Amplified spontaneous emission spectra of poly(9,9-dioctylfluorenyl-2,7-diyl) under pulsed laser excitation

• Spectral and ASE from conjugated polymers PFO and PDHF.
• Effect of the solvents and concentrations on the spectral and ASE of PFO and PDHF.
• Three ASE peaks are attributed from monomeric, excimeric and dimeric states.
• ASE from PFO was compared with PDHF.
• PDHF and PFO have good photochemical stability.

Photophysical parameters such as absorption, fluorescence spectra, stokes’ shift, fluorescence quantum yield and amplified spontaneous emission (ASE) of a soluble conducting polymer poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) were measured in different solvents. The absorption spectra of PFO in tetrahydrofuran (THF) have shown two bands at 390 and 437 nm. The results showed that the optical density of the band 437 nm increased by increasing the concentration. This is a strong indication that PFO in solution aggregates at higher concentrations. On the other hand, at lower concentrations, the fluorescence spectra of PFO in THF have shown three bands; 422 (dominant), 445 (shoulder) and 470 nm (hump). For the higher concentrations, the band at 422 nm totally vanished while the band 470 nm became a dominant. Therefore, the band at 470 nm could be attributed to the dimer state. The ASE action was tested in a transverse pumping configuration where the conducting polymer was pumped by laser pulses from the third harmonic of an Nd:YAG laser (355 nm). It could be seen that there were three ASE peaks at 425, 450 and 475 nm. The spectral and ASE properties of PFO were compared with the conjugated polymer poly[9,9-di-(2′-ethylhexyl)fluorenyl-2,7-diyl] (PDHF) under the same operating conditions. The most important features are: (1) the ASE intensity and the photochemical stability of PDHF were remarkably high compared with PFO, (2) PFO has an ASE action even under low concentrations (3) and the ASE emission from PFO is tunable in the wavelength region between 425, 450 and 475 nm.