Frenkel Exciton Model of Low Temperature Photoluminescence in ?-PTCDA Single Crystals

Abstract

PACS: 71.35.Aa; 78.55.Kz Dedicated to Professor Dr. Roland Zimmermann on the occasion of his 60th birthdayRecent studies of the recombination dynamics in a-PTCDA (3, 4, 9, 10 perylene tetracarboxylic dianhydride) with time-resolved photoluminescence (PL) techniques in the 100 ns range have revealed six distinct PL contributions. In the present work, we demonstrate that the PL channel dominating at low temperature (T ¼ 11 K) can be assigned to recombination from an indirect minimum of the dispersion of Frenkel excitons. The approach used is a straightforward extension of previous calculations applied to the linear optical properties of this prototypic molecular semiconductor.

Charge-transfer interactions—their manifestations in electroabsorption spectra

“…Hitherto, complete theoretical reconstitution of experimental EA signals has been achieved for polyacenes [8], fullerene [9], PTCDA [18] (where some controversies still exist [19,20]), for the sexithiophene single crystal [21] and sexithiophene film [12] (where the alternative interpretational paradigm [13,14] has been proposed and illustrated on a phenomenological model, but never supported by microscopic calculations). In spite of the difficulties (mostly of technical nature) in parametrizing the microscopic Hamiltonians, the good agreement between the calculated and experimental spectra lends support to the conceptual picture outlined in this paper.…”

Influence of exciton transfer on the optical cycle of α-PTCDA

“…From the minima of the excited state potentials, the observed low-energy CT band with /E PL S ¼ 1:67 eV can be assigned to the anion-cation stack, whereas the excimer PL band with /E PL S ¼ 1:72 eV dominating at high temperatures can be [3] and PL [10,17] line shapes (dashed lines) with the experimental absorption coefficient of polycrystalline thin films [5] and the dominating PL band at low temperature [6] (solid lines). The absorption of dissolved PTCDA molecules [18] is shown for comparison (short-dashed line).…”

“…Based on the calculated dispersion, a realistic thermalization scenario for the Frenkel excitons is depicted in Fig. 3 together with the optical cycle [17].…”

“…2 and the largest subband of the Frenkel exciton PL in Fig. 1 can be reproduced quantitatively [10,17], cf. Fig.…”

Frenkel exciton model of electron energy loss spectroscopy in -PTCDA

“…As shown previously, a microscopic model including the elongation of an effective internal mode and the transfer of neutral molecular excitations can account for the anisotropy of the dielectric tensor [21,22], the excitonic dispersion, and the dominating low-temperature PL band and its radiative lifetime [23,24]. The aim of the present work is to extend this Frenkel exciton approach to electron energy loss spectroscopy (EELS).…”