  Even the best quality 2D materials have non-negligible concentrations of
vacancies and impurities. It is critical to understand and quantify how defects
change intrinsic properties, and use this knowledge to generate functionality.
This challenge can be addressed by employing many-body perturbation theory to
obtain the optical absorption spectra of defected transition metal
dichalcogenides. Herein metal vacancies, which are largely unreported, show a
larger set of polarized exitons than chalcogenide vacancies, introducing
localized excitons in the sub-optical-gap region, whose wave functions and
spectra make them good candidates as quantum emitters. Despite the strong
interaction with substitutional defects, the spin texture and pristine exciton
energies are preserved, enabling grafting and patterning in optical detectors,
as the full optical-gap region remains available. A redistribution of excitonic
weight between the A and B excitons is visible in both cases and may allow the
quantification of the defect concentration. This work establishes excitonic
signatures to characterize defects in 2D materials and highlights vacancies as
qubit candidates for quantum computing.
