Bulg. J. Phys. vol.33 no.s3 (2006), pp. 143-150

Vibronics of Mixed Frenkel and Charge-Transfer Excitons

I.J. Lalov, I. Zhelyazkov
Faculty of Physics, University of Sofia, BG-1164 Sofia, Bulgaria
Abstract. The vibronic spectra (exciton + one quantum of intramolecular vibration) of a molecular chain (like stacks in Me-PTCDI and PTCDA crystals) are studied in the case of strong mixing of a Frenkel exciton (FE) and charge-transfer excitons (CTEs). The mechanisms governing the vibronic spectra are the linear and quadratic exciton-phonon coupling. The positions, maximal values and integral intensity of the linear absorption peaks corresponding to the bound and unbound (many-particle) states have been calculated using FE and CTEs's parameters of the Me-PTCDI crystal. The calculated spectra show: (i) the relative spectral separation of the vibronics of CTEs and FE; (ii) a bigger integral intensity of the many-particle states in the case of weak exciton-phonon coupling; (iii) the dominant role of the bound states in the case of intermediate and strong exciton-phonon coupling.

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