The Design And Fluorescent Study Of Highly Stable All-inorganic Perovskite Quantum Dots Material Composite

Owing to the property of easy synthesis,long carrier diffusion length,high absorption coefficient,high photoluminescence quantum yield and tunable band gap,perovskite quantum dots（PQDs）have attracted extensive attentions both in academia and industry fields,exhibiting potential application prospects in light-emitting diodes（LEDs）,backlight displays,solar cells,lasers,photodetectors,catalysis and energy storage fields.However,the formation energy of PQDs is low,which is sensitive to the external environment.When exposed to heat,light,water and oxygen,the crystal structure of PQDs trends to distort and collapse,triggering the deterioration of material properties.Hence,how to achieve highly stable fluorescence with negligible influence on fluorescence property is the main challenge for perovskite materials.The construction of composite is an effective approach to improve the stability of PQDs.Inorganic materials are competent candidates as templates for PQDs loading to achieve the improvement of stability due to their high specific surface,easy surface functionalization and good chemical inertia characteristics.In addition,the combination of inorganic materials and PQDs has enriched interface properties,which is favored for the collaborative improvement of fluorescence properties and the broadening of application fields.This thesis focuses on enhancing the stability of PQDs.By constructing PQDs@inorganic material composite,it aims to regulate the fluorescence performance,improve the stability,reveal the mechanism of stability improvement and explore the related application in LEDs.According to the coupling models between inorganic materials and PQDs,we have systematacially studied the growth dynamics process of PQDs when combined with the outer,internal surface and molecular pores of inorganic materials.PQDs coupled with the outer surface of inorganic materials are composed of attapulgite（ATP）@PQDs composite and hexagonal boron nitride（h-BN）@PQDs composite.PQDs coupled with the internal surface of inorganic materials is PQDs@double shell-hollow Si O₂ composite.PQDs coupled with molecular pores of inorganic materials is PQDs@metal-organic frameworks（MOFs）composite.This thesis mainly includes the following three aspects:（1）Fluorescence composite constructed by the rivet of PQDs on the outer surface of 1D attapulgite and 2D hexagonal boron nitride:The rich Si-OH bonds on the surface of ATP take the advantage of introducing silane coupling agent for amino functionalization.The grafted amino silane coupling agent could be utilized as a bridging agent to promote the combination of ATP and PQDs.Comparing with the morphology,optical and stability of ATP@PQDs composite with or without bridging agents,the working mechanism of bridging agent for the construction of composites is proposed,and the correlation between interface engineering and optical properties is verified.The composite remains 29%of its relative PL intensity when the heating temperature increases to 120℃,while that value recovers to 81%when the temperature reduces to20℃.In addition,the composite still retains 84%of its relative PL intensity after 30 h UV light irradiation.The study on the dosage of bridging agents indicates that the fluorescence property is not completely improved with the increase of the dosage of bridging agent,and appropriate bridging agent dosage is necessary to maintain stable fluorescence.Besides,due to the weak van der waals forces between the layer of h-BN,h-BN is exfoliated to thin layer with the assistance of urea in the ball milling process,which introduces amino functional groups on the surface of h-BN.PQDs are in situ nucleation and growth on the surface of h-BN with amino functional groups protection.In addition,the thin layer of h-BN owns good thermal conductivity,which accelerate the heat loss of PQDs with significantly improved thermal and environmental stability.The composite remains 80%of its relative PL intensity when the heating temperature increases to 120℃,achieving 6 times enhancement compared to pure PQDs.In addition,the composite still retains 90%of its relative PL intensity after storage 22 days in atmospheric environment.（2）Fluorescence composite constructed by the encapsulation of PQDs in the inner surface of 3D double shell-hollow Si O₂ spheres:The polystyrene nanosphere is prepared by an emulsification polymerization method,subsequently followed by the hierarchical silica coating with polystyrene nanosphere as the core.The double shell-hollow silica is obtained by removing the template.The hierarchical silicon shell is composed of two layers,in which the inner shell is functionalized with amino functional groups,while the outer shell layer remains chemically inert.The difference in inner and outer surface promotes the selective growth of PQDs.In addition,the mesoporous and hollow structure ensures that the precursor ions could enter the cavity,while the matured PQDs are prevented from escaping.PQDs are observed to be encapsulated in the cavity of double layer-hollow silica and exhibit excellent thermal and optical stabilities by morphology and stability tests.The composite remains 65%and 89%of its relative PL intensity when the heating temperature increases to 100℃and after 17 h UV light irradiation,respectively.（3）Fluorescence composite constructed by the encapsulation of PQDs in the intramolecular pore structures of 3D metal-organic frameworks:MOF-808 with abundant intramolecular pore structure is modified by disodium ethylenediamine tetraacetic acid to achieve the effective adsorption of toxic Pb（II）in aqueous solution.The adsorbed Pb（II）in MOF-808 could be served as Pb（II）source for the in-situ loading of PQDs,which achieves the transition from Pb（II）chelation to PQDs.Besides,the release process of adsorbed Pb（II）in MOF-808 is slow to promote the multiple loading of PQDs for reversible switching of fluorescence signal,which has a broad application prospect in anti-counterfeiting field.The as-prepared PQDs@MOF-808 composites show excellent optoelectronic properties and enhanced thermal stability,maintaining stable fluorescence under harsh external environment.The composite remains 23%of its relative PL intensity when the heating temperature increases to 120℃,while that value recovers to 92%when the temperature reduces to 20℃.In addition,the composite still retains 85%of its relative PL intensity after 17 h UV light irradiation.More importantly,the dissociative Pb（II）from decomposed PQDs@MOF-808 composite could be adsorbed and recycled again to effectively suppress Pb（II）leakage,which is economically attractive and environmentally friendly.