Theory of nonlinear optical response of excitons in solidC60

Time-resolved photoelectron spectroscopy of low-energy excitations of 4×4 C60/Cu(111)

“…For example, the 5-fold degenerate HOMO and the 3-fold degenerate LUMO allow to create 15 singly excited states. Suitable linear combinations lead to a 3-fold (triplet) F 1g , a 3-fold (triplet) F 2g , a 4-fold G g and a 5-fold H g degenerate eigenvector of the symmetry matrices (3 + 3 + 4 + 5 = 5 · 3) [24,25]. Hara and coworkers [26] calculated that the eigenvalues of F 1g and the F 2g are lower than the eigenvalues of G g and H g .…”

Frenkel and charge-transfer excitons inC60

“…Additionally, it also provides an important test quantity regarding the applicability of different theoretical approaches to describe these electronic excitations. Theoretical predictions for the multiplet width spanning a wide range from 150 meV to 600 meV have been reported [9,11,12]. Furthermore, the nature of the energetically higher lying excitations that are observed as absorption maxima at about 2.4 eV and 2.7 eV is still under discussion.…”

“…While there exist several studies of the low energy components and their excitation energies [7,8], the energy of the highest lying 1 H g excitation and thus the total width of the multiplet have not been experimentally determined yet, although it has important consequences for the understanding of optical properties such as e.g. second or third harmonic generation (SHG, THG) [9,10]. Additionally, it also provides an important test quantity regarding the applicability of different theoretical approaches to describe these electronic excitations.…”

“…Furthermore, the nature of the energetically higher lying excitations that are observed as absorption maxima at about 2.4 eV and 2.7 eV is still under discussion. From a number of experiments both have been controversially assigned to either Frenkel excitons (on-ball) or charge transfer excitons [9,[13][14][15][16][17][18].…”

Difference frequency Fermi resonance interface modes in organic multilayer structures

“…Rather intense electric dipole forbidden second-harmonic generation at a fundamental photon energy of 1.8 eV in C 60 is attributed to resonance enhanced molecular transitions of equal energy from the ground state to an intermediate excited state (magnetic dipole allowed) and from the intermediate state to a final excited state (electric dipole allowed) that then necessarily has an electric dipole allowed transition back to the ground state [10]. It would be interesting to try to match the energy difference between these two excitations to that in another molecular material.…”