  n this study, we utilize a rigorous ab initio-based finite momentum
Bethe-Salpeter equation to investigate the photoluminescence emission in
two-dimensional hexagonal tungsten carbide (h-WC). This thermodynamically
stable monolayer exhibits an indirect optical gap, resulting in phonon-assisted
emission. We observe that light absorption is a direct process centered around
the direct quasiparticle gap, while light emission is indirect and requires
modes between $\Gamma$-$M$ in the phonon dispersion. The emission lines feature
prominent phonon replicas at cryogenic temperatures, particularly near-infrared
wavelengths (1.09 and 1.17 eV), and we observe exciton thermalization with the
crystal beyond 25 K. Additionally, non-radiative recombination is a remarkably
fast process, occurring at order of a few femtoseconds (4.8 fs at 0 K and 2.8
fs at 300 K) compared to radiative recombination (2.3 ps at 0 K and 214 ns at
300 K). These optical characteristics of 2D h-WC may facilitate the promise of
photon-emitter devices for near-infrared signal communication.
