Integrating sphere setup for the traceable measurement of absolute photoluminescence quantum yields in the near infrared

There is an increasing interest in chromophores absorbing and emitting in the near-infrared (NIR) spectral region, e.g., for applications as fluorescent reporters for optical imaging techniques and hence, in reliable methods for the characterization of their signal-relevant properties like the fluorescence quantum yield (Φ(f)) and brightness. The lack of well established Φ(f) standards for the NIR region in conjunction with the need for accurate Φ(f) measurements in transparent and scattering media encouraged us to built up an integrating sphere setup for spectrally resolved measurements of absolute fluorescence traceable to radiometric scales. Here, we present the design of this setup and its characterization and validation including an uncertainty budget for the determination of absolute Φ(f) in the visible and NIR. To provide the basis for better measurements of Φ(f) in the spectral window from ca. 600 to 1000 nm used, e.g., for optical imaging, the absolute Φ(f) of a set of NIR chromophores covering this spectral region are measured and compared to relative values obtained using rhodamine 101 as Φ(f) standard. Additionally, the absolute Φ(f) values of some red dyes that are among the most commonly used labels in the life sciences are presented as well as the absolute quantum yield of an optical probe for tumor imaging.     

Size-dependent absolute quantum yields for size-separated colloidally-stable silicon nanocrystals

Size-selective precipitation was used to successfully separate colloidally stable allylbenzene-capped silicon nanocrystals into several visible emitting monodisperse fractions traversing the quantum size effect range of 1-5 nm. This enabled the measurement of the absolute quantum yield and lifetime of photoluminescence of allylbenzene-capped silicon nanocrystals as a function of size. The absolute quantum yield and lifetime are found to monotonically decrease with decreasing nanocrystal size, which implies that nonradiative vibrational and surface defect effects overwhelm spatial confinement effects that favor radiative relaxation. Visible emission absolute quantum yields as high as 43% speak well for the development of "green" silicon nanocrystal color-tunable light emitting diodes that can potentially match the performance of their toxic heavy metal chalcogenide counterparts.     

Stable CdS QDs with intense broadband photoluminescence and high quantum yields

Aqueous synthesis of CdS quantum dots (QDs) using thiolactic acid (TLA) as a capping agent was reported. These QDs exhibited excellent colloidal and photostability over a span of 2 years and showed intense broadband and almost white photoluminescence suitable for solid state lighting devices. The photoluminescence (PL) property of the aqueous CdS QDs is optimized by adjusting various processing parameters. The highest quantum yield (QY) achieved for TLA capped CdS QDs of average size 3.5 nm was ∼50%. Luminescence lifetime measurements of CdS-TLA QDs indicated longer lifetimes and a larger contribution of the surface-related emission, indicating removal of quenching defects.     

Spectroscopic characterization of coumarin-stained beads: quantification of the number of fluorophores per particle with solid-state 19F-NMR and measurement of absolute fluorescence quantum yields

The rational design of nano- and micrometer-sized particles with tailor-made optical properties for biological, diagnostic, and photonic applications requires tools to characterize the signal-relevant properties of these typically scattering bead suspensions. This includes methods for the preferably nondestructive quantification of the number of fluorophores per particle and the measurement of absolute fluorescence quantum yields and absorption coefficients of suspensions of fluorescent beads for material performance optimization and comparison. Here, as a first proof-of-concept, we present the first time determination of the number of dye molecules per bead using nondestructive quantitative ((19)F) NMR spectroscopy and 1000 nm-sized carboxylated polystyrene particles loaded with varying concentrations of the laser dye coumarin 153 containing a CF(3) group. Additionally, the signal-relevant optical properties of these dye-loaded particles were determined in aqueous suspension in comparison to the free dye in solvents of different polarity with a custom-built integrating sphere setup that enables spectrally resolved measurements of emission, transmission, and reflectance as well absolute fluorescence quantum yields. These measurements present an important step toward absolute brightness values and quantitative fluorescence analysis with particle systems that can be exploited, for example, for optical imaging techniques and different fluorescence assays as well as for the metrological traceability of fluorescence methods.     

On-wafer spectrofluorometric method for determination of relative quantum yields of photoacid generation in chemically amplified resists

Chemically amplified resists (CARs) that employ acid catalysts are widely used throughout the semiconductor industry due to the need for high throughput in the lithography process. The quantum yield of the particular photoacid generator (PAG) used to generate a given acid ultimately limits the photospeed of the CAR. Determination of quantum yields of photoacid generation is therefore an important component of resist design. We report the development of an on-wafer spectrofluorometric technique for this purpose. This technique is based on one first reported by Feke et al. (J. Vac. Sci. Technol. 2000, B18, 136- 139), which involves doping the resist formulations containing the candidate PAGs with a fluorescent pH indicator dye, coating one wafer per PAG, patterning the wafers with a dose ramp, and spectroscopically imaging the wafers. The response curve of each PAG is spatially and spectrally encoded in the fluorescence images of each wafer. We investigate the efficacy of coumarin 6, a dye that was introduced as an acid sensor by Pohlers et al. (Chem. Mater. 1997, 9, 3222-3230) for this application. We further apply this technique to the determination of the quantum yield of photoacid generation of four candidate PAGs for prototype 193-nm CARs. This technique is convenient, fast, robust, and nondestructive.     

两种测量电压有效值方法的比较

为准确测量不同频率的交变电压有效值,介绍两种常用的测量方法——热等效法和公式计算法,并分析各自的特点。分别利用这两种方法搭建测量电路,对不同频率正弦波有效值进行测量。对测量数据进行分析,客观比较两测量电路的精度和频率响应。分析结果表明:热等效法适合测量高频信号的电压有效值,而公式计算法适合测量低频信号的有效值,该结论为不同场合测量有效值的各种应用做出参考。     

Synthesis and photoluminescence of ZnS quantum dots

Single-phase zinc sulphide (ZnS) quantum dots were synthesized by a chemical method. The influence of the pH value of the Zn(CH3COO)2 solution on the size and photoluminescence properties of the ZnS quantum dots was evaluated. X-ray power diffraction, transmission electron microscopy, and ultraviolet-visible spectroscopy were used to characterize the structure, size, surface states, and photoluminescence properties of ZnS quantum dots. The results showed that the crystal structure of ZnS quantum dots was a cubic zinc blende structure, and their average diameter was about 3.0 nm. ZnS quantum dots with good distribution and high purity were obtained. A strong broad band centered at about 320 nm was observed in the excitation spectrum of ZnS quantum dots. Their emission spectrum peaking at about 408 nm, was due mostly to the trap-state emission. The relative integrated emission intensity of ZnS quantum dots decreased as the pH value of the Zn(CH3COO)2 solution increased, which could be ascribed to the increase in average diameter of the ZnS quantum dots as the pH value of Zn(CH3COO)2 solution increased.     

Comparison of absolute spectral irradiance responsivity measurement techniques using wavelength-tunable lasers

Independent methods for measuring the absolute spectral irradiance responsivity of detectors have been compared between the calibration facilities at two national metrology institutes, the Helsinki University of Technology (TKK), Finland, and the National Institute of Standards and Technology (NIST). The emphasis is on the comparison of two different techniques for generating a uniform irradiance at a reference plane using wavelength-tunable lasers. At TKK's Laser Scanning Facility (LSF) the irradiance is generated by raster scanning a single collimated laser beam, while at the NIST facility for Spectral Irradiance and Radiance Responsivity Calibrations with Uniform Sources (SIRCUS), lasers are introduced into integrating spheres to generate a uniform irradiance at a reference plane. The laser-based irradiance responsivity results are compared to a traditional lamp-monochromator-based irradiance responsivity calibration obtained at the NIST Spectral Comparator Facility (SCF). A narrowband filter radiometer with a 24 nm bandwidth and an effective band-center wavelength of 801 nm was used as the artifact. The results of the comparison between the different facilities, reported for the first time in the near-infrared wavelength range, demonstrate agreement at the uncertainty level of less than 0.1%. This result has significant implications in radiation thermometry and in photometry as well as in radiometry.     

人发中微量元素测定的几种消解方法比较

应用微波和电热板两种加热方式与三种不同的酸体系组合成五种消解方法(分别为微波炉+HNO_3,微波炉+HNO_3—H_2O_2,电热板+HNO_3,电热板+HNO_3—H_2O_2和电热板+HNO_3—HClO_4等五种方法),对人发标样进行消解处理;用ICP—MS分析方法测定其中十几种元素的含量,通过回收率及RSD％的比较,根据实验室的条件和实验要求,选择较适合的消解方法。     

Comparison of structural and photoluminescence properties of zinc oxide nanowires grown by vapor-solid and vapor-liquid-solid methods

Different kinds of ZnO nanowires were synthesized by vapor-solid and vapor-liquid-solid methods via a chemical vapor transport and condensation process. The samples were characterized by scanning electron microscopy, X-ray diffraction (XRD) and photoluminescence analyses. The control on the growth morphologies can be achieved by the source materials and by using a thin gold layer as a catalyst. 15-80 nm nanowires were obtained and XRD patterns show two different growth directions. High intensity green light from photoluminescence spectroscopy was observed which shows that the experimental results could be useful for light-emitting materials and other optoelectronic device applications.     

Impact of peptide modifications on the isobaric tags for relative and absolute quantitation method accuracy

In this study, the impact of amino acid modifications on the accuracy of the iTRAQ (isobaric tags for relative and absolute quantitation) method was evaluated. MCF-7 breast cancer cells, cultured in the presence of 17β-estradiol and tamoxifen, were used as a model system. The cells were labeled and analyzed by reversed-phase liquid chromatography and pulsed Q dissociation ion trap tandem mass spectrometry detection. Database searching was performed by using various combinations of amino acid modification allowances, i.e, Lys/Tyr/Cys and amino terminal iTRAQ labeling, Lys methylation, acetylation and carbamylation, and Cys/Met oxidation. Other than the intended Lys/amino terminal iTRAQ labeling, such modifications occur as a result of either enzymatic or sample preparation related reactions and are typically ignored in quantitation analysis to minimize the rate of false-positive peptide identifications. The study revealed that the modifications with the greatest impact on protein identification and quantitation pertain to Lys and Tyr amino acid residues, that by enabling such modifications the number and type of identified proteins will change (by up to 10%), and that the rate of false-positive protein identifications can be maintained below an upper threshold of 5% if appropriate data filtering conditions are used. In addition, the interference of possible posttranslational modifications (i.e., phosphorylation) with iTRAQ quantitation was examined.     

Identification and control of the origin of photoluminescence from silicon quantum dots

We present a detailed investigation into the origin of photoluminescence (PL) from silicon quantum dots in hydrogenated amorphous silicon nitride annealed in oxygen ambient. On the basis of structural characterization, temperature-dependent PL, time-resolved PL, and PL excitation spectra, we identify that the luminescence of the oxidized samples originates from the localized exciton radiative recombination via the surface states related to Si-N or Si-O-Si bonds. In combination with the results due to annealing in argon and hydrogen environments, we have further shown that control of the origin of the PL can be realized by modifying the radiative defect density through annealing treatment.     

Ring interferometer for two-sided measurement of the absolute lengths of end standards

Special features of a two-sided interferometer based on a ring optical scheme previously proposed [V. M. Khavinson and L. F. Khavinson, in Investigations in the Field of Length and Angle Measurements, N. P. Gerasimov, ed., Proceedings of the D. I. Mendeleyev Institute for Metrology (Energoatomizdat, Leningrad, 1983), pp. 14-18], which exploits an alternative measurement method to the conventional method for measuring absolutely the lengths of precision gauge blocks. Both measuring surfaces of a gauge are viewed directly without an auxiliary platen wrung onto one of them. The two-sided method results in improved consistency of measurement results because the elimination of wringing avoids the contact error that can occur in the gauge length obtained when the conventional method is used. A variety of means to control the optical phase differences in the interferometer are considered.