藻胆体的光谱特性和光能传递

一，螺旋藻藻胆体光谱特性及其光能传递的研究 1，完整藻胆体与解离藻胆体吸收光谱的比较研究 对螺旋藻完整藻胆体和解离藻胆体的吸收光谱中进行了比较研究。随着PBS逐渐解离，其吸收光谱表现出如下变化特点：在紫外区，吸收峰始终位于355nm，尖形峰逐渐变成钝形峰;在红区，完整藻胆体和解离藻胆体都有很强的光吸收，吸收峰呈平顶状，其半带宽逐渐变小，紫外区与红区相对吸收强度比值逐渐变小，四组导数吸收光谱中的小峰数目越来越少。室温荧光发射光谱表明，PBS在低于0.9mol/L的磷酸缓冲液中变得不稳定，并开始逐渐解离，解离的PBS与完整的PBS相比，其荧光发射峰逐渐蓝移。 2，藻胆体在解离过程中荧光发射和光能传递的研究 完整藻胆体的室温荧光发射光谱中只有一个峰，在678nm。说明在完整藻胆体中，光能传递效率高。在77K荧光发射光谱中，完整藻胆体只有一个峰，位于682nm，这是L_(cm)(TE_1)的荧光峰;严重解离的藻胆体的主峰在656nm，是PC的荧光;在679nm有一个小峰，是APC-B的荧光(TE_2)。据此，我们提出螺旋藻藻胆体的光能传递链为：(此处表从略，见全文) 二，螺旋藻藻胆体核心及其与藻蓝蛋白的重组 PC+core混合物，浓缩重组48h后，其室温荧光发射峰位于663nm，与PC的室温荧光发射峰643nm和PC+core混合物（未重组）的室温荧光发射峰648nm相比，说明部分APC与部分PC发生了重组，使部分PC吸收的光能传递给了APC，使荧光发射峰红移;与藻胆体核心室温荧光发射峰664nm相比，则非常接近，说明重组效果较好。PC+core混合物（未重组），其77K荧光发射光谱中有两个峰：654nm,679nm,分别是PC,APC-B的荧光峰，F679/F654的比值为32.0%。我们以F679/F654比值的变化来判断PC与core是否发生了重组。PC+core混合物，经48h浓缩重组后，77K荧光发射光谱中有F657,F679两个峰，F679/F654的比值则为45.9%，比未重组的混合物32.0%升高了，说明部分PC与core发生了重组，部分PC吸收的光能传递给了APC和APC-B，使F679加强，F654减弱。 三，螺旋藻藻胆体一类囊体膜光谱特性与光能传递的研究 藻胆体一类囊体膜的吸收光谱，室温荧光发射光谱和77K荧光发射光谱表明：藻胆蛋白能将捕获的光能传递给叶绿素a，叶绿素a捕获的光能不能逆传给藻胆蛋白。 四，藻胆体一类囊体膜的重组 藻胆体一类囊体膜的吸收光谱说明，一部分被洗下来的PBS能重新结合到类囊体膜上，但并没有达到100%的重组。 五，整体螺旋藻光谱特性及其光能传递的研究 整体螺旋藻光谱特性与PBS-类囊体膜的光谱特性极为相似，表现出同样的规律：PBS的吸收面积与叶绿素a相比，叶绿素a的吸收是主要的。 从PBS-类囊体膜和整体螺旋藻的吸收光谱，室温荧光发射光谱，77K荧光发射光谱的研究中可知，二者表现出极为相似的规律：PBS藻胆蛋白捕获的光能能传递给叶绿素a，叶绿素a捕获的光能不能逆传给PBS藻胆蛋白。主要的捕光物质是叶绿素a。 另外，我们还对Spirulina platensis 6 and Spirulina maxima的藻胆体在解离过程中的荧光发射和光能传递进行了研究，表现规律与Spirulina platensis相同。

发状念珠藻光合特征及其在复水－失水过程中能量传递变化的研究

摘要 "发状念珠藻（Nostoc flagelliforme Born. Et Flah.），俗名发菜，是生长于干旱、半干旱土壤表面的陆生蓝藻，具有极强的抗旱能力。发菜光合作用方面的研究大多处于整体细胞水平，且研究手段非常有限。本实验对发菜光合特征进行深入研究，并探讨了发菜在干湿交替过程中能量传递的变化情况。 叶绿素和藻胆素是发菜细胞中两种主要的光合色素。发菜复水后光合活性完全恢复时，在室温（20℃）或低温（77K）下，其绝大部分的荧光是由于藻胆素被激发而产生。在室温下，大部分荧光来自藻胆体;当叶绿素被激发后，产生的荧光非常微弱。在低温下，藻胆素被激发后，荧光发射光谱中可分辨出藻胆蛋白、光系统Ⅰ和光系统Ⅱ的发射峰;叶绿素被激发后，荧光发射光谱包括光系统Ⅰ和光系统Ⅱ的荧光。相比之下，室温荧光发射光谱不适于用做发菜细胞光合作用方面的研究。 我们设计了一种新方法，从野生发菜细胞中分离得到类囊体膜及细胞质膜，并对其性质进行分析。发菜细胞外复杂的胶质结构使得现有破碎其它蓝藻细胞的方法无法破碎发菜细胞。通过实验发现，联合使用细胞破碎仪和毛地黄皂甙（0.3%）可有效破碎发菜细胞;并且毛地黄皂甙在低浓度下（≦0.5%），对色素与蛋白的结合不会造成破坏作用。随后，通过蔗糖密度梯度离心可将细胞质膜与类囊体膜分离。发菜类囊体膜的光谱性质与其它蓝藻相似。细胞质膜除结合有类胡萝卜素外，还结合有少量叶绿素前体。类囊体膜和细胞质膜膜脂及脂肪酸组成相似。其中，十六碳烯酸[16：1(9)]和亚麻酸[18：3(9,12,15)]是含量最高的两种脂肪酸，分别占总脂肪酸含量的三分之一左右。高含量的多不饱和脂肪酸可能和发菜极强的抗旱能力有关。 我们首次对发菜捕光色素蛋白复合物－藻胆体的组成和结构进行分析。发菜藻胆体为“3核＋6杆”的半圆盘结构。组成藻胆体的藻胆蛋白包括藻蓝蛋白和别藻蓝蛋白。两个藻蓝蛋白六聚体通过连接肽组成藻胆体的“杆”结构。在“杆”结构中等量分布着两条连接肽（分子量分别为29kDa和34kDa）为杆连接肽和核杆连接肽。而“核”结构中核膜连接肽的分子量为103kDa。 发菜在无霜期，几乎每天经历一次复水－干燥过程：夜间的结露使发菜在黑暗中复水，而清晨太阳升起后，在光照下迅速失水进入休眠状态。我们研究了发菜在黑暗中的复水过程及在光照下失水过程中藻胆体与光系统能量传递的变化情况。发菜在黑暗中复水后，光系统Ⅱ活性无法恢复。藻胆体内及藻胆体与光系统Ⅰ的能量传递在5分钟内恢复;而藻胆体与光系统Ⅱ的能量传递只能部分恢复。我们设想，发菜在复水过程中通过双扳机－水和光－控制光合活性的恢复，以及在黑暗中部分恢复藻胆体与光系统Ⅱ的能量传递，将减少不必要的能量消耗与通过光合作用储备尽可能多的化学能－这两个生存策略有机的结合起来。发菜在光照下的失水过程中，光合活性在含水量降至90％前基本保持稳定，随后迅速下降。而在含水量达到150％后，藻胆体内的能量传递便开始受到抑制，并且随着含水量的降低，该抑制现象逐步加剧。这样，发菜在干燥过程中，通过抑制藻胆体内的能量传递，减少了传递到光系统Ⅱ反应中心的能量，从而避免了在光合活性下降过程中过剩光能对光系统Ⅱ产生的破坏作用。"

Numerical analysis of gain saturation, noise figure, and carrier distribution for quantum-dot semiconductor-optical amplifiers

The gain saturation behaviors and noise figure are numerically analyzed for quantum-dot semiconductor optical amplifiers (QD-SOAs). The carrier and photon distributions in the longitudinal direction as well as the photon energy dependent facet reflectivity are accounted in the rate equations, which are solved with output amplified spontaneous emission spectrum as iterative variables. The longitudinal distributions of the occupation probabilities and spectral-hole burning are presented for electrons in the excited and ground states of quantum dots. The saturation output power 19.7 dBm and device gain 20.6 dB are obtained for a QD-SOA with the cavity length of 6 rum at the bias current of 500 mA. The influences of them electron intradot relaxation time and the QD capture time on the gain spectrum are simulated with the relaxation time of 1, 30, and 60 ps and capture time of 1, 5, and 10 ps. The noise figure as low as 3.5 dB is expected due to the strong polarization sensitive spontaneous emission. The characteristics of gain saturation and noise figure versus input signal power for QD-SOAs are similar to that of semiconductor. linear optical amplifiers with gain clamping by vertical laser fields.

New observations on the pressure dependence of luminescence from Eu2+-doped MF2 (M = Ca, Sr, Ba) fluorides

The luminescence from Eu2+ ions in MF2 (M = Ca, Sr, Ba) fluorides has been investigated under the pressure range of 0-8 GPa. The emission band originating from the 4f(6)5d(1) -> 4f(7) transition of Eu2+ ions in CaF2 and SrF2 shows the red-shift as increasing pressure with pressure coefficients of -17 meV/GPa for CaF2 and -18 meV/GPa for SrF2. At atmospheric pressure, the emission spectrum of BaF2:Eu2+ comprises two peaks at 2.20 and 2.75 eV from the impurity trapped exciton (ITE) and the self-trapped exciton (STE), respectively. As the pressure is increased, both emission peaks shift to higher energies, and the shifting rate is slowed by the phase transition from the cubic to orthorhombic phase at 4 GPa. Due to the phase transition at 4-5 GPa pressure, the ITE emission disappears gradually, and the STE emission is gradually replaced by the 4f(6)5d(1) -> 4f(7) transition of Eu2+. Above 5 GPa, the pressure behavior of the 4f(6)5d(1) -> 4f(7) transition of EU2+ in BaF2: EU2+ is the same as the normal emission of Eu2+ in CaF2 and SrF2 phosphors.

A novel extremely broadband superluminescent diode based on symmetric graded tensile-strained bulk InGaAs

A novel broadband superluminescent diode (SLD), which has a symmetric graded tensile-strained bulk InGaAs active region, is developed. The symmetric-graded tensile-strained bulk InGaAs is achieved by changing the group III TMGa source flow only during its growth process by low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE), in which the much different tensile strain is introduced simultaneously. At 200mA injection current, the full width at half maximum (FWHM) of the emission spectrum of the SLID can be up to 122nm, covering the range of 1508-1630nm, and the output power is 11.5mW.

Detailed model and investigation of gain saturation and carrier spatial hole burning for a semiconductor optical amplifier with gain clamping by a vertical laser field

A detailed model for semiconductor linear optical amplifiers (LOAs) with gain clamping by a vertical laser field is presented, which accounts the carrier and photon density distribution in the longitudinal direction as well as the facet reflectivity. The photon iterative method is used in the simulation with output amplified spontaneous emission spectrum in the wide band as iterative variables. The gain saturation behaviors and the noise figure are numerically simulated, and the variation of longitudinal carrier density with the input power is presented which is associated with the ON-OFF state of the vertical lasers. The results show that the LOA can have a gain spectrum clamped in a wide wavelength range and have almost the same value of noise figure as that of conventional semiconductor optical amplifiers (SOAs). Numerical results also show that an LOA can have a noise figure about 2 dB less than that of the SOA gain clamped by a distributed Bragg reflector laser.

Photon iterative numerical technique for steady-state simulation of gain-clamped semiconductor optical amplifiers

The photon iterative numerical technique, which chooses the outputs of the amplified spontaneous emission spectrum and lasing mode as iteration variables to solve the rate equations, is proposed and applied to analyse the steady behaviour of conventional semiconductor optical amplifiers (SOAs) and gain-clamped semiconductor optical amplifiers (GCSOAs). Numerical results show that the photon iterative method is a much faster and more efficient algorithm than the conventional approach, which chooses the carrier density distribution of the SOAs as the iterative variable. It is also found that the photon iterative method has almost the same computing efficiency for conventional SOAs and GCSOAs.

Unselective regrowth buried heterostructure long-wavelength superluminescent diode realized with MOVPE

A novel unselective regrowth buried heterostructure (BH) long-wavelength superluminescent diode (SLD), which has a grade-strained bulk InGaAs active region, was developed by metalorganic vapor-phase epitaxy (MOVPE). The 3 dB emission spectrum bandwidth of the SLD is about 65 nm with the range from 1596 to 1661 nm at 90 mA and front 1585 to 1650 nm at 150 mA. An output power of 3.5 mW is obtained at 200 mA injection current under CW operation at room temperature. (c) 2006 Elsevier B.V. All rights reserved.

Dual-wavelength distributed feedback laser for CWDM based on non-identical quantum well

Using non-identical quantum wells as the active material, a new distributed-feed back laser is fabricated with period varied Bragg grating. The full width at half maximum of 115 nm is observed in the amplified spontaneous emission spectrum of this material, which is flatter and wider than that of the identical quantum wells. Two wavelengths of 1.51 mu m and 1.53 mu m are realized under different work conditions. The side-mode suppression ratios of both wavelengths reach 40 dB. This device can be used as the light source of coarse wavelength division multiplexer communication systems.

Analysis of semiconductor microlasers with an equilateral triangle resonator by rate equations

Semiconductor microlasers with an equilateral triangle resonator (ETR) are analyzed by rate equations with the mode lifetimes calculated by the finite-difference time-domain technique and the Pade approximation. A gain spectrum based on the relation of the gain spectrum and the spontaneous emission spectrum is proposed for considering the mode selection in a wide wavelength span. For an ETR microlaser with the side length of about 5 mum, we find that single fundamental mode operation at about 1.55 mum can be obtained as the side length increases from 4.75 to 5.05 mum. The corresponding wavelength tuning range is 93 nm, and the threshold current is about 0.1 to 0.4 mA.

Photoluminescence of rapid-thermal annealed Mg-doped GaN films

We report the investigation of temperature and excitation power dependence in photoluminescence spectroscopy measured in Mg-doped GaN epitaxial layers grown on sapphire by metalorganic chemical vapor deposition, The objective is to examine the effects of rapid-thermal annealing on Mg-related emissions. It is observed that the peak position of the 2.7-2.8 eV emission line is a function of the device temperature and annealing conditions, The phenomenon is attributed to Coulomb-potential fluctuations in the conduction and valence band edge and impurity levels due to the Mg-related complex dissociation. The blue shift of the 2.7-2.8 eV emission line with increasing excitation power provides clear evidence that a donor-acceptor recombination process underlies the observed emission spectrum. In addition, quenching of minor peaks at 3.2 and 3.3 eV are observed and their possible origin is discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.

Different transfer paths for thermally activated electrons and holes in self-organized Ge/Si(001) islands in a multilayer structure

We investigated the temperature dependence (10-250 K) of the photoluminescence (PL) emission spectrum of self-organized Ge/Si(001) islands in a multilayer structure. With elevated temperature, we find that the thermally activated holes and electrons are gathered by the Ge islands in different ways. The holes drift from the wetting layer into the islands, while the electrons, confined in Si due to type-II band alignment, leak into the Ge islands by the electrostatic interaction with the holes accumulated there. It results in an increase of the integrated intensity of island-related PL at a certain temperature range and a reduction of the phonon energy in the phonon-assisted PL of the islands by involving a type-I transition into a type-II transition. (C) 2001 American Institute of Physics.

Photostimulated luminescence of AgI clusters in zeolite-Y

AgI clusters in zeolite-Y (AgI/Y) were prepared by Ag+ exchange followed by reaction with NaI in solution. The formation of the clusters was determined by transmission electron microscopy and Auger electron spectroscopy. The clusters were uniform and even in size, 1.0-2.0 nm. The fluorescence spectrum of the clusters consists of two emission bands, which are attributed to AgI and Ag clusters, respectively. Photostimulated luminescence (PSL) is observed by stimulation at 675 or at 840 nm. The PSL spectrum of AgI/Y is consistent with the emission spectrum of Ag clusters and thus the PSL is considered to be caused by the charge transfer or carrier migration from the zeolite framework or from the AgI clusters to the Ag clusters. The appearance of PSL indicates that these materials may find application as a medium for erasable optical memory. (C) 1998 American Institute of Physics. [S0021-8979(98)02407-4].

A Broadband Long-Wavelength Superluminescent Diode Based on Graded Composition Bulk InGaAs

A novel unselective regrowth buried heterostructure long-wavelength superluminescent diode （SLD） with a graded composition bulk InGaAs active region is developed by metalorganic vapor phase epitaxy （MOVPE）. At a 150mA injection current, the full width at half maximum of the emission spectrum of the SLD is about 72nm, ranging from 1602 to 1674nm. The emission spectrum is smooth and flat. The ripple of the spectrum is less than 0.3dB at any wavelength from 1550 to 1700nm. An output power of 4.3mW is obtained at a 200mA injection current under continuous-wave operation at room temperature. This device is suitable for the applications of light sources for gas detectors and L-band optical fiber communications.

The Incident Angle Dependence of Quantum Efficiency of GaAs Based RCE Photodetectors

The theoretical analysis and experimental measurement on the incident angle dependence of quantum efficiency of GaAs based resonant cavity enhanced (RCE) photodetector is presented. By changing the angle of incoming light, about 40 nm wavelength variation of peak quantum efficiency is obtained. The peak quantum efficiency and optical bandwidth at different mode corresponding to different angle incidence is characterized with different absorption dependence on wavelength. The convenient angle tuning of resonant mode will be helpful to relax the strict constraint of RCE photodetector to light source with narrow emission spectrum such applications in space optical detections and communications.