FeCoCr alloy-nanoparticle embedded bamboo-type carbon nanotubes for non-linear optical limiting application

We demonstrate pyrolytic synthesis of nitrogen-doped multiwalled carbon nanotubes (NCNTs) incorporated with graphite-encapsulated FeCoCr alloy nanoparticles (FeCoCr@CN sample) and report their non-linear optical absorption (NLA) behaviour. The NCNTs present in the FeCoCr@CN sample were bamboo-type with box-shaped compartments. The improved electrical conduction in NCNTs, due to high degree of graphitization associated with optimum defect-concentration in the graphitic layer covering the FeCoCr-nanoparticles and nanotube structure, provides the non-linear absorption conditions required for their application in optical limiting devices. Our results emphasize the excellent optical limiting performance of our samples which originates mainly due to excited state absorption (ESA) and free carrier absorption (FCA) processes. The defect induced modification of the electronic properties of the graphitic carbon framework (due to nitrogen-doping) culminates the enhanced ESA of the laser beam. In addition, the choice of metallic FeCoCr-alloy nanoparticles provide two fold advantage in enhancing NLA: (i) it induces high graphitization on its surface than that expected due to the individual constituent metals, thereby enhancing the ESA effect, and (ii) being metallic, it leads to NLA via FCA. Our results highlight the superior NLA performance of our FeCoCr@CN sample, making it an excellent choice for its direct industrial use as laser shields. (C) 2020 Elsevier B.V. All rights reserved.