Luminescence kinetics

Feofilov (89) made a study of the spectra and luminescence kinetics of CaF2 Tb. Emission from both the 5D4 and 5Z)3 states was observed (90), His data were collected at -183°C using a taw meter (97), and the decay time r of the 5D3 state was found to be 2 x 10 3 sec. For the 5D4 state, however, a sharp deviation from exponential form was observed. 

The influence of excitation temperature on the the a-value parameter for tunnelling luminescence kinetics is described in [94],... 

Fig. 4.16. (a) Reversible change of the tunnelling luminescence kinetics due to the step-like temperature stimulation (schematicaly). (b) The tunnelling luminescence kinetics for F, Vk defects in KCI-SO4 due to the temperature stimulation after X-ray excitation at 125 K [106],... 

Fig. 4.17. The tunnelling luminescence kinetics for Ag°, Ag2+ defects in KCl-Ag (curves la, 2a) due to the temperature stimulation cycle shown in curves lb, 2b [106], The excitation...

Let us now analyze, following Rogulis and Kotomin [102], the experimental non-stationary tunnelling luminescence kinetics observed after a sudden temperature change for V, F pairs in KBr, Ag° and in KCl-Ag as well as for an electron thermal release from Ag° (Ag° and Ag2+ in NaCl-Ag). 

Fig. 4.18. The tunnelling luminescence kinetics for F, Vk pairs in KBr (upper curves 1, 2, 3) vs. temperature stimulation (lower curves 1, 2, 3 respectively), a is the slope change after the stimulation is switched off. According to the partial lightsum method [37, 87-90] the insert (curve 4) yields the relative dissimilar defect distribution occurring after the temperature stimulation. Arrows show the change of both the tunnelling luminescence decay intensity I(t) and the spatial defect distribution caused by the stimulation a close defect concentration increases whereas that for the distant pairs decreases.

Fig. 4.19, The tunnelling luminescence kinetics for the Ej-, Tb3+ pairs in Na20 3Si02-Tb3+ glass. The ultraviolet excitation was at 120 K with further short thermal excitation of electrons above the mobility edge (curve 1) and prolonged heating up to 70 K below the excitation...

The influence of anisotropy of acceptor wavefunction upon tunnelling luminescence kinetics was treated in [104]. The conclusion was drawn that for the static tunnelling luminescence it just results in the redefinition of the (7o parameter. However, we are interested here in the non-steady-state kinetics and shall demonstrate below that, particularly at this stage, anisotropic recombination reveals distinctive behaviour which allows us to identify it. 

Fig. 4.20. The influence of the tunnelling recombination anisotropy upon the non-steady-state luminescence kinetics. Curves 1 and 2 correspond to the defect reorientation switching-on and -off, respectively at the moments given by broken lines [106],...

Let us consider now the tunnelling luminescence kinetics for the transient processes when the temperature stimulation is suddenly switched on and off, respectively. This is different from the transient kinetics treated above, which arises due to an inertial passage between two quasi-steady states corresponding to different temperatures. 

Luminescence Kinetics, Luminescence Lifetimes. The Einstein coefficient A for spontaneous emission gives the probability of radiative transition. Since this probability is the same for all molecules of the same excited species, it follows that the decrease in the number of excited molecules within a differential time increment is simply proportional to the number of excited... 

When an intense pulse of monochromatic laser light is focussed on a transparent liquid or solid, there is an emission of white light over a wide continuous spectral range. This process is known as self-phase modulation . We will not consider its physics. For our purpose it is important to note its photochemical implications. On the one hand, this pulse of white light can be used to provide a probe light in ps and fs flash photolysis (sections 8.1 and 8.2). On the other hand, it can be a source of stray light in some luminescence measurements. This comes as a surprise to many users of lasers for luminescence kinetics measurements, but it is an unavoidable problem. 

In the nanosecond (ns) time-scale the use of kinetic detection (one absorption or emission wavelength at all times) is much more convenient than spectrographic detection, but the opposite is true for ps flash photolysis because of the response time of electronic detectors. Luminescence kinetics can however be measured by means of a special device known as the streak camera (Figure 8.2). This is somewhat similar to the cathode ray tube of an oscilloscope, but the electron gun is replaced by a transparent photocathode. The electron beam emitted by this photocathode depends on the incident light intensity I(hv). It is accelerated and deflected by the plates d which provide the time-base. The electron beam falls on the phosphor screen where the trace appears like an oscillogram in one dimension, since there is no jy deflection. The thickness of the trace is the measurement of light intensity. 

The streak camera gives a time resolution of about 5 ps. It requires a rather complex calibration procedure since the incident light intensity appears as the thickness of trace on the screen. It is used mostly for luminescence kinetics measurements, one of its advantages being that it can record single events. 

Lewis FD, Letsinger RL, Wasielewski MR (2001) Dynamics of photoinduced charge transfer and hole transport in synthetic DNA hairpins. Acc Chem Res 34 159-170 Li Z, Cai Z, Sevilla MD (2001) Investigation of proton transfer within DNA base pair anion and cation radicals by density functional theory (DFT).J Phys Chem B 105 10115-10123 Li Z, Cai Z, Sevilla MD (2002) DFT calculations on the electron affinities of nucleic acid bases dealing with negative electron affinities. J Phys Chem A 106 1596-1603 Lillicrap SC, Fielden EM (1969) Luminescence kinetics following pulse irradiation. II. DNA. J Chem Phys 51 3503-3511... 

Figure 6.18 Transient absorption spectra, uncorrected for luminescence, observed after 532 nm excitation of a [Ru(deebpy)(bpy)2]2+-modified Ti02 film in neat CH3CN under argon. The apparent negative absorption change observed beyond 570 nm is due to emission. This part of the spectrum is included to illustrate the correspondence between absorption and luminescence kinetics. Reprinted with permission from C. A. Kelly, F. Farzad, D. W. Thompson and G. J. Meyer, Langmuir, 15, 731 (1999). Copyright (1999) American Chemical Society...

Luminescence kinetics studies of host-sensitized energy transfer in Eu -doped Cap2 crystals have also been reported and both radiative transfer and exciton diffusion have been found to contribute to the results. The diffusion distance is found to be about 25 A at low temperatures and increases by about an order of magnitude at high temperatures. Single-step electric dipole-dipole interaction also contributes to the energy transfer with the critical interaction distance calculated to be about 16 A. 

Moreover, by means of the method of luminescent-kinetic spectroscopy we have shown that Eu(III) ion in excited state forms more stable complex (up to two orders of magnitude) with sulfoxides, sulfones, ketones and amines then that in ground state. Since it is known that excitation of the europium is caused by electron transitions in the inner metal-centered 4f-states, our findings testify that f-electrons participate in the chemical bonding. 

Bioluminescence-based analytical assays were used to measure various analytes in nanoliter sample volumes. Nanoliter volumes of multiple bioluminescent analytical assays were deposited in an array format and lyophilized. ATP-firefly luciferase (FFL) and NADH-bacterial luciferase (BL) platform reactions were compared. We achieved parallel sample delivery via sample-hydrated membranes. A CCD camera measured the luminescent kinetics for each assay. These miniaturized assays and instruments can he prepared as micro-analytical systems to operate in point-of-care (POC) diagnostic devices. 

We present the results on FMN reduction using either dithiothreitol (DTT) or nicotinamide dinucleotide (NADH) to produce a steady-state luminescent kinetics in a one-enzyme system. 

Topics, which have formed the subjects of reviews this year, include the luminescence kinetics of metal complexes in solution, photochemical rearrangements of co-ordination compounds, photochromic complexes of heavy metals with diphenylthiocarbazone derivatives, the photochemistry of actinides, actinide separation processes, and light-induced electron-transfer reactions in solution and organized assemblies. A discussion has also appeared on assigning excited states in inorganic photochemistry. ... 

Luminescence Kinetics of Microcrystalline Adenine Following Pulse Irradiation... 

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