Prompt luminescence

Prompt Luminescence. Before going on to discuss the mechanisms by which the stored energy can be released from the lattice we shall pause here to discuss what happens to the electronic excitation energy if it is not stored in the lattice by any of the mechanisms discussed above. In wide-band-gap insulators such as those discussed here direct band-to-band recombination of electrons with holes is not generally observed and indirect, Shockley-Read recombination via localized states in the band gap is the main cause of electron-hole recombination. The recombination process results in the emission of phonons or photons. Since we are interested in luminescence emission in this paper it is the emission of photons that we shall consider. The emission wavelength can be characteristic of the position (in terms of energy) of the localized state within the band gap, or via the process of energy transfer, it may... 

The N3 optical center is one of the best known in steady-state luminescence spectra diamond. It is connected with three substitutional nitrogen atoms botmded to a common carbon atom or a vacancy, the ground state being a level and the excited state where luminescence originates a state (C3V point group). The zero-phonon line occurs at 2.985 eV and absorption and emission spectra show very closely a mirror relationship (Bokii et al. 1986). The N3 prompt luminescence decay is exponential and equal to 40 ns. Time-resolved luminescence spectroscopy enables to detect that N3 center has some metastable levels between the emitting and ground state. One of the decay paths of these metastable levels is delayed N3 luminescence, which occurs... 

Transient UV-vis absorption spectra showed that theTi02/Ru(II) films yield prompt electron injection upon photolysis ( >108s 1) These same films displayed photoluminescence decays with parallel first- and second-order components, the first-order component having a rate constant of about lxl06s-1. These two sets of results provide further support for the existence of at least two populations of adsorbed Ru(II), one of which injects electrons rapidly and another which does not inject electrons and is thus capable of luminescing on a longer time scale. The second-order component of the luminescence decay is attributed to bimolecular triplet-triplet annihilation of surface-bound Ru(II). (Note that the second-order rate constants reported for luminescence decay have units of s-1 because they are actually values for k2(Asi))... 

Fig. 9. Microscope luminescence imaging of a model system consisting of oxirane acrylic beads (diameter < 250 pm) containing [Eu(HL)]+ or fluorescein. The left panel shows the prompt fluorescence image and the right panel the TR luminescence image. The figures represent the average luminescence intensities measured for each bead. Reprinted with permission from...

Long-lived photoluminescence, at 826 nm, is reported (t 15 (is) for thin films of the processable, -conjugated polymer, poly(3-hexylthio-phene) (93JA8447). Excitation of the n—n transition with 518 nm light (So >S ) yields only very weak luminescence of 826-nm light, even at 18 K. The emission is enhanced, to point where it can be observed at room temperature, when the excitation wavelength is 250 nm, but it is completely quenched by oxygen. Prompt fluorescence decays within... 

The involvement of the CIEEL process in the thermolysis of [21] immediately offers new insight into many previously perplexing proposals of dioxetane or dioxetanone intermediacy in various chemi- and bio-luminescent reactions. For example, the discovery of activated chemiluminescence for [21], and the finding that intramolecular electron transfer can generate a very high yield of electronically excited singlet (Horn et al., 1978-79), prompts speculation that an intramolecular version (34) of the CIEEL mechanism is... 

Trends in biochemical screening assays seem to favor the use of multi-function PMT-based readers that allow for various MTP well densities (96, 384, and 1536 well plates), can handle a number of readout formats such as prompt fluorescence, luminescence, fluorescence polarization, time-gated fluorescence, and luminescent oxygen channeling or AlphaScreen. Examples of this type including the Perkin Elmer EnVision, TECAN-Ultra, BMG FluoStar, and LJL Analyst GT can be employed for a variety of the assay technologies described above. 

The good encryption of lanthanide ions in DOTA-type molecules has also prompted the development of luminescent probes based on this structure, particularly by substituting DTMA, 1,4,7,10-tetrakis(methylcarbamoylmethyl)-1,4,7,10-tetraazacyclododecane. For instance, phenacyl and phenylphenacyl substituents have been grafted onto DTMA and the corresponding ligands, LI and L2 (Fig. 4.40) form stable 1 1 complexes in water with lanthanide ions (log/fi 12-13 at 295 K). The structure of [Tb(Ll)(H20)]3+ (Fig. 4.44) shows the ion well encapsulated into the cavity formed by the macrocyclic platform and... 

An example of the utility of the time-resolved technique in eliminating the interference from background fluorescence in bioimaging is shown in Figure 13.17b. Nagano and coworkers compared time-resolved luminescence microscopy with conventional microscopy using live cultured HeLa cells injected with a Eu + complex Eu-36 (or Eu-37). In the prompt fluorescence images, both the luminescence of Eu-36 (or Eu-37) and weak autofluorescence from... 

Six types of Eu(dik)3 complexes were accurately analyzed in the absence and presence of phen, using both infusion ESI-MS and ELD. The LOD by FLD for compounds extracted with acetonitrile were 1-100 ppb. Using ESI-MS, high sensitive and prompt discrimination of luminescent europium S-diketonates can be achieved. The combination of laser samphng and ion trap MS is a powerful analytical technique for the direct analysis of complex samples. Thus, the generation of both negative and positive ions by laser desorption directly within a quadrupole ion trap was apphed to analyze complex samples such as Cr(acac)3. ... 

Some degree of temporal resolution of emission may be obtained by incorporating a phosphoroscope attachment in the simple apparatus described above. A mechanical or electronic device is used to allow periodic and out-of-phase excitation and detection of luminescence. In the simplest case a mechanical shutter interrupts the excitation beam periodically and the detection system is gated so that emission is observed only after a fixed interval of time has elapsed after excitation. Under these conditions short-lived processes such as prompt fluorescence will have decayed to zero intensity and only longer-lived emission will be recorded. For mechanical devices the limit of measurable lifetime is of the order of 1 ms, thus allowing time resolved studies to be made of certain phosphorescence and delayed emission procesres (see ... 

Photophysics of Fullerenes - Interest in the synthesis, derivatization, and chemistry of the various fullerenes has almost reached the epidemic stage and these exotic molecules continue to attract the photochemist. There have been numerous publications concerned with the fundamental photophysical properties of fullerenes in solution and the solid state over the past five years or so but there are still some important issues to resolve. Lately, the characterization of fullerenes and related carbon nanotubes has been reviewed, along with the luminescence properties of The prompt and delayed fluorescence spectral... 

Figure 24-6 Photoluminescence methods (fluorescence and phosphorescence). Fluorescence and phosphorescence result from absorption of electromagnetic radiation and then dissipation of the energy by emission of radiation (a). In (b), the absorption can cause excitation of the analyte to state 1 or state 2. Once excited, the excess energy can be lost by emission of a photon (luminescence, shown as solid line) or by nonradiative processes (dashed lines). The emission occurs over all angles, and the wavelengths emitted (c) correspond to energy differences between levels. The major distinction between fluorescence and phosphorescence is the time scale of emission, with fluorescence being prompt and phosphorescence being delayed.

In the oxidized sample, a prompt Chl-a fluorescence with a 0.42 ns lifetime is seen [Fig. 3 (A), trace (a)]. In the sample maintained at -450 mV and illuminated to photoaccumulate O ", the prompt fluorescence lifetime is 0.18 ns [trace (b)]. In the sample maintained at -450 mV but kept in the dark, the signal shows a prompt and a delayed fluorescence (or delayed light emission) with lifetimes of 1.06 ns and 4.3 ns, respectively [trace (c)]. Note that in the extended time region [panel (B)], only trace (c) still has a measurable emission tail. These results show that neither the sample in the oxidized state nor that with O" photoaccumulated show any delayed light emission. Only the sample in which Qa is pre-reduced shows the A3-ns luminescence. These results support the notion that the delayed emission is a recombination luminescence originating from the [P680 <1)"] state. 

In McElroy s lab, we established that the reaction of ATP and luciferin with purified luciferase involves two steps 9 the first forms an active intermediate, later determined to be the adenylate, and the second is the reaction with oxygen, leading to an excited state and light emission. The prompt decline of luminescence over the first minutes was shown to be due to luciferase inhibition, not substrate exhaustion. All evidence indicates that the flash of the firefly is initiated by the introduction of oxygen into the photocytes, triggered by a nerve impulse, which actually does not end on the photocytes, but on adjacent cells.10 12 More recently, nitric oxide (NO)... 

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