Exciton hopping

If an exciton hops about, starting from some initial site and ends up at another site at the time of its disappearance for one reason or another, the linear distance between these sites is called the diffusion length, lA. The diffusion length is related to the diffusion coefficient D through the exciton lifetime t ... 

Dias FB, Maiti M, Hintschich SI, Monkman AP (2005) Intramolecular fluorescence quenching in luminescent copolymers containing fluorenone and fluorene units A direct measurement of intrachain exciton hopping rate. J Chem Phys 122(5) 054904... 

Dias FB, Knaapila M, Monkman AP, Burrows HD (2006) Fast and slow time regimes of fluorescence quenching in conjugated polyfluorene-fluorenone random copolymers The role of exciton hopping and dexter transfer along the polymer backbone. Macromolecules 39(4) 1598—1606... 

Such a mechanism would be consistent with the absence of reaction by a two-photon absorption process, because such a process does not produce excitons in high concentration and, therefore, reduce blexcitonic process. The temperature effect is simply a manifestation of reduced exciton hopping at lower temperature. 

Figure 1. One-exciton band (energy vs wave vector) for a 15-srte lattice described by the Hamiltonian in Eq. (1), with only nearest-neighbor exciton hopping, 7, and constant intermolecular spacing, r = 1. Left and right panels refer to negative and positive 7, respectively. The arrows mark one-photon absorption and emission processes. The emission process for 7 > 0 is forbidden...

Disordered systems likely to show dispersive exciton hopping. 

Exciton hopping to the same chromophore and using equi-energetic states depend on dipole-dipole orientation and the interaction distance, Rq-... 

Figure4.4 Illustration of singlet exciton transfer in a polymer film with an inhomogeneously broadened density of states. The exciton hops quickly on the timescale of a few picoseconds until it reaches a quasiequilibrium level in the bottom section of the...

Wasielewski and coworkers demonstrated that ultrafast energy transfer can take place in ZnPc-perylenediimide (PDI)-based jr-stacked aggregates. Tetra-PDI-substituted ZnPc 1 self-assembles in solution forming stacked hep-tamers, as evidenced by SAXS/WAXS, and forms long fibrous structures in the solid state (Figure 1). Selective excitation of the PDl component results in ultrafast energy transfer (1.3 ps) from the stacked peripheral PDl chro-mophores to the central ZnPc stack. Subsequently, exciton hopping between the ZnPc units occurs in the femtosecond timescale. 

Recent work by Venikouas and Powell (1977) has provided a more quantitative insight in the energy transfer processes in YVOr-Eu . At low temperatures there is only acting an (inefficient) one-step transfer process from vanadate to Eu . Transfer within the vanadate host lattice is unimportant. At higher temperatures, however, thermally activated exciton hopping occurs yielding an efficient Eu phosphor at room temperature. Activator-induced host traps play an important role in the transfer process to the Eu ion. 

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