A Streak Camera Study of Amplified Spontaneous Emission in Polyfluorene Thin Film

Abstract

ABSTRACT : We report on the photoluminescence (PL) properties of poly[2,7-(9-9-dioctylfluorene)] (PF) thin film under strong optical pumping using a streak camera system. When the excitation energy density increases -above 72 μJ·cm 2 , the emission spectrum becomes narrower and PL decay curve comes to be faster simultaneously. These behaviors are clear evidence of Amplified Spontaneous Emission (ASE) due to a waveguided Stimulated Emission in slab structure of thin film. ASE threshold of 72 μJ·cm -2 is comparable with previous reports and PF is attractive as a gain medium for plastic lasers. Since the first investigation on the electroluminescence (EL) of poly(p-phenylenevinylene), 1 semiconducting π-conjugated polymers have become more attractive materials for applications in optoelectronic devices such as light emitting diodes (LED), plastic lasers, and optical amplifiers. 2-5 Among the π-conjugated polymers, particularly a number of polyfluorene polymers and its copolymers could be promising candidates for realizing these devices due to the unique properties of good thermal and oxidative stability, good solubility in common organic solvents, excellent charge transport ability, and high photoluminescence (PL) quantum efficiency.