Photoexcitation dynamics in polyfluorene-based thin films: Energy transfer and amplified spontaneous emission

Abstract

The dynamics of photoexcitations in thin films based on the polymer poly(9,9-dioctylfluorene) is investigated by a combination of stationary spectroscopy, femtosecond absorption and time-resolved fluorescence measurements. Excitation energy transfer to keto defects within the polyfluorene host matrix and to guest molecules in a dye doped host/guest system is observed and modeled by rate equations. Characteristic parameters for the exciton dynamics are extracted. At high excitation densities, amplified spontaneous emission from the edge of the films arises accompanied by strongly nonexponential signal decay in transient absorption. The underlying coupled excited-state and photon dynamics in the films are included in the model, which describes the measured data consistently for various excitation densities.