Nonlinear optical properties of carbon nanotube hybrids in polymer dispersions

A series of double-walled carbon nanotubes (DWNTs) and multi-walled nanotubes (MWNTs) functionalized with selected organic chromophores, fluorescein 5(6)-isothiocyanate (FITC), rhodamine B isothiocyanate (RITC) and fullerene (C60) were synthesized by covalently linking these electron-donor groups to the metallic nanotubes. These versatile carbon nanotube composites show remarkable nonlinear optical (NLO) performance, due to a merged effect of the complementary NLO characteristics of the moieties of the composites. The hybrids were characterized by UV–vis spectroscopy and Raman spectroscopy. Evidence suggests charge transfer species are formed between the chromophores and the nanotubes. The optical limiting performance of the DWNT, MWNT hybrids and carbon NanoBuds is found to be superior to that of single-walled nanotubes. Thermally induced light scattering from nanotube moieties is the primary mechanism dominating the NLO response. Reverse saturable absorption from fullerene moieties makes a significant contribution to the NLO response of fullerene containing hybrids and NanoBuds. Photoinduced charge transfer from the fullerenes or the organic chromophores (FITC and RITC) to nanotubes followed by absorption in the charge separated excited state may enhance the nonlinear absorption, thus an effective optical limiting response.