EPR and optical absorption studies of vanadyl impurity in lithium hydrogen oxalate single crystal

Electron paramagnetic resonance (EPR) and optical absorption studies of vanadyl ions in lithium hydrogen oxalate monohydrate single crystal and powder are reported at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes, $a{b}^1$, $b^1{c}^1$ and $a{c}^1$ indicate four different vanadyl complexes. The detailed investigation of EPR spectra indicates that one of the VO^{2 +} sites (the intense one) may enter the lattice substitutionally and the other three occupy the interstitial positions. From the angular variation, the spin Hamiltonian parameters are evaluated and discussed. The optical absorption spectrum shows four bands. From the optical and EPR data, various bonding parameters are determined and the nature of bonding in the crystal is discussed.     

EPR and optical absorption studies on VO ions in zinc lactate trihydrate

EPR and optical absorption studies of VO²⁺-doped zinc lactate trihydrate single crystals are done at room temperature. The EPR spectra of VO²⁺ are characteristic of tetragonally compressed octahedral site. The angular variation of the EPR spectra shows single site occupying interstitial position in the lattice. The spin Hamiltonian parameters are evaluated as g_x=1.9771, g_y=2.0229, g_z=1.9236 and A_x=76, A_y=104, A_z=197 (×10⁻⁴) cm⁻¹. Using these parameters and optical absorption data various bonding parameters are determined and the nature of bonding in the complex is discussed.     

EPR and optical absorption study of Cr doped diammonium hexaaqua magnesium sulphate single crystal

EPR measurements of Cr³⁺ doped diammonium hexaaqua magnesium sulphate single crystals are made at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular orientations. The value of g=1.9763±0.0002 and are evaluated. On the basis of EPR data the site symmetry of Cr³⁺ in the crystal is discussed. Optical absorption studies of single crystals are also carried out at room temperature. The orbital energies of the chromium ion are estimated from the optical absorption spectrum. The different bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained as B=676,C=3371, , h=1.258 and k=0.21.     

EPR and optical absorption study of Cr-doped ammonium oxalate monohydrate single crystals

The electron paramagnetic resonance (EPR) study of the Cr³⁺-doped ammonium oxalate monohydrate (AOM) single crystal is done at room temperature. Two magnetically inequivalent sites for chromium are observed. The hyperfine structure for Cr⁵³ isotope is also obtained. The spin Hamiltonian parameters are evaluated as: D=(309±2)×10⁻⁴ cm⁻¹, E=(103±2)×10⁻⁴ cm⁻¹, g=1.9820±0.0002, A=(161±2)×10⁻⁴ cm⁻¹ for site I and D=(309±2)×10⁻⁴ cm⁻¹, E=(103±2)×10⁻⁴ cm⁻¹, g=1.9791±0.0002, A=(160±2)×10⁻⁴ cm⁻¹ for site II, respectively. On the basis of EPR data the site symmetry of Cr³⁺ doped single crystal is discussed. The optical absorption spectra are recorded in 195-925 nm wavelength range at room temperature. The energy values of different orbital levels are determined. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The values of different parameters are B=803, C=3531, D_q=2208 cm⁻¹, h=0.59 and k=0.21, where B and C are Racah parameters, D_q is crystal field parameter and h and k are nephelauxetic parameters, respectively.     

EPR and optical absorption study of Cr-doped tetramethyl ammonium cadmium chloride single crystals

EPR study of Cr³⁺-doped tetramethyl cadmium chloride (TMCC) single crystals is carried out at room temperature. The crystal field and spin-Hamiltonian parameters are evaluated from the resonance line positions of different lines observed in the EPR spectra. The g and D parameter values are found to be g=1.9741±0.0002 and D=553±2×10⁻⁴ cm⁻¹, respectively. EPR data indicate that the site symmetry of Cr³⁺ ion in the crystal is distorted octahedron. Cr³⁺ ions enter the lattice substitutionally replacing Cd²⁺ sites and bind to the neighboring extra Cd vacancies necessary for charge compensation. The optical absorption spectra are measured in 195–925 nm wavelength range at room temperature. From optical study the energy values of different orbital levels are estimated. Further, the bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained to be B=722, C=2845, Dq=2043 cm⁻¹, h=1.015 and k=0.21.     

Dynamical Jahn-Teller distortion in single crystals of Cu(II) doped magnesium potassium phosphate hexahydrate: a variable temperature EPR study

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II)-doped magnesium potassium phosphate hexahydrate have been carried out at room temperature. The temperature dependence of g and A values has been obtained for the polycrystalline sample and the ground state is unambiguously identified. These results indicate the existence of a dynamic Jahn-Teller distortion for Cu(II) ion. The g and A tensor direction cosines are evaluated and compared with Mg-O directions, which confirms that Cu(II) enters substitutionally in the lattice.     

Observation of three sites for vanadyl in a biomineral, zinc sodium phosphate hexahydrate: an EPR investigation

Single crystal EPR study has been carried at room temperature for VO(II) doped zinc sodium phosphate hexahydrate. Single crystal rotations in each of the three mutually orthogonal crystallographic planes namely bc, ac, and ab indicate three chemically inequivalent sites, with intensity ratios of 25:13:1. The spin Hamiltonian parameters obtained for the two intense sites are: Site I: g_xx=1.983, g_yy=1.985, g_zz=1.933; A_xx=7.39 mT, A_yy=7.15 mT, A_zz=19.03 mT; Site. II: g_xx=1.985, g_yy=1.985, g_zz=1.937; A_xx=7.36 mT, A_yy=7.25 mT, A_zz=18.67 mT. The two VO bond directions in the two sites are approximately at right angles to each other. The powder spectrum clearly indicates two chemically inequivalent sites, confirming the single crystal analysis. Admixture coefficients, Fermi contact, and dipolar interaction terms have also been evaluated.     

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.     

Single crystal EPR investigation on Mn(II) doped biomineral: cobalt potassium phosphate hexahydrate

Single crystal EPR study of Mn(II) doped in cobalt potassium phosphate hexahydrate has been carried out at room temperature. The impurity shows a 30 line pattern EPR spectra along a particular crystallographic axis suggesting the existence of only one type of impurity in place of Co(II) ion in the host lattice. The spin Hamiltonian parameters have been estimated as: g₁₁=2.011, g₂₂=1.998, g₃₃=1.991, and A₁₁=−8.9, A₂₂=−8.8, A₃₃=−8.4 mT and D₁₁=−15.2, D₂₂=−9.4, D₃₃=24.6 mT, respectively. The sign of A is designated as negative and D as positive. The covalency of metal-oxygen bond has been estimated. The relaxation times, calculated as a function of temperature, indicate spin-lattice relaxation narrowing at room temperature.     

EPR and optical absorption studies of V O ions in L-asparagine monohydrate

Electron paramagnetic resonance (EPR) studies of V O²⁺ ions in L-asparagine monohydrate single crystals are reported at room temperature. It is found that the V O²⁺ ion takes up an interstitial site. The angular variations of the EPR spectra in three mutually perpendicular planes are used to determine the principal g and A values and their direction cosines. The values of g and A parameters are: g_x=1.9011, g_y=2.1008, g_z=1.9891 and A_x=100, A_y=78, A_z=126 (×10⁻⁴) cm⁻¹. The optical absorption spectrum of V O²⁺ ions in L-asparagine monohydrate is also studied at room temperature. The band positions are calculated using the energy expressions and compared with the observed band positions to confirm the transitions. The best-fit values of the crystal field (Dq) and tetragonal (Ds and Dt) parameters are evaluated from the observed band positions.     

Growth, EPR and optical absorption spectra of l-threonine single crystals doped with Cu ions

We investigated the crystal growth, electron paramagnetic resonance (EPR) and optical absorption spectra of l-threonine doped with Cu²⁺. The quality, size and habit of the single crystals grown from aqueous solution by the slow solvent evaporation and by the cooling methods vary when the impurities are introduced during the growth process. The variations with the magnetic field orientation of the EPR spectra of single-crystal samples at room temperature and 9.77 GHz in three crystal planes (ab, bc and ac) show the presence of copper impurities in four symmetry-related sites of the unit cell. These spectra display well resolved hyperfine couplings of the of Cu²⁺ with the I_Cu= of the copper nuclei. Additional hyperfine splittings, well-resolved only for specific orientations of the magnetic field, indicate that the copper impurity ions in the interstitial sites have two N ligands with similar hyperfine couplings. The principal values of the g and A_Cu tensors calculated from the EPR data are g₁=2.051(1), g₂=2.062(2), g₃=2.260(2), A_Cu,1=16.9(5)×10⁻⁴ cm⁻¹, A_Cu,2=21.8(6)×10⁻⁴ cm⁻¹, A_Cu,3=180.0(5)×10⁻⁴ cm⁻¹. The principal directions corresponding to g₃ and to A_Cu,3 are coincident within the experimental errors, reflecting the orientation of the bonding planes of the copper ions in the crystal. The values of the crystal field energies are evaluated from the optical absorption spectrum, and the crystal field and bonding parameters of the Cu impurities in the crystal are calculated and analyzed. The EPR and optical absorption results are discussed in terms of the crystal structure of l-threonine and the electronic structure of the Cu²⁺ ions, and compared with data reported for other systems. The effects of the impurities in the growth and habit of the crystals are also discussed.     

EPR spectra of Fe centers in layered TlGaSe2 single crystal

A single-crystal TlGaSe₂ doped by paramagnetic Fe ions has been studied at room temperature by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe³⁺ ions was observed. The spectra were interpreted to correspond to the transitions among spin multiplet (S=5/2, L=0) of Fe³⁺ ion, which are splitted by the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe³⁺ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe³⁺ site and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of GaSe₄ tetrahedrons, and the rhombic distortion of the CF is caused by the Tl ions located in the trigonal cavities between the tetrahedral complexes.     

EPR and optical study of Mn doped ammonium oxalate monohydrate

Studies on fine and hyperfine structures of paramagnetic resonance spectra in single crystals of Mn²⁺: ammonium oxalate monohydrate are reported. As sufficient numbers of lines were not obtained at room temperature, measurements have been done at liquid nitrogen temperature and at the frequency of X-band. The Mn²⁺ spin Hamiltonian parameters have been evaluated employing a large number of resonant line positions observed for various orientations of the external magnetic field and the surrounding crystalline field has been discussed. The values of the zero field parameters that give good fit to the observed EPR spectra have been evaluated. The values obtained for g, A, B, D, E and a are 2.0002±0.0002, (100±2)×10⁻⁴, (79.5±2)×10⁻⁴, (257±2)×10⁻⁴, (85±2)×10⁻⁴ and (−18±1)×10⁻⁴ cm⁻¹, respectively. The percentage of covalency of the metal-ligand bond is also determined. The optical absorption study has been done at room temperature. The observed bands are assigned as transitions from the ⁶A_1g(S) ground state to various excited quartet levels of Mn²⁺ ion in a cubic crystalline field. The electron repulsion parameters (B and C), the crystal field splitting parameter(Dq) and the Trees correction (α) providing good fit to the observed optical spectra have been estimated and the values obtained for the parameters are B=897, C=2144, Dq=910 and α=76 cm⁻¹.     

Theoretical studies of the optical and EPR spectra for V in Y2O3 crystal

In this paper, we give an alternative suggestion that both the observed optical and electron paramagnetic resonance (EPR) spectra of Yttrium oxide (Y₂O₃):V³⁺ are attributed to V³⁺ ions at the S₆ site of Y₂O₃. This suggestion is different from the opinion in the previous paper that the optical and EPR spectra are attributed to V³⁺ ions at the C₂ and S₆ sites, respectively. From the suggestion, the optical band positions and spin-Hamiltonian parameters are calculated by diagonalizing the complete energy matrix for 3d² ions in trigonal symmetry. The results are in good agreement with the experimental values, suggesting that both the observed optical and EPR spectra in Y₂O₃:V³⁺ may be due to V³⁺ at S₆ site of Y₂O₃ crystal.     

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.     

ESR and optical study of Mn doped potassium hydrogen sulphate

The ESR spectrum of Mn²⁺ doped potassium hydrogen sulphate at liquid nitrogen temperature (77 K) has been analyzed and site of entered Mn²⁺ in the lattice has been discussed. The values of the zero field parameters that give good fit to the observed ESR spectra have been obtained. The obtained g, A, B, D, E and a values are 2.0002, 66×10⁻⁴ cm⁻¹, 26×10⁻⁴ cm⁻¹, 59×10⁻⁴ cm⁻¹, 32×10⁻⁴ cm⁻¹ and −8×10⁻⁴ cm⁻¹, respectively. The percentage of covalency of the metal-ligand bond has also been estimated. From the optical absorption study at room temperature, the distortion has been suggested. The observed bands are assigned as transitions from the ⁶A_1g(S) ground state to various excited quartet levels of Mn²⁺ ion in a cubic crystalline field. The electron repulsion and crystal field parameters B, C, Dq and α providing good fit to the observed optical spectra have been evaluated and the values obtained for the parameters are B=627 cm⁻¹, C=2580 cm⁻¹ , Dq=790 cm⁻¹ and α=76 cm⁻¹.     

The domain structure of ferroelastic BiVO4 crystal studied by Gd EPR

The domain structure of ferroelastic BiVO₄ single crystal has been investigated using the electron paramagnetic resonance (EPR) of the Gd³⁺ ions existing as an impurity in the crystal. Two sets of Gd³⁺ EPR signals were obtained in the crystallographic ca-plane. These two sets of signals originated not from the two kinds of substitutional sites but from the twin-domain structure in the host crystal. It is found that the BiVO₄ crystal investigated with Gd³⁺ EPR has the prominent (W-plane) domain wall. The domain structure is stable in contrast with a previous report by Baran et al. From the observed W-plane of the domain wall, it is suggested that a ferroelastic transition in BiVO₄ is 4/mmm F 2/m instead of 4/m F 2/m. The model of twinning mechanism improved in a previous report by Mn²⁺ EPR is confirmed by Gd³⁺ EPR.     

EPR and optical absorption studies of Cr ions in potassium sodium dl-tartrate tetrahydrate

EPR spectra of Cr³⁺ ions doped in potassium sodium dl-tartrate tetrahydrate single crystals are recorded at 77 K. The spin Hamiltonian and zero field parameters g, |D| and |E| are measured from the resonance lines obtained at various rotations of the magnetic field. The values obtained are: g_x=1.9257±0.0002, g_y=1.9720±0.0002, g_z=2.0102±0.0002, |D|=313±2 (×10⁻⁴) cm⁻¹ and |E|=101±2 (×10⁻⁴) cm⁻¹. From the results of EPR study, the site symmetry of Cr³⁺ ion in the crystal is discussed. The optical absorption at room temperature is also studied. From the observed band positions, the crystal field splitting parameter (D_q) and the Racah inter-electronic repulsion parameters (B and C) are evaluated. The bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed.