Solid-State Fluorescent Carbon Dots with Aggregation-Induced Yellow Emission for White Light-Emitting Diodes with High Luminous Efficiencies

Abstract

For practical applications of carbon dots (CDs), a major challenge is to prevent the notorious aggregation-caused quenching (ACQ) effect. Herein, a new type of CDs (CD1) has been developed that can transform from ACQ to an enhancement of fluorescence by aggregation-induced emission (AIE). The blue fluorescence of the CDs is suppressed by ACQ. However, this is accompanied by the phenomenon of AIE at a longer wavelength, resulting in the emergence and gradual enhancement of yellow fluorescence. The obtained CD1 solid powder shows a bright yellow emission with a photoluminescence quantum yield (PLQY) of 65%. The photoluminescence (PL) spectra, absorption spectra, and time-resolved PL decay curves indicate that Förster resonant energy transfer from dispersed CD1 particles to large CD1 agglomerations leads to the enhancement of yellow fluorescence. To exploit its high PLQY and strong AIE, CD1 is applied as a color-converting layer on blue light-emitting diode (LED) chips to fabricate white LEDs (WLEDs). The obtained devices show white light coordinates of (0.29, 0.38) and (0.32, 0.42), which are close to pure white light (0.33, 0.33), and luminous efficiencies of 97.8 and 93.9 lm·W–1 and show good stability. The low cost, easy fabrication, controllability, and favorable fluorescence properties signify that CD1 of AIE will have superior performance in a variety of applications.

Evaluation of the Environmental Impact and Efficiency of N-Doping Strategies in the Synthesis of Carbon Dots

“…Furthermore, CDs can be produced through green and simple methods of synthesis [7], using even waste biomass as a precursor [8,9]. Given this, it is not surprising that CDs have attracted significant attention from the research community, and that they have been gaining several practical applications, such as in sensing [10][11][12], bioimaging [13], fabrication of light emission devices [14,15], and in photocatalysis [2].…”

“…Given this, it is not easy to predict the efficiency exerted by using different nitrogen precursors on the QY FL of the resulting CDs. This makes difficult the rational development of CDs with high QY FL , which is a feature required for most (if not all) current applications of these NPs [1][2][3][10][11][12][13][14][15]. In fact, it has not been fully assessed whether using either a nitrogen-rich solvent in a solvothermal route or a nitrogen-rich small organic molecule in a hydrothermal route would offer a greater potential.…”

Solid-state fluorescent carbon dots: quenching resistance strategies, high quantum efficiency control, multicolor tuning, and applications

“…In fact, some of them show solid-state fluorescence, 67 while others experience solid-state quenching. 47 Zhang et al 47 (Figure 6h).…”

“…Zhang et al 47 proposed that uniform particle size is also a key factor to realize solid fluorescence of CDs. In the presence of KCl, CDs were prepared with CA and Lcysteine as raw materials by one-step microwave method.…”

“…On the one hand, the addition of salt crystals, such as KCl and NaOH, can act as a dispersion matrix to isolate CD nanoparticles in situ, and reduce the formation of defects, both of which contribute to the improvement of solid-state fluorescence intensity of CDs. On the other hand, controlling the proportion of reactants or energy of reaction system can avoid the excessive carbonization of reactants, so that CDs have a low conjugated structure, which also contributes to the improvement of solid-state fluorescence intensity of CDs.Zhang et al47 prepared two kinds of CDs by one-step microwave method using CA and L-cysteine as raw materials with and without KCl, named as CDs1 and CDs2.CDs1 exhibit bright solid-state fluorescence with QY of 65%, while CDs2 show no solid-state fluorescence(Figure 5a, b). KCl can act as a temperature conduction medium, so that raw materials can be uniformly heated.…”