scholarly journals A Test for Bottlenecks in the Vibrational Relaxation of CH3Cl and CH3Br by Ar

1988 ◽  
Vol 9 (1-3) ◽  
pp. 47-62 ◽  
Author(s):  
Kenneth M. Beck ◽  
Robert J. Gordon
Keyword(s):  
Decay Rate ◽  
Relaxation Rate ◽  
Vibrational Relaxation ◽  
Energy Levels ◽  
Fluorescence Decay ◽  
Rotational Relaxation ◽  
Translational Energy ◽  
Time Resolved ◽  
Level Model ◽  
Relaxing Gas

The method of time-resolved optoacoustics was used to measure the rate of vibrational relaxation of CH3Cl(ν6) and CH3Br(ν6) by Ar. The pressure pulses generated by the relaxing gas revealed that the rate of production of translational energy from ν6 = 1 is approximately twice the decay rate of IR fluorescence from ν3 = 1. No evidence was found for a previously proposed bottleneck in rotational relaxation, which would have resulted in an acoustic relaxation rate slower than the fluorescence decay. The faster rates observed here can be explained qualitatively by a rapid energy release from energy levels above ν3 which precedes the IR fluorescence. A simple three-level model, however, is unable to explain our observations quantitatively.

Exciton dynamics in thick GaN MOVPE epilayers deposited on sapphire.

1997 ◽  
Vol 2 ◽  
Author(s):  
J. Allègre ◽  
P. Lefebvre ◽  
J. Camassel ◽  
B. Beaumont ◽  
Pierre Gibart
Keyword(s):  
Layer Thickness ◽  
Buffer Layers ◽  
Rate Equations ◽  
Time Resolved ◽  
Versus Layer ◽  
Level Model ◽  
Shallow Impurities ◽  
Aln Buffer ◽  
Time Resolved Photoluminescence

Time-resolved photoluminescence spectra have been recorded on three GaN epitaxial layers of thickness 2.5 μm, 7 μm and 16 μm, at various temperatures ranging from 8K to 300K. The layers were deposited by MOVPE on (0001) sapphire substrates with standard AlN buffer layers. To achieve good homogeneities, the growth was in-situ monitored by laser reflectometry. All GaN layers showed sharp excitonic peaks in cw PL and three excitonic contributions were seen by reflectivity. The recombination dynamics of excitons depends strongly upon the layer thickness. For the thinnest layer, exponential decays with τ ~ 35 ps have been measured for both XA and XB free excitons. For the thickest layer, the decay becomes biexponential with τ1 ~ 80 ps and τ2 ~ 250 ps. These values are preserved up to room temperature. By solving coupled rate equations in a four-level model, this evolution is interpreted in terms of the reduction of density of both shallow impurities and deep traps, versus layer thickness, roughly following a L−1 law.

scholarly journals Architecture of Polyglutamine-containing Fibrils from Time-resolved Fluorescence Decay

2014 ◽  
Vol 289 (39) ◽  
pp. 26817-26828 ◽  
Author(s):  
Christoph Röthlein ◽  
Markus S. Miettinen ◽  
Tejas Borwankar ◽  
Jörg Bürger ◽  
Thorsten Mielke ◽  
...  
Keyword(s):  
Fluorescence Decay ◽  
Time Resolved Fluorescence ◽  
Time Resolved

Synthesis and Photophysical Properties of a Conformationally Flexible Mixed Porphyrin Star-Pentamer

2009 ◽  
Vol 62 (7) ◽  
pp. 692 ◽  
Author(s):  
Toby D. M. Bell ◽  
Sheshanath V. Bhosale ◽  
Kenneth P. Ghiggino ◽  
Steven J. Langford ◽  
Clint P. Woodward
Keyword(s):  
Energy Transfer ◽  
Photophysical Properties ◽  
Fluorescence Decay ◽  
High Yield ◽  
Free Base ◽  
Time Resolved ◽  
Zinc Porphyrin ◽  
Relative Contribution ◽  
Synthetic Strategy ◽  
Decay Times

The synthesis of a porphyrin star-pentamer bearing a free-base porphyrin core and four zinc(ii) metalloporphyrins, which are tethered by a conformationally flexible linker about the central porphyrin’s antipody, is described. The synthetic strategy is highlighted by the use of olefin cross metathesis to link the five chromophores together in a directed fashion in high yield. Photoexcitation into the Soret absorption band of the zinc porphyrin chromophores at 425 nm leads to a substantial enhancement of central free-base porphyrin fluorescence, indicating energy transfer from the photoexcited zinc porphyrin (outer periphery) to central free-base porphyrin. Time-resolved fluorescence decay profiles required three exponential decay components for satisfactory fitting. These are attributed to emission from the central free-base porphyrin and to two different rates of energy transfer from the zinc porphyrins to the free-base porphyrin. The faster of these decay components equates to an energy-transfer rate constant of 3.7 × 109 s–1 and an efficiency of 83%, whereas the other is essentially unquenched with respect to reported values for zinc porphyrin fluorescence decay times. The relative contribution of these two components to the initial fluorescence decay is ~3:2, similar to the 5:4 ratio of cis and trans geometric isomers present in the pentamer.

scholarly journals Unravelling the mechanisms of vibrational relaxation in solution

2017 ◽  
Vol 8 (4) ◽  
pp. 3062-3069 ◽  
Author(s):  
Michael P. Grubb ◽  
Philip M. Coulter ◽  
Hugo J. B. Marroux ◽  
Andrew J. Orr-Ewing ◽  
Michael N. R. Ashfold
Keyword(s):  
Vibrational Relaxation ◽  
Chlorinated Solvents ◽  
Time Resolved ◽  
Vibrational Cooling ◽  
Solvent Molecules

Time resolved vibrational cooling towards equilibrium in perfluorinated and chlorinated solvents provides detailed insights into the transfer of energy between solute and solvent molecules.

scholarly journals Thulium-Doped Silica Fibers with Enhanced Fluorescence Lifetime and Their Application in Ultrafast Fiber Lasers

Fibers ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 66 ◽  
Author(s):  
Jakub Cajzl ◽  
Pavel Peterka ◽  
Maciej Kowalczyk ◽  
Jan Tarka ◽  
Grzegorz Sobon ◽  
...  
Keyword(s):  
Optical Fibers ◽  
Fluorescence Lifetime ◽  
Energy Levels ◽  
Local Environment ◽  
Alumina Nanoparticles ◽  
Fluorescence Lifetimes ◽  
Transfer Coefficients ◽  
Relaxation Energy ◽  
Time Resolved ◽  
Conventional Solution

In this work we report on the thulium-doped silica-based optical fibers with increased fluorescence lifetime of the 3F4 level thanks to the modification of the local environment of thulium ions by high content of alumina. The determination of the cross-relaxation energy-transfer coefficients from the measurements of the fluorescence lifetimes of the 3F4 and 3H4 energy levels of Tm3+ ions in the experimentally prepared optical fiber is provided as well. Preforms of optical fibers were prepared either by conventional solution-doping of Tm3+ and Al3+ ions or by dispersion-doping of Tm3+ ions with alumina nanoparticles. Optical fibers were characterized by means of Tm, Al, and Ge concentrations, refractive index profiles, optical spectral absorption and luminescence, and by time-resolved fluorescence spectroscopy. Highly aluminium-codoped thulium silicate optical fibers exhibited fluorescence lifetimes of over ~500 μs with maximum value of 756 μs, which means a fluorescence lifetime enhancement when compared to the thulium-doped fibers reported elsewhere. We show an application of the thulium-doped fiber in a compact all-fiber ring laser that is passively mode-locked by using graphene-based saturable absorber. The output pulsewidth and repetition rate were 905 fs and 32.67 MHz, respectively.

On the breakdown of characteristics solutions in flows with vibrational relaxation

1967 ◽  
Vol 27 (1) ◽  
pp. 49-57 ◽  
Author(s):  
B. S. H. Rarity
Keyword(s):  
Relaxation Time ◽  
Mach Number ◽  
Supersonic Flow ◽  
Steady Flow ◽  
Speed Of Sound ◽  
Vibrational Relaxation ◽  
Precise Measure ◽  
Derivatives Of ◽  
Relaxing Gas ◽  
Flow Case

The breakdown of the characteristics solution in the neighbourhood of the leading frozen characteristic is investigated for the flow induced by a piston advancing with finite acceleration into a relaxing gas and for the steady supersonic flow of a relaxing gas into a smooth compressive corner. It is found that the point of breakdown moves outwards along the leading characteristic as the relaxation time decreases and that there is no breakdown of the solution on the leading characteristic if the gas has a sufficiently small, but non-zero, relaxation time. A precise measure of this relaxation time is derived. The paper deals only with points of breakdown determined by initial derivatives of the piston path or wall shape. In the steady-flow case, the Mach number based on the frozen speed of sound must be greater than unity.

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