ABSTRACT
We present in this paper a comprehensive study of the migration dynamics of the charges underlying transient photoluminescence (PL) processes in poly(para-phenylene vinylene) (PPV) samples from room temperature to 13 K. In order to interpret experimental data, we have modelled the long-time PL decays (from 100 to 1000 ps) using a time function proportional to [Formula: see text] in which the parameter α is evaluated in a Monte Carlo simulation on polymeric chains. The one dimensional chains (2000 sites long) are formed by random sequences of long and short conjugated segments whose bimodal distributions have been elaborated in previous works in order to reproduce the PL band shapes and peak positions. Intra-chain and inter-chain dynamics are taken into account in the migration of the photogenerated charges from short to long conjugated segments. The statistical analysis is performed by averaging over a total of 10(6) trials for each initial conditions. The values of α have been determined for pristine PPV films and PPV composite films with single-walled carbon nanotubes. This theoretical analysis is in good agreement with experimental data and provides a coherent description for the migration of the photogenerated charges in such inhomogeneous polymeric systems.
ABSTRACT
We report in this paper experimental data on steady state and transient photoluminescence of poly-p-phenylene vinylene in the form of nanofibers prepared with a template method and converted at 110 degrees C. Results are compared to those obtained from films of different thicknesses converted at the same temperature. Data are analyzed by a model of bimodal distribution of conjugation lengths and the photoluminescence band shapes, evaluated in the framework of this model, are also presented.
ABSTRACT
We present new results of temperature dependence of photoluminescence spectra carried out on poly-p-phenylene vinylene (PPV) and on PPV composite films with single-walled carbon nanotubes. By performing studies at different temperatures (87 and 300 K), we show that a distribution of conjugated PPV segments is needed to interpret experimental data. At the microscopic scale, such a distribution corresponds to the morphological picture of poorly packed short chain segments and well-packed ordered long chain segments. Within this scheme, a new interpretation emerges for explaining the specific behavior of the photoluminescence bands. In particular, the two most intense components of the photoluminescence spectra of PPV thermally converted at 300 degrees C (2.23 and 2.43 eV at 300 K) change drastically their relative intensity when the observation temperature decreases. This effect is interpreted as due to the inhibition of charge migration to longer segments and to radiative recombination occurring mainly on n = 5 conjugated segments.
