Multicolor tunable highly luminescent carbon dots for remote force measurement and white light emitting diodes

Synthetic strategies, properties and sensing application of multicolor carbon dots: recent advances and future challenges

Recently, carbon dots (CDs) as newly developed carbon-based nanomaterials due to advantages such as excellent photostability and easy surface functionalization have generated wide application prospects in fields such as biological imaging and chemical sensing. The multicolor emission carbon dots (M-CDs) were acquired through the selection of different carbon source precursors, change of synthesis conditions and synthesis environment. Therefore, the aim of this review is to summarize the latest research progress in polychromatic CDs from the perspectives of synthesis strategies, luminescent mechanisms, luminescent properties and applications. This review focuses on how to prepare MCDs by changing raw materials and synthesis conditions such as reaction temperature, synthesis time, synthesis pH, and synthesis solvent. This review also presents the optical properties of MCDs, concentration effects, solvent effects, pH effects, elemental doping, and surface passivation on them, as well as their creative applications in the field of sensing applications. It is anticipated that this review will serve as a guide for the development of multifunctional M-CDs and inspire future research on controllable design and preparation of M-CDs.

Nitrogen-doped carbon dots for efficient deep-blue light-emitting diodes with CIE closely approaching the HDTV standard color Rec.BT.709

Here, we demonstrate deep-blue carbon dots (CDs) with luminescence centered at 415 nm and PLQY exceeding 60% via nitrogen doping. A bright and high-color-purity CDs-based light-emitting diode (CLED) is achieved with an external quantum efficiency (EQE) of 1.74%, a maximum luminance of 1155.0 cd m^-2, and a colour coordinate (0.16, 0.08) closely approaching the HDTV standard color Rec.BT.709 (0.15, 0.06) specification.

Multiple Stimuli-Response Polychromatic Carbon Dots for Advanced Information Encryption and Safety

Optical information encryption and safety have aroused great attention since they are closely correlated to data protection and information safety. The development of multiple stimuli-response optical materials for constructing large-capacity information encryption and safety is very important for practical applications. Carbon dots (CDs) have many gratifying merits, such as polychromatic emission, diverse luminous categories, and stable physicochemical properties, and are considered as one of the most ideal candidates for information protection. Herein, carbon core, functional groups, solvents, and other crucial factors are reviewed for outputting polychromatic emission of multiple luminous categories. In particular, substrate engineering strategies have been emphasized for their critical role in yielding excellent optical features of multiple luminous categories. High-capacity information encryption and safety strategies are reviewed by relying on the rich optical properties of CDs, such as polychromatic emission, multiple luminous categories of fluorescence, afterglow, and upconversion, as well as external-stimuli-assisted optical changes. Some perspectives for preparing excellent CDs and further developing information security strategies are proposed. This review provides a good reference for the manipulation of polychromatic CDs and the development of next-generation information encryption and safety.

The Emerging Development of Multicolor Carbon Dots

As a relatively new type of fluorescent carbon-based nanomaterials, multicolor carbon dots (MCDs) have attracted much attention because of their excellent biocompatibility, tunable photoluminescence (PL), high quantum yield, and unique electronic and physicochemical properties. The multicolor emission characteristics of carbon dots (CDs) obviously depend on the carbon source precursor, reaction conditions, and reaction environment, which directly or indirectly determines the multicolor emission characteristics of CDs. Therefore, this review is the first systematic classification and summary of multiple regulation methods of synthetic MCDs and reviews the recent research progress in the synthesis of MCDs from a variety of precursor materials such as aromatic molecules, small organic molecules, and natural biomass, focusing on how different regulation methods produce corresponding MCDs. This review also introduces the innovative applications of MCDs in the fields of biological imaging, light-emitting diodes (LEDs), sensing, and anti-counterfeiting due to their excellent PL properties. It is hoped that by selecting appropriate adjustment methods, this review can inspire and guide the future research on the design of tailored MCDs, and provide corresponding help for the development of multifunctional MCDs.

Color Conversion Light-Emitting Diodes Based on Carbon Dots: A Review

This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump wavelength. White LEDs are typically obtained by pumping broad band visible-emitting CDs by an UV LED, or yellow-green-emitting CDs by a blue LED. The most important methods used to produce CDs, top-down and bottom-up, are described in detail, together with the process that allows one to embed the synthetized CDs on the surface of the pumping LEDs. Experimental results show that CDs are very promising ecofriendly candidates with the potential to replace phosphors in traditional color conversion LEDs. The future for these devices is bright, but several goals must still be achieved to reach full maturity.

Circularly Polarized Photodetectors Based on Chiral Materials: A Review

Circularly polarized light (CPL) plays an important role in many photonic techniques, including tomographic scanning based on circular polarization ellipsometry, optical communication and information of spin, and quantum-based optical calculation and information processing. To fully exploit the functions of CPL in these fields, integrated photoelectric sensors capable of detecting CPL are essential. Photodetectors based on chiral materials can directly detect CPL due to their intrinsic optical activity, without the need to be coupled with polarizers and quarter-wave plates as in conventional photodetectors. This review summarizes the recent research progress in CPL photodetectors based on chiral materials. We first briefly introduce the CPL photodetectors based on different types of chiral materials and their working principles. Finally, current challenges and future opportunities in the development of CPL photodetectors are prospected.

Recent advances in synthesis and applications of room temperature phosphorescence carbon dots

Recently, room temperature phosphorescence (RTP) feature of carbon dots (CDs) has gradually diverted researchers' attention from fluorescence and sparks new research boom due to its ultra-long luminescence lifetime and large Stokes shift. Some attempts have been made to construct CDs-based RTP materials, and had seen some important progress. However, few review articles were published to systematically summarize them. Herein, we summarize the recent synthesis advances of the RTP CDs, mainly focusing on matrix-assisted method and self-protection method. Different construction methodologies lead to different RTP properties and luminescence mechanisms. Based on this fact, we discuss the correlation between them and further summarize their potential applications in sensing, light-emitting diodes, anti-counterfeiting, and information protection filed. Finally, the currently existing problems and development perspectives of CDs-based RTP materials was proposed.

Fluorescent Carbon Dots: Fantastic Electroluminescent Materials for Light-Emitting Diodes

Fluorescent carbon dots (CDs) have emerged as fantastic luminescent nanomaterials with significant potentials on account of their unique photoluminescence properties, high stability, and low toxicity. The application of CDs in electroluminescent light-emitting diodes (LEDs) have aroused much interest in recent years. Herein, the state-of-the-art advances of CD-based electroluminescent LEDs are summarized, in which CDs act as active emission layer and interface transport layer materials is discussed and highlighted. Besides, the device structure of CD-based LEDs and preparation methods of CDs are also introduced. Furthermore, the opportunities and challenges for achieving high performance CD-based electroluminescent LED devices are presented. This review article is expected to stimulate more unprecedented achievements derived from CDs and CD-based electroluminescent LEDs, thus further promoting their practical applications in future solid-state lighting and flat-panel displays.

The Rapid and Large-Scale Production of Carbon Quantum Dots and their Integration with Polymers

Carbon quantum dots (CDs) have inspired vast interest because of their excellent photoluminescence (PL) performances and their promising applications in optoelectronic, biomedical, and sensing fields. The development of effective approaches for the large-scale production of CDs may greatly promote the further advancement of their practical applications. In this Minireview, the newly emerging methods for the large-scale production of CDs are summarized, such as microwave, ultrasonic, plasma, magnetic hyperthermia, and microfluidic techniques. The use of the available strategies for constructing CD/polymer composites with intriguing solid-state PL is then described. Particularly, the multiple roles of CDs are emphasized, including as fillers, monomers, and initiators. Moreover, typical applications of CD/polymer composites in light-emitting diodes, fluorescent printing, and biomedicine are outlined. Finally, we discuss current problems and speculate on their future development.

One-step preparation of red-emitting carbon dots for visual and quantitative detection of copper ions

A one-step solvothermal method for the preparation of carbon dots with red fluorescence (R-CDs) was put forward, in which sodium citrate and formamide were chosen as precursors, while formamide was adopted as the solvent. The fluorescence emission peak of the as-prepared R-CDs remained the same (600 nm) when the excitation wavelength increased from 490 nm to 560 nm, and the fluorescence quantum yield is 35.3%. Furthermore, the fluorescence intensity of the as-prepared R-CDs could be selectively quenched by copper ions, and the mechanism of Cu²⁺ quenching R-CDs is the combination of static and dynamic quenching. As a result, the R-CDs were applied for the construction of a fluorescent sensor without any modification for the quantitative and visual detection of copper ions, which is a typical contaminant in water. The limit of detection for the fluorescent sensor was as low as 5 nmol/L, and it can be used to fast and directly confirm whether the content of copper ions in drinking water meets the criteria of the United States Environmental Protection Agency and the World Health Organization.

Fluorescent probe based on N-doped carbon dots for the detection of intracellular pH and glutathione

Carbon dots (CDs) as fluorescent probes have been widely exploited to detect biomarkers, however, tedious surface modification of CDs is generally required to achieve a relatively good detection ability. Here, we synthesized N-doped carbon dots (N-CDs) from triethylenetetramine (TETA) and m-phenylenediamine (m-PD) using a one-step hydrothermal method. When the pH increases from 3 to 11, the fluorescence intensity of the N-CDs gradually decreases. Furthermore, it displays a linear response to the physiological pH range of 5-8. Au³⁺ is reduced by amino groups on the surface of N-CDs to generate gold nanoparticles (AuNPs), causing fluorescence quenching of the N-CDs. If glutathione (GSH) is then added, the fluorescence of the N-CDs is recovered. The fluorescence intensity of the N-CDs is linearly correlated with the GSH concentration in the range of 50-400 μM with a limit of detection (LOD) of 7.83 μM. The fluorescence probe was used to distinguish cancer cells from normal cells using pH and to evaluate intracellular GSH. This work expands the application of CDs in multicomponent detection and provides a facile fluorescent probe for the detection of intracellular pH and GSH.

Water-soluble carbon dots with blue, yellow and red emissions: mechanism investigation and array-based fast sensing application

This work prepared three kinds of CDs with blue, yellow and red emissions and further in-depth investigated their luminescence mechanisms through theoretical calculations together with experimental data. Afterwards, a sensor array by using these CDs for fast discriminating different types of sulfur-containing species was constructed.