Excellent color rendering index single system white light emitting carbon dots for next generation lighting devices

Facile Molecular-Level Refinements for Carbon Quantum Dots via Hydrogen-Bonding-Assisted Selective Isolation

A novel method for synthesizing and refining high-purity carbon quantum dots (CQDs) using citric acid and diethylenetriamine as precursors is presented, achieved through molecular-level control by exploiting the differences in hydrogen-bonding strength. This process involves precipitation using melamine, extraction into ethanol, and encapsulation with (3-aminopropyl)triethoxysilane (APTES). The resulting APTES-encapsulated CQDs exhibited an enhanced color purity, higher photoluminescence quantum yield, and improved fluorescence stability over a broad pH range. Utilizing these well-defined high-purity CQDs with uniform surface states, it has been revealed that ferric ions are photochemically sensed through the inner filter effect (IFE) mechanism, while mercury ions are detected through the photoinduced electron transfer (PET) mechanism. The versatility of CQDs, coupled with our advanced refinement technology, is expected to contribute significantly to the development of advanced research applications, particularly in displays and sensors.

Carbon Dots: Synthesis, Characterizations, and Recent Advancements in Biomedical, Optoelectronics, Sensing, and Catalysis Applications

Carbon nanodots (CNDs), a fascinating carbon-based nanomaterial (typical size 2-10 nm) owing to their superior optical properties, high biocompatibility, and cell penetrability, have tremendous applications in different interdisciplinary fields. Here, in this Review, we first explore the superiority of CNDs over other nanomaterials in the biomedical, optoelectronics, analytical sensing, and photocatalysis domains. Beginning with synthesis, characterization, and purification techniques, we even address fundamental questions surrounding CNDs such as emission origin and excitation-dependent behavior. Then we explore recent advancements in their applications, focusing on biological/biomedical uses like specific organelle bioimaging, drug/gene delivery, biosensing, and photothermal therapy. In optoelectronics, we cover CND-based solar cells, perovskite solar cells, and their role in LEDs and WLEDs. Analytical sensing applications include the detection of metals, hazardous chemicals, and proteins. In catalysis, we examine roles in photocatalysis, CO2 reduction, water splitting, stereospecific synthesis, and pollutant degradation. With this Review, we intend to further spark interest in CNDs and CND-based composites by highlighting their many benefits across a wide range of applications.

Lysozyme adsorption on carbonaceous nanoparticles probed by second harmonic light scattering

The first hyperpolarizability (β) of two different sizes (15 and 35 nm) of carbonaceous nanoparticle (CNP) is reported for the first time using second harmonic light scattering (SHLS). The β values of the CNPs were found to be larger than those of organic molecules like pNA but lower than those of plasmonic nanoparticles like gold and silver. SHLS was further used to investigate the adsorption of a model protein Lysozyme (Lyz) on these CNPs, which is crucial for the design of safe and effective CNP-based therapeutics. The change in SH intensity from the CNPs on the addition of Lyz was recorded and fitted to the modified Langmuir adsorption model (MLM). The binding constant, free energy changes and surface coverage values show that Lyz is physisorbed on the CNPs forming less than a monolayer. The temperature dependent SH intensity measurements enabled direct determination of enthalpy and entropy changes for Lyz adsorption. The enthalpy and entropy changes reveal that Lyz adsorption is endothermic and entropically driven.

One-Step Colloidal Synthesis of Non-Toxic Electroactive Carbon Dots with a Better Threshold Cytotoxicity and Cytocompatibility

Carbon dots (CDs), because of their characteristic size (<10 nm) and highly fluorescent nature, can be internalized in biological cells or can be tagged to the key components of a living system. While these attributes can be potentially exploited for biomedical applications, the toxicity of CDs remains an important issue to be addressed. Both the synthesis approach and morphological attributes critically determine the dose-dependent toxicity and cytocompatibility of CDs. Against this perspective, we report herein a one-step colloidal synthesis of CDs using different reaction solvents that lead to the formation of three types of CDs (type I, type II, and type III CDs). The cytocompatibility and cellular uptake of CDs in human mesenchymal stem cells (hMSCs) are dependent on the nature of functionalization and concomitantly on the type of precursors. In particular, type I CDs are synthesized using citric acid, hexadecylamine, and octadecene that are immiscible in culture media. The type II CDs synthesized using citric acid and octadecene emit green fluorescence at a 488 nm excitation and were found to be agglomerated when internalized in hMSCs, whereas the type III CDs, synthesized using citric acid and deionized water, exhibit an agglomeration-free behavior. Further, type III CDs show a wide particle distribution, wide emission bandwidth range of 280-700 nm, threshold toxicity of 1 mg/mL, and good cytocompatibility with hMSCs, much better than those in the published reports. When benchmarked against commercial graphene quantum dots, the as-synthesized type III CDs have better electrical conductivity and cytocompatibility at a given dosage. Thus, the electroactive nature of synthesized type III CDs along with their inherent fluorescent property and less cytotoxicity would enable their potential applications in bio-imaging, directional lineage commitment, and cell-based therapy.

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.

Waste to white light: a sustainable method for converting biohazardous waste to broadband white LEDs

The Covid-19 pandemic has generated a lot of non-degradable biohazardous plastic waste across the globe in the form of disposable surgical and N95 masks, gloves, face shields, syringes, bottles and plastic storage containers. In the present work we address this problem by recycling plastic waste to single system white light emitting carbon dots (CDs) using a pyrolytic method. The synthesized CDs have been embedded into a transparent polymer to form a carbon dot phosphor. This CD phosphor has a broad emission bandwidth of 205 nm and is stable against photo degradation for about a year. A white LED with CRI ∼70 and CIE co-ordinates of (0.25, 0.32) using the fabricated CD phosphor is reported. Further our phosphor is scalable and is environmentally sustainable, and will find wide application in next generation artificial lighting systems.