Study On The Two-photon Fluorescence Of Perovskite-structured Mn-CsPb(Cl/Br)₃ Nanocrystals And The Optical Second Harmonic Of Perovskite-structured LiNbO₃ Crystals

Perovskite materials are composed of metal cations and non-metallic anions,which form octahedrons and show rich magnetic,electrical and optical properties,and can be applied in various fields.In this thesis,we Study on the two-photon fluorescence of Mn-Cs Pb(Cl/Br)₃ perovskite nanocrystals and the optical second harmonic of lithium niobate crystals.Lead halide perovskite nanocrystals have been widely used in optoelectronic devices due to their high photoluminescence quantum yield,narrow and tunable emission spectrum.We prepared the perovskite nanocrystals by thermal injection method,then we designed experiment for measuring the two-photon luminescence(TPL).Through the results of pure CsPbCl₃,Mn²⁺doped CsPbCl₃ and Mn²⁺doped Cs Pb(Cl/Br)₃perovskite nanocrystals,we found that the TPL from the host CsPbCl₃ perovskite nanocrystals was weakened after doping with Mn²⁺,and the TPL from the Mn²⁺defect state was enhanced.When Br^—was introduced,the TPL from the Mn²⁺defect state is sharply weakened,and the TPL from the host CsPbCl₃ perovskite nanocrystals is enhanced.We explained the results by considering the energy transfer from exciton to Mn-dopant optical transitions.The effect of Mn-modulation made the TPL to cover the entire visible light region,which can be applied in biological detection.LiNbO₃ crystal has a high Curie temperature,a large piezoelectric and electro-optic coefficient,and is one of the most promising ferroelectric materials.we firstly designed X-cut and Z-cut LN crystals,secondly calculated the four non-zero independent values in the second-order nonlinear susceptibility;thirdly measured the polarization dependent SHG intensities,and lastly,fitted the results with theoretical calculations and obtained the all tensor elements of the second-order nonlinear susceptibility of our LN single crystals.