Excitons in two-dimensional layered perovskite compounds: (C6H5C2H4NH3)2Pb(Br,I)4 and (C6H5C2H4NH3)2Pb(Cl,Br)4

Exciton properties of microcrystalline (C6H5C2H4NH3)2Pb(BrxI4−x) and (C6H5C2H4NH3)2Pb(ClxBr4−x) films were investigated. The halogen ion replacement made it possible to shift the exciton absorption and photoluminescence bands continuously towards green-blue-violet regions. Blue shift in these bands could be explained by the valence band structure composed with the np orbital of halogens and 6s orbital of lead. The degree of hybridization of halogen (np) orbital into Pb (6s) orbital could be determined the band gap of mixed crystals. In the mixed crystals, the types of photoluminescence turned to self-trapped exciton process from free exciton emission due to the lattice distortion.