Spectroscopy of Molecular Excitons

High pressure effects on the photoluminescence intensity of sexithiophene single crystals

“…With increasing temperature, the ®ne structure broadens and the contribution to the PL spectrum from aggregates decreases. At 300 K, this thermal de-trapping gives rise to a purely excitonic recombination to the phonon band of the ground electronic state involving the internal CC stretching mode of 181 meV [19]. A similar temperature behavior has been recently reported for a thin ®lm of T6 [20].…”

“…4. The shift of all the luminescence features at low and high temperatures is similar, indicating that radiative traps are related to the same excitonic band [19]. The decrease of the intermolecular distance (high pressure) enhances the exciton transfer rate between chains.…”

Influence of Solvents on Protolytic and Aggregation Properties of Aminomethylated Calix[4]resorcine

“…[23,24] With the reduction of the substance concentration in ethanol ( These multiplets are observed in molecules containing more than one molecule in the unit cell. [25] This fact indicates that the flow of association processes of L molecules with increasing concentrations of EtOH; a similar pattern is also observed in Me 2 CO at C L = 5•10 -3 М (Figure 4.I-1). It should be noted that the absorption at the region of 200-300 nm in EtOH, H 2 O and Me 2 CO is influenced by solvents, and at the region of 300-350 nm in Me 2 CO the influence of solvents is also observed.…”

Hidden symmetry and magnetospectroscopy of quantum wells near filling factorν=2

“…However, the most spectacular consequence of this mixing is intensity borrowing that manifests itself as a nonlinear dependence of the intensities of the doublet components on the concentrations of the species; for excitons in binary alloys this nonlinearity is usually rather strong. 48 Exciton-trion doublets in absorption spectra of QW's have been observed in a number of papers, so it is natural to expect a similar behavior of intensities if the ME's are free. The proper way to investigate this effect would be to measure the ME spectra as a function of e at fixed B ͓thus keeping E C (B) and U(B) unchanged͔: such a measurement is possible in mixed-type QW's.…”

“…We describe the electron-ME attraction by a pseudo-potential U(B)Ͻ0, and, for 0Ͻ e Ͻ1, we divide all space into occupied ͑by an electron͒ and empty ''lattice sites'' with concentrations e and 1Ϫ e , respectively. Application of the mean-field theory of binary alloys 48 to this problem suggests that the exciton spectra of the mixed crystal should consist of doublets whose components can be assigned to the specific species constituting the alloy. Note, however, that excitons are collective excitations and, therefore, each exciton state involves both species, the degree of mixing being dependent on the ratio of the exciton bandwidth to the chemical shift ͓the corresponding ratio in our problem is E C (B) to U(B)].…”