The energy levels of the configurations fd and f13d in cubic crystal fields have been calculated as a function of the f- and d-electron crystal-field parameters. The results are used to explain the spectrum of Yb++ in SrCl2. Both the calculated energies and calculated intensities agree well with experiment.

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Poly­(3-hexylthiophene) (P3HT) is a well-studied benchmark system for semiconducting polymers used in optoelectronic devices. In these materials, aggregation can improve charge transport efficiency or enhance emission yields depending on the interchain packing. This may be inferred from the absorption and emission spectra when analyzed using exciton coupling models such as the well-known H- and J-coupling model of Kasha. The more recently developed weakly coupled H-aggregate (WCH) model quantifies the degree of disorder via the ratio of the electronic origin intensity to that of the first vibronic band. Here, the underlying assumptions of this approach are tested experimentally for P3HT aggregates formed by solvent poisoning using bulk and single-molecule-based spectroscopic techniques. Specifically, we show that the contribution of residual monomeric chains to the aggregate spectrum must be accounted for to properly assign the spectra as H- or J-type. A modification of the WCH model is introduced to account for multiple emissive species.