Laser-induced Fluorescence Emission Spectra Research Articles

Detection of chlorophylls in spores of seven ferns.

Fern spores were traditionally classified into chlorophyllous (green) and nonchlorophyllous (nongreen) types based on the color visible to the naked eye. Recently, a third type, "cryptochlorophyllous spores", is recognized, and these spores are nongreen under white light but contain chlorophylls. Epifluorescence microscopy was previously used to detect chlorophylls in cryptochlorophyllous spores. In addition to epifluorescence microscopy, current study performed some other approaches, including spore-squash epifluorescence, absorption spectra, laser-induced fluorescence emission spectra, thin layer chromatography (TLC), and ultra-high performance liquid chromatography with ultraviolet and mass spectrometric detection (UHPLC-UV-MS) in order to detect chlorophylls of spores of seven ferns (Sphaeropteris lepifera, Ceratopteris thalictroides, Leptochilus wrightii, Leptochilus pothifolius, Lepidomicrosorum buergerianum, Osmunda banksiifolia, and Platycerium grande). Destructive methods, such as TLC and UHPLC-UV-MS, successfully detected chlorophylls inside the spores when their signals of red fluorescence under epifluorescence microscope were masked by spore wall. Although UHPLC-UV-MS analysis was the most sensitive and reliable for determining the chlorophylls of spores, spore-squash epifluorescence is not only reliable but also cost- and time-effective one among our study methods. In addition, we first confirmed that Lepidomicrosorium buergerianum, Leptochilus pothifolius, Leptochilus wrightii, and Platycerium grande, produce cryptochlorophyllous spores.

Optical properties and pyrolysis of shock-heated gas-phase anisole

Anisole (C6H5OCH3) has previously been identified as a fluorescence tracer for fuel/air mixing studies based on laser-induced fluorescence (LIF) that provides stronger signal than the frequently-used toluene (Faust et al. (2013)). Reliable and quantitative application of anisole LIF at high temperature requires knowledge about its photophysical properties and its thermal stability. In this work, ultraviolet absorption and LIF of anisole were measured as a function of time in shock-heated gases at temperatures between 565 and 1620K and at pressures of 1.3 and 2.9bar. Absorption spectra were acquired with 50µs time resolution in the 240–310nm spectral range. LIF emission spectra of anisole were recorded at different fixed reaction times behind reflected shock waves using 266-nm laser excitation. Relative fluorescence quantum yields were determined that extend previously reported data beyond 980K. After the onset of pyrolysis of anisole at T >1000K, effective absorption cross-sections and the corresponding LIF signals after 266-nm excitation are reported. To aid the interpretation of these experiments, the products of anisole pyrolysis were investigated using a shock tube coupled to a high-repetition-rate time-of-flight mass spectrometer (HRR-TOF-MS) for time-resolved multispecies measurements. Concentration-time profiles for anisole and products such as benzene, C2H4, and CO were measured and compared to simulations using two kinetics models from literature.

Photosynthetic pigment laser-induced fluorescence indicators for the detection of changes associated with trace element stress in the diatom model species Phaeodactylum tricornutum.

This work reports changes on cell number, growth rate, trace element content, chlorophyll a (Chl a) and carotenoid concentrations, and laser-induced fluorescence (LIF) spectra of Phaeodactylum tricornutum exposed to Co, Ni, Cu, Zn, Cd, Hg, Pb, and a mixture of all elements combined (Mix). The total levels of trace elements associated with the cells were significantly higher in the exposed than in control ones. Concomitantly, specific cell growth was significantly lower in exposed P. tricornutum, suggesting that trace elements affected the microalgae physiology. The LIF emission spectra showed two typical emission bands in red (683-698 nm) and far-red (725-730 nm) regions. Deviations in LIF spectra and changes in F685/F735 ratio were investigated as indicators of trace element-induced changes. Fluorescence intensity emitted by exposed microalgae decreased in far-red region when compared to control cells, suggesting Chl a damage and impairment of pigment biosynthesis pathways by trace elements, confirmed by Chl a and carotenoid concentration decrease. Significant increase in F685/F735 ratio was detected for all elements except Zn and more accentuated for Co, Hg, and Mix. Significant deviations in wavelength emission maxima in red region were also more significant (between 8 and 13 nm) for Co, Hg, and Mix. Growth changes agreed with deviations in LIF spectra and F685/F735 ratio, supporting their applicability as indicators. This study clearly shows F685/F735 ratio and the deviations in wavelength emission maxima as adequate trace element stress indicators and P. tricornutum as a promising biomonitor model species. LIF-based techniques can be used as time-saving, highly sensitive, and effective alternative tool for the detection of trace element stress, with potential for remote sensing and trace element contamination screening in marine coastal areas.

Characterisation of estuarine intertidal macroalgae by laser-induced fluorescence

The article reports the application of laser-induced fluorescence (LIF) for the assessment of macroalgae communities of estuarine intertidal areas. The method was applied for the characterisation of fifteen intertidal macroalgae species of the Tagus estuary, Portugal, and adjacent coastal area. Three bands characterised the LIF spectra of red macroalgae with emission maxima in the ranges 577–583 nm, 621–642 nm and 705–731 nm. Green and brown macroalgae showed one emission maximum in the red region (687–690 nm) and/or one in the far-red region (726–732 nm). Characteristics of LIF emission spectra were determined by differences in the main fluorescing pigments: phycoerythrin, phycocyanin and chlorophyll a (Chl a). In the green and brown macroalgae groups, the relative significance of the two emission maxima seems to be related to the thickness of the photosynthetic layer. In thick macroalgae, like Codium tomentosum or Fucus vesiculosus, the contribution of the far-red emission fluorescence peak was more significant, most probably due to re-absorption of the emitted red Chl a fluorescence within the dense photosynthetic layer. Similarly, an increase in the number of layers of the thin-blade green macroalgae Ulva rigida caused a shift to longer wavelengths of the red emission maximum and the development of a fluorescence peak at the far-red region. Water loss from Ulva's algal tissue also led to a decrease in the red/far-red Chl fluorescence ratio (F685/F735), indicating an increase in the density of chloroplasts in the shrinking macroalgal tissue during low tide exposure.

Temporally and spectrally resolved UV absorption and laser-induced fluorescence measurements during the pyrolysis of toluene behind reflected shock waves

Toluene is frequently used as fluorescence tracer in high-temperature combustion applications. A quantitative analysis of laser-induced fluorescence (LIF) signals requires the knowledge of photophysical properties and decomposition kinetics. Using spectrally and temporally resolved ultraviolet absorption and LIF measurements, we studied the spectral properties of toluene and its pyrolysis products behind shock waves between 810 and 1,755 K. Transient absorption spectra were acquired between 220 and 300 nm. The temporal behavior of the absorption at 266 nm was compared to simulations based on literature kinetics models of toluene pyrolysis and available high-temperature absorption cross-sections of toluene, benzyl radicals, and C7H6 as a product from benzyl decomposition. Experiment and simulation agree well at the beginning of the pyrolysis process, whereas for longer reaction times deviations occur presumably due to the build-up of high molecular weight species, which contribute to the observed absorption but have unknown spectral properties. Additionally, LIF emission spectra were recorded following 266-nm excitation at selected reaction times. From measurements up to 1,220 K, the relative fluorescence quantum yield of toluene was derived, extending existing data to higher temperatures. Products from toluene pyrolysis were found to be the major contributors to the LIF signal at higher temperatures.

Investigation of toluene LIF at high pressure and high temperature in an optical engine

Toluene laser-induced fluorescence (LIF) emission spectra were acquired in an optical engine with excitation at 248 nm. Toluene was homogeneously seeded in pure nitrogen and air which were used as intake gases. Data were acquired during the compression phase without ignition leading to simultaneous increases in temperature and pressure from 20°C and 1 bar to 500°C and 23.6 bar. Compared to LIF emission spectra at high temperature and atmospheric pressure reported in the literature, the toluene-LIF emission signal shifts to longer wavelengths when temperature and pressure increase simultaneously, whereas the spectrally integrated emission intensity is slightly affected by the pressure level.

Wavelength resolved laser-induced fluorescence emission of [formula omitted] trapped in an ion cyclotron resonance cell

We have measured the wavelength resolved fluorescence emission laser-induced fluorescence (LIF) spectrum of C 6 F 3 H 3 + confined in an open cylindrical ion cyclotron resonance Penning trap. Ion cyclotron resonant azimuthal quadrupolar excitation successfully mass-selects and traps the ions for 10 s for repeated laser interrogation, and establishes that the observed fluorescence is from C 6 F 3 H 3 + ions. Electron-induced fluorescence (EIF) emission spectra of the same species were acquired for comparison. Vibrational structure was resolved for both LIF and EIF, and our assignments are consistent with prior literature values in the absence of ion trapping and high magnetic field (3 T). This work represents the first determination of wavelength resolved LIF emission spectra of organic ions in a Penning trap.

Electronic spectroscopy of B atoms and B2 molecules isolated in para-H2, normal-D2, Ne, Ar, Kr, and Xe matrices

We report spectroscopic observations on B atoms isolated in cryogenic parahydrogen (pH2), normal deuterium (nD2), Ne, Ar, Kr, and Xe matrices, and of B2 molecules in Ne, Ar, Kr, and Xe matrices. The 2s23s(2S)←2s22p(2P) B atom Rydberg absorption suffers large gas-to-matrix blue shifts, increasing from +3000 to +7000 cm−1 in the host sequence: Xe<Kr<Ar≈Ne≈nD2≈pH2. Much smaller shifts are observed for the 2s2p2(2D)←2s22p(2P) B atom core-to-valence transition. We assign pairs of absorption peaks spaced by ≈10 nm in the 315–355 nm region to the B2 (A 3Σu−←X 3Σg−) Douglas–Herzberg transition. We assign a much weaker progression in the 260–300 nm region to the B2 (2)3Πu←X 3Σg− transition. We report a novel progression of strong peaks in the 180–200 nm region which we suspect may be due to B2 molecules, but which remains unassigned. Ultraviolet (UV) absorption spectra of B/pH2 solids show two strong peaks at 216.6 and 208.9 nm, which we assign to the matrix perturbed 2s23s(2S)←2s22p(2P) and 2s2p2(2D)←2s22p(2P) B atom absorptions, respectively. This assignment is supported by quantum path integral simulations of B/pH2 solids reported in the following article in this journal [J. R. Krumrine, S. Jang, G. A. Voth, and M. H. Alexander, J. Chem. Phys. 113, 9079 (2000)]. Laser induced fluorescence emission spectra of B/pH2 solids show a single line at 249.6 nm, coincident with the gas phase wavelength of the 2s23s(2S)→2s22p(2P) B atom emission. The UV laser irradiation results in photobleaching of the B atom emission and absorptions, accompanied by the formation of B2H6.

A CCD-OMA device for the measurement of complete chlorophyll fluorescence emission spectra of leaves during the fluorescence induction kinetics.

A new device for the measurement of complete laser induced fluorescence emission spectra (maxima near 690 and 735 nm) of leaves during the induction of the chlorophyll fluorescence is described. In this the excitation light (cw He/Ne laser, 632.8 nm) is switched on by a fast electro-mechanical shutter which provides an opening time of 1 ms. The emitted fluorescence is imaged onto the entrance slit of a multichannel spectrograph through a red cut-off filter (greater than 645 nm). A charge coupled device (CCD) sensor with 2048 elements simultaneously detects the complete chlorophyll fluorescence emission spectrum in the 650-800 nm wavelength range. Scanning is accomplished electronically and the integration time for a complete fluorescence emission spectrum can be selected from 10 ms up to 260 ms. Shutter, detector system and data acquisition are controlled by an IBM-PC/AT compatible computer. A maximum of 32 spectra can be measured at selected times during the fluorescence induction kinetics with the shortest time resolution of 10 ms. The instrument permits the determination of various fluorescence parameters: a) the rise-time of the fluorescence to the maximum level fm, b) the changes in the shape of the fluorescence emission spectra during the induction kinetics, c) the induction kinetics in the fluorescence ratio F690/F735 as well as d) the fluorescence decrease ratio Rfd at any wavelength between 650 to 800 nm. These fluorescence parameters provide information about the functioning of photosynthesis. The ratio F690/F735 allows the non-destructive determination of the chlorophyll content of leaves. The application of this instrument in ecophysiological research and stress physiology of plants is outlined.

Stress and Phase Transformation Phenomena in Oxide Films: Real-Time Spectroscopic Measurements

ABSTRACTIn situ optical methods are reviewed for characterization of phase transformation processes and evaluation of residual stress in solution-deposited metastable oxide films. Such low density films most often are deposited as disordered phases making them prone to crystallization and attendant densification when subjected to increased temperature and/or applied pressure. Inherent stress imparted during film deposition and its evolution during the transformation are evaluated from phonon frequency shifts seen in Raman spectra (TiO2) or from changes in the laser-induced fluorescence emission spectra for films containing rare earth (Sm+3:Y3Al5O12) or transition metal (Cr+3 :Al2O3) dopants. The data in combination with measured increases in line intensities intrinsic to the evolving phase are used to follow crystallization processes in thin films. In general, film deposition parameters are found to influence the crystallite ingrowth kinetics and the magnitude of stress and stress relaxation in the film during the transformation. The utility of these methods to probe crystallization phenomena in oxide films will be addressed.