Luminescence decay constants

Horrocks, W. de W. Jr. Sudnick, D. R. Lanthanide ion probes of structure in biology. Laser-induced luminescence decay constants provide a direct measure of the number of metal-coordinated water molecules. J. Am. Chem. Soc. 1979,101(2), 334-340. 

Fig. 7.37. Plots of lanthanide ion luminescence decay constants, k (ms 1), vs. mole fraction of H2O (/h->o) ln HtO-DtO mixtures for Eu(III) and Tb(III). The number of coordinated H20 s, n, for the indicated complexes is given on the right-hand ordinates aquo ions ( ) NTA complexes (pH 6.0) (O) EDTA (1 1) complexes (pH 6.0) (V) EDTA (2 1) complexes (pH 7.5) (A) 11231.

From the lifetimes of the excited states of dilute solutions of Eu3+ and Tb3+ in H2O and D2O the number of coordinated water molecules can be obtained. A typical plot of the lanthanide ion luminescence decay constant against mole fraction of water in H2O-D2O mixtures is shown in Fig. 7.37. The observed decay constant, k0bs is comprised of... 

In hydration studies, the relation of knjo to the number of water molecules in the primary coordination sphere of the lanthanide is usually calibrated with a series of solid compounds of known hydrate structure, e.g. crystalline Eu and Tb compounds in which n varies from zero to nine isolated from H2O and from D2O solutions. The results of lifetime studies for crystalline hydrates reported by Horrocks and Sudnick (1979) are listed in table 2. For crystals with n = 0, all the measured k values were identical whether prepared from H2O or from D2O solution. This confirms that only O-H oscillators directly bound to the metal ion can significantly affect the luminescence decay constants. 

Luminescence decay constants for and Tb crystalline hydrates and the number (n) of water... 

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))... 

If the 4f5d levels are situated at still lower energy, no 5d->-4f emission is observable. In stead emission from the Pq level occurs. Weber 48) has studied in Y3Al50i2-Pr3+ the nonradiative decay from the luminescent 4f5d level of Pr3+ to the Po,i,2 and i/e level. For temperatures below 250 K the decay time of the 5d - 4/ luminescence is constant and amounts to about 2.10 sec (as is to... 

Figure 41 (A) Rate constants for Ru(bpy)2+ luminescence decay versus concentration...

Several years later Schanze and Cabana reported a study of the distance dependence of photoinduced ET in a second series of oligo-proline bridged dyads (51a-c, Scheme 22 and Table 4) [126,127]. In this study the authors were able to study photoinduced ET in CH3OH, a solvent that is demonstrated to stabilize the extended conformation of the proline spacers [126]. Rate constants for forward ET in 51a-c are determined by using luminescence decay techniques, and an overall distance dependence of 3 = 1.0 A 1 is obtained from the rate data (Table 4). By... 

In absorption spectrometry, <7i is usually fairly constant, and x1 fitting has no advantages. Typical examples of data with nonconstant and known standard deviations are encountered in emission spectroscopy, particularly if photon counting techniques are employed, which are used for the analysis of very fast luminescence decays [27], In such cases, measurement errors follow a Poisson distribution instead... 

Europium(III) exchanged zeolites have been studied by a number of research groups. Arakawa and coworkers (20, 21 ) report the luminescence properties of europium(III)-exchanged zeolite Y. Emission spectra were measured under a variety of conditions and bands for europium(II) were observed after thermal treatment of the europium(III) Y zeolites. A mechanism was proposed for the thermal splitting of water which involved the cycling of europium between the two different oxidation states. Europium MSssbauer experiments (22 ) also show that on thermal treatment of europium-(III) zeolites that europium(II) is formed. Stucky and coworkers (23, 24) studied the phosphorescence lifetime of these europium-(lll) zeolites and showed that the inverse of the lifetime (the decay constant) was linearly related to the number of water molecules surrounding the europium(III) ion in the zeolite supercages. These studies involved zeolites A, X, Y and ZSM-5. 

One of the characteristic features of the luminescence in a-Si H is the broad distribution of recombination times. Fig. 8.14 shows the luminescence decay extending from 10" s to 10 s (Tsang and Street 1979). The data are inverted in the lower part of the figure to give the distribution of lifetimes, which has its peak at 10" -10" s at low temperature and is 2-3 orders of magnitude wide. The shape of the distribution is sensitive to the excitation intensity for reasons discussed shortly and the time constants are even longer at very low intensity. 

Cs2ZrCl6. A series of sharp transitions are observed that reflect the undistorted octahedral nature of these excited states. Excitation into these features produces the upconversion luminescence spectrum shown in Fig. 19 a. The 10 K excitation scan of this luminescence is compared to the absorption spectrum in Fig. 19b. The upconversion excitation scan closely follows the absorption profile over the full energy range. This observation leads to the conclusion that at 10 K the dominant mechanism for upconversion in 2.5% Re + Cs2ZrCl6 under these conditions is GSA/ETU. Time-dependent measurements confirm this conclusion (Fig. 19 a, inset), showing the characteristic delayed maximum and a 10 K decay constant (/Cdec = 1400 s ) approximately two times that of the excited... 

The parent complex, cls-IrCl9(phen) , has an essentially pure MLCT emitting level. The decay constants of this state are similar to those of the MLCT emitting states of the bipy series. The luminescent state of IrCl2(5,6-dlmethylphen)2 , however, has almost complete IL character. As expected for ligand localized transitions, the radiative and nonradlative rate constants of this state are much smaller than those of the MLCT emitting states in the bipy system (Table 9). The emitting levels of the other substituted phen complexes are proposed to have fairly equal contributions from the zero-order IL and MLCT states (194). 

FIGURE 10. Calculated splittings and component decay constants of the luminescent excited state of ruthenocene (53). 

Investigations of Ru(tpy)2 (tpy = 2.2 6.2"-tcrpyridinc) luminescence quenching by Fe(OH2)6 in aqueous acidic glasses have produced a distance decay constant of 1.59 0.05 4., 20,85 substantially larger than those... 

Figure 6. Plot of the first-order constant for Ojf Aj) IR luminescence decay in benzene as a function of the concentrations of DABCO ( ) and DABCO-2HI2(A).

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