As a new member of the carbon material family, carbon dots (CDots) endow carbon materials with luminescent property and expand their application in fluorescent field. Because of their unique optical property, they have attracted much more attention for their potential applications in the photoelectrical conversion, [1] photo catalysis, [2] bioimaging systems, [3] and light-emittaing devices (LEDs) [4] since CDots were discovered in 2004. [5] In early research, CDots had low photoluminescence (PL) quantum yield (QY) and the emission was limited at blue light emission. Over a decade, researchers have put much more effort to improve their PL QY through surface passivation and heteroatom doping methods to induce better charge/carrier transport. Since then, the PL QY of CDots can reach up to 94% for strong blue emission [6] and ≈60% for green emission. [7] This progress leads to potential applications for CDots in bioimaging, optoelectronic devices, and LEDs due to their low toxicity, biocompatibility, and excellent photostability. [3e,8] However, efficient red emissive CDots are still highly desired because red light has deep tissue penetration for bioimaging and is one of the primary colors for white LEDs. There are a few reports on the synthesis of red emissive CDots. For example, using expensive polythiophene phenylpropionic acid as a precursor, Wang and co-workers developed hydrothermal reaction processes to prepare red emissive CDots with low PL QY of 2.3%. [9] Our group reported synthesis of red emissive CDots with 8% PL QY using citric acid (CA) and thiourea, which results in S-and N-doped CDots with enhanced electron delocalization. [10] Lin and co-workers demonstrated synthesis of red emissive CDots with PL QY of 26%. The CDots were prepared through solvothermal route using phenylenediamine isomers. [11] Xiong and co-workers reported the red-emitting CDots with PL QY of ≈24%. The red emission was achieved by tuning the surface state from precursors p-phenylenediamine and urea that were prepared carefully through silica column chromatography. [12] Recently, Yang's group used dopamine and o-phenylenediamine as precursors and obtained near infrared emissive CDots by generating large sp 2 domains. The final QY of the CDots can reach to ≈30%. [13] Despite these efforts, the final materials are expensive for practical applications and lack of clear understanding of luminescence mechanism. Thus, Multiple-color-emissive carbon dots (CDots) have potential applications in various fields such as bioimaging, light-emitting devices, and photocatalysis. The majority of the current CDots to date exhibit excitation-wavelengthdependent emissions with their maximum emission limited at the blue-light region. Here, a synthesis of multiple-color-emission CDots by controlled graphitization and surface function is reported. The CDots are synthesized through controlled thermal pyrolysis of citric acid and urea. By regulating the thermal-pyrolysis temperature and ratio of reactants, the maximum emission of the resulting CDot...

Multiple‐color‐emission carbon dots are prepared from citric acid and urea at different reaction temperatures and ratios by regulating the graphitization and surface functional groups, as described in article number https://doi.org/10.1002/adma.201704740 by Hongyou Fan, Zaicheng Sun, and co‐workers. As‐prepared carbon dots exhibit good solubility in organic solvent and good compatibility with polymers, which provides great potential for phosphor‐based light‐emitting diodes (LEDs).

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Defects play a significant part in promoting photocatalytic activity for H 2 production. Various methods such as chemical reduction have been performed to metal oxide based photocatalysts. Herein, we present the NaBH 4 reduction route to introduce the defects into the graphitic carbon nitride (g-C 3 N 4 ) to enhance photocatalytic activity. A new −C≡N group is observed in the FTIR spectra of treated g-C 3 N 4 nanosheets indicating the presence of structural defects. At the same time, the B signal appears in the X-ray photoelectron spectroscopy analysis, suggesting that B is doped in the g-C 3 N 4 during the treatment. All these results manifested that multiple types of defects are introduced in the g-C 3 N 4 during the NaBH 4 treatment. The UV− vis spectra illustrate that the absorption band edge of g-C 3 N 4 is extended from 420 to 450 nm after NaBH 4 treatment. This demonstrates that the band gap of g-C 3 N 4 turns narrow owing to the introduction of defects. Photocatalytic H 2 production of defective g-C 3 N 4 is ∼5-fold better than that of pristine g-C 3 N 4 . To understand the enhanced mechanism, the apparent quantum efficiency, photoluminescent spectra, transient photocurrent and electrochemical impedance spectra are investigated. The results show that the charge separation efficiency is greatly strengthened in the defective g-C 3 N 4 . Upon these findings, the enhancement of catalytic activity can be attributed to both the broad light adsorption range and highly efficient charge separation process.

Carbon dots (CDs) have been demonstrated to be fluorescent materials for the new phosphor-free white light-emitting diodes (WLEDs). Herein, we synthesized a novel white CDs (WCDs). The spectrum highly matches the solar light spectrum (AM 1.5), which is a potentially high-color-quality lighting source material. The CDs contain blue, green, and red emissive centers produced from catechol, o-phenylenediamine, and their complexes, respectively. In addition, the photoluminescence mechanism had been revealed; three emission centers could be excited by a single UV source actuated by the formation of H-and J-aggregates and FRET between the CDs. Then the phosphor-free WLEDs were fabricated with a UV chip encapsulated with silicon resin containing the asobtained CDs, which exhibit CIE coordinates of (0.33,0.33), a color rendering index (CRI) of 93, and a correlated color temperature (CCT) of 5453 K. The WLEDs show super stability and a high solar spectrum matching degree of 85−114%, protecting the eyesight. This provides a new way to design healthy lighting materials.