Optical properties and structural phase transitions of lead‐halide based inorganic–organic 3D and 2D perovskite semiconductors under high pressure

Optical absorption, photoluminescence and Raman scattering of lead‐halide based inorganic–organic perovskite semiconductors were measured under quasi‐hydrostatic pressure at room temperature. For the 3D perovskite semiconductor, (CH 3 NH 3 )PbBr 3 , the free exciton photoluminescence band exhibits red‐shifts with pressure, and jumps to a higher energy by 0.07 eV at 0.8 GPa, which is associated with a phase transition from a cubic to an orthorhombic structure confirmed by Raman scattering. Above the phase transition pressure, the exciton band shows blue‐shifts with further increasing pressure, and eventually disappears above 4.7 GPa. The results are compared with those for the 2D perovskite semiconductor, (C 4 H 9 NH 3 ) 2 PbI 4 . First principles pseudopotential calculations were performed to investigate changes in octahedral distortion and electronic band structures with pressure. The calculations have explained the origins of the intriguing changes in the electronic states with pressure in view of bonding characters between atomic orbitals in octahedra. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)