Multicolour nitrogen-doped carbon dots: tunable photoluminescence and sandwich fluorescent glass-based light-emitting diodes

Fluorescent carbon dots functionalization

Carbon dots (CDs), as a new type of luminescent zero-dimensional carbon nanomaterial, have been applied in a variety of fields. Currently, functionalization of CDs is an extremely useful method for effectively tuning their intrinsic structure and surface state. Heteroatom doping and surface modification are two functionalization strategies for improving the photophysical performance and broadening the range of applications for fluorescent CDs. Heteroatom doping in CDs can be used to tune their intrinsic properties, which has received significant research interests because of its simplicity. Surface modification can be applied for varying active sites and the functional groups on the CDs surface, which can endow fluorescent CDs with the unique properties resulting from functional ligand. In this review, we summarize the structural and physicochemical properties of functional CDs. We focused our review on the latest developments in functionalization strategies for CDs and discuss the detailed characteristics of different functionalization methods. Ultimately, we hope to inform researchers on the latest progress in functionalization of CDs and provide perspectives on future developments for functionalization of CDs and their potential applications.

Polymer-Assisted Self-Assembly of Multicolor Carbon Dots as Solid-State Phosphors for Fabrication of Warm, High-Quality, and Temperature-Responsive White-Light-Emitting Devices

White-light-emitting devices (WLEDs) are considered to be a promising illumination source; especially, the WLEDs based on carbon dots (CDs) with white fluorescence have attracted extensive research interest. Herein, we report the design and implementation of solid white-light-emitting phosphors (WCDs@PS), which combine blue and orange emissive CDs (BCDs and OCDs) assisted by polystyrene (PS) through a self-assembly technique. Based on these phosphors (OCDs/BCDs = 1.2:1), the obtained WLEDs display a warm white light with International Commission on Illumination (CIE) coordinates of (0.35, 0.36), a high color rendering index of 93.2, a low correlated color temperature of 4075 K, and a luminous efficiency of up to 14.8 lm·W^-1. Interestingly, these WLEDs exhibit temperature-dependent emission performance, whose light-emission spectrum can be adjusted in situ from white (λ ∼ 400-730 nm) to blue (λ ∼ 440 nm) in the range of 20-80 °C. A change in CIE coordinates from (0.35, 0.36) to (0.32, 0.23) was also observed. The temperature-driven tunable LEDs as a thermochromism device could broaden the application of CDs-based lighting systems in special displays.

Microwave-assisted synthesis of polyamine-functionalized carbon dots from xylan and their use for the detection of tannic acid

A facile and straightforward microwave-assisted method was used to prepare polyamine-functionalized carbon dots (CDs) from a precursor comprising renewable xylan and branched polyethyleneimine (BPEI). The as-prepared BPEI-CDs were monodispersed sphere particles with an average diameter of about 8.62 nm, and exhibited excellent fluorescent property and high stability, as well as excitation-independent emission behavior. Furthermore, it is attractive that the BPEI-CDs can be used as novel fluorescent probes for detecting tannic acid (TA) sensitively and selectively. At the optimum condition, the TA detection system was established in water solution and ethanol solution with a dynamic range from 0.1 to 5 μM, and their detection limit of 36.8 nM and 44.9 nM were also determined, respectively. Most importantly, the BPEI-CDs-based sensors can be successfully applied to detect TA in real lake water and white wine samples, suggesting the low-cost and excellent BPEI-CDs are potential suitable for TA detection in practical application.

Upconverting Carbon Nanodots from Ethylenediaminetetraacetic Acid (EDTA) as Near-Infrared Activated Phototheranostic Agents

This work describes the synthesis of nitrogen-doped carbon nanodots (CNDs) synthesized from ethylenediaminetetraacetic acid (EDTA) as a precursor and their application as luminescent agents with a dual-mode theranostic role as near-infrared (NIR) triggered imaging and photodynamic therapy agents. Interestingly, these fluorescent CNDs are more rapidly and selectively internalized by tumor cells and exhibit very limited cytotoxicity until remotely activated with a NIR illumination source. These CNDs are excellent candidates for phototheranostic purposes, for example, simultaneous imaging and therapy can be carried out on cancer cells by using their luminescent properties and the in situ generation of reactive oxidative species (ROS) upon excitation in the NIR range. In the presence of CNDs, NIR remote activation induces the in vitro killing of U251MG cells. Through the use of flow imaging cytometry, we have been able to successfully map and quantify the different types of cell deaths induced by the presence of intracellular superoxide anions (^. O₂ ^- ) and hydrogen peroxide (H₂ O₂ ) ROS generated in situ upon NIR irradiation.

Carbon dots produced via space-confined vacuum heating: maintaining efficient luminescence in both dispersed and aggregated states

Aggregation-induced quenching (AIQ) of emission is an obstacle for the development of carbon dots (CDots) for solid-state luminescent devices. In this work, we introduce a method to avoid AIQ and to produce highly luminescent CDots through a space-confined vacuum heating synthesis. In the presence of CaCl₂, a mixture of citric acid and urea forms an inflated foam under vacuum heating at 120 °C. Upon gradually increasing the heating temperature to 250 °C, blue emissive molecular species are first formed, and are then transformed into uniform-sized green emissive CDots through dehydration and carbonization processes taking place in the confined ultrathin spaces of the foam walls. The green luminescence of these CDots originates from conjugated sp² domains, and these CDots exhibit a high photoluminescence quantum yield (PLQY) of 72% in ethanol solution. Remarkably, due to the existence of only one type of recombination center in these nanoparticles, AIQ does not take place in CDot-based close-packed films, which show strong emission with a PLQY of 65%. Utilizing the differences in the emission properties of vacuum heating produced CDots, CDots synthesized through microwave-assisted heating, and commercial green fluorescent organic ink (namely, excitation-dependent vs. excitation-independent emission, and different stability against photobleaching), multilevel data encryption has been demonstrated.

Multi-color carbon dots for white light-emitting diodes

Single metal-doped CDs with color-tunable properties have been successful synthesized by regulating the precursor molar ratios.

Aggregation-induced red shift in N,S-doped chiral carbon dot emissions for moisture sensing

Herein, we report aggregation induced red shifted emissions in N,S-doped chiral carbon dots for moisture sensing in common organic solvents and commercial products.

Highly fluorescent dual-emission red carbon dots and their applications in optoelectronic devices and water detection

Synthesis of dual-emission nitrogen and sulfur co-doped (N,S)-CDs with a quantum yield up to 29.7% and their applications in white LEDs and water detection.

Photoluminescence of PdS2 and PdSe2 quantum dots

PdS₂ and PdSe₂ QDs are fabricated via liquid exfoliation using NMP solvent. The PL behaviors of these QD solutions are studied. The obtained results suggest promising optoelectronic applications with group-10 TMD QDs in the future.

Exploration of the synthesis of three types of multicolor carbon dot originating from isomers

Currently, the synthesis of carbon dots (CDs) exhibiting long-wavelength emission is still challenging. Herein, we have synthesized for the first time three types of CD with multicolor emission derived from isomers. Importantly, their particle size, nitrogen-doping amount and band gaps collectively regulate the fluorescence emission of the proposed CDs.

Fabricating highly luminescent solid hybrids based on silicon nanoparticles: a simple, versatile and green method

In this work, we report a simple but novel method to transfer highly luminescent silicon nanoparticles (Si NPs) from solutions to solids without sacrificing their excellent photoluminescence (PL) properties. Hybrid Si NP/clay phosphors that glowed ultrabright and had colorful PL properties were first obtained. More importantly, large-area and flexible films with superior PL properties can be easily obtained via combining the Si NP/clay hybrids with different kinds of polymer. The Si NP-based phosphors and films from our method show high stabilities with no significant loss of PL performance after long-term storage (several months). In addition, bright yellow-emitting Si NPs were prepared and used as down-converters for white-light-emitting diodes (W-LEDs). Overall, this work presents a simple, versatile and green method to fabricate Si NP-based solid hybrids with superior PL properties, which has promise to be applied in the future in solid-state lighting fields.

Solvent-Controlled Synthesis of Highly Luminescent Carbon Dots with a Wide Color Gamut and Narrowed Emission Peak Widths

Carbon dots (CDs) have tremendous potential applications in bioimaging, biomedicine, and optoelectronics. By far, it is still difficult to produce photoluminescence (PL) tunable CDs with high quantum yield (QY) across the entire visible spectrum and narrow the emission peak widths of CDs close to those of typical quantum dots. In this work, a series of CDs with tunable emission from 443 to 745 nm, quantum yield within 13-54%, and narrowed full width at half maximum (FWHM) from 108 to 55 nm, are obtained by only adjusting the reaction solvents in a one-pot solvothermal route. The distinct optical features of these CDs are based on their differences in the particle size, and the content of graphitic nitrogen and oxygen-containing functional groups, which can be modulated by controlling the dehydration and carbonization processes during solvothermal reactions. Blue, green, yellow, red, and even pure white light emitting films (Commission Internationale de L'Eclairage (CIE)= 0.33, 0.33, QY = 39%) are prepared by dispersing one or three kinds of CDs into polyvinyl alcohol with appropriate ratios. The near-infrared emissive CDs are excellent fluorescent probes for both in vitro and in vivo bioimaging because of their high QY in water, long-term stability, and low cytotoxicity.

Supramolecular Cross-Link-Regulated Emission and Related Applications in Polymer Carbon Dots

Involvement of clear photoluminescence (PL) mechanism in specific chemical structure is at the forefront of carbon dots (CDs). Supramolecular interaction exists in plenty of materials, offering an inherent way to administrate the optical and photophysical properties, especially in terms of newly developed polymer carbon dots (PCDs). However, supramolecular-interaction-derived PL regulation is always ignored in the shadow of many kinds of PL factors, and we still have a limited understanding on the distinct chemical structure and mechanism of supramolecular effect in PCDs. Herein, several distinct photoluminescent phenomena of PCDs under aqueous and solid state are reviewed in terms of supramolecular cross-linking, with highly emphasizing the importance of supramolecular cross-link-enhanced emission (SCEE) effects, and the regulated function of supramolecular interaction's intensity and types between PCDs for special PL behaviors of PCDs. In addition, we categorize the photoluminescent phenomena in PCDs into the following aspects: supramolecular cross-link-enhanced dilute-solution-state emission, concentration-controlled multicolor emission, supramolecular regulation for quenching-resistant solid-state fluorescence, as well as supramolecular cross-link-assisted room-temperature- phosphorescence (RTP) under solid states. Furthermore, the applications of PCDs in light-emitting diodes (LED), solar cells, and anticounterfeiting and data encryption, etc., are presented, based on the distinct supramolecular cross-link-regulated photoluminescent phenomena, especially the solid-state emission. Finally, a brief outlook is given, highlighting the currently existing problems and development direction of supramolecular cross-link-regulated emission in PCDs.