Optical Properties of Layered Perovskite Materials with Natural Quantum-Well Structure

本文研究了新型层状钙钛矿材料（C_<10>H_<21>NH_3）_2PbI_4（简称C_<10>PbI_4）及其相关化合物的性质，重点研究了其光学性质。发现了一些非常有趣的现象，这些现象被认为是源于这些材料的二维特性，包括C_<10>PbI_4的三阶非线性光学系数的测定；其峰值估计为0.7 X10^<-9>esu，与众所周知的一维材料聚二乙炔的峰值相当。研究了C_<10>PbI_4在70 ~ -40ºC温度范围内的晶体结构。确定了三种结构相变。详细研究了C_<10>PbI_4的吸收光谱、反射光谱和发光光谱。由激子引起的最低能量跃迁在0‰左右发生相变。C_<10>PbI_4在…More中的电吸收研究表明激子具有很强的二维特征，其结合能可能高达590 meV.4。C_<10>PbI_4的磁吸收光谱被提高到高达40 t的磁场，法拉第组态的反磁位移产生360 meV的激子结合能。在Voigt结构中没有观察到峰移，可能是由于激子的二维限制。在波长范围为1.77 ~ 1.50 μ m的C_<10>PbI_4上观测到光学三次谐波的产生。λ = 1.53mum时chi^<(3)>的最大值为0.7X10^<-9>esu，与激子跃迁发生三光子共振。已观察到C_<10>PbI_4的光导电性。激子解离产生的载流子被认为在[PbI_4]层内传输。这可能是第一次在严格的二维结构中观察载流子输运。研究了C_<10>PbI_4的光学性质。由于该化合物在室温以下不发生相变，因此在低温下表现出激子特征，比C_<10>PbI_4更好地分辨。以上结果表明，具有天然量子阱结构的钙钛矿材料C_<10>PbI_4是一种理想的二维物质。由于这种二维结构，在其电学和光学性质中观察到很强的各向异性。进一步研究这种化合物和其他相关化合物的计划正在进行中，重点是它们的非线性光学和激子动力学。少

Properties of new layered perovskite materials, especially (C_<10>H_<21>NH_3)_2PbI_4 (abbreviated to C_<10>PbI_4) and related compounds, have been studied with emphasis placed on their optical properties. Some very interesting phenomena, which are believed to stem from the two-dimensional character of these materials, have been found, including the determination of the third-order nonlinear optical coefficient of C_<10>PbI_4 ; its peak value is estimated to be 0.7 X10^<-9>esu, which is as large as those of polydiacetylenes, well-known one-dimensional materials.1. The crystal structure of C_<10>PbI_4 has been analyzed over a temperature range of 70ﾟC to -40ﾟC. Three structural phase transitions have been identified.2. Optical properties, including absorption, reflection and luminescence spectra, of C_<10>PbI_4 have been studied in detail. The lowest-energy transition due to excitons shifts appreciably around 0ﾟC upon a phase transition.3. The electro-absorption studies of C_<10>PbI_4 in … More dicate a very strong two-dimensional character of the exciton, its binding energy being possibly as large as 590 meV.4. Magneto-absorption spectra of C_<10>PbI_4 have been taken up to magnetic fields as high as 40 T. Diamagnetic shifts in the Faraday configuration yield an exciton binding energy of 360 meV. No peak shifts are observed in the Voigt configuration, probably owing to the two-dimensional confinement of the exciton.5. Optical third-harmonic generation has been observed on C_<10>PbI_4 over the wavelength range 1.77-1.50mum. The largest value of chi^<(3)> is 0.7X10^<-9>esu for lambda= 1.53mum, which is three-photon resonant with the exciton transition.6. Photo-conductivity of C_<10>PbI_4 has been observed. Carriers generated by exciton dissociation are believed to be transported within the [PbI_4] layers. This is probably the first observation of carrier transport in strictly two-dimensional structures.7. Optical properties of C_<10>PbI_4 are being studied. Since this compound does not undergo phase transitions below room temperature, it reveals exciton features at low temperatures which are mudi better resolved than C_<10>PbI_4.From the above results, it has become established that C_<10>PbI_4, a perovskite material with a natural quantum-well structure, is an ideally two-dimensional substance. Very strong anisotropies due to this two-dimensional structure have been observed in its electrical and optical properties. Plans are under way to further study this and other related compounds, focusing on their nonlinear optics and exciton dynamics. Less