  This study investigates the electronic band structure of Chromium Sulfur
Bromide (CrSBr) through comprehensive photoluminescence (PL) characterization.
We clearly identify low-temperature optical transitions between two closely
adjacent conduction-band states and two different valence-band states. The
analysis of the PL data robustly unveils energy splittings, bandgaps and
excitonic transitions across different thicknesses of CrSBr, ranging from
monolayer to bulk. Temperature-dependent PL measurements elucidate the
stability of the band splitting below the N\'eel temperature, suggesting that
magnons coupled with excitons are responsible for the symmetry breaking and
brightening of the transitions from the secondary conduction band minimum
(CBM2) to the global valence band maximum (VBM1). Collectively, these results
not only reveal band splitting in both the conduction and valence bands, but
also point to an intricate interplay between the optical, electronic and
magnetic properties of antiferromagnetic two-dimensional van der Waals
crystals.
