Preparation and Broadband Optical Limiting Performance of Reduced Graphene Oxide Covalently Functionalized with Poly(N-vinylcarbazole)

Graphene shows ultrafast carrier relaxation dynamics and ultra-broadband resonate nonlinear optical (NLO) response due to its extended π-conjugate system and the linear dispersion relation holding for its electronic band structure. In comparison with graphene, functionalized graphene derivatives would be expected to show more excellent NLO and optical limiting (OL) performance. By using as-synthesized graphene carbanions as initiator in the anionic polymerization, poly(N-vinylcarbazole)-covalently functionalized reduced graphene oxide (RGO) derivative (RGO-PVK) was in situ synthesized. RGO-PVK was characterized by infrared spectroscopy, X-ray electron spectroscopy and UV-Vis absorption spectroscopy. This soluble material was embedded into an optically nonactive transparent polymethylmethlacrylate (PMMA) matrix to produce the PMMA-based RGO-PVK film. The NLO and OL properties of RGO, RGO-PVK, and annealed RGO-PVK films under 532 nm and 1 064 nm laser irradiation were also investigated using the open-aperture Z-scan technique.The results show that in contrast to RGO, the covalent grafting of PVK chains to the RGO surface significantly improve NLO and broadband OL performance of the resultant material. Upon excitation with laser light, the achieved nonlinear coefficients and OL thresholds of the annealed RGO-PVK/PMMA film are 306.17 cm/GW and 0.37 GW/cm² at 532 nm, and 350.32 cm/GW and 0.31 GW/cm² at 1 064 nm, respectively. These findings would make it suitable for protecting the human eyes, optical sensors and optoelectronic devices from the laser beam in the visible and near-infrared spectral region.