Synthesis And Luminescence Properties Of Solid-State Carbon Dots And Red Perovskite Quantum Dots

Carbon dots have many advantages,such as easy preparation,and good biocompatibility,and show great application potential in white LED,latent fingerprint,cell imaging and visible light communication.However,when they are dried in solid state,their emission will undergo severe quenching due to fluorescence resonance energy transfer（FRET）,which greatly limits their practical application.Therefore,developing new types of carbon dots that maintain fluorescence emission in solid state is crucial for promoting the development of carbon dots.Perovskite quantum dots have attracted great attention due to their excellent properties such as high quantum efficiency,high defect tolerance,and narrow emission peakss.However,poor stability has always been an important problem restricting their practical application.In addition to the poor stability,the red emitting CsPb(Br_xI_1-x)₃ quantum dots are susceptible to anion exchange effects,which results in that the luminescence performance of Cs Pb(Br_xI_1-x)₃ quantum dots being far inferior than the bromine green perovskite quantum dots.Therefore,it is very necessary to explore an effective route to enhance the stability of Cs Pb(Br_xI_1-x)₃ quantum dots.This work contains two parts:one is to solve aggregation induced emission quenching of carbon dots through surface metal functionalization and in situ dispersion,respectively;the other is to improve the PLQY and stability of Cs Pb(Br_xI_1-x)₃ quantum dots by Sr²⁺doping and silica encapsulation.This paper achieves blue and green solid-state emission fluorescence carbon dots that resist aggregation induced fluorescence quenching through surface functionalization of carbon dots and matrix dispersion,respectively;The control of the emission peak position of perovskite quantum dots was achieved by selecting a mixed halogen method,and efficient red CsPb(Br_xI_1-x)₃ quantum dots were prepared through a dual strategy of Sr²⁺ion doping and surface coating with SBA-15.On the basis of material preparation,materials with different luminescent properties are applied in different fields,hoping to provide reference ideas for the development,performance optimization,and practical application of quantum dot materials.The specific research content is as follows:1.A blue fluorescent carbon dot with self quenching resistance was synthesized by hydrothermal method,with an average particle size of 2-4 nm.The honeycomb hexagonal structure can be seen in high-resolution transmission electron microscopy photos,indicating that the carbon dot structure contains a large amount of sp² carbon.The obtained carbon dots emit bright blue light in both liquid and solid states（with emission peaks located approximately 450 nm）,and the luminescence exhibits excitation wavelength independent characteristics.A white LED device with a color rendering index of 96 and a light efficiency of 40 lm/W was fabricated using this solid-state carbon dot.In addition,the luminescence intensity and fluorescence lifetime of the obtained liquid fluorescent carbon dots exhibit good linear temperature response characteristics in the temperature range of 20-70℃,and can enter TCA-8113 cells（tongue squamous cell carcinoma cells）through endocytosis.Under laser confocal scanning microscopy,bright blue fluorescence is displayed and intact cell morphology is maintained.In addition,cytotoxicity experiments show that the obtained carbon dots have low toxicity.Based on the characteristics of liquid carbon dots,they were used for temperature sensing analysis within cells,and the results showed that the obtained carbon dots are expected to serve as an efficient nano thermometer.2.Using biuret as the raw material and dispersant,a green solid carbon dot with an average size of 2-3 nm,a quantum efficiency of 58%,a luminescence peak at 510nm,and a fluorescence lifetime of 13.7 ns was synthesized using a one-step microwave heating method.The XRD of the obtained carbon dots contains the same diffraction peak as biuret,indicating that the carbon dots can be nested in situ within the lattice structure of biuret,effectively suppressing the aggregation induced fluorescence quenching effect.A white LED device with a color rendering index of 92.7 was prepared by using the green fluorescent carbon dot and CaAlSiN₃:Eu²⁺phosphor as the light conversion layer.A combination LED was prepared using this green fluorescent carbon dot and a 405 nm micro sized LED（μLED）,achieving a visible light communication system with a modulation bandwidth of up to 101 MHz（carbon dots only）and 165 MHz（μLED+carbon dots）.3.A pure red mixed halogen perovskite quantum dot with an emission peak of 635nm and a half height width of 30 nm was prepared using a traditional thermal injection method using a dual strategy of Sr²⁺doping and coating mesoporous silica SBA-15.The successful doping of Sr²⁺improves the structural stability of the quantum dot.The confinement growth in the SBA-15 channel has achieved a better anti anion exchange performance of the quantum dot.Under the cooperation of the two,a pure red perovskite quantum dot with ultra-high quantum efficiency has been achieved.A white LED device with a color rendering index of 92 was successfully constructed by mixing this material withβ-sialon commercial fluorescent powder.A wide color gamut white LED with 98%NTSC（Rec.2020）was encapsulated by mixing it with green CsPbBr₃ quantum dots,proving that the prepared red quantum dots also have good application prospects in backlight display.