  Stable excitons in semiconductor monolayers such as transition-metal
dichalcogenides (TMDCs) enable and motivate fundamental research as well as the
development of room-temperature optoelectronics applications. The newly
discovered layered magnetic materials present a unique opportunity to integrate
optical functionalities with magnetism. We predict that a large class of
antiferromagnetic semiconducting monolayers of the MPX$_3$ family exhibit giant
excitonic binding energies, making them suitable platforms for magneto-optical
investigations and optospintronics applications. Indeed, our investigations,
based on first principles methods combined with an effective-model
Bethe-Salpeter solver, show that excitons in bare Neel-MnPS$_3$ are bound by
more than 1 eV, which is twice the excitonic energies in TMDCs. In addition,
the antiferromagnetic ordering of monolayer samples can be inferred indirectly
using different polarization of light.
