Application of gauge R&R to the rigorous measurement of quantum yield in fluorescent organic solid state systems

A rigorous measurement of the photoluminescence quantum yield (PLQY) of three luminescent solid state organic material systems is presented. Poly(9,9-dioctylfluorene), perylene (2.97 M in poly(methyl methacrylate)), and perylene red (0.78 M in poly(methyl methacrylate)), were measured using a Ti:sapphire laser yielding 47 ± 3%, 79 ± 3%, and 51 ± 2%, respectively. A GaN diode laser with differing variability was used to measure the PLQY for perylene and perylene red yielding 71 ± 1% and 53 ± 2%, respectively. Variations due to sample preparation (<0.5%), sample degradation (none), and measurement system repeatability (Ti:sapphire ≈2%, GaN ≈1%) have been determined for each material. Variance in laser intensity is found to be the largest source of error which upon propagation to the PLQY, agrees closely with the uncertainty found by means of the rigorous statistics. This suggests reduction of laser intensity variation could allow much greater precision in absolute determinations of PLQY. Some small systematic bias from calibration and self-absorption corrections cannot be ruled out. The current limit of precision for this measurement is ±1% using the more stable GaN laser though this apparently depends on the material and sample fabrication.     

国产绝对荧光量子产率测量系统的研制

为实现物质荧光量子产率的绝对法测量,研制了一套绝对荧光量子产率测量系统。系统主机采用国产荧光分光光度计,激发和发射波长范围均为200～900 nm。光路设计采用积分球技术,保证了样品的散射和发射光线被充分收集,具备进行绝对法荧光量子产率计算的基础。光谱校正采用罗丹明B量子计数器和标准钨灯相结合的方式,确保测量结果的准确性。研制的荧光量子产率分析软件具备自动光谱校正和自动计算量子产率功能。测试结果表明,系统的测量准确性较高,可满足大部分荧光物质的测试要求。     

Measurement of the internal photoeffect quantum yield in semiconductors

A method for measuring the internal photoeffect quantum yield in various semiconductors is described. It is based on the fact that the dependence of the charge-carrier separation coefficient at a p-n junction on the wavelength of incident radiation in the proposed structure is constant in a wide range of short wavelengths. The results of measurements of the spectral sensitivity at two wavelengths, one of which is chosen in a region where the quantum yield is a priori equal to unity, is calculated for the second wavelength.     

原子吸收光谱中的背景吸收及仪器校正技术的发展

介绍了火焰原子吸收光谱（FAAS）和石墨炉原子吸收光谱（GFAAS）背景吸收干扰的特点,讨论了氘灯连续光源背景校正,塞曼效应背景校正,自吸收效应背景校正的原理和优缺点,对现代原子吸收分光光度计中各种背景校正方式的发展进行了综述。     

自吸搅拌式浮选机的吸气量研究

吸气量是自吸搅拌式浮选机的一个重要参数,吸气量的大小对浮选性能具有重要影响。通过实验和CFD计算机流体动力学仿真,对自吸搅拌式浮选机的吸气量变化规律进行了研究,找出了叶轮转速的变化和叶轮浸没深度的变化对浮选机吸气量的影响规律,以及仿真吸气量与实际吸气量之间的关系,并提出了浮选机设计时确定吸气量大小的建议。     

Photoelectron microscopy of cell surfaces

Photoelectron micrographs of fixed, unstained, uncoated chicken embryo fibroblasts and absolute photoelectron quantum yields in the 180-230 nm wavelength band of L-fucose, D-galactose, D-glucose, N-acetyl-D-glucosamine, and the sucrose polymer Ficoll are reported. The quantum yields of the saccharides are low compared to the reference dye, phthalocyanine, and fall in the same range as those previously measured for amino acids and membrane phospholipids. Photoelectron micrographs of the unstained and uncoated cells inhibit considerable surface detail. The photoelectron quantum yield data and the micrographs indicate that surface relief is the dominant source of contrast.     

Contrast effects in photoelectron microscopy; UV dose-dependent quantum yields of biological surface components

The relative brightness of photoelectron microscopy images as a function of exposure to UV light has been determined from model systems representative of biological cell surface components. Quantitative data for amino acid homopolymers, L-α-dipalmitoylphosphatidylcholine, and the polysaccharide Ficoll are reported as the absolute photoelectron quantum yields. The photoelectron quantum yields increase substantially over the initial values. For example, the quantum yields of poly-L-tyrosine at 200 nm is initially about 5 × 10^?8 electrons/incident photon. The quantum yield increases with 254 nm irradiation, leveling off at about 5 × 10^?4 electrons/incident photon after a dose of 3 × 10²¹ quanta cm^?2. Pre-irradiation of poly-L-tyrosine in the presence of certain chemical agents, for example, the Lewis base diborane (B₂H₆), results in a substantial reduction of the dose-dependent increase in quantum yield. Exposure to the reducing agent stannane (SnH₄) essentially eliminates the effect. These chemical treatments provide methods of controlling the UV dose-dependent effects in the photoelectron images.     

Development and application of quantum dots for immunocytochemistry of human erythrocytes

Recent developments in quantum dot technology have resulted in the introduction of new fluorescence immunocytochemical probes. In contrast to organic fluorophores, which are not photostable, the high quantum yield and remarkable photostability of quantum dots solve major problems associated with immunocytochemical studies of erythrocytes. We report here the first application of quantum dots to immunocytochemical studies of human erythrocytes capable of being used in high‐magnification, three‐dimensional erythrocyte reconstruction techniques. The procedure consists of stabilizing human erythrocytes with a homofunctional imidoester cross‐linker to minimize fixative‐induced autofluorescence followed by reacting with a quantum dot – monoclonal antibody complex to label band 3 protein. Our new procedure clearly showed a non‐homogeneous, raft‐like distribution of band 3 protein in the erythrocyte membrane. We also demonstrate the applicability of our technique to studies of erythrocyte membrane modifications occurring during the invasion of a malaria parasite.     

Mechanisms of cell-cell adhesion identified by immunofluorescent labelling with quantum dots: A scanning near-field optical microscopy approach

Scanning near-field optical microscopy (SNOM) has been employed to simultaneously acquire high-resolution fluorescence images along with shear-force atomic force microscopy from cell membranes. Implementing such a technique overcomes the limits of optical diffraction found in standard fluorescence microscopy and also yields vital topographic information. The application of the technique to investigate cell-cell adhesion has revealed the interactions of filopodia and their functional relationship in establishing adherens junctions. This has been achieved via the selective tagging of the cell adhesion protein, E-cadherin, by immunofluorescence labelling. Two labelling routes were explored; Alexa Fluor 488 and semiconductor quantum dots. The quantum dots demonstrated significantly enhanced photostability and high quantum yield making them a versatile alternative to the conventional organic fluorophores often used in such a study. Analysis of individual cells revealed that E-cadherin is predominantly located along the cell periphery but is also found to extend throughout their filopodia. We have demonstrated that with a fully optimised sample preparation methodology, quantum dot labelling in conjunction with SNOM imaging can be successfully applied to interrogate biomolecular localisation within delicate cellular membranes.     

Development of a high-voltage waveguide photodetector comprised of Schottky diodes and based on the Ge–Si structure with Ge quantum dots for portable thermophotovoltaic converters

This paper demontstrates the possibility of developing a high-voltage waveguide photodetector comprised of Schottky diodes and based on a Au/Ge — Si structure with Ge quantum dots pseudomorphic to a silicon matrix, which ensures an increase in the external quantum yield and open-circuit voltage. It is shown on this photodetector that there is a great increase and broadening in sensitivity up to λ = 2.1 μm, which coincides with the main radiation range of a black (gray) body at the emitter temperatures from 1200 to 1700 °C, practically used in thermophotovoltaic converters. This state of the ensemble of Ge quantum dots by means of molecular beam epitaxy can be obtained only under the condition of low growth temperature (250–300 °C). It is established that, below the Si absorption edge, photoresponse on the photodetectors under consideration is determined by two main mechanisms: absorption on the ensemble of Ge quantum dots and Fowler emission. It is shown by the analysis of the Raman scattering spectra on the optical photons of Ge–Si structures that the quantum efficiency of photodetectors based on them in the first case is due to the degree of nonuniform stress relaxation in the array of Ge quantum dots. The photoresponse directly associated with the Ge quantum dots is manifested on Schottky diodes with a superthin intermediate oxide layer SiO₂, which eliminates the second mechanism. In further development, the proposed photodetector architecture with pseudomorphic Ge quantum dots can be used both for portable thermophotovoltaic converters and fiber-optic data transmission systems at wavelengths corresponding to basic telecommunication standards (λ = 0.85, 1.3 and 1.55, 1.3, and 1.55 μm) on the basis of silicon technologies.     

摆线齿轮泵内转子加工工艺及工装设计

摆线转子泵具有体积小、结构紧凑、零件少、重量轻、噪声低、工作平稳、自吸性强及良好的高转速特性等特点,广泛用于纺机、印机、机床、轻工机械等需低压连续润滑或间断供油润滑的机械设备上.分析了内转子齿廓为短幅外摆线圆内等距线,而不宜采用普通外摆线及长幅外摆线的原因,确定了磨削参数、机床的改装方法及专用工艺装备.     

MULTIVARIATE STATISTICAL ANALYSIS OF FEG-STEM EDX SPECTRA

A multivariate statistical analysis method has been used to examine the information content of a series of EDX spectra acquired using a FEG-STEM recorded across a segregated grain boundary in a ferritic steel. The spectra have been factored into a set of orthogonal information components (eigenspectra), each of which corresponds to an independent source of information. Two meaningful eigenspectra are identified: one is related to the segregation of P and Cr and the other to a combination of self-absorption and coherent bremsstrahlung. Spectra are reconstructed from the meaningful eigenspectra to reduce noise and improve the sensitivity for detection of trace element segregation.     

影响内啮合摆线齿轮泵性能的因素

在工业设备中,内啮合摆线齿轮泵以其结构紧凑、体积小、重量轻、自吸性能好、对污染不敏感、工作可靠、寿命长、便于维修、成本低等优点得到了广泛的应用.文中重点对影响内啮合摆线齿轮泵性能的因素进行了分析,为内啮合摆线齿轮泵的优化设计和制造提供参考和依据.     

High energy photocathodes for laser fusion diagnostics

Laser fusion experiments at the National Ignition Facility require time-resolved x-ray images of the ignition target self-emission. The photon energies are expected to be greater than 10 keV. Photoemission quantum yield measurement data and photoelectron energy spectrum data are presently unavailable in this photon energy range, but are essential in the design of x-ray imaging diagnostics. We developed an apparatus to measure the quantum efficiency of primary and secondary photoelectron emission and to estimate the energy spectrum of the secondary photoelectrons. The apparatus has been tested using photon energies less than 10 keV to allow comparisons with prior work. A method for preparing photocathodes with geometrically enhanced photoefficiency has been developed.     

内啮合摆线齿轮泵摆线轮齿廓参数化设计分析

利用齿轮啮合原理推导出了摆线齿轮的齿廓曲线方程,讨论了两种齿根过渡曲线的处理方法,并利用Visual Basic 6.0在AutoCAD平台上实现了齿轮完整齿廓曲线的参数化绘制,这对于进一步分析齿轮的啮合特性及力学性能具有重要的意义。     

An in situ set up for the detection of CO2 from catalytic CO oxidation by using planar laser-induced fluorescence

We report the first experiment carried out on an in situ setup, which allows for detection of CO(2) from catalytic CO oxidation close to a model catalyst under realistic reaction conditions by the means of planar laser-induced fluorescence (PLIF) in the mid-infrared spectral range. The onset of the catalytic reaction as a function of temperature was followed by PLIF in a steady state flow reactor. After taking into account the self-absorption of CO(2), a good agreement between the detected CO(2) fluorescence signal and the CO(2) mass spectrometry signal was shown. The observed difference to previously measured onset temperatures for the catalytic ignition is discussed and the potential impact of IR-PLIF as a detection technique in catalysis is outlined.     

CsPbBr3纳米片–萘之间的高效三线态能量传递

铯铅卤化物钙钛矿纳米晶是光伏和发光应用领域中理想化的三线态敏化材料,具有较高的荧光量子产率和量子限域效应。以三层厚度的CsPbBr₃纳米片（NPLs）为三线态给体,实现了从NPLs到1-萘甲酸（NCA）分子的高效三线态能量传递（TET）。CsPbBr₃ NPLs采用配体辅助再沉淀方法制备,其与NCA分子结合后,稳态荧光被大幅淬灭,荧光寿命从复合前的6.743 ns缩短到0.995 ns,TET效率达到85.3%。通过与大尺寸纳米立方体对比发现,对于CsPbBr₃-多环芳烃复合体系,量子限域效应是获得高效TET的关键。研究结果表明,CsPbBr₃ NPLs作为三线态敏化剂,可应用在基于TET的光子上转换、光催化氧化-还原反应和室温磷光等领域。     

一种用于LED特性检测的实验仪器的研究

介绍了一种基于微型光纤光谱仪的LED特性检测仪器的设计原理。为了降低积分球测量光通量中所引起的自吸收误差与温度升高对LED光通量的影响误差,选取将LED与探测器成90°放置的解决方法。同时,光谱仪模块采取非对称交叉式Czerny-Turner分光结构来达到微型化高分辨率的目的。基于正向电流对LED光通量的影响,提出可调可显示的恒流源的设计。研究结果对研制检测LED特性的微型检测装置具有一定的指导意义,由于恒流源电流的可读可调节的设计,电流变化对LED光学特性的影响可以较为清晰地体现出来。     

A mathematical model of multichannel continuously scanning systems for digital X-ray analysis

A mathematical model of continuously scanning systems for digital X-ray analysis is developed. The systems contain a linear array of detectors that can be used not only in systems of radiation sources with an anisotropic angular distribution and a nonuniform distribution of the quantum yield over the focal spot but also in systems of detectors with nonuniform spatial sensitivity to incident radiation. The systems also make it possible to normalize the records of the radiation image of a tested object and perform digital filtering of the results.     

Improving autofluorescent proteins: comparative studies of the effective brightness of Green Fluorescent Protein (GFP) mutants

We study the photophysical behavior of 8 mutants of Green Fluorescent Protein (GFP) using fluorescence correlation spectroscopy (FCS) on the single molecule level and double resonance excitation of bulk samples. Experimental data reported here and the previously published data on the RH/R(-) equilibrium and fluorescence quantum yields Phi(Fl) (Jung et al., 2005; Biophys J 88:1932-1947) are analyzed with respect to single molecule as well as conventional fluorescence microscopy. The fraction of GFP molecules in a dark state, [D], reduces the effective absorption cross section under photostationary conditions. The determination of the excitable fraction [B] and its fluorescence quantum yield Phi(Fl) gives the effective brightness Phi(eff). Our results show that in its wavelength range, eGFP is, among the GFPs, the best fluorophore for most microscopic applications. However, in the red shifted YFP-proteins, there is still potential for improvement, since a pronounced dark state population is detectable in all mutants investigated so far. We propose to use the mutant T203Y/E222Q in imaging studies, whenever the expression yield is not a limiting factor. In FCS experiments, where the useful concentration range of the expressed molecules is restricted to concentrations below micromolarity, our data suggest the use of wt-GFP or mutant T203Y, as these represent photochemical buffers. Both mutants might surpass the limitations given by out-of-focus bleaching in live cell microscopy.