| Optical limiting is an important application of nonlinear optics, useful for the protection of human eyes, optical elements and optical sensors from intense laser pulses. An optical limiter is such a device that strongly attenuates high intensity light and potentially damaging light such as focused laser beams, whilst allowing for the high transmission of ambient light. Preparation of the required nonlinear optical active materials for practical optical limiters, however, still presents a significant chemical challenge. As an important broadband optical limiting material, carbon nanotubes (CNTs), which exhibit the unique structural characterisitcs, outstanding mechanical and electrical properties, and rich chemical reactivity as well, have stimulated extensive research activities across the world. Like other carbon materials such as graphene and carbon black, CNTs are insoluble in any organic solvents. It's thus very interesting to design and synthesize CNT-based solution-processed organic/polymeric materials, which is the key issue for the development of CNT-based molecular optoelectronic and photonic devices. For these reasons, we designed and synthesized two kinds of novel and highly soluble CNT-based optical limiting functional materials. This thesis was divided into three parts, as follows:The synthesis, chemical modifications and optical limiting performance of CNTs and their derivatives were reviewed in Chapter 1.In Chapter 2, the poly(N-vinylcarbazole)-grafted MWNTs (MWNT-PVK) hybrid materials were synthesized in the presence of S-1-Dodecyl-S'-(α,α'-dimethyl-α"-acetic acid) trithiocarbonate (DDAT)-covalently functionalized multiwalled carbon nanotubes (MWNT-DDAT) as reversible addition-fragmentation chain transfer (RAFT) agent. Incorporation of the PVK moieties onto the MWNTs surface can considerably improve the solubility and processability of MWNTs. For all MWNT-PVK hybrid materials, they are soluble in some common organic solvents such as toluene, THF, chloroform, DMF and others. In contrast to the UV/Vis spectrum of DDAT-PVK, which was synthesized by use of DDAT as RAFT agent under the same synthetic condition, in the visible region, the absorption spectrum of MWNT-PVK exhibited a typical electronic absorption characteristics of solubilized carbon nanotubes, in which the absorbance decreases gradually in the range of 350 to 600 nm. At the same level of linear transmission the MWNT-PVK with 79.2% PVK moieties in the material structure possesses best optical limiting performance in comparison with the other MWNT-PVK composites, MWNTs and C60. The significant nonlinear optical responses manifest the MWNT-PVK materials suitable candidate for viable optical limiting devices. Light scattering, originating from the thermal-induced micro-plasmas and/or micro-bubbles, is responsible for the optical limiting.In Chapter 3, a soluble polyhedral oligomeric silsesquioxane (POSS) functionalized multi-walled carbon nanotube (MWNT) hybrid material (MWNT-POSS) was synthesized, in which the POSS content was estimated to be 44wt.%. This material exhibits a remarkable optical limiting performance for nanosecond laser pulses at 532 nm. Thermally-induced nonlinear scattering is the primary mechanism for the nonlinear optical response. This behaviour demonstrates that the MWNT-POSS hybrid material is a suitable candidate for viable optical limiting devices. |
