Modulating non-linear optical absorption through controlled graphitization of carbon nanostructures containing Fe3C-graphite core-shell nanoparticles

Abstract

Carbonaceous materials containing Fe/Fe3C(core)-graphite(shell) nanoparticles-embedded carbon globules and carbon nanotubes are synthesized using pyrolysis. The thickness of the graphitic shell on the Fe/Fe3C nanoparticles was varied by exposing Fe-acetylacetonate and toluene precursors to different initial temperatures (reaction tube insertion temperatures) Tin. Furthermore, the thickness of the graphitic layer and the degree of graphitization along with the defect concentration in the graphitic layer was controlled by this process. A proposed mechanism for the formation of such carbonaceous nanostructures due to variation of Tin is provided. Non-linear absorption (NLA) experiments were carried out to explore the effect of graphitization and the role of defects on the laser intensity dependent NLA behaviour of these samples. We demonstrate that degree of graphitization and defect concentration in the highly graphitized layers considerably enhances the NLA behaviour of high intensity laser radiation in the material. The enhancement of NLA coefficient is mainly attributed to the excited state absorption (ESA) and free carrier absorption (FCA) processes. Our results emphasize that the reported carbonaceous materials with optimum amount of defects in the graphitized framework are attractive for optical limiting in laser safety applications.