The Preparation And Photoelectrical Properties Of White Emitting Diodes With Full Spectral Carbon Dots

Photoluminescent carbon dots(CDs),as a new emergent carbonic nanomaterial,have attracted much attention due to their superior properties such as high photostability,low toxicity,as well as optical properties.There is a high demand for high quantum yield(QY)full spectral CDs with a stable fluorescence performance for application in light-emitting diodes(LED).Herein,full spectral CDs were synthesized by hydrothermal method.A variety of characterization methods were adopted to study the corresponding microstructure and luminescent properties of full spectral CDs.Moreover,to avoid aggregation-induced solid-state fluorescence quenching of CDs,CDs-based solid-state composites materials were fabricated.Subsequently,the LED devices were constructed by integrating the CDs-based solid-state composites materials with the blue In Ga N LED chips.The main contents of this paper are as follows:1.A series of full spectral CDs with tunable excitation-independent fluorescence emission wavelengths have been successfully prepared by hydrothermal method with a precursor comprising ammonium citrate and ethylenediamine tetraacetic acid(EDTA).Under UV light,these CDs emitted outstanding luminescence in colours from dark blue to red.Alterations of the photoluminescence(PL)emission of these full-colour CDs were tentatively proposed to benefit from surface functional groups,such as C=O and C=N.An energy-level model was proposed to explain the continuously adjustable full-colour emissions.The white light may be attributed to the overlap of diverse light emissions induced by the electron transitions between the energy levels.More importantly,to avoid solid-state quenching,the multicolor CD films were fabricated by incorporating the multicolour CDs into Polyamideresin-650(P-650).Finally,flexible full-color CD-based sandwich glasses were successfully constructed through a facile spin-coating technology.This demonstrates that these materials are promising for applications in LEDs and full-colour displays.2.White fluorescent carbon dots(WCDs)were synthesized by combining red carbon dots(RCDs)with ethanol or N-(b-aminoethyl)-g-aminopropyl methldimethoxy silane(AEAPMS)for the first time.Interestingly,the RCDs have excitation-independent behavior while the WCDs exhibit excitation-dependent behavior.These WCDs emit bright white light with quantum yields(QYs)of 50.8% and57.1%.Solvatochromism effects of the CDs were ascribed to the intermolecular charge transfer between the CDs and solvents.The solvents further increase the charge carrier density and induce the charge transfer.Investigation of the white fluorescence mechanism of the CDs revealed a multilevel emissive recombination channel,which might be from the distribution of diverse surface-state PL centers.Additionally,because the latter WCDs exhibit excellent optical properties and a great film-forming ability,workable white CD-based glass thin-films were constructed using facile screen-printing technology.Finally,the as-fabricated white light-emitting diodes(W-LEDs)exhibited an optimized color coordinate(CIE)of(0.33,0.34),color rendering index(CRI)of 51 and correlated color temperature(CCT)of 6735 K.Therefore,the WCDs reveal the strong feasibility of being used for lighting and displays.