Although several groups have synthesized dual-emission carbon dots (D-CDs) and paid more attention to their emission centers in recent years, the luminescence mechanism of D-CDs is still unclear. Here, we synthesized multiemission CDs via the one-pot hydrothermal method. The prepared CDs exhibit three fluorescence (FL) emissions (370, 425, and 505 nm) under one-wavelength excitation of 320 nm. In addition, various emission origins dominate the unique multiemission property, which is illuminated by means of the radiation decay process, CD internal graphite domains, and abundant functional group characterization. The characterization results fully indicate that there are three energy states: band gap state (carbon-core state), surface defect state, and molecular state. In addition, the peculiar concentration-dependent and polarity-modulated properties further support the explanation of CD multienergy states. Strikingly, the CD FL quantum yield is up to 50.68%. As CDs can show bright green FL excited over 400 nm, the color of concentrated CD solution incredibly turns from maroon to green in visible light observed from different angles. Our findings mainly account for this luminescence mechanism of CDs. This work utilizes time-resolved emission spectra for the first time to distinguish and identify multiemission origins, which would provide scientific inspiration for finding effective ways to regulate or control these luminescence processes.

Blue luminescent carbon dots (CDs) with a high photoluminescence (PL) quantum yield (48.3 ± 5.3%) were prepared by the one-pot hydrothermal reaction of citric acid with poly(ethylenimine) (PEI). The CDs display bright PL, narrow emission spectra, pH-dependent PL intensity, high photostability, and up-converted luminescence. The CDs exhibit a quenching of both down- and up-conversion PL in the presence of morin and thus serve as useful probes for morin detection. Both down- and up-conversion measurements allow the quantification of concentrations from 0 to 300 μmol/L with a detection limit of 0.6 μmol/L, and this dual-mode detection increases the reliability of the measurement. The proposed method of determination is simple, sensitive, and cost-effective, with potential applications in clinical and biochemical assays.

New Cu-doped dual-emission carbon dots (D-CDs) were synthesized rapidly and simply via a one-pot solvothermal method, and its special photoluminescence mechanism was studied. D-CDs have two fluorescence (FL) emission peaks under one-wavelength excitation and can be used as dual-signal sensor which is usually designed with two or more substances. The prepared CDs show excellent water solubility, photostability, salt tolerance, oxidation resistance, and special optical properties. The raw material ratio, solvent, pH, time, and synthesis temperature were optimized. The characterizations of CDs including transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma spectroscopic analysis, X-ray diffraction assignation of phases, thermogravimetric analysis and differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, FL spectrum, and ultraviolet-visible spectrum (UV-vis) were conducted. The investigation on mechanism indicates that the unique dual-emissive property is mainly caused by the energy-level gaps generated by the surface defects of CDs. The prepared D-CDs have good potential in dual-signal analysis and visualization sensing. To demonstrate the practical application, ferric ions, vitamin A acetate, and pH have been determined successfully.

The electrochemiluminescence (ECL) ratiometric assay is usually based on two different ECL luminophores, and the choice of two suitable luminophores and shared co-reactant makes its construction challenging. The single-emitter-based ECL ratio mode could overcome the limitation of two luminophores and simplify the construction process, so it is an ideal choice. In this work, CdTe quantum dots (CdTe QDs) were modulated using black phosphorus (BP) nanosheet to simultaneously emit the cathodic and anodic ECL signals, and H 2 O 2 and tripropylamine (TPrA) served as the cathodic and anodic co-reactants, respectively. MicroRNA-126 (miRNA-126) was selected as the template target to exploit the application of BP-CdTe QDs in the single-emitter-based ECL ratio detection. Through the target recycling triggering rolling-circle amplification (RCA) reaction, a large amount of glucose oxidase (GOx)-modified single strand 1 was introduced. GOx catalyzed glucose to produce H 2 O 2 in situ, which acted as a dual-role moderator to quench the anodic ECL emission with TPrA as the co-reactant while enhancing the cathodic emission, thereby realizing the ratiometric detection of miRNA-126 with a low detection limit of 29 aM (S/N = 3). The dual-ECL-emitting BP-CdTe QDs with TPrA-H 2 O 2 as dual co-reactant provide a superior ECL ratio platform involving enzyme catalytic reaction, expanding the application of single-emitter-based ratio sensing in the diverse biological analysis.

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As a persistent organic pollutant, perfluorooctane sulfonate has drawn a worldwide attention. In this contribution, a novel molecularly imprinted polymer based on mesoporous silica nanoparticles was prepared for efficient separation and enrichment of perfluorooctane sulfonate in water samples. The polymer was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, and N2 adsorption/desorption experiments. The static adsorption experiments and the adsorption kinetic tests were conducted. The results showed that the adsorbents had high adsorption capacity (21.10 mg/g) and short adsorption equilibration time (25 min). Meanwhile, the effect of mesoporous silica nanoparticles on the adsorption capacity was investigated. The results indicated that the mesoporous structure helped to increase the adsorption capacity of adsorbent to adsorbate. Besides, the adsorbents show good specificity and good reusability with the adsorption capacity of adsorbent toward perfluorooctane sulfonate decreasing <5% after five adsorption–desorption cycles. The mesoporous silica nanoparticles molecularly imprinted polymer has been used successfully for the removal of perfluorooctane sulfonate in environmental water samples with relative standard deviation ≤4.64%.

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Studies on multiemission fluorescent carbon dots (CDs) excited at one wavelength are extremely promising because of their label-free property, facile synthesis, multicolor visualization, and prevention of background interference. In this study, a novel template strategy to develop multiemission carbon dots (M-CDs) using fluorescent precursors has emerged. We attempted to elucidate the relationship between precursor substances and luminescence origins. The M-CDs prepared by calcein demonstrate three emissions, ultraviolet (UV), blue, and green, which are attributed to the solvent, surface defect, and precursor aromatic ring luminophores, respectively. Also, through a regular adjustment of the amount of NaOH or the solvothermal synthesis time, the expected optical requirements were successfully met by the M-CDs, which is a better capability than that of previously reported M-CDs. In addition, a multicolor sensor designed with M-CDs and rhodamine B (RhB) has been successfully applied in cell imaging. When exposed to different pH media, the fluorescence (FL) emission shows a linear relationship with the pH value, displaying a profuse color evolution from dark blue to light blue, cyan, green, yellow, and finally, orange.