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Nitrogen, boron co-doped carbon quantum dots (gCQDs), and a coloration probe (PPD-NPs) with response to cobalt ions (Co2+) were prepared by using 4-hydroxyphenylboric acid as the common precursor, with ethylenediamine and p-phenylenediamine (PPD) adopted as nitrogen-doped reagents, respectively. A noticeable brown-to-purple color change can be observed with the addition of Co2+, and a broad absorption band emerges at 535 nm. At the same time, gCQDs, which is introduced as the fluorescence signal source, will be significantly quenched due to the enhanced inner filtration effect, induced by the overlap between the emission spectrum of gCQDs and the emerging absorption band. Therefore, a colorimetric/fluorescent dual-mode sensing probe for Co2+ is constructed by combining the recognition unit PPD-NPs and the fluorescent gCQDs into PPD-NP/gCQD. Under the optimized experimental conditions, the calculated limits of detection are 1.51 × 10−7 M and 3.75 × 10−7 M for the colorimetric mode and the fluorescence mode, respectively, well qualified for the determination of Co2+ maximum permitted level in drinking water. The feasibility of the proposed method has been verified in tap water, lake water, and black tea samples. [ABSTRACT FROM AUTHOR]

Double perovskite Cs 2 AgInCl 6 is a new direct band gap semiconductor material. Compared with traditional perovskite CsPbX 3 (X = Cl, Br, I), double perovskite Cs 2 AgInCl 6 has good stability and wide fluorescence half peak width. This study reports the mechanochemical synthesis, characterization and application of a lead-free double perovskite Cs 2 AgInCl 6 doped with Na and Bi ions. It was found that through a facile room temperature mechanical ball milling process, the double perovskite structure can be obtained within 30 min. Then, Na and Bi ions were used to dope to optimize its luminescence properties. By this synthesis method, the sample with the best doping ratio obtained in the experiment is Cs 2 Ag 0.7 Na 0.3 In 0.9 Bi 0.1 Cl 6 with the photoluminescence quantum yield (PLQY) of 32.7%. The X-ray diffraction (XRD) and photoluminescence (PL) results show that Na and Bi ions can promote the crystallization and optimize the luminescence properties of Cs 2 AgInCl 6. The theoretical calculation results show that both conduction band minimum (CBM) and valance band maximum (VBM) of Cs 2 Ag 0.7 Na 0.3 In 0.9 Bi 0.1 Cl 6 are flat, which is favorable for the generation of self-trapped excitons. Packaging Cs 2 Ag 0.7 Na 0.3 In 0.9 Bi 0.1 Cl 6 sample on an ultraviolet (UV) LED chip, and a warm white LED with good performance can be obtained, which shows a bright potential application in the field of white LED. [Display omitted] • By ball milling, the doped Cs 2 AgInCl 6 can be synthesized quickily without pollution. • The doped perovskite has unique optical properties, and the mechanism is explored. • The products can be used as the effective warm white-light emitting phosphors. [ABSTRACT FROM AUTHOR]

Herein, we presented an ingenious method for the detection of trace ascorbic acid (AA) using fluorescent sensing system, which was composed of periodate (IO 4 −) and nitrogen-boron co-doped carbon dots (N, B-CDs). Highly photoluminescent carbon dots with a quantum yield of 84.5% were synthesized by a one-step hydrothermal method using citric acid, ethylenediamine and boric acid as raw materials. The fluorescence of N, B-CDs could be statically quenched by IO 4 −, and non-fluorescent complexes were formed on the surface of carbon dots at the same time. With the pre-addition of ascorbic acid, the process of fluorescence quenching by IO 4 − was inhibited due to the preferential redox reaction between AA and IO 4 −. Based on the principle mentioned above, we designed the "inhibition" fluorescent sensor that can easily realize the detection of AA, and an extremely low limit of detection of 0.035 nM with a linear interval of 0–1600 pM was obtained. In addition, the sensing system has been applied to the detection of AA in human urine and obtained satisfactory results. The developed "inhibition" fluorescent sensor with high sensitivity and selectivity, has shown great potential and application prospects in the field of biosensing. [Display omitted] • The carbon dots (N, B-CDs) were synthesized by citric acid, ethylenediamine and boric acid. • The N, B-CDs showed a high quantum yield of 84.5% with an intense blue fluorescence. • The "inhibition" fluorescent sensor was constructed of periodate (IO 4 −) and N, B-CDs. • The sensing platform was highly sensitive with a very low detection limit of 0.035 nM. [ABSTRACT FROM AUTHOR]

[Display omitted] • This is the first time that carbon dots were synthesized using cysteine and ethylenediamine as precursors. The synthesis method is green and simple, and the prepared N -CDs have good fluorescence stability. • The developed experimental conditions for the detection of Fe3+ using nitrogen-doped carbon dots as fluorescent probes have been fully optimized to significantly improve the sensitivity. • The method is simple, sensitive and highly feasible, with LOD as low as 0.069 μM in deionized water. And, linear models were also constructed in tap water and lake water with LOD of 0.21 μM and 0.59 μM, respectively. In this study, we synthesized stable nitrogen-doped carbon dots by a simple and economical one-step hydrothermal method using l -cysteine and anhydrous ethylenediamine as precursors. The prepared carbon dots have bright and stable blue light emission near 383 nm and can be used as fluorescent probes to detect the concentration of Fe3+ in environmental waters. It was demonstrated that due to intermolecular electrostatic interaction, a non-fluorescent complex N -CDs/Fe3+ is formed by coordination of Fe3+ with amino and carboxyl functional groups on the surface of carbon dots. Therefore, in combination with internal filtration effect, the fluorescence of carbon dots can be quenched in the presence of Fe3+, and the degree of quenching is linearly related to the concentration of Fe3+. The limit of detection in deionized water was as low as 0.069 μM with R2 of 0.998 and a linear range of 0.3 to 20 μM. In addition, satisfactory recoveries were achieved for the determination of Fe3+ in environmental water samples. The method is reliable, with highly sensitivity and selectivity, and has potential for practical applications in environmental metal analysis. [ABSTRACT FROM AUTHOR]