Method For Controlling Luminescence Of Manganese-doped Two-dimensional Perovskite Nanosheets

All-inorganic halide perovskite has become one of the hot materials in the field of optoelectronic functional materials due to its excellent optical properties such as high fluorescence quantum yield,narrow fluorescence emission peak,and wide emission wavelength that can cover the entire visible light region.Doping is an important method to adjust the photoelectric properties of nanocrystals.Doping with two-dimensional halide perovskite as the host material,due to the strong exciton binding energy and weak electromagnetic shielding effect of the two-dimensional perovskite,will help to enhance the host-impurity interaction,thus showing Optoelectronic properties different from doped three-dimensional perovskite.In view that the researches about doped halide perovskites mostly use three-dimensional nanocrystalline hosts,this paper will focus on the research of doping two-dimensional halide perovskites.The main work is as follows:First,two-dimensional doped perovskite nanosheets were prepared by post-synthesis doping.Using the pre-prepared CsPbBr3 nanosheets as host materials,the MnCl2 solution was added to the nanosheets for synthesis and doping.The experimental results show that the post-synthesis doping process includes both rapid Cl and Br halogen ion exchange process and slow MnCl2 and CsPbBr3 molecular exchange process.The former causes the intrinsic fluorescence peak of the perovskite to be greatly blue-shifted,while the latter gives the nanosheet a new fluorescence peak of Mn impurity.Structural analysis shows that the doping process after synthesis will not seriously change the lattice structure of the nanosheet but will cause the shrinkage of the nanosheet lattice.Compared with the three-dimensional perovskite nanocube whose size exceeds the Bohr radius,the thinner thickness of the two-dimensional perovskite nanosheets greatly accelerates the diffusion process of MnCl2 molecules into the crystal.Compared with molecular exchange time in three-dimensional doping system(70 hours),two-dimensional doping system makes the molecular exchange process between MnCl2 and CsPbBr3 shortened to 10 minutes.Secondly,the effects of two different impurity feeding processes on the optical properties of nanocrystals were studied.In the first way,a fixed concentration of MnCl2/DMF solution was added to the nanosheet solution,which obtain different feeding ratio by changing the addition volume.With the increase of the feeding ratio,the relative intensity of the Mn impurity emission peak and the perovskite intrinsic emission peak gradually increased,and the nanosheet chromaticity transform from the blue light region to the yellow light region.When the Mn:Pb feed ratio is between 3-5,the chromaticity of the nanosheets is in the warm white light region.In the second way,the same volume of MnCl2/DMF solution was injected to the nanosheet solution,which obtain different feeding ratio by changing the MnCl2 concentrations.When the feed ratio is 4,the nanosheets also emit warm white fluorescence.Although the above two methods both can be used to adjust the chromaticity of nanosheets,the effects on the intrinsic fluorescence peak position of perovskite behave different.The two have different effects on the intrinsic fluorescence peak position of perovskite.Both doping methods show that the blue shift phenomenon of intrinsic peak is dependent on the concentration of MnCl2 solution,indicating that the rapid Cl and Br ion exchange process is the main reason for determining the intrinsic fluorescence peak position.