Biexcitons

PA at l. 48 eV appeal s instantaneously, shows spectral relaxation to the red, and decays on the same timescale of SE, as shown in Figure 8-9. We assign the observed PA to singlet Bu exciton transitions towards higher lying even parity (A ) states. We can speculate on the nature of this state within the proposed model. A possible candidate for the final slate is the inirachain biexciton. However, its energy level is located below the two-exciton stale by an amount equal to the bind-... 

Recently, a biexcitonic quenching mechanism has been proposed to explain the variation of scintillation intensity in liquid argon (LAr) with the LET and quality of incident radiation (Hitachi et al., 1992). According to this, quenching occurs mainly in the track core due to high-energy deposition density. This... 

This is a stepwise function that approaches unity with increasing AG , because the excited state becomes the unique reaction product when the recombination to the ground state is switched off. This function, shown in Figure 3.54, resembles the experimental results obtained in Refs. 191-193. A typical example of such data is shown in Figure 3.55. However, the plateau approached by most of the curves obtained experimentally is lower than 1. This can be an indication of some unknown channel of charge recombination or additional quenching of excitations by either the survived ions or through biexcitonic annihilation of triplets [194] (see Section XIII.C). 

The photoinduced ionization of benzophenon in acetonitrile has also been reported to proceed via triplet-triplet annihilation at very low laser pulse intensities [272], The biexcitonic ionization in this system has been studied by applying the transient photoconductivity technique and described with the conventional (Markovian) rate equations, with the time-independent rate constants [273], Such equations can be represented as follows... 

It is likely that there is only one exception to this rule given in the earliest DET [274]. There the non-Markovian kinetic equation for nonlinear (biexciton) annihilation after 8-pulse excitation was derived from first principles ... 

The first kernel represents the biexciton ionization, the second one controls the geminate recombination of charged products, and the last one governs the bimolecular recombination of separated ions. 

The experimentally detected linearity of cr(/o) dependence was imperatively attributed in the pioneering works to the biexcitonic origin of the photocurrent [266,267],... 

Figure 3.97. The Stern-Volmer constant of biexcitonic quenching at xD = 0.5 ns, D — 10 5 cm2s 1, ct = 5 A, rc = 10A, No = 0.2M, and the exponential rates of the forward and backward electron transfer with W/(a) = 500ns, W/ (cf) = 500ns and L= 1A. The dashed line shows the Markovian result, = 4.84M/ns. (From Ref. 199.)...

This is the biexcitonic analog of what we obtained for impurity quenching in Eq. (3.288). It determines the initial distribution of ions that can be obtained from Eq. (3.772), setting LR = WR = 0 ... 

Figure 3.99. The normalized distribution of ions produced by the biexcitonic ionization, according to Markovian theory (thick line) and non-Markovian UT distributions at different excitation lifetimes (dashed lines) (1)td = 1()6 ns, (2) zD — 100ns,(3)td — 10 ns. (From Ref. 275.)...

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