Recently, research about the application of luminescent carbon dots (L-CDs) and white LED by NUST Research Institute of Nano Optical and Electronic Material has been progressed with a series of results, which were published on Scientific Reports with Nature Publishing Group (impact factor 5.1) and Angewandte Chemie International Edition with German Wiley Publishing House. First-year postgraduate LI Xiaoming is the first author of both the two articles, and professor ZENG Haibo is the independent corresponding author.
Luminescent carbon dots (L-CDs) with high quantum yield value (44.7%) and controllable emission wavelengths were prepared via a facile hydrothermal method. Importantly, the surface states of the materials could be engineered so that their photoluminescence was either excitation-dependent or distinctly independent. This was achieved by changing the density of amino-groups on the L-CD surface. The above materials were successfully used to prepare multicolor L-CDs/polymer composites, which exhibited blue, green, and even white luminescence. In addition, the excellent excitation-independent luminescence of L-CDs prepared at low temperature was tested for detecting various metal ions. As an example, the detection limit of toxic Be2+ ions, tested for the first time, was as low as 23 μM.
Figure 2: Multicolor composites based on carbon dots with polymers: L-CDs/PAM blue and white phosphors, L-CDs/PAA and L-CDs/PVP composites, L-CDs/PVP composite films using L-CDs prepared at 160 and 240°C.
(a) Typical PL quenching of LCD-160 in the presence of Be2+ ions; (b) Typical PL quenching of LCD-160 in the presence of Fe3+ ions; both the insets are concentration-dependent fluorescence response. (c) Performance of sensors based on prepared carbon dots: comparison of fluorescence intensities in the absence and presence of different metal ions.
As an important energy-saving technique, white-light-emitting diodes (W-LEDs) have been seeking for low-cost and environment-friendly substitutes for rare-earth-based expensive phosphors or Pd2+/Cd2+-based toxic quantum dots (QDs). In this work, precursors and chemical processes were elaborately designed to synthesize intercrossed carbon nanorings (IC-CNRs) with relatively pure hydroxy surface states for the first time, which enable them to overcome the aggregation-induced quenching (AIQ) effect, and to emit stable yellow-orange luminescence in both colloidal and solid states. As a direct benefit of such scarce solid luminescence from carbon nanomaterials, W-LEDs with color coordinate at (0.28, 0.27), which is close to pure white light (0.33, 0.33), were achieved through using these low-temperature-synthesized and toxic ion-free IC-CNRs as solid phosphors on blue LED chips. This work demonstrates that the design of surface states plays a crucial role in exploring new functions of fluorescent carbon nanomaterials.
Although NUST Research Institute of Nano Optical and Electronic Material was founded last year, various kinds of research have been put forward. On the first half of this year, a 973 Project has been formally started; recently, this institute was awarded 5 Provincial Natural Funds and 3 National Natural Funds; Apart from the above high-level papers, another one will be published on Nano Letters (Impact Factor 12.9).
This research was funded by National Key Scientific and Research Project (2014CB931700-02) and Excellent Youth Fund of National Funds Committee.