P2O5对Bi2O3-B2O3-ZnO体系玻璃结构及热性能的影响

采用传统的熔融冷却的方法制备了(40-x)Bi2O3-30B2O3-30ZnO-xP2O5(0≤x≤15mo1％)体系玻璃.使用红外光谱、拉曼光谱、DSC和热膨胀仪研究了封接玻璃的结构和热性能.红外光谱及拉曼光谱结果表明,P2O5作为网络形成体,以[PO4]进入到玻璃的网络结构中,玻璃的网络结构性增强.玻璃结构中[BO3]三角体结构单元相对含量有增多趋势,[BO4]四面体、[BiO3]三角体、[BiO6]八面体结构单元相对含量减少.随着P2 O5含量的增加,玻璃化转变温度和玻璃的初始析晶温度升高;玻璃的密度减小.Bi2O3-B2O3-ZnO-P2O5体系封接玻璃热膨胀系数减小,从8.289×10-6℃-1减小到6.354×10-6℃-1.玻璃的软化点逐渐增大,从416℃升高到524℃.     

A novel Eu3+‐ and self‐activated vanadate phosphor of Ca4La(VO4)3O with oxyvanadate apatite structure

Pure and Eu³⁺‐activated Ca₄La(VO₄)₃O phosphors were prepared via three‐step solid‐phase synthesis. The phase formation and structure were investigated by X‐ray diffraction (XRD) with Rietveld refinements. All the samples crystallized in an apatite‐type structure. The morphological properties were measured via by SEM and EDS measurements. Ca₄La(VO₄)₃O is a new vanadate optical material with a direct band feature and a band energy of 3.1 eV. The undoped Ca₄La(VO₄)₃O phosphor presents self‐activated yellow luminescence from 400 nm to 750 nm with a maximum wavelength of 525 nm originating from VO₄ groups. Luminescence characteristics of Ca₄La(VO₄)₃O indicate that the phosphor is not sufficient for practical applications. In Eu³⁺‐activated Ca₄La(VO₄)₃O, there is an efficient energy transfer from VO₄ to Eu³⁺ ions. The luminescence spectra, concentration quenching, decay curves, color chromaticity, and quantum efficiencies (QE) of Ca₄La(VO₄)₃O:Eu³⁺ were investigated. The phosphor presents optimal Eu³⁺ doping concentration of about 20 mol%. The dominant red emission in Ca₄La(VO₄)₃O:Eu³⁺ is 615 nm from electronic ⁵D₀→⁷F₂ dipole transitions. The quantum efficiency and the luminescence stability of the pure and Eu‐activated Ca₄La(VO₄)₃O were reported. The luminescence was discussed on the structural characteristics.     

Crystallization kinetics and enhanced Bi NIR luminescence of transparent silicate glass‐ceramics containing Sr2YbF7 nanocrystals

Bismuth‐doped glasses and crystals have been widely investigated due to their intriguing potential applications in superbroadband fiber amplifier and lasers in new NIR spectral range. However, few reports have been devoted so far to bismuth‐doped transparent glass‐ceramics. Here, this work reports on bismuth‐doped silicate glasses and glass‐ceramics, which were prepared by melt‐quenching and consequent annealing processes, respectively. On the basis of the analyses on crystallization kinetics, nucleation and growth rate of crystalline phase can be modulated and Sr₂YbF₇ nanophase can, therefore, be precipitated uniformly inside the glass matrix in a controlled way to maintain proper transparence especially in optical telecommunication windows. Once the nanophase comes into being, enhanced bismuth NIR luminescence can be observed by more than 40 times upon excitation of 470 nm. Similar enhancement can appear upon different excitation schemes and the mechanism is discussed accordingly. Such Bi doped transparent glass‐ceramics with improved luminescence efficiency might find application in fiber lasers for future optical fiber communication.     

Large Piezoelectricity and Ferroelectricity in Mn‐Doped (Bi0.5Na0.5)TiO3‐BaTiO3 Thin Film Prepared by Pulsed Laser Deposition

Mn‐doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (MnBNBT) thin films were prepared on SrRuO₃ (SRO)‐coated (001) SrTiO₃ (STO) single crystal substrates by pulsed laser deposition under different processing conditions. Structural characterization (i.e., XRD and TEM) confirms the epitaxial growth of STO/SRO/MnBNBT heterostructures. Through the judicious control of deposition temperature, the defect level within the films can be finely tuned. The MnBNBT thin film deposited at the optimized temperature exhibits superior ferroelectric and piezoelectric responses with remanent polarization P_r of 33.0 μC/cm² and piezoelectric coefficient d₃₃ of 120.0 ± 20 pm/V.     

Impedance spectroscopy of bismuth sodium titanate: Barium titanate ceramics with manganese doping

In this work we use Impedance Spectroscopy (IS) to study lead‐free ceramics of perovskite structure (Bi_1/2Na_1/2TiO₃)_0.925(BaTiO₃)_0.075 with Mn doping of 0, 0.2, 1.0, and 2.0 at.%. We compare our IS results with permittivity results, using dielectric to resistivity transformation equations which allow us to display results either as permittivity or as resistivity. We observe ionic conductivity dominating at lower temperatures, giving way to electronic conductivity at higher temperatures. The permittivity shows deviations from Curie‐Weiss behavior characteristic of relaxor ferroelectrics. The 0.2% Mn samples show the highest ionic resistivity, which will reduce heating for high voltage piezoelectric applications. They also have the highest Curie‐Weiss temperature and Burns temperature.     

The origin of the heterogeneous distribution of bismuth in aluminosilicate laser glasses

As one kind of novel and burgeoning laser materials, bismuth‐doped silicate glasses have aroused increasing attention for the super broadband near‐infrared (NIR) emission. However, the large optical scattering loss, resulting from optical heterogeneity in glass color and refractive index, limits their further applications in telecommunication system. Thus, it is urgent to uncover the essence of heterogeneity in Bi‐doped silicate glasses and subsequently improve glass optical performance. It will give us some hint to homogenize the glass component and Bi active centers so as to boost the development of Bi‐based glass materials. Here, taking 1 typical Bi‐doped calcium aluminosilicate glass as an example, we revealed the origin of the optical heterogeneities in glass color and refractive index through the NIR emission spectra, electron probe microanalyzer (EPMA) of elements and X‐ray photoelectron spectroscopy (XPS) of Bi 4f_5/2, Bi 4f_7/2, and Al 2p. The inhomogeneous distribution of Bi and aluminum components is responsible for the heterogeneity in this glass system. In addition, we found that tetrahedral coordinated aluminum favors the existence of Bi NIR centers, consequently resulting in enhanced Bi NIR emissions. Furthermore, based on our results and the role of Al³⁺ in glass network, we demonstrate the homogenizing of glass component by finely tuning glass composition. This work will enrich the understanding of Bi‐doped laser glass and provide a guideline for the design of component‐derived Bi‐doped silicate glasses and fibers with efficient NIR emission and high optical quality.     

BiVO4的液相燃烧法制备及可见光下光催化性能研究

采用液相燃烧法合成了单斜晶相的BiVO4,并利用XRD,UV-Vis DRS等方法对BiVO4的结构进行了表征。研究了BiVO4在可见光下光催化降解亚甲基蓝的性能,结果表明光照4 h内,亚甲基蓝的降解效率高达94.2%。     

掺杂三氧化二锑的钛酸铋钠钾陶瓷的显微结构和电学性能

采用固相合成工艺制备了（1–x）[0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3]–xSb2O3（BNKT–xSb）压电陶瓷,研究了Sb2O3掺杂对BNKT陶瓷的显微结构和电学性能的影响规律。研究表明：Sb2O3掺杂量x小于0.020时,不改变基体的钙钛矿结构,且Sb具有可变化合价,能形成＂施主＂和＂受主＂2种掺杂而起到＂软化＂或＂硬化＂的作用。当Sb2O3掺杂量x≤0.005时,其压电系数d33随Sb2O3掺杂量的增加而增大,此时Sb2O3表现出了＂软化＂的特征;当Sb2O3掺杂量x〉0.005时,d33降低,从而又表现出了＂硬化＂的特性;当Sb2O3掺杂≥0.010时,诱使陶瓷室温下反铁电微畴的形成,导致铁电性和压电性的骤减。     

Upconversion Luminescence and Mechanism of Cerium Doped YVO4 Crystals

在 YVO4晶体中分别掺入摩尔分数为 2%的 Ce2（CO3）3和 CeO2,在中频感应加热炉中采用提拉法生长了掺 Ce 的 Ce：YVO4晶体。用 X 射线衍射测试了这两种晶体的物相,发现两种样品都主要以 YVO4相存在。X 射线光电子能谱测试表明,在两种样品中铈离子都是以＋3、＋4 混合价态的形式出现的。光谱测试表明,两种样品的光谱特性非常相似,同时发现,两种方式掺杂的 Ce：YVO4晶体在 620 nm 的光激发下,均可发出以 450 nm 为中心的蓝色宽带荧光。分析认为,在 Ce：YVO4晶体中由 620nm 引发的上转换发光的激发过程,不可能直接起源于 Ce3＋的基态2F5/2,它起源于由特殊的“Ce–O”构型形成的电荷迁移态的基态。     

钨与铋摩尔比对Bi2WO6微晶形貌及光学性能的影响

以Bi（NO3）3·5H2O和Na2WO4·2H2O为原料,采用水热法合成了Bi2WO6微晶。采用x射线衍射、场发射扫描电子显微镜、透射电子显微镜和紫外一可见漫反射光谱研究n（W）／n（Bi）摩尔比对合成Bi2WO6粉体的形貌和光学性能的影响。结果表明：不同的n（W）／n（Bi）比对水热法合成Bi2WO6微晶有很大影响;在n（W）/n（Bi）=0．5：1．0～2：2范围内均可制备出斜方晶系钨铋矿型结构的Bi2WO6微晶。当n（W）／n（Bi）=1：2时,Bi2WO6的结晶性能最好;随n（W）／n（Bi）比增加,Bi2WO6的形貌由卡片状球形结构向致密球形结构转变。光学性质研究表明,所制备的微晶表现出较强的紫外吸收特性,随n（W）／n（Bi）比增加,其带隙呈现减小的趋势,当n（W）／n（Bi）=1.5：2.0时所得样品的带隙最小,为2．58eV。