ESR and optical study of Cu2+ doped calcium malonate dihydrate

The ESR study of Cu(2+) doped calcium malonate dihydrate has been done at room temperature. Four magnetically in-equivalent sites for Cu(2+) have been observed. The spin-Hamiltonian parameters evaluated with the fitting of spectra to rhombic symmetry crystalline field are for Cu(2+) site (I): g(x)=2.0963+/-0.0002, g(y)=2.1316+/-0.0002, g(z)=2.4137+/-0.0002, A(x)=(32+/-2)x10(-4)cm(-1), A(y)=(34+/-2)x10(-4)cm(-1), A(z)=(49+/-2)x10(-4)cm(-1), for site (II): g(x)=2.0668+/-0.0002, g(y)=2.0800+/-0.0002, g(z)=2.3561+/-0.0002, A(x)=(34+/-2)x10(-4)cm(-1), A(y)=(36+/-2)x10(-4)cm(-1), A(z)=(51+/-2)x10(-4)cm(-1), for site (III): g(x)=2.0438+/-0.0002, g(y)=2.0623+/-0.0002, g(z)=2.2821+/-0.0002, A(x)=(34+/-2)x10(-4)cm(-1), A(y)=(36+/-2)x10(-4)cm(-1), A(z)=(53+/-2)x10(-4)cm(-1), and for site (IV): g(x)=2.0063+/-0.0002, g(y)=2.0241+/-0.0002, g(z)=2.2357+/-0.0002, A(x)=(35+/-2)x10(-4)cm(-1), A(y)=(37+/-2)x10(-4)cm(-1), A(z)=(54+/-2)x10(-4)cm(-1). The ground state wave function of Cu(2+) has also been determined. The g-anisotropy has been estimated and compared with the experimental value. Further with the help of optical study the nature of bonding of metal ion with different ligands in the complex has been discussed.     

ESR and optical studies of Cu2+ doped zinc glutamate dihydrate

The ESR study of the Cu2+ doped zinc glutamate dihydrate is carried out at room temperature. Two magnetically nonequivalent sites for Cu2+ are observed. The spin Hamiltonian parameters are determined with the fitting of spectra to rhombic symmetry crystalline field. The parameters are as follows: Cu2+(I): gx=2.0170±0.0002, gy=2.0768±0.0002, gz=2.2334±0.0002, Ax=(74±2)×10(-4), Ay=(99±2)×10(-4), Az=(134±2)×10(-4) cm(-1)and Cu2+(II): gx=2.0180±0.0002, gy=2.0550±0.0002, gz=2.1633±0.0002, Ax=(100±2)×10(-4), Ay=(100±2)×10(-4), Az=(115±2)×10(-4) cm(-1). The ground state wave function is also determined. The g-anisotropy is evaluated and compared with the experimental value. Using the data of optical absorption study undertaken at room temperature the nature of bonding in the complex is also discussed.     

ESR and optical study of Mn2+ doped ammonium selenate single crystals

ESR and optical absorption studies of manganese doped ammonium selenate single crystals are performed at X-band and room temperature to ascertain the site symmetry and location of impurity ions in the lattice. Manganese ions are expected to enter the lattice interstitially. Various spin Hamiltonian parameters are determined. Optical absorption study is also done and associated distortion in the crystal lattice is estimated.     

Mn2+-doped ZnS–CdS alloy nanocrystals for the photocatalytic hydrogen evolution reaction

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Ferromagnetism in colloidal Mn2+ -doped ZnO nanocrystals

High-temperature hydrolysis of Zn(II) and Mn(II) alkoxides in a high boiling point solvent in the presence of surfactants was used to prepare surfactant-coated Zn(1-x)Mn(x)O nanocrystals with average size of 5.5 nm and x = 0.04 +/- 0.03. The magnetic properties of the nanocrystals were measured both for isolated particles diluted in a hydrocarbon matrix and for a nanocrystal powder. Nanocrystals of manganese oxide and ZnO coated with manganese oxide were prepared for comparison to the Zn(1-x)Mn(x)O nanocrystals. We find that the manganese ions primarily substitute zinc ions in the hexagonal ZnO lattice, and part of them are ferromagnetically coupled up to room temperature even in isolated noninteracting nanocrystals. The rest of the ions are magnetically disordered or uncoupled. Surprisingly, these small Zn(1-x)Mn(x)O nanocrystals poses relatively large low-temperature magnetic coercivity and relatively high blocking temperature in the isolated form, which indicate large magnetic anisotropy. In the nanocrystal powder the coercive field decreased significantly. This study highlights the advantages of working with noninteracting single domain particles of these intriguing materials.     

EPR and optical study of Mn2+ doped ammonium tartrate single crystals

EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.     

Sodium citrate dihydrate doped with Mn3+ ions

Sodium citrate dihydrate doped with Mn³⁺ ions, namely trisodium(I) managnese(III) citrate(3−) dihydrate, [Na₃Mn_0.011(C₆H₅O₇)(H₂O)₂]_n, was obtained during attempts to prepare some complex Mn^III citrates from a concentrated strong alkaline solution containing Na⁺, Mn³⁺ and citrate ions. The compound is isostructural with the recently described Na₃(C₆H₅O₇)·2H₂O [Fischer & Palladino (2003). Acta Cryst. E 59 , m1080–m1082]. The essential difference between these two structures is the presence of a very small proportion (0.205 wt%) of Mn³⁺ ions, which are positioned at the special 4e Wyckoff position in C2/c, where they are in a highly distorted octahedral environment of O atoms from two citrate anions.     

Cooperative near-IR to visible photon upconversion in Yb3+-doped MnCl2 and MnBr2: comparison with a series of Yb3+-doped Mn2+ halides

Yb3+-doped MnCl2 and MnBr2 crystals exhibit strong red upconversion luminescence under near-infrared excitation around 10 000 cm(-1) at temperatures below 100 K. The broad red luminescence band is centred around 15 200 cm(-1) for both compounds and identified as the Mn2+ 4T1g-->6A1g transition. Excitation with 10 ns pulses indicates that the upconversion process consists of a sequence of ground-state and excited-state absorption steps. The experimental VIS/NIR photon ratio at 12 K for an excitation power of 191 mW focused on the sample with a 53 mm lens is 4.1% for MnCl2:Yb3+ and 1.2% for MnBr2:Yb3+. An upconversion mechanism based on exchange coupled Yb3+-Mn2+ ions is proposed. Similar upconversion properties have been reported for RbMnCl3:Yb3+, CsMnCl3:Yb3+, CsMnBr3:Yb3+, RbMnBr3:Yb3+, Rb2MnCl4:Yb3+. The efficiency of the upconversion process in these compounds is strongly dependent on the connectivity between the Yb3+ and Mn2+ ions. The VIS/NIR photon ratio decreases by three orders of magnitude along the series of corner-sharing Yb3+-Cl--Mn2+, edge-sharing Yb3+-(Cl-)2-Mn2+ to face-sharing Yb3+-(Br-)3-Mn2+ bridging geometry. This trend is discussed in terms of the dependence of the relevant super-exchange pathways on the Yb(3+)-Mn2+ bridging geometry.     

Ca2+- and Mg2+-doped covalent organic frameworks exhibiting high hydrogen and acetylene storage

A multiscale theoretical investigation has been performed to study the hydrogen and acetylene storage in Ca²⁺- and Mg²⁺-doped COFs (COF-105 and COF-108). The first-principles calculations show that the Ca²⁺ and Mg²⁺ can be immobilized at the COFs surfaces, and the doped Ca and Mg cations can adsorb five H₂ molecules and three C₂H₂ molecules with ideal binding energies. The Grand Canonical Monte Carlo (GCMC) simulations were carried out to obtain the hydrogen and acetylene uptakes of Ca²⁺- and Mg²⁺-doped COFs at room temperature in the different pressure ranges. Our results demonstrate that, at T = 298 K and p = 100 bar, the total gravimetric uptakes of H₂ in Ca²⁺-doped COF-105 and COF-108 reach 6.78 and 6.54 wt%, respectively, and a higher uptakes of 7.14 and 7.27 wt% have been reached for Mg²⁺-doped COF-105 and COF-108, respectively. At T = 298 K and p = 1 bar, the acetylene uptakes of Ca²⁺-doped COF-105, Ca²⁺-doped COF-108, Mg²⁺-doped COF-105, and Mg²⁺-doped COF-108 are 406.42, 366.24, 308.07, and 319.88 cm³/g (corresponding to the excess uptakes of 358.37, 316.38, 236.7109, and 245.42 cm³/g), respectively. The Ca²⁺-doped COF-105 displays a highest acetylene storage capacity among all materials reported. The Ca²⁺- and Mg²⁺-doped COFs can be very practical hydrogen or acetylene storage medium in the future.     

Surface ion engineering of Mn2+-doped ZnS quantum dots using ion-exchange resins

We report the engineering of surface ions present as defects in doped quantum dots (Qdots) following their synthesis. This was achieved by treating the Qdots with cation-exchange resin beads (CB). An aqueous dispersion of Mn(2+)-doped ZnS Qdots, when treated with different amounts of CB, resulted in two kinds of changes in the emission due to Mn(2+) ions. First, the intensity increased in the presence of a smaller amount of CB, to the extent of a doubled quantum yield. With increased CB as well as incubation time, the emission intensity decreased systematically, accompanied by an increasing blue shift of the peak emission wavelength. Electron spin resonance results indicated the removal of clusters of Mn(2+) present in the Qdots by the CB, which has been attributed to changes in the emission characteristics. Transmission electron microscopy studies revealed that for smaller amounts of CB there was no change in the particle size, whereas for greater amounts the particle size decreased. The results have been explained on the basis of the removal of Mn(2+) (and also Zn(2+)) ions present on the surfaces of Qdots in the form of clusters as well as individual ions.     

Thermal,optical and electrical properties of MnO2-doped mixed sodium potassium phosphate glasses

Journal of Thermal Analysis and Calorimetry - Glasses in the system (1???x)(0.5NaPO3–0.5KPO3)–xMnO2, with 0?≤?x?≤?50 mol%,...     

4-Mercaptophenylacetic acid functionalized Mn2+-doped ZnS nanoparticles fluorescence quenching caused by the addition of Cu2+

This paper reports that 4-mercaptophenylacetic acid functionalized Mn²⁺-doped ZnS nanoparticles (4-MPAA-ZnS-Mn²⁺ NPs) as fluorescent probes for the detection of copper ions in solution. The fluorescence quenching was due to the aggregation of copper ions with 4-MPAA-ZnS-Mn²⁺ NPs. These aggregations were confirmed by using UV lamp, UV–visible spectroscopy and dynamic light scattering (DLS). These 4-MPAA-ZnS-Mn²⁺ NPs were applied as fluorescent probes to detect copper ions in aqueous solution.     

Activation of high-T(C) ferromagnetism in Mn2+-doped ZnO using amines

We report the discovery that high-TC ferromagnetism in manganese-doped ZnO (Mn2+:ZnO) can be activated by amine binding and calcination. The activation of ferromagnetism is attributed to the incorporation of uncompensated p-type dopants into the ZnO lattice upon amine calcination, a process that has substantial precedence in the literature surrounding p-type ZnO. The experimental observations are consistent with a microscopic mechanism involving formation of bound magnetic polarons upon introduction of p-type dopants into Mn2+:ZnO. These results clearly demonstrate that Mn2+:ZnO ferromagnetism is critically sensitive to defects other than the magnetic dopants themselves, offering some insight into the diversity of experimental observations reported previously for this material.     

An EPR and optical absorption study of VO2+ ions in sodium hydrogen oxalate monohydrate (NaHC2O4.H2O) single crystals

Electron paramagnetic resonance of VO(2+) doped sodium hydrogen oxalate monohydrate (NaHC(2)O(4).H(2)O) single crystals and powders are examined at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes namely ac*, b*c* and ab* indicate four different VO(2+) complexes with intensity ratios of 4:2:1:1. It is found from the EPR analysis that the Na(+) ions are replaced with the substitutional magnetically inequivalent VO(2+) ions. The powder spectrum also clearly indicates four different VO(2+) complexes, confirming the single crystal analysis. Crystalline field around the VO(2+) ion is nearly axial. The optical absorption spectrum show two bands centered at 15408 and 12453 cm(-1). Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed.     

Theoretical investigation on the optical and EPR spectra for Cu2+-doped ZnO-CdS nanocomposites

The three optical absorption bands and EPR parameters of the [CuO₆]¹⁰⁻ center in the ZnO-CdS composite nanopowders are theoretically studied from the perturbation formulas based on the cluster approach. In the formulas, the contributions to EPR parameters arising from the ligand orbital and spin–orbit coupling interactions via covalence effect are considered. For the studied [CuO₆]¹⁰⁻ cluster, the Cu–O bond lengths are suggested to show a relative elongation ratio ρ (≈ 4.1%) along the z-axis due to Jahn–Teller effect. The defect models suggested in this work are different from the previous assumption that the impurity Cu²⁺ can replace the host Zn²⁺ site when it enters the lattices of the ΖnO and ΖnS nanocrystals, forming the tetrahedral [CuΧ₄]⁶⁻ clusters (Χ = O, S). The validity of the proposed model is discussed. The differences between the present calculations and the previous ones for the interstitial Cu²⁺ center in ZnO nanocrystals are analyzed in view of the dissimilar impurity behaviors due to the new composition CdS and distinct preparation conditions.     

In situ reversible tuning of photoluminescence of Mn2+-doped ZnS quantum dots by redox chemistry

Herein we report the development of a new method for in situ reversible tuning of photoluminescence properties of quantum dots (Qdots) by partial oxidation of population of the emitting species and subsequent chemical reduction of the oxidized form. The concept has been demonstrated using Mn(2+)-doped ZnS Qdots stabilized by acetyl acetonate. Treatment of an aqueous solution of the Qdots (with Mn(OAc)(2) being the source of Mn used for the synthesis of the Qdots) by potassium peroxodisulfate (KPS) led to reduction of intensity of emission due to Mn(2+) ((4)T(1)-(6)A(1)). Subsequent treatment of the solution containing KPS-treated Qdots with NaBH(4) led to regaining of intensity, thus providing reversibility to the tuning, which was possible for more than one cycle. Electron spin resonance (ESR) spectroscopic investigations revealed reduction of the population of Mn(2+) upon treatment with KPS, whereas it went back up upon further treatment with NaBH(4). Interestingly, a mixed population of oxidation states of Mn was indicated to be present in the Qdots prepared using KMnO(4) as the source of Mn. The fluorescence intensity of the Qdots so prepared increased upon treatment with NaBH(4) following synthesis, which was not possible when the source of Mn was Mn(OAc)(2). Transmission electron microscopic and X-ray diffraction studies indicated that oxidation and reduction did not change the sizes of Qdots significantly.     

Infrared optical constants of crystalline sodium chloride dihydrate: application to study the crystallization of aqueous sodium chloride solution droplets at low temperatures

Complex refractive indices of sodium chloride dihydrate, NaCl·2H(2)O, have been retrieved in the 6000-800 cm(-1) wavenumber regime from the infrared extinction spectra of crystallized aqueous NaCl solution droplets. The data set is valid in the temperature range from 235 to 216 K and was inferred from crystallization experiments with airborne particles performed in the large coolable aerosol and cloud chamber AIDA at the Karlsruhe Institute of Technology. The retrieval concept was based on the Kramers-Kronig relationship for a complex function of the optical constants n and k whose imaginary part is proportional to the optical depth of a small particle absorption spectrum in the Rayleigh approximation. The appropriate proportionality factor was inferred from a fitting algorithm applied to the extinction spectra of about 1 μm sized particles, which, apart from absorption, also featured a pronounced scattering contribution. NaCl·2H(2)O is the thermodynamically stable crystalline solid in the sodium chloride-water system below the peritectic at 273.3 K; above 273.3 K, the anhydrous NaCl is more stable. In contrast to anhydrous NaCl crystals, the dihydrate particles reveal prominent absorption signatures at mid-infrared wavelengths due to the hydration water molecules. Formation of NaCl·2H(2)O was only detected at temperatures clearly below the peritectic and was first evidenced in a crystallization experiment conducted at 235 K. We have employed the retrieved refractive indices of NaCl·2H(2)O to quantify the temperature dependent partitioning between anhydrous and dihydrate NaCl particles upon crystallization of aqueous NaCl solution droplets. It was found that the temperature range from 235 to 216 K represents the transition regime where the composition of the crystallized particle ensemble changes from almost only NaCl to almost only NaCl·2H(2)O particles. Compared to the findings on the NaCl/NaCl·2H(2)O partitioning from a recent study conducted with micron-sized NaCl particles deposited onto a surface, the transition regime from NaCl to NaCl·2H(2)O is shifted by about 13 K to lower temperatures in our study. This is obviously related to the different experimental conditions of the two studies. The partitioning between the two solid phases of NaCl is essential for predicting the deliquescence and ice nucleation behavior of a crystalline aerosol population which is subjected to an increasing relative humidity.     

Multi-spot paper chromatograms of sodium orthophosphate

The formation of two zones on paper chromatograms was investigated by chromatographing orthophosphoric acid and the primary, secondary and tertiary sodium salts, using pyridine-ethyl acetate/water as mobile phase. Movement of the species from the origin depends on washing the paper with acid and suggests an exchange of protons for sodium as a prerequisite condition. Washing with EDTA does not alter this requirement. Zone movement and multi-spot formation require that the forming solvent contain at least 5% of water (v/v). Between this value and saturation, increasing water content enhances zone disengagement. A solute spot of a sodium salt exchanges with the protons to produce a fast-migrating protonated phosphate species. If the solute sample has a sodium content less than the amount of exchangeable protons, a single fast spot is produced ; if the concentration exceeds this capacity, a second slower spot results.