Nonlinear Optical Effects And Nonlinear Mechanisms Of Graphene Materials And Their Hybrid Gel Glasses

The widely use of laser and the related technology has caused series of social and military security issues. The optical limiting (OL) materials based on the nonlinear optical (NLO) theory are the most used limiters, which are sensitive to both the laser intensity and the laser wavelength. Graphene, as the new emerging carbon-based nanomaterials, has attracted significant interests and becomes the research hotspot because of the unique electronic band structure and photoelectric properties. Graphene oxide materials with different dimensionality have different electronic band structure, which strongly affects the photoelectric properties. Therefore, it is of great significance to investigate the NLO and OL properties of graphene oxide materials with different dimensionality. However, up to now, most of the NLO and OL studies of graphene were carried out in solvents, in which agglomerations form easily. Based on this, the immobilization of graphene materials is very important.In this paper, graphene oxide materials with different dimensionality, including two dimensional graphene oxide nanosheets (GONSs), one dimensional graphene oxide nanoribbons (GONRs) and zero dimensional graphene quantum dots (GQDs) were prepared. In order to investigate the relationship between the NLO properties of GONRs and the unzipped level of carbon nanotubes (CNTs), partial unzipped carbon nanotubes (PUCNTs) were prepared. The immobilization of graphene oxide materials was achieved by preparing hybrid glasses using sol-gel process. The NLO and OL behaviors and the related nonlinear mechanisms of samples were investigated using ns and ps open-aperture Z-scan technology. The influence of the morphology and matrix on the NLO and OL properties was discussed in detail.The main results were as follows:(1) the band gaps of graphene oxide materials with different dimensionality were produced in the sequence: GONRs>GONSs>GQDs. The NLO and OL effects of graphene suspensions were arisen from nonlinear scattering (NLS) and nonlinear absorption (NLA). Furthermore, the morphology-and laser pulse-dependent NLO and OL behaviors were discovered:in ns laser pulse, the GONRs showed the most prominent OL properties as the strong NLS and two-photon absorption; in ps laser pulse, the GONSs behaved the strongest saturated absorption effect. From the results, it can be deduced that the influence of morphology on the NLO properties would also happened in other kinds of materials, and therefore we provided a good idea to design new OL materials. (2) The agglomeration of graphene materials in aqueous phase was prevented by introducing them into, organically modified SiO2 gel glasses. The hybrid glasses performed high linear transmission and good thermostability. The NLO and OL properties of graphene materials were enhanced in glass matrix as a result of enhanced NLA and nonlinear refraction. This reseach provides a good idea for the immobilization and devices design of graphene materials, and therefore promoted the application in the NLO field. (3) GONRs showed similar NLO properties to CNTs and PUCNTs. NLS was the main nonlinear mechanism. Their hybrid gel glasses were more suitable for the NLO applications as they showed better NLO effects and thermostability compared with GONSs and GQDs hybrid gel glasses.