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1.
Zheng Wen-Chen 《辐射效应与固体损伤》2013,168(1-2):169-178
Abstract The tetragonal distortions of local octahedral environments of Cr3+, Fe3+ and Gd3+ ions in Rb2CdF4, Cs2CdF4, RbCdF3 and CsCdF3 crystals have been studied by analyzing their EPR spectra. From the studies, it is found that the tetragonal distortions for Cr3+ and Fe3+ impurity ions, which substitute Cd2+ and have nearly the same ionic radius, are close to each other, whereas that for Gd3+ impurity ion, having a larger ionic radius, is larger than those for Cr3+ and Fe3+ ions in the same crystal. It appears that not only the impurity-ligand distance, but also the tetragonal distortions of impurity centres in crystals are closely related to the size of impurity. 相似文献
2.
In this work, the mechanism of enhanced photocatalysis of TiO2 with Fe3+ was studied using Sulfadiazine (SD) as the model compound. Results indicated that degradation rate of SD was enhanced by the addition of Fe3+ in TiO2 suspension. The crystalline structure of TiO2 particles was stable in suspensions. The hydroxyl radical generated by TiO2/Fe3+ (both TiO2 and Fe3+) photocatalysis was in a higher yield. Moreover, Fe2+ was found not to give an obvious impact on the SD degradation in TiO2 suspension, whereas Fe3+ had a notable effect. The adsorption amount of TiO2 was greatly enhanced by the addition of Fe3+ in suspensions. Finally, an interaction model of SD degradation in TiO2 suspension containing Fe3+ was also proposed by investigating of surface behaviors of TiO2 particles. It will be beneficial to use Fe3+ as the electron acceptors on the surface of TiO2 particles, which helps to improve the yield of hydroxyl radical. 相似文献
3.
F. Macco W. Lehmann W. Breitling A.E. Slawska-Waniewska R. Weber U. Dürr 《Solid State Communications》1978,26(7):429-434
The magnetic excitation spectrum of K2FeF4 and Rb2FeF4, two K2NiF4-structure planar antiferromagnets with rather large anisotropy and spins perpendicular to the c-axis, has been measured by Raman and FIR-spectroscopy. One of the two predicted one-magnon transitions and the two-magnon mode have been observed in K2FeF4 (Rb2FeF4) at 48.5 cm-1 (37.6 cm-1) and 182.0 cm-1 (160.5 cm-1) respectively. The magnetic field and temperature dependence of the spectra are reported too. The data are discussed on the basis of an easy plane spin model Hamiltonian. In K2FeF4: Mn2+ a low lying magnetic impurity mode is observed at 40.5 cm-1. 相似文献
4.
Natural zeolite supported Fe3+-TiO2 photocatalysts were synthesized for the sake of improving the recovery and photocatalytic efficiency of TiO2. The as-prepared materials were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Methyl orange was used to estimate the photocatalytic activity of the samples. The results showed that zeolite inhibited the growth of TiO2 crystallite sizes. The Fe3+ concentration played an important role on the microstructure and photocatalytic activity of the samples. The iron ions could diffuse into TiO2 lattice to the form Fe-O-Ti bond and gave TiO2 the capacity to absorb light at lower energy levels. The photocatalytic activity of the samples could be enhanced as appropriate dosages of Fe3+ were doped. 相似文献
5.
Yang Zi-Yuan 《Physica B: Condensed Matter》2011,406(20):3975-3979
The local structure distortion and the spin Hamiltonian (SH) parameters, including the zero-field splitting (ZFS) parameter D and the Zeeman g-factors g‖ and g⊥, are theoretically investigated by means of complete diagonalization method (CDM) and the microscopic spin Hamiltonian theory for tetragonal charge compensation CrF5O defect center in Cr3+:KMgF3 crystals. The superposition model (SPM) calculations are carried out to provide the crystal field (CF) parameters. This investigation reveals that the replacement of O2− for F− and its induced lattice relaxation Δ1(O2−) combined with an inward relaxation of the nearest five fluorine Δ2(F−) give rise to a strong tetragonal crystal field, which in turn results in the large ZFS and large anisotropic g-factor Δg. The experimental SH parameters D and Δg can be reproduced well by assuming that O2− moves towards the central ion Cr3+ by Δ1(O2−)=0.172R0 and the five F− ions towards the central ion Cr3+ by Δ2(F−)=0.022R0. Our approach takes into account the spin-orbit (SO) interaction as well as the spin-spin (SS), spin-other-orbit (SOO), and orbit-orbit (OO) interactions omitted in previous studies. This shows that although the SO interaction is the most important one, the contributions to the SH parameters from other three magnetic interactions are appreciable and should not be omitted, especially for the ZFS parameter D. 相似文献
6.
Chang-Chun Ding Shao-Yi Wu Qing-Sheng Zhu Guo-Liang Li Zhi-Hong Zhang Yong-Qiang Xu 《Molecular physics》2013,111(12):1478-1484
The local lattice distortions and the electron paramagnetic resonance (EPR) parameters (g factors, hyperfine structure constants and zero-field splittings) for Cu2+, Mn2+ and Fe3+ in ZnWO4 are theoretically studied based on the perturbation calculations for rhombically elongated octahedral 3d9 and 3d5 complexes. The impurity centres on Zn2+ sites undergo the local elongations of 0.01, 0.002 and 0.013 Å along the C2 axis and the planar bond angle variations of 8.1°, 8.0° and 8.6° for Cu2+, Mn2+ and Fe3+, respectively, due to the Jahn–Teller effect and size and charge mismatch. In contrast to the host Zn2+ site with obvious axial elongation (~0.31 Å) and perpendicular (angular) rhombic distortion, all the impurity centres demonstrate more regular octahedral due to the above local lattice distortions. The copper centre exhibits significant Jahn–Teller reductions for the spin-orbit coupling and orbital angular momentum interactions, characterised by the Jahn–Teller reduction factor J (≈0.29 ? 1). The calculated EPR parameters agree well with the experimental results. The local structures of the impurity centres are analysed in view of the corresponding lattice distortions. 相似文献
7.
提出了解释掺杂离子局域结构畸变的配体平面移动模型,建立了此模型下晶体微观结构与自旋哈密顿参量之间的定量关系.在考虑自旋与自旋、自旋与另一电子轨道和轨道与轨道作用等微小磁相互作用的基础上,采用全组态完全对角化方法,对Al2O3晶体中V3+的局域结构和自旋哈密顿参量进行了系统的研究.结果表明,V3+掺入Al2O3晶体后,上下配体氧平面间距离增大了0.0060 nm.从而成功地解释了Al2O3:V3+晶体的自旋哈密顿参量.在此基础上,研究了三角晶场下3d2离子自旋哈密顿参量的微观起源.研究发现,自旋三重态对自旋哈密顿参量的贡献是主要的,微小磁相互作用对自旋哈密顿参量的贡献只与自旋三重态有关. 相似文献
8.
Fe-ZSM-5 samples containing a combination of 57Fe3+ in framework (FW) and regular iron in extra-framework (EFW) sites were prepared by introducing 57Fe in hydrothermal synthesis, then exchanging Fe2+ of natural isotope composition into the lattice. The stability for one part of Fe2+ and Fe2+ ? Fe3+ reversibility for the other part in catalytic decomposition of N2O is demonstrated by in situ Mössbaer measurements. Formation of dinuclear FeFW–O–FeEFW pairs is not prevailing. 相似文献
9.
Spherical Zn2SiO4:Eu@SiO2 phosphor particles in core-shell structure: Synthesis and characterization
Spherical SiO2 particles have been coated with Zn2SiO4:Eu3+ phosphor layers by a Pechini sol-gel process. The microstructure and luminescent properties of the obtained Zn2SiO4:Eu3+@SiO2 particles were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and lifetime. The results demonstrate that the Zn2SiO4:Eu3+@SiO2 particles, which have regular and uniform spherical morphology, emitted an intensive red light emission at 613 nm under excitation at 395 nm. Besides, the effects of the Eu3+ concentration, annealing temperature and charge compensators of Li+ ions on the PL emission intensities were investigated in detail. 相似文献
10.
B.M. Mothudi O.M. Ntwaeaborwa A. Kumar K. Sohn H.C. Swart 《Physica B: Condensed Matter》2012,407(10):1679-1682
Long persistent SrAl2O4:Eu2+ phosphors co-doped with Dy3+ were prepared by the solid state reaction method. The main diffraction peaks of the monoclinic structure of SrAl2O4 were observed in all the samples. The broad band emission spectra at 497 nm for SrAl2O4:Eu2+, Dy3+ were observed and the emission is attributed to the 4f65d1 to 4f7 transition of Eu2+ ions. The samples annealed at 1100–1200 °C showed similar broad TL glow curves centered at 120 °C. The similar TL glow curves suggest that the traps responsible for them are similar. The long afterglow displayed by the phosphors annealed at different temperatures, may be attributed to the Dy3+ ions acting as the hole trap levels, which play an important role in prolonging the duration of luminescence. 相似文献
11.
Michèle D. FaucherO.K. Moune 《Journal of luminescence》2002,96(1):37-49
A spectroscopic study is carried out in which the effects of added Ca2+ and Ru4+ transition metal ions on some characteristics of the emission of Gd2O2S : Tb3+ phosphors (energy levels, intensities, lifetimes) are examined and compared. In order to distinguish the Tb3+ emissions from impurity ones, the electronic energy levels of trivalent terbium are determined and the energy level scheme is completed by a crystal field analysis. The optical spectra reveal no terbium doped impurity phase; however, other rare earth ions present as impurities in the starting materials are detected. They are identified, and the influence of the added Ca2+ and Ru4+ on their emission lines is also examined. 相似文献
12.
采用共沉淀法制备了纳米晶ZrO2-Al2O3∶Er3+发光粉体.所制备的粉体室温下具有Er3+离子特征荧光发射,主发射在绿光,其中位于547 nm、560 nm的绿光最强,并得出稀土离子与基质之间有能量传递.对不同煅烧温度下的样品研究表明:因不同温度下所制得的样品晶相不同.研究了纳米晶ZrO2-Al2O3∶Er3+及ZrO2-Al2O3∶Er3+/Yb3+的上转换发光,并分析了上转换的跃迁机制.发现ZrO2-Al2O3∶Er3+的绿光为双光子过程,而ZrO2-Al2O3∶Er3+、Yb3+的上转换光谱中,红光和绿光也为双光子过程,而极弱的蓝光为三光子过程.讨论了Er3+的浓度猝灭现象.最适宜掺杂浓度的原子分数为2%(Er3+/Zr4+). 相似文献
13.
Multilayered TiO2(Fe3+, PEG) films were deposited on glass and SiO2/glass substrates by sol-gel dipping method. The influence of Fe3+ and PEG(polyethylene glycol) concentrations, the number of layers, the thermal treatment time and the temperature on the optical and microstructural properties of the TiO2 films were studied.As-deposited TiO2(Fe3+, PEG) films were very porous, but after the thermal treatment at 500 °C, the PEG decomposed and burned out to porosity decreasing. Homogeneous nanostructured films were obtained, where the amorphous and the anatase phases coexist. XRD analysis showed that no rutile phase is observed in the films deposited on SiO2/glass as compared with those deposited directly on glass and that the presence of the anatase phase in the films without PEG is more evident in the three-layers film. The XRD intensity of the main peak of anatase from 25° decreases with the increase of PEG concentration.The optical gap of the TiO2(Fe3+, PEG) films is found in 2.52-2.56 eV range and does not essentially depend on the PEG content. 相似文献
14.
A nonhydrolytic hot solution synthesis technique was used to grow monodisperse ternary oxide nanocrystals of ZnGa2O4:Eu3+. The shape of ZnGa2O4:Eu3+ nanocrystals was a function of the type of precursor, and their size was controlled by changing the concentration ratio of Zn precursor to surfactant. The crystal structure of synthesized ZnGa2O4 nanocrystals was a cubic spinel with no detectable secondary phases. Photoluminescence of red-emitting ZnGa2O4:Eu3+ nanocrystals resulted in a high (5D0-7F2)/(5D0-7F1) intensity ratio, suggesting that the Eu3+ ions occupy tetrahedral Zn2+ sites or distorted octahedral Ga3+ sites with no inversion symmetry in ZnGa2O4 nanocrystals. 相似文献
15.
M.G. Brik 《Journal of luminescence》2011,131(12):2642-2645
In the present paper, we report on consistent crystal field calculations of the Cr3+ ions energy levels in KAl(MoO4)2 using actual D3d site symmetry of the Cr3+ position and employing the exchange charge model (ECM) of the crystal field. In addition to the energy level calculations, the Huang-Rhys factor S=5.7 and effective phonon energy ?ω=268 cm-1 were evaluated in the single configurational coordinate model. Detailed treatment of the microscopic crystal field effects in the ECM framework allowed to obtain analytical dependence of the crystal field strength 10Dq on the Cr-O interionic distance and extracting from it the values of some parameters of the electron-vibrational interaction (EVI) in the KAl(MoO4)2:Cr3+ system. All obtained results are compared with experimental data and discussed; agreement between the calculated and experimental parameters is good. 相似文献
16.
Ce3+ and Dy3+ activated Li2CaGeO4 phosphors were prepared by a solid-state reaction method, and characterized by XRD (X-ray diffraction) and photoluminescence techniques. The characteristic emission bands of Dy3+ due to 4F9/2→6H15/2 (blue) and 4F9/2→6H13/2 (yellow) transitions were detected in the emission spectra of Li2CaGeO4:Dy3+. Ce3+ broad band emission was observed in Li2CaGeO4:Ce3+ phosphors at 372 and 400 nm due to 5d→4f transition when excited at 353 nm. Co-doping of Ce3+ enhanced the luminescence of Dy3+ significantly and concentration quenching occurs when Dy3+ is beyond 0.04 mol%. White-light with different hues can be realized by tuning Dy3+ concentration in the phosphors. 相似文献
17.
V.P. Solntsev A.P. YelisseyevT.B. Bekker A.E. KokhS. Yu. Stonoga A.V. DavydovA. Maillard 《Optics Communications》2012,285(24):5205-5209
Optical absorption and luminescence spectra of ytterbium and terbium codoped BaB2O4 (β-BBO and α-BBO) crystals grown in different conditions have been studied. Low-temperature absorption peaks were observed in all samples. Features related to rare earth ions were observed in absorption and luminescence spectra. Absorption and emission in the range 860-1000 nm are caused by 2F5/2↔2F7/2 transitions in Yb3+ ions. Emission peaks at 500, 550, 590 and 630 nm correspond to 5D4→7F6, 7F5, 7F4, and 7F3 transitions of Tb3+ ions, respectively. The probable reasons of variations in spectroscopic features related to Yb in BBO host are discussed. It has been shown that the replacement of Ва2+ by Yb3+ in the lattice of ВаВ2О4 results in the decrease in the symmetry of oxygen surrounding of Yb3+. 相似文献
18.
基于Newman的晶场叠模型与微观自旋哈密顿理论,建立了ZnGa2O4:Fe3+晶体材料中磁性离子Fe3+局域结构与其自旋哈密顿(spin-Hamiltonian,SH)参量(包括二阶零场分裂(zero-field splitting,ZFS)参量D,四阶ZFS参量(a-F),Zeeman g因子:g//,g⊥,△g(=g//-g⊥))之间的定量关系.采用以全组态完全对角化方法为理论背景的CFA/MSH(Crystal Filed Analysis/Microscopic Spin Hamiltonian)研究软件,研究了ZnGa2O4:Fe3+材料中磁性离子Fe3+的SH参量与其局域结构的依赖关系.研究表明:对于ZnGa2O4:Fe3+晶体材料,当磁性离子Fe3+的局域结构畸变参数△R=0.0487 nm,△θ=0.192°时,其基态SH参量理论计算结果与实验测量符合很好,进一步表明Fe3+掺入晶体材料后将引起磁性Fe3+离子局域结构的微小畸变,但其仍然保持D3d点群对称局域结构.在此基础上研究分析了SH参量的微观起源,结果表明:ZnGa2O4:Fe3+晶体材料的SH参量主要来源于SO(spin-orbit)磁相互作用机理,来自其他磁相互作用机理(包括SS(spin-spin),SOO(spin-other-orbit),OO(orbit-orbit),SO-SS-SOO-OO)的贡献比较小. 相似文献
19.
A series of green phosphors Zn1.92−2xYxLixSiO4:0.08Mn2+ (0≤x≤0.03) were prepared by solid-state synthesis method. Phase and lattice parameters of the synthesized phosphors were characterized by powder X-ray diffractometer (XRD) and the co-doped effects of Y3+/Li+ upon emission intensity and decay time were investigated under 147 nm excitation. The results indicate that the co-doping of Y3+/Li+ has favorable influence on the photoluminescence properties of Zn2SiO4:Mn2+, and the optimal photoluminescence intensity of Zn1.90Y0.01Li0.01SiO4:0.08Mn2+ is 103% of that of commercial phosphor when the doping concentration of Y3+/Li+ is 0.01 mol. Additionally, the decay time of phosphor is much shortened and the decay time of Zn1.90Y0.01Li0.01SiO4:0.08Mn2+ is 3.39 ms, shorter by 1.83 ms than that of commercial product after Y3+/Li+ co-doping. 相似文献
20.
F. Güell 《Journal of luminescence》2004,106(2):109-114
Up-conversion blue emissions of trivalent thulium ions in monoclinic KGd(WO4)2 single crystals at 454 and 479 nm are reported for a single pump laser source at 688 nm. We grew thulium-doped KGd(WO4)2 single crystals at several concentrations from 0.1% to 10%. We recorded a polarized optical absorption spectrum for the 3F2+3F3 energy levels of thulium at room temperature and low temperature (6 K). From the low temperature emission spectra we determined the splitting of the 3H6 ground state. The blue emissions are characterized as a function of the dopant concentration and temperature from 10 K to room temperature. To our knowledge, this is the first time that sequential two-photon excitation process (STEP) generated blue emissions in thulium-doped single crystals with a single excitation wavelength. 相似文献