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

Femtosecond time-resolved photoluminescence spectroscopy is used to study t he 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 ra nge can be described by the summation of two exponential functions. Analysi s of the spectral dependence of the time constants extracted from these fit s 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 transi tions correspond to processes in which two, one, or zero phonons are excite d in the host polymer during the emission event. By separating out these th ree contributions, it is determined that the effective lifetime of the inho mogeneously broadened excitons increases monotonically from 980 fs at 280 m eV above the peak in the density of states (DOS), to 114 ps near the peak i n the DOS. (C) 2001 American Institute of Physics.