Study On Hydrochromic Materials Of All Inorganic Lead Halide Perovskite Nanocrystals And Their Applications In Anti-Counterfeiting

All-inorganic cesium lead halide perovskite(CsPbX3,X=Cl,Br,I)nanocrystals have shown excellent photophysical properties,including high photoluminescence quantum yield(PLQY),tunable emission covering the full visible range,and narrow emission spectra,resulting in great potential applications in photovoltaic fields,such as solar cells,light emitting diodes,photodetectors and lasers.In addition to CsPbX3 nanocrystals,other related ternary compounds,such as CsPb2X5and Cs4PbX6 nanocrystals have also been studied.However,the research on these two perovskite materials is still in its infancy,and there are still many challenges.For example,it’s still hard to realize the controllable synthesis and there is still much debate about whether they are luminescent.In addition,how to achieve the transformation among CsPbX3,CsPb2X5 and Cs4PbX6 is also a key issue of our concern.In this thesis,the research on the preparation,optical properties and structural transformation about all-inorganic lead halide perovskite materials is carried out,and the fluorescence changes caused by the structural transformation are applied in anti-counterfeiting.The main research contents include:1.We developed two different hot injection methods to synthesize high-purity Cs4PbX6 nanocrystals,and found that the key parameter for forming Cs4PbX6 nanocrystals rather than CsPbX3 nanocrystals is the molar ratio of cesium to lead.The results of both methods confirm that pure Cs4PbX6 nanocrystals are non-luminescent.In addition,it is worth noting that we did not find the coexistence of Cs4PbX6 and CsPbX3 phases in a single particle.2.Through the water-triggered method,we realized the transformation from Cs4PbX6 to CsPbX3 nanocrystals.For Cs4PbX6 nanocrystals with different halide,the transformation rate is Cs4PbCl6>Cs4PbBr6>Cs4PbI6,which is directly related to the solubility of CsX in water.This transformation process is very sensitive to ambient humidity,so Cs4PbX6 nanocrystals can be applied in humidity sensors.The Cs4PbX6 nanocrystals can be used to prepare various non-luminescent invisible patterns by hand-drawing or printing for anti-counterfeiting.3.The reversible transformation between luminescent structure(CsPbX3)and non-luminescent structure(CsPb2X5)was realized by water infiltration and evaporation process.After the treatment of moisture,CsBr was stripped from CsPbBr3 nanocrystals,resulting in the transformation to CsPb2Br5.At the same time,the water droplets that dissolved Cs+and Br-are confined in the porous substrate.When water evaporates in the air,CsPb2Br5 nanocrystals,Cs+and Br-will recrystallize to CsPbBr3 nanocrystals.In addition,the reversible transformation was verified by theoretical calculations.This hydrochrmic material shows broad application prospects in anti-counterfeiting.