A simple and green approach for the synthesis of photoluminescent N,S-carbon dots (N,S-CDs) has been proposed using a single natural source precursor (bamboo leaf) as raw materials. The ...as-synthesized N,S-CDs exhibited a highly stable, excitation wavelength-dependent emission, excellent photobleaching, alkali, and salt tolerance. Here, the mechanism of N,S-CDs luminescence was studied via the UV–vis absorption spectrum and photoluminescence spectroscopy. Based on the quenching properties of nitrophenol compounds on the fluorescence of N,S-CDs, the interaction between N,S-CDs and nitrophenol compounds was investigated on detail in aqueous solution. More importantly, the study on photophysical properties of the N,S-CDs may provide the basis for the development of the N,S-CDs for the fluorescent probe of nitrophenol compounds.
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•High fluorescence N,S-CDs were synthesized with bamboo leaves as carbon source.•The spectral characteristics of N,S-CDs such as absorption and fluorescence were examined in detail.•Different nitrophenols exhibited different fluorescence quenching effects on N, S-CD.•The interaction between nitrophenols and N,S-CDs, and the mechanism of fluorescence quenching are discussed.
A simple label-free method for the detection of Hg2+ ions with high selectivity and sensitivity has been developed by using fluorescent Au NCs in aqueous media. The sensing mechanism was based on the ...high-affinity metallophilic Hg2+-Au+ interactions, which effectively quenched the fluorescence of Au NCs.
Temperature-dependent photoluminescence (PL) properties of inorganic perovskite CsPbBr
3
nanocrystal (NC) films were studied by using steady-state and time-resolved PL spectroscopy. The closely ...packed solid films were obtained by dropping NC solution on silicon substrates. It was found that the PL intensities of the NC films, which are dependent on the size of NCs, slightly decreased with increasing temperature to 300 K, while the PL intensities dropped rapidly with increasing temperature above 300 K and were nearly quenched at 360 K. Further the corresponding average PL lifetimes increased significantly with increasing temperature below about 320 K and then significantly became shorter. The PL quenching mechanisms were demonstrated through heating and cooling experiments. The experimental results indicated inorganic perovskite NCs exhibited a thermal PL quenching in the temperature range of 80-300 K and a thermal degradation at temperatures above 300 K. The linewidths, peak energies, and lifetimes of PL emissions for the NC films as a function of temperature were discussed in detail.
The photoluminescence stability of all-inorganic perovskite nanocrystals (CsPbBr
3
) with different size is studied.
The recently developed method of direct quenching and partitioning (DQ&P) was utilized to produce ultra-high strength martensitic steels with retained austenite. The DQ&P steels have high surface ...hardness while retaining good impact toughness and elongation values. The toughness and elongation properties are attributed to the retained austenite which is stabilized in the DQ&P process. The aim was to study if DQ&P processing could be utilized for improved abrasive wear resistance. Two medium-carbon (0.3%) chemical compositions were selected with varying amounts of silicon, aluminum and chromium. The processing route for DQ&P involved interrupted water quenching with two different quench stop temperatures (TQ) (175 and 225°C). Direct quenched (DQ) variants were also produced for comparison of both mechanical properties and wear characteristics. Compared to the DQ treatment, improved impact toughness and elongation to fracture were achieved with the DQ&P treatment while initial strength and hardness was reduced. An impeller-tumbler testing device was used to measure the impact-abrasive wear performance of the different experimental microstructures and compared with that of a reference commercial 500 HB steel. No advantage of the increased ductility of the DQ&P steels was apparent; wear resistance was shown to only correlate with the initial surface hardness of the steels.
•Direct quenching and partitioning was utilized to produce wear resistant steel.•The direct quenching and partitioning improved impact toughness and elongation.•Retained austenite transformed into martensite during impeller-tumbler wear testing.•Wear resistance was found to correlate with initial surface hardness.
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•The luminescence quenching of Ru(II)-diimine complexes by Cr(VI) ion in acidic aqueous media was investigated by applying steady-state and time-resolved measurements.•The ...experimental results show an upward curvature dependency to Stern–Volmer (S–V) equations.•Stern–Volmer quenching rate constants for the dynamic process (KD) and the bimolecular quenching rate constants (kq) are calculated by applying the Stern–Volmer equation to the luminescence decay data.•The analysis of the experimental data using ground-state complex formation and the sphere of action models emphasizes the presence of a static quenching insignificant in comparison with the dynamic one.
Luminescence quenching of Ru(bpy)(CN)42−, Ru(phen)(CN)42−, Ru(bpy)32+ and Ru(phen)32+ by hexavalent chromium ion in aqueous media were investigated by steady-state and time-resolved measurements. Effect of pH on the luminescence quenching process is also investigated. It has been found that luminescence changes due to the interaction of all Ru(II) complexes with Cr(VI) ions were high at pH values less than or equal to 5.0 and negligible at pH ≥ 8.0. The experimental data of the quenching process were analyzed using Stern–Volmer (S–V) equations. The steady state luminescence emission data shows an upward curvature, indicating that the quenching is preceded by both dynamic and static quenching. For all studied complexes, the lifetime of the excited 3MLCT state decreases with increasing Cr(VI) concentration implying that the diffusion is mainly responsible for the quenching process. The Stern–Volmer dynamic quenching constants (KD) and the bimolecular quenching rate constant for the quenching process (kq) were calculated by applying the Stern–Volmer equation to the luminescence decay data. The bimolecular quenching rate constants (Kq) were found to increase in the order Ru(bpy)(CN)42− < Ru(phen)(CN)42− < Ru(phen)32+ < Ru(bpy)32+ which correlates will with the oxidation potentials of Ru(II) complexes. The association constants for Ru(II)-Cr(VI) system were calculated using the Benesi-Hildebrand equation and found to be 3.0 × 103, 2.5 × 103, 1.2 × 103, 7.1 × 103 M−1 for Ru(bpy)(CN)42−, Ru(phen)(CN)42−, Ru(bpy)32+ and Ru(phen)32+ respectively, which is interpreted in terms of the dynamic (diffusion) and the sphere of action (static) quenching models.
An improved aptamer-based fluorescent Pb2+ biosensor utilizing the binding induced quenching of AMT to G-quadruplex has been rationally designed with a LOD of 3.6 nM. The utility of the developed ...biosensor was demonstrated by the successful detection of Pb2+ in real complex clinical samples with satisfactory recovery and good reproducibility.
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•Development of eco-friendly GQDs for precise determination of the antiretroviral drug lamivudine.•Offers superior sensitivity and selectivity in lamivudine quantification, unaffected ...by common excipients.•Promotes sustainable pharmaceutical analysis with low reagent consumption and energy-efficient techniques.
In this study, graphene quantum dots (GQDs) were employed for quantitatively analyzing lamivudine using a fluorescence quenching technique. This approach allows for sensitive determination of the concentration of lamivudine in different matrices without requiring derivatization. The mechanism behind the fluorescence intensity quenching between GQDs and lamivudine molecules was explored using the Stern Volmer equation, revealing dynamic quenching behavior. Additionally, various factors affecting fluorescence quenching efficiency such as pH, GQDs concentration, and incubation time were carefully tuned. Moreover, our developed method successfully met ICH guidelines for validation parameters including linearity, accuracy, precision, and selectivity demonstrating excellent performance. The results showed good accuracy and precision, with a mean recovery value of 101.91% for method accuracy and a relative standard deviation of 0.682 and 1.489 for intraday and interday precision, respectively. Finally, the greenness and blueness of the developed method were also investigated to assess its environmental friendliness and analytical practicality. Greenness evaluation using the AGREE tool demonstrated that the developed method has a low environmental impact with an AGREE score of 0.75, Besides, the blueness evaluating using the BAGI tool indicated that the developed method is practical, reliable, and well-suited for routine analysis of lamivudine in various samples.
•MgTi2O5: xEu3+ phosphors are synthesized by solid-state reaction method.•Under 465 nm excitation, intense red emission was obtained at 615 nm.•Internal quantum efficiency of the phosphor was ...determined to be 31.65 %.•Phosphors have high color purity and warm light emission.•Synthesized red phosphor is a suitable candidate for pc-wLEDs.
As one of the critical components for achieving high-quality white light emitting diodes (w-LEDs) are efficient phosphors, a series of intense red emitting Eu3+doped magnesium dititanate (Mg(1-x)Ti2O5: xEu3+; x = 0, 0.005, 0.008, 0.01, 0.02 and 0.03 mol) phosphors were prepared via solid-state reaction method. The X-ray diffraction (XRD) patterns confirmed the phase purity and orthorhombic structure of the prepared phosphors. The Ti-O functional groups were detected from the Fourier transform infrared (FTIR) spectra and Field emission scanning electron microscopy (FESEM) images revealed agglomerated spherical-like shaped phosphor particles. Under 465 nm excitation, intense red emission corresponding to 5D0→7FJ (J = 0, 1, 2, 3, and 4) transitions of Eu3+ ions were recorded in the photoluminescence (PL) spectra with an intense peak at 615 nm. The optimum concentration of Eu3+ ions was determined to be 1 mol% and the concentration quenching mechanism was due to the interaction between adjacent Eu3+ ions. The lifetime values of the samples were in the millisecond range and the internal quantum efficiency was determined to be 31.65 %. The Commission Internationale de l'Eclairage (CIE) coordinates of the optimum sample Mg0.99Ti2O5:0.01Eu3+ are (0.6421, 0.3575), lies in the red region with 99.9 % color purity and have warm correlated color temperature (CCT) values. Therefore obtained results suggest that the prepared Mg(1-x)Ti2O5:xEu3+phosphors can be used as an efficient red phosphor for w-LED applications.
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Photosystem II (PSII) is vulnerable to high light (HL) illumination resulting in photoinhibition. In addition to photoprotection mechanisms, plants have developed an efficient PSII repair mechanism ...to save themselves from irreversible damage to PSII under abiotic stresses including HL illumination. The phosphorylation/dephosphorylation cycle along with subsequent degradation of photodamaged D1 protein to be replaced by the insertion of a newly synthesized copy of D1 into the PSII complex, is the core function of the PSII repair cycle. The exact mechanism of this process is still under discussion. We describe the recent progress in identifying the kinases, phosphatases and proteases, and in understanding their involvement in the maintenance of thylakoid structure and the quality control of proteins by PSII repair cycle during photoinhibition.
Graphene quantum dots (GQDs) have attracted great attention as next‐generation luminescent nanomaterials due to the advantages of a low‐cost process, low toxicity, and unique photoluminescence (PL). ...However, in the solid‐state, the strong π−π stacking interactions between the basal planes of GQDs lead to aggregation‐caused PL quenching (ACQ), which impedes practical application to light‐emitting devices. Here, surface functionalized GQDs (F‐GQDs) by polyhedral oligomeric silsesquioxane (POSS), poly(ethylene glycol) (PEG), and hexadecylamine (HDA) to reduce π−π stacking‐induced ACQ is presented. The POSS‐, PEG‐, and HDA‐functionalized GQDs show a significant enhancement in PL intensity compared to bare GQDs by 9.5‐, 9.0‐, and 5.6‐fold in spin‐coated film form and by 8.3‐, 7.2‐, and 3.4‐fold in drop‐casted film form, respectively. Experimental results and molecular dynamics simulations indicate that steric hindrance of the functionalization agent contributes to reducing the π−π stacking between adjacent GQDs and thereby enabling quenching‐resistant PL in the solid‐state. Moreover, the GQD‐based white light‐emitting diodes fabricated by mounting HDA‐GQDs on a UV‐LED chip exhibits efficient down‐conversion for white light emission with a high color rendering index of 86.2 and a correlated‐color temperature of 5612 K at Commission Internationale de l'Éclairage coordinates of (0.333, 0.359).
Surface functionalization enables quenching‐resistant, strongly enhanced solid‐state photoluminescence of graphene quantum dots (GQDs). Steric hindrance of chemically grafted polyhedral oligomeric silsesquioxane, poly(ethylene glycol), and hexadecylamine significantly reduce the π−π stacking between adjacent GQDs, thereby minimizing aggregation‐caused quenching. Encapsulation‐free, highly photo‐stable GQD‐based white‐light emitting diodes exhibit a high color rendering index of 86.2.
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