Magnetic Semiconducting Alloys

The electronic band structure and related band parameters such as, lattice parameters, energy band gaps, density of states and magnetic moment of Zn1−xMnxO ternary system in the hypothetical hexagonal wurtzite structure have been investigated. The calculations are performed using a full-potential linearized augmented plane wave method based on density functional theory in the generalized gradient approximation of Perdew-Burke-Ernzerhof. The evolution of the features of interest with increasing the Mn doping concentration from 0 to 1 in the ZnO structure has been examined and discussed. Our findings show that the behaviour of all studied band parameters with respect to the alloy composition x is consistent with those reported experimentally in the literature. The present study may be useful for spintronics applications.

Density functional study of half-metallicity and spin polarization in Fe1−xTxS2 with T = Mn,Ni

Alloying effects by Mn and Ni substitution on FeS2 have been studied using density-functional calculations. Standard generalized gradient approximation (GGA) and local hybrid functional have been utilized to account for exchange-correlations. The alloys Fe1−xTxS2 with T = Mn,Ni have been investigated for concentrations together with the ground states of the pure compounds. The electronic structure is discussed with the main goal to identify candidates for ferromagnetic half-metals, which are of interest for spintronics applications. Depending on the used calculation framework, interesting candidates have been found at different concentrations. However, at mean concentration of the Mn-doping and low concentration for Ni-doping, both GGA and hybrid functional agree to predict half-metallic character. For the Mn alloys we also note the proximity to a low-spin to high spin transition.