Effects of Organic Moieties on Luminescence Properties of Organic–Inorganic Layered Perovskite-Type Compounds

The effects of organic moieties on the luminescence properties of organic–inorganic layered perovskite-type compounds were investigated. Three single crystals were fabricated, namely, (C4H9NH3)2PbBr4 {C4}, (C6H5CH2NH3)2PbBr4 {Ben}, and (C6H5C2H4NH3)2PbBr4 {Phe}. Among the single crystals, the exciton emission of Phe showed the highest quantum efficiencies. The quantum efficiencies of C4 and Ben only were 0.02 and 0.17 times that of Phe, respectively. The radiative and nonradiative decay rates were calculated from the quantum efficiencies and luminescence lifetimes. The relative values of the quantum efficiencies were in accordance with the values of the radiative decay rates. The results indicate that the luminescence properties of the organic–inorganic hybrid compounds may be governed by the excitonic properties of the inorganic layer and not by the concentration of any structural defects. Focusing on the geometry of the inorganic layers, the Pb–Br–Pb bond angles between the adjoining PbBr6 2– octahedra of each compound were 150° (Ben), 152° (Phe), and 155° (C4). In addition, only Phe showed structural distortion inside the PbBr6 2– octahedron with Br–Pb–Br bond angles of 171°. The increase in the radiative decay rate can be attributed to the increase in the reduced mass of the excitons from these structural distortions that lead to a decrease in the Bohr radius of the excitons. The results indicate that the luminescence properties of the organic–inorganic hybrid compounds are governed by the structural geometry of the inorganic layer.