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1.
In manganese-doped PbWO4 crystals, low-intensity signals of triclinic clusters Mn4+-V O and Fe3+-V Pb have been revealed in addition to signals of Mn2+ tetragonal centers. The Mn4+-V O cluster is formed by a Mn4+ ion in the W6+ position, which is associated with a vacancy of the nearest neighbor O2?ion, and the Fe3+-V Pb cluster consists of a Fe3+ ion substituting for Pb2+ with a local compensation of by a lead vacancy. It has been shown that, in PbWO4: Mn, there is also a small amount of Mn4+ tetragonal centers located in the Pb2+ position with a nonlocal compensation of an excess charge. 相似文献
2.
F.K Lotgering 《Journal of Physics and Chemistry of Solids》1975,36(11):1183-1191
Y3Fe5O12 (YIG) doped with ≦ 0.01 Co per molecule in combination with small dopes of V or (and) Mn show a decrease of the permeability in the dark (disaccommodation, DA) as well as when irradiated (photomagnetic effect, PE) with white light. All materials investigated exhibit DA and PE at 77 K, whereas in some cases effects occur at room temperature. The origin is attributed to domain wall pinning by magnetically anisotropic Co2+ ions that exchange electrons with Co3+ or other (V5+, Mn3+) ions. In view of the wide separation between the cobalt ions (?30 Å) the charge transport via iron ions is supposed to play an essential part.For a sample with higher cobalt dope the shape of the hysteresis loop at 77 K changes in the dark and the change can be hastened by irradiation. This phenomenon is attributed to the growth of a uniaxial anisotropy in the bulk of the material by Co2+, Co3+ ordering.From the electric resistivity of certain V and Si doped YIG materials it is concluded that V5+ ions oxidize Fe2+ ions according to V5++Fe2+ → V4++Fe3+. 相似文献
3.
A. Bianconi A. Giovannelli I. Dovoli S. Stizza L. Palladino O. Gzowski L. Murawski 《Solid State Communications》1982,42(8):547-551
The X-ray Absorption Near-Edge Structure (XANES) of V in vanadium-iron glasses (50P2O5 + (50?x)FeO + xV2O5) have been measured. The effective charge of V ions in glasses has been determined. At low V2O5 concentration (x ~ 5) only V4+ with 6-fold coordination is present on the contrary a static mixed valence state (V4+, V5+) has been found at high concentrations 20?x?50. The results explain the electron hopping conductivity effects at high V2O5 concentration (x ~ 50) involving V4+ ? V5+ pairs and at low V2O5 concentration (x?10) involving V4+ ? Fe3+ pairs. 相似文献
4.
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. 相似文献
5.
A. Gavaix A. Vasson A.-M. Vasson C.A. Bates P. Steggles 《Journal of Physics and Chemistry of Solids》1976,37(11):1051-1057
Cross-relaxation, which occurs when a V3+ transition is resonant with a monitored Cr3+ transition, leads to a marked reduction of the spin-lattice relaxation time of Cr3+ in Al2O3. Measurements and an analysis of the temperature dependence of this effect give a value of 8.34 ± 0.49 cm?1 for the zero-field splitting of V3+, an ion which is strongly coupled to the lattice. 相似文献
6.
From optical and thermal bleaching experiments it is concluded that the 400 nm absorption band which appears in Al2O3 after γ-irradiation is a composite V band. One of its components is attributed to the V-OH center which also is responsible for a localized vibrational band at 3316 cm-11 analogous to the one observed for the VOH center in MgO. The irradiation also results in electron trapping at Cr3+ impurity ions to produce a band at 227 nm. Annealing at 170°C destroys the V-OH center by releasing holes which convert the Cr2+ to Cr3+ with an attendant thermoluminescence. 相似文献
7.
用固相反应法制备了La0.45Ca0.55Mn1-xVxO3(x=0.00,0.10)多晶样品.通过X射线衍射谱、质量磁化强度-温度曲线、电子自旋共振谱,研究了V5+替代Mn3+/Mn4+对La0.45Ca0.55MnO3电荷有序相和自旋玻璃态的影响.实验结果表明,当x=0.10时,不仅母体的电荷有序相基本破坏,而且母体在40K左右出现的自旋玻璃态也被融化.电荷有序相被破坏的主要原因是用V5+替代Mn3+/Mn4+后,增加了Mn3+与Mn4+的比例,使铁磁双交换作用优于反铁磁超交换作用;自旋玻璃态的融化是由于V替代Mn后破坏了反铁磁背景下有少量铁磁成分的自旋玻璃态的形成条件. 相似文献
8.
采用石墨电阻加热的温梯法生长了V∶YAG晶体,晶体的不同部位呈现两种不同的颜色:浅绿色和黄褐色.通过对比分析不同颜色V∶YAG晶体的室温吸收光谱,推断出石墨发热体高温下扩散出来的C可以起到还原作用,提高晶体中V3+tetra离子的浓度,同时诱导了F心的形成.在1300℃下,对不同颜色的V∶YAG晶体进行真空退火处理,发现处于八面体格位中的V3+离子在热激发作用下与近邻的四面体格位Al3+离子存在置换反应,由此产生一定浓度的四面体格位V3+离子.同时,F心在退火过程中被完全消除,释放出来的自由电子被高价态的V离子俘获,可以进一步提高晶体中四面体格位V3+离子的浓度.
关键词:
V∶YAG晶体
四面体格位
碳还原
真空退火
F心 相似文献
9.
A solution combustion route for the synthesis of Eu3+-activated M2V2O7 (M = Sr, Ba) and their luminescent properties have been investigated. Structure and luminescent characteristics of Sr2V2O7:Eu3+ and Ba2V2O7:Eu3+ nanophosphors have been studied by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, fluorescence
spectrometry and Fourier transform infra-red spectroscopy. The incorporation of Eu3+ activator in these nanoparticles has been checked by luminescence characteristics. These nanoparticles have displayed red
color under a UV source which is due to characteristics transition of Eu3+ from 5D0 → 7F2 at 613 nm in both Sr2V2O7:Eu3+ and Ba2V2O7:Eu3+ nanophosphors. In addition, the optimal Eu3+ - doped contents of Sr2(1-x)Eu2xV2O7 and Ba2(1-x)Eu2xV2O7 nanophosphors for both were 4 mol%. 相似文献
10.
A. A. Galeev N. M. Khasanova A. V. Bykov G. R. Bulka V. M. Vinokurov N. M. Nizamutdinov 《Applied magnetic resonance》1996,11(1):61-86
Dopant Fe3+ ions in tetrahedral and octahedral positions of Ge4+ in the crystal Li2Ge7O15 were studied using EPR. Fe3+ substitutes for Ge4+ with a local charge compensation. The octahedral site and the tetrahedral sites significantly differ by the value of the invariant sumS(B 4) of theB 4 tensor of the spin Hamiltonian of Fe3+. The irreducible tensor products {V 4 ? V 4}4 and {V 4?V 4}2 theV 4 tensor of the crystal field calculated using the point-charge model for octahedral and tetrahedral complexes provide the predominant contribution of the crystal field to theB 4 andB 2 tensors of the spin Hamiltonian of Fe3+, respectively. A comparison of the fourth-rank tensorsB 4 of the spin Hamiltonian and {V 4?V 4}4 of the crystal field determined at 300 K with those determined at 77 K supports the conclusion that the phase transition is accompanied by combined rotation of the [GeO4] tetrahedra with the [Ge(1)O6] octahedron almost unaltered. The spectrum lines are narrow and the variety of point defects in the vicinity of the paramagnetic impurity ions Fe3+, Cr3+ and Cu2+ is not detected. These facts are inconsistent with the statistically distributed model for the Li(2) atom. In specific cases at 300 K, when the wings of the two spectrum lines of theM→M+1 and theM+2 →M+3 transitions of Fe3+ ions belonging to one system of translationally equivalent positions overlap an extra line appears in the center between these lines. It is suggested that this effect is due to the soft phonon mode above the phase transition temperature. 相似文献
11.
Kongping Wu Shulin Gu Kun Tang Shunming Zhu Mengran Zhou Yourui Huang Mingxiang Xu Rong Zhang Youdou Zheng 《Physica B: Condensed Matter》2012,407(13):2429-2433
Mn doped Zinc oxide (ZnO) thin films were prepared by metal organic chemical vapor deposition (MOCVD) technique. Structural characterizations by X-ray diffraction technique (XRD) and photoluminescence (PL) indicate the crystal quality of ZnO films. PL and Raman show a large fraction of oxygen vacancies (VO2+) are generated by vacuum annealed the film. The enhancement of ferromagnetism in post-annealed (Mn, In) codoped ZnO could result from VO2+ incorporation. The effect of VO2+ on the magnetic properties of (Mn, In) codoped ZnO has been studied by first-principles calculations. It is found that only In donor cannot induce ferromagnetism (FM) in Mn-doped ZnO. Besides, the presence of VO2+ makes the Mn empty 3d-t2g minority state broadened, and a t2g-VO2+ hybrid level at the conduction band minimum forms. The presence of VO2+ can lead to strong ferromagnetic coupling with the nearest neighboring Mn cation by BMP model based on defects reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Mn 3d electrons trapped in oxygen vacancies. 相似文献
12.
F.M. Michel-Calendini 《Solid State Communications》1984,52(2):167-172
The spin-unrestricted Xα method is used to obtain the molecular orbital diagrams relevant to cubic Fe2+, Fe3+ and axial Fe+ ?V0 to Fe3+ ?V0 defects in SrTiO3, where V0 is an oxygen vacancy. The relative energies of the lower spin multiplets are determined through the transition-state model of Slater. The electronic structures and the term patterns allow to discuss the stability and the ground term of each center trapped in cubic SrTiO3. The mechanisms of ligand-metal and intervalence charge transfers are examined and compared to the abundant experimental data provided by EPR and optical measurements. The different behaviours of ferroelectrics like BaTiO3: Fe and LiNbO3: Fe in regard to the mechanisms implied in the photorefractive effects are reviewed according to the theoretical electronic structures with a special emphasis to the Fe2+ ? Fe3+ charge transfer. 相似文献
13.
Trace amounts of trivalent vanadium in zinc oxide single crystals can be converted into divalent ions by heating the samples in an atmosphere of zinc vapor. The ESR spectra of V2+ have been investigated at low temperature and the parameters of the spin-Hamiltonian were determined by making use of a computer program. The parameter values for V3+ have been refined. The ions are assumed to be at substitutional Zn2+ sites. 相似文献
14.
M. Abou-Ghantous C.A. Bates L.C. Goodfellow 《Journal of Physics and Chemistry of Solids》1976,37(11):1059-1068
APR experiments have been carried out on V3+ and Cr4+ ions in Al2O3 partly to remove discrepancies in earlier measurements, and partly to provide additional information necessary for the theoretical analysis which follows. We find |G-| ~ 45± 10 cm?1 and ~ 160±30 cm?1 for V3+ and Cr4+ respectively. It is shown that all the data for both ions can only be explained satisfactorily if a moderately strong Jahn-Teller effect operates in the cubic 3T1, ground state of the ion. Full details are given, γ is found to be 0.14 and 0.36 for V3+ and Cr4+ respectively and important contributions from second-order Jahn-Teller effects are also present. The results also show that it is necessary to use a multimode full-lattice model of the Jahn-Teller effect as the constraints of the cluster model are broken. The implications of the proposed model on thermal conductivity, phonon spectroscopy and optical measurements are also briefly discussed. It is also pointed out that some important errors exist in the literature concerning the interpretation of experimental data for these systems. 相似文献
15.
The results of a study of the insulator-metal phase transition in V3O5 occuring at T = 450 K are presented. Conductivity, thermopower, magnetic, structural and optical data are reported. On a basis of the data obtained we conclude that the high-temperature phase is a poor metal with strong electron correlations and localized magnetic moments. The metal-non-metal transition is presumably driven by the spatial ordering of V3+ and V4+ ions. 相似文献
16.
As a possible explanation of the SLAC anomalous eμ events, we computed the cross section for e+ + e? → V+ + V? → μ± + e± + neutrinos, taking into account the spin correlations of V±. If one assumes that the vector meson has an anomalous magnetic moment (κ ≈ 1), the spin effects are considerable. The V± production hypothesis seems to be a viable alternative to that of the heavy lepton production. 相似文献
17.
UV–visible, infrared and Raman spectra, together with thermal properties, were measured for glasses from the system Bi2O3–B2O3–V2O5 before and after successive gamma irradiations. The UV–visible spectrum of the undoped glass before irradiation reveals five UV bands at 210, 275, 310, 350 nm, an intense band at 380 nm and a visible band at 420 nm due to the possible combined presence of trace iron impurities and Bi3+ ions. The V-doped glasses reveal six UV bands and two visible bands, probably arising from vanadium ions in three possible valencies, V3+, V4+ and V5+, beside that due to trace iron impurity beside Bi3+ ions. The spectra reveal an obvious resistance of the glasses to successive gamma irradiation. The Raman and infrared spectra show characteristic absorption bands, which indicate the sharing of Bi3+ ions as glass-forming (BiO6) octahedral units together with the presence of various groups of the borate network. 相似文献
18.
By simultaneously using both a V3+:YAG and a Co2+:LaMgAl11O19 saturable absorber in the cavity, for the first time to our knowledge, a diode-pumped doubly Q-switched Nd:GdVO4 laser has been realized. The dependence of pulse width, pulse repetition rate, pulse energy and peak power on the incident
pump power are measured. Under the absorbed pump power of 8.59 W, both the pulse temporal profile of the passive double-switching
with the pulse width of 25.29 ns, and the passive single-switching just using V3+:YAG with pulse width of 30.46 ns are obtained. The pulse duration is partly compressed in contrast to the purely passively
Q-switched laser with V3+:YAG. 相似文献
19.
N. I. Kadyrova Yu. G. Zaynulin A. P. Tyutyunnik N. V. Melnikova A. A. Mirzorakhimov 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(6):620-623
AMn3V4O12 (A = Ca, Ce, and Sm) compounds with a perovskite structure are synthesized at high pressures and temperatures. The crystalline structure of these compounds (space group \(Im\bar 3\)Z = 2) is determined via X-ray analysis. If ions in the A sublattice are changed in the order Ca2+–Sm3+–Ce3+, the valence is redistributed from Ca2+Mn32+V44+O12 to Sm3+Mn32+V43.75+O12, and to Ce3+Mn32+V43.75+O12. The temperature dependences of the electrical resistivity are studied. 相似文献
20.
P. Peka M. U. Lehr H. -J. Schulz R. Schwarz K. W. Benz 《Applied Physics A: Materials Science & Processing》1994,58(5):447-451
In CdTe doped with vanadium the photoluminescence due to the 3
T
2(F) 3
A
2(F) transition of V3+(d
2) is detected. Its decay time is determined as (630±20) s, a result comparable to the analogous emissions in various host lattices. Further emissions around 5000 cm–1 and 9000 cm–1 are caused by charge-transfer transitions or bound-exciton decay. Excitation and sensitization spectra yield information on the positions of the energy levels within the gap, which are discussed using two different models. At T=4.2 K, the distance of the V2+/V3+ donor level is 7300 cm–1 and 5700 cm–1 referred to the valence and the conduction band edges, respectively. The absence of V2+(d
3) centres is tentatively ascribed to the existence of deeply bound excitons. 相似文献