Preparation,Optical Properties And Stability Of Copper Doped,Manganese Doped And Silica Coated CsPbX₃ Quantum Dots

Perovskite quantum dots(PQD)have low cost,high photoluminescence quantum yields(PLQYs)and narrow and adjustable emission spectra.These advantages make them attractive luminescent materials for lighting and display applications.In recent years,Cs Pb X₃ PQD(X=Cl,Br,I)has attracted a lot of attention from material scientists as a promising photoelectric material.Compared with organic-inorganic hybrid perovskite materials,all inorganic perovskites have the advantages of simple preparation method and good stability.Despite its sufficient advantages,the toxic nature of Pb and the limited tolerance of all inorganic perovskite to moisture,ultraviolet(UV)light and adjacent environment cannot be ignored.It is urgent to find solutions to these worrying problems.Generally speaking,there are several strategies to improve the photoelectric properties of perovskite quantum dots and maintain the octahedral structure.The first strategy is A-site doping.The doping of A-site organic cations may improve the stability of perovskite and adjust the band gap,so as to enhance its photoelectric properties.The second strategy is B-site doping,which is also the most common strategy.B-site doping is the most effective method to reduce toxic Pb,and it is found that metal cation B-site doping can effectively improve the optical properties of perovskite quantum dots,such as photoluminescence quantum yield(PLQYs),changing band gap width,fluorescence lifetime and so on.The previous research on perovskite quantum dots has made great achievements,but there are still many problems to be solved about the stability of Cs Pb X₃ PQDS.The main content of this paper is to prepare all inorganic perovskite quantum materials and silica coated composite perovskite quantum materials by thermal injection method,and explore the properties and stability of Cs Pb X₃ PQDS and their composites respectively.The research results of this paper can be summarized into the following three aspects:(1)In this work,We use hot-injection method to prepare Mn doped Cs Pb Br₃ perovskite QDs.Consequently,the properties of Pb-based perovskite QDs were improved.In order to gain their enhanced stability,different Mn/Pb ratio of Cs Pb Br₃ PQDs structure was achieved.The Mn substitution ratio reaches 38%,which leads to an increase of 3.8 times of the steady-state PL intensity and the lifetime increases to 267 ns.In comparison to the undoped sample,the quantum efficiency achieved the improved as large of 30.6%.Stability of the Mn:Cs Pb Br₃PQDs with distinct Mn/Pb ratios against polar solutions was tested.Doping with Mn²⁺improved the stability of PQDs according to our research.(2)Cu²⁺doped Cs Pb Cl₃ quantum dots were successfully synthesized by thermal injection method.The presence of Cu²⁺changes the fluorescence emission intensity of Cs Pb Cl₃.With the increase of Cu²⁺ion concentration,the luminescence intensity of Cu²⁺doped Cs Pb Cl₃quantum dots also enhanced,which increases the steady-state photoluminescence intensity by4.2 times and the lifetime.With the continuous increase of the doping amount of Cu²⁺,the fluorescence intensity gradually decreases,which is because the defect energy level of the quantum dot changes with the addition amount of Cu²⁺.In addition,we tested Cu²⁺:Cs Pb Cl₃PQD with different Cu/Pb ratios in water.(3)CsPbBr₃ quantum dots were synthesized by a typical thermal injection method.During the synthesis process,TOES played a key role in helping the unstable Cs Pb Br₃ form a core-shell structure.The sediment Cs Pb Br₃/Si O₂ extracted from gel solution has good thermal stability,photostability and polar solvent stability.After 35 days of static storage and 35 days of ultraviolet radiation,the PL fluorescence intensity of the QD composite powder decreased by 3.4%and 9%respectively.The polar solvent stability test showed that the PL fluorescence intensity of Cs Pb Br₃/Si O₂ in deionized water and ethanol remained 92.3%and 97.6%respectively after four days.Cs Pb Br₃/Si O₂ composite powder is uniformly mixed with K2Si F6:Mn(red light emitting)powder in a certain proportion,and then coated with resin silica gel on the blue LED chip(emission wavelength 450nm)and encapsulated to obtain white LED after high temperature curing.When lighting(20m A),the luminous efficiency reaches58.9 lm/w,the color temperature is 5829 K,and the color gamut area is 126.8%of the NTSC international standard.Because of its excellent light color parameters,Cs Pb Br₃/Si O₂ shows great application potential in the field of LED lighting and white light display.We investigated the factors affecting the optical properties and stability of all inorganic perovskite quantum dot Cs Pb X₃ from two aspects:B-site cation doping and silica coating.The results show that B-site cation doping can improve the optical properties of Cs Pb X₃,such as quantum yield and fluorescence lifetime,and improve the stability in water.The stability of Cs Pb X₃ coated with silicon dioxide has been greatly improved,and we used it to prepare LED white light emitting devices.It is found that it has good luminous performance,which paves the way for subsequent applications.