Study On The Optical Anisotropy Of One-dimensional Perovskites

Optical anisotropy is the basis for polarization optical elements such as polarizers,wave plates,and phase matching device.Study on the optical anisotropy is of great significance for polarization-sensitive photodetectors and light emitting devices.In recent years,organic-inorganic hybrid perovskites have attracted tremendous attention due to their simple synthetic process and excellent optical properties.Among them,three-dimensional and two-dimensional perovskites have been widely studied while one-dimensional perovskites have rarely been reported which has both excellent optical properties and large anisotropy.In order to design and optimize polarization-sensitive optoelectronic devices based on one-dimensional perovskite,this thesis mainly focuses on the optical anisotropy of one-dimensional perovskites.The main contents are as follows:Firstly,the one-dimensional perovskite C₄N₂H₁₄Pb I₄ crystals were successfully synthesized by the aqueous method and we conducted structure and spectroscopy characterizations.Structural characterizations show that the crystals have excellent crystallinity qaulity and reliable synthesis repeatability.Spectral characterizations reveal that both free exciton and self-trapped exciton emission and reflection can be observed.At room temperature,the broadband self-trapped exciton emission dominates and emits warm white light.Further studies reveal that the broadband luminescence is mainly caused by Jann-Teller-like self-trapped excitons.The temperature dependent luminescence shows that the peak of self-trapped exciton emission red-shifts with the decreased temperature,which is due to the thermal expansion effect and the electron-phonon interaction.The optical anisotropy of one-dimensional perovskite crystal C₄N₂H₁₄Pb I₄ was further systematically studied.Polarization-dependent spectroscopy measurement shows that its luminescence emission,excitation and reflection all exhibit optical anisotropy.The maximum linear dichroic ratios of luminescence emission,excitation and reflection are 5.5,7 and 1.3 respectively.Further inverstigations suggest that the optical anisotropy is originated from the anisotropy of transition dipole moment and the quantum confinement effect in one-dimensional perovskite.The crystals also exhibit circular polarization emission at low temperature,with a circular dichroism value of 4.7%,which is mainly owing to the distortion of the crystal lattice and the destruction of the inversion symmetry.In order to further improve the optical anisotropy,one-dimensional double-chain perovskite C₅H₁₆N₂Pb₂I₆ crystals were synthesized by reducing the symmetry of the crystal.Spectral characterizations show that the linear dichroic ratio of PL emission and reflection increased to 17.43 and 1.6,which proved that it was feasible to increase anisotropy by reducing symmetry.By reducing the symmetry of the crystal structure,the octahedral structure is more prone to distort,which increases the anisotropy of the transition dipole moment,therefor increasing the optical anisotropy.In addition,the complex dielectric constants of the perovskites were further obtained through the Kramers-Kronig relationship and the birefringence and dichroism of the perovskite are calculated.The dichroism and birefringence have reached 1.5 and 1.3,respectively,which are higher than the largest birefringence in liquid crystals.In summary,the systhesis,mechanism of luminescene and optical anisotropy of one-dimensional perovskite have been systematically studied,and the anisotropy was improved by reducing the symmetry of crystals.This research is of great significance for polarization sensitive optoelectronic devices based on one-dimensional perovskites.