The two-dimensional nature of monolayer transition metal dichalcogenides (TMDs) significantly enhances Coulomb interactions of exciton pairs, leading to large exciton binding energies and strong spin-orbit coupling at the direct band gap. This creates new opportunities for excitonic devices and fundamental studies, particularly in exploring correlated phases like exciton superfluids. Additionally, excitons in monolayer TMDs exhibit a valley pseudo-spin linked to charge carrier momentum, which can be manipulated optically, presenting potential applications in information technology. The functionalities of TMDs are further enhanced by artificially stacked heterostructures, such as heterobilayers, which can host interlayer excitons with extended lifetimes. To establish TMD structures as platforms for exciton physics, we utilize optical spectroscopy to investigate excitons in monolayer TMDs and their heterostructures. Our initial findings highlight the significant impact of surface effects on these atomically thin materials, particularly regarding charge carrier density modifications. We demonstrate a photogating effect driven by charge transfer from environmental molecules, which can be diminished by light exposure. We also explore charge carrier density control via field effect devices, revealing a strong Fröhlich exciton-phonon interaction that can be suppressed by electron doping. Finally, we conduct a detailed photoluminescen
