Multicolor Carbon Research Articles

Bright tunable multicolor carbon dots for white light-emitting diodes and fingerprint detection

In this study, in order to achieve high quantum yield (QY) and tunable multicolor carbon dots, the influence of quantum size effects and surface state changes were considered comprehensively. Blue-emitting seed carbon dots (S-CDs) were synthesized using 1,2,4-benzenetricarboxylic acid and urea as precursors. Green-emitting carbon dots (G-CDs) were then prepared by oxidizing S-CDs with 3 % H2O2, followed by treatment with 0.1 M NaOH to produce strong blue-emitting carbon dots (B-CDs). Compared with S-CDs, the QY of G-CDs and B-CDs increased by 35 times and 75 times, respectively. The improvement in quantum yield (QY) and the adjustment in emission wavelength were attributed to the disruption of hydrogen bonds and modifications in surface groups caused by treatments with hydrogen peroxide and sodium hydroxide. By combining B-CDs and G-CDs with commercial red phosphors, warm W-LEDs with a color rendering index as high as 91.4 and a correlated color temperature of 5437 K was successfully prepared, which was suitable for indoor lighting. In addition, B-CDs and G-CDs were used as fluorescent markers for latent fingerprints identification on different substrates, the results showed that B-CDs and G-CDs significantly enhanced the resolution of fingerprint imaging. The synthesized G-CDs and B-CDs offer several advantages, including high quantum yield, excellent photostability, low cost and a straightforward synthesis method. These properties provide a solid material foundation for enhancing the performance of white LEDs and detecting latent fingerprints.

Electrochemical synthesis of multicolor carbon dots with room temperature phosphorescence to thermally activated delayed fluorescence via surface state modulation

Solid-state multicolor carbon dots (CDs) have attracted tremendous attention due to their wide applications. However, the fluorescence quenching of solid-state CDs occurs due to the π-π stacking or energy transfer between adjacent carbon dots. In addition, it is difficult to observe the afterglow of solid-state CDs due to their self-quenching and deliquescence. Here, electrochemically prepared multicolor CDs emit the solid-state fluorescence and afterglow emission with lifetimes up to 657 ms by embedding the CDs into urea matrix. More importantly, the surface amino groups and C = O bonds regulate the afterglow emission of CDs from phosphorescence and thermally activated delayed fluorescence at room temperature. Surface amino groups of multicolor CDs can enhance the spin–orbit coupling, increase the intersystem crossing (ISC) and reverse intersystem crossing (RISC). Thus it can promote the generation of triple excited states and regulate the singlet–triplet energy gap value from 0.384 to 0.026 eV. The formation of covalent bonds stabilizes the single and triple excited states and inhibits the non-radiative recombination, which achieves the enhanced fluorescence and visual afterglow of multicolor CDs. The fluorescence and afterglow CDs can be applied to dual signal imaging and anti-counterfeiting, which broadens the practical applications for solid-state CDs via surface state modulation.

Photoluminescent Multicolor Carbon Dots for UV Detection and Dynamic Anticounterfeiting.

Carbon dots (CDs) are an emerging type of fluorescent carbon nanomaterial with broad application prospects. Among them, photochromic CDs have been widely used in the field of optoelectronic devices but rarely in ultraviolet (UV) detection. In this work, we successfully developed photochromic CDs that exhibit reversible emission under light stimulation in an amine solvent system. Notably, the CDs showed ultrafast photochromic behavior in diethylamine solvent, shifting the fluorescence color from cyan-green to orange-red after 2 s of irradiation, with the solution color changing from pale yellow to pale purple. Furthermore, this performance could recover without additional stimuli, simply by standing for several tens of seconds. Structural analysis indicated that rapid photochromism arises from changes in the surface functional group radicals of the CDs, with the reversibility attributed to fluctuation in these radicals. Leveraging the excellent photochromic properties of CDs, we further developed a device for detecting UV indices in sunlight. This opens up broad prospects for developing high-performance UV detection devices based on CDs.

Multi-color emission composites of white carbon dots and dyes through inner filter effect

A series of multi-color carbon dot composites were obtained by transforming white carbon dots (WCDs) into three primary colors using the dyes' inner filter effect (IFE). WCDs were combined with three distinct dyes (methyl red, bromocresol green, and methylene blue), and three fluorescence colors (red, yellow, and blue) were obtained. The colors of the emitting light excited by the same UV light were similar to the colors of the respective dyes, and have a large Stokes shift. The presence of the IFE between WCDs and dyes was proved through a variety of methods, the analysis of the relationship between the UV of dyes and fluorescence spectra of WCDs, the excitation-emission matrix, as well as the comparison PL decay profiles of WCDs before and after dye addition. The Stern-Volmer quenching constant KSV exhibited no temperature dependence during the IFE process with increasing concentrations of dyes. The UV spectra of the mixture of WCDs and dyes were simply the sum of two individual components, which implies that there is no chemical interaction between WCDs and dyes. Since methyl red and bromocresol green are acid-base indicators, the fluorescence color of the carbon dot composite also changed continuously during the dilute NaOH solution titration process. In furtherment, distributing the binary system of “WCDs + dye” within poly (vinyl alcohol) (PVA), three colors fluorescent composite films of “WCDs / Dye / PVA” were produced successfully.

The controllable synthesis of multi-color carbon quantum dots modified by polythiophene and their application in fluorescence detection of Au3+ and Hg2+

Herein, hydrothermal method was used to prepare a series of multi-color polythiophene modified carbon quantum dots. Under UV excitation, fluorescence their maximum emission wavelengths appear at 612 nm, 570 nm, and 540 nm respectively. The prepared CD-BTH and CD-BN can have specific detection of Au3+ and Hg2+ through fluorescence quenching effect. The detection limits for Au3+ are 3 nM and 5.4 nM respectively, and for Hg2+ are 23 nM and 90 nM respectively. CD-KN detects Au3+ specifically through fluorescence resonance, with a detection limit of 33 nM. Under the interference of other metal ions, three types of polythiophene modified quantum carbon dots exhibit excellent selectivity for the responsive ions. Meanwhile, this article also elucidates the law that as the electron withdrawing ability of the side chains of polythiophene derivatives increasing, the fluorescence emission peaks of the prepared polythiophene modified carbon dots shifts red and the fluorescence quantum yield is higher.

Water sensitized and highly bright multicolor Ni-doped carbon dots nanoarchitectonics in polar solvents towards stable flexible films

To address the issues of low photoluminescence quantum yields (PLQYs), broad PL spectra, and poor stability, multicolor carbon dots (CDs) were synthesized by using different precursors. Blue-emitting CDs were created via a solvothermal synthesis by using citric acid and ethylenediamine while green-emitting CDs were fabricated using O-phenylenediamine. Ni doping further increased the PLQYs and stability of CDs. Ni-doped CDs (Ni-CDs) with blue- and green-emitting were synthesized through a one-step solvothermal method. The PL peak wavelengths of Ni-doped blue CDs (Ni-BCDs) and Ni-doped green CDs (Ni-GCDs) were located at 450 and 540 nm, respectively. After Ni-doping, the average particle size of green-emitting CDs was increased from 2.35 to 2.65 nm. Compared with undoped CDs, Ni-CDs exhibited narrow PL spectra, high PLQYs, and long fluorescent lifetime. The PLQYs of Ni-BCDs and Ni-GCDs were increased to 83.92 and 35.60 %, respectively. Interestingly, the PL peak wavelengths of Ni-doped CDs revealed a red-shift with increasing the solvent polarity (e.g. acetone, acetonitrile, N, N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, ethanol, methanol, and H2O). In addition, the PL peaks of green-emitting Ni-CDs generated a large red-shift with increase the ratio of water in organic solvents compared with blue one. Namely, solid Ni-GCDs powders also revealed water dependent PL. After incorporating the CDs in flexible films, Ni-GCDs still revealed high brightness and stability. These results supplied important possibility for the application of multicolor CDs.

White carbon dots with high quantum yield and multicolor carbon dots synthesized by the microwave method in one step

In the field of optics, carbon dots (CDs) have been extensively studied and have made rapid advancements in related fields, including bioimaging, optoelectronic devices and optical probes. However, it is difficult to efficiently synthesize high quantum yield (QY) white fluorescence CDs and multicolor CDs, which restricts their development in the field of optics. In this work, we chose formamide as the reaction solvent and used citric acid (CA) and 4-bromo-1,2-diaminobenzene to synthesize high-performance white fluorescent CDs20 with a QY of up to 87.5% and excellent stability (28 days). The reaction solvents (water, N,N-dimethylformamide and ethanol) were changed to obtain colorful CDs20 (orange, green and yellow) covering a broader visible spectrum via a microwave method. The solid model, which combines white fluorescent CDs20 and polyvinyl alcohol (PVA), exhibits strong white fluorescence as well as a solution state. To develop white-emitting diodes suitable for indoor use, a white CDs20 / PVA mixture with brilliant white fluorescence might be placed on ultraviolet (UV) chips (365 nm). The white LED had a high color purity (0.34, 0.25), excellent correlation color temperature (4250 K) and color rendering index (72.5). The results above show that white CDs have great promise for use in optical device fields.

Multicolor lignin-derived carbon quantum dots: Controllable synthesis and photocatalytic applications

The cost-effective, high-performance fabrication of multicolor carbon quantum dots (CQDs) from biomass is critical to its prospective application. Lignin, with its phenylpropane structural unit and abundant functional groups, is a reliable precursor for the formation of high-quality CQDs. Here, CQDs from renewable lignin were successfully prepared via a two-step method, and controllable preparation of CQDs to emit blue, green, yellow, and red fluorescence was achieved by adjusting the N-containing acid dopant. The investigated fluorescence mechanism revealed that the energy bandgap of the lignin-derived CQDs decreased and the emission wavelength redshifted as the graphitization degree and number of C=O surface groups increased. The light absorption region of the Bi7O9I3 photocatalysts modified with blue CQDs to red CQDs gradually broadened in the redshifted direction. In particular, compared with pure Bi7O9I3 (70.9%), the red CQDs-modified Bi7O9I3 (RCQD/BOI) can remove 94.7% of antibiotics within 60 min of light irradiation. The superior photocatalytic activity of RCQD/BOI is attributed to the established internal electric field that accelerates charge transfer and effectively separates the photogenerated e+-h+ inside Bi7O9I3. Furthermore, through radical capture, electron paramagnetic resonance (EPR) experiments validated the photocatalytic mechanism of RCQD/BOI and revealed that h+, O2− and OH are key reactants in the photocatalytic degradation process. This promising and sustainable approach for the synthesis of multicolor lignin-derived CQDs opens the avenue of high-value utilization of biomass resources, green production of CQDs nanomaterials, and efficient development of CQDs-based photocatalysts for wastewater treatment.

Efficient preparation strategy of high quantum yield multicolor CDs for warm white LED

Multicolor carbon dots (CDs) possess tremendous potential applications, especially in optoelectronic devices. However, further applications in warm white LED have been constrained due to the extremely low quantum yield (QY) of multicolor CDs. In this work, fluorescence enhancement multicolor CDs (o-CDs(cat.) (emitted yellow, Em = 550 nm, QY = 85.4 %), m-CDs(cat.) (emitted blue, Em = 440 nm, QY = 35.7 %), p-CDs(cat.) (emitted red, Em = 610 nm, QY = 73.8 %)) with almost 15 % QY improvement, without changing the fluorescence emission wavelength, was successfully achieved by introducing MnSO4 into the reaction system. The relevant mechanism may be the catalytic effect of MnSO4, which leads to the increased content of C = N and pyridine N, further suppressing non radiative transitions, leading to the increasement of QY. Finally, the obtained high QY multicolor CDs were applied to warm white LED with the color coordinates (CIE) of (0.33,0.36), color rendering index (CRI) of 90, correlated color temperature (CCT) of 3473 K. Laying the foundation for the research methods and mechanisms of metal ion caused high QY of CDs.

Novel strategy of multidimensional information encryption via multi-color carbon dots aggregation-induced emission

Novel strategy of multidimensional information encryption via multi-color carbon dots aggregation-induced emission

Synthesis of Multicolor Carbon Dots Catalyzed by Inorganic Salts with Tunable Nonlinear Optical Properties.

The nonlinear optical properties of carbon dots have been in the spotlight in recent years. In light of the complexity and diversity of factors affecting the nonlinear optical properties of carbon dots, how to reveal the origin and physical mechanism of the nonlinear optical properties of carbon dots accurately has become a problem. In this work, a template-free method was designed to prepare carbon dots via solid-phase reaction with phloroglucinol as a single carbon source and sodium bisulfate as the catalyst. This method is simple, green, safe, and easy to be prepared on a large scale. Three carbon dots with different luminous colors were obtained by simply adjusting the reaction temperature. The rise of reaction temperature affects the surface functional groups, and then hinders the luminescence of surface states, leading to the change of luminescence properties. The nonlinear optical properties of carbon dots were analyzed by the Z-scan technique. Surprisingly, all carbon dots have nonlinear optical responses, but there are differences in performance. Results prove the increase in sp2 domains may contribute to the significant improvement of the nonlinear optical properties of carbon dots, indicating a direction to improve the nonlinear optical properties of carbon dots.

A shining transmutation of lignin into multicolor carbon dots via the dynamic solvent-fractionation engineering

As a fascinating luminescent subclass, the rapid growth of versatile carbon dots from ideally sustainable biomass has been shouldering the duty of relieving energy and environment pressures that is committed to carbon neutrality. Despite the renewable lignin with conjugated aromatic structure, tunable linkages and functional species (e.g.,–OH, –COOH and –OCH3), the fabrication of multicolor lignin-derived carbon dots (LCDs) covering the red-emissive luminescence is awkward by lacking the task-specific techniques and modulating mechanisms. Herein, a library of blue, green and red-emissive LCDs is built through a stepwise solvent-fractionation engineering with dynamic ethanol sieving and dichloromethane/water extraction. By refined lignin, it is revealed that their average molecular weights and –OH/COOH contents dominate the nanosize, reactivity, lifetime, and photophysical features of LCDs. We then showcase the gradient lignin structure to involve LCDs properties capable of driving their potential functions in the multi-target sensing and solid-state luminescent films. Monitoring tetracycline and metal-ions (Fe3+, Al3+ and/or Ag+) with the ideal selectivity and sensitivity within a broad concentration is accomplished via evaluating the linear correlations. Transparent solid-state luminescent composite films that demonstrate the promising scalability of reserving perishable fruit are successfully prepared using red-emitting LCDs as additives in polyvinyl alcohol matrix. Hence the in-depth understanding of lignin chemistry will provide a technical guidance to achieving multicolor LCDs with tailored fluorescence performances and functionalities.

Preparation of multicolor carbon quantum dots by hydrothermal method and their functionalization applications

Carbon quantum dots (CQDs) have become a popular research topic because of their many unique virtues, especially the significance of tunable photoluminescence properties. However, the synthesis of multicolor CQDs is still at an exploratory stage, and there are many dilemmas that have not yet been well resolved, such as long-wavelength emission and solid-state luminescence. Here, we selected suitable carbon and dopant sources as precursors for the synthesis of CQDs through the rational design of the experiments in an aqueous system, and the as-prepared CQDs possessed blue, green, yellow and red emissions, with optimal emissions of approximately 475 nm, 530 nm, 580 nm, and 645 nm, respectively. Furthermore, the corresponding PLQYs were 30.13 %, 36.84 %, 39.16 % and 21.36 %, respectively. It was found that the redshift of the emission wavelengths can be attributed to the synergistic effect of the increase in the sp2 conjugate size and the surface states. To conquer the aggregation caused quenching (ACQ) of CQDs and realize the solid-state luminescence of CQDs, we successfully prepared solid-state fluorescent films and solid-state phosphors. Finally, multicolor CQDs were successfully applied to prepare monochromatic and white light-emitting diodes (WLEDs). The adopted green synthesis technology can provide a good technical support for the future development of CQDs synthesis.

Highly stable multicolor carbon dots created using o-phenylenediamine and terephthalic acid systems towards flexible emitting films

Multicolor carbon dots (CDs) with high stability are desired for various light emitting devices and bio-images. In this paper, the green and red emitting CDs were created by o-phenylenediamine and terephthalic acid (TA) as precursors at different temperatures via a solvothermal reaction. An efficient response surface methodology is developed to analyze the formation mechanism. Using optimized conditions, the green and red emitting CDs reveal photoluminescence quantum yields (PLQYs) of 34.0 % and 26.8 %, respectively. The result of response surface method indicates that temperature, precursor concentration, and TA amount significantly influence the PLQYs of the CDs. The formation mechanism of the CDs was proposed by analyzing solvatochromism phenomena, oxidation processes, and fluorescence lifetimes. Initially, green CDs with surface state luminescence were formed followed by the subsequent generation of red CDs exhibiting molecular and carbon core state emission during oxidation. These CDs reveal high stability, in which the PL intensity almost remained unchanged after 7 months. Furthermore, three-color CDs/polymer films (λem = 500, 536, and 568 nm) were successfully fabricated by using these two types of CDs. Sample 180-CDs/polystyrene film had photochromic properties, while other films had good photostability.

Reaction-time-controlled carbon dots nanoarchitectonics with stable and bright photoluminescence for white light emission

It is still a challenge for multicolor carbon dots (CDs) with stable and bright photoluminescence (PL). The controlling of synthesis becomes a hot topic. In this paper, CDs with blue-, green- and red-emitting named as B-CDs, G-CDs, and R-CDs were prepared using three isomers of phenylenediamine as precursors by one-step solvothermal synthesis. Green and red emitting CDs with C, N and O components named as samples G-CDs and R-CDs revealed uniform nanoparticle distribution with average sizes of 7.2 and 5.7 nm, respectively. The PL peak wavelength of three kinds of CDs were 430, 546 and 613 nm, and their average fluorescence lifetime was 5.32, 22.35, 8.74 ns, respectively. The full width at half maximum of PL spectra of the samples was 65.12, 92.63, 83.62 nm, and their PL quantum yields were 8.19, 43.43, and 5.14%, respectively. The brightly luminescent CDs were further embedded in prepared polyvinyl alcohol films to prepare a white emitting layer by adjusting the ratios of CDs with different emitting color. The composite CDs revealed stable and bright white emitting in the film with a Commission Internationale d'Eclairage (CIE) coordinate of (0.28, 0.33). The result suggested that these unique luminescent CDs have potential applications in various luminescence fields.

Unveiling Unconventional Luminescence Behavior of Multicolor Carbon Dots Derived from Phenylenediamine.

Fluorescence regulation of carbon dots (CDs) during their preparation has become a hot research topic. In this work, multicolor fluorescent CDs with unconventional luminescence behavior are prepared by using o-, m-, or p-phenylenediamine (o-PD, m-PD, or p-PD, respectively) and 2,3-dihydroxynaphthalene with rich hydroxyl groups as reaction precursors. Tunable multicolor fluorescent CDs with bright blue, yellow, and red colors can be obtained by a solvothermal method under the joint action of ethanol and hydrochloric acid. The fluorescence emission of the synthesized CDs follows a rule of o-PD to m-PD to p-PD from blue to red, which is contrary to most previously reported results (the luminescence from blue to red following an order of m-PD to o-PD to p-PD). Our results reveal that the differences in the polymerization, surface states, functional groups, and graphite N content of CDs might be the main reasons for the unconventional luminescence behavior. In addition, these multicolor CDs have good applications in the fields of light-emitting diode lighting and anticounterfeiting.

Preparation of multicolor carbon dots with thermally turn-on fluorescence for multidimensional information encryption

Carbon dots (CDs) with superior fluorescence properties have attracted a growing number of research interests in anti-counterfeiting. However, the preparation of CDs with thermally turn-on fluorescence and full-color-emitting in visible spectrum is still a big challenge due to the complicated reaction mechanism in the formation of CDs. Here, a simple precursor-oriented strategy for the preparation of multicolor CDs with heat-stimuli turn-on fluorescence is reported. Comprehensive experimental characterizations and theoretical calculations revealed that the emission wavelength of CDs can be readily tuned from 460 nm to 654 nm with selected precursors, which was ascribed to the extent of conjugated sp2-domains (core states) and the amount of oxygen- and nitrogen-containing groups bound to sp2-domains (surface states). After simply mixing two or three kinds of CDs, a full-color range of fluorescence emission was realized, and the CDs-based fluorescence inks were successfully fabricated. Particularly, all the printed patterns from the inkjet exhibited a thermal-induced enhancement in fluorescence. On this basis, combining CDs with heating-induced “turn-off” fluorescence materials can lead to multidimensional and multistage encryption. These results demonstrate that the thermochromic and photochromic CDs with much more enhanced security exhibit promising application in data storage and encryption.

Bioinspired multicolor carbon dots: A comprehensive cytotoxicity, phytotoxicity and bioimaging in animal cells and plants.

During past decades, carbon dots (CDs) as a kind of nanoparticles with interesting fluorescence properties have retained their place as one of the best bioimaging agents although their effects on plants have been rarely studied. In this study, we synthesized two kinds of concentration-dependent multicolor CDs with two solvent approaches, phosphate buffered saline (PBS) and Ethanol 20%. We confirm the nature of CDs through Fourier transform infrared spectroscopy, atomic force microscopy, dynamic light scattering, zeta potential, X-ray powder diffraction, and high-resolution transmission electron microscopy. Afterward, cytotoxicity, phytotoxicity, and bioimaging of animal cells and plants by both synthesized CDs have been examined. Eventually, PBS-based CDs were recommended during this study as an efficient bioimaging agent for animal cells and plants because of appealing features of this CD, such as a small size range of less than 10 nm, surface charge with average of -24 mV, a high quantum yield of 35.82%, the higher fluorescence intensity of approximately 400 a.u. for blue fluorescence light and 250 a.u. for green fluorescence light. Other features showing the superiority of PBS-based CDs include high photostability, low phytotoxicity (P≤0.05 and P≤0.01) and above all, there is no significant cytotoxicity at the concentration range of 500-7.81 μg/mL.

Blue, Yellow, and Red Carbon Dots from Aromatic Precursors for Light-Emitting Diodes.

In this work, multicolor fluorescent carbon dots with red (R-CDs), yellow (Y-CDs), and blue (B-CDs) emissions were prepared by choosing proper aromatic precursors with different amounts of benzene rings through a simple solvothermal method. The characterization showed that the prepared carbon dots were spherical with a size under 10 nm, rich surface functional groups, and good stability. The emission wavelengths were located at 440, 530, and 580 nm under the excitation of 370 nm. The relative fluorescence quantum yield (QY) of R-CDs, Y-CDs, and B-CDs was 11%, 59%, and 33%, respectively. The related characterization demonstrated that the redshift in the photoluminescence was caused by the synergistic effect of the increasing graphitic nitrogen content, quantum size effect and surface oxidation state. By mixing the three prepared CDs into a PVA matrix, the transparent and flexible films produced relucent blue, yellow, and red emissions under 365 nm UV light, and solid-state quenching was effectively avoided. LEDs were fabricated by using B-CDs, Y-CDs, and R-CDs/PVA with a semiconductor chip. These CDs-based LEDs produced bright blue, yellow, and red light with CIE color coordinates of (0.16, 0.02), (0.38, 0.58), and (0.50, 0.49) were successfully manufactured utilizing the prepared blue, yellow and red multicolor carbon dots as the solid luminescent materials. The results showed that the synthesized CDs can be potentially applied in multi-color monitors as a promising candidate for light-emitting diodes (LEDs). This work blazes a novel trail for the controllable preparation of multicolor fluorescent carbon dots.

Turning Waste into Treasure: Multicolor Carbon Dots Synthesized from Waste Leather Scrap and their Application in Anti-Counterfeiting

Using biomass materials to prepare carbon dots (CDs) has received significant interest. As a cheap and environmentally friendly material, waste leather scrap can be used for the preparation of CDs and performance tuning. Herein, waste leather scrap is used as a precursor reactant to fabricate multicolor (red, green, and blue) carbon dots (R-CDs, G-CDs, and B-CDs) with a tunable emission wavelength via a simple one-step hydrothermal/solvothermal strategy using only a nitrogen source (p-phenylenediamine or o-phenylenediamine) for doping. The morphology, structure, and optical properties of the CDs were investigated by transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, ζ-potential measurements, X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–vis), spectroscopy, photoluminescence (PL), and UV-differential reflectance spectroscopy (UV-DRS). Results showed that the sizes of R-CDs, G-CDs, and B-CDs are 10.0, 7.4, and 2.5 nm, respectively, and all have a typical crystal plane of graphitic carbon structure rich in chemical groups such as C═O, −OH, C–N, etc. The detailed characterization and comparison of the three types of CDs confirm that the size and functional groups can effectively add other energy levels for electron transitions and tuning of luminescent properties of CDs. The emission wavelengths of R-CDs, G-CDs, and B-CDs are 612, 535, and 429 nm, and at the same time, the energy levels were calculated by UV–vis DRS to be 2.11, 2.43, and 2.58 eV, respectively. Because of the stable optical properties and excellent chemical performance, CDs can be employed as ink and flexible films. The utilization of renewable waste leather scrap, along with convenient hydrothermal/solvothermal methods, paves the way to the sustainable, cost-effective synthesis of CDs for practical applications in anti-counterfeiting.