  A novel material consisting of a monolayer of C$_{60}$ buckyballs with
hexagonal symmetry has recently been observed experimentally, named
graphullerene. In this study, we present a comprehensive \textit{ab-initio}
theoretical analysis of the electronic and optical properties of both pristine
and impurity-engineered monolayer graphullerene using spin-dependent density
functional theory (spin-DFT). Our findings reveal that graphullerene is a
direct band gap semiconductor with a band gap of approximately 1.5 eV at the
$\Gamma$ point, agreeing well with experimental data. Notably, we demonstrate
that by adding impurities, in particular substitutional nitrogen,
substitutional boron, or adsorbent hydrogen, to graphullerene results in the
formation of spin-dependent deep donor and deep acceptor levels, thereby giving
rise to a variety of half-semiconductors. All the impurities exhibit a magnetic
moment of approximately $\mu_B$ per impurity. This impurity engineering enables
the tuning of spin-polarized exciton properties in graphullerene, with
spin-dependent band gap energies ranging from 0.43 eV ($\lambda \sim$ 2.9
$\mu$m) to 1.5 eV ($\lambda \sim$ 820 nm), covering the near-infrared (NIR) and
short-wavelength infrared (SWIR) regimes. Our results suggest that both
pristine and impurity-engineered graphullerene have significant potential for
the development of carbon-based 2D semiconductor spintronic and opto-spintronic
devices.
