Research On Synthesis And Optical Properties Of Multinary Semiconductor Nanocrvstals

Nanomaterials have received wide-spread attention and research due to their unique optical,electromagnetic and mechanical properties and huge latent applications.After reaching nanoscale,semiconductor crystals begin to exhibit strong quantum confinement effect,perform an excitonic electron state and highly tunable properties,thus may be applied in many fileds like display and illumination,photovoltaic and solar cells,biological research and mew medical therapy,light detection,photocatalysis and so on.However,early quantum dots concentrate on?-?(?-?)binary semiconductor materials,usually with cadmium(Cd),lead(Pb)or mercury(Hg).Hence,these quantum dots are not suitable for large-scale commercial applications due to their heavy-metal-containing compositions.Seeking and developing new quantum dot systems thus become imperative,which need to own optical properties similar to the classical ?-? or ?-? binary quantum dots,bright emission in the visible and near-infrared regions,and with heavy-metal-free compositions at the same time.In order to achieve these objectives,a strategy is adopted for forming a multi-element system by alloying of semiconductor nanocrystals:including introducing a third constituent element into the ?-?(?-?)binary semiconductor system and forming ?-?-? ternary semiconductor system,or directly applying multinary-structured perovskite system,trying to achieve an appropriate balance between heavy-metal-free composition and optical properties through a multi-system.The specific efforts and work are stated as following:1.CuInS2 quantum dots are synthesized by a one-pot strategy in colloidal phase,and the reactivities between Cu+ and In 3+can be balanced through tuning precursor and ligand system:reducing reactivities of all precursors,adjusting the ratio of Cu:In to 1:2 and introduce di-n-hexylamine as ligand.Based on this,applying nitric acid in hexane and n-butanol phase for etching and growing zinc sulfide with nucleation from CuInS2 quantum dots by a two-step growth for introducing ZnS shell structure are able to further optimize the internal and surface structure of CuInS2 quantum dots,respectively,to improve photoluminescence quantum yield.2.FA0.33 Cs0.67PbBr3-xIx perovskite nanocrystals are synthesized by a hot-inj ection strategy.Partially substituting Cs+ by FA+,adjusting the halogen precursor ratio(Br:I)and applying oleic acid,oleylamine as ligands are able to synthesize FA0.33Cs0.67PbBr3-xIx nanocrystals and achieve the relative balance of halogen precursors,inprove the stability of the phase and optical properties of them.On this basis,by prolonging the reaction time and tuning ligands,including introducing bis-(2-ethylhexyl)-amine as the third ligand and adjusting the ration of oleic acid to oleylamine,are able to further modulating the morphology of nanocrystals and synthesizing FA0.33Cs0.67PbBr3-xIx nanowires and nanosheets.3.FAPbBr3 perovskite nanocrystals can also be synthesized by a hot-injection strategy,and promoted exhibiting quantum confinement effect by excess halogen(Br)precursor.What's more,morphology of FAPbBr3 nanocrystals can further optimized by a ligand system consisting of 4 ligands,including oleic acid,hexanoic acid,hexylamine,di-n-hexylamine and finally synthesize HexAm2FAPb2Br7 nanosheets with significant quantum confinement effects.