Synthesis And Application Of Carbon Dots And Inorganic Perovskite Quantum Dots Confined In Mesoporous Silica

After decades of development,mesoporous silica has become one of the most widely used materials.Mesoporous silica materials with a variety of morphologies,pore structures and particle sizes are emerging.Among them,dendritic mesoporous silica nanospheres（DMSNs）have attracted more and more attention because they can be easily mass-produced and have three-dimensional stellate pores,high specific surface area and the surface can be modified by post-grafting technique.These advantages also make them commonly used as matrices.Carbon dots and all-inorganic perovskite quantum dots are two types of quantum dots that have attracted much attention since their discovery because of their outstanding physical and chemical properties.Carbon dots have many merits such as a wide range of raw materials,simple synthesis methods and stable fluorescent properties.They can be applied in physics,biology and chemistry.However,the nature of its luminescence has not been clearly understood and due to the aggregation-induced quenching effect,research on solid-state carbon dots has rarely been reported,which makes the application of carbon dots very limited.All-inorganic perovskite quantum dots have great advantages in optical performance,such as tunable emission wavelength,high quantum yield,and wide color gamut.In recent years,their application in photoelectric conversion devices（especially solar cells）achieved a rapid development.However,poor stability has become a stumbling block on its way forward,and it is urgent to adopt simple and effective strategies to enhance its stability.Based on above,in this thesis we used DMSNs as matrices for the first time.On the one hand,their unique hierarchical porosity provides a confined space for the growth of quantum dots.On the other hand,the quantum dots are anchored in matrices by the chemical interaction with the functional groups grafted on the mesopores.Thereby,the nanocomposites in which quantum dots are uniformly dispersed in the mesoporous silica are obtained.The main contents of research are as follows:1.Deep understanding of the luminescence mechanism of carbon dots.Carbon dots were synthesized by solvothermal method using 3-aminophenol as precursor and ethanol as solvent.The solutions of carbon dots dispersed in different solvents（DMSO and H₂O）have different fluorescent colors.The photoluminescence spectra show that there are two emission peaks.Adjusting the volume ratio of the two solvents will make the relative intensity of the two peaks changes significantly,which indicates that the fluorescence of carbon dots may come from two kinds of luminescent centers.Adding small molecules with multiple carbonyl groups to it has a large impact on the intensity of the long-wavelength emission peak of the carbon dots,indicating that one of the luminescent centers should be related to the carbonyl groups.Then,we employed dendritic mesoporous silica nanospheres as matrices and used solvothermal or hydrothermal methods to induce the confined growth of carbon dots,and finally prepared solid-state multicolor carbon dots@dendritic mesoporous silica nanocomposites.The fluorescence emitted from the carbon dots dispersed in the nanocomposites is very similar to the molecular luminescence,which expands a new direction for the subsequent research on the luminescence mechanism of carbon dots.2.By directly mixing and heating all-inorganic perovskite precursors,surfactants,solvents,and dendritic mesoporous silica nanospheres in one-pot to prepare nanomaterials composed of all-inorganic perovskite quantum dots and dendritic mesoporous silica.All-inorganic perovskite quantum dots are uniformly dispersed in the confined space of the porous structure with ultra-small size（⁵ nm）and cubic crystalline phase.The luminous color of the nanocomposites can be tuned by changing the proportion of the halogen component.Under the dual effects of physical confinement and chemical bonding,all-inorganic perovskite quantum dots with pure cubic phase are separated from each other,effectively preventing their agglomeration,and the hydrophobic groups on the surface of the matrices’channels also avoid their contact with water.So that the nanocomposites have good optical performance and enhanced stability.When the halogen is bromine,the quantum yield of the nanocomposites is 55%,and the half-peak width is only 19 nm.After soaking in water for 7 hours,the photoluminescence intensity does not decrease obviously.After 45hours of UV light irradiation,the photoluminescence intensity can be maintained about 90%of the original.We successfully fabricated multi-color light emitting diodes（LEDs）using these nanocomposites as fluorophores.This study provides new ideas for the application of all-inorganic perovskite materials in lighting devices.