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1.
The local lattice distortions and the EPR parameters (anisotropic g factors and the hyperfine structure constants) for the orthorhombic Pt3+ center in YAG are theoretically investigated from the perturbation formulas of these parameters for a 5d7 ion in an orthorhombically elongated octahedron. The [ PtO6] 9- cluster on Al3+ site is found to experience the axial elongation of about 0.01 Å along Z axis, and the planar impurity-ligand bond lengths suffer the relative variation of about 0.11 Å? along X and Y axes due to the Jahn-Teller effect. As a result, the above local lattice distortions produce significant orthorhombic deformation, whereas the original slight trigonal distortion of the host [ AlO6] 9- octahedron is entirely depressed by the Jahn-Teller effect. The calculated EPR parameters based on the above lattice distortions show good agreement with the experimental data, and the local structure of the impurity center is also discussed.  相似文献   

2.
Electron paramagnetic resonance (EPR) and optical absorption studies of Li2O–MoO3–B2O3 with varying concentrations of Li2O, MoO3 and B2O3 have been carried out at room temperature. Two series of glasses, one with constant MoO3 (CM) and another with constant borate (CB), have been investigated. Characteristic EPR spectra of Mo5+ have been observed centered around g ≅ 2.00, which are attributed to Mo5+ ion in an octahedral coordination sphere with an axial distortion. The spectra also show strong dependence on the concentration of Li2O and B2O3. Spin concentrations (N) and magnetic susceptibilities (χ) have been calculated. In the CM series, the N values decrease with increasing Li2O content up to 30 mol%, while in the CB series variation of N is found to increase initially up to 20 mol%, and with further increase in the Li2O content the N values tend to decrease. The variation of magnetic susceptibilities is almost similar to that observed with the variation of N. From the optical absorption spectra, an absorption edge (α) has been evaluated. In the CM series, the values of α show a blueshift. On the other hand, in the CB series a redshift is observed. The observed variations in spectral parameters are explained by considering the molybdoborate network. Addition of Li2O to the CM and CB series results in modification of [MoO6/2]0 → [MoOO5/2] and [BO3/2]0 → [BO4/2] → [BOO2/2] groups, respectively, leading to creation of nonbridging oxygens. The optical basicity of the glasses has been evaluated in both the CM and the CB glasses. The optical basicity can be used to classify the covalent-to-ionic ratios of the glass, since an increasing optical basicity indicates decreasing covalency. It is observed that the covalency between Mo5+ ions and oxygen ligands increases in the CB series, whereas in the CM series the covalency between Mo5+ ions and oxygen ligands decreases. Authors' address: R. P. Sreekanth Chakradhar, Glass Technology Laboratory, Central Glass and Ceramic Research Institute, Kolkata 700032, India  相似文献   

3.
Yue-Xia Hu  Xue-Feng Wang 《哲学杂志》2013,93(11):1391-1400
The perturbation formulae of the spin Hamiltonian parameters (the anisotropic g factors, hyperfine structure constants and superhyperfine parameters) are established for a 5d7 ion in an orthorhombically elongated octahedron based on the cluster approach. These formulae are applied to the theoretical studies of the EPR spectra and the local structures for the tetragonal and orthorhombic Ir2+ centers in AgCl. For the tetragonal Ir2+ center, the uncompensated substitutional [IrCl6]4 cluster is found to experience a relative elongation of about 0.08 Å along the C 4 axis due to the Jahn–Teller effect. For the orthorhombic center, the ligand octahedron also suffers Jahn–Teller elongation (by about 0.08 Å) along the [001] (or Z) axis. Meanwhile, the ligand Cl intervening in the impurity Ir2+ and the next nearest neighbor silver vacancy VAg along the [100] (or X) axis may undergo an inward displacement of 0.004 Å towards the center of the octahedron due to electrostatic repulsion of the VAg. The calculated spin Hamiltonian parameters based on the above local structures show good agreement with experimental data for both centers.  相似文献   

4.
Electron paramagnetic resonance [EPR] and thermally stimulated luminescence [TSL] studies were conducted on self [α]-irradiated239Pu doped calcium chloro phosphate andγ-irradiated239Pu/238UO 2 2+ doped calcium chloro phosphate to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain trap parameters from both TSL and EPR data. TSL glow peaks around 135 K (# peak 1), 190 K (# peak 2), 435 K (# peak 5) and 490 K (# peak 7) were observed and their spectral characteristics have shown that Pu3+ and UO 6 6− act as luminescent centres in calcium chloro phosphate with respective dopants. EPR studies have shown the formation of the radical ions H0, PO 4 2− , O, O 2 and [ClO]2− under different conditions. Whereas the [ClO]2− radical being stable up to 700 K, was not found to have any role in TSL processes, the thermal destruction of other centres was found to be primarily responsible for the TSL peaks observed. The trap depth values were determined both by using the TSL data and also the temperature variation of EPR spectra of these centres.  相似文献   

5.
Electron paramagnetic resonance (EPR) study of Cu2+-doped sodium zinc sulfate tetrahydrate is done at liquid nitrogen temperature. Two magnetically equivalent sites for Cu2+ are observed. The spin-Hamiltonian parameters determined by fitting the EPR spectra to the rhombic-symmetry crystalline field are g x  = 2.2356, g y  = 2.0267, g z  = 2.3472, A x  = 27 × 10−4 cm−1, A y  = 54 × 10−4 cm−1and A z  = 88 × 10−4 cm−1. The ground state wave function is also determined. The g-anisotropy is evaluated and compared with the experimental value. With the help of optical study, the nature of bonding in the complex is discussed.  相似文献   

6.
The EPR parameters (g factors g , g and zero-field splitting D) of Mn4+ ion in h-BaTiO3 crystal are calculated from the complete high-order perturbation formulas based on a two-mechanism model for the EPR parameters of 3d 3 ions in trigonal symmetry. In the model, not only the widely used crystal-field mechanism, but also the charge-transfer mechanism (which is not considered in crystal-field theory) are included. The calculated results are in reasonable agreement with the experimental values. The relative importance of charge-transfer mechanism to EPR parameters and the defect structure of Mn4+ centre in h-BaTiO3 crystal obtained from the calculations are discussed.   相似文献   

7.
A Cu2+-doped single crystal of catena-trans-bis(N-(2-hydroxyethyl)-ethylenediamine) zinc(II)-tetra-m-cyanopaladate(II) [ZnPd(CN)4(C4H12N2O2)] complex has been investigated by electron paramagnetic resonance (EPR) technique at room temperature. EPR spectra indicate that Cu2+ ions substitute for magnetically equivalent Zn2+ ions and form octahedral complexes in [ZnPd(CN)4(C4H12N2O2)] hosts. The crystal field affecting the Cu2+ ion is nearly axial. The optical absorption studies show two bands at 322 nm (30864 cm−1) and 634 nm (15337 cm−1) which confirm the axial symmetry. The spin Hamiltonian parameters and the relevant wave function are determined.  相似文献   

8.
Duan’s simple model is extended to analyze the mixing of the 4f N − 15d configuration with the 4f N states. The explicit static coupling and traditional dynamic coupling are considered, and the parameters are fitted according to the absorption spectrum in LiYF4: Nd3+. The parameter values obtained are as follows: T 32 = −28i × 10−7, T 52 = −1151i × 10−7, A 322 = 192i × 10−12 cm, A 524 = i × 10−12 cm, A 726 = 54i × 10−12 cm, and A 766 = −680i × 10−12 cm. Compared to the experimental measurements, the present model yields better results than those obtained from the Judd-Ofelt theory. The text was submitted by the authors in English.  相似文献   

9.
An EPR study of the solid solutions LaSrAl1−x CuxO4, which are isostructural to La2CuO4, shows that microphase separation of the structure occurs already at small copper concentrations (x≈0.01). A phase enriched with Cu appears along with a phase of La2AlO4, which contains isolated CuO6 centers. It is established that the nature of the states and the deformations of the CuO6 centers is determined by internal Jahn-Teller factors. When x⩽0.1, EPR signals are detected for new dynamic centers, which are identified as CuO6 Jahn-Teller centers with a hole delocalized among the four in-plane oxygen ions (the total spin S=1). When 0.1⩽x<1, local CuO 6 hole centers transform into magnetic Jahn-Teller polarons, which include five or more CuO6 fragments, in the copper phase of the structure. Their transformations and the conditions for observing them are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 622–628 (April 1998)  相似文献   

10.
The electron paramagnetic resonance (EPR) parameters (g-factors g , g and zero-field splitting D) of two tetragonal 3d3 impurity centers M3d-VMg and M3d-Li+ (where M3d = Cr3+ or Mn4+, VMg is the Mg2+ vacancy) in M3d-doped MgO crystals are calculated from the high-order perturbation formulas including both the crystal-field (CF) and the charge-transfer (CT) mechanisms for 3d3 ions in the tetragonal symmetry. The calculated results are in reasonable agreement with the experimental values. From the calculations, it can be found that the relative importance of the CT mechanism for EPR parameters increases with increasing valence state of the 3d3 ion. So, for the high-valence 3d n ions in crystals, a reasonable explanation of EPR parameters should take into account both CF and CT mechanisms. The defect structures (characterized by the displacement ΔR of O2− in the intervening M3d and VMg or Li+ at the Mg2+ site) for these tetragonal impurity centers are obtained from the calculations. The results are consistent with the expectations based on the electrostatic interactions.  相似文献   

11.
The electron paramagnetic resonance (EPR) parameters (g andg factors and hyperfine structure constantsA ,A ) for Co2+ in Ca(OH)2 are studied from the second-order perturbation formulas on the basis of the cluster approach. In these formulas, the contributions to EPR parameters from the state interactions and covalency effects are considered and the parameters related to both effects are obtained from the optical spectra and impurity structure of the studied system. From the study, it is found that the β angle between the metal-ligand bond and the C3 axis changes from 61° in a pure crystal to 53.68(26)° in the impurity center of a Co2+-doped Ca(OH)2 crystal because of the impurity-induced local lattice relaxation. The reduction of the angle β in the impurity center is also supported by the result obtained by analyzing the EPR zero-field splitting for Mn2+ in the same Ca(OH)2 crystal. The EPR parameters of Ca(OH)2:Co2+ are also reasonably explained by considering the suitable local lattice relaxation.  相似文献   

12.
The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd3+ ions in CaNb2O6 crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10−20 cm2 with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd3+ ions in CaNb2O6 crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω t are Ω 2=5.321×10−20 cm2,Ω 4=1.734×10−20 cm2,Ω 6=2.889×10−20 cm2. The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β 1=36.03%,β 2=52.29%,β 3=11.15%,β 4=0.533%. The emission cross section at 1062 nm is 9.87×10−20 cm2.  相似文献   

13.
K P SANTHOSH 《Pramana》2011,76(3):431-440
Decay of neutron-deficient 128 − 137Gd parents emitting 4He to 32S clusters are studied within the Coulomb and proximity potential model. The predicted half-lives are compared with other models and most of the values are well within the present experimental limit for measurements (T 1/2 < 1030 s). The lowest T 1/2 value for 28Si emission from 128Gd indicates the role of doubly magic 100Sn daughter in cluster decay process. It is also found that neutron excess in the parent nuclei slows down the cluster decay process. Geiger–Nuttal plots for all clusters are found to be linear with different slopes and intercepts. The α-decay half-lives of 148 − 152Gd parents are computed and are in agreement with experimental data. The role of doubly magic 132Sn daughter in cluster decay process is also examined for various neutron-rich Ba, Ce, Nd, Sm and Gd parents emitting clusters ranging from 4He to 32Si. Alpha-like structures are most probable in the decays leading to 100Sn, while non-α-like structures are probable in the decays leading to 132Sn. The neutron–proton asymmetry in parent and daughter nuclei is responsible for the reduced decay rate in the decay leading to 132Sn.  相似文献   

14.
Electron paramagnetic resonance (EPR) studies on a single crystal of diamagnetic compound La2Si2O7, potentially a phosphorescent/luminescent/laser material, with the Gd3+ ion substituting for the La3+ ion, were carried out at X-band (9.61 GHz) over the 4–295 K temperature range. The asymmetry exhibited by the Gd3+ EPR line positions for the orientations of the external magnetic field about the magnetic Z- and Y-axes in the ZY-plane was ascribed to the existence of monoclinic site symmetry at the site of the Gd3+ ion, as confirmed by the significant values of the spin Hamiltonian parameters g YZ , b 2 −1, b 4 m (m = 1, 3), b 6 m (m = 1, 3, 5), estimated by fitting all EPR line positions observed at room temperature for the orientation of the magnetic field in the magnetic ZX- and ZY-planes using a rigorous least-squares fitting procedure. At 8 K measurements were only carried out for orientation of B in the magnetic ZX-plane, due to difficulty in orientation of the crystal inside the cryostat, enabling estimation of all spin Hamiltonian parameters b n m except those characterized by negative m values and g YZ . The absolute sign of the zero-field splitting parameter b 2 0 was determined to be negative from the relative intensities of the lines at 8 K. Authors' address: Sushil K. Misra, Physics Department, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec H3G 1M8, Canada  相似文献   

15.
A new method for the determination of trace mercury by solid substrate-room temperature phosphorimetry (SS-RTP) quenching method has been established. In glycine-HCl buffer solution, xylenol orange (XO) can react with Sn4+ to form the complex [Sn(XO)6]4+. [Sn(XO)6]4+ can interact with Fin (fluorescein anion) to form the ion associate [Sn(XO)6]4+·[(Fin)4], which can emit strong and stable room temperature phosphorescence (RTP) on polyamide membrane (PAM). Hg2+ can catalyze H2O2 oxidizing the ion association complex [Sn(XO)6]4+·[(Fin)4], which causes the RTP to quench. The ΔIp value is directly proportional to the concentration of Hg2+ in the range of 0.016–1.6 fg spot−1 (corresponding concentration: 0.040–4.0 pg ml−1, 0.40 μl spot−1), and the regression equation of working cure is ΔIp=10.03+83.15 m Hg2+ (fg spot−1), (r=0.9987, n=6) and the detection limit (LD) is 3.6 ag spot−1(corresponding concentration: 9.0×10–15 g ml−1, the sample volume: 0.4 μl). This simple, rapid, accurate method is of high selectivity and good repeatability, and it has been successfully applied to the determination of trace mercury in real samples. The reaction mechanism for catalyzing H2O2 oxidizing the ion association complex ([Sn(XO)6]4+·[(Fin)4]) SS-RTP quenching method to determine trace mercury is also discussed.  相似文献   

16.
The powder EPR spectra of portlandite (Ca(OH)2), brucite (Mg(OH)2) and hydrotalcite ([Mg3Al(OH)8]+[0.5CO 3 - ·nH2O]-), doped with 63CU2+, have been measured as a function of temperature. In all materials a static, temperature independent Jahn-Teller site and a dynamic, temperature dependent Jahn-Teller site was observed. In the rapidly reorienting situation the EPR spectrum of the dynamic site is still anisotropic. From the observed anisotropy it could be inferred that the hydroxyde ions surrounding the Cu2+ ion are situated at the vertices of an elongated octahedron which is compressed along its trigonal axis (c-axis). The angle between the axis of elongation of the Cu octahedra and the c-axis turned out to be 490 both for portlandite and brucite. The temperature range over which the averaged dynamic site could be observed varied considerably for the three materials.  相似文献   

17.
The analytical expressions for spin-Hamiltonian parameters of Jahn-Teller paramagnetic centres [AgF2F6]6? in fluorite crystals are deduced. Comparison with the experimental EPR data for CdF2, CaF2 and SrF2 yields information about the local structure of centres [AgF2F6]6?. It is found that two Ag2+-F? bonds of the centre (along the 〈111〉 direction) are shorter than the rest six bonds by factor 1.1. Euler angles of six non-axial fluorines are almost the same as those in the undistorted fluorite structure.  相似文献   

18.
The origin of the 9Li isotope is sought in missing-mass spectra measured in 11B(π, d)X, 12C(π, pd)X, and 14C(π, dt)X stopped-pion absorption reactions. The parameters of the three observed low-lying excited states coincide with the literature data. A state with excitation energy E x = 9.1 ± 0.1 MeV, lying above the threshold of 9Li decay into 6He + t, is observed for the first time.  相似文献   

19.
Crystals of CaF2: Cu (with a copper impurity content higher than 0.1 at. %) grown by the Czochralski method from a melt in a mixed helium-fluorine atmosphere are investigated using electron paramagnetic resonance (EPR) spectroscopy. It is found that the crystals contain paramagnetic centers whose magnetic properties at low temperatures are identical to those of [CuF4F4]6? (S=1/2) single centers. The magnetic properties of the centers exhibit a qualitative change in the temperature range 77–300 K. These changes are described within a model according to which the center is treated as a cluster composed of three [CuF4F4]6? impurity complexes involved in exchange interactions and interactions occurring in the field of Jahn-Teller lattice distortions.  相似文献   

20.
Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u N q+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A 252Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments (FF). Emission of (LiF) n Li+ clusters are observed for both the N beams and the 252Cf fission fragments. The observed cluster size n varies from 1 to 6 for N q+ projectiles and from 1 to ≈40 for the 252Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and (ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative cluster ions (LiF) n F closely resembles that of the positive secondary (LiF) n Li+ ions. The desorption yields of positive ions scale as Y(n) ∼ q 5. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼S e 3 with the electronic stopping power S e , as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering). We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions.  相似文献   

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