Preparation And Properties Of Single-matrix Warm White Lead-free Double Perovskite Quantum Dots

Lead（Pb）halide perovskite quantum dots（LHP QDs）have attracted a lot attention for their excellent optical properties with bright narrow band,tunable wavelength and high photoluminescence quantum yield.Lead halide perovskite structure belongs to the cubic system with chemical formula of ABX₃,in which A represents a monovalent cation,such as methylammonium（CH₃NH₃⁺）,formamidinium（CH（NH₂）₂⁺）as well as cesium（Cs⁺）.B site is taken up by one divalent cation like tin(Sn²⁺)besides lead(Pb²⁺)ions.Besides all the advantages,concerns on its toxicity arise for accumulated Pb in bodies,which can do harm to human nervous system,digestive system,and hematopoietic system.All the potential risks make there more uncertainty for lead halide perovskite to apply on photoelectric field.At the meantime,lacking of stability is also a tricky problem for lead perovskites.They are allergic to water and oxygen of high contents as well as high temperature,which can cause fast degradation.Efforts have been made to modify the structure of perovskite to cater both superior optical properties and high stability without lead.In the past few years,researches on lead-free halide perovskite have been made great progress.Meanwhile,with the deepening of understanding,lead-free halide perovskite has aroused wide attention for its lead-free chemical composition,excellent thermal stability,high exciton binding energy and luminous efficiency with lower toxicity than lead halide perovskite.A₂B（I）B（III）X₆ type double perovskite appears as a new approach and this kind of perovskite differs from ABX₃ type for its special self-trapped exciton（STE）widely observed in lead-free double halide perovskite,for which the unique optical properties formed.Particularly,Cs₂AgInCl₆ with dopants is a superior candidate as a novel material for photoelectricity.The advanced stability,low toxicity,STE wide white emission peaks and the high photoluminance quantum yield（PLQY）of doped Cs₂Ag In Cl₆ make it interesting as a potential optical material.The adjustments for Cs₂Ag In Cl₆ are discussed by doping ion and both the optical properties and stabilities have been optimized.The concrete contents on Cs₂Ag_1-xNa_xIn Cl₆:Bi and Cs₂Rb_xAg_1-xIn_0.875Bi_0.125Cl₆ powder are as follows:1.The lead-free double perovskite Cs₂Ag_1-xNa_xInCl₆:Bi nanocrystal synthesized by hydrothermal and fully characterized by HRTEM and XRD.The lattice of crystal particles spacing is about 0.34 nm,which shows doping Na can affect the structure of the unit cell.Its broad emission peak starts from 400 nm and ends at 780 nm,covering the whole visible spectrum.And the emission become stronger as the contents of Na goes higher till x=0.8 where the summit is.This optimized method is much more convenient and the product has a promising prospect in lighting applications.2.The lead-free double perovskite Cs₂Rb_xAg_1-xIn_0.875Bi_0.125Cl₆was synthesized by facile hydrothermal method and the properties were characterized in detail on both structure and properties.The Cs₂Rb_xAg_1-xIn_0.875Bi_0.125Cl₆ exhibits bright white emission accompanied by a broad peak of 600 nm,which ends at over than 820 nm.As the stability test conducting,blue shifts resulted from the micro scale change of the product have been observed.3.Commercial chips and epoxy resin were used encapsulate the obtained material into LED devices.Both devices shows wide emission covering the full visible spectrum reveals the possibility of usage in lighting devices,performs high stability during tests.Overall,the lead-free double perovskite Cs₂Rb_xAg_1-xIn_0.875Bi_0.125Cl₆ is promising materials in lighting applications.