High temperature optical dephasing mechanism for dye molecules in PMMA glass

Picosecond photon echo experiments on rhodamine B and octadecyl rhodamine B in a PMMA matrix between 1.0 and 12.5 K are compared. The two dyes have identical first electronic excited state transitions but different masses and moments of inertia. Echo decay times are identical and individual decays at the same temperature from the two systems are superimposable. The high-temperature echo data can be fit to an activated process with an energy of 15 cm−1. We conclude that in this glassy matrix, high-temperature dephasing is caused by a mode of the host and not a mode of the guest as has been suggested for glasses and is common in crystals.