Self-assembly Induced Emission Of Cu Clusters:Mechanism Exploration And WLEDs Application

Because of the specific properties including HOMO-LUMO electronic transition,intense light absorption,and size-dependent fluorescent emission,metal nanoclusters(NCs)have been considered as one of the most competitive color conversion materials in light-emitting diodes(LEDs).However,the monotonous emission color and the low emission stability and intensity of individual metal NCs strongly limit their universal application.Inspired by the concept of “aggregation induced emission”(AIE)in organic molecules,the utilization of highly ordered metal NCs assemblies opens a door to resolve these problems.After self-assembly,the emission stability and intensity of metal NCs assemblies are greatly enhanced.At the same time,the emission color of metal NCs assemblies become tunable.We termed this process as “self-assembly induced emission”(SAIE).In this paper,we use low-cost,earth abundant and more practical Cu NCs as the subject to convey this concept that the compact and ordered arrangement can efficiently improve the metal NCs' emission stability,tunability,and intensity.We aim to introduce the synthesis of 2D Cu NCs self-assemblies and their emissions.We further explore some factors that can affect the SAIE of 2D Cu NCs self-assemblies,such as ligands,inter-NC distance and metal defects.We then discuss the utilization of the obtained 2D Cu NCs as color conversion to improve the performance of LEDs.In chapter 2,Cu NCs self-assembly architectures with strong red emission are prepared by replacing alkylthiol ligands with aromatic thiols.The introduction of aromatic ligands is able to influence the ligand-to-metal charge transfer and/or ligand-to-metal–metal charge transfer,thus permitting the tuning of the emission color and enhancing of the emission intensity.The emission color can be tuned from yellow to dark red by choosing the aromatic ligands with different conjugation capabilities,and the photoluminescence quantum yield is up to 15.6%.Achieving full-color emission Cu NCs self-assembly architectures allows the fabrication of Cu NCs-based white light-emitting diodes.In chapter 3,we demonstrate the capability to control the self-assembly induced emission of Cu NCs by modulating the inter-NC distance in the self-assembly materials,which is capable of tuning the emission color from green to red.The inter-NC distance is mainly modulated by controlling the experimental variables during the NC self-assembly,such as the species of the solvents and ligands,duration of assembly,temperature,and so forth.These experimental variables influence the balance of inter-NC weak interactions,thus altering the distance of as-assembled NCs.The variation of the inter-NC distance greatly influences the photo-physical behavior of Cu NCs,and in particular the ligand-to-Cu–Cu charge transfer,permitting the tuning of the emission color.As the Cu NCs self-assembly materials exhibit strong,stable,and color-tunable SAIE,they are employed as the color conversion materials for fabricating white light-emitting diodes.In chapter 4,the surface metal defects of the assembled fluorescent materials are deliberately engineered by utilizing immiscible reaction conditions.Metal defects have an effect on luminescent energy levels,which are relative to the dynamic process of exciton radiation transition and regulate the photophysical properties of the materials.Further studies demonstrate the surface metal defects possess shallow energy level and multi sublevels,broaden the emission color from blue to red,the span range of the variation ascends to 160 nm.Moreover,the continuous alteration of emission color from yellow to red is achieved by simply adjusting the relative ratio of the surface and deep metal defects.Based on the full-color emission of copper clusters,the white light emitting diodes(WLEDs)with different color temperatures(warm,cold,and pure white)are prepared for potential illumination application.