Excitons singlet Frenkel

Frenkel excitons in the standing film and, in the lying film, by short-range inter molecular annihilation of singlet excitons highly mobile between adjacent PHP molecules (Rc 0.8 nm). A fit to the experimental data (from Eq. 5) yields (3 = 10.8 x 108 s-1 and yrio = 1-3 x 1010 s values close to those determined from Eq. 11 (see Fig. 12). 

Another type of quasiparticle is the exciton, a neutral excitation well known in semiconductors, where it often dominates the onset of electronic optical absorption. Frenkel excitons, either singlet (spin 0) or triplet (spin 1), are... 

A useful measure for exciton migration is the diffusion length L = (Dto)1/2. Experimental data show that for Frenkel excitons in molecular crystals at room temperature the diffusion coefficient D 10 3 cm2/s and the lifetime of singlet excitons to 10 8s. This gives a typical diffusion length L 10 6cm (for anthracene crystals L 5 10 6cm). 

When the bandwidth is large these will be Wannier, when it is small these will be Frenkel excitons. The excitons can be of singlet and of triplet character. The latter species can be observed in ESR. ... 

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