The influence of different fabrication processes on characteristics of excess Bi2O3-doped 0.95 (Na0.5Bi0.5)TiO3–0.05 BaTiO3 ceramics

In this study, we will develop the influences of the excess x wt% (x=0, 1, 2, and 3) Bi₂O₃-doped and the different fabricating process on the sintering and dielectric characteristics of 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃ ferroelectric ceramics with the aid of SEM and X-ray diffraction patterns, and dielectric–temperature curves. The 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ ceramics are fabricated by two different processes. The first process is that (Na_0.5Bi_0.5)TiO₃ composition is calcined at 850 °C and BaTiO₃ composition is calcined at 1100 °C, then the calcined (Na_0.5Bi_0.5)TiO₃ and BaTiO₃ powders are mixed in according to 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ compositions. The second process is that the raw materials are mixed in accordance to the 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ compositions and then calcining at 900 °C. The sintering process is carried out in air for 2 h from 1120 to 1240 °C. After sintering, the effects of process parameters on the dielectric characteristics will be developed by the dielectric–temperature curves. Dielectric–temperature properties are also investigated at the temperatures of 30–350 °C and at the frequencies of 10 kHz–1 MHz.     

Nature of intrinsic luminescence in the glasses of CaO–Ga2O3–GeO2 system

The intrinsic luminescence of glasses of the CaO–Ga₂O₃–GeO₂ system has been investigated. High chemical purity and optical quality glasses, both undoped and doped with transition and rare-earth ions with different compositions, were obtained by high-temperature synthesis. The influences of the basic glass composition, impurities (Cr³⁺, Mn²⁺, Eu²⁺, Nd³⁺, Ho³⁺, Er³⁺, and Ce³⁺) and different kinds of excitation, on the intrinsic luminescence of the CaO–Ga₂O₃–GeO₂ glasses were investigated. The nature and possible mechanisms of the intrinsic luminescence in glasses of this system are discussed. The proposed models of intrinsic luminescence are supported by electron spin resonance spectroscopy.     

Fluorescence spectra and homogeneous line widths of Cr in glass nucleating ferroelectric Li2Ge7O15

We report optical studies of the new material – Cr³⁺-doped lithium–germanate glass, containing Li₂Ge₇O₁₅ (LGO) nanocrystalline particles. While only broadband ⁴T₂–⁴A₂ fluorescence from the low-field octahedral Cr³⁺ sites was observed from Cr³⁺ ions in the glass, in LGO nanocrystals high-field Cr³⁺ centers emit ²E–⁴A₂ (R–lines) fluorescence. The process of crystallization in the course of isothermal annealing of glasses was monitored spectroscopically and the nucleation of LGO crystallites was observed starting from the smallest clusters. Using the ²E–⁴A₂ fluorescence spectra it is possible to detect the ferroelectric phase transition in LGO:Cr³⁺ nanocrystals, whose critical temperature was found to be similar to that of the bulk crystals. Long-lived spectral holes were burned in the inhomogeneously broadened R-lines of Cr³⁺ in LGO nanocrystals at low temperatures. The linear temperature dependence of hole widths shows that the homogeneous broadening of ⁴A₂–²E transitions of Cr³⁺ in nanocrystals is due to interaction of Cr³⁺ electronic levels with the two-level systems (TLS) of the surrounding glass. The range of the Cr³⁺-TLS elastic dipole–dipole interaction is estimated.     

Luminescence properties of β-(Ga1−xInx)2O3 solid solutions

In this work, luminescence properties of β-(Ga_1−xIn_x)₂O₃ solid solutions were investigated with the purpose of making the new thermoluminophors for ultraviolet (UV) dosimetry. The doping of aliovalent cation admixture (Mg, Mo) in the β-Ga₂O₃ ceramic sample brings about the appearance of high-temperature thermoluminescence glow peaks with a maximum at 395 and 435 K. The maximum of the thermoluminophor photosensitivity shifts when the composition of solid solution changes.     

Photo-operated two-photon absorption effects in the GeSe2–Ga2S3–PbI2 glasses

The possibility to operate the two-photon absorption (TPA) of newly synthesized GeSe₂–Ga₂S₃–PbI₂ glasses using the CO laser beam (λ=5.5 μm) as a photoinducing one has been demonstrated. As the fundamental laser beam we have used the illumination of 10.6 μm passively modulated 0.5 ns CO₂ laser with a rate repetition of about 10 Hz. We have established that the maximal photoinduced TPA is observed for the 8% doped samples (up to 14 cm/GW), which is achieved at a pump CO laser pump power density equal to about 0.6 GW/cm². The undoped PbI₂ samples show the TPA maximum at a pump power density of about 0.2 cm/GW. The minimal TPA values were observed for the samples with 5% of PbI₂. The obtained results show that these materials can be used as effective optically operated optical limiters.     

Er3+单掺和Er3+/Yb3+共掺碲酸盐玻璃的光谱性质及能量传递

采用高温熔融法制备了新型Er3+单掺和Er3 +/Yb3+共掺的TeO2-Bi2O3-SiO2-B2O3玻璃,测试并分析了样品的吸收光谱、发射光谱以及Er3 +/Yb3共掺杂样品的发射光谱和荧光寿命.计算出了玻璃的J-O强度系数Ωt(t=2,4,6);系统讨论了Er3+/Yb3+共掺杂样品在808 nm激光激发下,Yb...     

Eu3+掺杂5Li2O-1Nb2O5-5TiO2发光陶瓷的制备及性能研究

以Li₂CO₃、Nb₂O₅、TiO₂和Eu₂O₃为原料,采用固相法制备Eu³⁺掺杂的5Li₂CO₃-1Nb₂O₅-5TiO₂（LNT）发光介质陶瓷。通过密度、XRD和荧光光谱测试,对0.2%（质量分数）Eu₂O₃掺杂的陶瓷片进行性能表征。结果表明：1 120℃烧结致密的陶瓷片,其晶相结构为“M-相”与Li₂TiO₃两相复合构成;在400 nm的近紫外光激发下,样品有较强的橙光（592 nm）和红光（615 nm）发射,分别属于Eu³⁺的⁵D₀→⁷F₁的磁偶极跃迁和⁵D₀→⁷F₂的电偶极跃迁。     

Ce3+掺杂SiO2-Al2O3-Gd2O3玻璃的闪烁性能

通常, Ce离子掺杂的低密度玻璃有较高的发光效率, 而高密度的Ce离子掺杂玻璃其发光效率很低. 为了解释这一现象, 采用高温熔融法获得了SiO₂-Al₂O₃-Gd₂O₃三元系统的玻璃形成区, 并在还原气氛下制备了Ce³⁺掺杂SiO₂-Al₂O₃-Gd₂O₃以及SiO₂-Al₂O₃-Gd₂O₃-Ln₂O₃ (Ln=Y, La, Lu)闪烁玻璃, 研究了其光谱和闪烁性能. 测试结果显示: 随着Gd₂O₃含量增加, 玻璃紫外截止波长发生红移, 荧光强度降低, 衰减时间缩短; 加入Lu₂O₃, La₂O₃, Y₂O₃后, 紫外截止波长发生红移, 荧光强度降低, 衰减时间变短; 当Gd₂O₃超过10% mol时, X射线荧光积分光产额从相当于锗酸铋 晶体的61%降低到13%. 荧光强度降低、衰减时间缩短的原因是随着玻璃的紫外截止波长红移玻璃的能带宽度变窄, 使得Ce³⁺离子的d电子轨道开始接近玻璃的导带, Ce³⁺离子受辐射后跃迁到d电子轨道的电子会通过导带与玻璃中的空穴复合, 产生电荷迁移猝灭效应.     

Self-assembly of β-Ga2O3 nanobelts

Self-assembly of β-Ga₂O₃ (beta-gallium oxide) nanobelts with diameters of 50–100 nm and lengths of tens to hundreds of microns have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Under appropriate conditions such as nanobelts concentration, controlled solvent evaporation, β-Ga₂O₃ nanobelts assemble into a fan-like structure on the substrate. A tendency of these nanobelts to align parallel to each other was also observed. The mechanism behind the formation of self-assembly of β-Ga₂O₃ nanobelts has been proposed on the basis of lateral capillary forces.     

Characterization of optical waveguides in β-BaB2O4 crystals formed by 3.0 MeV Ni ions implantation

We report on the optical planar waveguides formation and modal characterization in β-BaB₂O₄ crystals by Ni²⁺ ion implantation at energy of 3.0 MeV and doses of 10¹⁴ ions/cm². The prism coupling method was used to investigate the dark-mode property at wavelengths of 633 nm and 1539 nm, respectively. The refractive index profiles of the waveguides with different doses were reconstructed by an effective refractive index method based on the reflectivity calculation method (RCM). The modal analysis indicates that the fields of TM modes can be well restricted in the guiding region, which means the formation of non-leaky waveguide in the crystal.     

Study of influence of metal ions on CdTe/H2O2 chemiluminescence

Water-soluble CdTe nanocrystals (NCs) were synthesized and applied to study the effect of metal ions on chemiluminescence (CL) of the CdTe/H₂O₂ system. The effects of experimental factors, such as pH, particle sizes of CdTe and reagent concentration, on kinetics curve and CL intensity of the CdTe/H₂O₂ system were examined. The results showed that under the optimal conditions Ba²⁺, Ca²⁺, Fe²⁺, Pb²⁺ and Cu²⁺ enhanced the CL intensity, and Cr³⁺, Ni²⁺, Zn²⁺ and Ag⁺ inhibited the CL intensity.     

Dy3+、Tm3+共掺杂Ca2MgSi2O7的发光特性

采用高温固相法合成了系列Ca₂MgSi₂O₇：Dy³⁺,Tm³⁺发光材料。对样品进行了XRD结构表征,测量了激发光谱、发射光谱、色温和荧光寿命。研究结果表明,Ca₂MgSi₂O₇：Tm³⁺在355 nm激发下显示出蓝色发光,在CIE1931中的色坐标为x=0.165 9,y=0.082 2,色纯度为89%。通过Dy³⁺和Tm³⁺的叠加激发谱带激发,即在349,353,365 nm激发下,Ca₂MgSi₂O₇：Dy³⁺,Tm³⁺显示出青白、冷白和暖白光,相关色温值分别为5 193,9 672,4 685 K。300~500 nm区域间可以有效地激发Ca₂MgSi₂O₇：Dy³⁺,Tm³⁺,并在400~600 nm之间产生蓝光和黄光复合产生的白光,表明该体系可用作白光LED的发光材料。     

超宽禁带半导体β-Ga_2O_3及深紫外透明电极、日盲探测器的研究进展

β-Ga_2O_3是一种新型的超宽禁带氧化物半导体,禁带宽度约为4.9 eV,对应日盲区,对波长大于253 nm的深紫外一可见光具有高的透过率,是天然的日盲紫外探测及深紫外透明电极材料.本文介绍了Ga_20_3材料的晶体结构、基本物性与器件应用,并综述了β-Ga_2O_3在深紫外透明导电电极和日盲紫外探测器中的最新研究进展.Sn掺杂的Ga_2O_3薄膜电导率可达到32.3 S/cm,透过率大于88%,但离商业化的透明导电电极还存在较大差距.在日盲紫外探测器应用方面,基于异质结结构的器件展现出更高的光响应度和更快的响应速度,ZnO/Ga_2O_3核/壳微米线的探测器综合性能最佳,在-6 V偏压下其对254 nm深紫外光的光响应度达1.3×10~3A/W,响应时间为20μs.     

Thermal vibration in superionic conducting glass 5Agl–3Ag2O–2V2O5

The X-ray diffraction measurement for superionic conducting glass 5Agl–3Ag₂O–2V₂O₅ was carried out at 12, 100, 200 and 290 K. The temperature dependence of structure factor S(Q) of 5Agl–3Ag₂O–2V₂O₅ has been discussed based on the theoretical treatment that includes thermal vibration of atoms in noncrystalline materials. The effective overall Debye–Waller temperature parameter B increases with the increase of temperature.     

Characterization of nonstoichiometric nickel manganite spinels NixMn3−x□3δ/4O4+δ by temperature programmed reduction

Cation deficient spinels Ni_xMn_3−x□_3δ/4O_4+δ (0≤x≤1) have been prepared by thermal decomposition of mixed oxalates Ni_x/3Mn_(3−x)/3(C₂O₄)·nH₂O in air at 623 K. They have been characterised by temperature programmed reduction (TPR) under H₂, the reaction being followed by gravimetric and powder X-ray diffraction measurements. It has been shown that TPR proceeds in several steps. The first steps correspond to the loss of nonstoichiometric oxygen leading to the formation of a stoichiometric oxide. During the following stages the manganese cations are reduced, causing the spinel structure to be destroyed, and the formation of solid solution of NiO in a cubic MnO. Subsequently, Ni²⁺ cations undergo a reduction to metallic nickel, and, finally, a mixture of nonstoichiometric MnO_1−δ and metallic nickel is formed. These oxides contain a high level of vacancies which vary with the nickel content with a maximum of δ≈1 near x=0.6. This nonstoichiometry is ascribed both to the presence of Ni³⁺ and excess of Mn⁴⁺.     

稀土离子(Eu3+,Tb3+,Ce3+)掺杂ZnAl2O4/SiO2微晶玻璃的制备与发光性能

采用凝胶法分别制备出4.5ZnO-5.5Al₂O₃-90SiO₂(ZAS)以及ZAS[DK]:RE³⁺ (RE=Eu,Tb,Ce) 透明微晶玻璃。利用X射线衍射仪(XRD)、透射电子显微镜(TEM)和荧光光谱仪(PL)等测试手段,研究了稀土离子掺杂浓度对ZAS微晶玻璃的结构和发光性能的影响。XRD结果表明,ZAS[DK]:RE³⁺ (RE=Eu,Tb,Ce)微晶玻璃包含ZnAl₂O₄晶相和SiO₂非晶相,ZnAl₂O₄平均晶粒尺寸约为30 nm,稀土离子的掺杂没有显著改变原来的ZnAl₂O₄晶体结构。TEM结果表明,900 ℃时ZnAl₂O₄从ZAS体系中析出。PL光谱显示,Eu³⁺ 存在 ⁵D₀→⁷F₂跃迁,ZAS[DK]:Eu³⁺在611 nm 处发出强烈的红色光;由于Tb³⁺ 的⁵D₄→⁷F₅ 跃迁,ZAS[DK]:Tb³⁺在541 nm 处发出明亮的绿色光;ZAS[DK]:Ce³⁺ 在381 nm处显示了蓝光发射,对应于Ce³⁺ 的5d→4f 轨道跃迁。ZAS[DK]:RE³⁺ (RE=Eu, Tb, Ce)的PL发射光谱存在着浓度猝灭现象,Eu³⁺、Tb³⁺ 和Ce³⁺的最佳单掺杂摩尔分数分别为20%、20%和3%。CIE色度图表明,ZAS[DK]: RE³⁺ (RE=Eu,Tb,Ce)的色坐标分别位于红光、绿光和蓝光区域。实验结果表明,ZAS:RE³⁺ (RE=Eu,Tb,Ce) 微晶玻璃是一种良好的可用于全色显示的白光LED材料。     

Electrical and magnetic properties of polyaniline/Fe3O4 nanostructures

We report on electrical and magnetic properties of polyaniline (PANI) nanotubes (150 nm in diameter) and PANI/Fe₃O₄ nanowires (140 nm in diameter) containing Fe₃O₄ nanoparticles with a typical size of 12 nm. These systems were prepared by a template-free method. The conductivity of the nanostructures is 10⁻¹–10⁻² S/cm; and the temperature dependent resistivity follows a ln ρT^−1/2 law. The composites (6 and 20 wt% of Fe₃O₄) show a large negative magnetoresistance compared with that of pure PANI nanotubes and a considerably lower saturated magnetization (M_s=3.45 emu/g at 300 K and 4.21 emu/g at 4 K) compared with the values measured from bulk magnetite (M_s=84 emu/g) and pure Fe₃O₄ nanoparticles (M_s=65 emu/g). AC magnetic susceptibility was also measured. It is found that the peak position of the AC susceptibility of the nanocomposites shifts to a higher temperature (>245 K) compared with that of pure Fe₃O₄ nanoparticles (190–200 K). These results suggest that interactions between the polymer matrix and nanoparticles take place in these nanocomposites.     

Structure and optical properties of sol–gel derived Gd2O3 waveguide films

Pure and rare earth doped gadolinium oxide (Gd₂O₃) waveguide films were prepared by a simple sol–gel process and dip-coating method. Gd₂O₃ was successfully synthesized by hydrolysis of gadolinium acetate. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structure of Gd₂O₃ films annealed at different temperature ranging from 400 to 750 °C were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Gd₂O₃ starts crystallizing at about 400 °C and the crystallite size increases with annealing temperature. Oriented growth of (4 0 0) face of Gd₂O₃ has been observed when the films were deposited on (1 0 0) Si substrate and annealed at 750 °C. The laser beam (λ=632.8 nm) was coupled into the film by a prism coupler and propagation loss of the film measured by scattering-detection method is about 2 dB/cm. Luminescence properties of europium ions doped films were measured and are discussed.     

Ln2Sn2O7：Er3+纳米晶的制备及发光性能研究

采用溶胶-凝胶法合成Ln₂Sn₂O₇:Er³⁺(Ln=La,Gd,Y)纳米晶。通过X射线衍射和场发射扫描电子显微镜测试了样品的晶体结构和形貌,同时对样品的上转换发光性能进行了测试。结果表明:在980 nm连续激发光的激发下,样品主要表现为绿光发射。发射中心在528,549 nm的绿光和672 nm处的红光发射分别对应Er³⁺离子的⁴S_3/2→⁴I_15/2、²H_11/2→⁴I_15/2和 ⁴F_9/2→⁴I_15/2跃迁。以La₂Sn₂O₇:Er³⁺纳米晶为例,Er³⁺离子的摩尔分数为7%、退火温度为1 150℃是其制备的最佳条件,此时其各个发射峰的强度最高。对La₂Sn₂O₇:Er³⁺的发光强度与激发功率关系的研究表明,其绿光和红光发射均为双光子过程。激发光吸收和能量转移是La₂Sn₂O₇:Er³⁺纳米晶上转换发光的主要机制。     

掺铒硫系玻璃的制备及其微结构光纤的中红外信号放大特性研究

为进一步揭示硫系玻璃基掺Er³⁺微结构光纤对于中红外波段信号的放大特性, 采用熔融淬火法研制了Er³⁺离子掺杂的Ga₅Ge₂₀Sb₁₀S₆₅硫系玻璃, 测试了玻璃样品的吸收光谱和2.7 μm波段荧光光谱, 利用Judd-Ofelt和Futchbauer-Ladenburg理论分别计算得到了Er³⁺离子的辐射跃迁概率、辐射寿命以及2.7 μm波段受激发射截面. 在此基础上, 建立了一个980 nm抽运下该玻璃基掺Er³⁺微结构光纤2.7 μm波段中红外信号的放大模型, 理论上研究了其作为2.7 μm波段中红外信号增益介质时的光放大特性. 结果显示, 硫系玻璃基掺Er³⁺微结构光纤具有优异的高增益和宽带放大品性. 在200 mW抽运功率激励下的100 cm光纤长度上, 最大小信号增益超过了40 dB, 高于30 dB信号增益的放大带宽达到了120 nm (2696—2816 nm). 研究表明, Ga₅Ge₂₀Sb₁₀S₆₅硫系玻璃基掺Er³⁺微结构光纤是一种理想的可应用于2.7 μm波段中红外宽带放大器的增益介质.