Effective radiative lifetime

The first example of hyperfine predissociation appears simultaneously with gyroscopic predissociation in the I2 B3no+ state (Broyer, et al., 1976). The predissociation due to gyroscopic coupling is very small in this particular case. Taking its effect into account, a residual effective radiative lifetime (nonzero for J = 0) has been found that shows a strong variation with v. This is actually a... 

TABLE III. Effective Radiative Lifetimes for Homonuclear Associative Ionization in Helium and Argon... 

The averaged results (for three series of experiments) for radiative lifetime x, effective radiative lifetime Xeff and a total lifetime (including non-Mossbauer radiation and electron conversion decay) equal... 

Rh(bpyL3+ is an example of a complex that exhibits an almost pure n-n phosphorescence and demonstrates one of the limitations of nearly pure ligand localized emissions. At 77K, the complex is highly emissive with a beautifully structured blue ligand phosphorescence (Amax = 446 nmfor the first peak) having at in the tens of msec,(17) but it has no detectable room temperature emission. It is this very long radiative lifetime that causes the absence of room temperature emission. The radiative decay is so slow that it cannot compete effectively against inter- and intramolecular radiationless decay at room temperature. 

Radiative lifetime of triplets. Biochemical effects Neutralization time for media at very high viscosity. Time for mitosis. Biochemical effects of metastables. DNA synthesis time Biological effects Late biological effects... 

As described in Chapter 3, the products of some chemical reactions are initially produced in electronically excited states. If the excited state has a sufficiently short radiative lifetime, it will emit light faster than collisional quenching by air molecules can occur (see Problem 1). The effective concentration of the emitting species (and hence emitted light intensity) is proportional to the concentrations of the reactants. As a result, the chemiluminescence intensity can be used to monitor one of the reactants if the second reactant is kept at a constant (excess) concentration. 

At high viscosities or low temperatures, dielectric relaxation time xj may be larger than the mean radiative lifetime t/ of the molecule. This may decrease the O—O separation between absorption and emission. On the other hand, at high temperatures solvent relaxation may be promoted thermally decreasing xd and O—O separation may again decrease. A maximum value for Av (O—O) is expected at some intermediate temperatures. Besides the relaxation effects, the O—O separation can also be affected by environmental modification of the potential energy surfaces. 

This alkalilike behavior of metastable noble-gas atoms effectively transforms the excitation energy of the metastable noble-gas atom into electronic energy of a rare-gas halide molecule with large reaction cross section. Because the electronically excited noble-gas halides have short radiative lifetimes and the ground-state noble-gas halides are not strongly bound, the process of formation of electronically excited noble-gas halides from metastable noble-gas atoms has been shown to be ideal for the operation of the electronic transition laser and has been successfully used in high-efficiency rare-gas halide lasers in recent years.21"23... 

Whether the singlet is a (n, jr ) state or an ( , it ) state can be established from solvent effect. A blue shift in polar solvent suggests an (n, 7i ) state, a red shift a (tc, tc ) state. A rough guess can be made from the radiative lifetime for fluorescence which is of the order of 10-5 s for biacetyl. Hence, it appears that the lowest excited singlet is an Sx (n, n ) state. From dilute solution value of f, we find that only 1 % of the initially excited molecules are capable of emission with a rate constant 1 x 105 s-1 == 1/t . Therefore 99% of the molecules must be transferred to the triplet state, assuming S S do not occur. The rate constant for... 

It is difficult to assess the effect of non-coordinated heteroatoms on emission efficiency because of the lack of quantum yield information. One compound, [Ru(bpym)3]2+ shows an interesting anomaly. Hunziker and Ludi reported an emission quantum yield of 0.0915) in aqueous solution while Rillema et al.27 reported 0.011 in propylenecarbonate. The radiative lifetimes estimated from the data of these two reports are very different... 

Regarding the latter issue, it has to be noticed that for the phosphorescence decay of isolated ligands, the values for rr may be in the ms to sec time range or longer [16]. For the complexes, the heavy atom effect may cause singlet-triplet mixing to an extent that a formal 3LC level exhibits tr as short as tenths of xs [1]. Consistent with this, we shall see later that radiative lifetimes for 3LC emitters of the Ir(III)-polyimine family are tr 50 xs or larger (kt 0.2 x 105 s-1 or smaller, Eq. 2). 

In a second step, Shen and Bray (1998a) studied the changes of the 5Do and 5Di lifetimes of SrFCl Sm2+ and CaFCl Sm2+ under pressure. In both systems they observed an exponential decrease as shown in fig. 13 for the case of the 5Do lifetime at room temperature. According to their analysis of the temperature effects, the measured lifetime of the 5Do 7Fo transition represents an almost pure radiative lifetime. A strong decrease under pressure therefore indicates an increase in the radiative rate Wj. This in turn was attributed to an increased elec-... 

Spontaneous emission and radiative lifetime of lanthanide excited state in condensed phases is determined by the electromagnetic field and the index of refraction as shown in eq. (3). In nanocrystals, spontaneous emission of photons is influenced by two mechanisms (1) the non-solid medium surrounding the nanoparticles that changes the effective index of refraction thus influences the radiative lifetime (Meltzer et al., 1999 Schniepp and Sandoghdar, 2002), (2) size-dependent spontaneous emission rate due to interferences (Schniepp and Sandoghdar, 2002). 

The dependence of radiative lifetime on the index of refraction, n, arises from the change in the density of states for photons in the medium of reduced light velocity and the modification of the polarizability of the surrounding medium. Since the nanoparticles occupy only a small fraction of the total volume, in order to compare the experimental results with eq. (3) it is necessary to introduce an effective index of refraction for the medium, eff, which consists of... 

---