434 resultados para Fluorescence Resonance Energy Transfer
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Infrared (1.2-1.6 mum) luminescence in a yttrium aluminium garnet (YAG) crystal, co-doped with Yb (10 at.%) and Cr (0.05 at.%) ions, was investigated under CW laser diode pumping (lambda = 940 nm). The Cr4+ emission band was observed with its peak at 1.35 mum and measured to be about 6% with respect to Yb3+ IR luminescence (lambda = 1.03 mum). Analysis of the crystal absorption and luminescence spectra allows one to conclude that Yb3+-Cr4+ energy transfer is a mechanism responsible for the B-3(2)(T-3(2))-B-3(1)((3)A(2)) emission of Cr4+ ions. This crystal is promising as an efficient source of the near infrared emission. (C) 2004 Elsevier B.V. All rights reserved.
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In this paper, we present results on upconversion luminescence performed on Yb3+-doped yttrium aluminum garnets under 940 nm excitation. The upconversion luminescence was ascribed to Yb3+ cooperative luminescence and the presence of rare earth impurity ions. The cooperative luminescence spectra as a function of Yb concentration were measured and the emission intensity variation with Yb concentration was discussed. Yb3+ energy migration quenched the cooperative luminescence of Yb:YAG crystals with doping level over 15 at%. (c) 2004 Elsevier B.V. All rights reserved.
Resumo:
Infrared (1.2-1.6 mu m) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05 at.%) ions, was investigated under CW laser diode pumping (lambda = 940 nm). The Cr4+ emission band was observed with its peak at 1.34 mu m and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda = 1.03 mu m). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the B-3(2)(T-3(2))-B-3(1)((3)A(2)) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 mu m) output. (c) 2004 Elsevier B.V. All rights reserved.
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We report near infrared broadband emission of bismuth-doped barium-aluminum-borate glasses. The broadband emission covers 1.3 mum window in optical telecommunication systems. And it possesses wide full width at half maximum (FWHM) of similar to 200nm and long lifetime as long as 350 mus. The luminescent properties are quite sensitive to glass compositions and excitation wavelengths. Based on energy matching conditions, we suggest that the infrared emission may be ascribed to P-3(1) --> P-3(0) transition of Bi+. The broad infrared emission characteristics of this material indicate that it might be a promising candidate for broadband optical fiber amplifiers and tunable lasers. (C) 2005 Optical Society of America.
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EU3+ -doped Y3Al5O12 (YAG:Eu3+) phosphors were synthesized by a facile sol-gel combustion method. In this process, citric acid traps the constituent cations and reduces the diffusion length of the precursors. YAG phase is obtained through sintering at 900 degrees C for 2h. There were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) observed. The charge transfer band of nanocrystalline phosphors shows a shift toward the high-energy side, compared with that of amorphous ones due to lower covalency of Eu-O bond for nanocrystalline phosphors. The higher concentration quenching in YAG:EU3+ nanophosphors may be caused by the confinement effect on resonant energy transfer of nanocrystalline. It also indicates that the sol-gel combustion synthesis method provides a good distribution of Eu3+ activators in YAG host. (c) 2005 Elsevier B.V. All rights reserved.
Resumo:
The synthesis and optical properties of Y3Al5O12:Tb3+ phosphors are reported in this paper. Y3Al5O12:Tb3+ phosphors were synthesized by a facile solution combustion method. Citric acid traps the constituent cations and also acts as a fuel. Y3Al5O12 (YAG) phase can crystallize through sintering at 900 degrees C for 2 h, and there were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) in the sintering process. The excitation spectra of crystalline Y3Al5O12:Tb3+ are different from that of amorphous one due to the crystal field effect. The emission spectra mainly show D-5(4) -> F-7(6) transition under UV excitation. The higher concentration quenching in Y3Al5O12:Tb3+ nanophosphors may be due to the confinement effect on resonant energy transfer of nanocrystalline. It is also indicated that the solution combustion synthesis method provides a good distribution of Tb3+ activators in Y3Al5O12 host. (c) 2005 Published by Elsevier B.V.
Resumo:
用群论的方法计算了Nd:YbVO4晶体的拉曼活性振动模数目,在室温下测得了其极化拉曼谱线,并指认了在不同几何配置下,各振动模式所对应的频率。同时,测得了室温下晶体的吸收谱,得到了中心波长为808am吸收峰的半高宽为12nm,并在J-O理论的基础上计算了晶体的光学参数,其三个晶场参数分别为Ω2=6.88945×10^-20cm^2。Ω4=4.13394×10^-20cm^2、Ω6=4.54503×10^-20cm^2,并由此得到^4F3/2能级的荧光寿命为178.69炉,1062nm处的荧光分支比为48.85%,积分发射截面为2.786710^-18cm^2。分别在808nm、940nm激发下测得晶体室温发射谱,观察到了Nd→Yb以及Nd←Yb间的能量传递现象。
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1.对嗜热蓝藻层理鞭枝藻(Mastigocladus laminosus)藻胆体的光谱特性和光能传递进行了研究。其完整藻胆体的吸收峰位于622 nm,室温荧光发射峰位于673 nm。在77K荧光发射光谱中,完整藻胆体的荧光峰只有一个,位于685 nm,是末端发射体1的荧光。在低浓度磷酸缓冲液中发生严重解离的藻胆体,其77K荧光发射光谱中有二个发射峰和一个发射肩。两个荧光发射峰分别位于644 nm和683 nm。前者为主峰,属于C-藻蓝蛋白的荧光,后者是次峰,属于末端发射体2的荧光。荧光发射肩位于660 nm附近,属于别藻蓝蛋白的荧光。据此,提出层理鞭枝藻藻胆体光能传递途径如下: 藻红蓝蛋白→c—藻蓝蛋白→别藻蓝蛋白→端发射体l、末端发射体2: 2.对嗜热蓝藻层理鞭枝藻藻胆体—类囊体膜的光谱特性和光能传递进行了研究。在吸收光谱中,其藻胆体——类囊体膜在可见光区域有5个峰,它们分别位于420 nm、438 nm、490 nm、624 nm和678 nm。420 nm、438 nm和678 nm为叶绿素a的吸收峰位置。490 nm是类胡罗卜素的吸收峰,624 nm是藻胆体的吸收峰。对藻胆体——类囊体膜用580 nm波长的光激发藻胆蛋白时,在室温荧光发射光谱中有一个发射峰和一个发射肩,分别位于657 nm和690 nm,前者属于藻胆蛋白的荧光,后者属于叶绿素a的荧光。这说明藻胆蛋白能将捕获的光能传递给类囊体膜上的叶绿素a。在77K荧光发射光谱中有4个峰,它们分别位于649 nm、660 nm、688 nm和730 nm。前二者属于藻胆蛋白的荧光,后二者属于叶绿素a的荧光。这同样说明藻胆蛋白能将捕获的光能传递给类囊体膜上的叶绿素a。当用436 nm波长光激发叶绿素a时,藻胆体——类囊体膜的室温荧光发射光谱中有两个荧光峰出现,位于685 nm的峰来源于光系统Ⅱ,位于713 nm的峰来源于系统I。这说明叶绿素a捕获的光能不能逆传递给藻胆体中的藻胆蛋白。在77K荧光发射光谱中也只有叶绿素a的荧光峰,位于695 nm的峰来源于光系统Ⅱ,位于730 nm的峰来源于光系统l。此结果同样说明叶绿素a捕获的光能不能逆传递给藻胆蛋白. 3.我们以多变鱼腥藻(Anabaena variabilis)为材料,对其藻胆体核心和藻蓝蛋白进行了重组实验,得到了具有光能传递效率的藻胆体核心——藻蓝蛋白复合物。在吸收光谱中,藻胆体核心有一吸收峰和一个吸收肩,分别位于654 nm和600 nm。藻蓝蛋白的吸收光谱中只有一个峰,位于620 nm.重组样品的吸收光谱有一吸收峰和一吸收肩,分别位于654 nm和620 nm.由于620 nm与654 nm的吸收比远大于核心的600 nm与654 nm的吸收比,因此,可以认为部分藻蓝蛋白已与核心重组。在室温荧光发射光谱中,藻胆体核心只有一个峰,位于676 nm。藻蓝蛋白只有一个峰,位于653 nm。重组样品有一荧光发射峰和一荧光发射肩,分别在669 nm和650 nm附近。669 nm荧光来源于核心,650 nm荧光来源于藻蓝蛋白。重组后的核心的650 nm荧光显著大于未重组的核心,这也说明部分藻蓝蛋白与核心已重组.在77K荧光发射光谱中,藻蓝蛋白只有一个峰,位于655 nm。藻胆体核心有二个峰,分别位于666 nm和686 nm。重组样品有两个荧光发射峰和一荧光发射肩,分别位于666 nm、683 nm和648 nm附近.重组的核心的别藻蓝蛋白的荧光(F666)和藻蓝蛋白的荧光(F648)都强于未重组的核心。这一结果同样说明有藻胆体——藻蓝蛋白复合物生成。 除以上研究工作之外,我们还对多变鱼腥藻藻胆体在解离过程中的光谱特性及光能传递、藻胆体——类囊体膜的光谱特性及光能传递、藻胆体解离重组、藻胆体核心在低浓度磷酸缓冲液中的光谱特性、以及温度对藻胆体核心的影响等进行了研究。研究结果有待整理。 本文编写:PBS:藻胆体;PEB:藻红胆素;PE:藻红蛋白;PUB:藻尿胆素;PEC:藻红蓝蛋白;PCB:藻蓝胆素;PC:藻蓝蛋白;PSⅡ:光系统Ⅱ;APC:别藻蓝蛋白;PS I:光系统I;TE:末端发射体
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全文分两部分,(1).PsⅡ反应中心色素分子光破坏的分子机理研究;(2).PSⅡ反应中心原初反应的动力学机理研究。 在第一部分中,在分离纯化的光系统Ⅱ反应中心Dl/D2/Cyt b559复合物中,采用高效液相色谱技术,首次发现PSⅡ反应中心去镁叶绿素分子的光照破坏,研究了去镁叶绿素的光破坏机理,观察到PsⅡ反应中心内部存在一个与光化学活性无关的去镁叶绿素分子,从而提供了PSⅡ反应中心存在两条电子传递链的第一个实验证据,提出了去镁叶绿素对PsⅡ反应中心的光保护假说和光合作用反应中心第二条电子传递支路的光保护假说。用高效液相色谱技术还观察到PSⅡ反应中心的6个叶绿素a分子,有三种不同的存在状态,认为PSl反应中心的最小色素组成为每个反应中心含有4个叶绿素a和2个去镁叶绿素。用光破坏的方法证明PsⅡ原初电子供体P680是由两个叶绿素n分子组成,认为P680是以一个二聚体形式存在,首次发现P680的光破坏过程包含失去中心镁原子的反应。 在第二部分中,用皮秒和飞秒时间分辨光谱技术,在PsⅡ颗粒、PsⅡ核心复合物和PSⅡ反应中心三个层次上,研究了PsⅡ原初反应的动力学性质,着重研究电荷分离和PsⅡ反应中心内部的能量传递过程。结果表明,B-胡萝卜素和P680之间的能量传递时间常数为350p8左右,去镁叶绿素a与P680之间的能量传递时间为lOOp8左右,提出了可能的动力学模型。 在目前分歧最大的原初电荷分离时间常数测定这一焦点问题上,得到的初步结果表明PsⅡ反应中心电荷分离时间为3-3.5pa左右,这一结论与文献上报道的21pa不同,丽倾向于支持国际上3p8的观点。
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细胞色素b6f蛋白复合体(Cyt b6f)是光合链中连接两个光系统(PSII 和PSI)的中间电子载体蛋白复合物,其主要的生理功能是催化电子传递和质子跨膜转移,形成跨膜质子电化学梯度,为ATP的合成提供能量,在光合作用光能转化过程中占有很重要的地位。细菌和莱茵衣藻Cyt b6f的晶体结构已于2003年底获得了近原子水平的解析,但有关该复合物中两种色素(Chl a和β-Car)的生理功能及其机理尚无明确的解释。预计它们将成为今后几年的研究热点,因为揭示Cyt b6f蛋白复合体中Chl a和β-Car分子的生理功能对于进一步阐明光合作用高效转能及其调控的分子机理具十分重要的意义。鉴于目前尚未见到海洋绿藻Cyt b6f的报道,本文以海洋绿藻—假根羽藻(Bryopsis corticulans)类囊体膜上的Cyt b6f蛋白复合体为对象,对其中的类胡萝卜素的分子结构与生理功能进行了比较系统地研究。 首先,我们改进了原用于菠菜类囊体膜Cyt b6f的分离、纯化流程,在原流程的基础上增加了一次2 mol/L NaBr洗膜,彻底地去除了膜表面的杂蛋白;还调整了第二次硫酸铵分级沉淀时的饱和度,并将38-45%饱和度下的沉淀物确定为需要收集的Cyt b6f制剂。采用此改进的流程,我们首次从假根羽藻类囊体膜中分离纯化了高活性、高纯度的Cyt b6f制剂。SDS-PAGE分析的结果显示该制剂的4个多肽亚基 (Cytf 、Cyt b6 、Rieske[Fe-s]及亚基IV)的表观分子量分别为34.8、24.0、18.7和16.7 kD;Cyt b6 / f 比值接近2.0, 其纯度值为9.9 nmol cyt f/mg;其催化电子传递的活性 (C10-PQH2→PC)为73 e/s。HPLC 和共振拉曼光谱分析表明,假根羽藻Cyt b6f中的类胡萝卜素为α-胡萝卜素分子,它是一种在Cyt b6f中尚未报道过的类胡萝卜素。定量分析表明,每个假根羽藻Cyt b6f单体中全反式(all-trans)和9顺式(9-cis)α-胡萝卜素的含量分别为0.2和0.7个分子,另外还含有1.2分子的Chl a。CD光谱分析表明该9-cis-α-胡萝卜素处在一个不对称的蛋白环境中。TLC分析表明该制剂是一种缺脂的Cyt b6f蛋白复合体。 采用稳态荧光激发光谱,时间分辨吸收光谱及Chl a的光破坏实验对假根羽藻Cyt b6f中α-胡萝卜素的功能进行了研究。结果表明,Cyt b6f中α-胡萝卜素可以将它吸收的光能传递给Chl a,其能量传递效率为62.4%,提出α-胡萝卜素分子与Chl a分子之间的单线态能量传递是遵从Föster 机制进行的;α-胡萝卜素分子对Chl a分子有一定的光保护作用,这种保护作用是通过清除单线态氧来实现的。另外还发现Cyt b6f中的Chl a分子可能与其周围的氨基酸残基存在相互作用,认为这是其进行自我光保护的一种方式。 此外,还采用HPLC研究了光和暗交替对假根羽藻Cyt b6f中α-胡萝卜素构型的影响,并对假根羽藻Cyt b6f选择结合α-胡萝卜素的原因进行了初步的分析。
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光系统II(PSII)是存在于类囊体膜中的多亚基色素蛋白复合物,是吸收光能、催化光诱导水裂解释放氧气、质子和电子的重要机构。它在体内的基本单位是由外周天线蛋白(LHCII)与PSII核心复合物结合形成的PSII-LHCII超分子复合物,这一结构保证了LHCII吸收的能量能够快速有效的传递到PSII反应中心(RC),进行原初光化学反应。 本论文分为两部分:1、利用捕光色素蛋白复合物(LHCII)与PSII核心复合物在以DGDG、PG、SQDG三种类囊体膜脂形成的脂质体中重组的方法,研究了LHCII与PSII在脂膜上结构与功能的相互作用;2、通过研究光破坏和色素置换对PSII RC的影响,探讨了RC中不同色素的功能。主要结果如下: 1、LHCII与PSII核心复合物的蛋白脂质体研究: 将OECC(粗提核心复合物)、pdOE(纯化核心复合物)、LHCII(大量天线)制剂分别与脂质体重组并研究了其光谱性质。LHCII在与脂质体重组前表现出典型的聚集态光谱特征,重组后吸收和荧光发射峰发生明显蓝移;LHCII、OECC和pdOE三种蛋白脂质体与重组前的样品相比荧光发射强度增加;表明脂环境影响了色素蛋白复合物的聚集状态以及色素和蛋白之间的相互作用。 OECC和pdOE分别与LHCII在脂质体中重组,得到两种重组蛋白(LHCII-OECC和LHCII-pdOE)脂质体,用冰冻蚀刻电镜技术和低温荧光光谱的方法研究其结构和功能特征。LHCII和核心复合物(OECC或pdOE)结合形成PSII-LHCII重组颗粒,并在脂质体中均匀排布,阻止了LHCII晶格状结构的形成。重组蛋白脂质体的吸收光谱既有LHCII的吸收特征,又有核心复合物的特征吸收峰,但低温荧光光谱的主要发射峰是核心复合物的特征峰(684 nm-685 nm),而不是LHCII的特征峰(680 nm);而且激发不同色素得到的荧光发射光谱基本一致,这些结果证明LHCII吸收的能量传递到了核心复合物中,在重组蛋白脂质体中不同色素蛋白复合物在结构和功能上都实现了相互偶联。 通过对OECC或pdOE与LHCII重组形成的蛋白脂质体放氧或DCPIP光还原活性的检测研究了PSII光化学活性特征。LHCII和核心复合物(OECC或pdOE)的重组蛋白脂质体与单独核心脂质体相比,在强光和弱光下光化学活性都明显提高。这从另一个角度证明了核心复合物与LHCII的功能偶联,LHCII的结合使捕光截面积增大,从而使PSII光化学活性增加。 用77K飞秒时间分辨荧光光谱分析了几种蛋白脂质体的能量传递和捕获情况。LHCII、OECC和pdOE三种蛋白脂质体的主要荧光衰减组分分别是670 ps(发射峰在680 nm)、650 ps(发射峰在690 nm)和570 ps(发射峰在685 nm)。LHCII-OECC和LHCII-pdOE脂质体的主要衰减组分分别是940 ps(发射峰在690 nm)和840 ps(发射峰在685 nm),并且出现了一个在核心复合物脂质体和LHCII脂质体中没有的40 ps组分,可以推测,这是LHCII和核心复合物之间达到平衡的时间组分,比激发态衰减的平均寿命要快得多,因此支持了PSII的trap-limited激发能衰减动力学模型。此外,可以看到天线的增大使Chl a荧光衰减的寿命延长,这一特性可能与PSII的光保护机制有关。 LHCII和OECC、LHCII和pdOE在脂质体中都成功的实现了重组,而且在结构和功能上没有明显差异;表明小天线以及23 kDa、17 kDa蛋白可能不是LHCII和核心复合物结合及能量传递所必需的。 2、受体侧光破坏和色素置换对PSII RC的影响: 在800 μmol.m-2 .s-1光照和无外加电子受体、供体的情况下,研究了PSII RC色素的受体侧光破坏情况。Chl a、Pheo和β-Car的光漂白几乎同时发生,其中在680 nm吸收的色素破坏最为显著,670 nm吸收的外周Chl比其他色素更加稳定。荧光发射强度呈先升高后降低的趋势,最大发射峰位逐渐蓝移,表明色素之间的能量传递受到破坏。用β-Car的主要吸收波长488 nm和514.5 nm激发得到两组谱带峰位和强度不同的拉曼光谱,表明在PSII RC中存在两个光谱性质不同的β-Car。光破坏过程中两组谱带的位置和带宽都没有明显变化,表明β-Car的光保护机制不涉及自身构象的变化。 将PSII RC与Cu-Chl a进行色素置换,得到了与Cu-Chl重组的RC(Cu-Chl-RC),含有0.5 Cu-Chl/2Pheo。与对照RC(按同样方式与Chl a置换的RC)和天然RC相比,Cu-Chl含量增加而Chl含量减少,660 nm的吸收增加而670 nm吸收降低,因此推测是外周Chl被替换。色素置换过程对RC的多肽组分及大部分的P680活性没有影响,CD光谱的变化也很小,表明产生CD信号的色素和蛋白环境也没有受到明显影响。但是Cu-Chl-RC的荧光发射强度明显降低,最大发射峰蓝移且峰形发生变化,Cu-Chl可能在重组RC中作为激发态的淬灭剂,阻碍了色素之间的能量传递。
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E2SiO5 thin films were fabricated on Si substrate by reactive magnetron sputtering method with subsequent annealing treatment. The morphology properties of as-deposited films have been studied by scanning electron microscope. The fraction of erbium is estimated to be 23.5 at% based on Rutherford backscattering measurement in as-deposited Er-Si-O film. X-ray diffraction measurement revealed that Er2SiO5 crystalline structure was formed as sample treated at 1100 degrees C for 1 h in O-2 atmosphere. Through proper thermal treatment, the 1.53 mu m Er3+-related emission intensity can be enhanced by a factor of 50 with respect to the sample annealed at 800 degrees C. Analysis of pump-power dependence of Er3+ PL intensity indicated that the upconversion phenomenon could be neglected even under a high photon flux of 10(21) (photons/cm(2)/sec). Temperature-dependent photoluminescence (PL) of Er2SiO5 was studied and showed a weak thermal quenching factor of 2. Highly efficienct photoluminescence of Er2SiO5 films has been demonstrated with Er3+ concentration of 10(22)/cm(3), and it opens a promising way towards future Si-based light source for Si photonics. (C) 2009 Elsevier B.V. All rights reserved.
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The effect of the Coulomb interaction on the energy spectrum and anisotropic distribution of two electron states in a quantum ring in the presence of Rashba spin-orbit interaction (RSOI) and Dresselhaus SOI (DSOI) is investigated in the presence of a perpendicular magnetic field. We find that the interplay between the RSOI and DSOI makes the single quantum ring behaves like a laterally coupled quantum dot and the interdot coupling can be tuned by changing the strengths of the SOIs. The interplay can lead to singlet-triplet state mixing and anticrossing behavior when the singlet and triplet states meet with increasing magnetic field. The two electron ground state displays a bar-bell-like spatial anisotropic distribution in a quantum ring at a specific crystallographic direction, i.e., [110] or [1 (1) over bar0], which can be switched by reversing the direction of the perpendicular electric field. The ground state exhibits a singlet-triplet state transition with increasing magnetic field and strengths of RSOI and DSOI. An anisotropic electron distribution is predicted which can be detected through the measurement of its optical properties.
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Er/Bi codoped SiO2 thin films were prepared by sol-gel method and spin-on technology with subsequent annealing process. The bismuth silicate crystal phase appeared at low annealing temperature while vanished as annealing temperature exceeded 1000 degrees C, characterized by X-ray diffraction, and Rutherford backscattering measurements well explained the structure change of the films, which was due to the decrease of bismuth concentration. Fine structures of the Er3+-related 1.54 mu m light emission (line width less than 7 nm) at room temperature was observed by photoluminescence (PL) measurement. The PL intensity at 1.54 gm reached maximum at 800 degrees C and decreased dramatically at 1000 degrees C. The PL dependent annealing temperature was studied and suggested a clear link with bismuth silicate phase. Excitation spectrum measurements further reveal the role of Bi3+ ions for Er3+ ions near infrared light emission. Through sol-gel method and thermal treatment, Bi3+ ions can provide a perfect environment for Er3+ ion light emission by forming Er-Bi-Si-O complex. Furthermore, energy transfer from Bi3+ ions to Er3+ ions is evidenced and found to be a more efficient way for Er3+ ions near infrared emission. This makes the Bi3+ ions doped material a promising application for future erbium-doped waveguide amplifier and infrared LED