Direct observation of excitons in polymer/carbon nanotube composites at room temperature: The influence of nanotube concentration

In this work, we have employed spectroscopic ellipsometry technique to study the optical properties of polymer/carbon nanotube (CN) composites as a function of nanotube concentration. Using a two-layer structural model based on Airy rigorous equations, the optical constants in various CN concentrations have been extracted. In the optical absorption spectra, we have observed a tuning of the excitonic transitions with the addition of single wall CN concentration. Based on theoretical calculations for the interaction of CNs with the surrounding effective media, the spectral evolution of the binding energy of optically active excitonic transitions with the addition of CNs suggests that the effective dielectric function of surrounding media decreases. Furthermore, using an oscillator Lorentz model, the absorption peaks, oscillator strengths and energy broadenings of the excitonic transitions have been extracted. (C) 2008 Elsevier B.V. All rights reserved.