We demonstrate the first white light-emitting device originating from single carbon dot components. A maximum external quantum efficiency of 0.083% at a current density of 5 mA cm(-2) with a color-rendering index of 82 is realized, indicating that carbon dots have great potential to be an alternative phosphor for fabricating white light electroluminescent devices.

The effects of the structures on the energy gaps in luminescent carbon nanoparticles (CNPs) were investigated. On the one hand, we fabricated CNPs with the different structures and a uniform size and then analyzed their photoluminescence (PL) behaviors. On the other hand, we calculated the dependence of the structures on the energy gaps in CNPs by a simple quantitative model. Both the experimental and calculated results show that the luminescent CNPs contain a mixture of sp(2) and sp(3) bonding and hence their PL behaviors and energy gaps are determined by the fraction of sp(2)-hybridized carbon atoms.

The desired control of size, structure, and optical properties of fluorescent carbon dots (CDs) is critical for understanding the fluorescence mechanism and exploring their potential application. Herein, a top-down strategy to chemically tailor the inexpensive coal to fluorescent CDs by a combined method of carbonization and acidic oxidation etching is reported. The size and optical properties of the as-made CDs are tuned by controlling the structures of graphitic crystallites in the starting precursor. The coal-derived CDs exhibit two different distinctive emission modes, where the intensity of the short-wavelength emission is significantly enhanced by partial reduction treatment. The evolution of the electronic structure and the surface states analysis show that two different types of fluorescence centers, nano-sized sp(2) carbon domains and surface defects, are responsible for the observed emission characteristics. The reduced CDs are demonstrated as an effective fluorescent sensing material for label-free and selective detection of Cu(II) ions with a detection limit as low as 2.0 nM, showing a great promise for real-world sensor applications.

Reported here is a green synthesis of graphitic carbon quantum dots (GCQDs) as a fluorescent sensing platform for the highly sensitive and selective detection of Fe3+ ions. Through the electrochemical ablation of graphite electrodes in ultrapure water, uniform GCQDs with graphitic crystallinity and oxygen containing groups on their surfaces have been successfully prepared. The absence of acid, alkali, salt and organic compounds in the starting materials effectively avoids complex purification procedures and environmental contamination, leading to a green and sustainable synthesis of GCQDs. The oxygen functional groups (e. g., hydroxyl, carboxyl) contribute to the water solubility and strong interaction with metal ions, which enable the GCQDs to serve as a fluorescent probe for the highly sensitive and selective detection of Fe3+ ions with a detection limit as low as 2 nM. The high sensitivity of our GCQDs could be attributed to the formation of complexes between Fe3+ ions and the phenolic hydroxyls of GCQDs. The fluorescence lifetime of GCQDs in the presence and absence of Fe3+ was tested by time-correlated single-photon counting (TCSPC), which confirmed a dynamic fluorescence quenching mechanism.

The size of C-nanodots can be electrochemically tuned by changing the applied potential during their preparation. The higher the applied potential, the smaller the resulting C-nanodots. Moreover, the surface oxidation degree of the C-nanodots can also be electrochemically tuned. The redshift of emission independent of the size provides an insight into the luminescence mechanism of C-nanodots.

We have developed a simple, one-step hydrothermal method for the synthesis of highly fluorescent carbon nanoparticles (F-CNPs) with a high quantum yield (68%) and good photostability. The method requires less reaction time and a lower reaction temperature as compared with the previous reported methods. The as-prepared F-CNPs exhibit excellent emission property and high stability, as well as excitation-independent emission behavior. Moreover, it is attractive that F-CNPs can be used as an effective fluorescent probe for the detection of mercury ions with good selectivity and sensitivity in an aqueous solution. (C) 2012 Elsevier Ltd.

与其它荧光纳米粒子相比，荧光碳纳米颗粒不仅具有良好生物相容性和易于表面功能化等优点，还具有发光稳定并可实现上转换荧光发射的特性，所以在生物医药领域具有重要的应用价值。结合近年来的最新研究成果，本文综述了金刚石、石墨和非晶等不同结构的荧光碳纳米颗粒的制备方法及其局限性；分析了不同结构碳纳米颗粒的荧光发射特性和在生物技术中应用的优缺点；阐述了荧光碳纳米颗粒在今后研究中需要解决的问题和发展方向。

We present a systematic investigation of the formation mechanism of carbogenic nanoparticles (GNPs), otherwise referred to as C-dots, by following the pyrolysis of citric acid (CA)-ethanolamine (EA) precursor at different temperatures. Pyrolysis at 180 degrees C leads to a CNP molecular precursor with a strongly intense photoluminescence (PL) spectrum and high quantum yield formed by dehydration of CA EA. At higher temperatures (230 degrees C) a carbogenic core starts forming and the PL is due to the presence of both molecular fluorophores and the carbogenic core. CNPs that exhibit mostly or exclusively PL arising from carbogenic cores are obtained at even higher temperatures (300 and 400 degrees C, respectively). Since the molecular fluorophores predominate at low pyrolysis temperatures while the carbogenic core starts forming at higher temperatures, the PL behavior of CNPs strongly depends on the conditions used for their synthesis.

通过混合氨基修饰碳点(N-CDs)与酞菁锌(PcZn)合成了静电结合的N-CDs/PcZn复合结构. 利用荧光光谱、紫外-可见吸收光谱、循环伏安测试和光催化活性表征证实了N-CDs的光激发电子通过界面转移到了PcZn分子上, 然后在PcZn上发生辐射复合, 导致PcZn的荧光发射增强. 由于N-CDs上的激发电子转移到了PcZn分子上, 促使了其与空穴的分离, 阻碍了N-CDs上的辐射复合发生, 因此提高了N-CDs/PcZn复合体系的光催化活性. 反应温度会影响N-CDs/PcZn复合体系的稳定性和光转换能力, 在常温下制备的N-CDs/PcZn复合结构具有最佳的光物理与化学性能.

Fluorescent carbon dots (CDs) have received great research interest in recent years, with applications in areas such as bio-imaging and chemical sensing. However, solid state photoluminescence of CDs and its related applications (e. g. optoelectronics) is a less explored territory. Here, we have systematically studied the photo emission of CDs in solid state. We found that their blue emission is highly dependent on whether the environment contains polar groups or not. Mechanism studies show that the blue emission of CDs may come from their C=O bonds conjugated with aromatic carbons, and the interaction between polar groups in environment and C=O bonds in CDs is responsible for the environment-dependent photo emission. Our conclusion here should assist the development of CDs' solid state applications.

Two types of carbon dots (C dots) exhibiting respective excitation-independent blue emission and excitation-dependent full-color emissions have been synthesized via a mild one-pot process from chloroform and diethylamine. This new bottom-up synthetic strategy leads to highly stable crystalline C dots with tunable surface functionalities in high reproducibility. By detailed characterization and comparison of the two types of C dots, it is proved concretely that the surface functional groups, such as C=O and C=N, can efficiently introduce new energy levels for electron transitions and result in the continuously adjustable full-color emissions. A simplified energy level and electron transition diagram has been proposed to help understand how surface functional groups affect the emission properties. By taking advantage of the unique excitation-dependent full-color emissions, various new applications can be anticipated. Here, as an example, a ratiometric pH sensor using two emission wavelengths of the C dots as independent references has been constructed to improve the reliability and accuracy, and the pH sensor is applied to the measurement of intracellular pH values and cancer diagnosis.

A new type of environmentally friendly phosphor based on carbon nanodots (CDs) has been developed through the dispersion of CDs by integrating the CDs with starch particles. The starch particles contain large numbers of hydroxyl groups around the surfaces, which can effectively absorb the CDs, whose surfaces are functionalized by lots of carboxyl and amide groups, through hydrogen bonding. Effective dispersion of CDs on the surfaces of starch particles can suppress the non-radiative decay processes and photoluminescence (PL) quenching induced by aggregation of CDs. The starch matrix neither competes for absorbing excitation light nor absorbs the emissions of CDs, which leads to efficient PL emitting. As a result, the starch/CD phosphors with a quantum yield of similar to 50% were obtained. The starch/CD phosphors show great potential in phosphor-based light emitting diodes, temperature sensors, and patterning.

UV and thermal stable, photoluminescent carbon dots (CDs) prepared by embedding CDs in ionic salt crystals such as NaCl, KCL, KBr are demonstrated. The salt crystal embedding matrix does not interfere with CDs strong emission, and provides effective protection to CDs from the environment. The degradation of 20% of the initial luminescence intensity of salt-encapsulated CDs (S-CDs) is 15 times slower under UV and 6 times slower under heat compared to that of CDs in silica matrix. We also demonstrate that the S-CDs can be applied as a color-converting phosphor for typical GaN UV light emitting diodes (LEDs) with significant improvements in stability as well as processability. (C) 2014 Elsevier B.V.

In this work, the optical properties of carbon nanoparticles (CNPs) can be modulated by the dopant-N atom and sp(2) C-contents. CNPs prepared with the low urea mass ratio of 0.2:1 (CNP1) exhibit blue emission (maximum PL quantum yield: 15%). Increasing sp(2) C- and dopant-N atom contents, as determined in CNPs prepared with high urea mass ratio of 2:1 (CNP2), lead to green emission (maximum PL quantum yield up to 36% in ethanol aqueous solution). Amplified spontaneous emission (ASE) can be observed only in CNP2 ethanol aqueous solution. Green lasing emission is achieved from CNP2 ethanol aqueous solution in a linear long Fabry-Perot cavity, indicating the potential of CNP2 as a gain medium for lasing. CNP2 shows superior photostability compared with C545T dye. The green emission from CNP2 is speculated to arise from electron-hole recombination (intrinsic state emission). The high PL quantum yield and small overlap between absorption and emissions of CNP2 ethanol aqueous solution are the key factors in realizing lasing emission.

To demonstrate the effects of surface atoms on photoluminescence (PL) and photocatalytic activities of luminescent carbon dots (CDs), we design and tailor the surface groups of CDs with heteroatoms by a facile and effective approach. The coexistence of O and N radicals in CDs results in strong PL while CDs containing O and Cl radicals show high photocatalytic activity. This is attributed to the different degrees and directions of energy band bending from inner to surface induced by O, N, and Cl radicals at the surface of CDs. The coexistence of both upward and downward band bending that are caused by the O and Cl radicals, respectively, in CDs is similar to an internal electronic field that facilitates the separation of electron-hole pairs and carrier migration, leading to high photocatalytic activity. These results may also be used for designing and tailoring optical-electronic properties of carbon nanostructures.

A facile and green method to tailor surface groups of carbon quantum dots (CQDs) is developed by hydrothermal treatment in an autoclave. The photoluminescence (PL) behaviors of CQDs depend on the types of surface groups. Highly efficient photoluminescence is obtained through amino-hydrothermal treatment of the CQDs reduced by NaBH4. The effects of surface groups on PL behavior are attributed to the degrees of energy band bending induced by surface groups. (C) 2014 Elsevier B.V.