Excitation-dependent Emission Research Articles

Tunable Blue-Light-Emitting Organic-Inorganic Zinc Halides with Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence.

Hybrid metal halides have received great interests in the field of solid-state lighting technologies due to their diverse structures and excellent emission properties. In this work, we report the synthesis and characterization of four blue-emitting zero-dimensional hybrid metal halides, namely, (2HP)2ZnCl2, (2HP)2ZnBr2, (2TP)2ZnCl2, and (2TP)2ZnBr2 (2HP = 2-hydroxypyridine, 2TP = pyridine-2-thiol). By changing the ligands and halides, a remarkable increase in the photoluminescence quantum yield of (2HP)2ZnCl2 (44.7%) compared to (2TP)2ZnBr2 (1.8%) is realized. The 2HP series features excitation-dependent emission characteristics, whereas the 2TP series does not due to the effect of a different organic ligand. Utilizing time-resolved and temperature-dependent photoluminescence spectroscopies, all four compounds exhibit both thermally activated delayed fluorescence and room-temperature phosphorescence properties. These materials have excellent ambient and thermal stabilities and are solution-processable. Our work shows the importance of carefully incorporating organic ligands with the appropriate inorganic metal center to achieve tunable emission properties.

Uncovering Integrated Dual-State ESIPT-Conductivity, Redox-Capacity, and Opto-Electronic Responses Toward Hg(II)/ Cr(III) of Aliphatic Fluorescent Polymers.

Excited-state intramolecular proton transfer (ESIPT)-associated dual-state emissive aliphatic dual-light emitting conducting polymers (DLECPs) having oxidation-reduction capacities are prepared polymerizing 2-acrylamido-2-methylpropane-1-sulfonic acid, methacrylic acid, and 2-methyl-3-(N-(2-methyl-1-sulfopropan-2-yl)acrylamido)propanoic acid monomers. Of as-synthesized DLECPs, nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies, fluorescent enhancements (I/I0), and computational investigation indicate intriguing photophysical features in DLECP3 (optimum composition). In DLECP3, ─CONH─, ─CON<, and ─COOH subluminophores are recognized by density-functional theory (DFT)/time-dependent-DFT calculations and experimental investigations. ESIPT-associated dual-state emission/conductivity, aggregation-enhanced emissions, selective opto-electronic responses toward Hg(II)/Cr(III) at 437/574nm, and redox properties of DLECP3 are supported by solid-state/solution spectroscopies, time-correlated single photon counting (TCSPC) measurements, dual-state excitation dependent emissions, microscopic images, electrochemical measurements, and DFT calculations. Here, preferential interaction of Hg(II)/Cr(III) with DLECP3 (amide)/DLECP3 (imidol) and reduction/oxidation of Hg(II)/Cr(III) to Hg(I)/Cr(VI) are substantiated by UV-vis, FTIR, and X-ray photoelectron spectroscopies; TCSPC measurements; NMR-titration; electrochemical studies; alongside computational calculations. The proton-electrical conductivities of DLECP3, Hg(II/I)-DLECP3, and Cr(III/VI)-DLECP3 in solids/solutions are 15.27 × 10-5/6.16 × 10-5, 19.60 × 10-5/25.52 × 10-5, and 26.69 × 10-5/27.60 × 10-5 S cm-1, respectively.

Time, temperature and concentration resolved Yb3+ luminescence study in co-sputtered Cu2-xGaxS2 (0.1 < x < 1.6) thin films with a Cu–Ga composition gradient

The broad class of Cu(Al,Ga,In) (S,Se,Te)2 solar absorber materials when doped with Yb3+ are interesting for thin film based luminescent solar concentrator (LSC's) application. In this work the strong and broad absorption properties of co-sputtered CuGaS2 (CGS) thin films combined with the luminescent properties of Yb are reported. Energy-dispersive x-ray spectroscopy (EDS), x-ray diffraction, transmission, excitation, and temperature dependent emission as well as radiative lifetime measurements are performed on thin films with varying Cu:Ga ratios and Yb3+ concentrations. It is found that Yb3+ emission can be broadly sensitized by the host in the range of 200–600 nm. A lower Cu:Ga ratio, crystallinity and post annealing in air provides a positive impact on the sensitization of Yb3+ emission. The temperature dependent time integrated decay curves show a clear thermal energy barrier of about 0.2 eV. Because the exponential tail, with a lifetime of 110 μs, is constant with temperature, we conclude that the barrier is connected to the thermal release of electrons trapped at the Yb2+ ground state. The low energy transfer efficiency from the host to the Yb dopant is attributed to efficient non-radiative electron-hole pair recombination. The prospects and design criteria of Cu(Al,Ga,In) (S,Se,Te)2 solar absorber materials for LSC applications is the further subject of the discussion.

Green Synthesis of Carbon Nanodots (CNDs) Moderated by Flavonoid Extracts from Moringa oleifera Leaves and Co-Doped Sulfur/Nitrogen (NS - CNDs - Fla) and Their Potential for Heavy Metals Sensing Application.

Carbon nano dots (CNDs) has received a lot of attention in recent years due to their potential use in various kinds of applications. Many conventional chemical methods have been used to synthesis CNDs, but these processes have several drawbacks, such as hazardous by products, harsh chemicals, and high costs. To overcome these issues, green chemistry has an importance in the development of CNDs. Thus, it is essential to explore green synthesis approaches for production the CNDs. In this context, a novel precursor using flavonoid extraction from Moringa oleifera leaves is proposed. Moringa oleifera is the "magic tree" which contains many bioactive compounds such as flavonoids, especially in its leaves. Natural flavonoids and glycosides with specific components of structure can bind to metal ions. The content of bioactive compounds such as total flavonoids found in Moringa oleifera leaves is 172.10mg/g. In addition, carbon (47.34%), nitrogen (51.67%), and sulfur (0.99%) are also the main composition. Then, the carbon nanodots (CNDs) synthesized in this research were moderated by flavonoid extract from Moringa oleifera using the hydrothermal method. The technique is easy, ecologically friendly, and requires neither specialized device or reagents. In practice, the CNDs produced are almost circular, with an average diameter of 3.49nm. Furthermore, we enhanced synthesis CNDs - Fla with heteroatoms of nitrogen (N) and sulfur (S). They display a broad excitation-emission spectrum, excitation-dependent emission, and extraordinary fluorescence. Therefore, the synthesis of CNDs using flavonoids from Moringa oleifera as precursors would be a great potential candidate for the development of novel types of heavy metals sensing.

Multistimuli Luminescence and Anthelmintic Activity of Zn(II) Complexes Based on 1H-Benzimidazole-2-yl Hydrazone Ligands

Three novel Zn(II) mononuclear complexes with the general formula ZnL2Cl2 (L = 2-(4-R-phenylmethylene)benzimidazol-2-hydrazines; R-H (1), R-CH3 (2), and R-OCH3 (3)) were synthesized and fully characterized by various means. These complexes demonstrate excitation-dependent emission, which is detected by a change in the emission color (from blue to green) upon an increase in the excitation wavelength. Moreover complex 1 shows reversible mechanochromic luminescence behavior due to the reversible loss of solvated methanol molecules upon the intense grinding of crystals. In addition, 1 exhibits vapochromic properties, which originate from the adsorption methanol vapor on the crystal surface. The strengthening of anthelmintic activity at the transition from free hydrazones to zinc-based complexes is shown.

Controlling the optoelectronic properties of nitrogen-doped carbon quantum dots using biomass-derived precursors in a continuous flow system

The synthesis of carbon quantum dots (CQDs) from high molecular weight biomass-derived precursors poses a significant challenge due to the complex molecular structures and low conversion efficiency. This work demonstrates a green, rapid, and sustainable continuous hydrothermal flow synthesis (CHFS) approach for nitrogen-doped carbon quantum dots (NCQDs) from various biomass-derived precursors, including high molecular weight polymeric sources like chitosan, lignin, and humic acid. We find that the precursor structure significantly impacts the size of the fabricated NCQDs and their optical properties. Citric acid, a low molecular weight precursor, yields NCQDs with excitation-independent emission, higher quantum yields, and low non-radiative losses, while NCQDs derived from polymeric precursors exhibit excitation-dependent, red-shifted, and lower efficiency emission. Theoretical calculations, performed to understand the configuration and distribution of nitrogen dopants within the NCQD structure, show that pyridinic and graphitic nitrogen atoms exhibit a strong preference to aggregate near the centre of the edge of the NCQD and not in the vertices nor in the graphitic core, thus affecting the HOMO and LUMO, bandgap, and light absorption and emission wavelengths. The life cycle assessment (LCA) analysis highlights the green and scalable advantages of the CHFS process for producing NCQDs compared to batch methods, making it a sustainable and economically viable approach for large-scale NCQD synthesis from high molecular weight biomass-derived precursors. Hence, the combination of experimental data and theoretical calculations provides a comprehensive understanding of the structure-property relationships in these NCQDs.

A simple green synthesis of carbon quantum dots from Prunus Armeniaca and their application as fluorescent probes for the selective and sensitive detection of Cd2+ metal ion

Abstract This study used a hydrothermal approach to synthesis carbon dots (CDs) from apricot peel, which were then used as a probe for the selective and sensitive detection of Cd2+ ions. The synthesized CDs’ surface groupings, structure, shape, biological nature, and overall size were examined using standard characterization techniques. With a quantum yield of 22.1%, these CDs showed excitation-dependent fluorescence emission. In addition, Cd2+ ions were distinguished from other metal ions by a noticeable drop in fluorescence intensity. The fluorescence probe showed a linear response ranging from 0–300 μM and a detection threshold (DT) of 0.21 μM, indicating its effectiveness for Cd2+ detection. Furthermore, the CDs demonstrated the practical application by detecting Cd2+ ion in actual water samples.

Biocompatible Fluorescent Graphene Oxide Quantum Dots for Imaging of Drosophila melanogaster.

Developing reliable biocompatible bioimaging agents is paramount for diagnosing critical diseases and disorders early through oral ingestion of fluorescent probes to image living organisms. Here, we prepared fluorescent, water-dispersed graphene oxide quantum dots via pyrolysis of a Glycyrrhiza glabra root in the water medium using a cost-effective and environmentally benign method to enable Drosophila melanogaster, an organism analogous to the human genome, to be imaged alive. The prepared graphene oxide quantum dots demonstrated a 2.6 nm diameter and 0.36 nm graphitic spacing with carboxylic acid, carbonyl, and hydroxyl functionalities. The selected area electron diffraction image analysis reveals a series of bright circular patterns that confirm the crystalline nature of the graphene oxide quantum dots. Raman and X-ray diffraction analyses also validate the crystallinity nature of prepared materials. The graphene oxide quantum dots exhibited blue fluorescence under ultraviolet-light irradiation with excitation-dependent emission properties from blue to red emission. The synthesized graphene oxide quantum dots consistently fluoresce in the larva-fed graphene oxide quantum dots without exhibiting toxicity. The current study evaluates the toxic effect of synthesized fluorescent graphene quantum dots by examining several screening and staining methods on D. melanogaster, a fruit fly, as a model.

Evaluation of sustainability of fabrication process and characterization studies of activated carbon nanocatalyst from waste chestnut peels

This study uses waste chestnut peels to synthesize low-cost activated carbon-based catalysts through pyrolysis and calcination, investing distinct structural and compositional variations for sustianble application in manufacturing innovation and allied industries. The X-ray diffraction (XRD) analysis indicated sharp crystalline peaks in the calcinated product, contrasting with the amorphous nature of carbon material with some partially crystalline and distorted graphitic phases of the pyrolyzed product. Fourier-transform Infrared spectroscopy (FT-IR) analysis shows the presence of various functional groups such as O–H, C–O, C–H, CO, and CC. The analysis made through the scanning electron microscope (SEM) and transmission electron microscope (TEM) depicted a packed and agglomerated structure with different irregular particle shapes in the calcined carbon, while the sample prepared through pyrolysis exhibited a network-like structure with some interconnected voids. Energy dispersive X-ray (EDX) analysis showed varying carbon content which is found to be 47.41 % in the case of the calcinated sample and 99.7 % in the product prepared through pyrolysis. The calcined carbon exhibited a band gap of 4 eV, while the pyrolyzed carbon showed a higher band gap of 4.8 eV. In addition, the catalyst prepared through the calcination process exhibited significantly higher luminance intensity than that produced through pyrolysis, while both samples showed an excitation-dependent emission property. This work presents two simple methods for synthesizing nanocarbon-based catalysts using waste lignocellulosic biomass. In addition, the optical properties of the resulting nanocarbons suggest that they can be further explored for their applications as catalysts or biosensing agents.

Porphyrin-based carbon dots as fluorescence probe for sensing of Fe3+ ion and S2- anion in aqueous solution

In this work, a facile bottom-up approach was employed to synthesize the porphyrin-citric acid-derived fluorescent carbon dots (Por-CA-CDs) using a single-step hydrothermal method. As-prepared Por-CA-CDs were well characterized using spectroscopic techniques such as FT-IR, high-resolution transmission electron microscopy, P-XRD, UV-Vis absorption, and photoluminescence spectroscopy. The synthesized Por-CA-CDs exhibited blue fluorescence with excellent photostability and diameter ranging from 2.4 to 6.4 nm. Por-CA-CDs show excitation-dependent emission behavior, with a quantum yield of 26% and were used for sensing of Fe3+ and S2− ions in an aqueous solution. Por-CA-CDs demonstrated a robust and selective reaction to Fe3+ compared to the other cations utilized in this investigation. The sensing capability of Por-CA-CDs with Fe3+ ions was evaluated with fluorescence spectroscopy, and results show a “Turn-Off” emission mode upon binding of Fe3+ with Por-CA-CDs. In metal ion sensing studies, the fluorescence intensity of Por-CA-CDs exhibited significant quenching upon the addition of Fe3+ at concentrations ranging from 0 to 230 μM, with a detection limit (LOD) of 3.2 × 10−8 M. The quenching efficiency and Stern-Volmer quenching constant were computed as 99.45% and 4.4 × 106 M−1, respectively. Interestingly, fluorescence of Por-CA-CDs can be regained with the addition of S2− (0-160 µM) with LOD of 4.3 × 10−6 M and Stern-Volmer quenching constant of 6 × 105 M−1. Most importantly, the toxicity assay revealed good reliability for samples in deionized, tap, and river water, suggesting applications for Fe3+ monitoring in complex environments.

Luminous blue carbon quantum dots employing Anisomeles indica (catmint) induce apoptotic signaling pathway in triple negative breast cancer (TNBC) cells.

Herein, luminous blue carbon quantum dots (CDs) employing Anisomeles indica (Catmint) were reported with imaging, self-targeting, and therapeutic effects on triple-negative breast cancer (TNBC, MDA-MB-231) cells. The salient features of CDs generated from catmint are as follows: i) optical studies confirm CDs with excitation-dependent emission; ii) high-throughput characterization authenticates the formation of CDs with near-spherical shape with diameter ranging between 5 and 15 nm; iii) CDs induce cytotoxicity (3.22 ± 0.64 μg/ml) in triple-negative breast cancer (TNBC, MDA-MB-231) cells; iv) fluorescence microscopy demonstrates that CDs promote apoptosis by increasing reactive oxygen species (ROS) and decreasing mitochondrial membrane potential; v) CDs significantly up-regulate pro-apoptotic gene expression levels such as caspases-8/9/3. Finally, our work demonstrates that catmint-derived CDs are prospective nanotheranostics that augment cancer targeting and imaging.

Unexpected tunable photoluminescence and emission mechanism during the gradual increase of cyclic glucose units

Excitation-dependent (λex-dependent) emission is one of the most common emission characteristics of nonconventional luminophores. Previously, we have reported D-xylose crystals has an obvious λex-dependent color tunable persistent room temperature phosphorescence (p-RTP) from blue to green, but its p-RTP emission at long wavelength is very weak. To further explore this attractive multicolor p-RTP behavior, and to enhance its tunability, the photoluminescence (PL) behavior of three common cyclodextrins (CDs), namely α-CD, β-CD and γ-CD, including solution and single crystals, were studied. Their single crystals demonstrate λex-dependent multicolor p-RTP properties in the order of β-CD>α-CD>γ-CD, rather than the strongest with the least glucose units (α-CD). Among them, the λex-dependent tunable p-RTP of β-CD and α-CD is superior to that of D-(+)-xylose single crystal. The above unexpected phenomena could be explained reasonably through detailed single crystal structure analysis and theoretical calculations. The emission behavior of solution and single crystals of CDs can be reasonably explained by the clustering-triggered emission (CTE) mechanism. Furthermore, CD-based covalent organic frameworks (COF) and supramolecules are readily fabricated, which own significantly enhanced p-RTP emission. Due to the intriguing PL property as well as hydrophilic rim and low biotoxicity of CDs, successful imaging of HCT116 cells and encryption applications were demonstrated. It is believed that the intrinsic PL properties of CDs, especially their regularly adjustable multicolor p-RTP that varies with the number of glucose units, have significant guidance for the development of a series of multicolor luminescent materials.

Design and evaluation of fluorescent chitosan-starch hydrogel for drug delivery and sensing applications

Composite bio-based hydrogels have been obtaining a significant attention in recent years as one of the most promising drug delivery systems. In the present study, the preparation of composite chitosan-starch hydrogel using maleic acid as a cross-linker was optimized with the help of response surface methodology. The synthesized hydrogel was fluorescent owing to clustering of large number of functional groups. Different analytical techniques, including XRD, FTIR, SEM, XPS, fluorescence and BET were utilized to characterize the prepared hydrogel. XRD analysis confirmed the formation of non-crystalline hydrogel with random arrangement of macromolecular chains. The composite hydrogel exhibited good swelling percentage with pH sensitivity, hemocompatibility and degradability. BET analysis confirmed that the variation in concentration of crosslinker significantly influences the pore volume of the hydrogel. The synthesized composite chitosan-starch hydrogel was utilized as a prospective candidate for controlling drug release. Cefixime as a model drug was loaded onto the synthesized hydrogel utilizing the swelling diffusion method. SEM micrographs showed uniform distribution of drug molecules in the drug loaded hydrogel. In vitro drug release experiments indicated the swelling dependent drug release behaviour of chitosan-starch hydrogel with higher drug release at pH 7.4 (93.08 %) compared to pH 1.2 (67.85 %). The composite chitosan-starch hydrogel was able to prolong and control the drug release up to 12 h. The drug release from the hydrogel followed Korsmeyer-Peppas and Makoid-Banakar model with Fickian diffusion mechanism. Further, the composite hydrogel displayed excitation dependent fluorescence emission with most intense blue emission band at 425 nm with an excitation wavelength of 350 nm. The inclusion of cefixime drug in the hydrogel matrix significantly reduced the fluorescence intensity; the decrease was linearly correlated to the concentration of the drug. Moreover, the fluorescence emission the chitosan-starch hydrogel was found to be dependent upon pH. The synthesized hydrogel is expected to be a potential candidate for controlled drug release as well as for fluorescent sensing applications.

Okra peel-derived nitrogen-doped carbon dots: Eco-friendly synthesis and multi-functional applications in heavy metal ion sensing, nitro compound detection and environmental remediation

The present study explores the kitchen waste okra peels derived synthesis of nitrogen doped carbon dots (N-CDs) via simple carbonization followed by reflux method. The synthesized N-CDs was characterized using, TEM, XPS, FTIR, XRD, Raman, UV–Visible and Fluorescence Spectroscopy. The N-CDs emits bright blue emission at 420 nm with 12 % of quantum yield as well as it follows excitation dependent emission. Further, the N-CDs were employed as a fluorescence sensor for detection of hazardous metal ions and nitro compounds. Among various metal ions and nitro compounds, the N-CDs shows fluorescence quenching response towards Cr6+, and Mn7+ metal ions as well as 4-nitroaniline (4-NA) and picric acid (PA) with significant hypsochromic and bathochromic shift for Mn7+, 4-NA and PA respectively. The developed fluorescent probe shows relatively low limit of detection (LOD) of 1.46 µg/mL, 1.05 µg/mL, 2.1 µg/mL and 2.2 µg/mL for the above analytes respectively. The N-CDs did not show any significant interference with coexisting ions and successfully applied for real water sample analysis. In addition, circular economy approach was employed for adsorption of dyes by reactivating leftover waste carbon residue which was obtained after reflux. Thus, the kitchen waste valorization and circular economy approach based N-CDs have potential applications in the field of detection of emerging pollutants, and environmental remediation.

Facile preparation of arginine-based carbon dots for highly selective detection of dopamine

Arginine-based carbon dots (Arg-CDs) were synthesized through a facile one-step hydrothermal method using arginine and urea as precursors. The as-prepared Arg-CDs displayed good aqueous solubility and typical excitation-dependent emission property, with the fluorescence quantum yield of 25.47 %. The fluorescence of Arg-CDs was gradually quenched by the addition of dopamine (DA) in the alkaline solution. However, under neutral and acidic condition, the fluorescence intensity of Arg-CDs remained unchanged upon the addition of DA. The sensing mechanism was probably due to the rapid oxidation of DA to dopaquinone in alkaline condition, which could quench the fluorescence of Arg-CDs through the Inner Filter Effect (IFE). Moreover, the fluorescence change of Arg-CDs was proportional to the concentration of DA under the optimized condition. Because of the linear relationship, the detection limit of dopamine was calculated to be 0.28 μM with the detection range from 10 to 100 μM. The interference experiment was carried out to further verify the specificity of this fluorometric method. Finally, the fluorometry based on Arg-CDs has been successfully used to the determination of DA in human serum with high accuracy and satisfactory recovery.

Excitation-Dependent Emission in Sb3+-Doped All-Inorganic Rare-Earth Double Perovskites for Anticounterfeiting Applications.

Achieving high-efficiency tunable emission in a single phosphor remains a significant challenge. Herein, we report a series of Sb3+-doped all-inorganic double perovskites, Sb3+:Cs2NaScCl6, with efficient excitation-dependent emission. In 0.5%Sb3+:Cs2NaScCl6, strong blue emission with a high photoluminescence quantum yield (PLQY) of 85% is obtained under 265 nm light irradiation, which turns into bright neutral white light with a PLQY of 56% when excited at 303 nm. Spectroscopic and computational investigations were performed to reveal the mechanism of this excitation-dependent emission. Sb3+ doping induces two different excitation channels: the internal transition of Sb3+: 5s2 → 5s5p and the electron transfer transition of Sb3+: 5s → Sc3+ 3d. The former one generates excited Sb3+ ions, which can undergo efficient energy transfer to populate the host self-trapped exciton (STE) state, yielding enhanced blue emission. The latter one leads to the formation of a new STE state with the hole localized on Sb3+ and the electron delocalized on the nearest Sc3+, which accounts for the newly exhibited low-energy emission. The difference in the excitation pathways of the two emitting STE states results in the highly efficient excitation-dependent emission, making the doped systems promising anticounterfeiting materials.

Temperature and pressure-induced excitation-dependent emissions in zero-dimensional hybrid metal halides with mixed halogens.

Zero-dimensional (0D) hybrid metal halides (HMHs) have emerged as a promising platform for exploring excitation-dependent multicolor luminescent materials owing to their diverse crystal structures and chemical compositions. Nevertheless, understanding the mechanism behind excitation-dependent emissions (EDEs) in 0D HMHs and achieving precise modulation remains challenging. In this work, the delicate regulations on the EDE of 0D (DMEDABr)4SnBr3I3 (DMEDA: N, N'-dimethylethylenediamine) with mixed halogens are achieved under low temperature and high pressure, respectively. The inhomogeneous halogen occupation at the atomic scale leads to the formation of Br-rich and I-rich SnX6 (X = Br, I) octahedra, which act as distinct luminescent centers upon photoexcitation. At low temperatures, the narrowed photoluminescence spectra could distinguish the individual emissions from different luminescent centers, resulting in a pronounced EDE of (DMEDABr)4SnBr3I3. In addition, the contraction and distortion of the luminescent SnX6 (X = Br, I) centers at high pressure further result in different degrees of emission shifts, giving rise to the gradual emergence and disappearance of EDE. This work elucidates the underlying mechanism of EDE in 0D HMHs and highlights the crucial role of halogens in determining the optical properties of metal halides.

NIR-responsive carbon dots as an oxidative-stress amplifier and hyperthermia-induced superior photothermal in-vitro anticancer activity

A facile wet chemistry-based strategy was developed to synthesize orange emissive Carbon dots (O-CDs) based on dehydration-induced ring-fusion of the precursor (1,3-dihydroxynaphthalene) in a dehydrating sulfuric acid medium. The O-CDs revealed significant Near-infrared (808 nm) light harvesting potential with outstanding photothermal conversion efficiency (∼58%) and hence exhibited excellent NIR-light stimulated photothermal anticancer performance. Furthermore, these fluorescent O-CD nanoprobes displayed excitation-dependent polychromatic emissions in the range of 540–640 nm, with the dual emission maxima at 540 and 580 nm, corresponding to yellow and orange emission at the excitation of 490 nm. Various mitochondrial, as well as cytoplasmic apoptosis-related proteins and genes were upregulated during photothermal treatment, which suggests that hyperthermia and oxidative stress have a major impact on cell death. The anticancer activity of O-CDs is likely due to the elevated reactive oxygen species (ROS) amplification in cooperation with the hyperthermia effect. This study offers a potential alternative to bio-nanomedicine for cancer treatment by carbon-based photothermal therapy.

Photoluminescence Study of Undoped and Eu-Doped Alkali-Niobate Aluminosilicate Glasses and Glass-Ceramics.

In this study, the photoluminescence (PL) behavior of two aluminosilicate glass series containing alkali-niobates ranging from 0.4 to 20 mol% was investigated. The glasses exhibit an intense visible emission centered at ~18,400 cm-1 for the peralkaline series and at higher energies (~19,300 cm-1) for the metaluminous glasses. However, the photoluminescence emission intensity varies significantly with the niobate content and the bulk chemistry. PL and fluorescence lifetime measurements indicate that the broad emission bands result from the overlap of different niobate populations, whose distribution changes with niobate content. The distinct PL behavior in the two glass series was related to the structural evolution of the niobate units upon niobium addition. An enhancement of the visible emission was observed for a higher fraction of distorted [NbO6] units. Eu-doping was carried out as a structural probe of the glass network, and also to determine if these glasses could be used as potential rare earth element (REE) activators. The crystal field strength around Eu ions is strongly dependent on the bulk chemistry and the niobate content. Furthermore, the peralkaline series showed energy transfer from the host [NbO6] to Eu3+, confirming the feasibility of exploring niobate glasses and glass-ceramics as lanthanide ion-activated luminescent materials. In addition, glass-ceramics (GCs) containing alkali-niobate phases with a perovskite-like structure were developed and studied to verify the optical performance of these materials. It was verified that the bulk chemistry influences crystallization behavior, and also the photoluminescence response. The transparent GC from the metaluminous series exhibits a quenching of the Eu3+ emission, whereas an enhanced emission intensity is observed for the peralkaline GC. The latter shows a strong excitation-dependent PL emission, suggesting energy transfer and migration of electronic excitation from one Eu population to another. Additionally, Eu3+ emissions arising from the D15 and D25 excited states were observed, highlighting the low phonon energy achievable in niobo-aluminosilicate hosts.

Lentils/urea as precursors for profound S and N doping of carbon dots for selective sequential determination of Hg(II) and S(II) in food and environmental samples

In this article, we described a new platform for probing toxic pollutants, namely Hg2+ and S2-, in aquatic environment by tracing the “on–off-on” fluorescence signals of quantum dots. To achieve this, red lentils and urea, as natural precursors, were utilized as sources of S and N doping, respectively, to fabricate blue fluorescent carbon quantum dots, namely, lentils/urea quantum dots (LUQDs) with good quantum yield and plentiful S-doping. In the present work, the quality-by-design (QbD) strategy was applied to control and select the optimum conditions for the microwave-aided synthesis of the carbon dots. LUQDs exhibit excitation-dependent emissions, where the maximum fluorescence emission was at 360 nm after excitation at 300 nm. During the detection step, the fluorescence of LUQDs is quenched by the incorporation of Hg2+ over the range of 0.50–70.0 μM. Next, S2- reacts with Hg2+, resulting in turning on the fluorescence emission of LUQDs in the range of 10.0–150.0 µM.The method was applied for the detection of both Hg2+ and S2- in tap, sewage, and river water samples with a recovery rate ranging between 98.96 % and 101.26 %; in addition, Hg2+ was detected in canned Tuna samples with a recovery of 98.70 %. Furthermore, the greenness of the developed method was confirmed through various greenness metrics.