Optical response of conjugated polymers excited at high intensity

The realisation of optically pumped lasing devices using poly(p-phenylenevi nylene) has intensified interest in the optical response of conjugated poly mers on ultra-short time-scales and at high optical injection density. We d escribe an investigation of these properties using time-resolved and time-i ntegrated techniques. We demonstrate the importance of exciton-exciton anni hilation at high injection densities and present evidence that this process produces photo-induced absorption (PA) through the generation of charges. We present a model which accounts for PA from both photoexcited singlet exc itons and the charge pairs; generated by annihilation. This model describes the time-evolution of the PA well and indicates that, in the presence-of e xciton-exciton annihilation, dissimilar stimulated emission and PA dynamics are consistent with a high quantum yield of excitons as deduced from PL li fetime and efficiency studies.