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Lifetime Components (lifetime + component)

Distribution by Scientific Domains
Polymers and Materials Science40%

Selected Abstracts

Competition between Host Aggregates and Isolated Guest Chromophores in Trapping Excitons in Polybenzazole Copolymers and Blends

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2006
Shanfeng Wang
Abstract Summary: Host,guest systems have been prepared using the blends and copolymers consisting of the host molecule poly(p -phenylene benzobisoxazole) (PBO) with a higher bandgap of 2.93 eV and the guest molecule poly(2,5-thienylbenzobisoxazole) (PBOT) with a lower bandgap of 2.57 eV. These systems have been investigated using photoluminescence (PL) spectra and time-resolved PL decay dynamics. Both PBOT-PBO copolymers and PBOT/PBO blends with the PBOT compositions less than 20% demonstrate higher intensities and narrower bandwidths in solid-state emission compared to that of PBOT, as well as larger fractions of the shorter lifetime component in PL decay dynamics. A general scheme on intrachain and interchain exciton migration and trapping mechanism has been proposed to interpret the phenomena in both solutions and thin films. Particularly, a competition in trapping exciton between PBO aggregates and isolated PBOT chromophores has been revealed. General scheme of exciton migration and trapping paths for host (D: donor),guest (A: acceptor) systems involving the isolated chromophores (A and D) and aggregates (AA and DD) in both ground state and excited state marked without or with an asterisk. [source]

Structural heterogeneity in glassy polymeric materials revealed by positron annihilation and other supplementary techniques

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
V. P. Shantarovich
Abstract A disagreement between effective sizes of elementary free volumes found from the four component PATFIT analyses of positronium annihilation lifetime spectra and experiments on low temperature sorption for two membrane materials of internal microporosity poly(tri-methyl-silyl-propyne) PTMSP and spiro-linked benzodioxane polymer PIM-1 is described and discussed. This disagreement can be minimized essentially using the fifth lifetime component but not the Gaussian distribution of the fourth component. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Positron Lifetime Study of the Crystal Evolution and Defect Formation Processes in a Scintillating Glass

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009
Jiaxiang Nie
The crystal evolution and defect formation in scintillating glasses as a consequence of thermal annealing were studied by annihilation lifetime spectroscopy and UV-Vis absorption spectroscopy. The annihilation lifetime spectra and UV-Vis spectra were recorded on glass 50SiO2,45ZnO,5BaF2 before and after annealing at 580°C for 16, 32, and 48 h, respectively. The results show that the three lifetime components (,1, ,2, and ,3) and the corresponding intensities (I1, I2, and I3) change systematically with increasing annealing time. This reflects the crystal evolution and defect formation in the glass matrix. The continued crystal evolution was also revealed by the UV-Vis spectra, as the absorption edge of the material shifted to a lower energy with prolonged annealing. [source]

Optimized protocol of a frequency domain fluorescence lifetime imaging microscope for FRET measurements

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2009
Aymeric Leray
Abstract Frequency-domain fluorescence lifetime imaging microscopy (FLIM) has become a commonly used technique to measure lifetimes in biological systems. However, lifetime measurements are strongly dependent on numerous experimental parameters. Here, we describe a complete calibration and characterization of a FLIM system and suggest parameter optimization for minimizing measurement errors during acquisition. We used standard fluorescent molecules and reference biological samples, exhibiting both single and multiple lifetime components, to calibrate and evaluate our frequency domain FLIM system. We identify several sources of lifetime precision degradation that may occur in FLIM measurements. Following a rigorous calibration of the system and a careful optimization of the acquisition parameters, we demonstrate fluorescence lifetime measurements accuracy and reliability. In addition, we show its potential on living cells by visualizing FRET in CHO cells. The proposed calibration and optimization protocol is suitable for the measurement of multiple lifetime components sample and is applicable to any frequency domain FLIM system. Using this method on our FLIM microscope enabled us to obtain the best fluorescence lifetime precision accessible with such a system. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc. [source]

Positron annihilation spectroscopic study of hydrothermal grown n-type zinc oxide single crystal

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
C. W. Hui
Abstract Positron lifetime and coincidence Doppler broadening spectroscopic (CDBS) measurements were carried out to study the defects in two hydrothermal (HT) grown ZnO single crystal samples (HT1 and HT2) obtained from two companies. Single component model could offer good fittings to the room temperature spectra of HT1 and HT2, with the positron lifetimes equal to 199 ps and 181 ps respectively. These two lifetime components were associated with saturated positron trapping into two VZn -related defects with different microstructures. The positron lifetimes of HT1 was found to be temperature independent. For the HT2 sample, the positron lifetime remained unchanged with T > 200 K and decreased with decreasing temperature as T<200K. This could be explained by the presence of an additional positron trap having similar electronic environment to that of the delocalized state and competing in trapping positrons with the 181 ps component at low temperatures. Positron-electron autocorrelation function, which was the fingerprint of the annihilation site, was extracted from the CDBS spectrum. The obtained autocorrelation functions of HT1 and HT2 at room temperature, and HT2 at 50 K had features consistent with the above postulates that the 181 ps and the 199 ps components had distinct microstructures and the low temperature positron trap existed in HT2. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]