Preparation And Properties Of CsPbX₃ Perovskite Quantum Dots

CsPbX₃ perovskite quantum dots（QDs）are the current research focus.Its excellent photoelectric properties such as narrow emission bandwidth,high photoluminescence quantum yield（PLQYs）and high defect tolerance make CsPbX₃ QDs have broad application prospects in LED,solar cells,photodetectors,lasers and biological imaging.However,the luminescence efficiency and stability still hinder the development of CsPbX₃ QDs.In this paper,CsPbX₃ QDs with high luminescent efficiency and high stability were prepared by doping,phase transformation and coating passivation layer.White LED devices were prepared,and the main contents are as follows:（1）Firstly,Na-doped CsPbBr₃ QDs were synthesized by an improved hot-injection method.Various characterization methods were used to confirm that Na ions enter the lattice of CsPbBr₃ to replace the position of Cs ions.The photoluminescence quantum yields（PLQYs）of CsPbBr₃ QDs were increased from 52.6%to 94.3%by adjusting the doping concentration of Na ions.The blue shift of photoluminescence（PL）spectra further proves that Na ions successfully enter CsPbBr₃ lattice.Then CsPbBr₃ and Na:CsPbBr₃ QDs were anion-exchanged by PbCl₂ and Pb I₂ solution post-treatment.The results showed that Na:CsPbBr₃ QDs still maintained high PLQYs after anion exchange.This part of work provides a new idea for improving the luminescence efficiency of perovskite quantum dots.（2）Mn ions were doped in Cs₄PbX₆ QDs by tri-precursor hot-injection method to adjust the band structure.When Mn:Cs₄PbX₆ QDs were excited by 289 nm excitation light source,the PL peak of Mn ions appeared at 610 nm,and no PL peak of CsPbCl₃ QDs at 410 nm was observed,indicating that the sample had high purity.The effect of Mn ions on the PL properties of Cs₄PbX₆ QDs is investigated by changing Pb:Mn molar ratios.When the Pb:Mn ratio is 1:1,the PLQYs of the QDs is up to 23.1%.Various test methods proved that Mn ions were successfully introduced into the lattice of Cs₄PbCl₆ QDs.Raman spectroscopy further proves that Cs₄PbCl₆ QDs reveal high crystallinity.The PL decay plots test results showed that with the increase of Mn ion doping amount,the average lifetime of Pb ion at 355 nm became shorter,while that of Mn ion at 610 nm became longer,which confirmed the process of exciton transfer from Pb ion to Mn ion.Finally,white light-emitting diode（LED）devices were fabricated by using 280 nm commercial LED chip as excitation source and CsPb（Cl/Br）₃,CsPbBr₃ and Mn:Cs₄PbCl₆ QDs as color conversion layers.The Commission Internationale de I’Eclairage（CIE）color coordinates of white LED are（0.3229,0.3037）.（3）A simple post-treatment method was designed.The pre synthesized 0D Cs₄PbCl₆ QDs was reacted with MX₂（M=Zn,Mn;X=Cl,Br）to prepare high PLQYs and high stability CsPb_x（Zn/Mn）_1-x（Cl/Br）₃ QDs by halogen anion driven cation exchange.After ion exchange,the PLQYs of samples treated with Zn Cl₂ and Zn Br₂ were up to 74.2 and 88.1%,respectively,in which the PLQYs were changed to 70 and 65%after 20 days in air conditions.The Mn Cl₂treated sample exhibited a new PL peak at 610 nm because of the insertion of Mn ions.The PLQYs of the Mn Cl₂ treated sample was 56%.In addition,CsPb_xZn₁–_x（Cl/Br）₃,CsPbBr₃,and CsPb（Br/I）₃ QDs were dispersed in polymethyl methacrylate solutions to prepare PL films.A commercial LED chip was used as an excitation source to prepare white LED.From the CIE chromaticity diagram,the bright white emission of the film exhibited the corresponding chromaticity coordinates of（0.29,0.30）which located in the white light area.The white emitting film exhibited high stability.（4）The fluorescence of CsPbX₃ QDs is easily quenched by polar solvents.The mesoporous silica particles（MSNs）are used as carriers to in situ grow CsPbX₃ QDs in the mesoporous of MSNs,which effectively improves the stability of CsPbX₃ QDs in polar solvents.After 21 days of post-treatment of CsPbX₃@MSNs composites with water and ethanol,The PL intensity remains above 50%of the initial intensity.Due to the growth of CsPbX₃ QDs in mesoporous,the surface defects were reduced,and the PLQYs was significantly improved（up to 86%）.Because CsPbX₃ QDs are located in the mesoporous,the anion exchange pathway is reduced,and transparent silica does not affect the luminescence properties of CsPbX₃ QDs.CsPbX₃@MSN composites have unique advantages for white-LEDs as solid-state luminescent materials.White-LED devices were fabricated using CsPbX₃@MSN composites as the solid-state light-emitting conversion layer.The color temperature was 6838 K,and the luminous efficiency was 8.9 lm/W.Its coincidence degree with the gamut space specified by NTSC 1953is 135%,and the coincidence degree with the gamut space specified by ITU-R B.T.2020（Rec.2020）is 95%.