Transition Metal Ion Doping Research Articles

Luminescent manganese-doped CsPbCl3 perovskite quantum dots

Nanocrystalline cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn2+ or Co2+. Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl4) to the QDs in toluene results in the formation of Mn‒doped CsPbCl3 QDs showing bright orange Mn2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn2+ emission, with all features of the CsPbCl3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs.

Femtosecond pulsed laser ablation in microfluidics for synthesis of photoluminescent ZnSe quantum dots

A simple but new toxic chemical free method, Femtosecond Laser Ablation in Microfluidics (FLAM) was proposed for the first time. ZnSe quantum dots of 4–6nm were synthesized and with the use of hyperbranched Polyethyleneimine (PEI) as both structural and functional coated layer. These aqueous nanosized micelles consisting of quantum dots exhibit deep defect states emission of bright green light centered at 500nm. A possible mechanism for the enhanced board band emission was discussed. The properties of toxic matters free and enhanced photoluminescence without doped transition metal ions demonstrate an application potential for biomedical imaging.

Effect of transition metal ion (Nb5+) doping on the luminescence properties of self-activated Ca2AgZn2V3O12 phosphors

Ca2AgZn2V3O12 self-activated vanadate phosphors were synthesized via a citrate assisted sol-gel method. The phase formation of the garnet structure was verified by X-ray diffraction (XRD) and Rietveld refinement analyses. From XRD patters, it is clear that the prepared samples were crystallized in cubic phase with a space group Ia3¯ d (230). The photoluminescence excitation spectrum showed a broad band in the UV region and a broad emission spectrum was observed in the wavelength range of 400–750 nm. The doping of transition metal ion (Nb5+) in the vanadium site changed the luminescence properties. Doping of Nb5+ ions increased the VO bond length from 1.7016 to 1.7148 Å which causes the increase in luminescence intensity and the red shift of emission spectrum. The increase in the luminescence intensity may also be attributed to the emission from Nb5+ ions. The thermal stability of the materials was measured and the activation energy was found to be 0.254 eV. The luminescence decay time was also measured and the values were found to be 158 and 154 μs for undoped and doped samples, respectively. The prepared phosphors exhibited a greenish yellow emission under UV excitation, indicating that they can be potential candidates for the application in UV-based WLEDs.

The effect of transition metal ions (M2 + = Mn2 +, Ni2 +, Co2 +, Cu2 +) on the chemical synthesis polyaniline as counter electrodes in dye-sensitized solar cells

The effect of transition metal ions (M2+=Mn2+, Ni2+, Co2+, Cu2+) on the chemical synthesis of polyaniline (PANI) used as a platinum-free counter electrode (CE) in dye-sensitized solar cells (DSSCs) was investigated. PANI was synthesized by co-polymerization of aniline in the presence of different transition metal ions by using potassium dichromate in acidic medium. It was found that the ion doping of PANI showed a certain catalytic activity for the regeneration of traditional iodide/triiodide (I−/I3−) redox couples. The power conversion efficiency (η) of PANI CEs doped with Mn2+, Ni2+, Co2+ (4.41%, 2.36% and 2.10%, respectively) were higher than 1.94%, the value measured for PANI CE without doping. Doping with Cu2+ decreased the power conversion efficiency of PANI CE (PANI-Cu2+η=1.41%). The electrical properties of the PANI, PANI-Ni2+, PANI-Co2+, PANI-Mn2+ and PANI-Cu2+ were studied by cyclic voltammetry (CV), impedance (EIS), and Tafel polarization curve. The experimental results confirmed that PANI was affected by the doping of different transition metal ions (M2+=Mn2+, Ni2+, Co2+, Cu2+). These results indicate a potential application of ion doped PANI as counter electrode in cost-effective DSSCs.

High performance of Mn-doped CdSe quantum dot sensitized solar cells based on the vertical ZnO nanorod arrays

Abstract Doping transition metal ions Mn2+ to semiconductor quantum dots (QDs) are extremely interesting for the development of photovoltaic devices. Quantum dot sensitized solar cells (QDSCs) are able to show promising power conversion efficiencies (PCE) by employing Mn2+ doped QDs. Herein we achieve effective CdS/Mn CdSe/ZnS QDs co-sensitized vertical ZnO nanorod arrays film that provides an appreciable enhancement in photovoltaic performance. The measured PCE of the solar cells with Mn2+ doped CdSe QDs is 4.14%, which is higher than the efficiency of 2.91% for the solar cells without Mn2+ or a ∼42% increase. The improvement in PCE is ascribed to a higher open-circuit voltage (Voc = 0.74 V) and a superior short-circuit current density (Jsc = 12.6 mA cm−2) with the introduction of Mn2+ into CdSe QDs. The enhancement seen with Mn2+ doped CdSe QDs are investigated and explained by the fact that the enhanced light absorption and reduced charge recombination by the formation of Mn CdSe passivation layer covering the QDs.

Study of photocatalytic activity and magnetic properties of Co, Mn metal ions doped nanocrystalline TiO2 prepared by Sol–Gel method

We report the growth of [Mn, Co]xTiO2 (x=0.01, 0.02 and 0.04) nanocrystals prepared by Sol–Gel technique, followed by freeze-drying treatment at −30°C temperature for 12h. The obtained Gel was thermally treated at different temperatures like 200, 400, 600 and 800°C. The average crystalline size of 6–60nm is achieved. The diffraction peak at 25.22°, 25.49° and 25.6° shows that the main crystal phase is anatase without any indication of other phases. Transition metal doping leads to the reduction in the oxygen vacancies on the TiO2 surface and suppresses the crystallization of other phases by adsorbing onto the surface of the TiO2 particles. The peak at 27.47° indicates the presence of the rutile phase at 800°C. Valence metal cation, Mn, Co ions can react with Ti4+ on the surface of TiO2, and Ti4+ is reduced to Ti3+ which inhibits the transformation of anatase to rutile. The photocatalytic degradation of formaldehyde has been successfully demonstrated using a 250W UV. The binary doped transition metal ions in TiO2 nanoparticles can lead the efforts of enhancing their environmental application as photocatalyst. Magnetic measurement was carried using VSM. The magnetic susceptibility of the Mn, Co doped TiO2 nanopowder increases with increase in doping concentration and exhibits room temperature ferromagnetism.

Fuel aided rapid synthesis and room temperature ferromagnetism of M0.1Co0.1Zn0.8O (M=Mn, Ni, Fe and Cu) DMS nanoparticles

A systematic investigation on the structural and magnetic properties of transition metals (M=Mn, Ni, Fe and Cu) doped Co0.1Zn0.9O (M0.1Co0.1Zn0.8O) nanoparticles synthesized by an easy and inexpensive microwave-assisted combustion method is presented. X-ray diffraction (XRD) and HR-SEM results show single phase nature with hexagonal wurtzite structure, and reveal the incorporation of metal ions into the lattice positions of Zn ions in CoZnO lattice. Size of the nanoparticles was found to vary between 25.3nm and 33.5nm. The magnetization measurements result into ferromagnetic state for all doped samples. Saturation magnetization varies with the type of doped ions indicating the role of interaction between doped ions and Co ions. Ferromagnetic interaction enhances at low temperatures and remains non-zero above room temperature as suggested by magnetization vs. temperature measurements. The room temperature ferromagnetism of the samples was attributed to the exchange interactions between free delocalized carriers (holes from valance band) and the localized d spins of doped transition metal ions.

Hydrothermal synthesis, structural analysis and room-temperature ferromagnetism of Y2O3:Co2+ nanorods

Co2+-doped Y2O3 nanorods of 70–100nm diameters and 0.3–2µm lengths with different compositions (x=0.00, 0.04, 0.08) in Y2−xCoxO3 were synthesized by an easy hydrothermal method. The X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy and transmission electron microscopy (TEM) results indicated the formation of a pure cubic phase structure of Y2O3 doped with Co2+ ions without any secondary phase formation. The TEM analysis indicated that the nanorods were grown along the [100] axis. The pure Y2O3 nanorods showed diamagnetism whereas the Co2+-doped ones exhibited room-temperature ferromagnetism. The existence of such room-temperature ferromagnetic behavior in Co2+-doped Y2O3 nanorods is due mainly to the existence of oxygen vacancies originating after the doping of transition metal ions in the Y2O3 host lattice. Oxygen vacancies act as defect centers in the bound magnetic polaron model to account for this dilute magnetic oxide of medium band gap with low transition-metal-ion concentration. The presence of defect-related oxygen vacancies was further confirmed by photoluminescence spectra analysis of our studied materials.

Templated synthesis of diluted magnetic semiconductors using transition metal ion-doped metal–organic frameworks: the case of Co-doped ZnO

At present, the deliberate and controlled doping of transition metal ions in semiconductor hosts remains a challenge for the development of diluted magnetic semiconductors (DMSs) with room-temperature ferromagnetic properties. In this work, Co-doped ZnO (Zn1−xCoxO, x = 0.03, 0.05, and 0.10) with different Co doping concentrations were successfully prepared via a simple thermal decomposition process using Co-doped Zn-containing metal–organic frameworks as precursors. X-ray diffraction and Raman scattering studies confirmed the incorporation of Co into the ZnO lattices. X-ray photoelectron spectroscopy indicated that the substituted Co ions were in the 2+ oxidation state and were incorporated at Zn2+ sites. The as-prepared Co-doped ZnO samples displayed an extended light absorption range compared to pure ZnO and were ferromagnetic at room temperature. Given the widely tunable range of the doping concentrations used and the abundance of metal–organic framework resources, the proposed synthetic strategy is potentially applicable to the fabrication of other transition metal ion-doped DMSs.

Effect of transition metal ion doping on photocatalytic properties of In–Ti oxides

Abstract

The effect of strong magnetic field on the microstructure of pure diopside and diopside doped with Fe3+or Mn2+

The current study investigates the effect of strong magnetic field on the micro-structure of pure diopside and diopside doped with Fe3+ or Mn2+. The microstructure changes were characterized by X-ray diffraction (XRD), UV–vis, and Raman spectroscopy. The results of XRD show that the strong magnetic field can increase the peak height of (311) diffraction and the height ratio of (310)/(311) is proportional to the strength of the magnetic field. UV–vis results show that the magnetic treatment and the transition-metal ion doping have some influences on the light absorbance of the diopside samples. With a fixed doping concentration, the UV–Vis absorbance of Fe3+-doped samples decreased after magnetic treatments, however, same UV–Vis absorbance increased for the Mn2+-doped samples. Result from Raman spectra suggests that Raman shift of the maximum peak value changed from 671 cm−1 before the magnetic treatment to 1015 cm−1 after the magnetic treatment. Meanwhile, the Raman intensities at 330 cm−1 and 395 cm−1 become more obvious after the magnetic treatment. The results of this study indicate a minor change in the relative positions among the ions, which then leads to polarizability changes.

Efficient and CO2-tolerant oxygen transport membranes prepared from high-valence B-site substituted cobalt-free SrFeO3−δ

The simultaneous high oxygen permeability and high chemical stability of perovskites for use as oxygen transport membranes are of critical importance for applications in oxyfuel processes and as membrane reactors for coupling reactions. Here cobalt-free and CO2-tolerant SrFe0.8M0.2O3−δ (M=Zr, Mo, and W) were exploited as materials for oxygen transport membranes, which exhibited stable cubic phase structures in both air and CO2-containing atmospheres. At 850°C and under the air/helium gradient across the membranes, oxygen permeation fluxes of 0.387, 0.216 and 0.201mLcm−2min−1 [STP] were reached for SrFe0.8Zr0.2O3−δ, SrFe0.8Mo0.2O3−δ and SrFe0.8W0.2O3−δ (membrane thickness: 1mm), respectively. More importantly, relatively stable oxygen permeation fluxes of 0.262, 0.145 and 0.164mLcm−2min−1 were still reached for above three membranes correspondingly and maintained for almost 600min when the sweep gas was switched to 10% CO2-containing helium when compared to the un-doped SrFeO3−δ membrane. Our findings suggest that the stable phase structure and improved CO2 resistance can be effectively achieved by facile doping of high-valence and redox-inactive transition metal ions into the SrFeO3−δ parent oxide. This process provides an efficient way for the development of CO2-tolerant oxygen transport membranes without applying other complex membrane structures (e.g., dual-phase membranes) or noble metals.

Spectroscopic and ultrasonic investigations on structural characterization of borate glass specimen doped with transition metal ions

The present work describes the glass samples of composition (x% V2O5–(80−x)% B2O3–20% Na2CO3) VBS glass system and (x%MnO2–(80−x)% B2O3–20% Na2CO3) in MBS glass system with mol% ranging from x=3, 6, 9, 12, 15 and 18 in steps of 3mol% are prepared by melt quenching technique. For these prepared glass systems, sound velocity (longitudinal and shear velocities) and density have been measured. The sound velocity (longitudinal and shear) was measured by using pulse-echo technique at 5MHz. The XRD study was carried to out to ascertain the amorphous nature of the glass specimen. Using these measured values, the elastic moduli, Poisson’s ratio, Debye temperature, acoustic impedance and thermal expansion coefficient of the two glass systems were evaluated. The elastic and mechanical properties of the prepared glass systems are analyzed from ultrasonic study and the structural characterization from spectroscopic study. The effects due to the doping of transition metal ions with borate have been discussed. In the V2O5 doped glass system,(VBS glass system) the sound velocity, density and elastic moduli, steeply increases after 12mol% comparatively with MnO2 doped glass system (VBS glass system). The present study critically observes the doping of V2O5 with borate enhances the strengthening of network linkage and hardening of the glassy network structure than MnO2. The IR spectral analysis reveals depolymerization of the borate network and conversion of BO3 or BO4 units with the formation of non-bridging oxygen. The FTIR spectral studies confirm the presence of various functional groups of the sample. FTIR spectrum of sample exhibits broad absorption bands indicating the wide distribution of borate structural units. The effect of Na2CO3, V2O5 and MnO2 contents on the structures of borate glass is evaluated from the FTIR spectra. The topological aspects of the prepared glass samples are exhaustively reported from SEM micrographs.

ChemNanoMat-A New Journal for Small Science with a Big Impact

<i>ChemNanoMat</i>-A New Journal for Small Science with a Big Impact

Reactive magnetron sputtering of Ni doped ZnO thin film: Investigation of optical, structural, mechanical and magnetic properties

Nickel doped ZnO (ZnO:Ni) thin films are considered to be promising materials for optoelectronic applications. The doping of transition metal ion modifies the optical and physical properties of the materials. Therefore, studies on optical and physical properties are important for such applications. In the present work, the ZnO:Ni thin films with different Ni concentrations were deposited on Si (100) and corning glass substrates at 400°C by reactive magnetron sputtering using Ar and O2 gas mixture. The (002) growth plane of the ZnO was identified from the X-ray diffraction experiment. It was also confirmed that the films exhibit strong preferred orientation (texture) of crystalline columns in the direction [001] perpendicular to the substrate surface. The optical transmittance, band gap, and refractive indices of the thin films were studied by UV–Vis spectroscopy, photoluminescence and spectroscopic ellipsometry. The optical band gap and refractive index of the thin films decreased with increase of Ni content. The Raman and FT-IR spectroscopic studies were used to explain the modes of vibrations of the functional groups in the material. The surface topography, grain size, distribution, and fine structure of the thin films were analyzed by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The hardness of the films was measured using a nanoindenter coupled with AFM. The growth of ferromagnetism by the effect of Ni content was studied by vibrating sample magnetometer (VSM) at room temperature.

Effect of transition metal ion doping on the photocatalytic activity of ZnS quantum dots: Synthesis, characterization, and application for dye decolorization

In this research, green and aqueous based synthesis routes were performed for chemical preparation of pure and transition metal ions doped ZnS quantum dots at room temperature. Doping of ZnS QDs by three transition metal ions (Mn2+, Co2+, Ni2+ ions) as dopants have been investigated by various techniques. In the optical absorption studies, a broad absorption band in the wavelength range of 280–300nm clearly reveals quantum size effect in ZnS QDs. The crystal structure and the approximate size of QDs were measured by XRD pattern. The average particle size of QDs was found to be around 1–3nm. In addition, the photocatalytic activities of the prepared ZnS QDs as their abilities to remove methyl violet (MV) cationic dye, as a model molecule, were studied. Effect of the experimental parameters, such as the type of dopant and the amount of QDs, pH of the initial dye solution, irradiation time, ionic strength of reaction media, and initial dye concentration on the decolorization efficiency (DE) of QDs as green nano-semiconductors were studied. The results demonstrated that doped QDS (for 5% of dopants) effectively bleached out MV, showing positive photocatalytic enhancement over pure ZnS nanoparticles.

Magnetic exciton relaxation and spin-spin interaction by the time-delayed photoluminescence spectra of ZnO:Mn nanowires.

ZnO:Mn nanostructures are important diluted magnetic materials, but their electronic structure and magnetic origin are still not well understood. Here we studied the time-delayed and power-dependent photoluminescence spectra of Mn(II) doped ZnO nanowires with very low Mn concentration. From the time-delayed emission spectra, we obtained their electronic levels of single Mn ion replacement of Zn ions in ZnO nanowire. The high d-level emissions show up unusually because of the stronger p-d hybridization than that in ZnS, as well as the spin-spin coupling. After increasing Mn doping concentration, the ferromagentic cluster of the Mn-O-Mn with varied configurations can form and give individual emission peaks, which are in good agreement with the ab initio calculations. The presence of clustered Mn ions originates from their ferromagnetic coupling. The lifetimes of these d levels show strong excitation power-dependent behavior, indication of strong spin-dependent coherent emission. One-dimensional structure is critical for this coherent emission behavior. These results indicate that the d state is not within Mn ion only, but a localized exciton magnetic polaron, Mn-O-Mn coupling should be one source of ferromagnetism in ZnO:Mn lattice, the latter also can combine with free exciton for EMP and produce coherent EMP condensation and emission from a nanowire. This kind of nanowires can be expected to work for both spintronic and spin-photonic devices if we tune the transition metal ion doping concentration in it.

Electrocatalytic Oxygen Reduction and Water-Oxidation on Transition Metal Ion-Doped MnO2, RuO2 and IrO2 in Alkaline Aqueous Solutions

We have synthesized metal oxides (MnO2, RuO2, IrO2, and transition metal (Ru, Ir and Ni) ion-doped metal oxides) using a precipitation method and exhaustively examined their bifunctional electrocatalytic activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements were used to study the structure and electronic states of the catalysts. The XRD and XPS data confirmed the successive modification of the structure and electronic states on the catalyst surface by doping transition metal ions into MnO2, RuO2 and IrO2. The samples showed stable performance in terms of their overpotential. The MnO2-based metal oxide exhibited a relatively lower overpotential for ORR. Mn1-nRunOx, Ru1-nNinOx, and Ru1-nIrnOx were identified as preferable catalysts for OER. From the samples examined in this study, Mn1-nRunOx (n = 0.1, 0.2, 0.8) and Ru0.9Ni0.1Ox showed promise as bifunctional catalysts.

Facile synthesis of ZnO and transition metal doped ZnO nanoparticles for the photocatalytic degradation of Methyl Orange

ZnO and transition metal doped ZnO nanoparticles (Zn0.99M0.01O; MMn, Co, Ni and Cu) have been successfully synthesized by thermally decomposing their oxalate precursor. The synthesized nanoparticles have been characterized using XRD, FT-IR and WD-XRF. The samples were found to possess hexagonal wurtzite phase of ZnO suggesting efficient doping of transition metal ions into ZnO lattice. The particle size of ZnO was found to be in the range 25–30nm from Transmission electron microscopy technique. The photocatalytic behavior of synthesized nanoparticles has been scrutinized using Methyl Orange (MO) as probe molecule. Undoped ZnO was found to be better photocatalyst than doped ZnO. Also, the degradation of dye followed first order kinetics. The generation of hydroxyl radicals on the surface of UV-irradiated ZnO has been detected by the Terephthalic acid Photoluminescence probing technique. Furthermore, 11 intermediates have been identified during the photodegradation process using LC-MS technique. Based on the identified intermediates, a pathway has been proposed for the degradation of MO over ZnO. The reusability of ZnO catalyst has also been studied and its photocatalytic efficiency was found to be unaltered ever after 5 cycles of use.

Doping transition metal ions as a method for enhancement of ablation rate in femtosecond laser irradiation of silicate glass

We present a doping method to improve the femtosecond laser ablation rate and promote ablation selectivity. Doping transition metal ions, Co2+ or Cu2+, in silicate glass apparently change absorption spectroscopy and induce resonant absorption at wavelengths of 600 and 800 nm, respectively. Comparing with femtosecond laser processing of the same glass without doping, we find that the threshold fluence decreases and the ablation rate increases in resonant absorption in doped silicate glass. Resonant absorption effectively increases multiphoton ionization for seed-free electron generation, which in turn enhances avalanche ionization.