Temperature Fluorescence

Many inorganic solids such as the various halides of metals like Zn, Cd, Cu, Sn, Sb, Mn, that do not show appreciable emission at room temperatures, frequently emit rather strongly at very low temperatures of the order of — 185°C42. Uranyl salts are the best illustiations of the effect of low temperature on luminescence bands. 

A study of the low-temperature (77 °K) emission and absorption spectra of naphthalene43 has established the nature of the comparatively weak absorption band on the long wavelength side of its ultra-violet spectrum the lowest singlet-singlet band in the crystal has been shown to be at 322 Low-temperature fluorescence study of some molecular and ionic hydroxynaph-thalenes in rigid solvents44 shows that emission occurs from the Franck-Condon state at a temperature of 77 °K, whereas at room temperature, normal fluorescence is observed. 

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Sanchez E J, Novotny L, Floltom G R and Xie X S 1997 Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation J. Chem. Phys. A 101 7019-23... 

The ESR spectrum of the pyridazine radical anion, generated by the action of sodium or potassium, has been reported, and oxidation of 6-hydroxypyridazin-3(2//)-one with cerium(IV) sulfate in sulfuric acid results in an intense ESR spectrum (79TL2821). The self-diffusion coefficient and activation energy, the half-wave potential (-2.16 eV) magnetic susceptibility and room temperature fluorescence in-solution (Amax = 23 800cm life time 2.6 X 10 s) are reported. 

Solid-surface luminescence analysis involves the measurement of fluorescence and phosphorescence of organic compounds adsorbed on solid materials. Several solid matrices such as filter paper, silica with a polyacrylate binder, sodium acetate, and cyclodextrins have been used in trace organic analysis. Recent monographs have considered the details of solid-surface luminescence analysis (1,2). Solid-surface room-temperature fluorescence (RTF) has been used for several years in organic trace analysis. However, solid-surface room-temperature phosphorescence (RTF) is a relatively new technique, and the experimental conditions for RTF are more critical than for RTF. 

Figure 1. (a) Room-temperature fluorescence spectra of benzo(a)pyrene on 80% a-Room-temperature fluorescence spectrum of 500 ng of benzo(a)pyrene on 80% a-<7clodextrin—NaCl. = 300 nm. 

Interactions in Solid-Surface Luminescence Temperature Variation. Solid-surface luminescence analysis, especially solid-surface RTF, is being used more extensively in organic trace analysis than in the past because of its simplicity, selectivity, and sensitivity (,1,2). However, the interactions needed for strong luminescence signals are not well understood. In order to understand some of the interactions in solid-surface luminescence we recently developed a method for the determination of room-temperature fluorescence and phosphorescence quantum yields for compounds adsorbed on solid surfaces (27). In addition, we have been investigating the RTF and RTF properties of the anion of p-aminobenzoic acid adsorbed on sodium acetate as a model system. Sodium acetate and the anion of p-aminobenzoic acid have essentially no luminescence impurities. Also, the overall system is somewhat easier to study than compounds adsorbed on other surfaces, such as filter paper, because sodium acetate is more simple chemically. 

Figure 3. Three-dimensional plot of the room-temperature fluorescence of a mixture of 500 ng each of benzo(a)pyrene and benzo(e)pyrene on 80% q-cyclodextrin-NaCl. Numbers along dashed lines show the approximate wavelengths (nm) represented by these lines. The excitation wavelength was varied from 250 nm (front spectrum) to 370 nm (back spectrum) at 2-nm increments. Benzo(a)pyrene emitted from approximately 380 nm to 540 nm, and benzo(e)pyrene emitted from 365 nm to 505 nm.

Room-Temperature Fluorescence and the Remote Detection of Solar-Stimulated Luminescence... 

Room-temperature fluorescence (RTF) has been used to determine the emission characteristics of a wide variety of materials relative to the wavelengths of selected Fraunhofer lines in support of the Fraunhofer luminescence detector remote-sensing instrument. RTF techniques are now used in the compilation of excitation-emission-matrix (EEM) fluorescence "signatures" of materials. The spectral data are collected with a Perkin-Elraer MPF-44B Fluorescence Spectrometer interfaced to an Apple 11+ personal computer. EEM fluorescence data can be displayed as 3-D perspective plots, contour plots, or "color-contour" images. The integrated intensity for selected Fraunhofer lines can also be directly extracted from the EEM data rather than being collected with a separate procedure. Fluorescence, chemical, and mineralogical data will be statistically analyzed to determine the probable physical and/or chemical causes of the fluorescence. 

Fig. 21.8 Room-temperature fluorescent decay profile for Ba3BP30- 2.

Figure 21.23 exhibits the room-temperature fluorescence decay profiles of Ba3BP30i2 Eu powders. The experimental decay curve can be fitted by an equation with two exponential terms corresponding to two decay times of 20 ns (98.97%) and 522 ns (1.03%), respectively. 

Such a qualitative conclusion is supported by the observation that the room-temperature fluorescence spectrum of BMPC in alcohols (Fig. 8) is a good mirror image... 

Polarization of the Emission. We have sought support for the weakly interacting chain segment model from measurements of room temperature fluorescence polarization (19) on dilute solutions of 1 in 3-methylpentane. An independent preliminary report of similar measurements on a dilute glassy solution at 77K and on a neat polymer has also appeared (21). In the latter case, the analysis is complicated by inter-chain energy transfer. 

Figure 2. Room-temperature fluorescence and excitation spectra of 1 in cyclohexane at various choices of excitation and emission wavelengths, and the fluorescence quantum yield at various wavelengths of excitation.

Examination of the corrected room temperature fluorescence properties of PET yarns revealed an excitation maximum at 342 nm with a corresponding emission maximum at 388 nm. At 77°K, in the uncorrected mode, the fluorescence spectra of PET yarns exhibited a structured excitation having maxima at 342 and 360 nm and a shoulder at 320 nm. At 77°K, PET yarns displayed a structured emission with maxima at 368 and 388 nm. As in solution, the copolymer yarns showed both fluorescence from the terephthalate portion of the polymer and the 4,4 -biphenyldicarboxyl ate portion of the polymer. Excitation at 342 nm produced an emission band centered at 388 nm. This excitation and emission correspond to the PET homopolymer emission. Excitation with about 325 nm light produced an emission with a maximum near 348 nm from the 4,4 -biphenyldicarboxyl ate portions of the polymer. 

Grubor, N.M., Shinar, R., Jankowiak, R., Porter, M.D., and Small, G.J. (2004) Novel biosensor chip for simultaneous detection of DNA-carcinogen adducts with low-temperature fluorescence. Biosens. 

Fluorescence Lifetimes. The fluorescence decay times of TIN in a number of solvents (11.14.16.18.19), low-temperature glasses (12.) and in the crystalline form (15.) have been measured previously. Values of the fluorescence lifetime, Tf, of the initially excited form of TIN and TINS in the various solvents investigated in this work are listed in Table III. Values of the radiative and non-radiative rate constants, kf and knr respectively, are also given in this table. A single exponential decay was observed for the room-temperature fluorescence emission of each of the derivatives examined. This indicates that only one excited-state species is responsible for the fluorescence in these systems. 

Fig. 3.4. Potential energy diagram of DMABN (top) the reaction coordinate contains both solvent relaxation and rotation of the dimethylamino group. Room temperature fluorescence spectrum in hexane and tetrahydrofurane (bottom) (adapted from Lippert et al., 1987).

Cr + ions in aluminum oxide (the ruby laser) show a sharp emission (the so-called Ri emission line) at 694.3 nm. To a good approximation, the shape of this emission is Lorentzian, with Av = 330 GHz at room temperature, (a) Provided that the measured peak transition cross section is c = 2.5 x 10 ° cm and the refractive index is = 1.76, use the formula demonstrated in the previous exercise to estimate the radiative lifetime, (b) Since the measured room temperature fluorescence lifetime is 3 ms, determine the quantum efficiency for this laser material. 

The fluorescence bands in [2.2] and [3.3] paracyclophanes should not bethought of as true excimer fluorescence since the ground state in these phanes is not free from interaction. In fact, the low-temperature fluorescence spectrum of [2.2] paracyclophane has been reported to show considerable structure, although this was not observed for [2.2] or [3.3] paracyclophanes at low temperature in a more recent report89a>. 

Fig. 10 Separation of fatty acids as their methylmethoxycoumarin esters flow rate, 0.5 ml /min room temperature fluorescence detection (excitation 325 nm, cutoff filter, 398 nm) eluent acetonitrile/water (80 20 v/v) to 100% acetonitrile in45 min. Peaks A. C14.0 + C16 1 B. 06 0 C. 07 0 D. 08 0 E. 08 1 G. C20 4 1. unknown.

Muenter and Cooper (30) measured the room-temperature fluorescence of two J-aggregated dyes, l,l -diethyl-2,2 -quino-cyanine and 1,1, 3,3 -tetraethyl-5,5, 6,6 -tetrachlorobenzimid-azolocarbocyanine, adsorbed on cubic AgBr grains. The quantum efficiency of spectral sensitization was inversely related to the relative fluorescence. The fluorescence by the dyes in the molecular state was low compared to that for the aggregated dyes. Addition of a styryl or thiohydantoin dye as a supersensitizer for the quinocyanine quenched its fluorescence and increased the relative efficiency from 0.06 to nearly 1.0. 

Fig. 2.9. Empirical energy diagram for DMABN in n-butyl chloride (energetics based on room-temperature fluorescence band maxima and on activation energies). In the small-barrier case, E. is to be viewed as a dynamical activation energy resulting from solvent viscosity. The Franck-Condon ground state (after emission from A ) is anomalously destabilized (large E3).

Fig. 2.10. Room-temperature fluorescence spectra of DMABN in aprotic solvents of...

Fig. 2.15. Room-temperature fluorescence spectra of BBPY in n-hexane,----------- diethyl...

Chapter 18 reports the investigations of Petrus and relates the room temperature fluorescence, and visible and UV spectral characteristics of citrus juices and related products to the detection of adulteration. 

The purpose of this presentation is to discuss the visible and ultraviolet absorption and room temperature fluorescence characteristics of alcoholic solutions of Florida produced orange juice and pulpwash samples, and to relate the characteristics to qualitative detection and quantitative approximation of adulteration of frozen concentrated and single-strength orance juices. Experimental details of our procedures may be found elsewhere (15). 

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