Ultrafast Nonlinear-Optical Response of Inorganic-Organic Self-Organized Quantum-Well Materials

点击翻译按钮获取中文摘要

We have performed linear and nonlinear spectroscopy on the following inorganic-organic perovskites : (C_6H_<13>NH_3)_2PbI_4 with monolayer inorganic sheets composed of PbI_6 octahedra, (C_6H_<13>NH_3)_2(CH_3NH_3)Pb_3I_<10> with trilayer inorganic sheets, (C_6H_<13>NH_3)_2(CH_3NH_3)_2Pb_3I_<10> with trilayer inorganic sheets, and (CH_3NH_3)PbI_3 with infinite inorganic sheets (i.e., three-dimensional perovskite).1. Size Effects on Bandgaps and Excitonic PropertiesWe have performed magnetooptical absorption measurements on the four compound, and determined Bohr radius and binding energies of excitons and bandgap energies. With decreasing well layer thickness, the bandgap and the binding energy are drastically increased and the Bohr radius is decreased correspondingly. Although this size dependence can basically be understood as a result of the quantum confinement effect based on the effective mass approximation, tight binding models based on the molecular excitation picture seems to be m … More ore appropriate for compounds with thin well layers.2. Exciton-Resonant Ultrafast Nonlinear SpectroscopyWe have performed four-wave mixing experiments on the exciton resonance region of (C_6H_<13>NH_3)_2PbI_4 and (C_6H_<13>NH_3)_2(CH_3NH_3)Pb_2I_7 using an OPA based on a Ti : Sapphire laser (pulse width-100 fs). x^<(3)>(omega ; omega, -omega, omega) of (C_6H_<13>NH_3)_2PbI_4 reaches 1.6 x lO^<-6>esu at the exciton resonance, and T_2=0.2 ps and T_1=7 ps. x^<(3)> of (C_6H_<13>NH_3)_2(CH_3NH_3)Pb_2I_7 have been found to be smaller than that of (C_6H_<13>NH_3)_2PbI_4 by about an order of magnitude, and T_2 be of the same order as that in (C_6H_<13>NH_3)_2PbL_4.3. Two-Photon Resonant SpectroscopyWe have performed spectrally-resolved four-wave mixing experiments on (C_6H_<13>NH_3)_2PbI_4 and (C_6H_<13>NH_3)_<2-> (CH_3NH_3)Pb_2I_<7->. The spectra obtained have suggested that the two-exciton states in these compounds are composed of stabilized biexciton states and weakly-bound two-exciton states. Moreover, we have observed twophoton resonant hyper Raman signal in (C_6H_<13>NH_3)_2PbI_4, for the first time. Detailed experiments are now underway in order to clarify the two-photon resonant states in this unique system. Less