Investigations of the optical spectra and EPR parameters in CaWO4:Yb3+

In this paper, we calculate the optical spectra data (crystal-field energy levels), the electron paramagnetic resonance (EPR) g factors gparallel, gperpendicular of Yb3+ and hyperfine structure constants Aparallel, Aperpendicular of 171Yb3+ and 173Yb3+ isotopes in CaWO4 crystal in a unified way from the crystal-field theory. All the calculated results are in good agreement with the experimental values. The signs of Aparallel and Aperpendicular for both isotopes 171Yb3+ and 173Yb3+ are suggested.     

EPR and optical absorption studies on VO2+ ions in L-asparagine monohydrate single crystals

X-Band electron paramagnetic resonance (EPR) studies of VO(2+) ions in l-asparagine monohydrate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of two magnetically inequivalent VO(2+) sites. Both the vanadyl complexes are found to take up interstitial position. The angular variation of the EPR spectra in three planes ab, bc and ca are used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are, site I: g(x)=1.9633, g(y)=2.0274, g(z)=1.9797, A(x)=88, A(y)=61, A(z)=161x10(-4)cm(-1); site II: g(x)=1.9627, g(y)=1.9880, g(z)=1.9425, A(x)=90, A(y)=66, A(z)=167x10(-4)cm(-1). The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. By correlating EPR and optical data different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.     

EPR studies of VO2+ ions in kainite single crystals

Electron paramagnetic resonance (EPR) spectra of VO2+ ions doped in Kainite (a mineral salt) single crystals and powder were recorded at room temperature at X-band frequencies.The angular variation studies of the spectra indicate that the VO2+ ion enters Mg2+ ion site substitutionally. The principal values of g and A-tensors were determined from the EPR spectral studies. Using these EPR parameters, the molecular orbital bonding parameters of VO2+ ion in the lattice have been evaluated and discussed.     

Investigations of the optical spectra and EPR g factors for the tetragonal Cu2+ centers in trigonal ZnCO3 crystal

Two distinctive theoretical methods, the complete diagonalization (of energy matrix) method (CDM) and the perturbation theory method (PTM), are employed to calculate the optical band positions and EPR g factors g_//, g_⊥ for the tetragonal Cu²⁺ centers in trigonal ZnCO₃ crystal. The results from the two methods coincide and are also in good agreement with the experimental values. So both the CDM and PTM are adequate for the investigations of optical and EPR data for d⁹ ions in crystals. The tetragonal distortion due to the static Jahn–Teller effect for the tetragonal Cu²⁺ centers in trigonal Zn²⁺ site of ZnCO₃ is also acquired from the calculations. The results are discussed.     

Studies of EPR parameters for Mn5+ -doped Li3PO4 and Li3VO4 crystals

The EPR parameters (zero-field splitting D and g factors g parallel, g perpendicular) of Mn5+ -doped Li3PO4 and Li3VO4 crystals are calculated from the complete high-order perturbation formulas based on a molecular orbital scheme for a 3d2 ion in tetragonal MX4 clusters. These formulas include not only the contribution coming from crystal-field excitations, but also that arising from charge-transfer excitations (which is discarded in crystal field theory). The calculated results are in reasonable agreement with the observed values. The contributions to EPR parameters coming from the charge-transfer excitations are comparable with those arising from the crystal-field excitations. It appears that for a high valence state 3dn ion in crystals, the reasonable explanations of EPR parameters should take the contributions due to both crystal-field and charge-transfer excitations into account.     

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 spectra of Cu2+ and VO2+ ions in ammonium hydrogen oxalate hemihydrate [(NH4)HC2O4 . (1/2)H2O] single crystals

Cu(2+) and VO(2+) doped ammonium hydrogen oxalate hemihydrate, [(NH(4))HC(2)O(4) . (1/2)H(2)O], single crystals have been studied at room temperature and at 113K in three mutually perpendicular planes. Both ions yield unexpectedly large number of lines. The calculated results of the Cu(2+) and VO(2+) doped in [(NH(4))HC(2)O(4) . (1/2)H(2)O] indicate that both ions substitute with the NH(4)(+) ion in the structure. The EPR spectra of Cu(2+) ions are characteristic of tetragonally elongated octahedral site and the spectra of VO(2+) are characteristic of tetragonally compressed complex. The angular variation of the EPR spectra has shown that two different Cu(2+) and VO(2+) complexes are located in different chemical environments, and each environment contains two magnetically inequivalent Cu(2+) and VO(2+) sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The principal g and the hyperfine (A) values of both ions are determined.     

The thermodynamic behaviour of Sm3+-doped LiKSO4 crystals

The influence of the point defects introduced by means of Sm³⁺ on the thermal properties of LiKSO₄ crystals was studied in the vicinity of the high-temperature phase at 708 and 940 K. The temperature dependence of the specific heat was found to vary monotonously with the Sm³⁺content, while the first transition temperature was unchanged. The change in the value of the specific heat was attributed to the correlation between the defect-defect interaction and the presence of internal local strain generated inside the crystal. The variation of the excess specific heat with the reduced temperature obeys the 3d Ising model.     

7Li Spin-flip satellites in the EPR sectra of NH3+ -doped LiKSO4

EPR spectra of lithium potassium sulfate doped with NH₃⁺ have been recorded at 9.05 GHz. A pair of satellites can be seen symmetrically situated on either side of the main lines. The separation of the satellite lines from the main line corresponds to the ⁷Li NMR frequency. The distance of the interacting ⁷Li nucleus from the unpaired electron in NH₃⁺ is estimated to be 3.29 Å.     

Investigations of the EPR parameters for Sm3+ ions in KY3F10 and LiYF4 crystals

In this paper, we calculate the EPR parameters (g factors g parallel, g perpendicular and hyperfine structure constants A parallel, A perpendicular) of rare earth ion Sm3+ in fluoride crystals KY3F10 and LiYF4 from the perturbation formulas of EPR parameters for a 4f5 ion in tetragonal symmetry. In these formulas, the crystal-field J-mixing of the first and second excited-state multiplets 6H(7/2) and 6H(9/2) into the ground state multiplet 6H(5/2), the mixtures among the states with the same J value via spin-orbit coupling interaction and the interactions between the ground Kramers doublet Gammagamma and the same irreducible representation as Gammagamma in other 11 Kramers doublets Gammax within 6HJ (J=5/2, 7/2, 9/2) states via crystal-field and orbital angular momentum (or hyperfine structure) are considered. The calculated results (which are in agreement with the observed values) 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.     

An EPR and optical absorption study of VO2+ ions in di-ammonium hydrogen citrate [(NH4)2C6H6O7] single crystals

Single crystal and powder EPR studies of VO2+ doped di-ammonium hydrogen citrate [(NH4)2C6H6O7] are carried out at room temperature. The angular variation of the EPR spectra show three different VO2+ complexes that are located in different chemical environment, and each environment contains two magnetically inequivalent VO2+ sites in distinct orientations occupying substitutional positions in the lattice. Crystalline field around the VO2+ ion is nearly axial. The optical absorption spectrum shows two bands centred at 16,949 and 12,345cm(-1). Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed.     

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.     

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.     

EPR of VO2+ in double format, Ba2Zn(HCOO)6(H2O)4 single crystals

VO(2+) doped single crystal of Ba(2)Zn(HCOO)(6)(H2O)(4) (BZFA) were investigated using electron paramagnetic resonance (EPR) technique at ambient temperature. Detailed investigation of EPR spectra indicated that the VO(2+) substitutes the Zn(2+) in the structure. The sites with different orientations were observed for VO(2+) in Ba(2)Zn(HCOO)(6)(H2O)(4).single crystal, but the only intense site among these sites was evaluated to obtain spin-Hamiltonian parameters, which are the principal axis values of the g and the hyperfine tensors. The covalent bonding parameter for VO(2+) and Fermi contact term were calculated using the spin-Hamiltonian parameters.     

EPR and optical absorption studies of VO2+ doped L-arginine phosphate monohydrate single crystals--part I.

The electron paramagnetic resonance (EPR) studies on VO2+ doped L-arginine phosphate monohydrate (LAP) single crystals at room temperature at X-band frequencies reveal the presence of two magnetically inequivalent VO2+ sites occupying interstitial positions in the lattice with fixed orientations and show very high angular dependence. The principal values of the g and A tensors indicate that the electrostatic field around the VO2+ ion is rhombic. The optical absorption spectra at room temperature show four absorption bands at 16155, 14775, 10928 and 10526 cm(-1), characteristic of rhombic symmetry. From EPR and optical absorption data, the molecular orbital bonding coefficients (beta2, epsilon2, P and k) and the crystal field parameters have been evaluated.     

Investigations of the EPR g factors and hyperfine structure constants for two trigonal Co2+ centers in Al2O3 crystals

The EPR g factors gparallel, gperpendicular and the hyperfine structure constants Aparallel, Aperpendicular for two trigonal Co2+ centers (i.e. Co2+(I) center at the substitutional site and Co2+(II) center at the interstitial site) in Al2O3 crystals are calculated from the second-order perturbation formulas based on the cluster approach. In these formulas, the contributions to EPR parameters from both the spin-orbit coupling parameter of central 3dn ion and that of ligand are included. The calculated results are in reasonable agreement with the observed values. Based on the calculations, the defect structures of both Co2+ centers in Al2O3 crystals are obtained and the negative sign of Aparallel for Co2+(I) center is suggested. The results are discussed.     

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.