Electro-absorption spectra of degenerate charge transfer states

Exciton Electro-Absorption at Non-Zero Wave Vector

“…The results of Ref. [4] indicate that the actual CT contributions need not have second-derivative shape. On the other hand, the eigenstates of Frenkel parentage, having now some CT character, may acquire considerable second-dervative admixtures.…”

“…Therefore, in the present context, (1) the degeneracies (crucial in EA spectroscopy [3,4]) had to be handled with special care, and (2) the "primarily Frenkel" or "primarily CT" character could not be arbitrarily attributed to the eigenstates.…”

“…As their contributions to the observed electroabsorption spectrum are weighted by vibronic effects, the above results highlight the importance of these effects in the context of EA spectroscopy. Accordingly, there is little hope that the description of EA spectra that , has focused so far on the purely electronic aspects of the problem [7,8,[3][4][5], may produce quantitatively correct results, especially in the energy region where vibronic replicas dominate. Either we have to reduce our expectations as to the agreement of the reproduced spectra with experiment, or a reasonably complete vibronic description has to be developed.…”

“…It was shown later [4] that the relevant states need not be exactly degenerate, and that it is the spectral width of the bands (usually substantial) that sets the energy scale according to which the states should be considered as quasi-degenerate. This allows many states, both Frenkel and CT, from various regions of the Brillouin zone, to be EA-active.…”

Charge-transfer interactions—their manifestations in electroabsorption spectra

“…(7), the lower eigenstate undergoes a red shift and the upper eigenstate undergoes a blue shift of equal size. According to the argument of the preceding section, the two eigenstates give rise to firstderivative signals: one simple, one inverted [6].…”