Phonon assisted

Henderson P T, Jones D, Hampikian G, Kan Y Z and Schuster G B 1999 Long-distance charge transport in dupiex DNA the phonon-assisted poiaron-iike hopping mechanism Proc. Natl Acad. Sc/., USA 96 8353-8... 

The corresponding level broadening equals half. In fact is the diagonal kinetic coefficient characterizing the rate of phonon-assisted escape from the ground state [Ambegaokar 1987]. In harmonic approximation for the well the only nonzero matrix element is that with /= 1,K0 Q /> = <5o, where is the zero-point spread of the harmonic oscillator. For an anharmonic potential, other matrix elements contribute to (2.52). 

A simplified schematic diagram of transitions that lead to luminescence in materials containing impurides is shown in Figure 1. In process 1 an electron that has been excited well above the conduction band et e dribbles down, reaching thermal equilibrium with the lattice. This may result in phonon-assisted photon emission or, more likely, the emission of phonons only. Process 2 produces intrinsic luminescence due to direct recombination between an electron in the conduction band... 

DSP crystal, a detailed picture of the lattice motion and related displacements was constructed and related to the topochemical postulate and the mechanism of phonon assistance. Holm and Zienty (1972) have measured the quantum yield for the overall polymerization process of a,a -bis(4-acetoxy-3-methoxybenzylidene)-p-benzenediacetonitrile (AMBBA) crystals in slurries and reported it to be 0.7 on the basis of the disappearance of two double bonds ( = 1.4 if assigned on the basis of the number of double bonds consumed). 

Hopping Models Hole-Resting-Site and Phonon-Assisted Polaron Transport... 

The phonon-assisted polaron-like hopping model is unique because it is built upon an understanding of the dynamical nature of DNA in solution. The fundamental assumption of this model is that the introduction of a base radical cation into DNA will be accompanied by a consequent structural change that lowers the energy for the system. 

Fig. 7.18 The radiative recombination time r as a function of the blue shift of the photon energy AE from the bulk silicon band edge zero-phonon transitions (dots) TO phonon-assisted transitions (line). This scatter plot shows the radiative time for each member of an ensemble uniformly distributed around a cubic geometry. The top scale indicates the equivalent cube size. Redrawn from [Hy2],...

For the red luminescence band, lifetimes of about 10 to 10 6 s are expected and the recombination is most probably phonon assisted. 

F ure 5.19 The energy-level schemes of donor D and acceptor A centers for (a) resonant energy transfer and (b) phonon-assisted energy transfer. 

The processes involved are stepwise energy transfer, cooperative sensitization of luminescence and cooperative luminescence. As an example of stepwise energy transfer a system containing Er and Yb may be considered. The latter ion absorbs at 970 nm (10,300 cm ) and in phonon assisted an Er ion... 

The photoluminescence (PL) spectrum in Figure 1.7 shows a number of lines related to nitrogen-bound excitons and free excitons. SiC has an indirect bandgap, thus the exciton-related luminescence is often assisted by a phonon. Bound exciton luminescence without phonon assistance can, however, occur because conservation in momentum can be accomplished with the help of the core or the nucleus of the nitrogen atom. That is why the zero phonon lines of the nitrogen atom are seen, denoted and Q , in the spectrum but not the zero phonon line of the free exciton. 

Electrical conduction in such disordered materials proceeds by a process of phonon-assisted tunnelling in which the probability of transfer between two sites is given by... 

In discussing low temperature-dependent mobility, we should mention charge transport by polarons, an intermolecular phonon-assisted hopping process 24>25>. Polarons (charge carriers trapped in their polarization field) arise from a strong electron-phonon interaction where there is a weak overlap of wave functions of... 

Finally, we should still mention work by Makram-Ebeid and Lannoo (1982a,b) that calculates (in the adiabatic approach) the effect of an electric field in enhancing, with phonon assistance, the tunneling rate. Very good... 

The soliton conductivity model for rrans-(CH) was put forward by Kivelson [115]. It was shown that at low temperature phonon assisted electron hopping between soliton-bound states may be the dominant conduction process in a lightly doped one - dimensional Peierls system such as polyacetylene. The presence of disorder, as represented by a spatially random distribution of charged dopant molecules causes the hopping conduction pathway to be essentially three dimensional. At the photoexitation stage, mainly neutral solitons have to be formed. These solitons maintain the soliton bands. The transport processes have to be hopping ones with a highly expressed dispersive... 

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