Theoretical investigation of the spin-Hamiltonian parameters and optical spectra for the doped Cu2+ in ZnCdO nanopowder

The spin-Hamiltonian (SH) parameters (g factors g_||, g_⊥ and hyperfine structure constants A_||, A_⊥) and d–d transitions for ZnCdO:Cu²⁺ are calculated based on the perturbation formulas for a 3d⁹ ion in tetragonally elongated octahedra. Good agreement between the calculated results (four SH parameters and three optical absorption bands) and the experimental results can be obtained. Since the SH parameters are sensitive to the local structure of a paramagnetic impurity center, the tetragonal distortion (characterized by the relative elongation ratio ρ ≈ 3.5% along the C₄ axis) of the impurity center due to the Jahn–Teller effect is also acquired from the calculations. The negative and positive signs of hyperfine structure constants A_|| and A_⊥ for ZnCdO:Cu²⁺, respectively, are also suggested in the discussions.     

EPR and optical absorption studies of Cu and VO impurities in diammonium d-tartarate single crystal grown in ammonium dihydrogen phosphate buffer

The study is extended by growing the Cu²⁺ and VO²⁺ doped diammmonium d-tartarate single crystal in buffered solution with different pH values and the results are discussed referring to the color center forming property by means of transition metal impurities which are stable point defects. XRD study shows that the crystals grown in ammonium dihydrogen phosphate buffer with pH value of 5.9 which is smaller than that of water, the monoclinic symmetry of the crystal changes to orthorhombic and the number of paramagnetic centers is doubled. The spin-Hamiltonian parameters are determined and the ground state wave functions of Cu²⁺ ions are constructed. The optical absorption spectrum of both Cu²⁺ and VO²⁺ doped single crystals show three absorption bands corresponding to the splitting of d orbitals of metal ions in octahedral environment with tetragonal distorsion. Two of the bands lie in visible range and third one lies in infrared region.     

Obtaining the Optical and EPR Parameters of Vanadyl-Doped Sodium Dihydrogen Phosphate Dihydrate Powders by Experimental and Theoretical Methods

In this study, the spin-Hamiltonian parameters (g and A), molecular orbital coefficients, and other spectroscopic properties of vanadyl-doped sodium dihydrogen phosphate dihydrate (NaH₂PO₄·2H₂O) powders have been investigated by experimental and theoretical methods, including electron paramagnetic resonance (EPR) and optical absorption spectroscopies. The results show axially symmetric crystalline field around VO²⁺ ion. The optical absorption spectra exhibit three characteristic bands of VO²⁺ ions in tetragonal symmetry. EPR and optical data were used in a complementary way to calculate spin-Hamiltonian parameters and molecular orbital coefficients. The octahedral and the tetragonal field parameters were theoretically calculated on the basis of crystal field theory. These parameters were used to determine various bonding parameters which characterize the nature of bonding in the complex. The theoretical results are supported by experimental results.     

EPR and optical investigation of VO(II) in Zn(C3H3O4)2(H2O)2 single crystals: An interstitial site

EPR spectroscopic investigations on single crystals of diaquabis[malonato(1-)-κ²O,O′] zinc(II) doped with VO(II) ion have been carried out at X-band frequencies and at 300 K. The single crystal, rotated along the three mutually orthogonally axes, has yielded spin-Hamiltonian parameters g and A as: g_xx=1.980, g_yy=1.972, g_zz=1.937 and A_xx=8.4, A_yy=6.1, A_zz=18.1 mT, respectively. These spin-Hamiltonian parameters reflect a slight deviation from axial symmetry to rhombic, which is elucidated by the interstitial occupation of vanadyl ions. The isofrequency plots and powder EPR spectrum have been simulated. The percentage of metal-oxygen bond has been estimated. The optical absorption spectrum exhibits four bands at 257, 592, 720 and 764 nm suggesting a C_4v symmetry. The admixture coefficients and bonding parameters have also been calculated by collaborating EPR data with optical data.     

Spectral studies on Cu ions in sodium–lead borophosphate glasses

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of Cu²⁺ ions in sodium–lead borophosphate glasses doped with different concentrations of Cu²⁺ ions have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in sodium–lead borophosphate glasses are present in octahedral sites with tetragonal distortion. The optical absorption spectra of all the glass samples show a single broad band, which has been assigned to the ²B_1g→²B_2g transition of Cu²⁺ ions. The optical band gap energy (E_opt) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. The emission bands observed in the ultraviolet and blue region are attributed to 3d⁹4s→3d¹⁰ triplet transition in Cu⁺ ion. The FT-IR spectra show that the glass system contains BO₃, BO₄ and PO₄ structural units.     

Theoretical explanation of absorption spectra and ESR parameters of Cu in shattuckite

The optical absorption spectra and electronic spin resonance parameters (ESR g factors g_‖, g_⊥ and hyperfine structure constants A_‖, A_⊥) for Cu²⁺ in shattuckite crystal are calculated from the two spin–orbital coupling parameters model, high-order perturbation formulas and complete diagonalization (of energy matrix) method (CDM) of 3d⁹ ion in tetragonal symmetry. The calculated results are in good agreement with the observed values. Since the ESR parameters are sensitive to the local structure of a paramagnetic impurity center, the defect structure of Cu²⁺ center in shattuckite crystal is estimated. The results are discussed.     

EPR and optical studies on transition metal doped LiRbB4O7 glasses

Electron paramagnetic resonance and optical investigations of copper and chromium doped LiRbB₄O₇ glasses are carried out. From the results and discussions, it is predicted that both the transition metal ions exhibit octahedral environment. In the case of Cr³⁺, the site symmetry is near octahedral, whereas in the case of Cu²⁺, it is tetragonally distorted octahedral environment. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. The bonding parameters are suggesting ionic.     

EPR and optical studies of Cu doped ammonium dihydrogen phosphate single crystals

Electron paramagnetic resonance (EPR) spectra of Cu²⁺ ion in ammonium dihydrogen phosphate are studied at liquid nitrogen temperature (77 K). Four magnetically inequivalent Cu²⁺ sites in the lattice are identified. The angular variation spectra of the crystal in the three orthogonal planes indicate that the paramagnetic impurity, Cu²⁺ enters the lattice substitutionally in place of NH₄⁺ ions. The spin Hamiltonian parameters are determined with the fitting of spectra to rhombic symmetry crystalline field. The ground state wave function of Cu²⁺ ion is constructed and found to be predominantly |x²-y²〉. The cubic field parameter (Dq) and tetragonal parameters (Ds and Dt) are determined from optical spectra at room temperature. By correlating EPR and optical absorption spectra, the bonding coefficients are calculated and nature of bonding of metal ion with different ligands in the crystal is discussed.     

EPR parameters and defect structures of the off-center Ti ion on the Sr site in neutron-irradiated SrTiO3 crystal

The EPR parameters (g factors and hyperfine structure constants A) for the tetragonal Ti³⁺ center in cubic phase and the rhombic Ti³⁺ center in tetragonal phase in the neutron-irradiated SrTiO₃ crystals are calculated from the third-order perturbation formulas of EPR parameters for d¹ ions. These low-symmetry Ti³⁺ centers in both phases of SrTiO₃ are due to the Ti³⁺ ion at “off center” on the Sr²⁺ site. From the calculation, the defect models (including the direction and magnitude of the Ti³⁺ off-center displacement) of the two Ti³⁺ centers in SrTiO₃ are estimated and the EPR parameters of both Ti³⁺ centers are reasonably explained on the basis of the defect models. The results are discussed.     

Synthesis, crystal structure, Cu doped EPR, thermal and voltammetric studies of [Ni(isonicotinamide)2(H2O)4]·(sac)2 single crystal

The single crystal of [Ni(ina)₂(H₂O)₄]·(sac)₂, (NINS), (ina is isonicotinamide and sac is saccharinate) complex has been prepared and its structural, spectroscopic and thermal properties have been determined. The title complex crystallizes in monoclinic system with space group P2₁/c, Z=2. The octahedral Ni(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate ina ligands through the ring nitrogen and four aqua ligands to form discrete [Ni(ina)₂(H₂O)₄] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bands. The magnetic environment of copper(II) doped NINS crystal has also been identified by electron paramagnetic resonance (EPR) technique. The g and A values of Cu²⁺ doped NINS single crystal were calculated from the EPR spectra recorded in three mutually perpendicular planes. These values indicated that the paramagnetic centre has a rhombic symmetry with the Cu²⁺ ion having distorted octahedral environment. The complex exhibits only metal centred electroactivity in the potential range of −2.00, 1.25 V versus Ag/AgCl reference electrode.     

A complex first-principles study of the L2,3-edge XANES spectra and crystal field effects for divalent 3d ions in cubic ZnS

A detailed first-principles analysis of the L_2,3 X-ray absorption near edge structure (XANES) spectra, crystal field strength 10Dq, covalent effects and molecular orbitals (MO) position for all divalent 3d ions from Sc²⁺ to Cu²⁺ in cubic ZnS is performed in the present paper. The calculations were done in the framework of the first-principles fully relativistic discrete variational multi-electron (DVME) based on numerical solution of the Dirac equation with the local density approximation. As a result of the performed calculations, the L_2,3 XANES spectra for all considered ions were calculated and assigned in terms of the electron configurations involved into the absorption transitions; fairly good agreement with available experimental data for Ti²⁺, Mn²⁺, Fe²⁺, Co²⁺ and Ni²⁺ is demonstrated. Experimental XANES spectra for Sc²⁺, V²⁺, Cr²⁺, Cu²⁺ not reported previously were also calculated for the sake of completeness of the present study to enable a systematic analysis of all calculated results for the whole series considered. It was shown that the L₃ and L₂ bands shift to the higher energies on increasing a 3d ion atomic number. In addition, the separation between the L₃ and L₂ bands, the crystal field strength 10Dq and mixture between the 3d ion and sulfur wave functions increase along the considered series, from Sc²⁺ to Cu²⁺. On the other hand, all orbitals of the 3d ions systematically lower down in the same direction. The above formulated trends were confirmed by the experimental data on the crystal field splittings and nephelauxetic effect.     

Theoretical investigations of the spin Hamiltonian parameters and local tetragonal distortions for Cu2+ in crystalline and amorphous TeO2 and GeO2

The spin Hamiltonian parameters (i.e., anisotropic g factors and hyperfine structure constants) and local tetragonal distortions for Cu²⁺ in crystalline and amorphous TeO₂ and GeO₂ are theoretically investigated using the high-order perturbation formulas of these parameters for a tetragonally elongated octahedral 3d⁹ cluster. The impurity Cu²⁺ occupying the octahedral sites are found to experience the relative tetragonal elongation ratios of about 11.4% and 9.5% for crystalline TeO₂ and GeO₂ and 10.8% and 6.6% for amorphous TeO₂ and GeO₂, respectively, along the C₄ axis due to the Jahn–Teller effect. This reveals the larger tetragonal elongation distortions for the Cu²⁺ centres in crystalline than amorphous systems (especially TeO₂). The theoretical spin Hamiltonian parameters show good agreement with the experimental data. The results are discussed.     

Investigation of the local structure of Cu2+ ions doped in alkali lead tetraborate glasses by their electron paramagnetic resonance and optical spectra

The local structure of the Cu²⁺ centers in alkali lead tetraborate glasses was theoretically studied based on the optical spectra data and high-order perturbation formulas of the spin Hamiltonian parameters (electron paramagnetic resonance g factors g_∥, g_⊥ and hyperfine structure constants A_∥, A_⊥) for a 3d⁹ ion in a tetragonally elongated octahedron. In these formulas, the relative axial elongation of the ligand O^2? octahedron around the Cu²⁺ due to the Jahn–Teller effect is taken into account by considering the contributions to the g factors from the tetragonal distortion which is characterized by the tetragonal crystal-field parameters Ds and Dt. From the calculations, the ligand O^2? octahedral around Cu²⁺ is determined to suffer about 19.2% relative elongation along the C₄ axis of the alkali lead tetraborate glass system, and a negative sign for A_∥ and a positive sign for A_⊥ for these Cu²⁺ centers are suggested in the discussion.     

Synthesis, crystal structure, Cu doped EPR and voltammetric studies of bis[N-(2-hydroxyethyl)ethylenediamine]zinc(II) squarate monohydrate

Crystal structure of [Zn(hydet-en)₂]·C₄O₄·H₂O (ZHES) (hydet-en is N-(2-hydroxyethyl)ethylenediamine) complex has been synthesized and characterized by analytical, spectroscopic (IR, UV/Vis) and voltammetric techniques. After doping Cu²⁺ ion, its magnetic environment has been identified by electron paramagnetic resonance (EPR) technique. The title complex crystalizes in monoclinic system with space group P2₁/c and with Z=4. Each hydet-en ligand acts as a tridentate ligand through the two N atoms and the hydroxyl O atom, resulting in a six coordinate Zn(II) ion. The EPR spectra were recorded in three perpendicular planes of Cu²⁺ doped ZHES single crystal. The calculated g and A values indicated that the paramagnetic center is rhombic symmetry with the Cu²⁺ ion having distorted octahedral environment. The molecular orbital bond coefficients of the Cu(II) ion in d⁹ state is also calculated by using EPR and optical absorption parameters. The dianion SQ²⁻ is oxidized reversibly in two consecutive steps to the corresponding radical monoanion and neutral form.     

Spectroscopical splitting of Cu ion energy levels in magnesium lead fluoro silicate glasses

Homogeneous 40.0 MgO-(10-x) PbF₂-50.0 SiO₂: x CuO glasses were prepared using melt-quenching technique under controlled conditions. Spectroscopic studies (UV-vis absorption, ESR, FT-IR) are carried out for these glasses. One broad characteristic visible absorption band is observed around 700-850 nm in these glasses, the optical band gap decreases as the content of the CuO increases in the glass network up to 0.7 mol % then reversal trend is observed. ESR spectra of all these glasses show resonance peaks characteristic of Cu²⁺ ions and hyperfine splitting is resolved with increasing the CuO content in the glass network. From the observed ESR spectra, the spin-Hamiltonian parameters have been evaluated and indicate that Cu²⁺ ions have octahedral coordination with a strong tetragonal distortion in these glasses. By correlating ESR and optical absorption data, the molecular orbital coefficients have been evaluated. FT-IR spectra give important information about the nature of bonds in the glass matrix. The density of the glasses is also measured and is found to decrease with the increase CuO contents in the glass matrix. The physical parameters along with spectroscopic parameters are measured.     

EPR g factors and tetragonal distortion for the isoelectronic Ni and Cu centers in the CuGaSe2 crystal

The EPR g factors, g_|| and g_⊥, for the isoelectronic 3d⁹ ions Ni⁺ and Cu²⁺ at the tetragonal Cu⁺ site of the CuGaSe₂ crystal are calculated from the high-order perturbation formulas based on a two-spin-orbit-parameter model. In the model, both the contributions to g factors from the spin-orbit parameter of central 3d⁹ ion and that of ligand ion are contained. The calculated results appear to be consistent with the experimental values. The tetragonal distortions (characterized by θ−θ₀, where θ is the angle between the metal-ligand bond and C₄ axis, and θ₀≈54.74° is the same angle in cubic symmetry) of Ni⁺ and Cu²⁺ centers, which are different from the corresponding angle in the host CuGaSe₂ crystal and from impurity to impurity, are obtained from the calculations. The difference of the sign of g_||−g_⊥ between the isoelectronic Ni⁺ and Cu²⁺ centers is found to be due to the different tetragonal distortions of both centers in the CuGaSe₂ crystal.     

Absorption spectra of Cu2+ in azurite

EPR and optical absorption studies in azurite have been carried out at room and low temperatures. The EPR spectrum reveals that the ground state for Cu²⁺ ion is ²B₁. Peak to peak linewidth of EPR spectrum is calculated (ΔH_p = 76 G) and found to be close with the observed value. The Cu²⁺ ion situated in D_4h symmetry with spin-orbit interaction exhibits bands at 11,806, 16,484, 17,952 and 19,793 cm^?1. The tetragonal field parameters are calculated to be Ds = ? 3364 cm^?1 and Dt = ? 604 cm^?1. The crystal field splitting parameter is found to be Dq = ? 1175 cm^?1.     

Theoretical analysis of spin-Hamiltonian parameters for the rhombic Cu2+ centres in CuGaSe2 crystals

The spin-Hamiltonian parameters (g factors g_i and hyperfine structure constants A_i, where i = x, y, z) of the rhombic Cu²⁺ centres in the CuGaSe₂ crystal are determined from the high-order perturbation formulae based on the cluster approach (sometimes also called two-spin-orbit parameter model). In the studies, some parameters in the analysis of g factors for the same centre within the tetragonal symmetry approximation in the previous paper are used, and the parameter due to the perturbation of rhombic crystal field caused by a charge compensator at, e.g., [110] direction are considered. As the result of a fitting process, the determined spin-Hamiltonian parameters are in reasonable agreement with the experimental values. The results are discussed.     

Absorption spectra of Cu2+ in shattuckite and plancheite

Optical and EPR measurements are carried out on shattuckite, a copper bearing silicate. The EPR spectrum observed at 120 K reveales hyperfine structure for parallel and perpendicular components. The measured values are g6 = 2.402, g⊥ = 2.038, A6 = 112 × 10^-4 cm^-1 and A⊥ = 49.5 × 10^-4 cm^-1 and they indicate a tetragonal distortion for the Cu²⁺ion. Further, the constants P and K are evaluated and found to be 0.014 cm^-1 and 0.0112 respectively. The bands observed at 8160, 13330 and 16125 cm^-1 are assigned to the electronic states of Cu²⁺, in a crystal field subjected to tetragonal (C_4V) distortion. The crystal field parameters evaluated are Dq = -1333, Ds = -1565 and Dt = -380 cm^-1. Correlating the EPR and optical data, the orbital reduction factors are calculated as k6 = 0.89 and k⊥ = 0.59. It is confirmed from EPR and optical studies that the Cu²⁺ion in shattuckite is sited in an elongated octahedron. Similar studies are carried out for plancheite. The observed optical absorption spectrum of plancheite is attributed to Cu²⁺ sited in an elongated octahedron and tetragonal field parameters are evaluated.     

Nephelauxetic effect for the isoelectronic 3d-ions (Cr, Mn, Fe) in SrTiO3

The exchange charge model of crystal field theory has been used to analyze systematically the ground state absorption spectra of isoelectronic Cr³⁺, Mn⁴⁺, and Fe⁵⁺ ions in an octahedral coordination in the SrTiO₃ crystal. The parameters of the crystal field acting on the valence electrons of impurity ions are calculated from the available crystal structure data. A special attention is paid to the analysis of dependencies of the crystal field invariants and covalence effects on the impurity ion. It is shown numerically that the covalence effects between the above impurity ions and ligands increase with an increase of the 3d-ion oxidation state.