| Inorganic lead halide perovskite CsPbX3(X=Br,Cl or I)nanocrystal is a kind of novel semiconductor materials.It shows great application prospects in solar cells,photodetectors,light-emitting diodes,lasers and other optoelectronic devices owing to its simple preparation methods,high photoluminescence quantum yield,narrow full width at half-maximum,tunable band gap and high charge carrier mobility.However,there are still some great challenges in perovskite materials,such as the degredation of luminescence properties owing to surface defects,poor stability and the toxicity of lead,etc.It is of great importance to stablize perovskite material,improve the optical properties,and reduce its toxicity for its commercial applicationIn this thesis,we mainly focus on B-site and X-site ions in ABX3 and realize the regulation over these sites to enhance the optical properties and the stability of CsPbX3 nanocrystals.The luminescence mechanisms are also explored via synchrotron radiation spectroscopy and discussed in detail.The contents of the thesis mainly include:(1)Preparation of Mn2+-doped CsPb(Br/Cl)3 nanocrystals and study of its luminescence mechanism.The Mn-doped CsPb(Br/Cl)3 was synthesized at room temperature.The results of X-ray diffraction and X-ray absorption fine structure(XAFS)showed that the introduction of Mn did not change the long-range order of CsPbX3 nanocrystals but caused local lattice contraction.X-ray excited photoluminescence spectroscopy(XEOL)showed that both the intensity and the wavelength of the perovskite excitonic emission band depend on excitation energy,while only the intensity of the Mn emission band was related to excitation energy.After fitting,it is found that the perovskite emission band consisted of two overlapping components.The red-shift and intensity variation of emission peak are primarily due to the changing intensity ratio of these two components.We conclude that the Mn emission band of Mn doped CsPb(Br/Cl)3 is caused by energy transfer between Mn and excitons in the perovskite band gap rather than direct Mn electrons excitation.(2)Study on the luminescence properties of Pr-doped CsPbC13.The CsPbC13 and doped perovskite nanocrystals with different Pr3+ concentrations were prepared by hot-injection method.The partial replacement of Pb2+in the perovskite lattice was achieved and the maximum doping was up to 9%.Pr3+ doping has little effect on the energy band structure and crystal structure of the host lattice.A new emission band was not formed after the introduction of Pr3+,but the photoluminescence quantum yield of CsPbC13 was dramatically improved(to a maximum of 78.9%).XAFS fitting results showed that the introduction of additional Cl-ions through doping PrCl3 increased Pb coordination number in the perovskite,therefore reduced the Cl vacancies.This passived the surface defects in the perovskite and then enhanced the optical properties of CsPbCl3 nanocrystals.XEOL results showed that the optical enhancement of perovskite nanocrystals was also prompted due to the enhanced electronic properties of CsPbCl3 by the formation of donor states from Pr3+below the conduction band.(3)The effect of excessive Br-on the stability of CsPbBr3 nanocrystals.A surface modifier,tetroctyl bromide,was used to introduce additional Br-ions into the prepared CsPbBr3 nanocrystals.The photoluminescence spectra showed that with the additional Br-source,CsPbBr3 nanocrystals exhibited excellent luminous stability compared to the original ones,because Br-can repair the surface trap states.There is also a phase conversion process from CsPbBr3 nanocrystals to Cs4PbBr6 nanocrystals during the treatment by extra Br-.Surface passivation provided by Cs4PbBr6 is also a reason for the enhanced luminous stability. |
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