Photophysical and Lasing Characterization of some Phenylenevinylene Based Polymers

摘要

Travelling-wave lasing is reported on two phenylenevinylene polymers (MEH-PPV, M3EH-PPV), two triphenylamine-vinylene-phenylenevinylene copolymers (TPA-MOP-PPV, TPA-MEH-PPV), and a ternaric condensation copolymer containing TPA-MEH-PV and M3EH-PV sub-units (TPA-MEH-M3EH-PPV). Waveguiding thin films on glass substrates are transversally pumped with picosecond lasers pulses (wavelength 347.15 nm, duration 35 ps). The laser emission occurs between 515 nm (TPA-MOP-PPV) and 646 nm (M3EH-PPV) with a spectral width between 7 nm and 13 nm. The threshold pump pulse energy densities are between 10 μJ cm~(-2) and 45 μJ cm~(-2). At high pump pulse energies a saturation of the generated amplified spontaneous emission signal is observed which is thought to be due to exciton-exciton annihilation processes. Additionally a diphenyl substituted phenylenevinylene polymer (DPOP-PPV) is investigated which shows no laser action despite high neat-film fluorescence quantum efficiency (φ_F = 0.72). Photo-induced absorption dominates over stimulated emission and hinders travelling-wave lasing. An absorption and emission spectroscopic characterization of the investigated polymers is carried out. An energy density dependent fluorescence quenching is observed and this behavior is discussed in terms of exciton-exciton annihilation processes.