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

我们对下列无机-有机钙钛矿进行了线性和非线性光谱研究：(C_6H_&lt；13&gt；NH_3)_2PbI_4由PbI_6八面体组成的单层无机片，具有三层无机片的(C_6H_&lt；13&gt；NH_3)_2(CH_3NH_3)Pb_3I_&lt；10&gt；，(C_6H_&lt；13&gt；NH_3)_2(CH_3NH_3)_2Pb_3I_&lt；10&gt；具有三层无机层的PbI_3和具有无限无机层(即三维钙钛矿)的(CH_3NH_3)PbI_3。尺寸效应对带隙和激子性质的影响我们对这四种化合物进行了磁光吸收测量，并测定了激子的玻尔半径、结合能和带隙能。随着势垒层厚度的减小，禁带宽度和束缚能急剧增加，玻尔半径相应减小。尽管这种尺寸依赖关系基本上可以理解为基于有效质量近似的量子限制效应的结果，但基于分子激发图的紧束缚模型似乎是m…矿石更适合于具有较薄井层的化合物。激子共振超快非线性光谱我们用钛宝石激光器(脉宽-100飞秒)的OPA对(C_6H_&lt；13&gt；NH_3)_2PbI_4和(C_6H_&lt；13&gt；NH_3)_2(CH_3NH_3)Pb2I_7的激子共振区进行了四波混频实验。在激子共振下，(C_6H_&lt；13&gt；NH_3)_2PbI_4的X^&lt；(3)&gt；(omega；omega，-omega，omega)达到1.6xLo^&lt；-6&gt；esu，T_2=0.2ps，T_1=7ps。(C_6H_&lt；13&gt；NH_3)_2(CH_3NH_3)Pb2I_7的X^&lt；(3)&gt；比(C_6H_&lt；13&gt；NH_3)_2PbI_4小约一个数量级，T_2与(C_6H_&lt；13&gt；NH_3)_2PbL_4.3相同。我们对(C_6H_&lt；13&gt；NH_3)_2PbI_4和(C_6H_&lt；13&gt；NH_3)_2-&gt；(CH_3NH_3)Pb2I_&lt；7-&gt；进行了光谱分辨四波混频实验。所得光谱表明，这些化合物中的双激子态由稳定的双激子态和弱束缚双激子态组成。此外，我们还首次在(C_6H_&lt；13&gt；NH_3)_2PbI_4晶体中观察到了双光子共振超拉曼信号。为了弄清这一独特系统中的双光子共振态，目前正在进行详细的实验。较少

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