Synthesis Of Novel Fluorescent Carbon Dots And The Applications Research

Fluorescent carbon dots?CDs?are a new type of carbon based fluorescent materials.It has been drawed more and more attention because of its extraordinary water solubility,chemical inertness,biocompatibility,non-bleaching,easy surface functionalization and so on.Consequently,CDs have potential applications in a new generation of biological imaging,detection,photocatalysis,and photoelectric devices.Although many literatures have been reported about CDs,as often the preparation,functionalization,and separation suffer from complex processing steps,low yield and difficult large-scale preparation.But most have been reported carbon dots were emitted short-wavelength luminescence,such as blue and green.However,there are few reports about the longwavelength emissive CDs,such as yellow and red.Now,the photoluminescence mechanism of CDs is not clear,and lack of approaches for regulating photoluminescence in CDs.In addition,the fluorescence of CDs always undergo aggregation-caused quenching in the solid state due to excessive resonance energy transfer or direct?-?interactions,which severely limit the application of CDs as luminescent materials in LED lighting,solid-state photoelectric devices,fingerprint development and sensor fields.Based on the above points,hydrothermal/solvent thermal synthesis of CDs,heteroatom doping,molecular luminescence regulation,and surface group control are used to control the luminescence behavior of CDs.Moreover,we investigated the mechanism of surface-state-controlled luminescence action and its application in photoelectric devices,fingerprint development and fluorescence sensor.The primary research contents are as follows:?1?.Using tartaric acid,arginine and boric acid as raw materials,a simple method of preparing N,B-CDs in a gram-scale was proposed.The as-prepared CDs have good water solubility,uniform size distribution and bright blue emission.Further analysis indicates that the CDs can be applied to detect the Fe³⁺quickly through static quenching,which possess a good linear relationship in the range of 0?80?M,and the detection limit is approximately0.74?M.In addition,the prepared N,B-CDs with positive charge and boric group enabled their use as recognition elements to bind bacteria through electrostatic interaction and covalent interactions to form the corresponding boronate ester with E.coli.bacterial membrane.This method could satisfy a linear range from 10² to 10⁷ with a detection limit of165 cfu mL^-1 for E.coli.The applicability of the developed method in practice has also evaluated the feasibility using tap water and orange juice samples,and satisfactory recoveries were obtained.?2?.A novel method of synthesizing self-quenching-resistant CDs powder is presented.Electron-deficient B atoms can inhibit the charge transfer between electron donor and acceptor.The introduction of guanidine functional group and boron hydroxyl groups would be particularly conductive to hydrogen-bonded matrices formation,so that the CDs appear a similar dispersed state in the liquid medium.Thus,we report a convenient and versatile approach to inhibiting the self-quenching in the solid states.A series of solid fluorescent CDs were obtained by controlling the reaction temperature only.Based on the solid-state fluorescence characteristics of CDs,multicolor LED devices were prepared by mixing the encapsulated resin and CDs as the matrix.By adjusting the proportion of different CDs,two primary colors and three primary colors white LED were obtained.By adjusting its color temperature and color rendering index,the fabricated white LEDs lamp exhibits low correlated?5040 K?and high color rendering index of 91,with the color coordinate of?0.344,0.357?.It validates that the CDs is a promising converter in the field of solid state lighting.?3?.In combination with the design mechanism of preparing self-quenching-resistant CDs powder,a series of solid-state fluorescence CDs emitting at long wavelength with low cost and high yield were obtained.A new strategy for tunable emission of CDs in the long wavelength region was explored.We realized the color-tunable fluorescence of CDs from yellow to deep red-emitting by modulating the content of boric acid doping on the surface electron transfer and surface state of CDs.The prepared CDs have excellent self-quenching-resistant character,small size and good monodispersity,which is very suitable for the detailed observation of latent fingerprints.Therefore,fingerprint detection by powder brush display method was realized by employing the tunable-emissive CDs and expanded the application of CDs in the field of crime scene investigation.?4?.By host–guest interactions between the Mg?OH?₂ nanosheets and CDs,the fluorescence CDs was introduced into Mg?OH?₂ nanosheets to form the CDs/Mg?OH?₂compound.The localized microenvironment provids by the two-dimensional structure Mg?OH?₂ nano-sheet can make the synthesized CDs uniformly dispersed among the layers and avoids aggregation induced fluorescence quenching.At the same time,it exhibits strong thermal stability.The CDs only loss the interlayer water molecules when temperature is below 200?,which had no effect on its structure.T_0.5 is higher than 150?,which fully satisfy the requirement of the LED working temperature?120??.At the same time,Ba₂Zn₇F₁₈:Eu²⁺and Ba₂YAlO₅:Eu³⁺phosphors were prepared,and their fluorescence performance and thermal stability were investigated.Three kinds of blue,green and red phosphor materials were investigated to explore their applications in LED.It provides new approach for dealing with the thermal stability of LED.