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1.
Analysis of the energy-level scheme and absorption spectrum of the Ni2+ ion in MgAl2O4 was performed. The recently developed first-principles approach to the analysis of the absorption spectra of impurity ions in crystals based on the discrete variational multi-electron (DV-ME) method [K. Ogasawara, et al., Phys. Rev. B 64 (2001) 115413) was used in the calculations. The method is based on the numerical solution of the Dirac equation; no phenomenological parameters are used in the calculations. As a result, complete energy-level scheme of Ni2+ and its absorption spectra were calculated, assigned and compared with experimental data on the ground and excited state absorption spectra. Numerical contributions of all possible electron configurations into the calculated energy states were determined. By performing analysis of the molecular orbitals population, numerical contributions of the oxygen 2p- and 2s-orbitals into the 3d molecular orbitals were determined.  相似文献   

2.
The spin-Hamiltonian (or EPR) parameters of tetragonal Cu2+ octahedral centers in ZnCdO nanopowders are calculated from the high-order perturbation formulas based on the cluster approach. In these formulas, the contributions to spin-Hamiltonian parameters due to the admixture between the d orbitals of dn ion and the p orbitals of ligand ions via covalence effect are considered. The crystal field parameters are calculated from the superposition model and so the optical absorption bands (related to the crystal field energy levels) and local structure of Cu2+ octahedral centers in ZnCdO nanopowder are also studied. The calculated spin-Hamiltonian parameters and optical absorption bands are in reasonable agreement with the experimental values. The tetragonal elongation ΔR (=R//R) of Cu2+ octahedron in ZnCdO nanopowder due to Jahn–Teller effect is acquired from the calculations. The results are discussed.  相似文献   

3.
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.  相似文献   

4.
Fully relativistic calculations of the energy levels, absorption spectra, molecular orbitals (MO) compositions, covalence effects and energies of the charge transfer (CT) transitions for three isoelectronic ions Cr3+, Mn4+, Fe5+ in the SrTiO3 (STO) crystal have been performed. The recently developed first-principles approach to the analysis of the absorption spectra based on the first principles discrete variational multi-electron method (DV-ME) (K. Ogasawara et al., Phys. Rev. B 64 (2001) 115413) was used in the calculations. As a result, energy levels of the above ions, their absorption spectra and energies of the lowest CT transitions were all calculated. By performing analysis of the MO population, it was shown that the degree of covalence of the chemical bonds between 3d ions and oxygen ions in SrTiO3 increases in the following order: Cr3+→Mn4+→Fe5+, whereas the CT energies monotonically decrease in the same order.  相似文献   

5.
Detailed study of dependence of the crystal field strength 10Dq and lowest charge transfer (CT) energies for different interionic distances in Cs2GeF6:Mn4+ and Cs2GeF6:Os4+crystals is presented. The calculations were performed using the first-principles discrete-variational Dirac-Slater (DV-DS) method. As a result, the functional dependencies of 10Dq and lowest CT energy on the metal-ligand distance R were obtained without any fitting or semiempirical parameters. It was shown that 10Dq depends on R as 1/Rn, with n=4.0612 and 4.3874 for Cs2GeF6:Mn4+ and Cs2GeF6:Os4+, respectively. Two approximations (linear and quadratic) are obtained for the dependence of the lowest CT energy on R; CT energy decreases when R increases with dE(CT)/dR=−638 and −1080 cm−1/pm for Cs2GeF6:Mn4+ and Cs2GeF6:Os4+, respectively, if the linear approximation is used. These values can be used for estimations of the lowest CT energies for Mn4+ and Os4+ ions in other hosts with fluorine ligands. Estimations of the electron-vibrational interaction (EVI) constants, Huang-Rhys parameters, and Stokes shifts for all the above-mentioned crystals were performed using the obtained 10Dq and E(CT) functions.  相似文献   

6.
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 2B1g2B2g transition of Cu2+ ions. The optical band gap energy (Eopt) 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.  相似文献   

7.
Co2+ and Ni2+ ions doped β-BaB2O4 nanopowders have been prepared by co-precipitation method and their structural properties are studied by spectroscopic techniques. Powder XRD data reveals that the crystal structure belongs to monoclinic and the average crystallite size is calculated. Optical absorption spectra data reveal octahedral site symmetry for Co2+ and Ni2+ ions. Crystal field (Dq) and inter-electron repulsion (B and C) parameters are evaluated for Co2+ doped β-BaB2O4 nanopowders as Dq=960, B=900 and C=3850 cm?1 and for Ni2+ doped β-BaB2O4 nanopowders, Dq=900, B=850 and C=3500 cm?1. FT-IR spectra showed the characteristic vibrational bands related to BO3 and BO4 molecules. Photoluminescence spectra contain the emission bands in ultraviolet and blue regions.  相似文献   

8.
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.  相似文献   

9.
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 ICu= 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 ACu tensors calculated from the EPR data are g1=2.051(1), g2=2.062(2), g3=2.260(2), ACu,1=16.9(5)×10−4 cm−1, ACu,2=21.8(6)×10−4 cm−1, ACu,3=180.0(5)×10−4 cm−1. The principal directions corresponding to g3 and to ACu,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.  相似文献   

10.
Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe3+ ions doped sodium borophosphate glasses (NaH2PO4-B2O3-Fe2O3). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe3+ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe3+ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123-295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility (χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θp) have been evaluated from the 1/χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe3+ ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed.  相似文献   

11.
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.  相似文献   

12.
The excitation spectrum of the Mn2+ emission has been measured in CaF2 and CdF2. The observed excitation bands have been assigned to transitions of the Mn2+ ions in a cubic environment. The calculated values for the crystal field (Dq) and Racah parameters (B,C) are Dq = 425 cm-1 for CaF2, Dq = 500 cm-1 for CdF2 and, B = 770 cm-1 and C / B = 4.48 for both compounds. The lifetime of the fluorescent level 4T1g(4G) has been measured in both compounds at different temperatures in the range from 10 to 500 K. The lifetime thermal dependence is explained taking into account different mechanisms (purely radiative, phonon assisted, and radiationless transitions) for the decay of excited Mn2+ ions.  相似文献   

13.
A first principles fully relativistic analysis (K. Ogasawara et al., Phys. Rev. B 2001, 64, 115413) of the dependence of 5d orbitals splitting (10Dq) and charge transfer (CT) energies on interionic distance has been performed for light lanthanides (Ce3+, Pr3+, Nd3+) in CaF2, SrF2, BaF2 crystals. The salient feature of the method is that four‐component molecular orbitals (MO) composed of atomic wave functions are used as the basis set. Without any fitting parameter, the power dependencies for 10Dq and linear dependencies for the CT energies on the distance between rare‐earth (RE) ions and ligands were obtained. A comparison with experimental values is discussed.  相似文献   

14.
X-band electron paramagnetic resonance (EPR) studies on divalent copper ions embedded in KMgClSO4·3H2O single crystals have been performed at low temperature (123 K). The angular variation of the EPR spectra reveals the presence of two Cu2+ sites, which have different orientations. The spin-Hamiltonian parameters of this six-coordinated cupric ion have been evaluated from the EPR spectra at 123 K. The forbidden lines due to ΔmI=±1 transitions are observed in between allowed transitions. The temperature variation EPR studies have also been performed both for a single crystal and a polycrystalline sample. The ground state wavefunction of Cu2+ ions has been estimated and is found to be an admixture of d3z2r2 and dx2y2. The temperature variation of the EPR spectra reveals that Cu2+ ions exhibit dynamic Jahn-Teller effect. From the polycrystalline EPR data, the temperature dependent magnetic susceptibilities are evaluated and discussed.  相似文献   

15.
The electronic states of lanthanide (Ln) doped CaGa2S4 are investigated by the molecular orbital calculations for a spherical cluster of LnCa8Ga12S24 using the FORTRAN program DVSCAT on the basis of the Discrete Variational method with Xα potentials (DV-Xα). In view of the SCF convergence, the Ln-doped lattice should contract to 85-90% of the mother crystal around the Ln atom for the lightweight lanthanides from Ce to Sm. On the other hand, the lattice contraction is very small for the heavyweight lanthanides, especially for Er, Tm and Yb in contrast to the generally known lanthanide contraction for Ln3+ ions. This is probably attributed to the effective charges of Ln atoms calculated here to be less than +1 for all lanthanides contrary to the chemically accepted value of +3. The energy level scheme of 4f and 5d related molecular orbitals is proposed for each Ln substituting Ca in CaGa2S4, showing that the optical processes relating to the 5d→4f transition must be complicated especially for the lightweight Ln-doped CaGa2S4.  相似文献   

16.
Systematic first-principles analysis of the energy level schemes and ground state absorption spectra of trivalent chromium in ZnAl2S4 and ZnGa2O4 crystals has been performed in the present paper. The recently developed first-principles approach to the analysis of the absorption spectra of impurity ions in crystals based on the discrete variational multi-electron (DV-ME) method [K. Ogasawara et al., Phys. Rev. B 64, 115413 (2001)] was used in the calculations. The method is based on the numerical solution of the Dirac equation; no phenomenological parameters are used in the calculations. As a result, complete energy level schemes of the Cr3+ ion and its absorption spectra in both crystals were calculated, assigned and compared with experimental data. By performing analysis of the molecular orbital (MO) population, it was shown that the covalency of the chemical bonds between the Cr3+ and S2- ions is more significant than that one between the Cr3+ and O2- ions.  相似文献   

17.
The equilibrium and photoinduced absorption spectra of copper-and silver-doped Bi12SiO20 crystals are studied. It is demonstrated that the impurity absorption is due to Ag2+, Ag+, Cu3+, Cu2+, and Cu+ ions occupying almost octahedral Bi3 positions. A mechanism of photochromism is suggested, involving changes in the charge states of copper and silver impurity ions according to schemes Cu2+-e → Cu3+ and Ag+-e → Ag2+.  相似文献   

18.
Photoluminescent phosphors CaGa2S4: Eu2+, RE3+ (RE3+ including all rare earth ions except for Sc3+, Pm3+, Eu3+ and Lu3+) were prepared by sintering at high temperature in a reductive atmosphere, and their luminescent properties were studied intensively. The influences of co-doping rare earth ions on their luminescent properties were also investigated. No remarkable differences were found from excitation spectra of co-doped phosphors CaGa2S4: Eu2+, RE3+ in contrast with that of phosphor CaGa2S4: Eu2+, but there were a few differences in emission spectra of Ce3+, Pr3+ or Ho3+ co-doped phosphors. Phosphors CaGa2S4: Eu2+, RE3+ (RE=Ce, Pr, Gd, Tb, Ho and Y) had persistent afterglow, and very short afterglow was shown for Nd3+ or Er3+ co-doped phosphors, but no long afterglow appeared when auxiliary activator was La3+, Sm3+, Dy3+, Tm3+ or Yb3+. Among the phosphors with long-lasting phosphorescence, in our experiments, CaGa2S4: Eu2+, Ho3+ had the longest and the highest brightness long yellow afterglow. Thermo-luminescence of all co-doped phosphors was measured to find the answer of different influences from different rare earth auxiliary activators.  相似文献   

19.
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.  相似文献   

20.
High-pressure phase transition of Ta2NiO6 with the trirutile-type structure was investigated from the viewpoint of crystal chemistry. A new quenchable high-pressure phase was found in the pressure range higher than 7 GPa and 900°C. The high-pressure phase has an orthorhombic cell (a=4.797(1) Å, b=5.153(2) Å and c=14.85(1) Å and space group; Abm2), and it is more dense by 9.6% than the trirutile-structured phase. Infrared spectra of the trirutile-type phase and the high-pressure phase show that Ni2+ ions in the high-pressure phase are still in octahedral sites. The crystal structure of the high-pressure phase is considered as a cation-ordering trifluorite-type structure, which can be stabilized by a crystal field effect of Ni2+ ions.  相似文献   

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