Optical dephasing and homogeneous optical bands in crystals and amorphous solids: Dynamic and stochastic approaches

Impurity spectroscopy in glasses and disordered crystals: Inhomogeneous broadening and electron phonon coupling

“…Most dephasing studies deal with broadening, rather than shift, since the latter is complicated by thermal expansion. Quadratic EPC theories treat both the shift and the broadening from common grounds [11,12,[24][25][26]. According to the nonperturbative quadratic EPC theory [11,12], weak interaction with a single harmonic pseudolocal mode results in the following homogeneous width G h (in frequency units):…”

“…In particular, the local phonons occurring as side bands seem to be responsible for dephasing, at least in the T interval between 1 and 20 K, and, moreover, the same coupling constant has been used to describe both the shift and broadening. The nonperturbative quadratic EPC theory yields the following expression for line shift n T , resulting from a weak interaction with a single harmonic pseudolocal mode with frequency o g [11,12]:…”

“…Quadratic EPC constant W characterizes the difference in the curvatures of potential energy surfaces for a (pseudo)local vibration. W depends on harmonic frequencies in the S 0 (o g ) and S 1 states (o à ) as [11,12]:…”

“…Because of the advanced theory [11,12] and a number of convincing experiments in selected systems, such as porphine/C 8 [25], 1,2,5,6-dibenzopyrene/C 8 [23], pentacene/naphthalene, pentacene/p-terphenyl [26], etc., quadratic EPC appears to be well understood. In particular, the local phonons occurring as side bands seem to be responsible for dephasing, at least in the T interval between 1 and 20 K, and, moreover, the same coupling constant has been used to describe both the shift and broadening.…”

“…The complexity of spectral transformations in the condensed phase is a result of interplay between static displacements of electronic energy levels, giving rise to solvent shifts and inhomogeneous broadening, and, on the other hand, the linear and quadratic electron-phonon coupling (EPC) processes. The theories of these phenomena have reached a reasonably high level of sophistication [6][7][8][9][10][11][12], but unifying concepts still seem to be missing.…”