Application of gel-casting to the fabrication of 1-3 piezoelectric ceramic-polymer composites for high-frequency ultrasound devices

A modified gel-casting technique was used to fabricate a 1-3 piezoelectric ceramic/polymer composite substrate formed by irregular-shaped pillar arrays of small dimensions and kerfs. This technique involves the polymerization of aqueous piezoelectric (PZT) suspensions with added water-soluble epoxy resin and polyamine-based hardener that lead to high strength, high density and resilient ceramic bodies. Soft micromoulding was used to shape the ceramic segments, and micropillars with lateral features down to 4 m and height-to-width aspect ratios of ∼10 were achieved. The composite exhibited a clear thickness resonance mode at approximately 70 MHz and a k eff ∼ 0.51, demonstrating that the ceramic micropillars possess good electrical properties. Furthermore, gel-casting allows the fabrication of ceramic structures with non-conventional shapes; hence, device design is not limited by the standard fabrication methods. This is of particular benefit for high-frequency transducers where the critical design dimensions are reduced. © 2012 IOP Publishing Ltd.

Low threshold current density 1.3 mu m metamorphic InGaAs/GaAs quantum well laser diodes

Very low threshold current density InGaAs/ GaAs quantum well laser diodes grown by molecular beam epitaxy on InGaAs metamorphic buffers are reported. The lasing wavelength of the ridge waveguide laser diode with cavity length of 1200 mm is centred at 1337.2 nm; the threshold current density is 205 A/cm(2) at room temperature under continuous-wave operation.

Metamorphic InGaAs quantum wells for light emission at 1.3-1.6 mu m

Metamorphic InGaAs quantum well structures grown on GaAs reveal strong light emission at 1.3-1.6 mu m, smooth surface with an average roughness below 2 nm. and good rectifying I-V characteristics. Dark line defects are found in the QW Post growth thermal annealing further improves the luminescence efficiency but does not remove those dark line defects. Some challenges of epitaxial growth using this method for laser applications are discussed. (c) 2006 Elsevier B.V. All rights reserved.

Mossbauer spectroscopy study of Fe-57 in R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.

Crystallographic and magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

The crystallographic and intrinsic magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) have been investigated. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions, mainly along the a- and b-axis rather than along the c-axis, are observed for all the compounds upon hydrogenation. Hydrogenation leads to an increase in Curie temperature. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and Tb(3)Fc(27.0)Cr(2.0)H(2.8), and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2 Abnormal crystallographic and magnetic properties of Ce3Fe29-xTxHy suggest that the Ce ion is non-triply ionized.

Structural and magnetic properties of hydrides R3Fe29-xVxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and intrinsic magnetic properties of the hydrides R3Fe29 - xVxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed in this work. The lattice constants a, b, and c and the unit cell volume of R3Fe29 - xVxHy decrease with increasing rare-earth atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in regular anisotropic expansions along the a-, b-, and c-axes in this series of hydrides. Abnormal crystallographic and magnetic properties of Ce3Fe27.5V1.5H6.5, like Ce3Fe27.5V1.5, suggest that the Ce ion is non-triply ionized. Hydrogenation leads to the increase in both Curie temperature for all the compounds and in the saturation magnetization at 4.2 K and RT for R3Fe29 - xVx with R = Y, Ce, Nd, Sm, Gd, and Dy, except for Tb. Hydrogenation also leads to a decrease in the anisotropy field at 4.2 K and RT for R3Fe29 - xVx with R = Y, Ce, Nd, Gd, Tb, and Dy, except for Sm. The Ce3Fe27.5V1.5 and Gd3Fe28.4V0.6 show the larger storage of hydrogen with y = 6.5 and 6.9 in these hydrides. (C) 1998 Elsevier Science B.V. All rights reserved.

Crystallographic and magnetic properties of R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and magnetic properties of nitride R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. Nitrogenation leads to a relative volume expansion of about 6%. The lattice constants and unit cell volume decrease with increasing rare-earth atomic number from Nd to Dy, reflecting the lanthanide contraction. On average, the Curie temperature increases due to the nitrogenation to about 200 K compared with its parent compound. Generally speaking, nitrogenation also results in a remarkable improvement of the saturation magnetization and anisotropy fields at 4.2 K and room temperature for R3Fe29-xVxN4 compared with their parent compounds. The transition temperature indicates the spin reorientations of R3Fe29-xVxN4 for R = Nd and Sm are at around 375 and 370 K which are higher than that of R3Fe29-xVx, for R = Nd and Sm 145 and 140 K, respectively. The magnetohistory effects of R3Fe29-xVxN4 (R = Ce, Nd, and Sm) are observed in low fields of 0.04 T. After nitrogenation the easy magnetization direction of Sm3Fe26.7V2.3 is changed from an easy-cone structure to the b-axis. As a preliminary result, a maximum remanence B-r of 0.94 T, an intrinsic coercivity mu(0)H(C) of 0.75 T, and a maximum energy product (B H)(max) of 108.5 kJ m(-3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

稀土配合物光致发光和电致发光性能的研究

有机电致发光器件(organic light-emitting diodes, OLEDs)由于具有全色、低压直流驱动、视角广、高效率和易于制备大屏幕等优点，在平板显示领域具有广阔的应用前景，已引起世界范围内科技界和企业界的广泛重视。稀土配合物作为发光及载流子传输层材料，具有窄带发射和发射波长分布范围广的特点，有利于实现高的色纯度。然而，有机电致发光的机理还未完全弄清楚，稀土配合物电致发光器件距离实际应用还比较远，需要进一步进行研究。本论文研究了Tb~(3+)、Eu~(3+), Sm~(3+)配合物的光致发光和电致发光性质，制备了绿色、红色和橙色电致发光器件，并对稀土配合物的电致发光机理进行了探讨。对于试配合物，以acac为第一配体，研究了第二配体AAP和bath对配合物和器件发光性能的影响并对器件的优化进行了讨论；以Tb(acac)_3bath为发光中心，发现电致发光中~5D_4→~7F_5跃迁相对~5D_4→~7F_5跃迁的增强现象；以Tfacac为第一配体，首次讨论了F取代H对于配体的三重态能级的降低和对配合物以及电致发光器件发光强度的增强作用，对于提高稀土配合物电致发光的性能提供了参考依据。对于铺配合物，以Tfacac为第一配体，以phen和bipy为第二配体，制备了红色电致发光器件并进一步验证了F取代H对于配体的三重态能级的降低作用；以HTH为第一配体，国际上首次报道了室温下Eu~(3+)离子的~5D_1→~7F_J的跃迁，并且其强度依赖于驱动电压的强度，光致发光和电致发光的不同表明二者的发光机理有所不同，并对铺配合物电致发光机理进行了讨论；以HTH为第一配体，国际上首次报道了衫配合物的电致发光现象，并且最大得到了21 cd/m~2的发光强度；为了改善稀土β-二酮配合物光稳定性和热稳定性差的缺点，引入了稀土芳香梭酸配合物，并对配体进行了引入长链的化学修饰，提高了配合物在一般有机溶剂中的溶解度，用旋涂法制备的器件的最大发光亮度达到了174 cd/m~2.

新型稀土配合物的合成及其光致发光与电致发光性能的研究

稀土配合物作为电致发光材料，具有色纯度高、发光效率高等优点，其作为有机电致发光材料（OLED）具有广阔的应用前景。目前，有关其电致发光（OLED）的研究取得了很大的进展，但将其作为OLED材料达到实用化，还需要很大一段距离。因此，有必要进一步地开发新型、高效、接近实用的稀土配合物并将其应用于OLED的制备中，开发出实用的OLED显示屏。本论文的工作中，将共扼适度的蔡环和多氟取代的烷基链引入到β-二酮配体中，合成了含三氟甲基、五氟乙基、七氟丙基和十五氟庚基的β-二酮配体（TFNB、PFNP、HFNH和PFND），并合成了DPPZ，以及其它配体biPy、phen，用这些配体合成了多种稀土配合物。运用多种手段研究了配合物的晶体结构、热稳定性、光致发光（PL）和电致发光（EL）性质，初步探讨了PL和EL发光机理。合成了四种稀土Eu配合物，它们的PL均表现为Eu3＋的特征发光，其荧光效率的大小顺序为：七氟＞五氟＞十五氟＞三氟。以这四种配合物为发光中心组装了掺杂类型的器件。器件性能表明：五氟配合物和七氟配合物具有最佳结构的器件在其所有驱动电压和电流密度下都可以得到纯的EL光谱（Eu3＋的特征发光）。七氟和五氟配合物的最大亮度都超过了1000cd/m2，效率分别达到了4.14 cd／A和5.41cd/A，流明效率分别为2.28和3.11m/W，这样的高效率，达到和超过了国际上报道的同类型器件的EL性能。我们综合比较了几种配合物的性能，得出了一定的结论，并总结出一些规律来指导材料的合成。合成了Sm的三氟、七氟配合物，利用吸收光谱、荧光光谱初步研究了它们的PL性能，并研究了七氟Sm配合物的EL性能。合成了三氟Pr和七氟Pr、Nd、Er和Yb的配合物，研究了它们的近红外发光性能。通过各种光谱的研究，表明在这些配合物的发光过程中，与可见发光的Eu、Sm配合物一样，“天线效应”起到了很大的作用，因此这些配合物均有较强的近红外发光（800-1700nm）。将咔哇基团引入狡酸中一得到Eu、Tb的配合物，它们具有很强的PL性能。

Ce~(3+)在稀土取代的卤磷酸盐中的发光与能量传递的研究

本工作用固相反方法、以炭保护或在N_2-H_2还原气氛中，两次灼烧，合成了一系列烯土取代的卤磷酸盐发光体，其反应是M_2~ICO_3 + M_3~(II)(PO_4)_2 + M_2~(III)O_3 + (NH_4)_2HPO_4 + M~(II)F_2 → M_x~IM_(10-2x)~(II)M_x~(III)(PO_4)_6F_2 + NH_3 + H_2O式中：M~I = Li~+, Na~+, K~+; M~(II) = Ca~(2+), Sr~(2+); M~(III) = Y~(3+), La~(3+), Gd~(3+); X = 0.5, 1, 2, 3。通过X－射线分析法和以Eu~(3+)作为荧光离子探针方法确定了样品的物相和晶体结构，表明它与M_(10)~(II)(PO_4)_6F_2同属六方晶系(Pb_3/m)。并用图解外推法求得样品的晶胞参数a和c分别为9.41和6.89 A。在研究了M~I, M~(II)和M~(III)为不同阳离子，X为不同值时，取代物的物相和结构变化以及对Ce~(3+)发光和能量传递影响规律的基础上，以Na_2Ca_6La_2(PO_4)_6F_2为基本体系比较详细地研究了Ce~(3+)的发光，Ce~(3+)-Mn~(2+), Ce~(3+)-Re~(3+) (Re~(3+) = Pr~(3+)、Nd~(3+)、Sm~(3+)、Tb~(3+)、Dy~(3+)、Tm~(3+)、Ho~(3+)、Er~(3+))以及Ce~(3+)-Mn~(2+)-Re~(3+) (Re~(3+) = Dy~(3+), Nd~(3+))的能量传递。实验发现，Na_2Ca_6La_2(PO_4)_6F_2:Ce~(3+)是较强的紫外光发射体，发射谱带是由338和358nm两个宽带峰组成的，相应于~2D-~2F_(5/2)和~2D-~2F_(1/2)跃迁。发射强度和~2D-~2F_(6/2)，~2D-~2F_(7/2)两种辐射跃迁几率相对大小与温度，Ce~(3+)的浓度有关；F~-含量对发射强度也有强烈的影响。我们认为，浓度和温度的影响是由于Ce~(3+)-Ce~(3+)的能量迁移作用。实验发现，Ce~(3+)能有效地敏化Mn~(2+)的发光，得到高效的黄色荧光发射体。Ce~(3+)对Re~(3+)的作用可以分为三类：A）. Ce~(3+)-Sm~(3+)、Tb~(3+)、Dy~(3+)、Tm~(3+)；B）．Ce~(3+)-Nd~(3+)，Pr~(3+)；C）. Ce~(3+)-Ho~(3+), Er~(3+)。在A，B类型中，Ce~(3+)能有效地敏化这些稀土离子，但能量传递效率(η_T)_A > (η_T)_B。在Ce~(3+)-Ho~(3+)、Ce~(3+)-Er~(3+)类型中，Ho~(3+)、Er~(3+)不产生可见辐射，Ce~(3+)的发射强度也显著降低。在Ce~(3+)-Mn~(2+)-Re~(3+)三元中心体系中，Ce~(3+)的能量可直接传递给Mn~(2+)和Re~(3+)中心，还可通过Ce~(3+)-Mn~(2+)-Re~(3+)的途径传递。通过研究中心离子的浓度效应，温度效应、测定激发光谱、荧光光谱、荧光衰减曲线的荧光寿命，能够证实：在Ce~(3+)-Mn~(2+)、Ce~(3+)-Re~(3+)、Ce~(3+)-Mn~(2+)-Re~(3+)的能量传递属于无辐射共振传递相互作用类型。符合M. Yokata等人提出的偶极－偶极相互作用扩散限制传递历程。我们还利用Ce~(3+)、Ce~(3+)-Mn~(2+)、Ce~(3+)-Re、Ce~(3+)-Mn~(2+))-Re~(3+)激活体系中Ce~(3+)的发射强度和荧光寿命等数据计算了Ce~(3+)的能量传递效率。发现两种结果相差较大，为了准确地表达Ce~(3+)的敏化效果，在分析上了产生这种误差的原因后，提出了两种传递效率表示式(η_f, η_R)。

Mossbauer spectroscopy study of Fe-57 in R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.

Crystallographic and magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

The crystallographic and intrinsic magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) have been investigated. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions, mainly along the a- and b-axis rather than along the c-axis, are observed for all the compounds upon hydrogenation. Hydrogenation leads to an increase in Curie temperature. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and Tb(3)Fc(27.0)Cr(2.0)H(2.8), and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2 Abnormal crystallographic and magnetic properties of Ce3Fe29-xTxHy suggest that the Ce ion is non-triply ionized.

单次分子镀法制备Sm和Eu厚靶

研究了在异丙醇-硝酸体系中单次分子镀流程制备Sm和Eu厚靶的实验条件。确定了在20μm铍箔上进行Sm和Eu分子镀实验的最佳工艺条件为:两极间距3cm,电流密度3.8mA/cm2,分子镀过程持续1h。用分光光度法测定了分子镀的沉积效率均高于95%,所制备Sm和Eu靶膜的厚度分别在1.6和1.5mg/cm2。