Low-threshold blue lasing in epitaxially grown para-sexiphenyl nanofibers

Random laser action and amplified spontaneous emission are observed near 425 nm in self-assembled parasexiphenyl nanofibers following subpicosecond optical pumping. The threshold excitation fluence (photoexcited density) is as low as 0.5 mu J/cm(2) (6 x 10(16) cm(-3)). The high degree of material crystallinity results in a very large singlet-singlet annihilation rate of approximate to 10(-7) cm(3)/s. In stationary conditions, assuming a standard singlet-to-triplet density ratio of 0.3 and bimolecular recombination as the only density-dependent loss mechanism, the equivalent current density necessary for lasing threshold is estimated to be as low as 3 kA/cm(2). The experimental findings suggest that such highly ordered molecular nanoaggregates have great potential as blue-emitting devices for integrated photonic applications. (c) 2004 Elsevier B.V. All rights reserved.