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The large extent of the singlet exciton in poly (phenylene vinylene) (PPV) and the small Stokes shift suggest an effective-mass calculation for determining the exciton binding energy E₁. We have carried out such a calculation using the electron and hole masses determined by a local-density-functional band-structure calculation. The resulting E₁ is 0. 4 eV, which leads to a gap of 2. 8 eV rather than the usually accepted 2. 4 eV.
Costa et al. (Thu,) studied this question.