利用核壳结构实现纳米颗粒的多色上转换发光

将多色荧光标记技术应用于生物信息检测可实现快速、实时、同步大规模检测目标生物分子的目的,利用上转换纳米粒子作为多色荧光探针可有效地避免生物组织自荧光对检测信号的影响。本文制备了具有核-壳结构的稀土氟化物纳米粒子,并通过在核与壳不同位置共掺杂不同浓度的敏化离子和发光离子来改变发光离子各发射峰之间的相对强度。利用不同颜色和强度的发射光谱实现了纳米粒子的多色上转换发光。利用透射电子显微镜成像、X射线衍射分析、发光光谱等测量手段对多色上转换发光纳米粒子进行了形貌、结构和上转换发光性质的表征。实验结果表明,具有核-壳结构的纳米粒子尺寸小于30 nm,呈球形。在980 nm红外光激发下,纳米粒子呈现从红色到蓝紫色的颜色可变的上转换发光。     

疏水基团修饰的核-壳型NaYF_4/NaLuF_4∶Yb~(3+),Tm~(3+)纳米粒子设计制备

通过异质核诱导,利用溶剂热法在较低温度下合成了具有疏水表面的上转换发光稀土核-壳Na YF4/Na Lu F4∶20%Yb,1%Tm纳米粒子,并利用X射线衍射仪、透射电子显微镜、傅里叶变换红外吸收光谱仪以及荧光光谱仪等测试设备对其进行了结构、形貌和上转换光谱的表征。测试结果表明,纳米粒子核为立方相,壳层为六角相。核-壳型纳米粒子的尺寸平均在20 nm以下,分布较为均匀。在980 nm近红外光激发下,核-壳型纳米粒子发射出较强的紫色和紫外荧光,且发光强度明显高于同尺寸立方相Na Lu F4∶20%Yb,1%Tm纳米粒子。这表明利用异质核诱导的方法制备的核-壳型纳米粒子在生物医学领域具有更高的应用价值。     

银/二氧化钛核壳纳米颗粒对碲化镉纳米晶的荧光增强研究

利用新合成的复合纳米结构银/二氧化钛核壳纳米颗粒,研究了金属银纳米颗粒对碲化镉纳米晶层荧光的增强情况.结果表明,这种新型复合金属纳米结构能极大地增强发光纳米晶层的荧光强度.银/二氧化钛核壳纳米颗粒是以水合肼、硝酸银和四异丙氧基钛为原材料,利用胶体化学法在水溶液中合成.透射电子显微镜图片表明这种新合成的银/二氧化钛纳米材料基本上呈球形,有较为明显的核壳结构,中间黑色的核是银纳米颗粒,外层颜色较浅部分是二氧化钛壳层.另外,包裹二氧化钛壳层后,银纳米颗粒的表面等离子吸收带从409 nm红移至430 nm,也证实了这种新型核壳纳米材料的形成.将此合成方法得到的银/二氧化钛纳米颗粒和碲化镉纳米晶用旋转涂覆方法进行直接组合后,得到了银纳米颗粒对碲化镉纳米晶荧光的明显增强,并对其增强的物理过程进行了讨论.这种能够增强荧光团发光的新型复合银纳米结构将在发光器件、荧光成像、生物探测等方面具有一定的应用价值.     

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.     

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.     

高浓度敏化剂掺杂的NaYF4∶Yb3+,Er3+纳米材料的合成及发光性能研究

为了探究泵浦功率对不同浓度敏化剂离子掺杂的上转换材料发光特性的影响,采用溶剂热法,成功制备了不同浓度敏化剂Yb3+掺杂的NaYF₄∶Yb3+, Er3+上转换纳米颗粒。首先对这种纳米晶体的结构和形貌进行了详细的分析,使用X射线粉末衍射仪和透射电子显微镜测试了制备的纳米晶体的结构和形貌。表征结果证明了制备的纳米颗粒均为结晶性良好、形状规则的六方相纳米晶体,随着Yb3+掺杂浓度的提高,纳米晶体的粒径有所增加。在此基础上,通过控制泵浦功率对不同浓度敏化剂Yb3+掺杂的NaYF₄∶Yb3+, Er3+上转换纳米颗粒在980 nm激发光下的光致发光特性做了详细的研究。对于不同浓度敏化剂掺杂的样品,随着泵浦功率的提高,上转换发光的强度增强,这可以归因于高泵浦功率促进材料对激发光的吸收。上转换发光的红绿比也得到了提高, 值得注意的是, 在不同浓度敏化剂Yb3+掺杂的样品中,发光的红绿比改变的程度和可调谐的范围有所不同。为了深入的了解上转换发光机制,对不同浓度样品中可能发生的电子能量传递机制进行了讨论并提出假设,认为上转换发光过程中,不同浓度样品中红绿比变化程度的不同是发光离子组合之间的平均距离和包括多声子弛豫、交叉弛豫和反向能量传递的非弛豫过程的综合作用。在低浓度敏化剂掺杂的样品中,由于掺杂浓度导致Yb3+和Er3+之间的平均距离较大,反向能量传递过程比较微弱。在非弛豫过程中,发生在同一发光中心Er3+上的多声子弛豫和相邻发光中心Er3+之间的交叉弛豫为主要过程。随着泵浦功率的提高,高能级的布居速率增加减弱了非辐射弛豫对发光的影响,材料的红绿比只有微弱的提高,绿光是上转换发光中的主要成分。随着掺杂浓度的提高,敏化剂离子Yb3+和激活剂离子Er3+之间的平均间距减小,反向能量传递过程得到增强,成为非辐射弛豫过程中的主要部分。由于泵浦功率增强而提高的高能级对上转换发光的贡献,通过相邻敏化剂和激活剂离子之间的反向能量传递过程得到迅速的衰减,使红光成为上转换发光中的主要成分。在980 nm的近红外光激发下,在不同浓度Yb3+掺杂的样品中存在不同侧重的非辐射弛豫过程, 由于多声子弛豫、交叉弛豫和反向能量传递共同作用,红绿比随着泵浦功率提高而增加。这种发光特性不但使得我们得到红光性能更好的上转换荧光材料,而且可以通过测定材料的红绿比来判定材料的掺杂浓度。经过进一步的设计和修饰,这种纳米材料很有潜力作为一种多功能光动力治疗纳米平台在生物检测领域中得到应用。不同浓度样品中可能发生的电子能量转移过程的提出,有利于对上转换发光机理的了解和稀土发光离子组合的设计和优化。     

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。     

核壳结构纳米颗粒Gd2O3:Tb3+/SiOx的制备及发光性能研究

以二甘醇为溶剂合成Gd2O3:Tb3+纳米颗粒,并在其表面包覆聚硅氧烷层,得到核壳结构纳米颗粒Gd2O3∶Tb3+/SiOx。为了研究Tb3+离子掺杂浓度对纳米颗粒发光性能的影响,采用几种不同Tb3+掺杂浓度进行纳米颗粒的合成,并对其发光性能进行了检测。结果表明:包裹聚硅氧烷层后的Gd2O3∶Tb3+纳米颗粒分散较好,聚硅氧烷层不会减弱Gd2O3∶Tb3+纳米颗粒的发光性能。Tb3+掺杂浓度对核壳结构纳米颗粒Gd2O3∶Tb3+/SiOx的发光存在浓度猝灭现象,猝灭摩尔分数为5%。这种具有发光特性的核壳结构纳米颗粒可作为生物传感器的探针用于生物分子的检测。     

一维NaYF4∶Er/Yb微米棒中上转换荧光的输运特性

稀土掺杂上转换(upconversion,UC)发光材料是一种把两个或多个长波长、低能量的近红外光子转换成一个短波长、高能量的可见或紫外光子的发光材料。由于其锐线发射、长寿命和无背底荧光等特性,在生物成像、检测与治疗、太阳能电池、药物输送和光催化等诸多领域具有极大的应用价值。目前,NaYF4∶Yb^3+/Er^3+微/纳晶体是公认的最重要的上转换发光材料之一,其相关的上转换发光机理、制备方法、光谱调制以及实际应用方面均已被科学家们进行了大量的研究。然而,荧光效率低这一严重问题一直制约着上转换发光材料实际应用的进程。另外,关于单颗粒上转换NaYF4∶Yb^3+/Er^3+微/纳晶体中荧光的产生、输运和耦合特性还不清楚。一维微/纳材料作为一种二维受限体系,为研究电子和光子的输运特性提供了一个理想模型。通过柠檬酸钠辅助的水热法合成了长径比可控的一维NaYF4∶Yb^3+/Er^3+微米棒和一维NaYF4∶Yb^3+/Er^3+@NaYF4∶Yb^3+/Tm^3+核-壳棒结构。采用激光共聚焦激发系统,在单颗粒一维NaYF4∶Yb^3+/Er^3+微米棒中,通过控制棒的长径比、激发方式和制备特殊的核-壳结构等方式,研究了荧光的产生和同步荧光图案,揭示了在一维棒结构中荧光光线的输运模式为:垂直于棒轴方向的荧光沿棒横截面的戒指形谐振腔趋肤传播和近似沿棒轴方向的荧光在棒介质中反复全反射以波导方式输运至棒端后靶向输出;在NaYF4∶Yb^3+/Er^3+@NaYF4∶Yb^3+/Tm^3+核-壳一维棒结构中,在单一波长激发下,获得了源自单颗粒的Tm^3+的蓝色和Er^3+绿色特征发射。采用点激发方式激发一维核-壳微米棒样品一端时,呈强烈蓝色荧光空间不对称的哑铃状分布,且中间出现了微弱绿色荧光,构筑出单颗粒单一波长激发下的局域色彩调制发射,并为微量稀土发光中心局域掺杂的检测提供了一种途径。在波导激发和点激发方式下,在对单颗粒一维NaYF4∶Yb^3+/Er^3+和NaYF4∶Yb^3+/Er^3+@NaYF4∶Yb^3+/Tm^3+核-壳微米棒的荧光产生和输运的调制中,实现了对离子荧光发射颜色的控制,并揭示了荧光在一维棒中传输耦合过程中,沿棒长模式荧光比沿径向模式荧光更容易传输耦合。该研究的一维棒荧光的输运和耦合特性,暗示了其在光子耦合器件、上转换波导激光以及荧光成像方面的潜在应用。     

Gd~(3+),Tm~(3+)和Yb~(3+)掺杂的Y_2O_3微晶中Gd~(3+)离子的紫外上转换发光及其增强的研究

采用均相沉淀法制备了Y(OH)3微米颗粒,经1 100℃焙烧后制备出具有上转换发光性质的Yb3+-Tm3+-Gd3+共掺的Y2O3微米晶体,讨论了Yb3+-Tm3+-Gd3+在Y2O3中能量传递过程及壳层对发光强度的影响。980 nm近红外光激发下的上转换光谱表明,在Yb3+-Tm3+-Gd3+共掺Y2O3体系中,核-壳结构大幅提高了Gd3+离子和Tm3+离子的上转换发光强度,尤其是样品在紫外发光部分的增强相比于可见和红外光部分更为明显。同时,通过研究Tm3+和Gd3+在不同波段的发光强度与泵浦功率的关系探讨了氧化物中上转换发光的机制。     

Luminescence of ZnO nanopowders

The luminescence of ZnO nanocrystals prepared by different methods was studied under pulsed electron beam excitation. It is shown that the luminescence intensity depends on the nanocrystal sintering conditions and does not depend on the nanocrystal size within the range 10–50 nm. The relative luminescence intensities for the 3.32 eV (free exciton) and 3.20 eV (bound exciton) bands showed a dependence on nanocrystal size. The role of the nanocrystal surface in excitonic luminescence is discussed.     

Highly luminescent (ZnSe)ZnS core-shell quantum dots for blue to UV emission: synthesis and characterization

We synthesized nearly monodisperse bare ZnSe nanocrystallites having luminescence which ranges in wavelength from 340 to 430 nm via nucleation due to supersaturation and growth followed by size selective precipitation. Bare ZnSe dots' outermost surface is passivated with organic HDA/TOP. In order to enhance the radiative emission from the semiconductor nanocrystals, we capped the bare ZnSe quantum dots with ZnS semiconductor materials of a wider band gap and 5% of lattice mismatch and produced highly luminescent core-shell (ZnSe)ZnS quantum dots. The core-shell (ZnSe)ZnS nanocrystals show 20 times or more as greatly enhanced luminescence quantum yields as those of bare ZnSe nanocrystals. The ZnSe bare dots and the (ZnSe)ZnS core-shell dots have cubic zinc blende structures as expected from the bulk structure. The observed shapes of bare ZnSe and core-shell (ZnSe)ZnS dots are nearly spherical or ellipsoidal with the aspect ratios of 1.2 and 1.4, respectively. They are not faceted.     

Spin-polarized Mn2+ emission from Mn-doped colloidal nanocrystals

We report magnetophotoluminescence studies of strongly quantum-confined 0D diluted magnetic semiconductors (DMS), realized in Mn(2+)-doped ZnSe/CdSe core-shell colloidal nanocrystals. In marked contrast to their 3D (bulk), 2D (quantum well), 1D (quantum wire), and 0D (self-assembled quantum dot) DMS counterparts, the ubiquitous yellow emission band from internal d-d ((4)T(1)→(6)A(1)) transitions of the Mn(2+) ions in these nanocrystals is not suppressed in applied magnetic fields and does become circularly polarized. This polarization tracks the Mn(2+) magnetization, and is accompanied by a sizable energy splitting between right- and left-circular emission components that scales with the exciton-Mn sp-d coupling strength (which, in turn, is tunable with nanocrystal size). These data highlight the influence of strong quantum confinement on both the excitation and the emission mechanisms of magnetic ions in DMS nanomaterials.     

Quenching of Si nanocrystal photoluminescence by doping with gold or phosphorous

Si nanocrystals embedded in SiO₂ doped with P and Au at concentrations in the range of 1×10¹⁸-3×10²⁰ cm⁻³ exhibit photoluminescence quenching. Upon increasing the Au concentration, a gradual decrease in nanocrystal photoluminescence intensity is observed. Using a statistical model for luminescence quenching, we derive a typical radius of ∼3 nm for nanocrystals luminescing around 800 nm. Au doping also leads to a luminescence lifetime reduction, which is attributed to energy transfer between adjacent Si nanocrystals, possibly mediated by the presence of Au in the form of ions or nanocrystals. Doping with P at concentrations up to 3×10¹⁹ cm⁻³ leads to a luminescence enhancement, most likely due to passivation of the nanocrystal-SiO₂ interfaces. Upon further P doping the nanocrystal luminescence gradually decreases, with little change in luminescence lifetime.     

Investigation of highly luminescent inorganic perovskite nanocrystals synthesized using optimized ultrasonication method

All-inorganic halide perovskite nanocrystals are next-generation materials with excellent optical and semiconductor properties suitable for display applications. In this study, we introduce an optimized ultrasonication method for the high-capacity synthesis of highly luminescent inorganic perovskite nanocrystals. After the synthesis of CsPbBr₃ with superior optical performance by ultrasonication method, halide anion exchange was performed to tune the stable emission wavelength over the entire visible range. In particular, the maximum photoluminescence wavelengths of the red and green perovskite nanocrystals were appropriate for light-emitting diode applications, and their full-width-at-half-maximum were very narrow, showing outstanding color purity. The materials also had excellent thermal and photo-stability, which is a necessary requirement for perovskite nanocrystal/organic light-emitting diode hybrid device applications. We formulated uniformly stable perovskite nanocrystal inks and optimized their physical and rheological properties for successful inkjet-printing. Finally, we fabricated a hybrid device with a color conversion layer based on the red and green perovskite nanocrystals synthesized using the optimized ultrasonication and halide-ion-exchange methods. The color reproduction range of the fabricated devices was 27.3 % wider than that of the National Television System Committee values, indicating very vivid colors.     

Fiber-optic color synthesizer

Full-color synthesis was achieved, for what we believe is the first time, utilizing a novel 3x1 hard polymer-clad fiber coupler along with red, green, and blue (RGB) LED primaries. By using RGB LEDs that are coupled to three input ports, the device rendered full color from the output port with a circular emitting pixel of 135 microm in diameter with an extended color gamut. The proposed fiber-optic color synthesizer can provide a compact waveguide solution for the beam scanning display and the tunable pure white source for LED backlighting.     

Radiative and nonradiative recombination of self-trapped exciton on silicon nanocrystal interface

The theory of the multiphonon and radiative recombination of a self-trapped exciton on the interface of a silicon nanocrystal in a SiO₂ matrix is developed. Self-trapped excitons play a key role in the hot carrier dynamics in nanocrystals under photoexcitation. The ratio of the probabilities of the multiphonon and radiative recombination of the self-trapped exciton is estimated. The probabilities of exciton tunnel transition from the self-trapped state to a nanocrystal are calculated for nanocrystals of various sizes. The infrared range spectrum of the luminescence of the self-trapped exciton is obtained.     

Blue–green luminescent CdZnSeS nanocrystals synthesized with activated alkyl thiol

Semiconductor nanocrystals with blue–green luminescence are potentially useful in various applications, but the preparation has not been easy compared to regular semiconductor nanocrystals with emission in the orange–red range. In this research alloyed CdZnSeS nanocrystals with luminescence covering the wavelength range from 430 to 560 nm are obtained by a one-step method with the assistance of alkyl thiol compound 1-dodecanethiol, which serves both as the sulfur source and surface ligand. The luminescence of CdZnSeS nanocrystals can be tuned from blue to green by altering the Cd:Zn molar ratio. Besides, the amount of 1-dodecanethiol in the reaction mixture can influence the emission wavelength by restricting the growth of nanocrystals. The dual control of both particle composition and size has enabled the tuning of luminescence to cover the blue–green spectral window. This research presents a convenient method to synthesize nanocrystals with tunable blue–green emission; these materials can be useful in advanced technologies such as photovoltaics, lighting and display.     

2017年10期电子期刊

为了增强β-NaGdF₄：Yb³⁺,Tm³⁺纳米晶的上转换发光,克服外延增长钝化壳增大尺寸的不足,利用阳离子交换法制备核壳纳米结构,研究了样品在980 nm激发下的上转换发光性质。首先,利用高温热分解法制备了直径为10 nm的β-NaGdF₄：Yb³⁺,Tm³⁺纳米晶;然后,将制备的纳米晶与Gd³⁺在油酸-十八烯混合溶液中在300℃进行交换反应。实验结果表明,随着表面Yb³⁺和Tm³⁺被Gd³⁺取代,钝化壳的形成抑制了内部Yb³⁺的表面去激发过程,增强了内部Yb³⁺（²F₅）→ Tm³⁺（³H₅,³F_2,3）的能量传递,上转换发光逐渐增强。交换30 min后,Tm³⁺的³H₄ →³H₆近红外发光增强达到最大,为对照样品的6.5倍,而尺寸基本保持不变。在生物成像方面,上转换纳米晶的尺寸必须与生物分子相匹配,同时发光强度要高,阳离子交换法既能增强近红外发光,又能保持原来小的尺寸,在生物成像领域具有很好的应用前景。