Electron Paramagnetic Resonance (EPR) and optical absorption spectra of VO ions in K2SO4---Na2SO4---ZnSO4 glasses

Electron Paramagnetic Resonance (EPR) spectra of K₂SO₄---Na₂SO₄---ZnSO₄ glasses containing 3 mol.% of vanadium sulphate have been studied. Spin-Hamiltonian parameters (g, g, A, A), the dipolar hyperfine coupling parameter (P), the Fermi contact interaction parameter (K) and the tetragonality of the V⁴⁺ site (Δg/Δg) have been calculated. The optical absorption spectra of VO²⁺ ions doped these glasses show three bands. By correlating the EPR and optical spectral data, the molecular orbital parameters have been evaluated. Results agree with similar studies made earlier.     

On the formation of radiation-induced defects in fluoroaluminate glasses

The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba₂CaMgAlF₁₄ were studied. The paramagnetic centers responsible for EPR signals were induced by ion bombardment of the substrates prepared from this glass. The N⁺, O⁺, Ar⁺ and Pb + ions with energy E = 150 keV were used. The integrated dose D was 2 × 10¹⁶ ions/cm². It is shown by means of isochronal anneal experiments and computer simulation of the EPR spectra that they contain four components: broad Gaussian line (GL) with g = 2.016 and σ oscillating in the range 30–40; two anisotropic spectra with g_z = 2.016, g_y = 2.009; g_x = 2.001 (FA₁) and g_z = 2.045; g_y = 2.010; g_x = 1.98 (FA₂) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and ΔH = 0.6 mT. The comparison of obtained results with literature data for γ-irradiated fluoride glasses and ion-implanted oxide glasses of different compositions permitted to conclude that GL is due to hole defects typical of fluoride glasses and localized on several anions (fluorines and oxygen(s)); anisotropic FA₁- and FA₂-spectra are attributed to molecular 0₂⁻-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O₂O⁻, 0₄⁻ , CO⁺, CO⁻) located in voids of damaged implantation layer.     

Stark level analysis for Er-doped ZBLAN glass

From the absorption and emission spectra recorded in a conventional way at 13 K, the Stark levels in manifolds from ⁴I_15/2 to ²H_9/2 for Er³⁺-doped ZBLAN (ZrF₄–BaF₂–LaF₃–AlF₃–NaF) glass have been investigated by means of the effective crystal field model previously proposed to describe the average of local symmetries occupied by rare earth ions in oxide glasses [1]. This model, based on the principle of descending symmetry, used the symmetry group chain scheme. Crystal field strength, homogeneous and inhomogeneous widths of levels have been determined, and the former models and results about optical properties for rare earth ions in heavy metal fluoride glasses are discussed. In fluoride glasses, the rare earth ions appear more evenly distributed than in oxide glasses, and the crystal field strength is weaker than in oxide glasses.     

EPR and optical absorption studies of Cr3+ ions in alkaline earth alumino borate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cr³⁺ ions in Calcium alumino borate (CaAB) glasses have been studied. The EPR spectra exhibit weak resonance signal at g ≈ 4.50 and intense resonance signal at g ≈ 1.98. A sharp resonance signal at g ≈ 1.97 was also observed at lower concentrations of chromium. The concentration dependence of the linewidth of the resonance signal at g ≈ 1.98 suggests the formation of Cr³⁺ ion clusters by magnetic superexchange interactions. The temperature dependence of the peak to peak intensity and the linewidth of the resonance signal at g ≈ 1.98 suggests that the exchange interactions between Cr³⁺ ions in the present sample were antiferromagnetic in nature with Néel temperature, T _N = 233 K. From the number of spins participating in the resonance at g ≈ 1.98, the paramagnetic susceptibility (χ) was calculated at different temperatures (233–295 K). A plot of 1/χ and T was found to obey Curie-Weiss law with negative Curie temperature. By measuring the relative intensities of the resonance signal at g ≈ 1.98, at different temperatures, the value of antiferromagnetic coupling constant (J) has been estimated. The optical absorption spectrum of chromium doped CaAB glass exhibits four bands, characteristic of Cr³⁺ ions, in nearly octahedral symmetry. From the band positions, the crystal field splitting parameter, Dq and the Racah interelectronic repulsion parameters, B and C were evaluated. The optical band gap (E_opt) and the Urbach energy (ΔE) were calculated from the ultraviolet absorption edges.     

Optical absorption of Nd, Sm and Dy in bismuth borate glasses with large radiative transition probabilities

This paper reports on the optical properties of Nd³⁺, Sm³⁺ and Dy³⁺ in bismuth borate glasses, with Bi₂O₃ content varying from 30 to 60 mol%. The variation of the optical properties with composition plays a dominant role in determining a good laser host material. The variation of the Judd–Ofelt intensity parameters Ω_t (t=2,4,6) and the radiative transition probabilities and the hypersensitive band positions, with composition, have been discussed in detail. The changes in position and intensity parameters of the transitions in the optical absorption spectra are correlated to the structural changes in the host glass matrix. The variation of Ω₂ with Bi₂O₃ content has been attributed to changes in the asymmetry of the ligand field at the rare earth ion site and to the changes in their rare earth–oxygen (R–O) covalency, whereas the variation of Ω₆ strongly depends on nephlauxetic effect. The shift of the hypersensitive band shows that the covalency of the R–O bond increases with increase of Bi₂O₃ content, due to increased interaction between the rare earth ions and the non-bridging oxygens. The radiative transition probabilities of the rare earth ions are large in bismuth borate glasses, suggesting their suitability for laser applications.     

SiO2对掺钕铝酸盐玻璃结构及光谱性质的影响

实验通过高温熔融法制备了不同SiO₂ 浓度的掺钕钙铝酸盐玻璃。采用拉曼光谱法分析玻璃结构变化, 发现随着SiO₂含量的增加, [AlO₄]网格中非桥氧逐渐转移至Si⁴⁺离子周围, 玻璃主体Al-O网络中非桥氧减少, 聚合度提高。实验测试了玻璃的吸收光谱和荧光光谱, 并运用Judd-Ofelt理论计算Nd³⁺离子⁴F_3/2→⁴I_11/2跃迁的J-O参数Ω, 自发辐射几率A_rad, 荧光分支比β, 受激发射截面σ_e, 辐射寿命τ_rad等。结果显示: 随着SiO₂浓度的增加, 钕离子周围环境结构对称性提高, 荧光发射峰半高宽变窄, 同时受激发射截面逐渐增大。研究结果表明含有低浓度SiO₂的掺钕钙铝酸盐激光玻璃有望用于超短脉冲激光领域。     

EPR and optical absorption studies of Cu ions in alkaline earth alumino borate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu²⁺ ions in alkaline earth alumino borate glasses doped with different concentrations of CuO have been studied. The EPR spectra of all the glasses exhibit the resonance signals, characteristic of Cu²⁺ ions present in axially elongated octahedral sites. The number of spins participating in the resonance has been calculated as a function of temperature for calcium alumino borate (CaAB) glass doped with 0.1 mol% of CuO. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures (T) and from the 1/χ-T graph, the Curie temperature of the glass has been evaluated. The optical absorption spectra of all the glasses show a single broad band, which has been assigned to the ²B_1g → ²B_2g transition of the Cu²⁺ ions. The variation in the intensity of optical absorption with the ionic radius of the alkaline earth ion has been explained based on the Coulombic forces. By correlating the EPR and optical absorption spectral data, the nature of the in-plane σ bonding between Cu²⁺ ion and the ligands is estimated. From the fundamental ultraviolet absorption edges of the glasses, the optical energy gap (E_opt) and the Urbach energy (ΔE) are evaluated. The variation in E_opt and ΔE is explained based on the number of defect centers in the glass.     

Al3+/Yb3+/P5+掺杂对石英玻璃紫外透过和紫外激发荧光的影响

采用溶胶-凝胶法结合高温真空烧结工艺制备了不同浓度的Al³⁺/Yb³⁺/P⁵⁺掺杂石英玻璃。研究了P⁵⁺和Al³⁺的引入对Yb³⁺掺杂石英玻璃紫外透过和紫外激发荧光光谱, 以及Yb4d电子结合能的影响, 并初步探索了其机理。研究结果表明, Al³⁺/Yb³⁺/P⁵⁺掺杂石英玻璃在190~300 nm波段的吸收主要来源于O^2-→Yb³⁺的电荷迁移吸收, 其谱带位置和Yb4d电子结合能随Yb³⁺的第二配位元素(Al、Si、P)电负性增大向高能方向移动。真空烧结条件下, 引入Al³⁺会引发石英玻璃中Yb³⁺还原为Yb²⁺, 其典型的吸收峰位于330 nm处; 然而, 在Al³⁺/Yb³⁺共掺的基础上再引入P⁵⁺, 且P⁵⁺/Al³⁺摩尔比大于1时, 可以有效抑制Yb²⁺的形成。紫外光激发引起的近红外发光(976 nm)是电子从电荷迁移态弛豫到Yb³⁺激发态向基态跃迁的结果, 可见发光(525 nm)归因于Yb²⁺的5d→4f跃迁。本文研究结果对通过优化工艺和调整组分制备出高性能的Yb³⁺掺杂光纤具有一定的指导意义。     

Investigations of the EPR parameters and substitutional sites of Ni ions in CuGaS2 and AgGaS2 ternary semiconductors

The electronic paramagnetic resonance (EPR) parameters (g factors g_//, g and zero-field splitting D) of Ni³⁺ ions at both M⁺ (M = Cu, Ag) and Ga³⁺ sites in MGaS₂ ternary semiconductors are calculated from the high-order perturbation formulas based on the two spin-orbit (SO) coupling parameter model for 3d⁷ ions in tetragonal symmetry. The calculated results suggest that Ni³⁺ ions replace the monovalent M⁺ ions in MGaS₂ crystals. This point is contrary to the previous assumption that Ni³⁺ ions substitute for the isovalent Ga³⁺ ions to attain the charge neutrality. The reasonableness of the suggestion is discussed.     

Eu3+掺杂硼酸盐玻璃的发光性质及其热稳定性研究

荧光玻璃具有发光中心分布均匀和热稳定好等优点, 成为LED领域研究的热点。本研究采用传统的高温熔融淬火法合成了一系列Eu³⁺掺杂的硼酸盐玻璃, 通过荧光光谱手段对其发光性质及热稳定性进行了表征; 利用Van Uitert模型对样品中Eu³⁺的浓度猝灭行为进行了研究。结果表明: 样品中Eu³⁺的浓度猝灭机理为Eu³⁺离子间的交换作用导致的无辐射能量传递; 利用Arrhenius公式对荧光玻璃样品的温度猝灭行为进行了分析。结果表明: 样品中Eu³⁺的发光温度猝灭属于Crossover过程; 最后分析了Eu³⁺与荧光玻璃基质之间的相互作用。     

Enhancement of red emission assigned to inversion defects in ZnAl2O4:Cr3+ hollow spheres

ZnAl₂O₄:Cr³⁺ hollow spheres composed of secondary nanoparticles with single spinel phase were fabricated using carbon templets. Monitoring the emission of 687 nm, two wide excitation bands attributed to the electrons of Cr³⁺ transiting from ⁴A_2g (⁴F) → ⁴T_1g (⁴F) and ⁴A_2g (⁴F) → ⁴T_2g (⁴F) were observed. The broad excitation band at about 397 nm was asymmetric and consisted of two peaks, indicating that there was a trigonal distortion existing in the lattices. The intensity of all emitting peaks revealed sharp increasing trend with the sintering temperature increase, and the intensity of emission at 698 nm assigned to inversion defects was more intense than that of emission at 687 nm assigned to octahedral Cr³⁺ ions in the undistorted spinel lattice. The samples with higher synthesized temperature revealed longer decay time, and the relative weightage of shorter decay time component decreased with the increase of sintering temperature, indicating that the surface defects decreased.     

Fluorescence line narrowing study of Cr ions in cordierite glass nucleating MgAl2O4 nanocrystals

The luminescence of Cr³⁺ ions in cordierite glass nucleating MgAl₂O₄ nanocrystallites has been investigated. The time resolved fluorescence line narrowing measurements and the temperature dependence of the homogeneous line width show that most Cr³⁺ ions are inside the nanocrystallites. Cr³⁺ ions occupy non-equivalent crystal sites, due to the Mg²⁺–Al³⁺ inversion effect. The values of the homogeneous line width compare well with those of previous studies in crystals. No surface effect has been observed due to the large size of the crystals.     

中子探测用含6Li玻璃闪烁材料最新进展

自上世纪50年代第一代玻璃闪烁材料开发以来, 玻璃闪烁材料在核物理、高能物理、工业探测(中子能谱测量、中子射线照相术及极端环境下α、β与γ射线的探测等)等领域发挥着越来越难以替代的作用. 中子探测用玻璃闪烁材料的研究集中于镧系离子(Ce³⁺、Tb³⁺、Pr³⁺等)掺杂含6Li、10B等中子吸收截面较大核素的硅酸盐、磷酸盐、铝酸盐上. 本文由中子探测用玻璃闪烁材料的性能特点、发展历程与发光机理出发, 重点关注了含⁶Li硅酸盐玻璃、磷酸盐玻璃、氟氧玻璃及其它玻璃闪烁材料的制备方法、光学性能、荧光衰减时间及中子探测效率等性能研究, 并对玻璃闪烁材料的发展趋势及未来应用方向作出了展望.     

离子交换和热处理对贵金属掺杂硅酸盐玻璃光致发光的影响

贵金属纳米颗粒-玻璃复合材料是一种重要的非线性材料。利用光致发光谱及配位场理论, 深入研究了离子交换及氢气热处理对硅酸盐玻璃中贵金属离子的引入、还原、成核及生长过程的影响, 发现延长离子交换时间有利于提高玻璃中金属离子的浓度。对于掺Ag⁺硅酸盐玻璃, 不仅存在孤立Ag⁺离子, 同时也存在Ag₂⁺团簇。H₂中热处理后, 样品中孤立Ag⁺离子浓度迅速降低, 同时出现Ag₃²⁺团簇。对于掺Cu⁺硅酸盐玻璃, 仅存在孤立Cu⁺和Cu²⁺, 没有发现Cu⁺团簇的发光峰, Cu²⁺的存在造成Cu⁺的发光强度显著降低。掺Ag⁺硅酸盐玻璃经H₂热处理后, 再经过第二次离子交换往玻璃中掺Cu⁺是十分困难的。     

Valency states of Yb, Eu, Dy and Ti ions in Li2B4O7 glasses

Absorption and emission spectra of Eu and Dy, Yb and Ti ions in Li₂B₄O₇ glasses grown in oxygen and hydrogen gas atmospheres were measured for valency states and lattice-sites analysis. For the Li₂B₄O₇ glass doped with Eu²⁺, Eu³⁺ and Dy³⁺ ions which were grown in oxidizing and reducing atmospheres, absorption and emission bands due to these ions were investigated before and after γ-irradiation. For the Yb³⁺-doped Li₂B₄O₇ glass, a weak, broad band was observed near the sharp 976.3 nm absorption band. The origin of this band is discussed in comparison with other glasses. Moreover, irradiation experiments using γ-rays were also performed in order to investigate the possibility of valency change of Yb ions. It was found that Ti⁴⁺ ions, which are produced under oxidizing atmosphere, change to Ti³⁺ ions after γ-irradiation with a dose of 10⁵ Gy. An additional absorption band observed at about 500 nm is due to the Ti³⁺ ions accompanied by charge-compensating vacancy and does not give any emission.     

缺陷诱导的Cr掺杂TiO2纳米粉末的铁磁性

用溶胶-凝胶法制备了金红石 Ti_1-xCr_xO₂ (x=0、0.04、0.08) 纳米粉末。磁性测量结果显示, 制备的 Cr 掺杂金红石 TiO₂ 纳米粉末具有室温铁磁性, 样品 x=0.04 和0.08 的饱和磁化强度M_s分别为 0.55×10^-3和 1.6×10^-3 emu/g, (emu/g=4π×10^-7Wb•m/kg)矫顽力H_c分别为 220和 40 Oe(Oe=10³/(4π)A/m)。Cr 掺杂量较大的样品的饱和磁化强度较大, 在 Ar 气中退火可以使粉末呈超顺磁性。Cr2p 区域的密集扫描 X 射线光电子能谱 (XPS)分析显示, 在所有的样品中 Cr都是以Cr³⁺存在。电子顺磁共振谱 (EPR)分析表明, 样品中的 Cr³⁺ 离子仅对其顺磁性有贡献。这些结果提示, 粉末微弱的室温铁磁性来源于掺杂引入的结构缺陷, 其中, 氧空位起重要作用。     

混合尖晶石型Zn6Ga8TiO20:Cr3+荧光粉的合成、结构表征与发光性能

采用高温固相法合成新型红色荧光粉Zn₆Ga_8-xTiO₂₀:xCr³⁺。用XRD、XRF和TEM对样品的成分和晶体结构进行表征, 发现所合成的荧光粉为单一的混合尖晶石结构, Cr³⁺能有效地掺杂进入基质Zn₆Ga₈TiO₂₀中, 并占据八面体格位。荧光光谱分析表明, 激发谱由四个峰组成, 峰值分别为281、337、420和555 nm, 其中281 nm对应Cr³⁺离子的⁴A₂→⁴T₁(4P)跃迁, 337 nm来自O^2-的2p轨道电子向Ga³⁺的4s4p轨道迁移跃迁, 420和555 nm分别对应Cr³⁺离子的⁴A₂→⁴T₁和⁴A₂→⁴T_2g的跃迁。发射光谱是由²E→⁴A₂的跃迁辐射零声子线(689 nm, R锐线)、处于畸变的环境中Cr³⁺发射的N线(696 nm)以及由晶格振动导致的声子伴随发射峰组成。这种荧光粉是一种可能应用在白光LED上的红色荧光粉。     

掺铈多组分硅酸盐玻璃电子辐照着色研究

采用吸收光谱、电子顺磁共振谱和光致发光谱对掺Ce多组分硅酸盐玻璃K509在10 MeV电子辐照下的色心动力学进行了研究。结果表明, 电子辐照引起K509玻璃可见光透过率降低的色心类型为非桥氧空穴色心HC1和HC2。在剂量率一定的情况下, 色心浓度随总剂量的增大呈指数函数增大; 在总剂量一定的情况下, 色心浓度随剂量率增大呈指数函数减小。Ce³⁺荧光强度的变化表明辐照过程中Ce³⁺浓度与辐照总剂量负相关, 与辐照剂量率正相关, 验证了掺Ce玻璃耐辐照机理: Ce³⁺吸收辐照产生的空穴从而抑制空穴色心HC1和HC2的形成, 且不引入额外的可见光波段吸收。通过对Ce³⁺宽带荧光峰进行高斯拟合, 得到了K509中Ce³⁺能级结构图。     

Ce掺杂SrMgF4超结构多晶体的吸收/光致发光光谱

稀土(RE)离子掺杂的钙钛矿型氟化物是可调谐光学材料的候选材料。本工作通过沉淀法合成了SrMgF₄: xCe (x = 0, 0.007, 0.013和0.035)粉末。X射线衍射(XRD)分析表明所获得的荧光粉具有单斜超结构, 价态分析证实存在Ce³⁺/Ce⁴⁺混合价, 在紫外光区通过不同波长的激发光观察到两个荧光带B和C。当Ce³⁺多面体的对称性从高对称变为低对称时, 源于单斜超结构的晶体场导致能级发生强烈的改变。     

Stark levels analysis for Er-doped oxide glasses: germanate and silicate

A model of effective crystal field Hamiltonian based on the principle of descending symmetry and using the symmetry group chain scheme is proposed to describe the average of local symmetries occupied by rare earth (RE) ions in glasses. Only three crystal field parameters, one for each rank, have to be fitted in this Hamiltonian. Based on the absorption and emission spectra measured in a conventional way at 13 K, the Stark levels in manifolds from ⁴I_15/2 to ²H_9/2 and their widths of Er³⁺ in two oxide glasses: germanate and silicate, are investigated. In the process, the scalar crystal field strength, homogeneous and inhomogeneous effective widths of levels are analyzed, and the former models and results about optical properties of rare earth ions in glasses are discussed. The cubic crystal field term is found to give the major contribution to the crystal field strength around the rare earth ion when the weak axial distortion completely removes the degeneracy.