Preparation And Stability Of All-inorganic CsPbBr₃ Nanocrystals By High-energy Ball Milling In One-step

All-inorganic halogen perovskite CsPbX3(X=Cl,Br,I)has great application prospects in the fields of light-emitting diodes,new displays,photodetectors and photovoltaic devices due to its excellent optoelectronic properties.At present,CsPbX3 nanocrystals(Nanocrystals,NCs)are mainly synthesized by liquid phase methods such as hot injection method and supersaturated recrystallization method.These liquid phase methods generally have problems such as complex preparation process,high cost and environmental pollution.In order to solve these problems,this paper used high-energy ball milling to synthesize CsPbBr3 nanocrystals in one step at room temperature,and synthesized Mn:CsPbBr3 nanocrystals by doping Mn2+instead of Pb2+,and used EVA resin to coat Mn:CsPbBr3 nanocrystals to adjust the nanocrystal light-emitting wavelength,improve stability,and reduce the content of Pb in the material at the same time.The main research content and conclusions of this article are as follows:(1)CsPbBr3 nanocrystals were synthesized by high-energy ball milling in one-step using CsBr and PbBr2 as raw materials,oleylamine(OAm)as ligand,and characterization methods such as XRD,SEM,TEM,XPS,UV-Vis,PL and PLQY were used to study on impact of ball grinding time and addition amounts of OAm on the phase composition,microscopic morphology,composition and luminescence properties of the material,and further explored the stability of CsPbBr3 nanocrystals in alcohol,air and water environments.The results show that when adding 0.4 mL OAm and high-energy ball milling for 25 min,we can synthesize CsPbBr3 nanocrystals with a uniform size of about 9 nm,and the fluorescence quantum yield(Photoluminescence Quantum Yield,PLQY)is 78%.In addition,compared with the nanocrystals synthesized by supersaturated recrystallization method,nanocrystals synthesized by the high-energy ball milling method show better stability:after being dispersed in alcohol for 2 h,the retention rate of the fluorescence intensity is 40%,while the fluorescence intensity of the nanocrystals synthesized by supersaturated recrystallization method disappear completely after dispersion in alcohol for 2 h;after being placed in the air environment for 60 d,the fluorescence intensity retention rate of nanocrystals synthesized by high-energy ball milling is still as high as 95%;after immersing in water for 8 hours,CsPbBr3 NCs synthesized by high-energy ball milling are almost completely transformed into CSPb2Br5 NCs,their fluorescence intensity increased to 80 times of that before immersion,and PLQY increased from 78%to 92%,while the fluorescence of nanocrystals synthesized by recrystallization method are seriously attenuated when immersed in water.The reason for the improved luminescence and stability of the material is that high-energy ball milling can provide more powerful energy,which makes the OAm and nanocrystals bond stronger,and it is not easy to fall off when exposed to water;at the same time,the hydrogen atoms of H2O also promote the combination between OAm and nanocrystals,resulting in better passivation effect of OAm on CSPb2Br5 defects.Multiple effects lead to a sharp increase in the PLQY of material.(2)Using MnBr2 and MnBr2-4H20 as manganese sources respectively,Mn:CsPbBr3 nanocrystals with different doping amount of Mn2+were synthesized by high-energy ball grinding,and the effects of two manganese-containing raw materials on the phase,microstructure,luminescence properties and stability of synthesized nanocrystals were studied.The results show that the structure,phase and morphology of nanocrystals synthesized by the two raw materials are basically same,and both can increase the intrinsic emission peak intensity of CsPbBr3 nanocrystals and obtain the transition emission of Mn2+with 610 nm as the center.When MnBr2 is used as the raw material,the luminescence intensity of synthesized nanocrystals is the highest when the doping amount of Mn2+is 75%;with MnBr2-4H2O as the raw material,infinite solid solution doping can be achieved and the luminescence intensity of material is the highest when the doping amount is 65%;Mn:CsPbBr3 nanocrystals synthesized with raw materials containing crystal water show stronger PL luminescence intensity and stability of alcohol and water.The reason is that the presence of crystal water can promote passivation effect of OAm on nanocrystal defects and connection between them,so the material shows higher luminescence intensity and stability.(3)EVA resin was used to coat the Mn2+doped nanocrystals prepared by the above-mentioned hydrated manganese source to prepare Mn:CsPbBr3 NCs/EVA film composites,and the effects of ratio of NCs to EVA and stirring time on morphology,luminescence properties and stability of film materials were studied.Studies have shown that when the ratio of NCs to EVA is 2.5 and stirring time is 30 min,the prepared NCs/EVA film materials have better optical properties and stability:after immersed in alcohol for 12 h,the luminescence retention rate of Mn2+is 68.82%;after immersed in water for 12 h,the luminescence retention rate is 27.40%;after 12 h of ultraviolet light exposure,the luminescence retention rate is 73.50%;after being placed in the daily air environment for 20 d,the luminescence retention rate is 71.52%.EVA resin coating can effectively slow down the contact speed of nanocrystals with polar solvents and oxygen molecules,and obviously improve the alcohol,water,light and air stability of nanocrystals.