Relative importance of delocalized and pseudolocalized lattice vibrations in impurity vibron relaxation

The novel dependence of the fluorescence spectrum of tetracene in p-terphenyl on the pseudolocalized vibrations produced by absorption is examined in detail. The results together with the fluorescence spectra obtained by selective excitation of the tetracene zero-phonon vibration bands are used to determine the importance of pseudolocalized vibrations in impurity vibron relaxation. Relative to the system delocalized phonons they are found to be unimportant. This result is interpreted in terms of the wave packet nature of pseudolocalized vibrations, electron-phonon coupling, and the system anharmonicity.