M.W. Pleil

Pulsed laser fluorescence microscopy of coal macerals and dispersed organic material

Abstract A new pulsed laser microscopy technique was applied to the study of fluorescence from liptinite macerals in the time and wavelength domains. Useful parameters for coal characterization are the fluorescence decay times and percentage contributions of the individual fluorescing compounds to the total intensity. Characteristic decay times in the nanosecond and sub-nanosecond range are obtained for sporinite, fluorinite, cutinite and resinite of the Lower Kittanning coal seam and alginite of the New Albany shale group of the Illinois Basin. Time-resolved emission spectra for the individual fluorophores are obtained and generally found to be broad but specific for each maceral type. The total sporinite fluorescence comes from fluorophores whose individual spectra peak in the blue-green and yellow regions. The percentage contributions from each fluorophore vary systematically with increasing coal rank. The previously observed red-shift in the conventional composite spectra is interpreted, especially for sporinite. The new laser microscopy is described in some detail. The reliability of the method was tested with mixtures of selected organic compounds in solution and subsequent analysis. The fluorescence decay times and time-resolved spectra agree with those for the pure substances under certain conditions. These conditions apply to the coal macerais studied. Generally, one-, two- and three-component mixtures can be resolved if the component lifetimes differ by a factor of two or more and the individual contributions to the total intensity exceed 10%. Fluorescence decay times of 200 ps and greater can be measured with an accuracy of about 100 ps.

Fast Analog Technique For Determining Fluorescence Lifetimes Of Multicomponent Materials By Pulsed Laser

This paper describes a system capable of measuring fluorescent lifetimes and time-resolved spectra of microscopic particles, thus substantially enhancing the usefulness of fluorescence microscopy as a characterizing tool. Tests and applications of this technique for identifying component lifetimes (in the nanosecond and subnanosecond range) and spectra in organic model compounds also are described. A multi-exponential decay fit to the data yields fluorescence decay times, percentage contributions (fractional intensities) and time-resolved spectra for each decay. Two-component non-interacting mixtures are resolved if the decay times differ by a factor of two and the percentage contribution from each fluorophore is more than 10%. For three-component mixtures, it is necessary for the resolution of the lifetimes that the decay times differ by at least a factor of three and the percentage contribution from each component be more than 15%.

Enhancement Of Fluorescent Fingerprints By Time-Resolved Imaging

Laser detection of latent fingerprints tends to fail when prints are located on certain types of surface, such as brown cardboard and wood, because the generally weak fingerprint fluorescence is overwhelmed by background luminescence from these substrates. The fingerprint and background fluorescence lifetimes, which are of nanosecond order, were measured for samples of the above surface types and for fingerprints treated by the most successful current detection procedures. Our results indicate that time-resolved imaging can in these situations improve image contrast by about an order of magnitude.

Primary scintillant fluorescent decay times in binary and ternary scintillators by near UV pulsed laser excitation

Abstract Primary scintillant fluorescence decay times and spectra of seven commercially available binary and ternary, plastic and acrylic scintillators are presented. Excitation is by a pulsed, near ultraviolet laser. Thus the decay times are those from the final energy transfer stage following nuclear particle excitation. Various fitting functions previously used in describing the emitted pulse shape are reviewed, and the fluorescence decay time contribution of the primary scintillant is discussed.

Fluorescence decay kinetics of “Polyester yellow” in solutions and in polymers

Abstract We present some studies of the fluorescence decay kinetics of “polyester yellow” in benzene, glycerol and polymethyl methacrylate. The fluorescence of the dye in glycerol showed the presence of three dominant components, which correspond to three conformers differing in the orientations of the malononitrile group with respect to the dialkylaminophenyl group. At high concentrations of the dye, a ground state dimerization was observed for the first time in nonpolar solvents and in polymers. Two different configurations were identified from their fluorescence decay kinetics.

Time-resolved fluorescence spectroscopy of crude oils and condensates

Abstract A pulsed laser fluorescence spectroscopy system, previously developed for coal characterization, was used to characterize thirteen crude oils and condensates. From time-resolved fluorescence spectra, three individual components (fluorophores) with decay times in the nanosecond and sub-nanosecond range were resolved. A good correlation was obtained between the fluorescence decay times of these components and API gravity. The fluorescence decay of normal crude oil was different from biodegraded crude oil. Two of the three resolved component spectra and decay times resembled those of anthracene and pyrene in solution.

Fluorescence Decay Times Of Multicomponent Microscopic Materials By Pulsed Laser Excitation

A fast analog technique developed for the determination of fluorescence emission parameters of microscopic geological particles is applied to a variety of samples. Presented here are fluorescence data from liptinite coal macerals, analysis of fluorescence emitted from crude oils, applications to fiber analysis and plastic scintillators. Characteristic decay times in the nanosecond and subnanosecond range are given along with time-resolved emission spectra.

Study of energy transfer in a solution of coumarin 460 and rhodamine 6G by time-resolved laser-induced fluorescence spectroscopy

Abstract A multi-photon fast analog technique has been used to study nonradiative energy transfer from coumarin 460 to rhodamine 6G molecules. At low acceptor concentrations (

Picosecond time-resolved photoluminescence characterization of a-SiC:H films prepared by electron cyclotron resonance plasma

Microwave excited electron cyclotron resonance (ECR) plasmas were used to produce five a-SiC:H films of varying relative carbon content. This was achieved by adjusting the relative hydrogen gas/organic liquid source flow rates and resulted in optical gaps between 2.3eV and 3.3eV. A time-correlated single photon counting technique incorporating a picosecond laser was used to acquire the fast photoluminescence decay emitted at several wavelengths for each sample. A lifetime distribution analysis of the photoluminescence decay reveals the presence of up to four distinct components. These resolved decay times range from 80ps to over 20ns. Each component decay has its own emission spectrum. The blue component has the fastest and the red the slowest decay. We present the variation of photoluminescence lifetime distributions with deposition parameters. We also present continuous wave (cw) and absorption photoluminescence spectra.

Fluorescence Decay Kinetics Of Polyester Yellow In Solutions And In Polymers

We have studied the fluorescence decay kinetics of polyester yellow in solutions and in polymers. The fluorescence of the dye in glycerol could be fitted with a sum of three exponential decays, which corresponds to three conformers differing in the orientation of the malononitrile group with respect to the dialkylaminophenyl group. At high concentrations of the dye, a ground state dimerization was observed for the first time in non-polar solvents and in polymers. From their fluorescence decay kinetics, two different configurations were identified.