Technology and Applications of Sol-Gel Materials

A brief review of some aspects of technology and applications of the sol-gel technology is presented. The content is divided into three parts concerning: (1) synthetic aspects of this technique, (2) optical sensors (optodes) and (3) pure and doped silica nanopowders manufactured by the sol-gel method. The versatility and applicability of the method is discussed. Also, several examples of active (”smart”) materials obtained by this technique are presented.     

Probing Si and Ti Based Sol-Gel Matrices by Fluorescence Techniques

The photophysical behavior of several probes incorporated in sol-gel–derived matrices (both monoliths and thin films) has been studied using steady-state and time-resolved fluorescence, along with fluorescence anisotropy to study the matrix structure and to elucidate probe-matrix interactions. The probes studied include laser and solvatochromic dyes along with porphyrins and phthalocyanines. It was found that spectral shifts, time-resolved decays, and quantum yields depend on the type of matrix and its preparation conditions combined with the drying time and the nature of retained solvent, which can be added to act as an anticracking agent. The differences between the results in the TiO₂ matrix, where electron transfer is most probably present, and SiO₂ are shown.     

Enhanced Ratiometric pH Sensing Using SNAFL-2 on Silver Island Films: Metal-enhanced Fluorescence Sensing

We have explored the opportunities for enhanced ratiometric pH sensing using the well-known carboxy seminaphthofluorescein (SNAFL-2) and silver island films (SiFs). Our results show that the metallic surfaces can provide up to a 40-fold increase in probe fluorescence intensity as compared to nonmetallic surfaces with the same probe coverage. However, while the S/N is significantly better for pH sensing, the emission wavelength ratiometric values are similar to that obtained in solution, due to the fact that the emission of both the acidic and basic forms of the probe are enhanced to similar extents. To the best of our knowledge this is the first report of enhanced ratiometric fluorescence sensing on metallic surfaces.     

Thermo-Sensitive Ba0.64Sr0.36TiO3 Thin Film Capacitors for Dielectric Type Uncooled Infrared Sensors

Ba_0.64Sr_0.36TiO₃ (BST) thin films are prepared on Pt/Ti/SiO₂/Si₃N₄/SiO₂/Si substrates by a sol-gel method. Thermo-sensitive BST thin film capacitors with a Metal-Ferroelectrics-Metal (M-F(BST)-M) structure are fabricated as the active elements of dielectric type uncooled infrared sensors. XRD are employed to analyze the crystallographic structures of the films. AFM observations reveal a smooth and dense surface of the films with an average grain size of about 35 nm. Rapid temperature annealing (RTA) process is a very efficient way to improve crystallization quality. The preferable annealing temperature is 800°C for 1 min. The butterfly shaped C-V curves of the capacitors indicate the films have a ferroelectric nature. The dielectric constant and dielectric loss of the films at 100 kHz are 450 and 0.038, respectively. At 25°C, where the thermo-sensitive capacitors work, the temperature coefficient of dielectric constant (TCD) is about 5.9 %/°C. These results indicate that the capacitors with sol-gel derived BST thin films are promising to develop dielectric type uncooled infrared sensors.     

Fluorescence investigations of pure and mixed evaporated dye layers

Fluorescence spectroscopy is used to investigate energy transfer processes in evaporated layers consisting of several different dyes. In this study films ofN,N-dimethylperylene-3,49,10-bis-dicarboximide (methylperylene pigment, MPP), coevaporated with copper phthalocyanine (CuPc) at varying ratios, and double layers of MPP and CuPc with different thicknesses are investigated. It is shown that energy transfer from MPP to CuPc occurs in both mixed and double layers. The energy transfer leads to a strong quenching of the MPP fluorescence and sensitized CuPc emission in the NIR region. The concentration dependence of the fluorescence quenching in mixed layers can be described by a Stern-Volmer plot. A simple model based on exciton diffusion between MPP molecules toward active quenching centers is used to determine the diffusion length.     

Metal Enhanced Fluorescence Solution-based Sensing Platform 2: Fluorescent Core-Shell Ag@SiO<Subscript>2</Subscript> Nanoballs

In this Rapid Communication, we present the development of monodisperse core-shell (silver core-silica shell) nanoparticles with various shell thicknesses featuring a fluorophore, subsequently named Metal-Enhanced Fluorescence (MEF) nanoballs. MEF nanoballs consist of a ≈130 nm silver nanoparticle core, a silica shell with up to 35 nm thickness and fluorophores doped within the silica shell. Fluorescent nanobubbles where the silver core is removed by chemical etching are used as control samples to show the benefits of using silver nanoparticles, i.e, Metal-Enhanced Fluorescence. Finally, we demonstrate the broad potential biological applications of MEF nanoballs by employing near-infra red emitting probes (Rhodamine 800) within the silica shell, for potential applications in cellular imaging and solution-based sensing. Kadir Aslan, Meng Wu, Contributed equally     

Enhanced Lanthanide Luminescence Using Silver Nanostructures: Opportunities for a New Class of Probes with Exceptional Spectral Characteristics

The photophysical effects of europium tetracycline immobilized in thin polyvinyl alcohol films coated onto silver nanostructures have been investigated. Complimentary to recent reports from our laboratories that the close proximity of luorophores to silver nanostructures can enhance their intrinsic radiative decay rate, we show that up to a 16-fold enhancement in lanthanide luminescence is possible, accompanied by a notable reduction in luminescence lifetime. These results suggest the potential future development of a new class of significantly brighter lanthanide based probes with exceptional spectral properties, which can probably undergo significantly more excitation–emission event cycles due to the reduced lifetime, substantially increasing detectability.     

Fluorescent Dyes in Sol-Gel Glasses

We review the sol-gel technology and the methods by which fluorescent dyes can be incorporated into inorganic glasses and organic-inorganic composites. The performance of the dyes in solar concentrators, tunable lasers, and active waveguides is presented.     

氧对钌(Ⅱ)配合物溶胶-凝胶膜荧光响应的影响

利用蓝光LED(λmax =4 6 0nm )构建的氧荧光猝灭检测系统 ,考察了不同Ru配合物以甲基硅氧烷(TMOS)和二甲基二甲氧基硅烷 (DiMe DMOS)为共先驱体 ,制备的有机改性溶胶 凝胶 (sol gel)膜内荧光猝灭行为。DiMe DMOS的加入量会影响敏感膜的极性 ,从而影响敏感膜对氧浓度的响应。利用自行构建的装置对水体中氧进行了检测 ,传感膜对氧饱和水溶液测定的相对标准偏差为 1 12 % (n =6 ) ,响应时间为 30s,对氮饱和水溶液测定相对标准偏差为 0 39% (n =6 ) ,响应时间为 90s,敏感膜使用寿命大于 6个月。     

溶胶-凝胶法制备TiO2-SiO2多层增透膜

在酸催化体系中以钛酸丁酯为前驱体制得TiO2溶胶,以正硅酸乙酯（TEOS）为前驱体制得SiO2溶胶,采用提拉法在普通载玻片上镀膜。辅助MASS膜系设计软件进行模拟计算,得到了透射率为99%的膜片。根据理论模拟结果,实验采用交叉镀膜,制备出了宽带增透TiO2-SiO2多层膜,其方法有别于以往的TiO2/SiO2复合膜法。用紫外-可见分光光度计测量了样品的透射光谱。实验发现,样品具有明显的宽带增透效果：在400-700nm波段,当光线垂直入射时,增透6%左右;45°角入射时,可增透10%。     

Gd2O3:Eu3+溶胶-凝胶薄膜发光特性研究

以无机稀土氧化物为原料制备了Gd2O3:Eu3 溶胶-凝胶薄膜,通过对不同Eu3 离子掺杂浓度、不同烧结温度薄膜发光强度的研究,得出Gd2O3薄膜中Eu3 离子的最佳掺杂浓度为10%、最佳热处理工艺为800℃下烧结2h;由薄膜和粉末激发谱的比较发现:薄膜中存在着比粉末更有效的能量传递,从而更有利于高能射线激发发光;首次观察到薄膜经过1000℃烧结2h后发光消失,并通过SEM和XRD的实验分析对这一现象进行了解释。     

低损耗有机无机混合溶胶凝胶波导的实验研究

利用有机无机混合的溶胶凝胶方法在硅基底上制备波导薄膜.采用正硅酸四乙酯和苯基三乙氧基硅烷作为反应先驱物,利用旋涂的方法成膜,对其折射率,传输损耗以及条形波导的光刻、刻蚀特性进行了研究.测量了波导薄膜折射率随成分变化的关系.实验表明,该方法工艺简单,可以获得具有较低损耗的波导薄膜.测试得到632.8 nm波段的损耗系数为0.23 dB/cm.采用ICP刻蚀工艺获得了较为平整的条形波导.     

准波导结构染料薄膜中荧光和放大自发辐射的泄漏模特性

通过理论分析和实验测量,研究准波导结构染料薄膜中荧光和放大自发辐射（ASE）的泄漏模特性。理论上,考虑薄膜传输损耗及染料吸收损耗对准波导结构中泄漏模特性的影响,通过计算准波导结构中泄漏模的光强分布,给出了相应的物理机制分析;实验上,以棱镜为衬底制备染料薄膜,根据棱镜耦合法测量不同出射角对应的泄漏模的荧光与ASE光谱,验证理论的正确性。此外,采用光束分析仪探测各泄漏模式对应的荧光及ASE的光强分布,研究了准波导结构中ASE的激励特性。结果证明,荧光峰及ASE峰的红移以及泄漏模的激发是界面反射率、薄膜传输损耗及染料吸收损耗等共同作用的结果,而界面反射率对ASE泄漏模激发特性有重要影响,染料的自吸收是荧光峰及ASE峰产生红移的主要因素。     

Metal-Enhanced Fluorescence Solution-Based Sensing Platform

In recent years our laboratories have reported the favorable effects for fluorophores placed in close proximity to surface immobilized silver nanostructures. These include; greater quantum yields, reduced lifetimes (increased photostability) and directional emission. However, while these findings are likely to find multifarious applications for surface assays based on enhanced fluorescence detection, a solution based enhanced sensing platform has yet to be realized. In this short, note, we show how SiO2-coated silver colloids, indeed provide for a solution based enhanced fluorescence sensing platform with a 3-5 fold enhancement typically observed.     

Fluorescence lifetime-enhanced spectral characterization of human serum

Frequency-domain fluorescence lifetime techniques were used for the characterization of pooled human serum, including normal serum, hyperlipid serum, and sera that had been stripped of various components. Fluorescence lifetime measurements of normal human serum revealed lifetime components primarily in the regions of 10² ps, 1–2 ns, 4–7 ns, and 9–10 ns. Phase-resolved fluorescence spectroscopy (PRFS), a frequency-domain technique that combines spectral and lifetime information, in measurements of phase-resolved fluorescence intensity (PRFI), provided the basis for comparison of the various sera. Measurements of PRFI vs excitation wavelength and emission wavelength yield a phase-resolved excitation-emission matrix (PREEM) at a given modulation frequency. Multifrequency measurements yield a three-way excitation-emission-frequency array. The multifrequency PREEMs of the various sera were compared with each other and with the corresponding two-way excitation-emission matrices (EEMs) that are obtained using conventional, steady-state fluorescence spectroscopy. Application of matrix-based analysis techniques to the steady-state and PRFS data arrays allowed direct comparison between the two approaches. Results demonstrate the enhanced discrimination among samples that is achieved through the additional dimension of fluorescence lifetime in PRFS.     

Enhanced dielectric and ferroelectric properties of Pb1−3x/2Lax(Zr0.5Ti0.5)O3 thin films with low lanthanum substitution

Effects of lanthanum (La) substitution (0.003 ≤ x ≤ 0.015) on the dielectric and ferroelectric properties of Pb(Zr_0.5Ti_0.5)O₃ thin films have been investigated. The films were synthesized on the Pt (1 1 1)/Ti/SiO₂/Si (1 0 0) substrates by a sol-gel method. Large dielectric constants of the films are obtained within range of 800-1600 which are almost comparable to those observed in bulk ceramics. The films also show improved remnant polarization values and reduced coercive field values with the increasing addition of La substitution. Our results suggest that low La substitution contributes to enhance film electric properties due to the improvement of non-180° domain wall mobility as well as the stabilization of tetragonal phase.     

Improved Routine Bio-Medical and Bio-Analytical Online Fluorescence Measurements Using Fluorescence Lifetime Resolution

Fluorescence techniques are widely used as sensitive detection methods in bio-analytics. The use of the bio-physical parameter fluorescence lifetime additional to the spectral characteristics of fluorescence has the potential to improve fluorescence-related detection methods in terms of selectivity in signal recognition, robustness against disturbing influences, and the accessibility of novel bio-chemical process parameters. This article describes the technical set up of a time-resolving instrument with either a fixed time-gated detection principle for improved evaluation of tissue metabolism by an online monitoring of the tissue autofluorescence or a direct fluorescence lifetime detection principle for lifetime-based fluorescent assays.     

烘烤温度对溶胶-凝胶法制备镧掺杂钛酸铋薄膜结构与铁电性质的影响

采用溶胶-凝胶法，在保持薄膜结晶温度和有机物分解温度相同情况下，发现烘烤温度（即溶剂的挥发温度）对镧掺杂钛酸铋薄膜的晶体结构、表面形貌和铁电性质均产生重要影响.在较低烘烤温度下得到的薄膜（117）择优取向明显.但随着烘烤温度增加，薄膜的（117）择优取向逐渐减弱.薄膜的表面晶粒形貌则从棒状逐渐转变为盘状.还测量了薄膜的铁电性质，发现在250℃烘烤温度下得到的薄膜具有最大的剩余极化强度，2Pr为28.4μC/cm2.对实验现象进行了定性解释. 关键词： 溶胶-凝胶法 烘烤温度 铁电薄膜