Exciton localization

Edington M D, RIter R E and Beck W F 1996 Interexciton-state relaxation and exciton localization In allophycocyanin trimers J. Phys. Chem. 100 14 206-17... 

Such renormalization can be obtained in the framework of the small polaron theory [3]. Scoq is the energy gain of exciton localization. Let us note that the condition (20) and, therefore, Eq.(26) is correct for S 5/wo and arbitrary B/ujq for the lowest energy of the exciton polaron. So Eq.(26) can be used to evaluate the energy of a self-trapped exciton when the energy of the vibrational or lattice relaxation is much larger then the exciton bandwidth. 

To verify effectiveness of NDCPA we carried out the calculations of absorption spectra for a system of excitons locally and linearly coupled to Einstein phonons at zero temperature in cubic crystal with one molecule per unit cell (probably the simplest model of exciton-phonon system of organic crystals). Absorption spectrum is defined as an imaginary part of one-exciton Green s function taken at zero value of exciton momentum vector... 

Fig. 7.19 Influe nee of QC on the basic properties of excitons localized in Si nanocrystals. Confinement energy dependence of (a) relative strength of no-phonon and TO phonon-...

Barford W, Trembath D (2009) Exciton localization in polymers with static disorder. Phys Rev B 80 165418... 

In the spectra for PMPS and PPS, broad peaks also exist around 472 nm. The FWHM (0.21 eV) of the sharp emission peak is similar for all polysilanes. The peak wavelengths of the sharp emissions of PMPS, PPS, PNPS, and PBPS are 357 nm, 378 nm, 409 nm, and 409 nm. The origin of the broad emission peak at 472 nm is the radiative transition of excitons localized at branching points or a CT from phenyl ir -orbitals to Si a-orbitals. The spectrum of PNPS is almost the same as that of PBPS, which may be due to the energetic equivalence of biphenyl and naphtyl substituents. Although both PMPS and PPS possess a phenyl substituent, their emission peaks differ due to the fact that PMPS has a linear structure and PPS has Si-branching. The EL spectra are... 

Excitons. Localization of the excitons occurs via the process of self-trapping to produce so-called Self Trapped Excitons (STE). For a description of STE s we refer to Figure 2 in which are sketched three typical configurations for STE s in an M+X crystal. Toyozawa (L5) discusses the formation of STE s in which the electron and hole are localized concentrically (STE 1 and STE 2) or eccentrically (STE 3). In types 2 and 3 the hole is trapped on an X2 molecule and the strong coulombic repulsion between it and the trapped electron make this type of STE highly unstable. 

In Fig. 3d shown with squares is the dependence of the localized exciton quantum well width on the parameter (x) obtained in accordance with Eq. (1) and experimental A/T (x) data. For convenience, we chose the thickness of the crystal layer as a unit of the exciton localization, while solid circles do that considering the localization in the QW. 

One can say that the obtained by us experimental results upon 2D exciton localization (taking place due to the growth of the crystal dielectric permeability anisotropy parameter) with o are very close to [27] where the behaviour of polaron excitons in parabolic quantum dots were considered and shown that the dot size decrease results in increasing the exciton binding energy. 

The exciton-phonon coupling strength may be characterized by the stabilization53 S obtained when the lattice is left to relax around an exciton localized on site n. If we consider the independent variables (b-qs + b flS) as continuous, we find, with the use of the last two terms of (2.44),... 

We note that the notions optical and electrical gap are here used in the context of the classical band theory of solids and can be confusing in application to molecular (van der Waals bonded) solids, where they have the opposite meaning the optical gap reflects the energy of excitonic (localized) states, while the electrical gap stands for the lowest energy between free carrier states. 

A triplet exciton localized at such a pair would be expected to spend, on average, fifty percent of its time at the molecule which originally absorbed the exciting photon and fifty percent at the partner site. Thus, triplet-triplet annihilation involving interaction of a second exciton with this pair-trapped species will, with equal probability, produce a DF photon nearly co-1 inear with the excitation polarization or else randomly oriented with respect to it. 

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