Fe(3+) ions in alkali lead tetraborate glasses--an electron paramagnetic resonance and optical study

Glass systems of composition 90R(2)B(4)O(7)+9PbO+1Fe(2)O(3) (R=Li, Na and K) and 90Li(2)B(4)O(7)+(10-x)PbO+xFe(2)O(3) (x=0.5, 1, 3, 4, 5, 7 and 9 mol %) have been investigated by means of electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra exhibit three resonance signals at g approximately 6.0, 4.2 and 2.0. The resonances at g approximately 6.0 and 4.2 are attributed to Fe(3+) ions in rhombic and axial symmetry sites, respectively. The g approximately 2.0 resonance signal is due to two or more Fe(3+) ions coupled together with dipolar interaction. The EPR spectra of 1 mol % of Fe(2)O(3) doped in lithium lead tetraborate glass samples have been studied at different temperatures (123-433 K). The intensity of g approximately 4.2 resonance signal decreases and the intensity of g approximately 2.0 resonance signal increases with the increase of temperature. The line widths are found to be independent of temperature. The EPR spectra exhibit a marked concentration dependence on iron content. A decrease in intensity for the resonance signal at g approximately 4.2 with increase in iron content for more than 4 mol % has been observed in lithium lead tetraborate glass samples and this has been attributed to the formation of Fe(3+) ion clusters in the glass samples. The paramagnetic susceptibility (chi) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/chi versus T graph. The optical absorption spectrum of Fe(3+) ions in lithium lead tetraborate glasses exhibits three bands characteristic of Fe(3+) ions in an octahedral symmetry. The crystal field parameter D(q) and the Racah interelectronic repulsion parameters B and C have also been evaluated. The value of interelectronic repulsion parameter B (825 cm(-1)) obtained in the present work suggests that the bonding is moderately covalent.     

EPR and optical investigations of manganese ions in alkali lead tetraborate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Mn2+ ions in different alkali lead tetraborate glasses 90R2B4O7+9.25PbO+0.75MnSO4 (R=Li, Na and K) and 90Li2B4O7+(10-x)PbO+xMnSO4 (x=0.1, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 and 2 mol%) have been studied. The EPR spectrum of all the glass samples exhibit three resonance signals at g=2.0, 3.3 and 4.3. The resonance signal at g=2.0 is attributed to the Mn2+ ions in an environment close to an octahedral symmetry. The resonance signals at g=3.3 and 4.3 have been attributed to the rhombic symmetry of the Mn2+ ions. The effect of temperature (123-433 K) and the composition dependence of EPR signals have been studied for Mn2+ ions in lithium lead tetraborate glasses. It is interesting to observe that the variation of paramagnetic susceptibility (chi) with temperature obeys Curie-Weiss law. From the slope of 1/chi versus T graph, the Curie constant (C) has been evaluated. The zero-field splitting (zfs) parameter D has been calculated for different alkali lead tetraborate glasses from the intensities of the allowed hyperfine lines. The optical absorption spectrum exhibits three bands. An intense and broad band at lower energy side has been assigned to the spin-allowed (5Eg-->5T2g) transition of Mn3+ ions in an octahedral symmetry. The intense and sharp band and a broad band at higher energy side have been assigned to charge transfer bands. A red shift is observed with increase of alkali ion size. The optical band gap energy (Eopt) decreases, whereas the Urbach energies (DeltaE) increases with increase of Mn content. The theoretical values of optical basicity (Lambdath) of the glasses have also been evaluated.     

Solution combustion derived nanocrystalline Zn(2)SiO(4):Mn phosphors: a spectroscopic view

Manganese doped nanocrystalline willemite powder phosphors Zn(2-x)Mn(x)SiO(4) (0.1(6)A(1) ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.     

The microstructures of biomineralized surfaces: a spectroscopic study on the exoskeletons of fresh water (Apple) snail, Pila globosa

In view of the importance in understanding biomineralization processes in different molluskan species, the common fresh water apple snail Pila globosa in Indian origin was taken to explore its mineralized exoskeleton structures. The detailed structural studies of the exoskeletons of P. globosa have been undertaken. The isolated layers present in these shells were studied by electron paramagnetic resonance (EPR), optical absorption, and infrared spectral techniques. The EPR spectra of the organic protein layer periostracum show the characteristic signals corresponding to Fe(3+) ions at g = 4.1 and 2.0. The EPR spectra of the ostracum (middle) layer at room temperature gives a complicated spectrum consisting of a number of Mn(2+) signals of at least three sets due to the aragonite nature of the material. The results indicate the presence of the multivalent manganese ions, which undergo the redox mechanisms. The thermal variation of the EPR spectra show marked effect on these samples both in g-values and the basic spectral pattern.     

Structural investigations on sodium-lead borophosphate glasses doped with vanadyl ions

Electron paramagnetic resonance (EPR), optical absorption, and FT-IR spectra of vanadyl ions in the sodium-lead borophosphate (Na(2)O-PbO-B(2)O(3)-P(2)O(5)) (SLBP) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO(2+) ions. The spin Hamiltonian parameters g and A are found to be independent of the V(2)O(5) content and temperature. The values of the spin Hamiltonian parameters indicate that the VO(2+) ions in SLBP glasses are present in octahedral sites with tetragonal compression. The population difference between Zeeman levels (N) is calculated as a function of temperature for an SLBP glass sample containing 1.0 mol % VO(2+) ions. From the EPR data, the paramagnetic susceptibility (χ) is calculated at different temperatures, and the Curie constant (C) is calculated from the 1/χ versus T graph. The optical absorption spectra of the glass samples show two absorption bands, and they are attributed to V(3+) and V(4+) ions. The optical band gap energy (E(opt)) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. It is observed that, as the vanadium ion concentration increases, E(opt) decreases and ΔE increases. The study of the IR absorption spectrum depicts the presence of BO(3), BO(4), PO(3), PO(4), and VO(5) structural units.     

EPR, optical and infrared absorption studies of Mn2+ ions doped in zinc malate trihydrate single crystal

Electron paramagnetic resonance (EPR) studies have been carried out on Mn2+ ions doped in zinc malate trihydrate single crystals in the temperature range 123-413 K on X-band frequency. The EPR spectrum at room temperature exhibits a group of five fine structure transitions each splits into six hyperfine components. Angular variation studies reveal that Mn2+ ions enter the lattice substitutionally. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The variation of zero-field splitting parameter (D) with temperature is measured. From the optical absorption spectrum, the crystal field splitting parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The infrared spectrum exhibits bands characteristic of the carboxylic acid salts.     

Optical absorption,infrared, Raman,and EPR spectral studies on natural iowaite mineral

Natural iowaite, magnesium–ferric oxychloride mineral having light green color originating from Australia has been characterized by EPR, optical, IR, and Raman spectroscopy. The optical spectrum exhibits a number of electronic bands due to both Fe(III) and Mn(II) ions in iowaite. From EPR studies, the g values are calculated for Fe(III) and g and A values for Mn(II). EPR and optical absorption studies confirm that Fe(III) and Mn(II) are in distorted octahedral geometry. The bands that appear both in NIR and Raman spectra are due to the overtones and combinations of water and carbonate molecules. Thus EPR, optical, and Raman spectroscopy have proven most useful for the study of the chemistry of natural iowaite and chemical changes in the mineral.     

EPR and IR spectral studies of the sea water mussel Mytilus conradinus shells

The electron paramagnetic resonance (EPR) and infrared (IR) spectral studies have been employed on the periostracum, the prismatic layer and the nacre of the shell of the marine bivalve molluscan Mytilus conradinus of the South Indian origin. All the layers of this shell show Fe3+ ion spin resonance signals in common. The inner layer namely nacre at room temperature shows EPR signals of Fe3+ ions and the heated one exhibits a sextet hyperfine pattern characteristic of Mn2+ ions. The prismatic layer of the shell also exhibits a similar spectrum, but of distinct pattern. The spin-Hamiltonian parameters have been evaluated for the prismatic and nacreous layers of this shell. Infrared spectra of the two main layers of the shell namely prismatic and the nacre exhibit the characteristic bands of CO3(2-) molecular ion in different symmetries of CaCO3.     

VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques

Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites.     

Structural studies of marine exoskeletons: redox mechanisms observed in the Cu-supported CaCO3 surfaces tudied by EPR

Electron Paramagnetic Resonance (EPR), optical and infrared (IR) spectral studies have been performed on the pure and Cu-adsorbed exoskeletons of marine environment. The EPR spectrum of exoskeletons at room temperature exhibits a sharp signal at g approximately 1.9970. The possible redox mechanisms have been noticed on heating these exoskeletons in which the low spin Mn(3+) reduces to Mn(2+). The optical absorption spectra also give the evidence of the presence of Mn(3+) ions. The effects of thermal sintering on the EPR spectra have been studied and discussed in detail. The Cu-adsorbed samples clearly showed the adsorption of the Cu(2+) ions over CaCO(3) and the redox mechanism in these samples have been monitored by EPR.     

Investigations of the EPR zero-field splitting and the defect structure for Mn(2+) and Fe(3+) ions in anatase crystals

The EPR zero-field splittings D of Mn(2+) and Fe(3+) ions in anatase crystals at room and low temperatures are calculated from the high-order perturbation formula of zero-field splitting D for 3d(5) ions in tetragonal symmetry based on the dominant spin-orbit coupling mechanism. The calculated results are consistent with the observed values. From the calculations, Mn(2+) and Fe(3+) ions are suggested to substitute for Ti(4+) ions in anatase (in the previous paper, Mn(2+) ion was suggested at an interstitial site rather than substitutional site) and the defect structures (characterized mainly by the local oxygen parameter u) for both tetragonal Mn(2+) and Fe(3+) impurity centers are estimated. The different zero-field splitting at room and low temperatures are due mainly to the change of local oxygen parameter u with the temperature. These results are discussed.     

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.     

EPR and photoluminescence studies of ZnO:Mn nanophosphors prepared by solution combustion route

Nanocrystalline ZnO:Mn (0.1 mol%) phosphors have been successfully prepared by self propagating, gas producing solution combustion method. The powder X-ray diffraction of as-formed ZnO:Mn sample shows, hexagonal wurtzite phase with particle size of ～40 nm. For Mn doped ZnO, the lattice parameters and volume of unit cell (a=3.23065 ?, c=5.27563 ? and V=47.684 (?)(3)) are found to be greater than that of undoped ZnO (a=3.19993 ?, c=5.22546 ? and V=46.336 (?)(3)). The SEM micrographs reveal that besides the spherical crystals, the powders also contained several voids and pores. The TEM photograph also shows the particles are approximately spherical in nature. The FTIR spectrum shows two peaks at ～3428 and 1598 cm(-1) which are attributed to O-H stretching and H-O-H bending vibration. The PL spectra of ZnO:Mn indicate a strong green emission peak at 526 nm and a weak red emission at 636 nm corresponding to (4)T(1)→(6)A(1) transition of Mn(2+) ions. The EPR spectrum exhibits fine structure transition which will be split into six hyperfine components due to (55)Mn hyperfine coupling giving rise to all 30 allowed transitions. From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed. The magnitude of the hyperfine splitting (A) constant indicates that there exists a moderately covalent bonding between the Mn(2+) ions and the surrounding ligands. The number of spins participating in resonance (N), its paramagnetic susceptibility (χ) have been evaluated.     

Spectral studies on VO ions in potassium thiourea bromide single crystals using EPR and optical absorption spectroscopy

Electron paramagnetic resonance (EPR) studies have been carried out on VO²⁺ ions doped in single crystals of ferroelectric material, potassium thiourea bromide (PTB) at room temperature and in the temperature range 103–343 K on X-band MW frequency. An isotropic octet spectrum characteristic of VO²⁺ ion was obtained due to the fast re-orientation of the VO²⁺ in PTB lattice, which exhibits glassy nature at certain range around room temperature. The temperature dependant EPR spectra of VO²⁺ ions in this host lattice has been attributed to the occurrence of multiple phase transitions due to the combined environment effects of KBr and thiourea materials in the single crystal. From the optical absorption spectrum, the crystal field splitting parameter Dq, tetragonal parameters Ds and Dt have been evaluated and discussed.     

多组分丝素蛋白-Cu(II)配合物的EPR谱解析

基于二阶微扰理论建立了对具有超精细耦合结构的多组分复杂EPR(顺磁共振)谱的解析拟合方法, 并以丝素蛋白-Cu(II)配合物的EPR谱为例进行解析分析, 从而有效地解释了Cu(II)离子在蚕吐丝过程中的作用. 该方法和应用程序能为类似问题的解决(如Fe(II)、Mn(II)、V(III)及其它顺磁性离子配合物EPR谱的解析)提供方便.     

多组分丝素蛋白-Cu(II)配合物的EPR谱解析

基于二阶微扰理论建立了对具有超精细耦合结构的多组分复杂EPR(顺磁共振)谱的解析拟合方法,并以丝素蛋白-Cu(II)配合物的EPR谱为例进行解析分析,从而有效地解释了Cu(II)离子在蚕吐丝过程中的作用.该方法和应用程序能为类似问题的解决(如Fe(II)、Mn(II)、V(III)及其它顺磁性离子配合物EPR谱的解析)提供方便.     

Preparation and properties of a monomeric high-spin Mn(V)-oxo complex

Oxomanganese(V) species have been implicated in a variety of biological and synthetic processes, including their role as a key reactive center within the oxygen-evolving complex in photosynthesis. Nearly all mononuclear Mn(V)-oxo complexes have tetragonal symmetry, producing low-spin species. A new high-spin Mn(V)-oxo complex that was prepared from a well-characterized oxomanganese(III) complex having trigonal symmetry is now reported. Oxidation experiments with [FeCp(2)](+) were monitored with optical and electron paramagnetic resonance (EPR) spectroscopies and support a high-spin oxomanganese(V) complex formulation. The parallel-mode EPR spectrum has a distinctive S = 1 signal at g = 4.01 with a six-line hyperfine pattern having A(z) = 113 MHz. The presence of an oxo ligand was supported by resonance Raman spectroscopy, which revealed O-isotope-sensitive peaks at 737 and 754 cm(-1) assigned as a Fermi doublet centered at 746 cm(-1)(Δ(18)O = 31 cm(-1)). Mn Kβ X-ray emission spectra showed Kβ' and Kβ(1,3) bands at 6475.92 and 6490.50 eV, respectively, which are characteristic of a high-spin Mn(V) center.     

Electron paramagnetic resonance, optical absorption and IR spectroscopic studies of the sulphate mineral apjohnite

Apjohnite, a naturally occurring Mn-bearing pseudo-alum from Terlano, Bolzano, Italy, has been characterized by EPR, optical, IR and Raman spectroscopy. The optical spectrum exhibits a number of electronic bands around 400 nm due to Mn(II) ion in apjohnite. From EPR studies, the parameters derived, g=2.0 and A=8.82 mT, confirm MnO(H(2)O)(5) distorted octahedra. The presence of iron impurity in the mineral is reflected by a broad band centered around 8400 cm(-1) in the NIR spectrum. A complex band profile appears strongly both in IR and Raman spectra with four component bands around 1100 cm(-1) due to the reduction of symmetry for sulphate ion in the mineral. A strong pair of IR bands at 1681 and 1619 cm(-1) with variable intensity is a proof for the presence of water in two states in the structure of apjohnite.     

EPR and optical absorption studies on Cr3+ ions doped in KZnClSO4 x 3H2O single crystals

EPR and optical absorption spectra of Cr3+ ions doped in KZnClSO4 x 3H2O single crystals have been studied at room temperature. The EPR spectrum exhibits a group of three fine structure transitions characteristic of Cr3+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in an octahedral symmetry. From the observed band positions, the crystal field parameters have been evaluated.     

Electron paramagnetic resonance, optical absorption, IR and Raman spectral studies on pelecypod shell

Pelecypod shell originated from Kolleru lake of Andhra Pradesh is used in the present work. It contains Mn(II) and Fe(III) in traces. The EPR spectrum of the compound is due to Mn(II) which is in three independent sites. The three g values are evaluated with slight differences. The hyperfine component varies from 9.33 to 9.49mT. The zero field splitting parameter is also ranges from 43.8(1) to 44.1(1)mT. Using the covalence parameter the number of ligands around metal is estimated as 20. In EPR spectrum Fe(III) is identified. The optical absorption spectrum is attributed to Mn(II) in octahedral geometry. Further 10 Dq band is attributed to Fe(II) in the optical absorption spectrum. NIR spectral results are due to water fundamentals, whereas IR and Raman spectrum is due to carbonate ion fundamentals.