缩合法合成磁性荧光高分子CdTe@Fe_3O_4/P(NIPAM-co-AA)复合微球及其表征

具有超顺磁性和荧光特性的CdTe@Fe_3O_4/P(NIPAM-co-AA)多功能复合微球是以P(NIPAMco-AA)为模板制备而成.首先,采用溶胀法使模板微球带有磁性;其次,辅助TEOS和APTES两种化学试剂实现对Fe_3O_4/P(NIPAM-co-AA)微球表面的氨基功能化;最后,携带氨基的磁性微球与巯基乙酸修饰的CdTe量子点通过酰胺缩合反应,将量子点键合到磁性微球表面上,最终获得单分散的磁性荧光高分子复合微球.分别采用扫描电子显微镜、透射电子显微镜、倒置荧光显微成像系统、荧光分光光度计以及振动样品磁强计等方法对所获复合材料的结构与性能进行了表征.结果表明:复合微球单分散性良好,平均粒径约为30μm,饱和磁化强度可达5.4emu/g,具有良好的超顺磁性和较高的荧光发光效率.该材料将磁性、荧光结合到微米级高分子共聚物上,不仅解决了纳米粒子分离和处理的困难,而且奠定了多功能材料在生物标记、荧光成像等诸多领域潜在的应用基础.     

Fe3O4@SiO2@TiO2复合纳米结构的尺寸与磁性调控

采用共沉淀法和溶剂热法制备了不同尺寸的Fe3O4纳米粒子,通过Stöber法和溶胶-凝胶法在Fe3O4磁核上包覆SiO2和TiO2壳层获得不同尺寸的Fe3O4@SiO2@TiO2复合纳米结构．采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和振动样品磁强计(VSM)等对其结构、形貌和磁性进行了研究．结果表明,大尺寸复合纳米粒子包覆均匀,分散性好,饱和磁化强度较大,有利于TiO2光催化剂的磁回收与再利用．     

壳核型磁性纳米纤维素微球的超声制备及表征

以纳米级的Fe3 O4液体作为磁核 ,在非水体系的纤维素DMAc(N N二甲基乙酰胺 ) /LiCl溶液中 ,使用包埋法 ,在超声波的辅助下制备得到了纳米尺度的壳核型磁性纤维素微球 .利用FT IR、XRD及AFM/MFM (原子力显微镜 /磁场力显微镜 )对得到的磁性微球进行了表征 ,证实该微球由磁性的核与纤维素的壳组成 ,微球大小为 30～ 5 0nm ,且具有良好的分散性 .并研究了超声条件对磁性微球尺寸的影响 .     

Fe3O4@SiO2@An磁性纳米荧光粒子的制备及对锌离子的识别

通过微乳法一步合成了SiO2包覆Fe3O4的磁性纳米颗粒(MNP)并通过硅烷偶联剂将表面氨基化,进一步通过化学成键将荧光分子蒽修饰到氨基化的纳米粒子表面,制得Fe3O4@SiO2@An磁性纳米荧光粒子.采用XRD、TEM、FTIR等实验方法对该粒子进行一系列的表征,其直径约为9nm,常温时具有超顺磁性,通过外加磁场,能够使粒子从溶液中简单有效地分离.该粒子在溶剂中具有较好的分散性,荧光实验表明,对锌离子具有较好的选择性,在锌离子存在下基于光诱导电子转移( PET,PhotoinducedElectron Transfer)机理,粒子荧光强度显著增强,检出限为2.8571×10-5mol/L.     

新型螯合磁性纳米Fe_3O_4的制备及其性能研究

采用共沉淀法制备了磁性四氧化三铁(Fe3O4)纳米粒子,并通过硅烷偶联剂对其表面进行改性,进一步在其表面偶联修饰氨基硫脲,制备了螯合磁性纳米Fe3O4粒子。利用广角X射线衍射仪(WAXD)、红外光谱仪(FTIR)、分光光度计等对磁性纳米粒子的结构和性能进行了表征。结果表明,纳米Fe3O4为反尖晶石结构,通过偶联修饰可以实现氨基硫脲在纳米粒子表面的化学改性。螯合磁性纳米粒子具有良好的分散性和磁响应性,且对多种金属离子(Pb2+、Hg2+、Zn2+、Cd2+)具有良好的螯合效果。     

Ag@Fe_3O_4@C-CdTe@SiO_2磁性荧光复合微球的制备与光学特征（英文）

先采用一步溶剂热法和水热法制备了碳包覆的Ag@Fe_3O_4核壳型磁性纳米粒子,然后通过表面氨基化改性后与巯基乙酸修饰的CdTe量子点反应,将量子点键合到磁性微球上,最后在其表面包覆上一层二氧化硅壳层,制备出具有荧光增强的Ag@Fe_3O_4@C-CdTe@SiO2磁性荧光复合材料。实验结果表明,该纳米粒子的平均粒径大约为150nm,磁饱和强度为224A/g(22.4emu/g),在室温下具有较好的磁性能。其中Ag@Fe_3O_4@C-CdTe磁性荧光纳米粒子的荧光强度大于Fe_3O_4@C-CdTe,其主要原因是内核为45nm的Ag纳米粒子具有表面等离子体共振作用,能够使其表面或附近的量子点荧光得到增强。     

磁性聚苯胺纳米微球的合成与表征

报道了具有核壳结构的Fe3 O4 聚苯胺磁性纳米微球的合成方法和表征结果 .微球同时具有导电性和磁性能 .在优化的实验条件下 ,可得到饱和磁化强度Ms 为 5 5 .4emu/g ,矫顽力Hc 为 6 2Oe的磁性微球 .微球的导电性随着微球中Fe含量的增加而下降 .微球的磁性能则随着Fe含量的增加而增大 .Fe3 O4 磁流体的粒径和磁性聚苯胺微球的粒径均在纳米量级 .纳米Fe3 O4 粒子能够提高复合物的热性能 .实验表明 ,磁流体和聚苯胺之间可能存在着一定的相互作用 ,但这种相互作用较为复杂 ,难于研究 .     

Ag@Fe3O4@C-CdTe@SiO2磁性荧光复合微球的制备与光学特征

先采用一步溶剂热法和水热法制备了碳包覆的Ag@Fe₃O₄核壳型磁性纳米粒子,然后通过表面氨基化改性后与巯基乙酸修饰的CdTe量子点反应,将量子点键合到磁性微球上,最后在其表面包覆上一层二氧化硅壳层,制备出具有荧光增强的Ag@Fe₃O₄@C-CdTe@SiO₂磁性荧光复合材料。实验结果表明,该纳米粒子的平均粒径大约为150 nm,磁饱和强度为224 A/g（22.4 emu/g）,在室温下具有较好的磁性能。其中Ag@Fe₃O₄@C-CdTe磁性荧光纳米粒子的荧光强度大于Fe₃O₄@C-CdTe,其主要原因是内核为45 nm的Ag纳米粒子具有表面等离子体共振作用,能够使其表面或附近的量子点荧光得到增强。     

Fe3O4@Au纳米材料的制备和光谱性质

采用共沉淀法制备了Fe3O4纳米颗粒,并以其为晶种利用晶种生长法制备了Fe3O4@Au磁性复合纳米粒子。吸收光谱显示Au壳层成功包覆在了Fe3O4纳米核的表面。以结晶紫为探针分子的表面增强拉曼散射（SERS）光谱展示了Fe3O4@Au良好的SERS活性。     

电介质球复合纳米天线对荧光定向发射的增强

在纳米光子学中,提高荧光物质的定向发光强度是许多应用要解决的关键问题。为了优化电介质纳米天线的荧光增强能力,本文提出了一种由硅纳米球二聚体与TiO 2微球组成的电介质球复合纳米天线。通过时域有限差分法,本文分别从量子产率增强、荧光收集效率增强以及荧光激发率增强3个方面研究了该复合纳米天线对荧光的增强效果。结果表明,这种复合纳米天线不仅可以解决单个TiO 2微球增强荧光时量子产率较低的问题,还可以弥补单个硅纳米球二聚体增强荧光时荧光收集效率较差的不足。该复合纳米天线可使CdSe量子点的量子产率增强约4倍、荧光收集效率增强约2倍。此外,由于硅纳米球二聚体与TiO 2微球对荧光激发过程具有增强效果,该复合天线最终可以产生较高的荧光定向增强倍数。在量子点发光的中心波长523 nm处,荧光定向增强约为3064倍。     

Enhancement of magnetocaloric effects in La0.8R0.2(Fe0.919Co0.081)11.7 Al1.3 (R=Pr, Nd) compounds

The magnetic properties and magnetocaloric effects (MCEs) in La_0.8R_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 (R=Pr, Nd) compounds have been investigated. When Pr and Nd substitute for La, the Curie temperature of compounds decreases. The values of the MCEs are enhanced significantly by a partial substitution of Nd for La. Under the field change of 2 and 5 T, the maximum magnetic entropy changes for La_0.8Nd_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 compound are −4.56 and −9.46 J/Kg K, respectively. It can be exploited for room temperature magnetic refrigeration material.     

Magnetocaloric effect in the La0.8Ce0.2Fe11.4−xCoxSi1.6 compounds

The effects of substitution of Co for Fe on the magnetic and magnetocaloric properties of La_0.8Ce_0.2Fe_11.4−xCo_xSi_1.6 (0, 0.2, 0.4, 0.6, 0.8 and 1.0) compounds have been investigated. X-ray diffraction shows that all compounds crystallize in the NaZn₁₃-type structure. Magnetic measurements show that the Curie temperature (T_C) can be tuned between 184 and 294 K by changing the Co content from 0 to 1. A field-induced methamagnetic transition occurs in samples with x=0, 0.2 and 0.4. The magnetic entropy changes of the compounds have been determined from the isothermal magnetization measurements by using the Maxwell relation.     

Tm3+ 掺杂ZrF4 -BaF2 -LaF3 -AlF3 -NaF-PbF2玻璃激光制冷中荧光再吸收效应的理论分析

固体材料的激光制冷是近年来发展起来的一个新的研究领域. 掺Tm³⁺的ZrF₄-BaF₂-LaF₃-AlF₃-NaF-PbF₂(ZBLANP)玻璃材料是激光冷却的典型材料之一. 与另一种制冷掺杂离子Yb³⁺相比,Tm³⁺具有更好的制冷潜力. 目前制约材料制冷的一个主要机理就是荧光再吸收. 首先根据Tm³⁺:ZBLANP的光谱参数,利用半经典的随机行走模型得到了不同情况下的平均荧光再吸收次数,随后分析了荧光光子界面出射的全反射效应,并对所得结果进行了修正. 计算结果表明,荧光再吸收会导致量子效率降低0.5%-1%,出射荧光波长红移达到2-10 nm,激光制冷的效率和功率降低. 为了有利于荧光出射和净制冷的实现, 宜采用小体积细长棒的制冷元. 关键词： 激光制冷 稀土离子 荧光再吸收     

Magnetocaloric properties in the Cr-doped La0.7Sr0.3MnO3 manganites

Single-phase polycrystalline samples of La_0.7Sr_0.3Mn_1-xCr_xO₃ with nominal composition of x=0.00, 0.20, 0.40 and 0.50 were prepared by a conventional solid-state reaction method in air. Investigations of magnetization were carried out in the temperature range 5-400 K and magnetic field range 0-8 T. It was found that the Curie temperature T_C decreases with increasing x and the maximum magnetic entropy change (−ΔS_M) for x=0.20 is ∼1.203 and ∼2.653 J/kg K, respectively for 2 and 6 T magnetic field near the temperature of 280 K.     

Structural and magnetic studies of Fe2O3/SiO2 granular nanocomposites

Fe₂O₃/SiO₂ nanocomposites were synthesized by mechanical alloying, using Fe and SiO₂ powders as precursors. After 340 h milling, the sample essentially consists of hematite and amorphous silica. TEM images show hematite particles embedded in and surrounded by an amorphous silica matrix. A broad size distribution—5–50 nm—of hematite particles is found, and other group of very small—2–3 nm—unidentified particles are observed. Room temperature Mössbauer spectra show a paramagnetic doublet, which may correspond to a non-crystalline phase in the sample (probably the small unidentified particles), and a sextet corresponding to hematite. Magnetic properties were investigated by measuring hysteresis curves at different temperatures (5–300 K) and by zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves (10 mT). The hysteresis loops were well fitted by a ferromagnetic contribution. No evidence of Morin transition is found down to 5 K.     

Uncompensated magnetization and exchange-bias field in La0.7Sr0.3MnO3/YMnO3 bilayers: The influence of the ferromagnetic layer

We studied the magnetic behavior of bilayers of multiferroic and nominally antiferromagnetic o-YMnO₃ (375 nm thick) and ferromagnetic La_0.7Sr_0.3MnO₃ and La_0.67Ca_0.33MnO₃ (8…225 nm), in particular the vertical magnetization shift M_E and exchange-bias field H_E for different thickness and magnetic dilutions of the ferromagnetic layer at different temperatures and cooling fields. We have found very large M_E shifts equivalent to up to 100% of the saturation value of the o-YMO layer alone. The overall behavior, including XMCD magnetization shift measured at the Mn-L edge of the LSMO layer only, indicates that the properties of the ferromagnetic layer contribute substantially to the M_E shift and that this does not correlate straightforwardly with the measured exchange-bias field H_E.     

Magnetic properties for the Mn2GeTe4 compound

Measurements of magnetic susceptibility χ, in the temperature range from 2 to 300 K, and of magnetization M vs. applied magnetic field B, up to 5 T, at various temperatures were made on polycrystalline samples of the Mn₂GeTe₄ compound. It was found that Mn₂GeTe₄ has a Néel temperature T_N of about 135 K, shows mainly antiferromagnetic behavior with a very weak superimposed ferromagnetic component that is attributed to spin canting. Also, the magnetic results suggest that a possible spin-glass transition takes place at T_f≈45 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory. The M vs. B results indicated that bound magnetic polarons (BMPs) occur in the compound, and that the effects from BMPs disappear at approximately 80 K. The M vs. B curves were well fitted by a Langevin type of equation, and the variation of the fitting parameters determined as a function of temperature. Using a simple spherical model, the radius of the BMP in the material was found to be about 27 Å; this value is similar to the effective Bohr radius for an acceptor in the II-IV-V₂ and I-III-VI₂ ternary semiconductor compounds.     

Piezoelectric, dielectric and magnetic properties of (1-x)Pb[Zr, Ti, (Mg1/2W1/2), (Ni1/3Nb2/3)]O3+x(Ni, Co, Cu)FeO4 composites

The phase structure, microstructure, piezoelectric properties, dielectric characteristic and the ME effect of magnetoelectric Pb[Zr_0.23Ti_0.36+0.02(Mg_1/2W_1/2)+0.39(Ni_1/3Nb_2/3)]O₃ (PZT)+xNi_0.8Co_0.1Cu_0.1Fe₂O₄ (NCCF) composite ceramics were prepared by the conventional solid state reaction method. The structural analysis of both the constituent phases and their composites was carried out by X-ray diffraction, energy dispersive spectrometry and scanning electron microscopy. The results showed cubic spinel structure for ferrite phase and tetragonal perovskite structure for ferroelectric phase. The piezoelectric constant, dielectric constant, Curie temperature, remanent polarization and coercive electric field decreased with increase of ferrite content. The coercive field strength, saturation magnetization and remanent magnetization increased with increasing ferrite content.     

Magnetoresistance of Fe3O4/Au/Fe3O4 and Fe3O4/Au/Fe spin-valve structures

A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe₃O₄ electrodes is presented. Fe₃O₄/Au/Fe₃O₄ spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe₃O₄ layers. By contrast, a negative GMR effect is measured on Fe₃O₄/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe₃O₄/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.