Laser action in polydialkylfluorene films:: Influence of low-temperature thermal treatment

We have used a variety of optical probes to investigate the changes occurring upon low-temperature thermal treatment to the emissive properties of dialkyl substituted polyfluorene thin films. We found that the low-temperature-driven morphological changes involving aggregates formation, which are observed in the absorption and photoluminescence spectra at low excitation intensities, give rise at high excitation intensities to laser action in the blue spectral range. In some cases, switching between two stimulated emission bands was also observed. (C) 1999 American Institute of Physics. [S0003-6951(99)02412-2].