Proceedings Article | 27 February 2002
Hans-Heinrich Hoerhold, Hartwig Tillmann, Cornelia Bader, Elisabeth Klemm, Wolfgang Holzer, Alfons Penzkofer
KEYWORDS: Polymers, Absorption, Laser damage threshold, Luminescence, Argon, Picosecond phenomena, Solids, Spectroscopy, Pulsed laser operation, Solid state lasers
Using the methodology of traveling-wave lasing in neat films (amplified spontaneous emission, ASE) we have investigated the novel polycondensation-type MEH-PPV 1(strictly linear and fully conjugated) and some of its alternating copolymer combinations with 2,5-dialkoxy-phenylenevinylene (2-5) and thianthrene-vinylene (6-8) units. Well-defined, solution- processable, high-molecular weight samples (Mw = 20.000 - 60.000) have been prepared via the polycondensation route employing the repetitive HORNER carbonyl-olefination. This is based on the reaction of appropriate xylylene bis(phosphonates) with dialkoxy-substituted phenylene dialdehydes and dibenzoyl-thianthrene (dibenzoyl-benzene), respectively. In previous studies Thianthrene-PPVs were reported to display green EL from single layer devices while the dialkoxy-PPVs are known to display orange or red EL. Here, traveling-wave lasing studies are performed on neat films. Solution cast amorphous film samples on glass substrates are transversally pumped with picosecond laser pulses (wavelength 347 nm, duration 35 ps). Lasing occurs at 622 nm for MEH-PPV 1, 646 nm (M3EH-PPV 2), 629 nm (MEH- DOO-PPV 3), 629 nm (DMO-DO18-PPV 4), 522 nm (Thianthrene- MEH-PPV 7) and at 647 nm and 630 nm for the new M3EH-OPV containing terpolymers (DP-MEH-OPV)0,25n(M3EH-OPV)0,75n5 and (Thianthrene-MEH-OPV)o,5n(M3EH-OPV(0,5n8, respectively. The spectral widths of emission are less than 13 nm. Laser threshold energy densities are found to be rather low, ranging between 4 and 18(mu) jcm-2. The effective lengths of amplification are roughly 1 mm. These results show that all the condensation polymers under investigation are good solid-state laser materials for optically pumped disk, ring and DFB lasers and that they are potential candidates for electrically pumped lasers. Furthermore, it is demonstrated that amorphous blends of the polycondensation-type MEH-PPV 1 with the electroactive DPOP- PPV (ratio 50:50, 30:70 p. wt.) Or Thianthrene-MEH-PPV 7 (ratio 50:50, 22:78 and 5.6:94.4 p. wt.) exhibit red ASE around 590 - 615 nm as the result of energy (exciton) transfer from the green emitting donor materials to the MEH- PPV acceptors.
