Optical and field emission investigations for multiwalled carbon nanotubes with different functionalized groups

UV-vis absorption, luminescence and field emission properties have been studied in pristine multiwalled carbon nanotubes (MWNTs) and MWNTs with different functionalized groups, i.e., MWNT attached with the carboxylic and hydroxyl group (s-MWNT), MWNT attached with dodecylamine (MWNT-CONHC12H25) and MWNT attached with polyaniline (s-MWNT doped PANI). Redshift in the absorption spectra and blue shift in photoluminescence with the increase of volume of the functional group on the surface of the MWNTs were observed. Soluble MWNTs and long alkyl grafted MWNTs are luminescent compared with pristine MWNTs, while in the polyaniline wrapped MWNTs, luminescence is quenched. The electron emission properties of these carbon nanotube films are highly dependent on the physical parameters of carbon nanotubes and the nanotube content of their films. s-MWNT films exhibit the most excellent field emission characteristics among all samples due to the cleanliness of s-MWNT samples and partially due to the structural defects on s-MWNT tips as well as the optimum tip density.