小粒径同质/异质壳层结构NaGdF_4:3%Nd~(3+)纳米颗粒的近红外发光特性

采用共沉淀法制备了粒径小于5 nm的六方相NaGdF_4:3%Nd~(3+)纳米颗粒.纳米颗粒表面缺陷会使发光中心产生严重的淬灭,对其表面包覆适当厚度的壳层可以有效地减少发光淬灭,提高发光性能.对NaGdF_4:3%Nd~(3+)核心纳米颗粒分别进行同质和异质包覆并且通过调节核壳比制备了不同壳层厚度的NaGdF_4:3%Nd~(3+)@NaGdF_4和NaGdF_4:3%Nd~(3+)@Na YF4纳米颗粒,研究了不同的壳层厚度对核心纳米颗粒发光的影响,并对两种不同核壳结构纳米颗粒的发光性能进行了对比.在808 nm近红外光激发下,NaGdF_4:3%Nd~(3+)纳米颗粒发射出位于约866,893,1060 nm的近红外发射.与核心纳米颗粒相比,核壳结构的纳米颗粒的荧光强度增强,荧光寿命增长,并且随着壳厚的增加,荧光强度出现先增强后减弱、荧光寿命逐步增长的趋势.与相同条件下同质包覆的NaGdF_4:3%Nd~(3+)@NaGdF_4纳米颗粒相比,异质包覆的NaGdF_4:3%Nd~(3+)@NaYF_4纳米颗粒光谱荧光强度增强,寿命增长.     

Cu/C核/壳纳米结构的气相合成、形成机理及其光学性能研究

采用乙酰丙酮铜为原料, 通过化学气相沉积大批量制备出Cu/C核/壳纳米颗粒和纳米线. 研究结果表明, 通过控制沉积温度可对Cu/C核/壳纳米材料的形貌和结构进行很好的控制. 比如, 沉积温度为400 ℃时可获得直径约200 nm的Cu/C核/壳纳米线, 沉积温度为450 ℃ 时可获得直径约200 nm的Cu/C核/壳纳米颗粒和纳米棒的混合产物, 沉积温度为600 ℃时可获得直径约22 nm的Cu/C核/壳纳米颗粒. 获得的Cu/C核/壳纳米结构是由一个新颖的凝聚机理形成的, 而这种机理不同于著名的溶解-析出机理. 紫外-可见光谱和荧光光谱分析结果表明: Cu/C核/壳纳米线和纳米颗粒均在225 nm处出现Cu的吸收峰, 同时在620 和616 nm处分别出现了纳米线和纳米颗粒的表面等离子共振吸收峰. Cu/C核/壳纳米线在312 和348 nm处、 Cu/C核/壳纳米颗粒在304 和345 nm处出现荧光发射谱峰. 关键词： Cu/C核/壳结构 纳米线 纳米颗粒 光学性能     

不同壳层厚度的LaF_3∶Eu~(3+)/LaF_3核壳结构纳米颗粒制备及发光性质

表面缺陷会使纳米材料的发光中心产生严重的猝灭,而适当厚度的同质包覆层会减少其猝灭。本文利用共沉淀法合成了LaF3∶Eu3+纳米颗粒和LaF3∶Eu3+/LaF3核壳结构纳米颗粒,研究了颗粒的晶体结构、形貌以及不同壳层厚度对发光性能的影响。研究发现:LaF3∶Eu3+核心和LaF3∶Eu3+/LaF3核壳结构均为六方结构。包覆同质壳层可以提高稀土离子的发光性能,包覆厚度的不同导致LaF3∶Eu3+/LaF3核壳结构的荧光强度与衰减时间均发生改变。其原因是未掺杂的LaF3壳层可以将发光中心Eu3+离子与LaF3∶Eu3+核心的表面隔离,进而减少表面对发光中心的猝灭,提高材料的发光性能。这种修饰作用与壳层厚度相关。     

热注射法合成用于生物成像的核壳上转换纳米晶

近几年来,稀土上转换发光纳米材料凭借其生物组织穿透深度大、无组织损伤、无背景荧光干扰和成像灵敏度高等诸多优点,在生物体荧光成像领域展现了巨大的潜在应用价值.本文采用"一次热注射"高温溶剂热法制备不同壳层厚度的NaYF_4:Yb, Tm@NaYF_4上转换发光材料.利用透射电子显微镜、粒径分析、荧光光谱等对产物进行表征,探讨壳层厚度对纳米粒子上转换发光强度的影响.结果表明,在980 nm近红外光照射下,上转换纳米材料能够发出紫外-可见光.而且,由于壳层包覆有效抑制了上转换发光的表面猝灭效应,核壳结构的NaYF_4:Yb, Tm@NaYF_4纳米粒子发光强度比NaYF_4:Yb, Tm提高了数十倍;当壳层厚度为22.7 nm时,上转换发光强度最强.此外,通过对上转换发光颗粒进行酸洗和聚乙二醇(PEG)修饰,提高了纳米材料的生物相容性,并成功将其应用于细胞的上转换荧光成像.     

铜铟硫纳米晶/PMMA复合薄膜的制备与光学性质表征

铜铟硫(CuInS₂)纳米晶具有发射光谱宽、波长易于调控、量子产率高、合成成本低、容易与封装材料复合等优点,在远程白光LED结构中具有广阔的应用前景。远程白光LED结构是针对LED散热问题提出的一种新型封装结构,在这种结构中复合荧光涂层(复合薄膜)与蓝光芯片进行隔离封装,这种结构对复合薄膜中纳米晶的热稳定性的要求大大降低。首先合成出了不同发光波长的CuInS₂纳米晶荧光材料,然后将其封装到PMMA基质中制备了系列的CuInS₂纳米晶/PMMA复合薄膜。通过荧光光谱和紫外可见光谱的方法,针对纳米晶复合薄膜出现的发光波长红移以及不同发光波长纳米晶/PMMA复合薄膜透过率不一致的现象进行了详细研究。     

核-壳结构ZnS∶Tb/CdS纳米晶的电致发光

利用微乳液方法合成出粒径为4 nm的核-壳结构ZnS∶Tb/CdS纳米晶。用XRD、TEM及荧光光谱等手段对合成的纳米晶的结构、形态和光学特性分别进行了表征。将ZnS∶Tb/CdS纳米晶制作成有机-无机杂化结构电致发光器件,其结构为ITO/poly(3,4-ethylene d ioxythiophene)∶poly(styrene sulfonate)(PEDOT-PSS)(70 nm)/poly(vinylcobarzale)(PVK)(100 nm)/ZnS∶Tb/CdS纳米晶(120 nm)/2,9-d im ethyl-4,7-d iphenyl-1,10-phenanthroline(BCP)(30 nm)/L iF(1.0 nm)/A l(100 nm)。当驱动电压为13 V时,可以测到Tb3+离子的两个特征峰。在电致发光光谱中未测到聚合物PVK的发光,说明电子和空穴是在纳米晶层上复合的。当驱动电压为25 V时,得到器件的最大亮度为19 cd/m2。     

碲化镉纳米晶中温度相关的能量转移

为了获得纳米晶之间以及单个纳米晶内部本体态至缺陷态两种能量转移在不同温度下对发光强度的影响,测量了碲化镉纳米晶层发光光谱随温度(78～300 K)的变化情况.碲化镉纳米晶层发光光谱显示:碲化镉纳米晶层在低温下有明显的本体(约520 nm)和缺陷(约605 nm)发光,且发光强度随温度的改变呈现出不同的变化规律.在温度变化的第一阶段(78～140 K),大尺寸碲化镉纳米晶发光效率高、表面缺陷少,小尺寸纳米晶至大尺寸纳米晶间的能量转移使得纳米晶本体发光强度逐渐升高、缺陷发光强度迅速降低.在温度变化的第二阶段(140～300 K),随着温度的升高,无辐射跃迁几率的增大使得碲化镉纳米晶缺陷态和本体态发光强度均逐渐降低.因此,能量转移仅在温度变化的第一阶段对发光强度的影响起主要作用,在第二阶段起次要作用.为了进一步验证能量转移对发光强度的影响,将碲化镉纳米晶用聚乙二醇包裹以减少纳米晶间的能量转移;将纳米晶层的干燥过程放在近真空环境下进行以减少单个纳米晶内部本体至缺陷态的能量转移.光谱结果显示在温度变化的第一阶段,这两种方式下得到的纳米晶层发光强度均逐渐降低,能量转移对发光强度的影响不再起主要作用.证实了能量转移对发光强度的影响规律的合理性.     

不同壳层厚度的LaF3：Eu3+/LaF3核壳结构纳米颗粒制备及发光性质

表面缺陷会使纳米材料的发光中心产生严重的猝灭，而适当厚度的同质包覆层会减少其猝灭。本文利用共沉淀法合成了LaF₃：Eu³⁺纳米颗粒和LaF₃：Eu³⁺/LaF₃核壳结构纳米颗粒，研究了颗粒的晶体结构、形貌以及不同壳层厚度对发光性能的影响。研究发现：LaF₃：Eu³⁺核心和LaF₃：Eu³⁺/LaF₃核壳结构均为六方结构。包覆同质壳层可以提高稀土离子的发光性能，包覆厚度的不同导致LaF₃：Eu³⁺/LaF₃核壳结构的荧光强度与衰减时间均发生改变。其原因是未掺杂的LaF₃壳层可以将发光中心Eu³⁺离子与LaF₃：Eu³⁺核心的表面隔离，进而减少表面对发光中心的猝灭，提高材料的发光性能。这种修饰作用与壳层厚度相关。     

SiO_2/Ag核壳结构纳米粒子的制备及其表面荧光增强

以罗丹明B掺杂的SiO2球为核,通过化学还原的方法制备了二氧化硅/银核壳结构复合纳米粒子。采用透射电镜(TEM)、紫外-可见-近红外(UV-Vis-NIR)分光光度计和荧光分光光度计对二氧化硅/银核壳结构纳米粒子的表面形貌、表面等离子共振和表面荧光增强特性进行了研究和表征。结果表明,二氧化硅/银核壳结构纳米粒子的表面等离子共振峰具有明显的可调谐性,且其表面荧光增强强烈依赖于银壳层的表面等离子共振,随银壳层厚度的增大而增强。     

Ag@SiO2纳米复合物对羧酸铕配合物的荧光增强

分别以苯氧乙酸和对苯二甲酸为阴离子配体,以邻菲罗啉为中性配体,稀土铕离子为中心体,合成了两种三元稀土铕配合物Eu(Phen)L3(L=苯氧乙酸)和Eu2(Phen)2L3’(L’=对苯二甲酸)。利用还原法制备纳米银溶胶,采用改进的Stber法在银纳米颗粒外面包裹二氧化硅,通过控制正硅酸四乙酯(TEOS)的滴加时间和滴加量以控制二氧化硅壳层的生长厚度,得到Ag@SiO2核壳结构颗粒。通过该核壳结构颗粒与DMF溶解的稀土铕配合物的相互作用,得到核壳型Ag@SiO2荧光纳米复合物。结果表明,所得纳米银粒径为50 nm左右,包覆的SiO2壳层厚度约为12 nm。SiO2包覆的纳米银对两种铕配合物的荧光发射有明显的增强作用。     

Photocatalytic properties of porous C-doped TiO2 and Ag/C-doped TiO2 nanomaterials by eggshell membrane templating

Porous organic carbon-doped titania (C-TiO₂) nanomaterials and their composites with Ag nanoparticles (Ag/C-TiO₂) were synthesized by an eggshell membrane templating method, and their structural and photocatalytic properties were systematically characterized. These nanomaterials, exhibiting a macroscopic morphology of a thin film, are composed of interwoven tubes, and the tube wall consists of nanocrystals. The doped organic carbon was composed of the active carbon and carbonate species, which could form a layer around the surface of TiO₂ nanoparticles, while the silver was incorporated into Ag/C-TiO₂ composites as separated Ag nanoparticles. The degradation of methylene blue under visible light irradiation was employed to evaluate the photocatalytic activity of these as-prepared TiO₂-based materials. Both C-TiO₂ and Ag/C-TiO₂ nanomaterials showed higher photocatalytic activity than pure TiO₂ material–commercial Degussa P25. These results can be accounted for the coupling effect of the incorporation of carbon species and Ag nanoparticles.     

Synthesis and characterization of TiO2/Fe2O3 core-shell nanocomposition film and their photoelectrochemical property

TiO₂/Fe₂O₃ core-shell nanocomposition film has been fabricated via two-step method. TiO₂ nanorod arrays are synthesized by a facile hydrothermal method, and followed by Fe₂O₃ nanoparticles deposited on TiO₂ nanorod arrays through an ordinary chemical bath deposition. The phase structures, morphologies, particle size, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer. The results confirm that Fe₂O₃ nanoparticles of mean size ca. 10 nm coated on the surface of TiO2 NRs. After depositing Fe₂O₃, UV-vis absorption property is induces the shift to the visible-light range, the annealing temperature of 600 °C is the best condition for UV-vis absorption property of TiO₂/Fe₂O₃ nanocomposite film, and increasing Fe content, optical activity are enhanced one by one. The photoelectrochemical (PEC) performances of the as-prepared composite nanorods are determined by measuring the photo-generated currents under illumination of UV-vis light. The TiO₂ NRs modified by Fe₂O₃ show the photocurrent value of 1.36 mA/cm² at 0 V vs Ag/AgCl, which is higher than those of unmodified TiO₂ NRs.     

Synthesis of CdSe and CdSe/TiO2 nanoparticles under multibubble sonoluminescence condition

CdSe and CdSe/TiO₂ nanoparticles were synthesized under multibubble sonoluminescence (MBSL) condition. The influences of TiO₂ introduced as the sensitizer on the morphology and crystal transformation were investigated. The morphology, phase and optical properties of the final products have been characterized by X-ray powder diffraction, transmission electron microscope, UV-vis absorption spectroscopy and photoluminescence spectroscopy. The results showed that as-prepared nanoparticles are well-crystallized, and the suppression of crystal pattern transition as well as the control of CdSe crystal growth can be implemented by coupling of TiO₂ semiconductor. Furthermore, the possible growth mechanism for different morphologies and crystal phases of the nanocrystals were also discussed.     

Preparation and characterization of SiO2/ZrO2/Ag multicoated microspheres

A new type of multicoated silica/zirconia/silver (SiO₂/ZrO₂/Ag) core-shell composite microspheres is synthesized in this paper. In the process, ZrO₂-decorated silica (SiO₂/ZrO₂) core-shell composites were firstly fabricated by the modification of zirconia on silica microspheres through the hydrolysis of zirconium precursor. Subsequently, on SiO₂/ZrO₂ composite cores, silver nanoparticles were introduced via ultrasonic irradiation and acted as “Ag seeds” for the formation of integrate silver shell by further reduction of silver ions using formaldehyde as reducer. The resulting samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared, energy-dispersive X-ray, and UV-vis spectroscopy, indicating that zirconia and silver layers were successfully coated on the surfaces of silica microspheres.     

Improvement in thermo mechanical and optical properties of in situ synthesized PMMA/TiO2 nanocomposite

In this paper, transparent thin films of nano titania filled Poly(methyl methacrylate) (PMMA) composites were synthesized by solvent casting method using tetra hydro furan as a solvent, with in situ nonaqueous ‘sol-gel’ transformation involving the mixing of titanium isopropoxide (as sol-gel precursor) and methanol. The present research work is focused at studying the effect of titania loading on optical and mechanical behavior of transparent nano hybrid thin films. The effect of nano Titanium dioxide (TiO₂) loading on PMMA morphology was studied by using a scanning electron microscope (SEM). Bowl shaped structures were obtained in pure PMMA thin film, which were deformed on incorporation of TiO₂ nanoparticles. This nanocomposite exhibits enhanced optical and mechanical properties. The peak of UV absorption is blue shifted to 261 and 266?nm with the incorporation of TiO₂. At this wavelength, the absorption is increased up to approximately 397%. The nanocomposites exhibit increased tensile strength up to 40% and modulus up to 16%. Tg of PMMA increased from 84.8 to 86.7?°C on adding 1.25% TiO₂ nanoparticles.     

Synthesis of robust water-soluble ZnS:Mn/SiO2 core/shell nanoparticles

Water-soluble Mn doped ZnS (ZnS:Mn) nanocrystals synthesized by using 3-mercaptopropionic acid (MPA) as stabilizer were homogeneously coated with a dense silica shell through a multi-step procedure. First, 3-mercaptopropyl triethoxy silane (MPS) was used to replace MPA on the particle surface to form a vitreophilic layer for further silica deposition under optimal experimental conditions. Then a two-step silica deposition was performed to form the final water-soluble ZnS:Mn/SiO₂ core/shell nanoparticles. The as-prepared core/shell nanoparticles show little change in fluorescence intensity in a wide range of pH value.     

Quantum confinement effects of CdTe nanocrystals sequestered in TiO2 matrix: effect of oxygen incorporation

Thin films of TiO₂ with high volume fraction (40–55%) and crystallite size (6–40 nm) of CdTe nanoparticles had been prepared by rf magnetron sputtering from a composite TiO₂:CdTe target at room temperature and 373 K. A detailed optical properties of nanocrystalline CdTe:TiO₂ films as-deposited and after thermal treatment (300 °C) are studied. The absorbance of the TiO₂ films with CdTe nanocrystallite dispersions depends both on the nanocrystallite size and volume fraction. The blue-shifts of the optical absorption edge concurrent with the CdTe nanocystal size reduction for as-deposited and after thermal treatment of nanocrystalline CdTe:TiO₂ thin films with respect to the bulk semiconductor agrees quite well with the strong quantum confinement theory. A slight deviation in absorption edge values than the predicted values from the strong quantum confinement model can be attributed to change in interplanar distance due to oxygen incorporation and inhomogeneous size distribution of CdTe nanocrystallites in these films.     

多孔TiO2/Al/SiO2纳米复合结构的紫外光吸收特性研究

在SiO₂玻璃衬底上用脉冲激光沉积(PLD)技术，分别沉积Ti和Ti/Al膜，经电化学阳极氧化成功制备了多孔TiO₂/SiO₂和TiO₂/Al/SiO₂纳米复合结构. 其中TiO₂薄膜上的微孔阵列高度有序，分布均匀. 实验研究了Al过渡层对多孔TiO₂薄膜光吸收特性的影响. 结果表明：无Al过渡层的多孔TiO₂薄膜其紫外吸收峰在27     

水溶性CdTe/CdS纳米晶表面SiO2壳层的反相胶束法包覆

"提出了一种水相中制备CdTe/CdS核壳结构纳米粒子的方法.用Te粉作为碲源,用Na2S作为硫源,在50 ℃下制备了CdTe/CdS核壳结构纳米粒子. 用紫外可见吸收光谱和荧光光谱分析了CdS壳层对CdTe核的影响. 随CdS壳层厚度的增加,紫外可见吸收光谱和荧光光谱均发生了红移. CdS壳层厚度较薄时,CdTe/CdS纳米晶的荧光强度较CdTe纳米粒子有显著提高;而CdS壳层厚度较厚时,CdTe/CdS纳米晶的荧光强度会逐渐降低. 用反相胶束法在CdTe/CdS核壳结构纳米粒子的表面包被一层SiO2,