Highly photoluminescent conjugated polymers: stimulated emission and device applications

Abstract

The recent emergence of semiconducting (pi) -conjugated polymers as solid-state laser materials has been made possible by the availability of numerous high photoluminescence efficiency polymers with emission wavelengths spanning the visible spectrum. As the first important step in exploring the feasibility of electrically pumped polymer laser diodes, we have demonstrated photopumped gain narrowing in submicron thick films, neat and undiluted, of photoluminescent conjugated polymers. The dramatic collapse of the emission line width (to as little as 7 nm) occurs at very low pump energy thresholds (approximately 10 (mu) J/cm2 per 10 ns pulse). Gain narrowing is found in over a dozen different polymers representing a variety of molecular structures and is explained in terms of amplified spontaneous emission in planar waveguides which allow the distance traveled by emitted photons to exceed the short intrinsic gain lengths. The short gain lengths arise from the high density of chromophores, the large density of states associated with the (pi) -(pi) * transition in quasi-one-dimensional systems, and the Stokes shift which minimizes self- absorption. Prospects for producing electrically pumped solid-state polymer diode lasers using this class of materials are discussed in the context of the low-threshold gain narrowing in submicron thick films.