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1.
The spin-Hamiltonian (SH) parameters (g factors g //, g ⊥ and hyperfine structure constants 63 A //, 63 A ⊥, 65 A //, 65 A ⊥) for Cu2+ ions in the trigonally-distorted tetrahedral sites of ZnO and GaN crystals are calculated from a complete diagonalization (of energy matrix) method (CDM) based on a two spin-orbit parameter model for d 9 ions in trigonal symmetry. In the method, the Zeeman and hyperfine interaction terms are added to the Hamiltonian in the conventional CDM. The calculated results are in good agreement with the experimental values. The calculated SH parameters are also compared with those using the traditional diagonalization method or perturbation method only within the 2 T 2 term. It appears that, for exact calculations of SH parameters of d 9 ions in trigonal tetrahedral clusters in crystals, the present CDM is preferable to the traditional diagonalization method or perturbation method within the 2 T 2 term. The local structures of Cu2+ centers (which differ from the corresponding structure in the host crystal) in ZnO : Cu2+ and GaN : Cu2+ are obtained from the calculations. The results are discussed. 相似文献
2.
We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa2Se4:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm
is due to intracenter transitions 4f6 5d–4f7 (8S7/2) of the Eu2+ ions. From the temperature dependence of the intensity (log I–103/T), we determined the activation energy (E
a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths:
0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu2+ ions in the CaGa2Se4 crystal found from the luminescence decay kinetics is 3.8 μsec.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009. 相似文献
3.
OH−- and Cu+-codoped NaCl crystals are colored electrolytically by using a pointed anode and a flat cathode at various temperatures and under various voltages. Absorption and fluorescence spectral properties of colored crystals are investigated. Absorption, excitation and fluorescence spectra reveal existence of V2, V2m, V3, OH−, U, UA, O2−–Va+, O2+, Cu+, Cu0, Cu− and OH−-perturbed Cu+ color centers in colored crystals. Formations of color centers are explained. 相似文献
4.
Fei-Hui Li 《Applied Surface Science》2009,255(16):7394-7402
The reduction process of Bi3+, HTeO2+ and their mixtures on Au electrode surface was studied by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. XRD and EDS methods were also used to measure the reductive products prepared under different potentials and provide the evidences of the reactions. The results indicate that the reduction of HTeO2+ occurs at more positive potential than that of Bi3+, but its reduction rate is slower and adsorption phenomenon exists during its reduction process. Bi2Te3 compound can be obtained potentiostatically at a proper potential in all the mixed solutions with concentration ratio CHTe+O2/CBi3+ in our research range (0.1-10). But pure Bi2Te3 compound can only be obtained at 42 mV in the solution with concentration ratio CHTe+O2/CBi3+ equaling to 1. And the formation of Bi2Te3 compound is an inductive co-depositing process: (1) HTeO2+ + 4e− + 3H+ → Te0 + 2H2O, (2) 3Te0 + 2Bi3+ + 6e− → Bi2Te3. 相似文献
5.
The alkaline-earth fluorohalide crystals MFX, where M=Ca, Sr, Ba, Pb and X=Cl, Br, I, form an important class of materials crystallizing in the PbFCl-type tetragonal structure which is also called the matlockite structure. These compounds have long been of interest because of the various defect species which can be detected by spin resonance and associated techniques. The crystals were prepared by slow cooling of the melt of a stoichiometric mixture of BaF 2 and the corresponding chloride or bromide under 0.2 bar of ultrapure argon (5N5), often slightly fluorinated. We have studied the mechanoluminescence (ML) of BaFBr:Sm 2+ and BaFCl:Sm 2+ crystals. It is seen that after the impact of a moving piston, initially the ML intensity increases with time, attains a maximum value and then it decreases with time up to a particular minimum value, and then it increases again, attaining a peak value and finally disappears. The first peak lies in the deformation region and the second peak lies in the post-deformation region. The ML intensity of the BaFCl:Sm 2+ crystal is much higher than the ML intensity of the BaFBr:Sm 2+ crystal. For different impact velocities, the ML intensity increases with velocity; and the total ML intensity attains a saturation value for higher impact velocities. The total ML intensity increases with the increase in the applied load. It is suggested that the moving dislocation produced during deformation of crystals captures holes from hole-trapped centers (like H centers), and the subsequent radiative recombination of the dislocation holes with electron gives rise to ML. Thermoluminescence (TL) of BaFBr:Sm 2+ and BaFCl:Sm 2+ crystals was studied after exposure to ultraviolet rays with the help of a TLD reader. The peak of TL for the BaFBr:Sm 2+ crystal is found at ~247°C and for BaFCl:Sm 2+ crystals at 283°C. The TL intensity initially increases with increase in the UV radiation and then it attains saturation for higher values of UV exposure. The absorption spectrum was recorded with the help of a UV–visible spectrophotometer (Shimadzu). The band found at 275 nm was attributed to H centers. 相似文献
6.
Wen-Zuo Li Yu-Wei Pei Hong-Jie Zhu Jian-Bo Cheng Qing-Zhong Li 《Molecular physics》2013,111(22):2671-2677
Some low-lying states of the nine-valence-electron systems HBS+ and HSB+ cations have been studied by large-scale theoretical calculations using three methods CASSCF, CASPT2, and DFT B3LYP with the contracted atomic natural orbital and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized and the energies were calculated. The potential energy curves of isomerization reactions between HBS+ and HSB+ were calculated as a function of HBS bond angle. The calculated results indicated that the ground-state HBS+ is linear, while the ground-state HSB+ is bent, which is in contradiction to Walsh's rules predicting linear structures for the HXY systems containing 10 or less valency electrons. 相似文献
7.
A. L. M. Davies 《辐射效应与固体损伤》2013,168(1):9-14
235U fission fragment and fast neutron irradiations induce, at 30 K, an important increase in the electrical resistivity of a-Fe80B20 and a-Fe78Mo2B20. This increase anneals out partially when the samples are heated up to 300 K in two stages. An interpretation in terms of structural defects in the short range order of the amorphous alloys is presented. 相似文献
8.
ABSTRACTWe compare a recently proposed mixed experimental/theoretical procedure for the derivation of molecular equilibrium structures with several commonly used spectroscopic approaches using experimental data for several isotopologues. We also examine the sensitivity of the results from these approaches to the replacement of the commonly employed atomic masses with nuclear masses. This point is of particular importance for ionic species like HCO+ and HOC+ which serve as numerical reference cases. The scatter of molecular equilibrium geometries derived by different approaches is found to exceed stated statistical uncertainties by about an order of magnitude. 相似文献
9.
10.
Ab initio values for the potential energy functions for ion–neutral interactions can be tested by comparison with gaseous ion transport coefficients, but only if special care is taken to compute the interaction potentials accurately over wide ranges of internuclear separation. This is illustrated here by a reanalysis of the ab initio values for the coinage metal ions interacting with rare gas atoms, precise calculations of the transport cross sections over extremely wide ranges of energy, and similarly precise calculations of the zero-field ion mobilities as functions of gas temperature and the field-dependent ion mobilities at various fixed temperatures. The calculations indicate that the mobilities for Ag+(1S) moving in Ne or Ar can distinguish between the existing, very similar ab initio potentials. They also show that substantial differences exist among the mobilities of the coinage metal anions and the ground and excited states of the cations. The techniques implemented are recommended for future ab initio calculations. 相似文献
11.
The damage characteristics of polyethylene terephthalate (PET) have been studied under bombardment by C60+, Au3+ and Au+ primary ions. The observed damage cross-sections for the three ion beams are not dramatically different. The secondary ion yields however were significantly enhanced by the polyatomic primary ions where the secondary ion yield of the [M + H]+ is on average 5× higher for C60+ than Au3+ and 8× higher for Au3+ than Au+. Damage accumulates under Au+ and Au3+ bombardment while C60+ bombardment shows a lack of damage accumulation throughout the depth profile of the PET thick film up to an ion dose of ∼1 × 1015 ions cm−2. These properties of C60+ bombardment suggest that the primary ion will be a useful molecular depth profiling tool. 相似文献
12.
S.D. MoreM.N. Meshram S.P. WankhedeP.L. Muthal S.M. DhopteS.V. Moharil 《Physica B: Condensed Matter》2011,406(5):1178-1181
Phase pure LiCaPO4 was prepared by following a specific procedure involving several annealing steps, not exceeding the temperature 800 °C at any stage. Luminescence of Cu+ and Eu2+ activators is studied. A single emission band is observed for both the activators in contrast to two bands reported in earlier literature. It is argued that in the earlier work the samples were contaminated by alpha Ca3(PO4)2 phase, which could be responsible for these differences. Thermoluminescence of LiCaPO4:Eu2+ was found to be four times more than the commercial phosphor LiF-TLD 100. Phase pure LiCaPO4 shows interesting luminescence properties different than those reported in the literature and hence it should prove fruitful to probe this material in future. 相似文献
13.
Abstract The optical properties of nominally pure and Er3+- or Pr3+ -doped yttria-stabilized zirconia single crystals were investigated under UV light excitation. In the excitation spectra of both types of doped crystals, a broad UV band is observed. Under excitation with light of different wavelengths inside this band, the luminescence features of the doped crystals are different. YSZ: Pr3+ samples exhibit the characteristic 4f → 4f emission of the Pr3+ ions. In YSZ: Er3+ crystals, both the Er3+ ion and the intrinsic luminescence are observed. Host to Er3+ ion radiative energy-transfer is also demonstrated. No dependence of the transfer process with the excitation wavelength was found. These results suggest that the UV band in Er3+ -doped crystals is associated with the lattice-dopant ion interaction rather than with the 4f5d interconfigurational band of the Er3? ions. 相似文献
14.
The defect structures and the electron paramagnetic resonance parameters for the substitutional Mo5+ centers in rutile type SnO2, TiO2 and GeO2 crystals are theoretically investigated from the perturbation formulas of these parameters for a 4d1 ion in rhombically compressed octahedra. The [MoO6]7? clusters suffer the Jahn–Teller effect and transform the ligand octahedra from original elongation on host tetravalent sites to compression in the impurity centers, with additional smaller rhombic (perpendicular) distortions when compared with those in the hosts. The defect structures and the importance of the ligand contributions are discussed. 相似文献
15.
W.L. Feng X.M. Li W.C. Zheng Y.G. YangW.Q. Yang 《Journal of magnetism and magnetic materials》2011,323(5):528-531
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. 相似文献
16.
17.
Theoretical analysis of spin-Hamiltonian parameters for the rhombic Cu2+ centres in CuGaSe2 crystals
The spin-Hamiltonian parameters (g factors gi and hyperfine structure constants Ai, 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. 相似文献
18.
We have investigated the photoluminescence (PL) and photostimulated luminescence (PSL) spectra at 300 K to study the effect
of isoelectronic impurities K+ and I− on the formation and energy structure of Eu2+-VCs isolated dipole centers and aggregate centers in the form of single crystals of CsEuBr3 in CsBr:Eu2+ single crystals. We have shown that K+ and I− impurities in a concentration of 5 mol% do not have a substantial effect on the energy spectrum of isolated dipole centers
in CsBr:Eu2+ single crystals and the processes for the formation of such centers during growth of CsBr:Eu single crystals from the melt
by the Bridgman method. We have established that in Cs0.95K0.05Br:Eu2+, more favorable conditions are realized for the formation of aggregate centers than in CsBr:Eu2+ and CsBr0.95K0.05Br:Eu2+ single crystals. So in order to improve the storage properties of phosphors based on CsBr:Eu2+, in particular for increasing the efficiency of PSL excitation, it is expedient to dope them with K+ impurity in a concentration up to 5 mol%.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 627–630, September–October, 2007. 相似文献
19.
Pablo J. Bruna 《Molecular physics》2013,111(3):429-446
Theoretical calculations on the fine, hyperfine and Zeeman (g-factor) parameters are reported for the X2Π and A2Σ+ states of FH+, ClH+ and BrH+. The fine-structure constants [spin–orbit (A), Λ-doubling (p, q) and spin–rotation constants (γ Π, γ Σ)] are evaluated up to second order (via SO/L couplings with several excited states) using a multireference configuration interaction (MRCI) method, a Breit–Pauli Hamiltonian and 6-311++(2d,2pd) basis sets. Hyperfine constants of magnetic and electric type [Frosch–Foley (a, b, c, d) and nuclear quadrupole (eQq 0, eQq 2)] are studied with density functional methods and various basis sets. Magnetic dipole moments (parameterized via g-factors) are calculated in second order like the fine structure constants. The situation is somewhat complex for X2Π since no less than five different g’s have to be evaluated in second order. In general, our results are in good agreement with those reported in the literature, mostly limited to the ground state. Our calculations confirm that, at equilibrium, all second-order properties are dominated by the couplings between the electronic states X and A. 相似文献
20.
Powder phosphors of CaLa1? x Eu x Al3O7, CaLa1? x Ce x Al3O7 and CaLa0.99? x Eu x Ce0.01Al3O7, where x = 0.01, 0.03, 0.05 and 0.07, were prepared by a combustion method. The powders were well characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence techniques. Emission spectra of Eu3+-doped powder phosphors showed strong red emission at 613 nm (5D0 → 7F2); no concentration quenching was observed. Generally, Ce3+ acts as an efficient sensitizer when doped with other trivalent lanthanide ions. However, interestingly, in the CaLaAl3O7 powder phosphors, the addition of Ce3+ with Eu3+ exhibited an adverse effect–decreased photoluminescence intensity. The reasons for this behavior are discussed. 相似文献