High-Sensitivity Ultrafast Spectroscopy of Exciton Dynamics in Nanomaterials

The development of next-generation optoelectronic devices is dependent upon the understanding of light-matter interactions of low-dimensional materials. Semimetals, semiconductors, and insulators comprise the family of these materials and many have been extensively studied for their robust optical properties. Understanding the fluence-dependent photophysics of nanomaterials helps to characterize their intrinsic behavior and nonlinear interactions in the presence of light. However, a comprehensive transient study of these materials perturbed with ultra-low excitation densities remains unexplored. This thesis presents the nature of several van der Waals materials, novel Dion-Jacobson perovskites, and singlet fission nanocapsules in low absorbed carrier density environments. Highly sensitive ultrafast, broadband, transient spectroscopy and photoluminescence spectroscopy are employed to probe the fluence dependence of exciton dynamics. The responses after sufficiently low pump fluence includes the crossover regime from net interband transitions in graphene, suppressed energy transfer in DJ perovskites, and fission of excitons in WSe2. The results of this work will largely impact the design and functionality of photodetectors, solar cells, and optical transistors.