Temperature dependence of the stimulated emission in a conjugated polymer

Summary form only given. With their combined light-emission and electronic transport functionality, PPV and its derivatives are currently investigated for various applications including light-emitting diodes and lasers. Although, the report of stimulated emission in a variety of conjugated polymers was followed rapidly by the demonstration of different optically pumped laser structures, the demonstration of an electrically injected solid-state polymer laser remains a difficult task because of the high current densities needed. Lasing in new materials is often first demonstrated at low temperatures where steeper carrier distribution functions and increased quantum efficiency facilitate population inversion. In close analogy to organic laser dyes, the gain mechanism in conjugated polymers can be described in terms of a four level system with inversion being established between the lowest unoccupied electronic state and vibronic levels of the ground state. The lasing threshold in four level systems depends strongly on the final state occupation, its value should decrease exponentially with temperature. Thus, the temperature effect on the lasing threshold is expected to be large. To check the validity of this model we performed measurements of photoluminescence and stimulated emission in films of poly(2,5-bis(2´-ethylhexyloxy)-1,4-phenylene-vinylene (BEH:PPV) in the temperature range of 15 to 300 K.