Green one-step synthesis of boron and nitrogen co-doped carbon dots based on inner filter effect as fluorescent nanosensors for determination of Fe3+

Significant efforts need to be devoted to enhancing the photoluminescence quantum yields (PLQY) of carbon dots (CDs) due to the typically low PLQY (< 10%) of currently synthesized CDs. Moreover, certain special industries such as textiles, paper, and food all have high requirements for water since Fe³⁺ can affect its color, odor, and taste. The traditional detection methods require expensive equipment, so a facile method to detect Fe³⁺ is urgently needed. In this work, the self-doping of nitrogen (N-CDs) has been achieved through tea residues as the carbon source to inhibit the oxygen-deficient state, and the doping of boric acid (BN-CDs) can activate the electron transition at the carbon site, which effectively enhanced the PLQY of CDs from 11.4% to 25.79% compared to N-CDs. Furthermore, as hydroxylated polyphenols in tea residues can adsorb metal ions, stable non-fluorescent matrix state complexes have been established between BN-CDs and Fe³⁺ to quench the FL owing to the inner filter effect. The linear relationship was formed in the concentration range of 0–60 μM, and the detection limit reached 0.07 μM. It demonstrates that along with the effective treatment of waste tea residues, the synthesized high fluorescence property BN-CDs are suitable to detect Fe³⁺ in water for textiles, paper, food, and other special industries.     

Dual-emission carbon dots-copper nanoclusters ratiometric photoluminescent nano-composites for highly sensitive and selective detection of Hg2+

A novel dual-emission photoluminescent (PL) nano-materials of carbon dots-copper nanoclusters (CDs-CuNCs) nano-composites is prepared for excellent sensitivity and selectivity toward Hg²⁺. The nano-composites are composed of blue photoluminescent CDs and red photoluminescent CuNCs with similar excitation wavelengths through the electrostatic assembly. The red photoluminescence of CuNCs was inhibited by the nano-composites exposed to Hg²⁺, while the blue photoluminescence of CDs remained stable. The color of the nano-composites slowly changed from pink to blue with the added of Hg²⁺ concentration. The limit of detection (LOD) of the nano-composites is 0.31 nmol/L (nM) toward Hg²⁺ in aqueous solution, when the signal to noise ratio is 3. In addition, a visual PL test paper is prepared. When the Hg²⁺ solution is added, the color of test paper transforms from pink to blue immediately. Therefore, the nano-composites are very important for efficient and sensitive detection of Hg²⁺, which show broad application prospects in environmental analysis, food safety detection, biological detection and medical diagnosis in daily life.     

Enhanced luminescence properties and device applications of Tb3+-doped Cs4PbBr6 perovskite quantum dot glass

Cs₄PbBr₆ perovskite quantum dots (QDs) have unique optoelectronic properties and are expected to become a new generation of luminescent materials. However, poor stability, low photoluminescence quantum yield (PLQY), and poor understanding as to the origin of photoluminescence behavior limit its further application. In this study, a series of Tb³⁺-doped Cs₄PbBr₆ perovskite QD glasses with excellent stability were obtained through the optimization of Tb³⁺ doping concentration and in-situ crystallization temperature. Density functional theory calculations and experimental characterization showed that an appropriate amount of lattice-incorporated Tb³⁺ ions can reduce structural defects in QDs, improve the PLQY, and reduce the QD heavy-metal requirements. Notably, the maximum PLQY value reached 47%, which is near to the Cs₄PbBr₆ perovskite crystal. Furthermore, a high-performance white light-emitting diode (WLED) device was prepared. The device featured a color rendering index of 80 and luminous efficiency of 41 lm W^?1. Finally, a QD glass with double emission peaks was prepared by controlling the in-situ crystallization temperature (550 °C). The temperature sensitivity of the QD glass was then studied using the fluorescence intensity ratio method. The maximum relative temperature sensitivity (Sr) reached 2.03% K^?1, which is higher than the previously reported value. Thus, the method proposed in this study can greatly improve the photoluminescence properties of Cs₄PbBr₆ QD glass and expand its applications in WLED and visual temperature sensing.     

In-doped LiCa2.98MgV3O12 rare-earth-free phosphor with a high photoluminescence quantum yield of 67.4%

Rare earth resources applied in numerous novel materials, are increasingly scarce in worldwide. Meanwhile, great attention has been focused on the blue rare-earth-free fluorescent phosphors as an excitation source of near-ultraviolet (NUV) chips, which are available in white-light-emitting diodes (WLEDs) that combined with yellow commercial phosphors. Many solutions have been found to improve the photoluminescence quantum yield (PLQY) of phosphor. In this study, we effectively increased PLQY by introducing indium ion to vanadate garnet phosphor forming a series of LiCa_3−XMgV₃O₁₂: xIn³⁺ (x = 0.01, 0.02, 0.04, 0.06, 0.08, and 0.10). The resultant In-doped vanadate garnet phosphors exhibit a relative increase in PLQY, and the optimal phosphors is LiCa_2.98MgV₃O₁₂: 0.02In³⁺ with a PLQY as high as 67.4%. These In-doped vanadate garnet phosphors have a broad emission at 480 under 320 nm where near UV-light excitation. It is revealed that the distortion of V-V and V-O bond length in [VO₄] crystal structure and unit cell volume data of phosphors have an extensive influence on PLQY. Therefore, these novel vanadate garnet phosphors can be the essential blue color choice for WLED devices application in illumination.     

Improving white light emission and quantum yield of Ce@Eu co-doped silicate glass by reducing Eu3+ to Eu2+ with Si3N4

Rare-earth-doped transparent glass shows great potential in white light-emitting diodes (wLEDs) application due to its excellent optical and luminous properties. Currently reported commercial wLEDs have a drawback in red emission missing, which leads to a relatively low color rendering index (CRI) and a relatively high correlated color temperature (CCT). In this work, Ce@Eu Sr–Si–O glass is fabricated using a high-temperature quenching method. The white light is available when the ratio of Ce³⁺/Eu³⁺ equals 1, and the emitting color can be adjusted from blue to red by controlling the ratio of Ce³⁺/Eu³⁺. To further optimize the white light, Eu³⁺ ions can be reduced to Eu²⁺ according to the reaction of 6Eu³⁺ + 2N³⁻ → 6Eu²⁺ + N₂↑ by introducing Si₃N₄. As a result, the standard white light emission can be achieved in the Ce@Eu silicate glass contributed by the blue light from Ce³⁺, red light from Eu³⁺, and yellow–green light from Eu²⁺ (two elements, three emission). This glass shows excellent luminous properties, such as a color coordinate is (0.3651, 0.3269) in CIE 1931 color coordinate diagram, a CRI is over 70, a high quantum yield of 36.02%, and a CCT of 4117 K.     

Solvent-Free Preparation of Tannic Acid Carbon Dots for Selective Detection of Ni2+ in the Environment

Carbon dots (CDs) are widely used nanomaterials that not only exhibit good biocompatibility and photostability, but also benefit from a simple preparation process and easy functionalization, making them promising for broad applications in the fields of heavy metal ion detection and optoelectronic devices. Based on the excellent optical properties of CDs and the current situation of increasing energy shortages, this paper selects the natural polyphenolic compound tannic acid (TA) found in biomass materials as the carbon source and innovatively adopts a simple and convenient solvent-free pyrolysis method without auxiliary reagents or solvents. The CDs with good water solubility and certain fluorescence properties were directly prepared under the condition of high temperature, and the obtained CDs exhibited blue fluorescence, and a high QY of 35.4% was obtained at 300 °C. The analysis and results demonstrate the selectivity of these CDs for the detection of various metal ion solutions. In particular, these CDs are sensitive to Ni²⁺ and can be used as fluorescent sensors for the efficient and sustainable detection of Ni²⁺, whereas previous sensors were often specific to Fe³⁺ and Hg²⁺. Thus, a new sensing technique has been developed for the detection of Ni²⁺ to achieve more sensitive and rapid detection.     

Experimental study and DFT calculations of improved giant dielectric properties of Ni2+/Ta5+ co-doped TiO2 by engineering defects and internal interfaces

High-performance ceramics with chemical formula (Ni_1/3Ta_2/3)_xTi_1?xO₂ with excellent dielectric properties are demonstrated. The dopants of Ni²⁺ and Ta⁵⁺ in TiO₂ caused the formation of oxygen vacancies and free electrons. The (Ni_1/3Ta_2/3)_xTi_1?xO₂ exhibited low loss tangent of 0.046 and a high dielectric permittivity of 3.5–4.5 × 10⁴ with a very weak dependence on temperature (?60 to 200 °C). Broadband dielectric spectroscopy shows at least four dominant sources in the dielectric relaxation response in the temperature range of ? 253–210 °C. DFT calculations indicate the formation of defect clusters, which are the largest contributors to the dielectric response, and these are found to be dominant even at temperatures down to ? 253 °C. Both grain boundary and surface layer mechanisms in the ceramics contribute to the dielectric response at the relatively high temperatures. The sample–electrode contact effect associated with oxygen vacancy diffusion is dominant at high temperatures above 150 °C.     

A highly sensitive turn-off fluorescent probe based on 2D Eu(III)-MOFs nanosheets for glutathione in vitro and living cells

Glutathione (GSH) is generally used as an effective and sensitive tumor marker because its abnormal levels are associated with high free radical level in tumor. In this work, GSH could be easily detected by a kind of designed Eu-based metal–organic frameworks (Eu-MOFs, named Eu(DTBA)) fluorescent sensor. Due to the “antenna effect” of 4,4′-dithiobenzoic acid (4,4′-DTBA) ligands on Eu³⁺, Eu(DTBA) emits the strong characteristic red light of Eu³⁺ under ultraviolet excitation. Moreover, the emission intensity strongly depends on GSH concentrations. Thus, Eu(DTBA) can serve as a turn-off fluorescent switch of GSH because its framework structure can easily be destroyed by GSH that leads to the fluorescence quenching. Remarkably, during sensing GSH, Eu(DTBA) has shown many appealing performances, such as broad a response window (0–20 mM), fast response (3 min), high sensitivity (LOD = 0.35 µM), and excellent anti-interference ability. The real bioimaging application has demonstrated that the reported Eu(DTBA) can be used as an excellent bioimaging agent to successfully distinguish tumor cells from normal cells in clinical diagnosis.     

碳量子点/Fe3+复合材料用于生物传感检测抗坏血酸

利用碱木质素为原料,在浓硫酸与浓硝酸环境中,先进行超声处理,随后转移至反应釜中,180℃水热反应12h,制备碳量子点（CDs）,并采用多种测试手段对其结构及形貌进行了表征。通过CDs溶液与Fe³⁺溶液相互作用,制备得到CDs/Fe³⁺复合材料。利用紫外光谱及荧光光谱研究了CDs及CDs/Fe³⁺复合材料的光学性能,发现CDs具有优异的荧光性能,其荧光量子产率达17.3%（硫酸喹啉为参比物质）,而CDs/Fe³⁺复合材料荧光猝灭明显。将CDs/Fe³⁺复合材料应用于人体内不同生物活性分子检测,发现CDs/Fe³⁺复合材料对抗坏血酸（AA）具有特异性识别,且在0~200μmol/L及200~350μmol/L范围内,AA浓度与CDs/Fe³⁺复合材料的荧光强度呈现良好的线性关系,同时具有优异的选择识别性,可应用于生物体内AA的检测,在生物传感方面具有潜在的应用价值。     

Tunable chromaticity and high color rendering index of WLEDs with CaAlSiN3:Eu2+ and YAG:Ce3+ dual phosphor-in-silica-glass

Phosphors-in-glass (PiG), which serves as a potential bi-replacement of both phosphors and organic encapsulants in high-power white light-emitting diodes (WLEDs), has captured much attention due to its high thermal stability and excellent luminescent properties. However, due to the high-temperature sensitivity and the chemical reactions between phosphors with glass matrix, a variety of phosphors, especially red phosphors could be hardly dispersed into the glass without thermal quenching and decomposition, which greatly limits the improvement of color rendering index and chromaticity tunability of the WLEDs. In this study, adopting the mesoporous silica (FDU-12) and commercial phosphors as raw materials, the phosphors-in-silica-glasses (PiSGs) embedded with red phosphor CaAlSiN₃:Eu²⁺ and yellow phosphor YAG:Ce³⁺ have been successfully prepared at low sintering temperature (950°C) and short preparation time (10 minutes) using spark plasma sintering. Owing to the well preservation of the originally emissive properties of the embedded phosphors, the warm WLEDs with tunable chromaticity and exhibited a superior performance with LE of 133 lm/W, CCT of 3970 K and CRI of 81 were fabricated by encapsulating the as-prepared PiSGs on the blue chips. Moreover, the PiSG composite exhibits a high thermal conductivity up to 1.6 W/m·K.     

Facile synthesis of melamine-based porous polymer networks and their application for removal of aqueous mercury ions

Based on a facile catalyst-free process using Schiff base chemistry, here, highly cross-linked porous aminal networks in high yields (up to 90%) were rapidly prepared via microwave irradiation. The polymer networks contained as high as 50 wt% of nitrogen (N), in situ doped with sulfur (S), with specific surface areas of up to 301 m² g⁻¹, and were also found to exhibit a solvent-based luminescence property. Adsorption kinetics and isotherm studies demonstrated that the Hg²⁺ removal by these polymers was extremely rapid (90% being attained within 5 min for a 400 mg L⁻¹ Hg²⁺ solution) and highly efficient (up to 1172 mg g⁻¹). Particularly these materials also exhibited an excellent selectivity towards Hg²⁺ over other interfering ions (Cd²⁺, Ni²⁺, Zn²⁺, Cu²⁺, Co²⁺, Ca²⁺, Mn²⁺ and Mg²⁺). Studies by FT-IR, Raman and XPS spectra showed that all the N-containing groups (triazine ring, primary amine, and secondary amine) as well as S-containing groups on the polymer matrix could be responsible for the Hg adsorption, through the mechanism of surface complexation.     

Effective Cd2+ chelating fiber based on polyacrylonitrile

A reusable chelating fiber containing polyamino–polycarboxylic acid ligands was prepared via the stepwise modification of polyacrylonitrile fiber with diethylenetriamine and chloroacetic acid. The amination and carboxylmethylation conditions were optimized, and the modified fiber was characterized by elemental analysis, XRD, SEM and FTIR. For Cd²⁺ in water, this chelating fiber has prominent adsorption abilities such as low adsorption limitation (0.001 mg/L), high adsorption capacity (1.34 mmol/g) and fast response speed (half-saturation adsorption time less than 0.5 min based on 1 mg/mL Cd²⁺). The effectiveness of this chelating fiber has been proved by using it to treat actual sewage water, where the concentration of Cd²⁺ was reduced from 0.540 to below 0.001 mg/L. This level easily meets drinking water standards (0.003 mg/L) issued by the World Health Organization. Moreover, this chelating fiber is also very effective at treating other metal ions such as Cu²⁺, Ca²⁺, Zn²⁺, Mg²⁺, Pb²⁺, Ni²⁺, Ag⁺ and Hg²⁺.     

Fabrication and characterization of anorthite-based ceramic using mineral raw materials

The purpose of this study is to design a novel single crystalline phase ceramic based on anorthite whose properties fulfill the tableware market requirements such as high appearance quality, strength and thermal shock resistance. To obtain the single phase anorthite ceramic, ball clay, quartz, calcite, feldspar and alumina were used as raw materials. The single phase anorthite ceramic was fabricated by slip casting and sintering at 1230 °C for 1 h. It has a high flexural strength of 103 MPa, which is higher than that of the conventional porcelain. The single phase anorthite ceramic had relatively low (4.9 × 10^?6 K^?1) thermal expansion coefficient which can be matched with applicable glaze easily. Furthermore, the single phase anorthite ceramic had high degree of whiteness (L* = 94) and excellent translucency behavior which could achieve a high-quality decorative effect.     

Embedding carbon dots in Eu3+-doped metal-organic framework for label-free ratiometric fluorescence detection of Fe3+ ions

Fluorescent detection is a new spectroscopic measurement for ions sensing due to the advantages of real-time determination with high selectivity, accuracy, and low cost. However, chemosensors based on fluorescent detection are usually determined by absolute intensity from a monochromatic emission signal, which is easy to be fluctuated by the external environment, especially for Fe³⁺ detection in complex fluids. Herein, we rationally design a dual-emission Eu³⁺: CDs@ZIF-8 to construct a ratiometric fluorescent sensor with self-calibrating ability for Fe³⁺ determination. High efficient carbon dots (CDs) are embedded in europium ions (Eu³⁺)-doped MOF by simple stirring preparation at room temperature. The label-free ratiometric fluorescent probe (I_CDs@ZIF-8/I_Eu) exhibits simultaneous blue and red emission under the same excitation at 365 nm. Remarkably, Eu³⁺: CDs@ZIF-8 displays the superiority of high selectivity to Fe³⁺, which shows ratiometric fluorescence characteristics (I₀/I) in a range of 0-6 μmol\L with a low limit of detection (LOD) of 0.897 μmol\L. Besides, the CDs-MOF nanocomposite holds good aqueous dispersibility and low cytotoxicity, which shows great potential applications in medical aid including biological detection and clinical diagnosis.     

Large enhancement of piezoelectric properties and resistivity in Cu/Ta co-doped Bi4Ti3O12 high-temperature piezoceramics

In this study, the electrical properties of Bi₄Ti₃O₁₂-based Aurivillius-type ceramics were tailored by a B-site co-doping strategy combining high valence Ta⁵⁺ and low valence Cu²⁺. A series of Bi₄Ti_3−x(Cu_1/3Ta_2/3)_xO₁₂ (BTCT) (x = 0, 0.005, 0.01, 0.015, 0.02, 0.025, and 0.03) ceramics were prepared by the conventional solid-state reaction method. The effect of Cu/Ta co-doping on the crystal structure, microstructure, dielectric properties, piezoelectric properties, ferroelectric properties, and electrical conductivity of these ceramics was systematically investigated. Co-doping significantly enhanced the piezoelectric properties and DC electrical resistivity of the resulting composites. The optimized comprehensive performances were obtained at x = 0.015 with a large piezoelectric coefficient (34 pC/N) and a relatively high resistivity of 9.02 × 10⁶ Ω cm at 500°C. Furthermore, the ceramic also exhibited stable thermal annealing behaviors and excellent fatigue resistance. The results of this study demonstrated great potential of the Cu/Ta co-doped Bi₄Ti₃O₁₂ ceramics for high-temperature piezoelectric device applications.     

Thermoresponsive nanocomposite hydrogels with high mechanical strength and toughness based on a dual crosslinking strategy

The practical application of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels are severely limited by their poor mechanical properties. Herein, we reported a series of dual crosslinked (DC) PNIPAM hydrogels with superior mechanical properties prepared by simple copolymerization of N-isopropylacrylamide and sodium acrylate (SA) in the laponite RDS suspension, following by a soaking process in multivalent metal cations (e.g., Ca²⁺, Al³⁺, Fe³⁺) aqueous solutions to form ionic coordination interactions with  COO groups of copolymer side chains. The effect of laponite RDS, AANa (sodium acrylate), and metal cation (e.g., Fe³⁺) concentrations on the mechanical properties and deswelling properties of the DC hydrogels are evaluated. The DC hydrogel prepared with 10 w/v% laponite RDS, 0.25 mol/L AANa and 0.45 mol/L Fe³⁺ possesses the best mechanical properties (ca. 1.1 MPa of tensile strength, 9.1 MPa of compression strength at 80% of compression strain, 1.4 MPa of elastic modulus and 1.3 MJ/m³ of toughness). Moreover, we also discovered that the DC hydrogels crosslinked by Fe³⁺ showed better mechanical properties due to the larger charge and ion radius of Fe³⁺.     

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb⁵⁺ ions substituted Ni_0.29Cu_0.18Zn_0.53Nb_xFe_2-xO₄ (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb⁵⁺ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πM_s = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb⁵⁺ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.     

Phase,domain, and microstructures in Sr2+ substituted low-temperature sintering PZT-based relaxor ferroelectrics

The Ag-Pd internal electrode of multilayer piezoelectric ceramics needs to be sintered below 1000°C, and lead wires and components need to be welded with lead-free solder at 260°C. PNN–PMW–PZT–xSr piezoelectric ceramics with high Curie temperature (T_c > 260°C) were synthesized at a low sintering temperature (960°C) to meet the requirements of multilayer piezoelectric devices. The relationship between structures (phase, domain, and microstructures) and electrical properties (piezo/ferroelectric properties, and dielectric relaxation) in the Sr²⁺ substituted ceramics was investigated. Rietveld refinement and Raman spectra show that Sr²⁺ substitution can cause the phase change and increase the force constant of [BO₆] octahedron. The piezoelectric response increases with increasing the content of the tetragonal phase (CTP) in the rhombohedral-tetragonal (R-T) coexisted ceramics. The ceramics with 0.6 mol% Sr²⁺ substitution have minimum activation energy for domain wall movement (E_a) of 0.0362 eV which favors the formation of nanometer-sized domains, and possess excellent electrical properties (d₃₃ = 623 pC/N, d₃₃^* =783 pm/V, T_c =295°C). The higher the CTP, the lower the E_a. The lower E_a favors the rotation of polarization direction and extension, and is beneficial to the generation of the nanometer-size domains, resulting in high piezoelectric properties.     

Enhanced energy storage properties and superior thermal stability in SNN-based tungsten bronze ceramics through substitution strategy

Tungsten bronze ceramics of composition Sr₂Ag_0.2Na_0.8Nb_5-xTa_xO₁₅ were synthesized by solid state methods to investigate the impact of Ta replacement on the structure and energy-storage properties (ESP). The study on the relationship between structure and electric properties revealed three main conclusions: (1) as the Ta⁵⁺ concentration increased, the crystal structure transformed from an orthorhombic Im2a phase to a tetragonal paraelectric P4bm phase; (2) a high recoverable energy storage density (1.44 J/cm³) and a moderate efficiency (82%) under low-electric fields was obtained in x = 0.3 sample; (3) both dielectric properties (?9.6 to 232.7 °C) and ESP (30–150 °C) exhibit an excellent thermal stability for x = 0.3 sample. In addition, a high current density (863.69 A/cm²) and a large powder density (70.21 MW/cm³) were achieved simultaneously. The current system could be a promising candidate in temperature-stable dielectric capacitors under low-fields and over a broad temperature range.     

The Role of N and S Doping on Photoluminescent Characteristics of Carbon Dots from Palm Bunches for Fluorimetric Sensing of Fe3+ Ion

This work aims to enhance the value of palm empty fruit bunches (EFBs), an abundant residue from the palm oil industry, as a precursor for the synthesis of luminescent carbon dots (CDs). The mechanism of fIuorimetric sensing using carbon dots for either enhancing or quenching photoluminescence properties when binding with analytes is useful for the detection of ultra-low amounts of analytes. This study revealed that EFB-derived CDs via hydrothermal synthesis exceptionally exhibited luminescence properties. In addition, surface modification for specific binding to a target molecule substantially augmented their PL characteristics. Among the different nitrogen and sulfur (N and S) doping agents used, including urea (U), sulfate (S), p-phenylenediamine (P), and sodium thiosulfate (TS), the results showed that PTS-CDs from the co-doping of p-phenylenediamine and sodium thiosulfate exhibited the highest PL properties. From this study on the fluorimetric sensing of several metal ions, PTS-CDs could effectively detect Fe³⁺ with the highest selectivity by fluorescence quenching to 79.1% at a limit of detection (LOD) of 0.1 µmol L⁻¹. The PL quenching of PTS-CDs was linearly correlated with the wide range of Fe³⁺ concentration, ranging from 5 to 400 µmol L⁻¹ (R² = 0.9933).