We report a study on the optical properties of thelayered polymorph of vacancy-ordered triple perovskite Cs3Bi2Br9. Theelectronic structure, determined from density functional theorycalculations, shows the top of the valence band and bottom of theconduction band minima are, unusually, dominated by Bi s and p states,respectively. This produces a sharp exciton peak in the absorptionspectra with a binding energy that was approximated to be 940 meV,which is substantially stronger than values found in other halideperovskites and, instead, more closely reflects values seen in alkalihalide crystals. This large binding energy is indicative of a strongly localized character and results in a highly structured emissionat room temperature as the exciton couples to vibrations in the lattice.