of the 0D polyhedral connectivity. The strongly-bound nature of these excitons is further demonstrated by the band contributions ("fatband plot") shown in Fig. , where the delocalization of the exciton wavefunctions in reciprocal space for the Ti compounds corresponds to real space localization of the exciton wavepacket. The large Stokes shifts (∼0.5 eV) and broad PL emission observed for this family of materials in both this and other studies is another characteristic result of localized bound excitons, as well as strong exciton-phonon coupling and low-energy dark excitons, with the photogenerated electron-hole pair readily localizing within the lattice to yield emissive self-trapped exciton (STE) states.