Synthesis And Luminescence Properties Of Trivalent Ions Doped CsPbX₃ Nanocrystals

All-inorganic lead halide perovskite nanocrystals CsPbX₃（X=Cl,Br and I）have many excellent optoelectronic properties such as tunable emission wavelength,large absorption coefficient,narrow emission width and high photoluminescence quantum yield,which are expected to have potential application for light-emitting diodes,solar cells,photodetectors,and lasers.Recently,with the efforts of researchers,there was a deeper understanding for CsPbX₃ nanocrystals.However,all-inorganic lead halide perovskite nanocrystals still face many challenges and disadvantages,such as their quantum yield and stability need to be further improved.Modification of all-inorganic lead halide perovskite nanocrystals by doping impurity ions is an important technical mean to enhance the luminescence and stability of nanocrystals,Therefore this article mainly reports the study on the B site doping of trivalent ions(Nd³⁺and Cr³⁺)in the CsPbX₃ nanocrystals,The main research contents are as follows:1.Synthesis and luminescence properties of Nd³⁺doped CsPb（Cl/Br）₃nanocrystals:We synthesized the Nd³⁺doped CsPb（Cl/Br）₃ nanocrystals by using the hot injection method and introducing Nd³⁺into the lattice of CsPbCl₃nanocrystals.With the increase of the doping level of Nd³⁺,we successfully enhanced the quantum yield of CsPbCl₃ to 58%and confirmed that the mechanism of improving emission was due to the reduction of defect states caused by Nd³⁺doping by using time-resolved photoluminescence spectroscopy.Furtherly,structural characterization（TEM,XRD,XPS and ICP-OES）proved that Nd³⁺have been doped into the lattice of the CsPbCl₃ nanocrystals.Then,in order to obtain the nanocrystals with adjustable emission wavelengths,the nanocrystals with mixed halogen with emission peaks in the range of 408 nm-503nm were obtained by anion exchange method at room temperature,the maximum quantum yield of green emission was 93%,and blue emission（461 nm）was obtained with a quantum yield of 82%.More importantly,the water stability of CsPbCl₃ nanocrystals was significantly improved after doping Nd³⁺.2.Synthesis and luminescence properties of Nd³⁺doped Mn:CsPbCl₃nanocrystals:Inspired by enhancing the band-edge emission of CsPb（Cl/Br）₃nanocrystals by doping Nd³⁺,we studied the effect of Nd³⁺on enhancing the luminescence of Mn:CsPbCl₃ nanocrystals.It is found that Nd³⁺can significantly enhance the emission intensity of Mn²⁺PL and increase the PL lifetime of Mn²⁺PL when the Mn²⁺doping concentration is low;however,in the case of high Mn²⁺doping concentration,Nd³⁺doping reduces the emission intensity of Mn²⁺ PL.Therefore,when the molar ratio of Mn/Pb/Nd is 1/1/1,the Mn²⁺emission wavelength at 605 nm and the luminous efficiency as high as 58%are achieved.Steady-state and time-resolved photoluminescence spectroscopy indicated that Nd³⁺played an important role in controlling Mn²⁺emission and reducing defect states,respectively.XRD also confirmed that Nd³⁺was successfully incorporated into the lattice of Mn:CsPbCl₃ nanocrystals.We also used SiO₂ to coat（Mn,Nd）:CsPbCl₃ nanocrystals,and the water resistance of the（Mn,Nd）:CsPbCl₃nanocrystals was significantly improved due to coating of SiO₂.3.Synthesis and luminescence properties of Cr³⁺doped CsPbBr₃nanocrystals:CsPbBr₃ nanocrystals are the most excellent luminescent materials in the family of all-inorganic lead halide nanocrystals.Therefore,we studied the effect of Cr³⁺on the luminescence and structure of CsPbBr₃ nanocrystals.By adjusting the optimal molar ratio of Cr Br₃ 6H₂O/PbBr₂,we prepared Cr³⁺doped CsPbBr₃ nanocrystals with high quantum yield of up to 96%.XRD,XPS and TEM structural characterization confirmed that Cr³⁺had been incorporated into the lattice of CsPbBr₃ nanocrystals.