Fluorescence Line Narrowing Research Articles

Fluorescence-line narrowing in CdSe quantum dots: Surface localization of the photogenerated exciton.

The electronic properties of shallow band-edge surface traps in nanometer-size CdSe quantum dots are probed using fluorescence-line-narrowing spectroscopy. We find large changes in electron-hole-pair radiative lifetimes and couplings to LO phonons as the temperature is changed from 1.75 to 10 K. We attribute these changes to the localization of the photogenerated hole at the surface of the dots, accompanied by thermally activated motion between these surface localized states. A simple model based on the observed exciton--LO-phonon couplings is constructed to estimate the extent of hole localization in the luminescing state. A size-dependent study (20--80 \AA{} diameter) indicates that surface effects diminish rapidly with increasing size.

Fluorescence Line-Narrowing Spectroscopy as an Off-Line Identification Method for Narrow-Bore Column Liquid Chromatography

Storage of the effluent from a column liquid chromatograph (LC) on a thin-layer chromatography (TLC) plate was utilized to identify analytes with fluorimetric techniques in the absence of time constraints. As an example, the deposited LC trace of an impure 1-chloropyrene sample was studied in situ by conventional excitation/emission spectroscopy and by fluorescence line-narrowing (FLN) spectroscopy, a high-resolution laser-induced fluorescence technique requiring cryogenic conditions. Pyrene and several mono-, di-, and trichlorinated pyrenes, present in the 1-chloropyrene sample, were identified with the use of the fingerprint structure of the vibrationally resolved FLN spectra. Quantitation on the basis of the FLN signals was achieved by standard addition; compounds could be detected down to the low picogram level. Various TLC materials were used to study the influence of the matrix on the FLN spectra; although peak intensities and hole burning effects are matrix-dependent, the line positions are not influenced.

Fluorescence line narrowing in erbium-doped silica fibers

The properties of erbium-doped silica fiber amplifier are significantly modified by the addition of only few percent of aluminum. For example, at room temperature, the 1.5 μm emission line width is multiplied by a factor two. In order to improve our knowledge on rare-earth transition broadening mechanism, primarily in fibers, nonresonant fluorescence line narrowing measurements were performed on erbium-doped silica fibers codoped with either aluminum or germanium, at low temperatures. An important variation in site distribution and Stark splitting was found depending on the matrix.

Electric Field and Conformational Effects of Cytochrome c and Solvent on Cytochrome c Peroxidase Studied by High-Resolution Fluorescence Spectroscopy

Electronic spectra of mesoporphyrin-substituted yeast cytochrome c peroxidase (MP-CcP) were measured as a function of pH, ionic strength, and binding of cytochrome c (cyt c) by fluorescence line narrowing (FLN) spectroscopy at 5 K. The FLN spectra provided information about the vibrational structure of the first excited singlet state of MP-CcP, the various tautomeric forms of mesoporphyrin, and the positions and widths of their 0,0 bands. The composite 0,0 band of MP-CcP at pH 6 could be resolved into three components with peak positions at 16,046, 16,103, and 16,203 cm-1. MP-CcP at pH 8 could be analyzed using two components with peak positions at 16,048 and 16,193 cm-1. The disappearance of the 16,103-cm-1 component at alkaline pH suggests that it is due to a "chemical substate" arising from protonation of His52 in the distal side of the porphyrin. Computer simulations of the electrostatic field that CcP imposes on its porphyrin show that, in the presence of charged axial histidines His52 and His175, the electrostatic field at porphyrin nitrogens increases, especially along the normal to the heme by about 200 mV/A. Electric field effects may account for pH-dependent spectral shifts of the 0,0 positions of the resolved components, although hydrogen bonding may also affect these positions. On the other hand, the peak position of the components was not affected by ionic strength or binding of cyt c, implying that the electrostatic field of the heme pocket of MP-CcP remains unchanged. Indeed, computed changes in ionic strength of the solvent show no modification of the electrostatic field at the porphyrin. The only detectable effect of ionic strength and binding of cyt c to MP-CcP is on the relative contributions of the components, suggesting some rearrangements in the vicinity of the heme. Finally, shifts in the position of the vibrational lines for MP-CcP components indicate either that the tautomers have different vibrational frequencies due to the nonsymmetry of the porphyrin and/or that tautomers experience various distortions. Comparison of the vibrational spectrum of the first excited singlet state of mesoporphyrin in CcP and horseradish peroxidase also suggests that the heme pocket in the two peroxidases provides different steric restrictions.

Optical Zeeman spectroscopy of the near-infrared lasing center in chromium:forsterite

Optical Zeeman spectra of the near-IR luminescent center in Cr:forsterite were obtained with an external magnetic field applied along the crystallographic a and c axes. The field-dependent sublevel splittings of the triplet spin ground state were resolved through fluorescence line narrowing (FLN) techniques. The excellent correspondence between the observed splittings and those calculated for the tetrahedral Cr4+ center, previously identified and characterized in forsterite by electron paramagnetic resonance, firmly establishes the identity of the near-IR center as tetrahedral Cr4+. A simple model for the FLN excitation–emission cycle, including the influence of the external field on the optical line positions and intensities, is described.

Luminescence of the Cr3+ ion in sodium beta - and beta "-alumina: Site selection by time-resolved fluorescence line narrowing.

Fluorescence of ${\mathrm{Cr}}^{3+}$ ions in the two different octahedral sites of the spinel block of \ensuremath{\beta}- and \ensuremath{\beta}''-alumina have been measured by time-resolved fluorescence line-narrowing spectroscopy. For the excitation either a pulsed or a chopped cw-dye laser was used. Lifetimes and splittings of the ground state ${(}^{4}$${\mathit{A}}_{2}$) and of the $^{2}$E state have been measured by tuning the excitation energy within the inhomogeneous profile of the ${\mathit{R}}_{1}$ and ${\mathit{R}}_{2}$ lines of the split $^{2}$E${\mathrm{\ensuremath{-}}}^{4}$${\mathit{A}}_{2}$ transition. In sodium \ensuremath{\beta}''-alumina, we have isolated several inequivalent emitting centers, which are related to different configurations of the stabilizing ${\mathrm{Mg}}^{2+}$ ions.

Laser-induced fluorescence line narrowing in Sm2+-doped fluoride glass.

Fluorescence line-narrowing experiments have been made for the ${\mathrm{Sm}}^{2+}$ ion in fluoride glass at 77 K under cw dye-laser excitation at various energies within the inhomogeneously broadened $^{7}$${\mathit{F}}_{0\mathrm{\ensuremath{-}}}^{5}$${\mathit{D}}_{0}$ and $^{7}$${\mathit{F}}_{0\mathrm{\ensuremath{-}}}^{5}$${\mathit{D}}_{1}$ absorption lines. The energies of the three Stark levels of the $^{7}$${\mathit{F}}_{1}$ and $^{5}$${\mathit{D}}_{1}$ manifolds have been obtained as a function of the $^{5}$${\mathit{D}}_{0\mathrm{\ensuremath{-}}}^{7}$${\mathit{F}}_{0}$ energy separation. From the analysis of this result, it has been found that the site-to-site variations of the energies of these Stark levels can be explained well only by taking into account the J-mixing effect. The low-energy levels of the 4${\mathit{f}}^{5}$5d configuration lie in the vicinity of the $^{5}$${\mathit{D}}_{\mathit{J}}$ states in this material. However, no effect of the crystal-field mixing of the 4${\mathit{f}}^{5}$5d states on the inhomogeneous distribution of the energies of the $^{7}$${\mathit{F}}_{1}$ and $^{5}$${\mathit{D}}_{1}$ states has been observed. The origin of the unusually intense $^{5}$${\mathit{D}}_{0\mathrm{\ensuremath{-}}}^{7}$${\mathit{F}}_{0}$ transition in ${\mathrm{Sm}}^{2+}$ is also discussed.

Fluorescence Line Narrowing Studies of Eu3+-Doped Silica Gel-Glasses

ABSTRACTBroadband fluorescence and fluorescence line narrowing (FLN) spectra are presented for Eu3+ ions in Eu2O3-SiO3 and Eu2O3-Al2O3-SiO3 systems prepared by the sol-gel process. Clustering of rare earth ions in silica glass can be a limiting factor in the design and engineering of optical device materials. The addition of Al2O3 is known to help disperse rare earth ions in sol-gel silica. In order to develop a more detailed understanding of how Eu3+ is incorporated in these materials, time-resolved, laser-induced FLN studies at 77 K have been performed using a pulsed dye laser to selectively excite subsets of ions in the inhomogeneously broadened 7F0⇆ 5D0 manifold. Fluorescence spectra are discussed in terms of rare earth ion clustering, energy transfer, and bonding site symmetry. It is concluded that Eu3+ ions cluster in sol-gel silica and that the addition of alumina assists in dispersing Eu3+ ions.

Fluorescence and superfluorescence line narrowing and tunability of Nd/sup 3+/ doped fibers

The inhomogeneous behavior of the 1.06 /spl mu/m-neodymium transitions in doped optical fibers have been investigated, using the fluorescence line narrowing technique, pumping on the /sup 4/F/sub 3/2/ and /sup 4/F/sub 5/2/ sublevels at 4 K. Each observed transition has been identified. As the pump wavelength varies, the shift of the main fluorescence line is 40 nm, with the two pumping levels. We have studied the spectral behavior of the superfluorescence as a function of the pump wavelength, the temperature, and the absorbed power. The spectral evolution depends on /spl lambda//sub p/ with 19 nm-tuning range at low temperature. At 300 K, the quasihomogeneous behavior of the transition decreases the tunability to 14 nm. Based on these results, we present a simple technique permitting precise prediction of gain and spectral line shapes of superfluorescent Nd-doped fiber sources.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fluorescence line narrowing in erbium-doped silica fibers

The properties of erbium-doped silica fiber amplifier are significantly modified by the addition of only few percents of aluminium. For example, at room temperature, the 1.5 μm emission linewidth is multiplied by a factor two. In order to improve our knowledge on rare-earth transition broadening mechanism, primarily in fibers, nonresonant fluorescence line narrowing measurements were performed on erbium-doped silica fibers codoped with either aluminum or germanium, at low temperatures. An important variation in-site distributionk and Stark splitting was found depending on the matrix.

Microscopic nature of inhomogeneous line broadening: Analysis of the excitation-line-narrowing spectra ofCf4+inCeF4

Optical transitions between 5[ital f] states of tetravalent californium ion doped (1 metal-atom %) into CeF[sub 4] exhibit unusually large inhomogeneous broadening. The nature of the inhomogeneous broadening in this system has been studied by using fluorescence line narrowing and excitation line narrowing (ELN). It is shown that the energy distributions of different electronic states of Cf[sup 4+] in this system are correlated. In the ELN experiments, reduced excitation linewidth was obtained when selectively monitoring fluorescence emission. A linear relation was observed between the excitation energies of crystal-field states of the [sup 5][ital G][sub 4[prime]] manifold and the fluorescence wavelength monitored across the inhomogeneous profile of a [sup 5][ital G][sub 6[prime]]--[sup 7][ital F][sub 6[prime]] transition. Analysis of these results by means of a microscopic theory proposed by Laird and Skinner [J. Chem. Phys. 90, 3880 (1989)] has provided insights into the structural properties of this disordered system.

High-resolution spectroscopy of organic molecules in solids: from fluorescence line narrowing and hole burning to single molecule spectroscopy

We give a short overview of the selective spectroscopy of organic molecules in solid solutions, starting from Shpol'skii matrices up to single molecule spectroscopy. We discuss the general principles of selective spectroscopy and different applications of this technique to molecular and solid-state studies. We examine in more detail two new fields to which we have contributed: persistent spectral hole burning in Langmuir-Blodgett (LB) films and the study of individual molecules. We show how persistent spectral hole burning provides information about structure and dynamics of LB films and how energy transfer can be studied in concentrated films. We probed the dynamics of the LB matrix as a function of the depth of the dye in a multilayer

Inhomogeneity study of Pr3+-doped yttrium aluminium garnet using time-resolved spectroscopy

The temporal behaviour of the excitation lineshape of the 1D2(1) level of YAG:Pr3+ for three different concentrations of Pr3+ (0.08, 0.24 and 0.6 at.%) is investigated. The satellite line structure in the vicinity of the main inhomogeneously broadened transition is related to ions in different crystal-field sites. Studies of the selectivity excited decay curves of the 1D2 luminescence reveal an almost exponential decay only for the 0.08 at.% sample after excitation of the absorption line centre. A non-exponential decay from the 0.24 and 0.6 at.% crystals is interpreted in terms of direct donor-acceptor energy transfer by cross relaxation. The technique of fluorescence line narrowing is used to analyse the effect of phonon-assisted spectral diffusion. Anti-Stokes emission from the 3P0 level following excitation of the 1D2 state is studied as a function of Pr3+ concentration. It is concluded that the anti-Stokes fluorescence in the diluted YAG:0.08 at.% Pr3+ system results from the excited-state absorption process while in YAG:0.6 at.% Pr3+ this anti-Stokes emission is attributed to up-conversion by energy transfer.

The fluorescence line narrowing of Sm3+ in ZBLAN fluoride glass

The fluorescence line narrowing (FLN) and time resolved fluorescence line narrowing (TRFLN) of Sm 3+ ions in ZBLAN fluoride glass have been investigated. The fluorescence transitions 4 G 5 2 − 6 H 5 2 and 4 G 5 2 − 6 H 7 2 were detected as the wavelength of the exciting light was varied. The homogeneous broadened luminescence of 4 G 5 2 − 6 H 5 2 by resonant excitation has been recorded at temperatures as low as 100 K; a 2.5 cm −1 linewidth was measured at this temperature, and the delay-time dependence and temperature dependence of the spectral width were studied.

Fluorescence line narrowing Zeeman spectroscopy of Cr3+-doped Gd3Sc2Al3O12 garnet crystals. II. Calculation of the lineshape

For pt.I see ibid., vol.4, p.7307 (1992). The R1 line of Cr3+ in an antiferromagnetic garnet crystal Gd3Sc2Al3O12 (GSAG) is broadened inhomogeneously and homogeneously. Site-selective techniques, such as fluorescence line narrowing (FLN), can remove the inhomogeneous broadening created by strain and compositional disorder. The FLN spectrum then reflects the broadening due to processes including spin-spin exchange interaction between Cr3+ ions in octahedral positions and Gd3+ ions in dodecahedral positions in the GSAG unit cell. A magnetic field can remove the homogeneous broadening due to antiferromagnetic exchange. The R1 line is associated with the spin-forbidden 2E to 4A2 transition. In general, the selection rule on the R1 line breaks down through spin-orbit interaction on the Cr3+ ion. Simulations of the FLN spectra of Cr3+:GSAG as a function of both temperature and magnetic field have been used to estimate the magnitude of the spin-spin exchange coupling constant, J approximately=0.25-0.33 cm-1. Such simulations also show that for the 2E to 4A2 transition to antiferromagnetic GSAG the Gd3+ spin in the Cr3+-Gd3+ spin exchange system is conserved in the presence of a magnetic field (B>2T), whereas the selection rule breaks down in the absence of a magnetic field.

Native and denatured Zn cytochrome [formula omitted] studied by fluorescence line narrowing spectroscopy

Fluorescence Line Narrowing (FLN) spectroscopy was employed to compare the environment around the porphyrin in folded and unfolded Zn-substituted cytochrome c (Zn cyt c). Parameters of the resolved spectra, including the inhomogeneous energy-distribution function, vibrational energy levels, and phonon coupling, were compared for guanidine-denatured Zn cyt c and native Zn cyt c. The spectra of denatured Zn cyt c showed increased broad background and decreased peak resolution when compared to the native protein, indicating that denaturation results in increased phonon coupling. The energy-distribution function for the unfolded protein was fitted to a single Gaussian centered at 17230 cm −1 with a width of approx. 360 cm −1, which proved to be blue shifted and much wider than that for native Zn cyt c (approx. 65 cm −1). Vibrational frequencies of the ground-state for Zn cyt c were identified and shown to change upon denaturation. Temperature-dependence of the FLN spectra of native Zn cyt c was analyzed and found to have step-like broadening between 40 K and 50 K. Such discontinuous spectral broadening behavior suggests that a discrete conformational change occurs in the protein at these temperatures.

Advances in High-Resolution Laser Spectroscopy of Coordination Compounds

Abstract Advanced laser spectroscopies are shown to be invaluable in providing unambiguous detail concerning the electronic structure of coordination compounds. The basic principles of two techniques which overcome the effect of inhomogeneous broadening, namely fluorescence line narrowing and hole-burning spectroscopy, are discussed. Their use and limitations in transition-metal complexes along with examples from our own work are given. These examples present a full range of d-d, ligand-centered singlet-triplet and charge-transfer transitions in both crystal-line and amorphous hosts.

Origin of inhomogeneous linewidth of Eu3+ fluorescence in several oxide glasses

The local structure around Eu3+ ions in several oxide glasses (silicate, borate, germanate, and aluminosilicate) was investigated using both Mössbauer spectroscopy and fluorescence measurement including the fluorescence line narrowing technique. The origin of inhomogeneous broadening of fluorescence spectra is discussed. Except for silicate glasses, the isomer shift of 151Eu varied with the population of oxygen species with different microscopic optical basicity. For silicate glasses, it was found that the isomer shift and Stark splitting of 7F1 level showed no compositional dependence. It was assumed that regardless of alkali content, Eu3+ ions in silicate glasses attract a certain number of nonbridging oxygens (NBOs), which is the only species with a negative charge, when incorporated stably into a glass matrix. Further, it was generally found that larger amounts of alkali ions or smaller amounts of macroanions, such as BO4■, AlO4■, and GeO62■, bring about smaller values of inhomogeneous linewidth, ΔνIH. It was concluded that the compositional dependence of ΔνIH in oxide glasses is successfully explained from the viewpoint of the NBO-donating ability of the glass matrix, which is related to the NBO concentration and the flexibility of the glass matrix.

Fluorescence-line-narrowing Zeeman spectroscopy of Cr3+-doped silicate and Li borate glass

This paper discusses the inhomogeneous broadening of the 2E to 4A2 emission (R line) in Cr3+-doped glasses. The impurity ion occupies approximately octahedral sites in silicate and borate glasses in which the R-line transition is broadened by site-to-site disorder associated with the glassy structure. The spectroscopic effects of disorder are to some extent removed by fluorescence line narrowing (FLN), which seeks to recover the homogeneous width of the R-line transitions. In the three glasses investigated, two silicate and a Li borate glass, the R-line width is approximately=190-200 cm-1. In magnetic fields up to 3.46 T and at low temperatures (T approximately=2 K) the narrowed R line splits into three components, one resonant with the excitation and two shifted to longer wavelengths.

Fluorescence line narrowing-Zeeman spectroscopy of Cr3+-doped Gd3Sc2Al3O12 garnet crystals

This paper discusses line broadening by compositional disorder and by spin-spin exchange interaction between the paramagnetic Cr3+ and Gd3+ ions in antiferromagnetic Gd3Sc2Al3O12 (GSAG) probed using fluorescence line narrowing (FLN) in the absence and presence of a magnetic field. The most intense R1 lines in Cr3+:GSAG, occurring at lambda =691.2 nm and 692.4 nm, have halfwidths of approximately=32 cm-1. The linewidths of the FLN spectra at 1.6 K are respectively 19 cm-1 and 13 cm-1, much larger than the width of the excitation laser beam (<0.2 cm-1): thus the contributions to the R1-line halfwidth from mechanisms of homogeneous and inhomogeneous broadening are approximately equal. In addition, the peaks of the FLN lines are shifted to lower energy from the laser excitation line by approximately=8 cm-1. As the temperature is increased gradually from 1.6 K to 10 K, the FLN peak is shifted to higher energy and is resonant with the excitation above 10 K. In the presence of an external magnetic field the broad FLN spectrum becomes resolvable into three sharp lines with the width of approximately=3 cm-1 at T=1.6 K. The peak of the line with maximum intensity is coincident with the excitation energy. The FLN spectrum at T=10 K and B=3.46 T is similar to that at T=10 K in the absence of a magnetic field. The temperature dependence and magnetic field dependence of the FLN spectra are discussed in terms of spin-spin exchange interaction between Cr3+ and Gd3+ ions in antiferromagnetic GSAG.