Spectra Of Transition Metal Ions Research Articles

Shift of the Infrared Absorption and Emission Spectra of Transition Metal Ions in Solid Solutions of Semiconductor Compounds

A universal theoretical model is proposed that explains the observed shift of IR absorption and emission bands in the spectra of transition metal ions in solid solutions of semiconductor compounds. The model has been used for estimating the long-wavelength shift of luminescence bands in the spectra of semiconductor solid solutions with increasing concentration in application to crystals of the ternary systems ZnMgSe(Cr2+) and CdMnTe(Fe2+). Description of the phenomenon is generalized to the case of multicomponent solid solutions.

Structural characterization of titania by X-ray diffraction, photoacoustic, Raman spectroscopy and electron paramagnetic resonance spectroscopy

A titania mineral (obtained from East coast, Orissa, India) was investigated by X-ray diffraction (XRD), photoacoustic spectroscopy (PAS), Raman and Electron Paramagnetic Resonance (EPR) studies. XRD studies indicated the presence of rutile (91%) and anatase (9%) phases in the mineral. Raman investigation supported this information. Both rutile and anatase phases have tetragonal structure (rutile: space group P42/mnm, a=4.5946(1) Å, c=2.9597(1) Å, V=62.48(1) (Å)3, Z=2; anatase: space group I41/amd, 3.7848(2) Å, 9.5098(11) Å, V=136.22(2) (Å)3, Z=4). The deconvoluted PAS spectrum showed nine peaks around 335, 370, 415,485, 555, 605, 659, 690,730 and 785nm and according to the ligand field theory, these peaks were attributed to the presence of V4+, Cr3+, Mn4+ and Fe3+ species. EPR studies revealed the presence of transition metal ions V4+(d1), Cr3+(d3), Mn4+(d3) and Fe3+(d5) at Ti4+ sites. The EPR spectra are characterized by very large crystal filed splitting (D term) and orthorhombic distortion term (E term) for multiple electron system (s>1) suggesting that the transition metal ions substitute the Ti4+ in the lattice which is situated in distorted octahedral coordination of oxygen. The possible reasons for observation of unusually large D and E term in the EPR spectra of transition metal ions (S=3/2 and 5/2) are discussed.

On the origin of dips in total fluorescence yield X-ray absorption spectra: Partial and inverse partial fluorescence yield at the L-edge of cobalt aqueous solution

Dips appearing in the L-edge total fluorescence yield (TFY) spectra of transition-metal ions in aqueous solutions have been recently attributed to, orbital mixing of the solute with the solvent orbitals. Here we compare the L-edge TFY, Oxygen Kα and Co2+ Ll(3s→2p3/2), Lη(3s→2p1/2), Lα(3d→2p3/2) and Lβ(3d→2p1/2) –edge partial fluorescence yield with the transmission spectrum. We thereby confirm that these mixed orbitals lead to electron delocalization between the valence d-orbitals of the transition metal and the valence bands of the solvent molecules, quenching their X-ray fluorescence.

The effect of silicate network modifiers on colour and electron spectra of transition metal ions

Coloured silicate glasses of Li 2O–SiO 2, Na 2O–SiO 2 and K 2O–SiO 2 systems were produced by melting at 1400 °C. As dyes, compounds of cobalt, nickel, chromium and manganese were used. The aim of this study was to determine the effect of glass matrix modifiers on colour and d–d electron spectra of chosen transition metal ions. From the analysis of colour and electron spectra of the obtained glasses it follows that the chemical composition of the glass matrix influences the coordination state as well as the oxidation state of the transition metal. Cobalt and nickel occur in examined glasses as divalent ions (Co 2+, Ni 2+) in both coordinations – octahedral and tetrahedral. A decrease of the electronegativity of modifiers (Li → Na → K) and an increase of the glass matrix basicity promotes the tetrahedral coordination of cobalt and nickel. Chromium and manganese occur in silicate glasses in various oxidation state, though Cr 3+ and Mn 3+ ions in octahedral coordination are dominant. The decrease of the electronegativity of the modifiers causes a shift of oxidation/reduction equilibrium towards higher valence of the transition metals (Cr 6+, Mn 3+).

Luminescence and surface effects of closed-shell transition metal ions in sol-gel silica glasses

Luminescence spectra of transition metal ions of closed-shell structures in sol-gel silica glasses are observed in the series: Ti 4+, V 5+, Cr 6+, Mn 7+ at temperatures between 300 and 4 K. The luminescence properties are found to be very sensitive to the inhomogeneities, surface effects and preparation conditions.

Interpretation of Higher Order Magnetic effects in the Spectra of Transition Metal Ions in Terms of SO(5) and Sp(10)

Small discrepancies in the fitted energy levels of the configurations ${3d}^{N}$ of transition metal ions are ascribed to effective three-electron magnetic operators ${y}_{i}$. Surprisingly it has been found that, of the 16 possible operators with ranks 1 in both spin and orbital spaces, four operators labeled by the irreducible representation (irrep) (11) of SO(5) are sufficient to obtain results which appear to be limited by the errors in the experimental energy levels. An interpretation is given involving products of operators labeled by the irreps of SO(5) and the symplectic group Sp(10).

Interpretation of the Emission Spectra of Trivalent Chromium-Doped Garnet Crystals Using Tanabe-Sugano Diagrams

The purpose of this paper is to provide an example of a real-world application in which Tanabe-Sugano diagrams can be used to relate the optical properties and performance of a material to its physical and chemical properties. Tanabe-Sugano diagrams illustrate the effect of the strength of the octahedral ligand field on the relative positions of the various energy level components that arise as a result of the splitting of the degenerate free-ion states. The application of these diagrams can also be extended to the spectra of transition metal ions found in solid state matrices where the predominant external force is the crystal field. In insulating materials, transition metal ions occupy sites with six anions as nearest-neighbors, forming a coordination sphere characterized as a distorted octahedron. Although the actual site symmetry is lower than Oh in most cases, an octahedral approximation is qualitatively sufficient for the present application involving an analysis and interpretation of the emission spectra of chromium-doped garnets.

Jahn-teller effect and zero-phonon line isotope shifts of transition metals in II–VI compounds

Highly resolved spectra of transition metal ions in II–VI compounds show extremely narrow zero-phonon lines to that isotope effects can be observed. An adequate description of the observed fine structures requires the inclusion of an intermediate Jahn-Teller effect using local vibrational T 2 modes. The observation of different isotope splittings at Ni impurities in CdS leads to the assumption that different local vibrational modes are coupled to the electronic states of that system and that the local vibrational modes have different dependencies on the mass of the impurity. The calculated energy shifts are in agreement with the observed isotope shifts of natural and enriched Ni and Cu doped II–VI compounds. The influence of uniaxial stress, magnetic field and temperature on the isotope shifts is also investigated.

Optimization of the electron spin resonance spectrometric determination of transition-metal ions by variation of temperature

The effect of variation in temperature on the first-derivative electron spin resonance spectra of transition metal ions in aqueous solution is reported. For the aquo ions of Mn(II), Cr(III), Fe(III) and vanadyl, and for hexafluoroferrate(III), an increase in temperature results in a decrease in line width with a concomitant increase in signal amplitude. In contrast, [Cu(H 2O) 6] 2+ and [Ti (H 2O) 4F 2] + show an increase in line width and a marked decrease in derivative amplitude as the temperature is raised. Consequently, the choice of the optimum temperature for each system results in greatly improved sensitivity and lower limits of detection. Recording spectra at more than one temperature is also useful for detecting a given metal ion in a multicomponent system that has overlapping resonance lines.

Linear representations of an empirical correlation energy correction for transition-metal ions

The empirical correlation energy correction (CEC) introduced by Pueyo and Richardson (J. Chem. Phys. 67, 3577 (1977)) to improve the theoretical calculation of the d-d spectra of transition-metal ions in ionic crystals has been analyzed. The contribution of relaxation energies and basis effects to this correction has been discussed by using SCF and frozen-orbital values computed with different basis sets. The CEC is not always a uniformly increasing function of the atomic number of the ion due to the presence of factors other than correlation energy in this correction. A search has been conducted to examine the possible relations between the CEC and the total quantum numbers of the multiplets. Linear expression in these numbers, analogous to those in atomic spectroscopy, describe the CEC with rather large deviations. The more accurate relation of this type is that involving the orbital and spin quantum numbers and Racah’s seniority number. As expected, this quantity increases with the number of the d electrons, being linear in the number of pairs. The CEC has been, then, represented by means of linear equations in pair-correlation terms. Two models are proposed for obtaining these energies. Results of this calculation suggest that the pair energy associated to the distributions with equal values of the mi quantum numbers could be the more significant part of the CEC.

Vibronic intensities in the electronic spectra of transition metal ions

Vibronic intensities in the electronic spectra of transition metal ions

Electronic spectra of transition metal ions in gel-derived and melt-derived glasses

The absorption spectra of 3d transition elements Cr, Mn, Fe, Co, Ni and Cu were studied in SiO 2R m O n compositions (R: a transition element), which were prepared at 500°C as coating films through the sol-gel process from a solution consisting of Si(OC 2H 5) 4, H 2O, HCl and the nitrate of a transition metal. Generally speaking, the characteristic features of the peaks corresponding to a particular valence and coordination state of an element were similar to those reported for silica glass prepared at a high temperature of 1450°C, although the concentration of the particular valence and coordination state was not equal. This indicates that the SiO 2 network similar to that prepared at high temperatures is already constructed at low temperatures around 500°C. The oxidation state of copper in glasses prepared or treated in air atmosphere was studied with melt-derived silicate and gel-derived silica glasses by measuring the optical absorption due to Cu 2+ ions and making chemical analysis. It has been shown that the redox equilibrium of copper in glass shifts towards the higher valence state as the temperature decreases in the wide temperature range from about 1550°C to 500°C and that at least a portion of the copper is present as Cu 2+ ions in SiO 2 glass prepared at low temperatures up to about 500°C.

Linear expansion of the eigenvalues of a Hermitian matrix and its application to the analysis of the electronic spectra of 3 d ions in crystals

It is shown that the eigenvalues E i of a Hermitian matrix H with matrix elements H ij = Σ k A k ij a k , where A k ij are known numbers and a k a set of parameters, can be exactly expanded as E i = Σ k( ∂E i ∂a k )a k . This property is applied to the analysis of the optical spectra of transition metal ions in crystals proposed by L. Pueyo, M. Bermejo, and J. W. Richardson ( J. Solid State Chem. 31, 217, 1980), and it is shown that this method represents the best fit of the Hamiltonian eigenvalues to the observed (or calculated) spectrum. Further advantages of using this property, in connection with the spectral analysis, are the minimization of the errors associated with the numerical approximations and a reduction in computer time. In the molecular orbital calculation of the optical or uv spectra of these systems, this linear expansion of the eigenvalues give a detailed interpretation of the improvements produced by refined calculations, such as those including configuration interaction. In particular, the changes in one-electron energy and in open-shell repulsion interactions associated with the refinement can be clearly and easily formulated. As examples, the computed spectra of CrF 4− 6 and CrF 3− 6 are discussed.

Vibronic intensities in the electronic spectra of transition metal ions

The relative vibronic intensities of the vibronic orgins due to the three odd parity vibrational modes have been calculated for the 2 Eg ↔4 A 2g transition of the octahedral MnF6 2- ion using a ligand polarization model. It is shown that within this model the relative intensities of the vibronic origins depend only on the vibrational force field and numerical results for six force fields are presented. The absolute intensities depend strongly on the assumed metal radial functions but using functions appropriate to Mn3+ or Mn4+ fair agreement with experiment is obtained. The combination of the previously calculated crystal field vibronic intensities with these ligand polarization intensities is considered. Cross terms between the two contributions are important, especially if closure is employed in the crystal field calculation.

Vibronic intensities in the electronic spectra of transition metal ions

The relative vibronic intensities of the vibronic origins due to the three odd parity vibrational modes have been calculated for the 2 Eg ↔2 A 2g transition of the octahedral MnF6 2- ion, using a crystal field model. Two methods for treating the sum over the intermediate odd parity states are considered, the closure approximation and the single 4 T 2u d 2 p state method. It is shown that in the latter limit the relative vibronic intensities depend only on the vibrational force field whereas using closure there is also some dependence on the radial functions employed. Calculations using six different force fields and several radial functions are presented several of which reproduce the experimental relative intensity for both methods, although there is a strong dependence of the calculated intensity on the force field.

Splitting of 3p Spectra of Transition-Metal Ions in X-Ray Photoemission of VCl3, CrCl3 and CrBr3

X-ray photoemission spectra of the 3 p electrons of transition-metal ions in VCl 3 , CrCl 3 and CrBr 3 have been measured. The results are compared with the existing theoretical spectra calculated on the basis of the ligand field theory. The spectra of V 3+ and Cr 3+ can be explained to some extent by the multiplet splitting due to the interaction between 3 d electrons and a 3 p hole in the crystal field. In contrast with the case of Ni 2+ , the values of the Slater-Condon parameters for V 3+ and Cr 3+ in their halides are nearly equal to those of the free ions and the effect of the hole-induced covalency has little influence on the spectra.

Phonon density of states deduced from the fine structure of an electronic transition at an impurity ion

The optical spectra of transition metal ions substituted in non-magnetic host lattices show a complicated fine structure caused by the coupling with non-localized vibrational modes of the host lattice. The theory of this effect is presented. It is shown that the observed vibronic structure images the phonon density of states in the Brillouin zone, modified by matrix elements and selection rules of the electronic transition. The spectra of Ni 2+( 3A 2g→ 1E g) and Co 2+( 4T 1g→ 2T 1g) substituted in CdI 2 are used to deduce the maxima of the phonon density of states of CdI 2 and to estimate the phonon dispersion curves. The spectra show the influence of the strong anisotropy of the lattice vibrations of these layered materials.

Electrode Potentials, Electronic Spectra and Oxidation State Stabilities

E.m.f. series and the electronic spectra of transition metal ions, particularly Co2+ and Ni2+, permit one to draw conclusions concerning the structure of molten salt solvents and the oxidation state stabilities of metal compounds dissolved in them. A few electrode potential measurements, current-voltage scans and color comparisons enable one to characterize a new solvent well.

Charge Transfer Spectra of Transition Metal Ions in Cadmium Halide Lattices

AbstractThe near ultraviolet spectra of CdCl2 and CdBr2 crystals doped with Fe2+, Co2+, and Ni2+ at 4.2 K and the magnetic circular dichroism spectra of Fe2+, Co2+, and Ni2+ doped in CdBr2 are measured. The intense bands observèd in the spectra are assigned to charge transfer transitions between the halide ions of the crystal lattice and the 3d orbitals of the guest ion.

The effect of exchange coupling on the spectra of transition metal ions. The crystal structure and optical spectrum of CsCrBr3

The effect of exchange coupling on the spectra of transition metal ions. The crystal structure and optical spectrum of CsCrBr₃