Structural Tunability,Optical Properties And Application Of Lead-free Metal Halide

In recent years,lead-free metal halide materials have been widely used in photovoltaic devices and energy catalysis due to their excellent optical properties such as high photoluminescence quantum yield,precise adjustable bandgap and superior charge carrier migration properties.Structure of lead-free metal halide materials play a crucial role in the optical properties.However,the relationship between structure and optical properties are still remained challenges.Thus,it is of great value to investigate the structural tunability of lead-free metal halide materials and elucidate the ralaionship between the structure and optical properties,which is beneficial for the development and application of material.A series of lead-free metal halide nanomaterials were successfully synthesized in this paper.The crystal structure of the material was controlled by ajusting the concentration of precursor and halogen components.We explore the effect of environment(water,temperature and solvent)on the crystal structure and tune the crystal structure of the material,which is favorable for enhancing optical properties of the material.The luminescence mechanism of materials was investigated.In addition,we achieve the applications in the fields of anti-counterfeiting,water detection,X-ray imaging and photothermal catalytic hydrogenation.The main contents include the following parts:(1)One dimensional(1D)CsMnBr3(red light emission)and zero dimensional(OD)Cs3MnBr5(green light emission)nanocrystals(NCs)were selectively synthesized by controlling the ratio of cesium acetate to manganese acetate as precursor.It is noted that the environment such as isopropanol,water molecules and temperature can affect the structure and optical properties of caesium manganese bromide.Such phase transition can be triggered by isopropanol:from 1D CsMnBr3 NCs(red-color emission)to 0D Cs3MnBr5 NCs(green-color emission).The phase transition process is beneficial for the improvement of the crystal quality and optical properties of materials.Furthermore,in a humid environment both 1D CsMnBr3 NCs and 0D Cs3MnBr5 NCs can be transformed into 0D Cs2MnBr4·2H2O NCs(blue-color emission),realizing the red/green/blue color-tunable emission,which is of great significance for the development of anti-counterfeiting.In addition,Cs2MnBr4·2H2O NCs can be reversibly transformed into CsMnBr3 and Cs3MnBr5 mixed phase materials during the thermal annealing dehydration step,and the mixture can be converted into single-phase Cs3MnBr5 crystals in isopropanol solution.We explore the effect of water molecules.temperature and isopropanol on the structure of material,realizing the red/green/blue color-tunable emission by means of phase engineering of cesium manganese bromides.The strategy paves a novel route to synthesize water-containing nanomaterials.The tunable optical properties of cesium manganese bromides show a potential application in anti-counterfeiting.(2)Based on the study of manganese bromide materials,we further developed 0D Cs3MnI5 nanocrystals and polycrystalline powders by adjustng the composition of halide.Cs3MnI5 polycrystalline powders show high fluorescence quantum yield(73%),which is attributed to the high exciton binding energy.The photoluminescence mechanism of the materials is investigated by femtosecond transient absorption spectra.In addition,Cs3MnI5 exhibits a sensitive response to water molecules.In a humidity environment,the Cs3MnI5 happen degration quickly.The decomposed Cs3MnI5 recovers the initial structure and optical property during a heat treatment.Thus,Cs3MnI5 with high fluorescence quantum yield and response to water molecules can be utilized for sensitive water detection.Cs3MnI5 also shows strong response ability for X-ray with a limit of detection of 0.4 μGy/s,which is significantly lower than the diagnostic value of medical X-ray(5.5 μGy/s).Besides,Cs3MnI5 has high light yield of 33600 ph/MeV,and spatial resolution of 7.45 lp/mm,being suitable for X-ray imaging.(3)The solution processed strategy of Cs2MoCl6 perovskite NCs was proposed.The organic molecules and high valence molybdenum ions was introduced to overcome the unstable problem of lead-free metal halide nanomaterials.CS2MoCl6 perovskite NCs anchored atomically dispersed Pd catalyst(PdSA/Cs2MOCl6)is successfully assembled,achieving semi-hydrogenation of phenyl acetylene at room temperature with high selectivity to styrene of 96%at full conversion.In addition,PdSA/Cs2MoCl6NCs have wide range absorption from visible to near-infrared region and excellent photothermal properties,which could further improve the activity(turnover frequency from 295 h-1 to 465 h-1)while without selectivity loss.The superior performance originates from the strong metal-support interaction effect and unique coordination structure and electronic property of Pd-Cl sites.PdSA/Cs2MoCl6 NCs exhibit efficient semi-hydrogenation of alkynes to industrially favorable alkenes under mild conditions.This strategy provides an idea for the design of new lead-free metal halide materials and opens up a road for its application in the field of photothermal catalyst.