Vertical recombination energy

This observed pattern of charge transfer and switching processes is consistent with the vertical-transition model (Franck-Condon principle) as discussed by Bearman et al. (1976), who interpreted the cross sections for ionic excitation in low-energy charge-transfer collision between HeJ and some diatomic neutrals. In analogy to that, in the cases of KrJ reactions, it is not the total recombination energy RE(KrJ) = 12.85 eV that is available, but only the effective recombination energy Reeff(KrJ) = 11.91 eV, which is determined, as shown in Fig. 6, by the vertical transition from KrJ to the repulsive state of JCr-Kr at the equilibrium distance f o(Kr2 ) ... 

The treatment of the time-dependent equation (4.1.23) has shown [55] that the transient kinetics is controlled by three parameters the ratio of the diffusion coefficients, D = D T2)/D T ) = exp(— a<5iyif)) (5T = T2 — T is temperature increment), oor /D and r /D. The first parameter, >, defines an increase in recombination intensity I(T2)/I(T ) (vertical scale) and thus permits us to get the hopping activation energy Ea. The parameter r /D could be found by fitting the calculated transient time to the experimentally observed one (horizontal scale). 

If there is no recombination to the triplet (kt = 0), then ions can recombine to either the ground or the excited state of the donor with the corresponding rate constants, kc(AGi) and kb(AGi). Assuming that their maximal values are the same, we represent them in Figure 3.81(a) as normalized bell-shaped curves marked by kc and kb and split by the value of the excitation energy of donor molecule, 8. At the point halfway between them should be a border vertical line. To the right of it recombination to the excited state dominates, to the left of it ions presumably recombine to the ground state. Quantitatively this statement is expressed by the %(AGi) dependence, which follows from Eq. (3.657) ... 

When one refers to the electron as being activated up to the conduction band, the vertical movement referred to is on an energy (and not a distance) scale. The subsequent horizontal movement (on a distance scale) of the positively charged hole that the electron has left in the valence band will be away from the surface, i.e., the hole will be impelled by the electric field toward the bulk and thus become physically separated from the electron that formerly occupied it. This reduces the probability of an undesirable event—the deactivation of an electron in the conduction band and its loss to the conduction band as a result of recombination with a hole. 

Figure 7.7 Excited states of the iodine molecule. Potential-energy surfaces of electronically-excited iodine molecules involved in dissociation and recombination reactions. Vertical lines indicate optical absorptions at 590 and 675 nm. Higher ionic states are not shown. See text. After Ref. [16] below.

Although micron-scale lateral phase separation has been observed in F8BT TFB blend thin films, these phase-separated domains are not pure at the submicron length scale, and a nanoscale vertical phase segregation may occur with enrichment of the lower surface energy component (TFB) at both air and substrate interfaces. Imaging of the spatial uniformity of electroluminescence emission on the microscopic scale indicates a spatially localized charge-carrier recombination in LEDs fabricated with these blends [53]. 

Figure B3.1 (a) The potential energy curves of Hg + Hg and Hg + Hg [adapted from P. Gross and M. Dantus, J. Chem. Phys. 106, 8013 (1997)]. The long-range attraction and the well (depth 370 cm ) in the ground state potential, Vg R), are hardly noticeable on the energy scale shown. The vertical asymptotic separation of the two potential curves is the resonance excitation energy of a Hg atom, corresponding to the Sq- Pi transition. When the two Hg atoms are closer, the electronic energy gap (4.89 eV for an isolated atom) is lowered due to the stronger attraction in the excited state. At the relative separation / x the iaser frequency matches the potentiai gap. In other words, the Franck-Condon "window" is where the two atoms are at the separation Rx apart. A verticai transition at Rx prepares a bound vibrationai state of the excited eiectronic state. This is known as iaser-assisted recombination, Probiem O. (b) Panei (a) drawn in the dressed states picture.

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