Influence of dielectric confinement on excitonic nonlinearity in inorganic-organic layered semiconductors

We have investigated photoinduced spectral changes of excitons in inorganic-organic layered semiconductors, (C6 H5 C2 H4 NH3) 2 Pb I4 (PhE- PbI4) and (C6 H13 NH3) 2 PbI4 (C6- PbI4), by means of the subpicosecond pump-probe spectroscopy. The two semiconductors consist of the same inorganic layers and different organic layers. In the two substances, the blueshift and the bleaching of the exciton are observed. It is found that both of the blueshift and the bleaching are considerably stronger in C6- PbI4 than in PhE- PbI4. The weight of the blueshift relative to the bleaching is larger in PhE- PbI4 than in C6- PbI4. These differences are qualitatively explained in terms of the stronger dielectric confinement in C6- PbI4 than in PhE- PbI4 due to the lower dielectric constant of the organic layers in C6- PbI4 than in PhE- PbI4. Delay time dependences of the blueshift and the bleaching and their polarization dependences are understood as being due to the exciton relaxation in the angular momentum space with rates of 2.7 and 4.1 ps-1 for PhE- PbI4 and C6- PbI4, respectively.