Amplified Spontaneous Emissions from π-Conjugated Dye Doped Polymer Film with Possible Dye Ordering

Abstract

Smooth polymer films doped with p-conjugated organic dyes, formed around a multimode silica fiber under the influence of capillary force, exhibited very narrow photoluminescence peaks upon laser excitation as compared with the fluorescence in solution. The peak position showed no dependence on the excitation wavelength, indicating that it could not be explained by a whispering gallery mode that should be observed in a medium with broad optical gain. The peaks can be explained by amplified spontaneous emissions (ASE) because the intensity depended linearly on the excitation intensity with a threshold. When the dye-doped film was formed on the portion of a fiber with the clad etched out and was excited by the linearly polarized laser propagating inside the fiber core, we observed ASE peaks not of the dyes but of the optical fiber itself, suggesting the possibility that the dyes were oriented with their transition moment pointing parallel to the film surface, therefore incapable to be photoexcited. These fiber ASE peaks shifted to longer wavelength when we varied the excitation wavelength to shorter wavelength, which clearly ruled out the possibility of silicate Raman scattering as the origin.

Amplified spontaneous emissions from π‐conjugate conductive polymer film: evanescent‐field modulation by a 1‐D photonic crystal substrate

“…This ASE peak seems to correspond to the 0-1 vibronic transition of MEH-PPV that is seen as a shoulder in the absorption spectrum, suggesting that efficient ASE was attained as the transition from an excited state down to the low populated first vibronic state of the ground level. The excitation threshold was much lower than that of a monomer dye film, where a mode selection was achieved owing to a possible dye ordering due to capillary force at the air-solution boundary during the film deposition [8].…”