Third-order optical nonlinearities of lead-free (Na1-xKx)(0.5)Bi0.5TiO3 thin films

(Na1-xKx)(0.5)Bi0.5TiO3 (NKBT) (x = 0.1, 0.2, and 0.3) thin films with good surface morphology and rhombohedral perovskite structure were fabricated on quartz substrates by a sol-gel process. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties were investigated by Z-scan technique performed at 532 nm with a picosecond laser. A two-photon absorption effect closely related with potassium-doping content was found in thin films, and the nonlinear refractive index n(2) increases evidently with potassium-doping. The real part of the third-order nonlinear susceptibility chi((3)) is much larger than its imaginary part, indicating that the third-order optical nonlinear response of the NKBT films is dominated by the optical nonlinear refractive behavior. These results show that NKBT thin films have potential applications in nonlinear optics. (C) 2007 Elsevier B.V. All rights reserved.

Surface characteristics of SiO2-TiO2 strip fabricated by laser direct writing

SiO2-TiO2 sol-gel films are deposited on SiO2/Si by dip-coating technique. The SiO2-TiO2 strips are fabricated by laser direct writing using all ytterbium fiber laser and followed by chemical etching. Surface structures, morphologies and roughness of the films and strips are characterized. The experimental results demonstrate that the SiO2-TiO2 sol-gel film is loose in Structure and a shrinkage concave groove forms if the film is irradiated by laser beam. The surface roughness of both non-irradiated and laser irradiated areas increases with the chemical etching time. But the roughness of laser irradiated area increases more than that of non-irradiated area under the same etching time. After being etched for 28 s, the surface roughness value of the laser irradiated area increases from 0.3 nm to 3.1 nm.

Luminescence temperature and pressure studies of Zn2SiO4 phosphors doped with Mn2+ and Eu3+ ions

Zn2SiO4:Mn2+, Zn2SiO4:Eu3+ and Zn2SiO4:Mn2+ Eu3+ phosphors were prepared by a sol-gel process and their luminescence spectra were investigated. The emission bands from intra-ion transitions of Mn2+ and Eu3+ samples were studied as a function of pressure. The pressure coefficient of Mn2+ emission was found to be -25.3 +/- 0.5 and -28.5 +/- 0.9 meV/GPa for Zn2SiO4:Mn2+ and Zn2SiO4:Mn2+ Eu3+, respectively. The Eu3+ emission shows only weak pressure dependence. The pressure dependences of the Mn2+ and Eu3+ emissions in Zn2SiO4:Mn2+ Eu3+ are slightly different from that in Zn2SiO4:Mn2+ and Zn2SiO4:Eu3+ samples, which can be attributed to the co-doping of Mn2+ and Eu3+ ions. The Mn2+ emission in the two samples, however, exhibits analogous temperature dependence and similar luminescence lifetimes, indicating no energy transfer from Mn2+ to Eu3+ occurs. (c) 2005 Elsevier B.V. All rights reserved.

Surface characterization study on SnO2 powder modified by thiourea

The SnO2 material prepared by sol-gel method was modified by thiourea solution in different concentrations (0.05, 0.1 and 0.2 mol dm(-3)). Then the structure and the average grain size of the SnO2 material were investigated by X-ray power diffraction. In order to understand the nature of the species on the SnO2 surfaces, the thermal gravimetric and differential thermal analyzer (TG-DTA) and IR spectra of these modified and unmodified sample were taken. The result indicates that the stability of oxygen adsorbed on thiourea-modified surface was improved and the amount of surface hydroxyl groups adsorbed on this grain surface was decreased. The thiourea adsorbed on SnO2 grain surface is translated to SO42- after sintered at 600 degrees C. SO42- species stabilize the resistance of the SnO2 sensor. (c) 2005 Elsevier B.V. All rights reserved.

Structure and visible luminescence of ZnO nanoparticles

ZnO nanoparticles were synthesized in ethanolic solution using a sol-gel method. The structural and optical properties were investigated by X-ray diffraction, transmission electron microscopy, UV absorption, and photoluminescence. After annealing at 200 degrees C, the particle size is increased and the peak of defect luminescence in the visible region is changed. A yellow emission was observed in the as-prepared sample and a green emission in the annealed sample. The change of the visible emission is related to oxygen defects. Annealing in the absence of oxygen would increase oxygen vacancies. (c) 2006 Elsevier Ltd. All rights reserved.

Porous ZnAl2O4 spinel nanorods doped with Eu3+: synthesis and photoluminescence

Eu3+-doped zinc aluminate (ZnAl2O4) nanorods with a spinel structure were successfully synthesized via an annealing transformation of layered precursors obtained by a homogeneous coprecipitation method combined with surfactant assembly. These spinel nanorods, which consist of much finer nanofibres together with large quantities of irregular mesopores and which possess a large surface area of 93.2 m(2) g(-1) and a relatively narrow pore size distribution in the range of 6 - 20 nm, are an ideal optical host for Eu3+ luminescent centres. In this nanostructure, rather disordered surroundings induce the typical electric-dipole emission (D-5(0) --> F-7(2)) of Eu3+ to predominate and broaden.

Structure and visible luminescence of ZnO nanoparticles

ZnO nanoparticles were synthesized in ethanolic solution using a sol-gel method. The structural and optical properties were investigated by X-ray diffraction, transmission electron microscopy, UV absorption, and photoluminescence. After annealing at 200 degrees C, the particle size is increased and the peak of defect luminescence in the visible region is changed. A yellow emission was observed in the as-prepared sample and a green emission in the annealed sample. The change of the visible emission is related to oxygen defects. Annealing in the absence of oxygen would increase oxygen vacancies. (c) 2006 Elsevier Ltd. All rights reserved.

Fabrication of low cost Si-based tunable high performance resonant cavity enhanced photodetectors

Low cost Si-based tunable InGaAs RCE photodetectors operating at 1.3similar to1.6 mum were fabricated using sol-gel bonding. A tuning range of 14.5 nm, a quantum efficiency of 44% at 1476 nm and a 3-dB bandwidth of 1.8 GHz were obtained.

Enhanced photocatalytic activity of TiO2 nano-structured thin film with a silver hierarchical configuration

TiO2 sol-gels with various Ag/TiO2 molar ratios from 0 to 0.9% were used to fabricate silver-modified nano-structured TiO2 thin films using a layer-by-layer dip-coating (LLDC) technique. This technique allows obtaining TiO2 nano-structured thin films with a silver hierarchical configuration. The coating of pure TiO2 sol-gel and Ag-modified sol-gel was marked as T and A, respectively. According to the coating order and the nature of the TiO2 sol-gel, four types of the TiO2 thin films were constructed, and marked as AT (bottom layer was Ag modified, surface layer was pure TiO,), TA (bottom layer was pure TiO,, surface layer was Ag modified), TT (pure TiO, thin film) and AA (TiO, thin film was uniformly Ag modified). These thin films were characterized by means of linear sweep voltammetry (LSV), X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy and transient photocurrent (I-ph). LSV confirmed the existence of Ago state in the TiO, thin film. SEM and XRD experiments indicated that the sizes of the TiO,, nanoparticles of the resulting films were in the order of TT > AT > TA > AA, suggesting the gradient Ag distribution in the films. The SEM and XRD results also confirmed that Ag had an inhibition effect on the size growth of anatase nanoparticles. Photocatalytic activities of the resulting thin films were also evaluated in the photocatalytic degradation process of methyl orange. The preliminary results demonstrated the sequence of the photocatalytic activity of the resulting films was AT > TA > AA > TT. This suggested that the silver hierarchical configuration can be used to improve the photocatalytic activity of TiO2 thin film.

Effect of dopant concentration on photocatalytic activity of TiO2 film doped by Mn non-uniformly

The thin films of TiO2 doped by Mn non-uniformly were prepared by sol-gel method under process control. In our preceding study, we investigated in detail, the effect of doping mode on the photocatalytic activity of TiO2 films showing that Mn non-uniform doping can greatly enhance the activity. In this study we looked at the effect of doping concentration on the photocatalytic activity of the TiO2 films. In this paper, the thin films were characterized by UV-vis spectrophotometer and electrochemical workstation. The activity of the photocatalyst was also evaluated by photocatalytic degradation rate of aqueous methyl orange under UV radiation. The results illustrate that the TiO2 thin film doped by Mn non-uniformly at the optimal dopant concentration (0.7 at %) is of the highest activity, and on the contrary, the activity of those doped uniformly is decreased. As a comparison, in 80 min, the degradation rate of methyl orange is 62 %, 12 % and 34 % for Mn non-uniform doping film (0.7 at %), the uniform doping film (0.7 at %) and pure titanium dioxide film, respectively. We have seen that, for the doping and the pure TiO2 films, the stronger signals of open circuit potential and transient photocurrent, the better photocatalytic activity. We also discusse the effect of dopant concentration on the photocatalytic activity of the TiO2 films in terms of effective separation of the photon-generated carriers in the semiconductor. (C) Versita Warsaw and Springer-Verlag Berlin Heidelberg. All rights reserved.

Preparation and luminescence properties of Eu2+ in SiO2 xerogels

Al-doped and B, Al co-doped SiO2 xerogels with Eu2+ ions were prepared only by sol-gel reaction in air without reducing heat-treatment or post-doping. The luminescence characteristics and mechanism of europium doping SiO2 xerogels were studied as a function of the concentration of Al, B, the europium concentration and the host composition. The emission spectra of the Al-doped and B, Al codoped samples all show an efficient emission broad band in the blue violet range. The blue emission of the Al-doped sample was centered at 437 nm, whereas the B, Al co-doped xerogel emission maximum shifted to 423 nm and the intensity became weaker. Concentration quenching effect occurred in both the Al-doped and B, Al co-doped samples, which probably is the result of the transfer of the excitation energy from Eu2+ ions to defects. The highest Eu2+ emission intensity was observed for samples with the Si(OC2H5)(4):C2H5OH:H2O molar ratio of 1:2:4. (c) 2006 Elsevier B.V. All rights reserved.

Preparation and optical property of a novel hydrophobic anti-reflection coating for KDP crystal

A novel inorganic-organic hybrid hydrophobic anti-reflection silica film used for laser crystal was obtained by sol-gel process. The film consisted of silica sols mixed with a small amount of polymethyl methacrylate (PMMA) or polystyrene (PS). The optical transparency, hydrophobic property and surface morphology of the film were characterized by UV-VIS-NIR spectrophotometer; contact angle instrument and Scanning Electron Microscopy (SEM), respectively. The results showed that the anti-reflection coating had good hydrophobility and optical transparency from 400 nm to 1200 nm. The contact angle reached to 130-140 degrees. SEM images indicated the hydrophobic films modified with PMMA or PS had compact structure compared to the pure silica sol film. (C) 2008 Elsevier B.V. All rights reserved.

有机/无机纳米杂化发光材料的制备与性质

近年来，纳米杂化技术，尤其是溶胶-凝胶技术为发光材料的发展开辟了一个崭新的途径，但目前这些工作尚处于研究的初始阶段，还有许多问题有待克服，例如：有机染料的热稳定性差，稀土有机配合物在溶胶体系中的溶解性、分散性差，以及发光基质在杂化体系中具有浓度淬灭效应、渗出效应等。为此，我们从分子设计角度去有目的的合成一类新型Sol-gel前体，以此制备出系列有机／无机杂化发光材料，取得了一批有意义的结果。1．经γ-射线辐照原位制备有机／无机纳米杂化材料基于Sol-gel方法及γ-射线辐照技术发明了一种制备有机／无机杂化材料的新方法，并制备了两类有机／无机杂化材料，一类是有机／无机两相间无强相互作用（共价键）的杂化材料，一类是两相间有弱相互作用（氢键）的杂化材料。从材料制备上看，反应条件温和，易控制，解决了长期困扰的样品开裂问题，制备工艺简单，易操作，易于工业化。从材料的结构表征上看，经γ-射线辐照聚合的样品的聚合比较完全，紫外-可见光谱及透射电子显微镜观察结果表明杂化样品中有机相、无 机相分散性良好，杂化是在分了水平上进行的。无机网络的限制不仅提高了杂化样品中聚合物的热稳定性和相转蛮温度，还提高了杂化样品中聚合物的机械力学性能。所发明γ-射线辐照原位制备有机／无机纳米杂化材料技术可以作为相关材料制备的通用方法。2．含有机染料有机／无机纳米杂化发光材料 设计并合成了一种官能化有机染料（可作Sol-gel前体），采用所发明的γ-射线辐照技术制备了两类有机／无机杂化发光材料，一类是相间有强相互作用(共价键)有机／无机的杂化发光材料（HEMA/KH570），一类是两相间只有弱相互作用（氢键）有机／无机杂化发光材料（HEMMTEOS）。所得杂化发光样品透明性良好，在可见光范围内透光率在90％以上，在紫外光下能发射出较强的蓝色（偏紫）荧光。在所研究体系中，随着有机染料浓度的增加，样品的发光强度在逐渐增大，有机／无机组分、组成的变化对杂化材料的荧光行为：荧光发射、荧光激发、荧光寿命影响不大；同有机溶液相比，杂化基体的限制使得有机染料的荧光发射波长发生红移，纯无机基体使之红移位置更大。杂化材料的最强荧光发射波长较染料本体杂化材料的短，表明了有机染料是均匀分散在杂化基体中的。3．含稀土有机／无机纳米杂化发光材料通过所合成的含酰亚胺键的有机芳香羧酸化合物(NP)的稀土配合物的紫外-可见、荧光、磷光光谱探讨了稀土配合物中有机配体与稀土衷心离子的能量传递与能级匹配的关系。钆配合物的低温磷光光谱结果表明，所合成的酰亚胺类芳香羧酸化合物(NP)的最低三重态能级为24690cm~(-1)，与稀土铕和铽的能级差分别为7426cm~(-1)和4190cm~(-1)。荧光光谱表明所合成芳香羧酸配体与稀土离子铽的能级匹配性好，与铕离子则较差，即铽的二元配合物的相对荧光效率比铕的高，荧光寿命则几乎相同在2ms左右。在芳香羧酸化合物（NP)的三元稀土配合物中，第二配体1,10-邻菲罗啉(Phen)是能量吸收，传递的主体。同相应二元配合物相比，铕的三元配合物的相对荧光效率提高了三倍，而铽的则降低了一半，三元配合物的荧光寿命为4ms，比二元的长近一倍。所研究稀土配合物的表现的均是基于中心稀土离子的特征跃迁的特征发光，即：Eu~(3+)的5D_0→7F_j (j = 0, 1, 2, 3, 4)跃迁，Tb~(3+)的~5D_4 → ~7F_j (j = 6, 5, 4, 3)跃迁。基于小分子模型配合物的研究，设计并合成了一种新型有机芳香羧酸Sol-gel前体(TAT)，从而原位合成了含稀土有机／无机纳米杂化发光材料。荧光光谱表明所制得的有机／无机杂化膜的发光谱带较窄，色纯度较高。在含稀土有机／无机杂化膜中，随着稀土离子浓度的增加，样品相对荧光强度增大，浓度淬灭效应及发光基质的渗出效应在所研究体系中未出现。同小分子稀土配合物相比，含稀土杂化膜的荧光发射谱带窄化、不劈裂、对称性好，而且荧光寿命普遍变小，发光中心趋于单一．透射电镜结果表明所制备含稀土有机／无机杂化膜，不仅有机／无机基体杂化在分子水平上，稀土离子在杂化基体中的聚集结构也在纳米层次上，一般在50～100nm，随着稀土离子浓度的增加，这种聚集结构尺寸略有增大，但小于100nm。通过三基色原理成功地制备了发白色荧光有机／无机杂化材料，该杂化材料在紫外光的激发下可同时发出红、绿、蓝三种荧光，色坐标测试结果为：X = 0.314，Y = 0.316，该位置已接近等能量白光色坐标的理论值X = 0.33，Y = 0.33，又接近实际显示的需要，有一定的理论及实践意义。

电化学电容分析法研究

生物分子识别及其之间的相互作用是各种生命运动现象的基础，任何分子层次上的生命科学方面的研究归根到底都是生物分子之间或是生物分子和其他有机、无机分子作用的研究。生物体组织的功能化也正是来源于生物分子活性位点的相互识别。例如，蛋白分子的三维结构组装作用，DNA分子之间及DNA和RNA之间的识别作用构成了生命体的遗传信息，酶对底物的专一催化作用，抗原-抗体的特异结合也是建立在对底物分子的结构识别基础上。因而对生物分子识别及相互作用的研究，可以帮助理解生物分子结构和功能及各种生命运动现象的本质。对生物分子识别进行实时，原位的跟踪监测而无需附加其他的标记分子和修饰等手段，一直是分析化学家研究的重点。本研究论文正是基于此研究思想来构造新型电化学分子识别传感器，并对免疫分子识别，金属离子的检测，磷脂仿生膜的离子诱导效应，自组装膜表面酸碱性及溶胶-凝胶内生物分子性质等方面进行了研究。1.利用电化学电容检测技术和实验装置原理，在金属铝片上通过阳极氧化的方法制备了电容测定所需的绝缘层，并以此层作为电化学测定的对电极，对电容测定起到了关键性的稳定作用，同时避免了在工作电极上烦琐的组装，提高了测定的敏感度。利用金属氧化膜为绝缘层，对protein A和小鼠免疫蛋白G的作用，鼠IgG和羊抗鼠IgG在溶液中的相互作用进行了实时的电容信号测定。表明电化学电容方法和测量装置的可行性。2.将功能化的烷基链自组装于电极表面，对其表面的酸碱平衡进行研究，电容分析方法是方便且直接的测量手段。通过对巯基丙酸的自组装电极的表面酸碱滴定及表面P_(ka)值的测定。讨论了界面电容变化的机理和影响因素。研究结果和应用其他方法测定值相一致。3.将磷脂分子和长链烷基硫醇通过疏水作用组装于金电极表面，在钙离子诱导作用下对该体系进行了电化学电容的测量。通过对电容信号的分析，推测钙离子和磷脂分子作用机理。4.将Sol-Gel技术应用于电容测定的绝缘层和生物分子固定化。通过控制硅醇聚合的酸度和时间，形成极小孔洞的致密的网状结构。利用功能化的硅醇，通过自组装技术将上述聚合产物固定于金电极表面，同时将生物分子聚合固定于溶胶表面或包埋于其网格内。对其电容信号的测定结果表明，该体系是良好的电容分析方法的研究基底。以钾离子传感器为例，研究了本体系的实际应用。将谷胱甘肽固定于溶胶表面，对溶液中的钾离子的电容响应进行测量，表明在较高浓度区有很好的线性。

新型溶胶-凝胶电化学生物传感器的制备

发展电化学生物传感器是化学传感器研究的一个重要领域，也是人们一直感兴趣的一个研究方向。而且人们一直在探求，在生物传感器的制备过程中将生物活性分子和电子媒介体有效地固定于电极基质材料中的新型固定化方法。溶胶-凝胶材料所具有的诸多特性，如可低温包埋、孔径可控性、不溶胀性、化学惰性、物理刚性、光透性、易于制备以及良好的生物相容性，赋予了溶胶-凝胶过程有效地固定化各种敏感试剂的能力，基于溶胶-凝胶技术的各种传感器也随之蓬勃发展起来。在本论文的工作中，主要是通过利用新型溶胶-凝胶复合材料以及将溶胶-凝胶技术与其它固定化技术相结合，来制备各种新型电化学生物传感器。主要内容如下：1．首次将HRP和聚毗咯共同电沉积到二茂铁梭酸修饰的碳陶瓷电极表面，制备了过氧化氢生物传感器。实验结果表明，这种将表面修饰和碳陶瓷电极相结合的方法，能够有效地应用于各种生物传感器的制备。而且这种方法也为异相双酶生物传感器的制备提供了可能性。2．将含有葡萄糖氧化酶的聚毗咯薄膜修饰到含有HRP和媒介体的碳陶瓷电极表面，发展了一种新型双酶安培检测葡萄糖传感器。在这种传感器的异相双层结构中，各种酶均保持了良好的生物活性，而且所得传感器也具有良好的抗干扰能力以及对底物检测的高灵敏度。这种方法有望于将各种H_2O_2生成酶与HRP相结合，制备具有高选择性的其它生物传感器。3．以铱超微粉为导电介质，将其与溶胶-凝胶过程相结合，首次制备了新型铱陶瓷电极。溶胶一凝胶铱复合材料表现出了良好的催化活性，过氧化氢既可以在铱陶瓷电极上被电化学氧化，也可以在低电位下被电化学还原。并利用溶胶一凝胶铱复合材料进一步制备了第一代铱陶瓷葡萄糖生物传感器。由于H_2O_2检测过程中所需要的低工作电位，使得铱陶瓷酶电极具有对底物的高度选择性。4．利用双相还原法制备并表征了铱纳米粒子，并将纳米技术、自组装技术以及溶胶-凝胶技术相结合，制备了溶胶-凝胶铱复合电极。实验结果表明，琉基功能化烷氧基硅烷能够组装到金电极表面形成凝胶薄膜修饰电极，通过铱纳米粒子与凝胶薄膜中自由疏基间的吸附作用，铱纳米粒子能够被容易地固定到凝胶薄膜中。所制备的铱陶瓷电极同样表现出了对H_2O_2高度的灵敏度以及选择性。5．利用二氧化硅凝胶的自组装技术构建了甲苯胺蓝修饰电极，并用于电化学催化氧化NADH的测定。实验中，详细探讨了甲苯胺蓝在凝胶组装修饰电极中的电化学行为。结果表明，此类修饰电极的双层结构有效地防止了催化剂的渗漏以及NADH检测过程中由于吸附作用而造成的电极污染问题。