Hole burning, softon--phonon scattering and anomalously fast dephasing of impurity electronic transitions in glasses

Solid state persistent hole burning data for impurity molecules embedded in glasses are presented which show that the pure dephasing associated with the impurity electronic transition is orders of magnitude faster than found in crystalline host media. This anomalously fast dephasing is explained in terms of a new theory which takes into account the two-level systems structure of glasses and softon--phonon scattering involving very low frequency phonons. As a result, the high temperature limit for the scattering where the dephasing frequency is linear in T occurs at temperatures of only a few Kelvin