新型Ba3SiO5:Eu荧光粉的合成及光谱性质

以BaCO_3、SiO_2、Eu_2O_3为原料在还原气氛下采用高温固相法制备了Ba_3SiO_5∶Eu荧光粉体。实验结果表明,制备Ba_3SiO_5的最佳工艺条件是Ba/Si比为3,1 200℃保温4 h。光谱分析表明,Ba_3SiO_5∶Eu荧光粉在254,365,410 nm激发下发射主峰为566 nm(Eu~(2+)的4f~n~(-1)5d→4f~n)宽带发射,量子效率分别为70%、50%、10%,荧光寿命为百纳秒级;以566 nm为监视波长测得激发谱为主峰在250～450 nm范围内的宽带发射,主峰为360 nm,且在410 nm出现小峰; Eu离子最佳掺杂浓度为5%,由发光强度随掺杂离子浓度变化曲线,可以得出Ba_3SiO_5中Eu离子能量传递是基于电四级-电四级作用。     

准分子激光轰击Y-Ba-Cu-O高温超导靶的空间分辨光谱研究

采用WP4-光学多道分析仪对准分子激光轰击Y_1Ba_2Cu_3O_x超导靶产生的等离子体辐射进行了空间分辨测量和研究。实验结果表明,在靶面的邻近区(d<0.4mm),等离子体辐射为较强的连续谱,并迭加有Y、Ba原子和Y~+、Ba~+离子基态电子跃迁的自吸收线。Y、Ba、Cu原子和相应的一价离子以及金属氧化物分子激发态的发射谱线仅在距靶面为0.4mm以外的区域出现。光谱的测量结果支持靶面表层发生爆炸、出射分子簇团和固体微粒的激光烧蚀沉积动力学机制解释。     

钡原子三重态的碰撞诱导受激辐射

在XeCl激光光泵的Ba蒸气中,首次观察到波长为551.9nm、606.3nm及611.1nm的受激辐射,它们分别对应于Ba原子的三重态跃迁:6s6d~3D_2—6s6p~3P_1、5d6p~3P_2-6s5d~3D_3及5d6p~3P_1—6s5d~3D_2.对于Ba原子的自旋禁戒跃迁6s7p~1P_1—6s6d~3D_2的可能性进行了探讨.     

原电池法室温制备Ba_(1-x)Ca_xMoO_4固溶体薄膜

在含Ca_~(2+)和Ba~(2+)的碱性溶液中,通过原电池法在室温条件下制备了Ba_(1-x)Ca_xMoO_4多晶固溶体薄膜。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和荧光分析(FA)对所制备的薄膜进行了分析表征,研究了Ba摩尔分数对薄膜的晶相结构、表面形貌和发光性能的影响。结果表明,原电池法制备的Ba_(1-x)Ca_xMoO_4薄膜致密、均匀、结晶完好,为四方相结构。随着初始溶液中Ba含量的增加,所得Ba_(1-x)Ca_xMoO_4固溶体薄膜的形貌逐渐从CaMoO_4微晶的球形转变为BaMoO_4微晶的四方锥形。在290nm紫外光的激发下,制备的薄膜均在350nm和495nm附近呈现两个宽的发射带,其中495nm的蓝光发射明显强于350nm的紫光发射。初始溶液中的Ba/Ca的量比对所制备的Ba_(1-x)Ca_xMoO_4固溶体薄膜的发射光谱的形状和发射波长影响甚微,但对其发射强度有明显影响。     

循环伏安法研究Ba2YCu3O7—y超导体

本文利用电化学循环伏安法(CV 法),以饱和 Ba(OH)_2水溶液为电解液,对单相Ba_2YCu_3O_(7-y)正交和四方结构超导体进行了研究.结果发现:在典型的正交相中确实存在Cu~(3+)→Cu~(2+)的还原峰,而四方相则无此峰出现.从而首次直接检测到 Ba_2YCu_3O_(7-y)烧结体中 Cu~(3+)离子.     

（Sr,Ba）Al12O19∶RE^3＋（RE=Ce,Tb）的VUV发光及Ce^3＋→Tb^3＋的能量传递

采用高温固相反应合成磁铅矿型(Sr,Ba)Al12O19∶RE3 (RE=Ce,Tb)发光材料,X射线衍射结果证明生成单一磁铅矿型结构。Ce3 产生302nm的发射峰和340nm左右的不太明显的肩,分别对应于5d→2F5/2和5d→2F7/2跃迁;激发光谱显示两个宽带峰,158nm峰对应于基质吸收,260 nm峰是由4f-5d跃迁引起的。Tb3 的发射光谱显示特征的5D3→7Fj(j=2,3,4,5)和5D4→7Fj(j=4,5,6)跃迁;在激发光谱中,160nm左右的峰是由基质吸收和Tb3 -O2-电荷迁移带交迭产生的,193nm峰是Tb3 的4f-5d自旋允许跃迁引起的,233nm弱的峰是自旋禁戒4f-5d跃迁产生的。Ce3 的发射和Tb3 的f-f跃迁吸收(~320 nm)完全交迭,并且Tb3 的发光强度随Ce3 的浓度增加而增强,从激发光谱看出,Tb3 发光部分来自于Ce3 的吸收,具有Ce3 →Tb3 能量传递。     

(Sr,Ba)Al12O19:RE3+(RE=Ce,Tb)的VUV发光及Ce3+→Tb3+的能量传递

采用高温固相反应合成磁铅矿型(Sr,Ba)Al12O19:RE3 (RE=Ce,Tb)发光材料,X射线衍射结果证明生成单一磁铅矿型结构.Ce3 产生302 nm的发射峰和340 am左右的不太明显的肩,分别对应于5d→2F5/2和5d→2F7/2跃迁;激发光谱显示两个宽带峰,158 nm峰对应于基质吸收,260 nm峰是由4f-5d跃迁引起的.Tb3 的发射光谱显示特征的.D3→1Fi(i=2,3,4,5)和5D4→7Fi(i=4,5,6)跃迁;在激发光谱中,160 nm左右的峰是由基质吸收和Tb -O2-电荷迁移带交迭产生的,193 nm峰是Tb3 的4f-5d自旋允许跃迁引起的,233 nm弱的峰是自旋禁戒4f-5d跃迁产生的.Ce3 的发射和Tb3 的f-f跃迁吸收(～320 nm)完全交迭,并且Tb3 的发光强度随Ce3 的浓度增加而增强,从激发光谱看出,Tb3 发光部分来自于Ce3 的0吸收,具有Cd →Tb3 能量传递.     

偶氮胂Ⅲ光度法同时测定硅钡合金中钡和钙

用偶氮胂Ⅲ为显色剂，在pH7.0下，以Ba-ASA Ⅲ-Zn-Phen多元配合物形式测定Ba，并用EGTA掩蔽Ca，消除对Ba的干扰；在pH10时测定Ca，并用硫酸铵消除Ba对Ca的干扰。此法经过简单分离后，可同时测定硅钡合金中Ba和Ca。     

Ba原子6s5d~3 D与6p5d~3 F态的超精细结构及态间跃迁的同位素移动的直接确定

提出并演示了一种光泵预选态的原子光谱测量方法,并对Ba原子的6s5d3 D态与6p5d3 F态的超精细结构及该跃迁的同位素移动进行了直接测量。首先利用791nm的激光激发Ba原子特定同位素及特定超精细结构的6s6s 1 S0→6s6p3 P1跃迁,并利用6s6p3 P1→6s5d3 D2的自发辐射有选择地分别将这些同位素制备到6s5d3 D2态不同的超精细能级上,再用778nm的激光扫出对应的6s5d3 D2→6p5d3 F2跃迁的荧光光谱,通过这几组光谱之间的对比直接实现了对22条超精细谱线的认定和归属,从而得到了135 Ba和137 Ba的6s5d3 D2能级与6p5d3 F2能级的超精细结构常数及该跃迁的同位素移动。     

TlBaCaCuO超导体的结构研究

对高温烧结的TlBaC_3CuO样品的结构用x光衍射、高分辨透射电镜、扫描电镜以及电子衍射和电子能量散色谱等方法进行了分析.发现样品呈典型的陶瓷颗粒显微形貌.确定其主要相为Tl_2Ba_2Ca_2Cu_3O_x 和 Tl_2Ba_2CaCu_2O_y.观测到这两相的单相颗粒及它们的共生体.研究了Tl_2Ba_2Ca_2Cu_3O_x的结构.     

Ionic conductivity of gadolinium-doped barium praseodymium oxide

To clarify the ionic conduction of Ba(Pr_0.6Gd_0.4)O_3−α, the electrical conductivity was measured in moist air and hydrogen atmospheres. The ionic transport number was estimated by a steam concentration cell, a hydrogen permeation cell, and a fuel cell. Temperature dependence of the conductivity in a moist air atmosphere differed from that in a moist H₂ atmosphere. The conductivity under reducing conditions increases with time according to the crystal structure change of Ba(Pr_0.6Gd_0.4)O_3−α due to oxygen loss in the lattice site. Under moist air conditions, the dominant conduction species in the Ba(Pr_0.6Gd_0.4)O_3−α electrolyte were mainly holes. However, the species changed into proton, oxide ion and hole by means of structure change in a reducing atmosphere. It was considered that the ionic conduction occurred due to the crystal structure change. It was predicted that this peculiarity of the conductivity of barium praseodymium oxide influenced the nonstoichiometric behaviour of Pr in the crystal structure.     

Theoretical and computational study of high-pressure structures in barium

Recent high-pressure work has suggested that elemental barium forms a high-pressure self-hosting structure (Ba IV) involving two "types" of barium atom. Uniquely among reported elemental structures it cannot be described by a single crystalline lattice, instead involving two interpenetrating incommensurate lattices. In this Letter we report pseudopotential calculations demonstrating the stability and the potentially disordered nature of the "guest" structure. Using band structures and nearly free electron theory we relate the appearance of Ba IV to an instability in the close-packed structure, demonstrate that it has a zero energy vibrational mode, and speculate about the structure's stability in other divalent elements.     

Microwave absorbing properties of rare-earth elements substituted W-type barium ferrite

W-type barium ferrites Ba(MnZn)_0.3Co_1.4R_0.01Fe_15.99O₂₇ with R=Dy, Nd and Pr were prepared by chemical coprecipitation method. Effects of rare-earth elements (RE) substitution on microstructural and electromagnetic properties were analyzed. The results show that a small amount of RE³⁺ ions can replace Fe³⁺ ions and adjust hyperfine parameters. An obvious increase in natural resonance frequency and high frequency relaxation, and a sharp decrease for complex permittivity have been observed. Furthermore, the matching thickness and the reflection loss (RL) of one-layer ferrite absorber were calculated. It reveals that thin and broad-band can be obtained by RE-substitution. But only when the magnetic moment of RE³⁺ is higher than that of Fe³⁺, can substitution be effective for higher RL. Dy-substituted ferrite composite has excellent microwave absorption properties. The frequency (with respect to −10 dB RL) begins from 9.9 GHz, and the bandwidth reaches far more than 8.16 GHz. The peak value is −51.92 dB at a matching thickness of 2.1 mm.     

Patterning nonanethiol protected gold films by barium atoms

Self assembled monolayers (SAM) formed from nonanethiols on thin gold films were exposed to a beam of ground state and metastable neutral barium atoms through a nickel mask. The interaction of the Ba atoms with the nonanethiol layer, followed by an etching process, creates well defined structures on the gold film, with features below 100 nm. We compared the interaction of ground state Ba atoms and SAM molecules with respect to metastable Ba atoms, finding that by using metastable atoms the Ba dose per SAM molecule is reduced. The results indicate that nanofabrication in the nanometer range with barium atoms is feasible. PACS 07.77.Gx; 42.82.Cr; 81.16.Ta     

Multiphoton double ionization of barium

The multiphoton double ionization of Ba from ~280 to 700 nm was investigated using laser pulses 5 ns long of peak intensity ~10¹⁰ W/cm². The spectrum consists of a number of strong resonances, which can be assigned to Ba⁺ transitions. Most of the assignments have been verified by pump-probe techniques. Thus, the Ba⁺⁺ observed is due to sequential ionization. The multiphoton ionization probability is highest for λ~500 nm, which matches a series of strong Ba and Ba⁺ transitions leading to double ionization     

Effect of barium doping on the physical properties of zinc oxide nanoparticles elaborated via sonochemical synthesis method

The aim of this work is to study the effect of barium (Ba) doping on the optical, morphological and structural properties of ZnO nanoparticles. Undoped and Ba-doped ZnO have been successfully synthesized via sonochemical method using zinc nitrate, hexamethylenetetramine (HMT) and barium chloride as starting materials. The structural characterization by XRD and FTIR shows that ZnO nanoparticles are polycrystalline with a standard hexagonal ZnO wurtzite crystal structure. Decrease in lattice parameters from diffraction data shows the presence of Ba²⁺ in the ZnO crystal lattice. The morphology of the ZnO nanoparticles has been determined by scanning electron microscopy (SEM). Incorporation of Ba was confirmed from the elemental analysis using EDX. Optical analysis depicted that all samples exhibit an average optical transparency over 80%, in the visible range. Room-temperature photoluminescence (PL) spectra detected a strong ultraviolet emission at 330 nm and two weak emission bands were observed near 417 and 560 nm. Raman spectroscopy analysis of Ba-doped samples reveals the successful doping of Ba ions in the host ZnO.     

Diffusion and desorption of barium and oxygen on tungsten dispenser cathode surfaces

Auger measurements have been made on the concentration of barium and oxygen diffusing out of a pore and slot onto the surface of a simulated tungsten dispenser cathode. Profiles of concentration vs distance from the source were obtained at different temperatures. It is found that at cathode operating temperatures very little gradient of oxygen concentration exists on the surface, and under steady state conditions Ba is the main diffusing species. Ba diffusion distances derived are consistent with previous measurements. However it is found that this distance increases with concentration in spite of the fact that the Ba surface lifetime decreases with concentration. Time dependent measurements made on a clean surface show that the rate of Ba and O build up is limited by the supply rate of oxygen to the surface. This supply rate is not diffusion limited but seems to be limited by the mechanism generating free oxygen. A comparison of emission microscope measurements on a tungsten matrix dispenser cathode with the simulated cathode data indicates that similar oxygen generation processes may be controlling the activation of these cathodes.     

钡钨阴极优化与热电子发射性能

分别从基体和铝酸盐两方面优化了钡钨阴极.在基体方面,首先采用窄粒度钨粉结合放电等离子体烧结获得了孔径分布窄的基体;再利用射频等离子体球化技术制备了球形钨粉,采用球形钨粉制备了多孔基体,获得了孔通道光滑、内孔连通性好、孔径分布更加窄的基体.与窄粒度钨粉基体相比,球形钨粉制备的阴极,空间电荷限制区的斜率由1.25增加至1.37,发射均匀性得到提高,拐点电流密度由6.6 A·cm^–2增至6.96 A·cm^–2.在此基础上,采用液相法改善了铝酸盐物相组成,发现空间电荷限制区的斜率增加至1.44,拐点电流密度增加至21.2 A·cm^–2.通过理论计算对钡钨阴极发射的物理本质进行了研究,发现钡钨阴极发射规律遵循偶极子理论.     

UV-photoemission study of barium,europium and ytterbium

Measurements are reported of the photoemission spectra and absolute yield of thin films of Eu, Ba and Yb for the photon energy range 2 to 21 eV. Transitions from the occupied 4f-states in Eu and Yb have been observed and the binding energies deduced. The excitation probability of the 4f electrons is found to be very low and an explanation based on their atomic-like nature is given. Transitions involving valence band states are compared with predictions based on published energy band schemes and the density of states for the unoccupied 5d band in Yb is deduced. The effect of chemisorbed oxygen on Ba and Eu surfaces is reported.     

Molten-salt synthesis and composition-dependent luminescent properties of barium tungsto-molybdate-based solid solution phosphors

Pr~(3+)-activated barium tungsto-molybdate solid solution phosphor Ba(Mo_(1-z)W_z)O_4:Pr~(3+)is successfully fabricated via a facile molten-salt approach. The as-synthesized microcrystal is of truncated octahedron and exhibits deep-red-emitting upon blue light excitation. Powder x-ray diffraction and Raman spectroscopy techniques are utilized to investigate the formation of solid solution phosphor. The luminescence behaviors depend on the resulting composition of the microcrystals with fixed Pr~(3+)-doping concentration, while the host lattices remain in a scheelite structure. The forming solid solution via the substitution of [WO_4] for [MoO_4] can significantly enhance its luminescence, which may be due to the fact that Ba(Mo_(1-z)W_z)O_4:Pr~(3+)owns well-defined facets and uniform morphologies. Owing to its properties of high phase purity,well-defined facets, highly uniform morphologies, exceptional chemical and thermal stabilities, and stronger emission intensity, the resulting solid solution phosphor is expected to find potential applications in phosphor-converted white lightemitting diodes(LEDs).