Energy dependence of electronic energy relaxation in poly(p-phenylenevinylene)

Femtosecond time-resolved photoluminescence spectroscopy is used to study the dynamics of optical emission from poly(p-phenylenevinylene) at 77 K over an energy range of 2.19-2.37 eV. All of the decay curves in this energy range can be described by the summation of two exponential functions. Analysis of the spectral dependence of the time constants extracted from these fits indicates that the transient photoluminescence at any given wavelength is due in general to the superposition of three transitions emanating from a single set of inhomogeneously broadened excitons. The three distinct transitions correspond to processes in which two, one, or zero phonons are excited in the host polymer during the emission event. By separating out these three contributions, it is determined that the effective lifetime of the inhomogeneously broadened excitons increases monotonically from 980 fs at 280 meV above the peak in the density of states (DOS), to 114 ps near the peak in the DOS. (C) 2001 American Institute of Physics.