The Fabrication And Characterization Of Carbon Dots Based Single Phase Phosphors For White Light-Emitting Devices

White light-emitting devices (WLED) with low cost, long life, high energyefficiency and good color rendering property have gained tremendous attentionof a cross-disciplinary research and become the representative of solid-statelighting for the excellent performance of energy conversion.At present, the technology of WLED has already became matured andcommercialized, but there are still some bottleneck problems. One of them is alimited kinds and performance of phosphors. Phosphors are keys to achieve highbrightness, high efficiency and high color rendering index WLED, but thecurrent commercial phosphors, such as rare earth and quantum dots, are ofnon-renewable resources or harmful to environment. The main idea of this paperis to fabricate carbon dots based phosphors with high quantum yield (QY), goodlight stability and low cost. The main content is as follows:（1） A kind of fluorescent water-soluble carbon dots(W-CDs) with uniformsize, good solvent dispersion and excitation-dependent PL behavior wereprepared by one-step hydrothermal method with aqueous glucose solution asraw materials. The influence of glucose solution concentration and reaction timewas explored. The structures of W-CDs were characterized with high-resolutiontransmission electron microscopy (HRTEM) and Fourier transform infrared(FT-IR) spectrometry; the fluorescent properties of W-CDs were measured byultraviolet and visible (UV-vis) spectroscopy and photoluminescence (PL)spectroscopy. The results show that the optimal hydrothermal synthesisconditions for obtaining W-CDs were25mmol/L glucose concentration reacting 8h under180℃. The as-prepared W-CDs， with diameter of5nm，emit bluefluorescence with a QY of1.13%and a ratio of red, green, blue (RGB)component of55%.（2） A series of water-soluble fluorescent carbon dots with N-doping (N-CDs)or N and P-doping (N,P-CDs) were prepared by one-step microwave-assistanthydrothermal method with ammonium citrate as carbon source and phosphate asadditive. The influence of reaction time and kind of additive was explored. Themorphology and microcosmic structures of N-CDs and N,P-CDs werecharacterized with HRTEM; the surface structure of them were measured byFT-IR spectrometry and X-ray photoelectron spectroscopy; the fluorescentproperties were tested by UV-vis spectroscopy and PL spectroscopy. Resultsshow that the optimal synthesis conditions for obtaining N-CDs were：5.000g ofammonium citrate in10mL of H2O was heated for140s under microwavepower750W. The as-prepared N-CDs have narrow diameter distribution with in3-5nm and emit blue light with the QY17%and RGB component60%. Inaddition, the N-CDs perform excitation-dependent PL behavior and goodthermostability. The optimal synthesis conditions for obtaining N,P-CDs were：5.000g of ammonium citrate and1.000g of triammonium phosphate (TAP) in10mL of H2O were heated for140s under microwave power of750W. Theas-prepared N,P-CDs, with narrow diameter distribution centered at~10nm,emit blue light with the QY of62%, RGB component of61%, CIE chromaticitycoordinate of (0.3776,0.3459) and CCT of4450k have excitation-dependent PLproperties and thermostability.