Observation of heterogeneity in the nanosecond dynamics of a liquid

We have measured the time-integrated fluorescence of coumarin 153 in a glas s-forming solvent in order to assess the inhomogeneous linewidth as a funct ion of temperature. A maximum of this width is observed at a temperature wh ere the structural relaxation time of the solvent matches the excited state lifetime of the dye of a few nanoseconds. This feature can be explained on ly on the basis of a relaxation time dispersion which originates from a spa tial distribution of solvent response times. Therefore, liquid dynamics in the regime of nanosecond time scales are heterogeneous with respect to the structural relaxation time. (C) 2001 American Institute of Physics.