Ultra-Broadband Random Laser and White-Light Emissive Carbon Dots/Crystal In-Situ Hybrids

Exploring Carbon Dots: Green Nanomaterials for Unconventional Lasing

In recent years, the progress toward lighting miniaturization is focused on luminescent nanomaterials. Among them, fluorescent carbon dots (CDs) are receiving increasing attention thanks to their astonishing optical properties complemented by their intrinsic biocompatibility and low toxicity. The CDs can be easily dispersed in water, organic solvents or incorporated in polymeric matrices, preserving their emission properties. However, the relationship between their structural and optical properties is still not fully elucidated, motivating a consistent research effort for the comprehension of their features. Nevertheless, CDs demonstrate to be efficient gain materials for lasing, thanks to their high quantum yield (QY), emission tunability in the visible and near infrared (NIR) range, short lifetimes, and high absorption cross section, even if the synthetic reproducibility, the low reaction yield and the spectral width of the emission may limit their effective exploitation. This review summarizes the latest advancements in the investigation of the characteristic properties of CDs that make laser action possible, illustrating optical geometries for lasing and random lasing, both in solution and solid state, and the few currently demonstrated breakthroughs. While the journey toward their effective application is still long, the potential of CD-based laser sources is promising in various technological fields and futuristic perspectives will be discussed.

Recent advances in fluorescence and afterglow of CDs in matrices

Carbon dots (CDs) are novel nanomaterials with dimensions less than 10 nm that have attracted much attention due to their outstanding optical properties. However, the development of solid-state fluorescence and afterglow methods has been relatively slow, although the properties of these materials under liquid conditions have been extensively studied. In recent years, embedding CDs in a matrix has been shown to prevent aggregation quenching and inhibit nonradiative transitions, thus realizing solid-state fluorescence and afterglow, which has greatly broadened the research and application areas of CDs. In terms of hydrogen bonding, ionic bonding, covalent bonding and spatial confinement, the interactions between CDs and matrices can effectively realize and improve the solid-state fluorescence and afterglow effects of CDs. Recent applications of CDs in matrices in optoelectronics, information security, sensing, biotherapeutics and imaging are also summarized. Finally, we summarize the challenges and developments of CDs in matrices.

Solid-State Red Carbon Dots Based on Biomass Furan Derivatives

In the preparation of carbon dots (CDs), precursors are crucial, and abundant precursors endow CDs with various structures and fluorescence characteristics. Furan (FU) and its derivatives are considered excellent carbonization materials due to their π conjugated structures and active functional groups, such as hydroxyl and aldehyde groups. Herein, we prepare FU-derivative-based CDs by a solvothermal method and investigate the influences of the precursor structure on the fluorescence characteristics. Surprisingly, CDs prepared from 5-hydroxymethylfurfural (HMF) with both aldehyde and hydroxyl groups exhibit red-shifted fluorescence characteristics in the solid state. We postulate that this solid-state fluorescence characteristic is due to the enhancement of supramolecular cross-linking fluorescence between CDs. The unique precursor structure leads to carboxyl groups on the surface of HMF-CDs that are conducive to the hydrogen bond formation. As the concentration of CDs increases, the hydrogen bonding effect increases, leading to a red-shift in the fluorescence wavelength. Therefore, basically full-color CDs/poly(vinyl alcohol) (PVA) phosphor-based light-emitting diodes can be achieved by controlling the degree of supramolecular cross-linking of CDs in PVA. This research provides a new approach for the preparation of solid-state luminescent CDs.

Crystallization-induced emission from F-doped carbon dots

Herein, F-doped CDs with bright red SSF were synthesized by a solvothermal method using trifluoroethanol as the solvent and m-hydroxybenzaldehyde as the carbon source. Strong F-F interactions are vital for inducing crystallization, and solid luminescence is achieved by blocking the nonradiative energy dissipation pathways of crystalline organizations.

Solid-State, Hectogram-Scale Preparation of Red Carbon Dots as Phosphor for Energy-Transfer-Induced High-Quality White LEDs with CRI of 97

In this study, pre-crystallization-controlled, solid-state preparation of red carbon dots (C-dots) from o-phenylenediamine on a hectogram scale with a 94% yield is reported. Highly efficient red phosphor (C-dots@MCC) is obtained by dispersing the C-dots in microcrystalline cellulose, which matched extremely well with the commercial Y3 Al5 O12 :Ce3+ (YAG) phosphor. White light-emitting diodes (WLEDs) fabricated from the two phosphors emitted warm white light with a correlated color temperature of 3845 K, CIE color coordinates of (0.38, 0.37), and an extremely high color rendering index (CRI) of 95, outperforming all the reported YAG-derived WLEDs. Furthermore, the CRI value of the WLED can be further increased to 97 after fine-tuning, which is the highest CRI for WLEDs of any C-dots derived devices reported so far. The superior performance of the WLED is attributed to a delicate energy transfer between YAG and C-dots@MCC. Most importantly, the WLED maintained excellent stabilities under varied currents, working durations, moistures, and temperatures.

Bright solid-state luminescence and high-temperature resistance of Ga-doped carbon dots with ultra-wideband white emission for light-emitting diodes

Fluorescent CDs tend to undergo solid-state aggregation quenching in powder form. This is caused by the stacking of π-π conjugate structures and excessive resonant energy transfer. Moreover, various forms of N play an important role in white CDs suitable for LED applications. White, single-component, non-N-doped CDs have never been reported for LED application. In this study, to overcome this limitation, we developed Ga-doped CD powders containing no N element that exhibit ultra-wideband white emission in the range of 420-800 nm for LED applications and were able to resist solid-state aggregation quenching. Furthermore, the Ga-doped CD powders demonstrated excellent luminescence stability under high temperatures. Another strength of the Ga-doped CD powders is their large Stokes shift, where the peak center of white emission shifts from 550 nm to 650 nm under 365 nm excitation as the Ga doping concentration is adjusted from 0.05 to 0.6 (Ga : H2O, mass ratio). The full width at half-maximum can reach 262 nm. Additionally, the Ga-doped CD powders exhibit good luminescence stability under long-time exposure to an air atmosphere. Their luminescent intensity retained 70%-74% of the initial values even after being left in natural placement for 100 days. Moreover, the Ga-doped CDs demonstrate afterglow features.

Carbon Dots for Electroluminescent Light-Emitting Diodes: Recent Progress and Future Prospects

Carbon dots (CDs), as emerging carbon nanomaterials, have been regarded as promising alternatives for electroluminescent light-emitting diodes (LEDs) owing to their distinct characteristics, such as low toxicity, tuneable photoluminescence, and good photostability. In the last few years, despite remarkable progress achieved in CD-based LEDs, their device performance is still inferior to that of well-developed organic, heavy-metal-based QDs, and perovskite LEDs. To better exploit LED applications and boost device performance, in this review, a comprehensive overview of currently explored CDs is presented, focusing on their key optical characteristics, which are closely related to the structural design of CDs from their carbon core to surface modifications, and to macroscopic structural engineering, including the embedding of CDs in the matrix or spatial arrangement of CDs. The design of CD-based LEDs for display and lighting applications based on the fluorescence, phosphorescence, and delayed fluorescence emission of CDs is also highlighted. Finally, it is concluded with a discussion regarding the key challenges and plausible prospects in this field. It is hoped that this review inspires more extensive research on CDs from a new perspective and promotes practical applications of CD-based LEDs in multiple directions of current and future research.

Centralized Excited States and Fast Radiation Transitions Reduce Laser Threshold in Carbon Dots

As a new type of solution-processed nano-laser material, carbon dots (CDs) have shown considerable potential in optical communication, laser displays, micro/nano processing, and biomedicine. Reducing the laser threshold of the gain material is of considerable significance for further development of CDs' applications in the field of micro/nano lasers. A series of blue-emissive CDs (B-CDs) are synthesized by changing the molar ratios of the precursors (citric acid (CA): L-Cysteine (L-Cys)). B-CDs have a structure of carbon nanoparticles with their surface being modified with 5-oxo-3,5-dihydro-2Hthiazolo [3,2-a]pyridine-7-carboxylic acid (TPCA). The laser can only be generated when the molar ratio of the precursors is between 1:1 and 2:1. With an increase in this ratio, the laser threshold decreases from 341.6 to 165.5 mJ cm^-2 . The decrease in the laser threshold is attributed to the increase in the radiation transition rate and centralized sp³ -related excited state levels, which are favorable for light amplification and population inversion. These results will be instructional for the reasonably design of CDs-based laser materials and prompt their potential use in practical photonics.

Antibacterial and antibiofilm mechanisms of carbon dots: a review

Due to the increasing bacterial resistance to conventional antibiotics, developing safe and effective approaches to combat infections caused by bacteria and biofilms has become an urgent clinical problem. Recently, carbon dots (CDs) have received great attention as a promising alternative to conventional antimicrobial agents due to their excellent antimicrobial efficacy and biocompatibility. Although CDs have been widely used in the field of antibacterial applications, their antibacterial and antibiofilm mechanisms have not been systematically discussed. This review provides a systematic overview on the complicated mechanisms of antibacterial and antibiofilm CDs based on recent development.