Abstract
In this work, the spectral and amplified spontaneous emission (ASE) properties of a conjugated polymer poly [9, 9-di-(2′-ethylhexyl) fluorenyl-2, 7-diyl] (PDHF) in tetrahydrofuran (THF) have been studied. Our results showed that the absorption spectra of PDHF in THF have only one peak under wide range of concentrations (0.012mol/m3 to 0.39mol/m3), it could be seen that the shape of the absorption did not change; this indicates no dimer formation in these solutions for all concentrations mentioned above. On the other hand, the fluorescence spectra of PDHF in THF, at low concentration, showed two peaks, the primary at 415nm and the secondary at 435nm. The effects of concentration and the temperature on PDHF in THF under same conditions were studied. For example, the intensity of the peak at 435nm became increasingly stronger for higher concentration and lower temperature. These are analogs to the excimeric behavior of organic molecules. Under high power pulsed laser excitation, we observed ASE at 418nm and 437nm. These ASE peaks could arise from the monomer and excimer states of the macromolecule respectively. The ASE spectra of PDHF were compared with the rhodamine 6G (Rh 6G). The most important and distinguishing features are that PDHF has a two times better photochemical stability than rhodamine 6G and high optical gain compared with the conventional laser dyes.
•Excimer behavior of a conjugated polymer PDHF under low concentrations.•PDHF under sufficient concentration and pump power excitation showed dual ASE.•The first peak due to monomer and second peak due to excimer.•PDHF has better photochemical stability under high power excitation.