NaGdF4:Eu3+和GdBaB9O16的VUV荧光性质

在真空紫外光激发下,六万结构的NaGdF₄:Eu³⁺中的Gd³⁺离子吸收一个光子,将能量分两步传递给Eu³⁺离子,发生红色双光子发射.立方结构的NaGdF₄:Eu³⁺中存在一定量的氧离子取代缺陷,使Gd³⁺离子4f-5d跃迁移到177nm附近,这与惰性气体放电产生的VUV光波长一致,并且其荧光色纯度较高.在VUV激发下,GdBaB₉O₁₆中的Gd³⁺离子发生双光子(紫外和红色或远红外)发射.     

SrMn0.5Fe0.5O3的自旋玻璃态和过渡金属离子价态的研究

采用固相反应法制备了SrMn_0.5Fe_0.5O₃陶瓷样品,并对样品的晶体结构,磁性和离子价态进行了系统的表征与分析. X射线衍射谱的Rietveld拟合表明样品属于理想的立方钙钛矿型结构,Mn离子和Fe离子随机占据B位的O八面体中心. X射线光电子能谱表明Mn离子为+3和+4的混合原子价态,Fe离子为+3价. 样品在大于230K的高温区域呈现Curie顺磁特性,在小于230 K的低温区域样品表现出自旋玻璃态行为,这种特性源于Mn离子和Fe离子之间的交换作用及自身价态和分布的不均匀性. 由于Fe³⁺离子占据O八面体的中心,对顺磁区的Mssbauer谱测量表现为四级分裂.     

AN INVESTIGATION FOR THE Cd2+-VACANCIES IN RbCdF3 and CsCdF3 CRYSTALS DOPED WITH Fe3+ IMPURITIES

This paper presents high-order perturbation calculations for the zero-field splitting parameters D, F, and a of Fe³⁺-V_Cd pairs in RbCdF₃ and CsCdF₃ crystals doped with Fe³⁺ impurities. In comparison with experimental data, the present results are better than those obtained in previous work by using the phenomenological su-perposition model of spin-Hamiltonian. Moreover, the crystal fields arising from the Cd²⁺-vacancy and their induced crystal lattice distortion are analysed and calculated. It is found that the contribution from the Cd²⁺-vacancies cannot be ignored. Mena-while, we obtain that a ligand F^- along the [001]-axis moves towards the central Fe³⁺ ion by Δ= 0.0020nm in RbCdF₃ and 0.0028nm in CsCdF₃. These results are quite different from Δ = 0.0104nm and Δ = 0.0112nm, respectively, obtained in previous work by using the superposition model of spin-Hamiltonian and ignoring the effect of the vacancy.     

Er3+单掺及Er3+/Yb3+共掺SiO2-Al2O3-La2O3玻璃光谱性质研究

研究了单掺Er³⁺及Er³⁺/Yb³⁺共掺SiO₂-Al₂O₃-La₂O₃玻璃的光谱性质随稀土离子浓度变化规律,应用McCumber理论计算了玻璃在1.53 μm的发射截面及积分吸收截面.结果表明:在Er³⁺离子掺杂浓度相同时,玻璃在980 nm吸收截面与Yb³⁺掺杂浓度成反比;当样品中Yb³⁺离子掺杂浓度为3.94×10²⁰ cm^-3时,玻璃在1.53 μm的吸收截面和发射截面最大,在1.40～1.60 μm积分吸收截面也最大;Er³⁺/Yb³⁺共掺SiO₂-Al₂O₃-La₂O₃玻璃在1.53 μm的荧光半高宽随Er³⁺掺杂浓度升高而增加,当Er³⁺离子掺杂浓度为2.41×10²⁰ cm^-3时,玻璃的荧光半高宽(FWHM)达到52.5 nm.     

Tm3+/Yb3+共掺碲酸盐玻璃的近红外发光及能量传递机理

采用高温熔融法制备了组分为TeO₂-ZnO-Na₂O的Tm³⁺离子单掺和Tm³⁺/Yb³⁺共掺碲酸盐玻璃,应用Judd-Ofelt理论计算分析了玻璃样品的强度参量Ω_t(t=2, 4, 6),自发辐射跃迁几率A,荧光分支比β和荧光辐射寿命τ_rad等光谱参量,测量得到了不同Yb³⁺离子掺杂浓度下玻璃样品的Tm³⁺离子上转换发光谱.结果显示,在980 nm泵浦光激励下玻璃样品发射出强烈的近红外上转换荧光.对Tm³⁺离子上转换发光分析表明,强烈的Tm³⁺离子近红外上转换发光主要来自于Yb³⁺/Yb³⁺离子间的共振能量传递以及基于单声子和双声子辅助的Yb³⁺/Tm³⁺离子间的非共振能量传递过程,并进一步计算得到了声子贡献比和能量传递系数.最后,计算分析了Tm³⁺:³F₄→³H₆能级间跃迁的1.8 μm波段吸收截面、受激发射截面和增益系数.研究表明,Yb³⁺/Tm³⁺共掺TeO₂-ZnO-Na₂O玻璃可以作为近红外波段固体激光器的潜在增益基质.     

Manganese location and magnetic structure determination of SrMn2—W hexagonal ferrite by means of neutron diffraction

The Mn cation distribution in the seven sublattices of theW-type structure has been determined from high temperature neutron diffraction data of a SrMn₂Fe₁₆O₂₇ powder sample. The Mn²⁺ ions enter the tetrahedral sites of blockS with a preference for site 4e. Mn³⁺ ions in small amounts are found in the octahedral sites, substituting for Fe³⁺, while 0.3 Fe²⁺ has been found in site 6g. The sample has the formula SrMn_2.4Fe_15.6O₂₇. The crystal structure has been described in the non-centrosymmetric Pˉ62c space group, instead of the usual P6₃/mmc one. The magnetic structure, obtained from low temperature (4.2 K) data, is collinear, with the spins parallel to thec axis, according to the Gorter model. The magnetic moments of the sites give an experimental magnetization valueM _s=28.4(1.5) μ_B/f.u., in good agreement with magnetic measurements and the theoretical value.     

红宝石Cr3+:Al2O3的电子云延伸效应及压力对电子云延伸效应影响(英文)

本文以Cr³⁺自由离子的3d电子径向波函数为基础,对Cr³⁺:Al₂O₃中的电子云延伸效应进行了理论研究,引入了电子云延伸效应系数κ,得到了Cr³⁺:Al₂O₃中Cr³⁺离子的最优化3d电子径向波函数.并研究了压力对电子云延伸效应系数κ的影响.     

Ce3+ 掺杂高密度氧化物玻璃的闪烁性能研究

用高温熔融法制备了以SiO₂-B₂O₃-Al₂O₃-Gd₂O₃为基质系统Ce³⁺掺杂的玻璃样品, 测试样品的密度、紫外——可见透射光谱、紫外激发光谱和主要的闪烁性能, 并且把一部分闪烁性能和PbWO晶体及BGO晶体做比较. 着重研究了不同Ce³⁺掺杂浓度与Gd³⁺ 离子的含量对玻璃样品闪烁性能的影响规律. 结果表明: 玻璃样品具有较大的密度; 样品的X射线激发发射光谱发射峰位置都在390 nm左右, 当Ce³⁺ 离子的掺杂浓度为1.0 mol%(摩尔分数)、Gd₂O₃含量为15 mol%时, 玻璃样品的发光峰强度达到BGO晶体发光强度的90%; 同样验证了Ce³⁺ 离子具有浓度猝灭效应; Gd³⁺可以敏化Ce³⁺离子发光, 但是Gd³⁺离子到达一定浓度时, 反而会产生猝灭效应, 降低了Ce³⁺ 离子的发光. Ce³⁺ 离子掺杂SiO₂-B₂O₃-Al₂O₃-Gd₂O₃系统的闪烁玻璃有望替代闪烁晶体广泛应用于高能物理中.     

Gd,Co共掺杂对BiFeO3陶瓷电输运和铁磁特性的影响

采用快速液相烧结法制备BiFeO₃和Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)陶瓷样品,研究Gd, Co共掺杂对BiFeO₃微观结构, 介电性能和铁磁性的影响. X射线衍射谱表明:所有样品的主衍射峰与纯相BiFeO₃相符合且 具有良好的晶体结构,随着Co³⁺掺杂量x的增大, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品的主衍射峰(104)与(110)逐渐相互重叠, 当x大于0.1时, 样品呈现正方晶系结构; J-V特性显示Gd³⁺, Co³⁺共掺杂有效地降低BiFeO₃陶瓷的漏导电流,其降低幅度为1-2个数量级; 当f=10³ Hz时, Bi_0.95Gd_0.05Fe_0.8Co_0.2O₃的介电常数是BiFeO₃的6倍, 而Bi_0.95Gd_0.05Fe_0.95Co_0.05O₃和 Bi_0.95Gd_0.05Fe_0.85Co_0.15O₃样品的介电损耗最小,均为0.01.室温下, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品磁性与BiFeO₃相比显著增强. 在磁场为30 kOe的作用下,Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)的剩余磁化强度M_r分别是BiFeO₃的34, 60, 105, 103, 180倍.样品磁性增强的主要原因是Gd, Co掺杂使BiFeO₃的晶格结构发生变化导致BiFeO₃自身储存的磁性能被释放, Gd³⁺的4f电子与Fe³⁺或Co³⁺的3d电子自旋相互作用及样品中存在局域的 Fe-O-Co磁耦合三者共同作用的结果.     

Er3+/Ce3+共掺碲铋酸盐玻璃的制备及光谱特性提高研究

采用高温熔融退火法制备了系列 80TeO₂-10Bi₂O₃-10TiO₂-0.5Er₂O₃-xCe₂O₃ (x=0,0.25, 0.5,0.75,1.0 mol%)和(80-y) TeO₂-10Bi₂O₃-10TiO₂-yWO₃-0.5Er₂O₃-0.75Ce₂O₃ (y=3,6,9,12 mol%)的碲铋酸盐玻璃.测试了玻璃样品400-1700 nm范围内的吸收光谱, 975 nm抽运下的上转换发光谱和1.53 μm波段荧光谱, 以及808 nm激励下的Er³⁺离子荧光寿命和无掺杂玻璃样品的Raman光谱, 并结合Judd-Ofelt理论和McCumber理论计算了Er³⁺离子光谱参数.结果表明, 在掺Er³⁺碲铋酸盐玻璃中引入Ce³⁺离子进行Er³⁺/Ce³⁺共掺, 通过Er³⁺离子⁴I_11/2能级与Ce³⁺离子²F_5/2 能级间基于声子辅助的能量传递过程,可以有效抑制Er³⁺离子上转换发光并明显增强其 1.53 μm波段荧光;同时,在现有Er³⁺/Ce³⁺共掺玻璃组分基础上引入WO₃, 可进一步提高1.53 μm波段荧光并展宽其荧光发射谱. 研究结果对于获取优异光谱特性的宽带掺Er³⁺光纤放大器玻璃基质具有实际意义.     

EPR spectra of Fe centers in layered TlGaSe2 single crystal

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.     

Twinned EPR spectra of Fe centers in ternary layered TlGaS2 crystal

TlGaS₂ single crystal doped by paramagnetic Fe³⁺ ions has been studied by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe³⁺ ions was observed. The spectra reveal a nearly orthorhombic symmetry of the crystal field (CF) on the Fe³⁺ ions. Two groups each consisting of four equivalent Fe³⁺ centers were observed in the EPR spectra. The local symmetry of the crystal field on the Fe³⁺ centers and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of the GaS₄ tetrahedrons. The rhombic distortion of the sulfur ligand CF is attributed to the effect of Tl ions located in the trigonal cavities between the tetrahedral complexes. The observed twinning of the resonance lines indicates a presence of two non-equivalent positions of Tl ions that confirms their zigzag alignment in the TlGaS₂ crystal structure.     

EPR and optical absorption studies of Fe ions in sodium borophosphate glasses

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 (θ_p) 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.     

Theoretical study of anisotropy spin-orbit coupling and local lattice structure for Fe<Superscript>3+</Superscript> ions in MgTiO<Subscript>3</Subscript>:Fe<Superscript>3+</Superscript> system

The anisotropy spin-orbit coupling matrices for a d⁵ configuration ion in a trigonal ligand-field have been established. On basis of the anisotropy spin-orbit coupling matrices, the ground state zero-field splitting of the Fe³⁺ ions in ilmenite-structure MgTiO₃:Fe³⁺ system has been studied. The calculated results show that the anisotropy of Fe³⁺ ions in the diamagnetic ilmenite MgTiO₃ is important and the EPR parameters depend sensitively on the anisotropy divergent parameter. Moreover, the effect of the anisotropy divergent parameter on the second-order parameter D is obviously larger than that on the fourth-order parameter (a-F). Based on this point, the local lattice structure of Fe³⁺ ion in MgTiO₃:Fe³⁺ system is determined by diagonalizing the complete energy matrices for a d⁵ configuration ion in a trigonal ligand-field and considering the second-order as well as the fourth-order EPR parameters D and (a-F) simultaneously. Our results are consistent with the experimental proposal that Fe³⁺ ions may locate at both the Mg²⁺ and Ti⁴⁺ sites.     

Anisotropy of hyperfine field in diamagnetically substituted YIG

The results of the nuclear magnetic resonance of ⁵⁷Fe in Al-, Ga- and In-substituted Y₃Fe₅O₁₂ garnets are reported. When diamagnetic Ga³⁺ or Al³⁺ ions are substituted for tetrahedral Fe³⁺ ions, four satellite lines in the NMR spectrum of octahedral Fe³⁺ ions appear. The substitution of In³⁺ ions for octahedral Fe³⁺ ions leads to three satellite lines in the spectrum of tetrahedral Fe³⁺ ions. The hyperfine fields of these satellites are explained using the independent bond model for the hyperfine interaction. Suprisingly large change of the anisotropic part of the hyperfine field relative to the isotropic one was found.     

Structures of Fe3+-Vo defects in ABO3 perovskite-type crystals

The displacements of Fe³⁺ ions and hence the structures of Fe³⁺-V_o defects in ABO₃ oxide perovskites are studied by analyzing their electron paramagnetic resonance data from the high-order perturbation formula of zero-field splitting on the basis of the spin-orbit coupling mechanism. The results suggest that the Fe³⁺ ions in the Fe³⁺-V_o defect centers are displaced away from the oxygen vacancy V_o by about 0.035 nm. The reasonableness of the displacement is discussed.     

A rapid combustion process for the preparation of MgSrAl10O17:Eu phosphor and related luminescence and defect investigations

Blue-emitting europium-ion-doped MgSrAl₁₀O₁₇ phosphor, prepared using the combustion method, is described. An efficient phosphor can be prepared by this method in a muffle furnace maintained at 500 °C in a very short time of few minutes. The phosphor is characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and BET surface area measurements. Photoluminescence (PL) spectra revealed that europium ions were present in divalent oxidation state. The thermoluminescence (TL) glow curve shows two peaks at around 178 and at 354 °C. The defect centres formed in the phosphor are studied using electron spin resonance (ESR). The ESR spectrum indicates the presence of Fe³⁺ ions in the non-irradiated system. Irradiated MgSrAl₁₀O₁₇:Eu exhibits lines due to radiation-sensitive Fe³⁺ ion and a defect centre. The centre is characterized by an isotropic g-value of 2.0012 and is assigned to a F⁺ centre. The radiation-sensitive Fe³⁺ ion appears to correlate with the main TL peak at 178 °C. During irradiation an electron is released from Fe²⁺ and is trapped at an anion vacancy to form F⁺ centre. During heating, an electron is liberated from the defect centre and recombines with Fe³⁺ emitting light.     

Electron paramagnetic resonance study of Fe<Superscript>3+</Superscript> ions at octahedral and tetrahedral mirror symmetry sites in the LiScGeO<Subscript>4</Subscript> crystal

An electron paramagnetic resonance (EPR) study of a synthetic single crystal of LiScGeO₄ doped with Cr ions carried out earlier at the X- and Q-bands at 300, K has indicated additional weak lines. A detailed analysis of these EPR lines, which were tentatively attributed to the Fe³⁺ ions at two different mirror symmetry sites, is presented in this paper. The angular dependences in the three crystallographic planes were resolved by fitting the two distinct spectra denoted Fe³⁺(I) and Fe³⁺(II) with a spin Hamiltonian (S=5/2) of monoclinic symmetry. The rank-4 crystal field tensors at tetrahedral and octahedral sites were calculated with the point-charge model to determine the principal axis orientations of their cubic, tetragonal and trigonal components. A comparative analysis of the zero-field splitting tensors and the crystal field ones indicates that Fe³⁺(I) ions substitute for Sc³⁺ at octahedral sites and Fe³⁺(II) ions substitute for Ge⁴⁺ at tetrahedral sites with no significant distorition of the coordination polyhedra in the structure of LiScGeO₄.     

Monitoring synchrotron X‐ray‐induced radiolysis effects on metal (Fe,W) ions in high‐temperature aqueous fluids

Radiolysis‐induced effects on aqueous tungsten ions are observed to form a precipitate within seconds upon exposure to a synchrotron X‐ray micro‐beam in a WO₃ + H₂O system at 873 K and 200 MPa. In situ Fe K‐edge energy‐dispersive X‐ray absorption spectroscopy (ED‐XAS) measurements were made on Fe(II)Cl₂ aqueous solutions to 773 K in order to study the kinetics of high‐temperature reactions of Fe²⁺ and Fe³⁺ ions with transient radiolysis species. The radiolytic reactions in a fluid sample within a hydrothermal diamond anvil cell result in oxidation of the Fe²⁺ ion at 573 K and reduction of Fe³⁺ at temperatures between 673 and 773 K and of the Fe²⁺ ion at 773 K. The edge‐energy drift evident in the ED‐XAS data directly reflects the kinetics of reactions resulting in oxidation and/or reduction of the Fe²⁺ and Fe³⁺ ions in the aqueous solutions at high temperatures. The oxidation and reduction trends are found to be highly consistent, making reliable determinations of reaction kinetics possible.     

GeFe2O4晶体的基态能级和零场分裂参量

GeFe₂O₄是一种单晶化合物，考虑到由3个〈111〉方向之一的一个 轴，从一个中心位置 到另一个中心位置之间，以Fe²⁺离子为中心离子和O^2-为配体构 成了三角（C 3v）对称体系.利用不可约张量理论，建立了3d⁴/3d⁶离子三角（C3 v）对称的晶体场和 自旋相互作用哈密顿矩阵，因此，由完全对角化的晶体场和自旋-轨道相互作用哈密顿矩阵 和电子顺磁共振理论公式求出单晶GeFe₂O₄中Fe²⁺离子 的电子顺磁共振零场分 裂参量D和F-a.并研究了自旋三重态对电子顺磁共振（EPR）零场分裂的贡献.结果显示自旋 三重态对基态零场分裂的贡献是较强的，理论计算结果与实验值相符. 关键词： 自旋三重态 晶体场 低自旋态 高自旋态 零场分裂