Origin of strong excitation wavelength dependent fluorescence of graphene oxide

Excitation wavelength-dependent lanthanide-disalicylaldehyde coordination hybrid capable of distinguishing D2O from H2O

The increasing demands in fields of anti-counterfeiting, fluorescence analysis, clinical therapy and LED illumination are urgently eager for more excellent optically switchable luminescent materials with the stable and multimodal fluorescence in single-component matrix. Herein, the lanthanide-disalicylaldehyde coordination hybrid H2Qj4/TbxEuy is proposed as an efficient luminescent matrix to connect terbium sensibilization with ESIPT (excited-state intramolecular proton transfer) effects, and three multi-emission hybrids are finally designed and synthesized by regulating Tb3+ and Eu3+ ratios. Surprisingly, the H2Qj4/Tb0.91Eu0.09 shows the excitation wavelength-dependent luminescence in solution which originates from two energy transfer ways of terbium sensibilization effect. It exhibits green and red lights under the 369 and 394 nm UV lamp, respectively. Three hybrids are further used as lab-on-a-molecule fluorescent probes to perform multianalyte detection for various solvents by selected fluorescent sensing channels. By means of PCA (principal component analysis) and HCA (hierarchical cluster analysis), all of them can successfully detect and discriminate17 common solvents, especially the H2O and D2O. Moreover, the H2Qj4/Tb0.91Eu0.09 also shows the wide linear responses of H2O content in D2O, discrimination of two-component solvent mixtures, hygroscopicity evaluation of D2O and information encryption which will advance the progress of multimodal luminescent materials and multianalyte chemosensors.

Photoluminescence quantum yield of carbon dots: emission due to multiple centers versus excitonic emission

Carbon dots (CDs) are recognized as promising fluorescent nanomaterials with bright emission and large variations of photoluminescence quantum yield (PLQY). However, there is still no unique approach for explanation of mechanisms and recipes for synthetic procedures/chemical composition of CDs responsible for the enhancement of PLQY. Here, we compare photophysical behavior and PLQY of two types of CDs synthesized by different routes, leading to the different extent of oxidation and composition. The first type of CDs represents a conjugated carbon system oxidized by F, N and O heteroatoms, whereas the second type represents a non-conjugated carbon system oxidized by oxygen. Photophysical data, photoemission spectroscopy and microscopy data yield the suggestion that in the first case, a structure with a distinct carbon core and highly oxidized electron-accepting shell is formed. This leads to the excitonic type non-tunable emission with single-exponent decay and high PLQY with a strong dependence on the solvent polarity, being as high as 93% in dioxane and as low as 30% in aqueous medium, but which is vulnerable to photobleaching. In the second case, the oxidized CDs do not indicate a clear core-shell structure and show poor solvatochromism, negligible photobleaching, low PLQY varying in the range of 0.7-2.3% depending on the solvent used, and tunable emission with multi-exponent decay, which can be described by the model of multiple emission centers acting through a clustering-triggered emission mechanism. The obtained results lead to a strategy that allows one to design carbon nanomaterials with principally different PLQYs that differ by orders of magnitude.

Exploration of the impact of graphene oxide, acetylenic gemini, and CTAT on the photophysical and aggregation properties of dipolar coumarin 153

Advanced spectroscopic techniques have been utilized to study the interaction between the laser dye coumarin 153 (C153) and graphene oxide (GO) nanoparticles. GO was synthesized using a modified Hummers' method and characterized by UV-vis spectroscopy, Raman laser spectroscopy, FTIR-ATR spectroscopy, FESEM, HR-TEM, and XRD techniques. The GO@C153 composite was formed by mixing two aqueous solutions of GO and C153 due to their strong interaction through stacking and hydrophobic interactions. In this case, GO acts as an effective fluorescence quencher for C153 molecules, which undergo H-type aggregation in the presence of GO. The Stern-Volmer equation and time-dependent fluorescence studies were utilized to analyse the mechanism of fluorescence quenching. According to the findings, both static and dynamic quenching processes are responsible for the reduction in fluorescence intensity. The effect of surfactants (both cetyltrimethylammonium p-toluenesulfonate (CTAT) and synthesized N,N'-dihexadecyl-N,N,N',N'-tetramethyl-N,N'-but-2-ynediyl-di-ammonium chloride (16-4-16)) on the aggregation and photophysical properties of the dye was investigated using surface tensiometry, conductometry, UV-vis absorption spectroscopy, steady-state fluorescence measurements, DLS, and time-dependent fluorescence spectroscopy. Surfactants change the microenvironment of the C153 dye, leading to spectrum shifting and a higher quantum yield, which causes a rapid rise in fluorescence intensity in the micellar medium. It has been noted that in a micellar medium rather than in an aqueous one, the luminous intramolecular charge transfer (ICT) state of C153 stabilises. Lastly, we investigated the photophysical behavior of the GO-C153-micelle ternary system and discovered that, in the presence of a micellar medium, the quenched and blue-shifted (H-type aggregation) fluorescence peak of C153 (in the presence of GO) began to intensify once more. The main goal of this work is to create an effective and fairly cost powerful fluorescence sensor. Additionally, the ternary system (GO-C153-micelle) analytical idea can be employed to identify the onset of micelle formation. In wastewater treatment analysis, the GO-C153-surfactant ternary system concept can also be used to regenerate the adsorbent (in this case, GO) from dye molecules by allowing the dye molecules to exit the adsorbent and enter the micellar medium.

Unraveling the Photoluminescence Properties of a Boron Nitride Nanosheet Dispersed in Different Solvents and Its Application to Generate White Light

Hexagonal boron nitride (h-BN) is an influential 2D nanomaterial; however, its practical optoelectronic applications rely primarily on controlling the structural defects. The photoluminescence depends explicitly on the developed vacancies and substitutional defects. The present work utilizes the concept of facile liquid-phase exfoliation of hexagonal (h) boron nitride (BN) powder in common organic solvents and cosolvent mixtures to obtain a layered boron nitride nanosheet (BNNS). Although the literature concerning the layered structure of BNNS obtained by different methods is substantial, what is lacking is a detailed photoluminescence study of the layered structure obtained by changing the solvent and cosolvent mixtures, and here lies the novelty of our work. The obtained layered structure was subjected to a detailed photoluminescence study by varying the temperature. We tried to correlate how the defects originating upon changing the solvent and cosolvent affected the photoluminescence of the layered BNNS. The obtained layered structure is suitably supported by optical and electron microscopy images. High-resolution transmission electron microscopy confirm the presence of a few layers, and X-ray photoelectron spectroscopy studies give an idea of the atomic composition of the obtained BNNS. The photoluminescence properties of the obtained BNNS in water were modulated by the addition of two different classes of block copolymers, e.g., Pluronic (F-68, P-407, and P-123) and Tetronic (T-904, T-908, and T-90R4) copolymers. As an application, we were successful in constructing a nanocomposite material made up of a BNNS-copolymer-organic fluorophore to check the possibilities of generating white light.

Green to deep-red emissive carbon dot formation by C+ion implantation on nitrogen beam created self-masked nano-template

We report the formation of green to red emissive arrays of carbon dot on silicon-nitride nano-templates by successive implantation of nitrogen and carbon broad ion beams. The patterned nano-templates are formed by 14 keV N2+ion-bombardment at grazing incident (70°) on Si. Subsequently, 5 keV C+ions are implanted at the selective sites of the pyramidal nano-template by taking advantage of the self-masking effect. The nano-pyramidal pattern and the implanted carbon dots at the specific sites are confirmed by atomic force microscopy and cross sectional transmission electron microscopy measurements. The developed carbon dots (CDs) are mostly amorphous and consists of SiC and graphitic nitrogen (CN). G-band and D-band carbons are identified by Raman spectroscopy, while the presence of SiC and CN are detected by XPS measurements. A change of band-gap is observed for C-implanted templates by the UV-vis spectroscopy. Excitation wavelength-dependent photoemission from the dots is found in the green to red region. Maximum intense PL is observed in the green-orange region for excitation wavelength of 425 nm and a redshift of PL with decreasing intensity is observed with the increase of excitation wavelength. The observed photoluminescence is described in terms of the combined effects of quantum confinement, graphitic nitrogen and defect induced additional states formation in the carbon dots. The potential applications of CDs are also addressed.

White light emission from helically stacked humin-mimic based H-aggregates in heteroatom free carbon dots

White light emission (WLE), particularly from heteroatom free carbon dots (CDs), is unusual. Besides, deciphering the origin of WLE from a H-aggregated molecular fluorophore in such kinds of CDs is a challenging task due to their non-fluorescent character resulting from a forbidden transition from a lower-energy excitonic state. Therefore, rigorous investigation on their elusive excited state photophysical properties along with their steady-state optical phenomena has to be carried out to shed light on the nature of distinct emissive states formed in the CDs. Herein, for the first time, we report WLE from imperfect H-aggregates of co-facially π-π stacked humin-like structures comprising furfural monomer units as a unique molecular fluorophore in CDs, as revealed from combined spectroscopic and microscopic studies, synthesized through hydrothermal treatment of the single precursor, dextrose. H-aggregates in CDs show a broad range of excitation-dependent emission spectra with color coordinates close to pure white light, i.e., CIE (0.35, 0.37) and a color temperature of 6000 K. Imperfect orientation between the transition dipole moments of adjacent monomer units in the H-aggregate's molecular arrangement is expected to cause ground state symmetry breaking, as confirmed by Circular Dichroism (CD) studies, which established helically stacked nature in molecular aggregates and produced significant oscillatory strength at lower energy excitonic states to enable fluorescence. TRES and TAS investigations have been performed to minimise the intricacies associated with excited state photophysics, which is regarded as an essential step in gaining a grasp on emissive states. Based on the observation of two isoemissive spots in the time-resolved area normalized emission spectra (TRANES), the existence of three oligomeric species in the excited state equilibrium of the pure/hybrid H-aggregates has been established. The exciton dynamics through electron relaxation from the higher to the lower excitonic states, charge transfer (CT) states, and surface trap mediated emission in excimer states of H-aggregates have also been endorsed as three distinct emissive states from femtosecond transient absorption spectroscopy (TAS) studies corroborating with their steady-state absorption and emission behavior. The results would demonstrate the usage of CDs as a cutting-edge fluorescent material for creating aggregate-induced white light emission.

Excitation wavelength-dependent multi-coloured and white-light emissive pyrene-based hydrazones: suppression of Kasha's rule

Multi-coloured and white-light emissions from pyrene-based hydrazones are described. They exhibit excitation wavelength-dependent emissions in solution due to the suppression of Kasha's rule. Interestingly, in dimethylformamide, 1-3 emit light that covers all the regions of primary colours as a function of excitation wavelength, and 1 and 2 emit white light (λex = 420 nm) in isopropanol.

Gelatin-assisted fabrication of reduced nanographene oxide for dual-modal imaging of melanoma cells

In this work we report a gelatin-based, simple two-steps approach for fabrication of reduced graphene oxide (rGO-GEL) possessing high stability and biocompatibility, as novel label-free intracellular contrast agents. Gelatin, a biopolymer that is known for its versatility, was employed not only to biocompatibilize the rGO, but also to prevent the aggregation of the GO nanosheets during the reduction process. To confirm the successful reduction process and the attachment of the gelatin to the rGO nanosheets, we employed multiple spectroscopic analyses such as FT-IR, Raman, UV-VIS and photoluminescence, while the morphology and the lateral dimensions of the resulting hybrid rGO-GEL were investigated by Scanning-Transmission Electron Microscopy (STEM). Cellular toxicity test proved that the rGO-GEL nanoflakes are nontoxic for melanoma B16-F10 cells, even at high concentrations. Finally, the intracellular tracking after 24 h of treatment was performed by non-invasive Super-resolution re-scan confocal microscopy as well as Confocal Raman imaging, thus implementing our nanoflakes as a suitable contrast agent candidate for cellular imaging of interest.

Red edge excitation shift spectroscopy is highly sensitive to tryptophan composition

Red edge excitation shift (REES) spectroscopy relies on the unique emission profiles of fluorophore-solvent interactions to profile protein molecular dynamics. Recently, we reported the use of REES to compare the stability of 32 polymorphic IgG antibodies natively containing tryptophan reporter fluorophores. Here, we expand on this work to investigate the sensitivity of REES to variations in tryptophan content using a subset of IgG3 antibodies containing arginine to tryptophan polymorphisms. Structural analysis revealed that the additional tryptophan residues were situated in highly solvated environments. Subsequently, REES showed clear differences in fluorescence emission profiles when compared with the unmutated variants, thereby limiting direct comparison of their structural dynamics. These findings highlight the exquisite sensitivity of REES to minor variations in protein structure and tryptophan composition.

Photoluminescence Properties of Graphene Oxide in Non-Aqueous Solvents

Detailed attention to the interaction between graphene oxide (GO) and various organic fluorophores has been documented in literature as a result of which the impact of GO on the photophysical properties of the fluorophores is well known to the scientific community. However, the photoluminescence (PL) properties of GO in polar aprotic solvents are yet to be established. In this article, the PL properties of GO in polar aprotic solvents using various spectroscopic techniques have been reported. n-π* transition due to the C=O bonds in the sp3 hybrid regions and π-π* transition due to C=C bonds in the sp2 hybrid are prominent in GO. The presence of quasi-molecules within sp2 -sp3 domains acts as PL centers located in the sp3 matrixes of GO are responsible for the PL properties. This study showcases the presence of multiple emissive states of GO in polar aprotic solvents and conveys the fact that the PL properties of GO are very much wavelength-dependent.

Asymmetric fabrication and in vivo evaluation of the wound healing potency of electrospun biomimetic nanofibrous scaffolds based on collagen crosslinked modified-chitosan and graphene oxide quantum dot nanocomposites

Asymmetric scaffolds were developed through electrospinning by utilizing biocompatible materials for effective wound healing applications. First of all, the chitosan surface was modified with decanoyl chloride and crosslinked with collagen to synthesize collagen crosslinked modified-chitosan (CG-cross-CS-g-Dc). Then, the asymmetric scaffolds were fabricated through electrospinning, where the top layer was a monoaxial nanofiber of the PCL/graphene oxide quantum dot (GOQD) nanocomposite and the bottom layer was a coaxial nanofiber having PCL in the core and the CG-cross-CS-g-Dc/GOQD nanocomposite in the shell layer. The formation of monoaxial (∼130 ± 50 nm) and coaxial (∼320 ± 40 nm) nanofibers was confirmed by transmission electron microscopy (TEM). The presence of GOQDs contributed to antioxidant and antimicrobial efficacy. These scaffolds showed substantial antibacterial activity against the common wound pathogens Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The scaffolds exhibited excellent cytocompatibility (MTT assay) and anti-inflammatory behaviour as analysed via the cytokine assay and biochemical analysis. The in vivo wound healing potential of the nanofibrous scaffolds was assessed with full-thickness excisional wounds in a rat model. The scaffolds accelerated the re-epithelialization as well as the collagen deposition, thereby facilitating the wound healing process in a very short span of time (10 days). Both in vitro and in vivo analyses thus provide a compelling argument for the use of these scaffolds as therapeutic biomaterials and their suitability for application in rapid wound regeneration and repair.

Amplification of oxidative stress by lipid surface-coated single-atom Au nanozymes for oral cancer photodynamic therapy

Single-atom nanozymes (SANs) are the latest trend in biomaterials research and promote the application of single atoms in biological fields and the realization of protein catalysis in vivo with inorganic nanoparticles. Carbon quantum dots (CDs) have excellent biocompatibility and fluorescence properties as a substrate carrying a single atom. It is difficult to break through pure-phase single-atom materials with quantum dots as carriers. In addition, there is currently no related research in the single-atom field in the context of oral cancer, especially head and neck squamous cell carcinoma. This research developed a lipid surface-coated nanozyme combined with CDs, single-atomic gold, and modified lipid ligands (DSPE-PEG) with transferrin (Tf) to treat oral squamous cell carcinoma. The study results have demonstrated that surface-modified single-atom carbon quantum dots (m-SACDs) exhibit excellent therapeutic effects and enable in situ image tracking for diagnosing and treating head and neck squamous carcinoma (HNSCC).

A "turn-off" photoluminescent sensor for H2O2 detection based on a zinc oxide-graphene quantum dot (ZnO-GQD) nanocomposite and the role of amine in the development of GQD

In this work, graphene quantum dots (GQD) were prepared through a hydrothermal process. The photoluminescence (PL) emission spectrum for GQD prepared with high NH₄OH concentration (sample D1-t) was attained at lower wavelength (406 nm), compared to GQD synthesized with low NH₄OH concentration (sample D2-t attained at 418 nm). From these results, a smaller particle size for D1-t was deduced; according to TEM images the GQD particles are around 5 nm. The Raman I_D3/I_G ratio which is related to C-O groups at the edges of GQD and the full width at half maximum was lower for D1-t than D2-t. This was ascribed to the amine group incorporation at the edges and at the basal planes in D1-t, whilst in D2-t they prefer principally the edges of the GQD structure. The ZnO nanoparticles bonded to GQD (ZnO-GQD, nanocomposites) enhance the PL emission intensity. The H₂O₂ detection tested by photoluminescence spectroscopy, was found to occur thanks to the ZnO from the nanocomposite and its interaction with H₂O₂, producing a quenching effect. This quenching was accentuated by the increase of the H₂O₂ concentration. Such properties suggest the ZnO-GQD nanocomposite as a candidate to be used as a sensor material.

Citric Acid-Based Intrinsic Band-Shifting Photoluminescent Materials

Citric acid, an important metabolite with abundant reactive groups, has been demonstrated as a promising starting material to synthesize diverse photoluminescent materials including small molecules, polymers, and carbon dots. The unique citrate chemistry enables the development of a series of citric acid-based molecules and nanomaterials with intriguing intrinsic band-shifting behavior, where the emission wavelength shifts as the excitation wavelength increases, ideal for chromatic imaging and many other applications. In this review, we discuss the concept of "intrinsic band-shifting photoluminescent materials", introduce the recent advances in citric acid-based intrinsic band-shifting materials, and discuss their potential applications such as chromatic imaging and multimodal sensing. It is our hope that the insightful and forward-thinking discussion in this review will spur the innovation and applications of the unique band-shifting photoluminescent materials.

Synthesis of photocatalytic cysteine-capped Cu≈10 clusters using Cu5 clusters as catalysts

We report an easily scalable synthesis method for the preparation of cysteine-capped Cu_≈10 clusters through the reduction of Cu(II) ions with NaBH₄, using Cu₅ clusters as catalysts. The presence of such catalytic clusters allows controlling the formation of the larger Cu_≈10 clusters and prevents the production of copper oxides or Cu(I)-cysteine complexes, which are formed when Cu₅ is absent or at lower concentrations, respectively. These results indicate that small catalytic clusters could be involved, as precursor species before the reduction step, in the different methods developed for the synthesis of clusters. The visible light-absorbing Cu_≈10 clusters, obtained by the cluster-catalysed method, display high photocatalytic activities for the decomposition of methyl orange with visible light.

Multicomponent Anti-Kasha's Rule Emission from Nanotubular Metal-Organic Frameworks for Selective Detection of Small Molecules

The peak photoluminescence (PL) of conventional fluorophores is independent of the excitation wavelength (called Kasha's rule), while the search of metal-organic framework materials with the so-called anti-Kasha's rule emission remains very limited. Herein, we report the observation of anti-Kasha's rule emission in a multicomponent PL three-dimensional nanotubular metal-organic framework (abbr. MOF-NT), [Zn(μ-L)(μ-bix)]_n·0.33nH₂O [H₂L = biphenyl-3,5-dicarboxylic acid; bix = 1,4-bis(imidazole-1-ylmethyl)benzene]. The MOF-NT crystalline sample represents a notable example of strong excitation-dependent fluorescence from the ultraviolet to the visible spectral region. Moreover, by virtue of electronic flexibility and high PL efficiency, MOF-NT shows a discriminative PL response between isomeric nitroaromatic compounds. The work demonstrated the intrinsic anti-Kasha's rule emission in the crystalline-state MOF materials, providing new visions for the development of advanced solid-state emissive materials.

Dynamically tunable multicolor emissions from zero-dimensional Cs3LnCl6 (Ln: europium and terbium) nanocrystals with wide color gamut

This study demonstrates dynamically tunable multicolor emissions from a single component, zero-dimensional (0-D) cesium europium chloride (Cs₃EuCl₆) and cesium terbium chloride (Cs₃TbCl₆) nanocrystals (NCs). Highly uniform colloidal Cs₃EuCl₆ and Cs₃TbCl₆ NCs are synthesized via the heating-up method. Excitation-wavelength-dependent multicolor emissions from Cs₃EuCl₆ and Cs₃TbCl₆ NCs are observed. Under excitation of 330-400 nm, both NCs exhibit blue photoluminescence (PL). Under wavelengths shorter than 330 nm, characteristic red and green emissions are observed from Cs₃EuCl₆ and Cs₃TbCl₆, respectively, owing to the atomic emissions from the f-orbitals in trivalent europium (Eu³⁺) and terbium (Tb³⁺) ions. Cs₃EuCl₆ and Cs₃TbCl₆ NCs exhibit broadband excitation spectra and enhanced absorption properties. Particularly, Cs₃EuCl₆ NCs exhibit a very narrow full-width at half-maximum in both blue and red PL and no overlap between the two spectra. The photophysical properties of these NCs are further investigated to understand the multicolor PL origins by time-resolved and temperature-dependent PL measurements. Finally, the potential applications of Cs₃EuCl₆ and Cs₃TbCl₆ NCs as anti-counterfeiting inks for high-level security are demonstrated. Given their broadband excitation with enhanced absorption properties and dynamically tunable colors with a wide color gamut, Cs₃EuCl₆ and Cs₃TbCl₆ NCs have great potential as novel multicolor NC emitters for many emerging applications.

Graphene oxide for photonics, electronics and optoelectronics

Graphene oxide (GO) was initially developed to emulate graphene, but it was soon recognized as a functional material in its own right, addressing an application space that is not accessible to graphene and other carbon materials. Over the past decade, research on GO has made tremendous advances in material synthesis and property tailoring. These, in turn, have led to rapid progress in GO-based photonics, electronics and optoelectronics, paving the way for technological breakthroughs with exceptional performance. In this Review, we provide an overview of the optical, electrical and optoelectronic properties of GO and reduced GO on the basis of their chemical structures and fabrication approaches, together with their applications in key technologies such as solar energy harvesting, energy storage, medical diagnosis, image display and optical communications. We also discuss the challenges of this field, together with exciting opportunities for future technological advances.

Interaction between graphene oxide and acetaminophen in water under simulated sunlight: Implications for environmental photochemistry of PPCPs

In recent years, graphene oxide (GO) as a new carbon material has been widely investigated as adsorbent and catalyst. However, effects of GO on the micro-pollutants such as pharmaceuticals and personal care products (PPCPs) under sunlight remains unclear. In this study, the degradation of PPCPs in a simulated sunlight-GO photocatalytic system was systematically investigated. Specifically, GO rapidly degrade 95% of acetaminophen (APAP) within 10 min under simulated sunlight irradiation (λ ≥ 350 nm). The influencing factors such as APAP concentration, pH, GO dosage, water matrixes (Cl^-, NO₃^-, HCO₃^-, SO₄^2-, Ca²⁺, Fe³⁺and fulvic acid) were investigated. At a GO dosage of 100 mg L^-1 and an initial pH of 7, the APAP (5 μM) photodegradation kinetic constant k_obs was calculated to be 0.4547 min^-1. In practical applications, the GO photocatalysis system still degrade over 90% APAP within 60 min in real surface water. The electron spin resonance and radical scavenging experiments revealed that the dominated active species for degrading APAP was photogenerated holes (h⁺), while other mechanisms (¹O₂ and O₂^•-/HO₂^•) played a minor role. Furthermore, the photochemical transformation of some other typical PPCPs were comparatively studied to reveal the relationship between degradation kinetics and molecular structure. Based on descriptive variables including molar refractive index parameter, octanol-water partition coefficient, dissociation constant and dipole moment, a quantitative structural-activity relationship (QSAR) model for predicting pseudo-first-order rate constants was established with a high significance (R² = 0.996, p < 0.05). This study helps to understand the interaction between GO and PPCPs and its effects on the photochemical transformation of PPCPs in water.

Effect of Cuprous Oxide Nanocubes and Antimony Nanorods on the Performance of Silicon Nanowire-Based Quasi-Solid-State Solar Cell

Antimony nanorods (SbNRs) anchored to vertically aligned SiNWs serve as cosensitizers and enhance the light absorption of NWs, and their favorably positioned valence band (VB) coupled with their p-type semiconducting nature allows fast hole extraction from SiNWs. Photocorrosion of SiNWs is effectively prevented by a monolayer of N-[3-(trimethoxysilyl)propyl]aniline (TMSPA). Upon assembling a quasi-solid-state solar cell with a SbNRs@TMSPA@SiNW photoanode, a triiodide-iodide (I₃ ^-/I^-) redox couple-based gel encompassing dispersed p-type cuprous oxide nanocubes (Cu₂O NCs) as the hole transport material. and an electrocatalytic NiO as the counter electrode, a power conversion efficiency (PCE) of 4.7% (under 1 sun) is achieved, which is greater by 177% relative to an analogous cell devoid of the Cu₂O NCs and SbNRs. SbNRs at the photoanode maximize charge separation and suppress electron-hole and electron-I₃ ^- recombination at the photoanode/electrolyte interface, thereby improving the overall current collection efficiency. Concurrently, the Cu₂O NCs facilitate hole scavenging from SbNRs or SiNWs and relay them rapidly to the I^- ions in the electrolyte. Optically transparent and mesoporous NiO with a VB conducive to accepting electrons from FTO permits abundant interaction with I₃ ^- ions. The high PCE is a cumulative outcome of the synergistic attributes of SbNRs, Cu₂O NCs, and NiO. The SbNRs@TMSPA@SiNWs/Cu₂O-gel/NiO solar cell also exhibits a noteworthy operational stability, for it endures 500 h of continuous 1 sun illumination accompanied by an ∼24.4% drop in its PCE. The solar cell architecture in view of the judiciously chosen components with favorable energy level offsets, semiconducting/photoactive properties, and remarkable stability opens up pathways to adapt these materials to other solar cells as well.

Polarity-dependent emission from hydroxyl-free carbon nanodots

Surface groups of carbon nanodots (CNDs) play a key role in modulating their photoluminescence (PL) properties. However, most of the as-prepared CNDs are complex mixtures of CNDs bearing different surface groups. Thus, the purification of CNDs is essential to reveal the PL mechanism of CNDs. Herein, we present a facile method to synthesize hydroxyl (-OH) free CNDs, followed by intelligently guided column chromatographic separation of CNDs with specific functional groups according to their degree of polarity. After systematic investigation of the separated non-polar CNDs (NP-CNDs) and polar CNDs (P-CNDs), it is revealed that radiative photon emission dominates in the NP-CNDs, which exhibits excitation wavelength-independent emissions. In contrast, an increase in the solvent polarity of P-CNDs improves Frank-Condon excited state stabilization to achieve excitation wavelength-dependent emissions. In particular, white-light emitting P-CNDs with CIE coordinates of (0.332, 0.336) are produced. These findings provide new insights into the nature of the PL mechanism for CNDs, which may pave the way towards the rational design of highly efficient and emission tunable CNDs for various applications.

Photo-Thermal Tuning of Graphene Oxide Coated Integrated Optical Waveguides

We experimentally investigate power-sensitive photo-thermal tuning (PTT) of two-dimensional (2D) graphene oxide (GO) films coated on integrated optical waveguides. We measure the light power thresholds for reversible and permanent GO reduction in silicon nitride (SiN) waveguides integrated with one and two layers of GO. For the device with one layer of GO, the power threshold for reversible and permanent GO reduction are ~20 and ~22 dBm, respectively. For the device with two layers of GO, the corresponding results are ~13 and ~18 dBm, respectively. Raman spectra at different positions of a hybrid waveguide with permanently reduced GO are characterized, verifying the inhomogeneous GO reduction along the direction of light propagation through the waveguide. The differences between the PTT induced by a continuous-wave laser and a pulsed laser are also compared, confirming that the PTT mainly depend on the average input power. These results reveal interesting features for 2D GO films coated on integrated optical waveguides, which are of fundamental importance for the control and engineering of GO’s properties in hybrid integrated photonic devices.

Preparation, Properties, and Application of Lignocellulosic-Based Fluorescent Carbon Dots

Carbon dots (CDs) are a relatively new type of fluorescent carbon material with excellent performance and widespread application. As the most readily available and widely distributed biomass resource, lignocellulosics are a renewable bioresource with great potential. Research into the preparation of CDs with lignocellulose (LC-CDs) has become the focus of numerous researchers. Compared with other carbon sources, lignocellulose is low cost, rich in structural variety, exhibits excellent biocompatibility,^[1] and the structures of CDs prepared by lignin, cellulose, and hemicellulose are similar. This Review summarized research progress in the preparation of CDs from lignocellulosics in recent years and reviewed traditional and new preparation methods, physical and chemical properties, optical properties, and applications of LC-CDs, providing guidance for the formation and improvement of LC-CDs. In addition, the challenges of synthesizing LC-CDs were also highlighted, including the interaction of different lignocellulose components on the formation of LC-CDs and the nucleation and growth mechanism of LC-CDs; from this, current trends and opportunities of LC-CDs were examined, and some research methods for future research were put forward.

Red edge effect and chromoselective photocatalysis with amorphous covalent triazine-based frameworks

Chromoselective photocatalysis offers an intriguing opportunity to enable a specific reaction pathway out of a potentially possible multiplicity for a given substrate by using a sensitizer that converts the energy of incident photon into the redox potential of the corresponding magnitude. Several sensitizers possessing different discrete redox potentials (high/low) upon excitation with photons of specific wavelength (short/long) have been reported. Herein, we report design of molecular structures of two-dimensional amorphous covalent triazine-based frameworks (CTFs) possessing intraband states close to the valence band with strong red edge effect (REE). REE enables generation of a continuum of excited sites characterized by their own redox potentials, with the magnitude proportional to the wavelength of incident photons. Separation of charge carriers in such materials depends strongly on the wavelength of incident light and is the primary parameter that defines efficacy of the materials in photocatalytic bromination of electron rich aromatic compounds. In dual Ni-photocatalysis, excitation of electrons from the intraband states to the conduction band of the CTF with 625 nm photons enables selective formation of C‒N cross-coupling products from arylhalides and pyrrolidine, while an undesirable dehalogenation process is completely suppressed.

Fluorescent Mechanism in Zero-Dimensional Carbon Nanomaterials: A Review

Fluorescent carbon dots (CDs) have acquired growing interest from different areas over decades. Their fascinating property of tunable fluorescence by changing the excitation wavelength has attracted researchers worldwide. Understanding the mechanisms behind fluorescence is of great importance, as they help with the synthesis and applications, significantly when narrowed down to applications with color-tunable mechanisms. But, due to a lack of practical and theoretical information, the fluorescence mechanisms of CDs remain unknown, preventing the production of CDs with desired optical qualities. This review focuses on the PL mechanisms of carbon dots. The quantum confinement effect determined the carbon core, the surface and edge states determined by various surface defects and the connected functional/chemical groups on the surface/edges, the molecular state solely determined the fluorophores in the interior or surface of the CDs, and the Crosslink Enhanced Emission Effect are the currently confirmed PL mechanisms.

Synthesizing Luminescent Carbon from Condensed Tobacco Smoke: Bio-Waste for Possible Bioimaging

Used cigarette filters, a waste material and a major source of land pollution, has been used as a raw material to study the nature of condensed tobacco smoke (tar) using microscopy, optical, IR, photoluminescence and Raman spectroscopy as well as X-ray diffraction and electron & fluorescence microscopy. The tar present in the cigarette filter bud has been used to synthesize luminescent low dimensional carbon using a simple methanol extraction technique. The collected material shows light blue emission under UV excitation with emission peak energy depending strongly on the excitation wavelength. Such excitation energy dependent emission is observed from the extract solution as well as dried film. Careful analysis has been carried out to understand its origin which reveals the presence of giant red-edge effect in the samples. A correlation between room temperature photoluminescence spectroscopy and fluorescence microscopy has also been carried out. Presence of amorphous phase carbon has been established using Raman spectroscopy and a quantum yield of more than 9% has been estimated which is moderately high in comparison with the one shown by carbon dots prepared by using other sources and can be used for bioimaging applications.

Nitrogen-Doped Graphene-Based Sensor for Electrochemical Detection of Piroxicam, a NSAID Drug for COVID-19 Patients

Nitrogen-doped graphene (NGr) was synthesized by the hydrothermal method using urea as a reducing and doping agent for graphene oxide (GO). The crystalline structure of GO was revealed by the XRD intense peak recorded at 2θ = 11.4°, indicating that the interlayer distance within the structure was large (d = 0.77 nm), and the number of layers (n) was 9. Further, the transformation of GO in NGr also led to the decrease in the interlayer distance and number of layers (d = 0.387 nm; n = 3). As indicated by elemental analysis, the concentration of nitrogen in the NGr sample was 6 wt%. Next, the comparison between the performance of bare GC and the graphene-modified electrode (NGr/GC) towards piroxicam (PIR) detection was studied. Significant differences were observed between the two electrodes. Hence, in the case of bare GC, the oxidation signal of PIR was very broad and appeared at a high potential (+0.7 V). In contrast, the signal recorded with the NGr/GC electrode was significantly higher (four times) and shifted towards lower potentials (+0.54 V), proving the electro-catalytic effect of nitrogen-doped graphene. The NGr/GC electrode was also tested for its ability to detect piroxicam in pharmaceutical drugs (Flamexin), giving excellent recoveries.

Subpicosecond Hot Hole Transfer in a Graphene Quantum Dot Composite with High Efficiency

Extraction of hot carriers is of prime importance because of its potential to overcome the energy loss that limits the efficiency of an optoelectronic device. Employing a femtosecond upconversion setup, herein we report a few picoseconds carrier cooling time of colloidal graphene quantum dots (GQDs) is at least an order of magnitude slower compared to that in its bulk form. A slower carrier cooling time of GQDs compared to that of the other semiconductor quantum dots and their bulk materials is indeed a coveted property of GQDs that would allow one easy harvesting of high energy species employing a suitable molecular system as shown in this study. A subpicosecond hot hole transfer time scale has been achieved in a GQD-molecular system composite with high transfer efficiency. Our finding suggests a dramatic enhancement of the efficiency of GQD based optoelectronic devices can possibly be a reality.

Fluorescence Enhancement of Lignin-Based Carbon Quantum Dots by Concentration-Dependent and Electron-Donating Substituent Synergy and Their Cell Imaging Applications

Black liquor is an important pollutant in the pulp industry, but it also has the potential for high-value utilization. In this study, lignin extracted from black liquor was hydrothermally prepared into lignin-based carbon quantum dots (L-CQDs) using a one-pot method. Physicochemical characterization suggested that the L-CQDs exhibited a lamellar core-shell multilayered graphene structure surrounded by oxygen-containing functional groups. The fluorescence intensity of the L-CQDs was strengthened depending on their own concentration dependence and the doping of external groups. The fluorescence intensity of L-CQDs varied between 89.09 and 183.66 under different concentrations, and the most intense fluorescence (183.66) was obtained at 0.1 mg mL^-1. At hydroxyl and amino adsorption capacities of 11.08 and 0.98 mmol g^-1, the hydroxylated RL-CQDs-5 and aminated NL-CQDs-3 exhibited the highest fluorescence intensities at 689.22 and 605.39, respectively. Moreover, when pristine L-CQDs were sequentially aminated and hydroxylated, the NRL-CQDs' fluorescence intensity reached 1224.92. Cell imaging experiments proved that cells cultivated with NRL-CQDs have brighter fluorescence compared with L-CQDs. The results will render L-CQDs more suitable for practical applications.

Development of an Efficient Immunosensing Platform by Exploring Single-Walled Carbon Nanohorns (SWCNHs) and Nitrogen Doped Graphene Quantum Dot (N-GQD) Nanocomposite for Early Detection of Cancer Biomarker

In this work, a novel electrochemical immunosensor based on nitrogen doped graphene quantum dot (N-GQD) and single-walled carbon nanohorns (SWCNHs) was developed for the detection of α-fetoprotein (AFP), a cancer biomarker. Thus, to fabricate the platform of the immunosensor, nanocomposite architecture was developed by decorating N-GQD on the surface of the SWCNHs. The resulting hybrid architecture (N-GQD@SWCNHs) functioned as an exceptional base for the immobilization of antibody (Anti-AFP) through carbodiimide reaction with good stability and bioactivity. The immunosensor was prepared by evenly distributing the bioconjugates (N-GQD@SWCNHs/Anti-AFP) dispersion on the surface of the glassy carbon electrode, and subsequently blocking the remaining active sites by bovine serum albumin to prevent the nonspecific adsorption. Cyclic voltammetry and electrochemical impedance spectroscopy technique was employed to investigate the assembly process of the immunosensor. Under optimal conditions, the immunosensor exhibited a broad dynamic range in between 0.001 ng/mL to 200 ng/mL and a low detection limit of 0.25 pg/mL. Furthermore, the sensor showed high selectivity, desirable stability, and reproducibility. Measurements of AFP in human serum gave outstanding recovery within 99.2% and 102.1%. Thus, this investigation and the amplification strategy exhibited a potential role of the developed nanocomposite based sensor for early clinical screening of cancer biomarkers.

Surface modified and functionalized graphene oxide membranes for separation of strontium from aqueous solutions

Graphene oxide-strontium (GO-Sr) composites prepared under different ambient conditions were characterized using morphological and spectroscopic techniques to optimize the uptake of Sr from aqueous solutions. These studies indicated that interactions among GO and Sr²⁺ ions are highly sensitive to size and aging of GO sheets, as well as pH of the ambience. Further, the extent of Sr uptake on GO sheets was found to be largely influenced by relative fractions of the associated -COOH, -OH, C-O-C functional groups and sp²-C domains. Membranes prepared using various forms of GO were evaluated for their Sr separation ability and, a window of parameters for optimum separation of Sr has been proposed. Among the variety of membranes studied, those made up of fresh and large GO sheets were found to exhibit superior Sr adsorption capacity (~296 mg/g) at limited GO mass. Further, adsorption efficiency of these GO membranes was observed to deteriorate with aging of GO sheets and rise of GO mass on membrane. The membrane based filtration procedure introduced in present work facilitates to provide a lamellar structure of GO sheets with abundant surface area, diverse and accessible sites for Sr²⁺ ion uptake and offer high Sr adsorption efficiencies.

A two-dimensional calcium (II) coordination polymer constructed from 2,2'-[terephthaloylbis(azanediyl)]diacetate: synthesis, structure and properties

A new two-dimensional (2D) coordination polymer, namely, poly[[diaqua-[μ₄-2,2'-[terephthaloylbis(azanediyl)]diacetato]calcium(II)] monohydrate], {[Ca(C₁₂H₁₀N₂O₆)(H₂O)₂]·H₂O}_n, (I), has been synthesized by the reaction of CaCl₂ with 2,2'-[terephthaloylbis(azanediyl)]diacetic acid (H₂L). The title compound was structurally characterized by single-crystal X-ray diffraction analysis, elemental analysis and IR spectroscopy. In the crystal structure of (I), each Ca^II cation binds to six carboxylate groups from four symmetry-related L^2- dianions. The hexadentate L^2- ligand links four symmetry-related calcium cations into a 2D layer-like structure, which can be simplified as a uninodal SP 2-periodic (3,6)III net with the point symbol (4³·6³). In the lattice, all layers pack in parallel arrays through weak interlayer hydrogen bonding and π-π interactions. The thermal stability and photoluminescence properties of (I) have been investigated. Thermogravimetric analysis reveals the different thermal stabilities of the two coordinated water molecules due to their different hydrogen-bonding interactions. The title coordination polymer exhibits an excitation-wavelength-dependent fluorescence in the solid state.

Excitation dependence and independence of photoluminescence in carbon dots and graphene quantum dots: insights into the mechanism of emission

Excitation-dependent, multicolor emission from different varieties of 0D carbon systems has attracted immense research attention. It is generally accepted that some variants of 0D carbon exhibit excitation dependent emission, while other variants do not. A third variant exhibits both excitation dependent as well as excitation independent emission. In this work we investigate the structure, composition, steady-state emission-excitation and photoluminescence decay dynamics of three distinctly different variants of 0D carbon - amorphous carbon dots (aCDs), graphene quantum dots (GQDs) and nitrogen-doped GQDs (NGQDs). We find that despite significant differences in the structure and composition there is a striking similarity in the excitation energy dependence of the emission characteristics of these three different dots. All of them exhibit excitation energy independent emission below some threshold wavelength (λ_th), and above this threshold the emission becomes excitation dependent. We also demonstrate that a similar trend is apparent for nearly all variants of 0D carbon reported in the literature. The threshold wavelength correlates well with the excitation wavelength for the most intense emission and the photoluminescence excitation peaks, suggesting a common origin of light emission in these carbon dots. The findings provide important clues for developing a unified general picture for understanding the light emission mechanism in 0D carbon nanostructures.

Photodynamic Inactivation of E. coli Bacteria via Carbon Nanodots

The increasing development of antibiotic resistance in bacteria has been a major problem for years, both in human and veterinary medicine. Prophylactic measures, such as the use of vaccines, are of great importance in reducing the use of antibiotics in livestock. These vaccines are mainly produced based on formaldehyde inactivation. However, the latter damages the recognition elements of the bacterial proteins and thus could reduce the immune response in the animal. An alternative inactivation method developed in this work is based on gentle photodynamic inactivation using carbon nanodots (CNDs) at excitation wavelengths λex > 290 nm. The photodynamic inactivation was characterized on the nonvirulent laboratory strain Escherichia coli K12 using synthesized CNDs. For a gentle inactivation, the CNDs must be absorbed into the cytoplasm of the E. coli cell. Thus, the inactivation through photoinduced formation of reactive oxygen species only takes place inside the bacterium, which means that the outer membrane is neither damaged nor altered. The loading of the CNDs into E. coli was examined using fluorescence microscopy. Complete loading of the bacterial cells could be achieved in less than 10 min. These studies revealed a reversible uptake process allowing the recovery and reuse of the CNDs after irradiation and before the administration of the vaccine. The success of photodynamic inactivation was verified by viability assays on agar. In a homemade flow photoreactor, the fastest successful irradiation of the bacteria could be carried out in 34 s. Therefore, the photodynamic inactivation based on CNDs is very effective. The membrane integrity of the bacteria after irradiation was verified by slide agglutination and atomic force microscopy. The method developed for the laboratory strain E. coli K12 could then be successfully applied to the important avian pathogens Bordetella avium and Ornithobacterium rhinotracheale to aid the development of novel vaccines.

Graphene Quantum Dots-Ornamented Waterborne Epoxy-Based Fluorescent Adhesive via Reversible Addition-Fragmentation Chain Transfer-Mediated Miniemulsion Polymerization: A Potential Material for Art Conservation

Epoxy-based adhesives have gotten significant attention in the conservation of antiquities and repair or reconstruction of artifacts due to their excellent adhesion strength. However, it has become hard to detect repaired work in artifacts due to the transparent nature of epoxy-based adhesives. Hence, the making of fluorescent adhesives has become an exciting topic for art conservators. Here, we have synthesized a new kind of waterborne epoxy-based fluorescent adhesive decorated with graphene quantum dots (GQDs) via reversible addition-fragmentation chain transfer (RAFT)-mediated surfactant-free miniemulsion polymerization. In this case, a new block copolymer (BCP), poly(1-vinyl-2-pyrrolidone)-block-poly(glycidyl methacrylate), has been synthesized via surfactant-free RAFT-mediated miniemulsion polymerization using a polymerization-induced self-assembly technique. The GQDs were prepared from citric acid by a hydrothermal process, and this was used for making a fluorescence-active BCP/GQD nanocomposite emulsion. The obtained BCP/GQD nanocomposite adhesive was transparent and showed blue fluorescence under ultraviolet-visible light, indicating the easy detection of its mark on the artifacts. The BCP and BCP/GQD emulsions were applied to adhere ceramic and glass substrates, and their adhesion strength was evaluated by lap shear tests. The BCP/GQDs showed better adhesion strength than the BCP only, indicating better adhesive performance. Additionally, the synthesis process was carried out in aqueous media, indicating the sustainability and environment-friendliness of the process. We believe that this kind of new waterborne epoxy-based fluorescent adhesive will provide a new contrivance among art conservators to repair or reconstruct artifacts.

Ultrafast Energy Transfer Determines the Formation of Fluorescence in DOM and Humic Substances

Humification is a ubiquitous natural process of biomass degradation that creates multicomponent systems of nonliving organic matter, including dissolved organic matter (DOM) and humic substances (HS) in water environments, soils, and organic rocks. Despite significant differences in molecular composition, the optical properties of DOM and HS are remarkably similar, and the reason for this remains largely unknown. Here, we employed fluorescence spectroscopy with (sub)picosecond resolution to elucidate the role of electronic interactions within DOM and HS. We revealed an ultrafast decay component with a characteristic decay lifetime of 0.5-1.5 ps and spectral diffusion originating from excitation energy transfer (EET) in the system. The rate of EET was positively correlated to the fraction of aromatic species and tightness of aromatic species packing. Diminishing the number of EET donor-acceptor pairs by reduction with NaBH₄ (decrease of the acceptor number), decrease of pH (decrease of the electron-donating ability), or decrease of the average particle size by filtration (less donor-acceptor pairs within a particle) resulted in a lower impact of the ultrafast component on fluorescence decay. Our results uncover the role of electronic coupling among fluorophores in the formation of DOM and HS optical properties and provide a framework for studying photophysical processes in heterogeneous systems of natural fluorophores.

Multicolor-Raman analysis of Korean paintworks: emission-like Raman collection efficiency

It has been reported that the scattering cross-sections of resonance Raman spectra strongly depend on the resonance between the laser's excitation energy and the electronic absorption band of pigments in solution. However, the actual collection of scattered photons is affected by diffuse scattering and self-absorption when studying painted colorants in artworks. Quantitative spectroscopic measurements are required to elucidate the apparent resonance Raman cross-sections in both solution and solid. In this study, we explored the excitation-dependent Raman scattering of natural and artificial Korean pigments painted on a wood block with six visible wavelengths. Our study shows that the Raman intensity profile agrees with the emission profile rather than with the absorption. We also assessed the validity of self-absorption and the outgoing resonance mechanism in the solid state for the results.

Self-assembled graphene-based microfibers with eclectic optical properties

The construction of graphene-based microfibers with reinforced mechanical and electrical properties has been the subject of numerous researches in recent years. However, the fabrication of graphene-based fibers with remarkable optical features still remains a challenge and has not been addressed so far. This paper aims to report a series of flexible self-assembled fibers, synthesized through a few-minute sonication of thermally oxidized graphene oxide nanosheets, so-called Nanoporous Over-Oxidized Graphene (NOG), in an acidic medium. These free-standing glassy fibers were classified into four distinct morphological structures and displayed a collection of intriguing optical properties comprising high transparency, strong birefringence, fixed body colorations (e.g. colorless, blue, green, and red), tunable interference marginal colorations, UV-visible-near IR fluorescence, and upconversion emissions. Moreover, they exhibited high chemical stability in strongly acidic, basic, and oxidizing media. The foregoing notable attributes introduce the NOG fiber as a promising candidate both for the construction of graphene-based photoluminescent textiles and the development of a wide variety of optical applications.

Graphene and its Derivatives-Based Optical Sensors

Being the first successfully prepared two-dimensional material, graphene has attracted extensive attention from researchers due to its excellent properties and extremely wide range of applications. In particular, graphene and its derivatives have displayed several ideal properties, including broadband light absorption, ability to quench fluorescence, excellent biocompatibility, and strong polarization-dependent effects, thus emerging as one of the most popular platforms for optical sensors. Graphene and its derivatives-based optical sensors have numerous advantages, such as high sensitivity, low-cost, fast response time, and small dimensions. In this review, recent developments in graphene and its derivatives-based optical sensors are summarized, covering aspects related to fluorescence, graphene-based substrates for surface-enhanced Raman scattering (SERS), optical fiber biological sensors, and other kinds of graphene-based optical sensors. Various sensing applications, such as single-cell detection, cancer diagnosis, protein, and DNA sensing, are introduced and discussed systematically. Finally, a summary and roadmap of current and future trends are presented in order to provide a prospect for the development of graphene and its derivatives-based optical sensors.

Aggregation and stability of sulfate-modified polystyrene nanoplastics in synthetic and natural waters

Nanoplastics (NPs) are becoming emerging pollutants of global concern. Understanding the environmental behavior of NPs is crucial for their environmental and human risk assessment. In this study, the aggregation and stability of polystyrene (PS) NPs were investigated under different hydrochemical conditions such as pH, salt type (NaCl, CaCl₂, Na₂SO₄), ionic strength (IS), and natural organic matter (NOM). The critical coagulation concentrations of PS NPs were determined to be 158.7 mM NaCl, 12.2 mM CaCl₂, and 80.0 mM Na₂SO₄. Ca²⁺ was more effective in destabilizing PS NPs, compared to Na⁺, owing to its stronger charge screening effect. In the presence of monovalent ions, NOM reduced aggregation through steric repulsion, whereas in the case of divalent ions, NOM induced aggregation through cation bridging. Initial and long-term stability studies demonstrated that, in waters with high IS and NOM content, NOM was the most significant factor affecting NPs aggregation. PS NPs would be highly suspended in all freshwaters, and even in wastewater, whereas they would aggregate rapidly and deposit in seawater. Finally, a statistical model was established to evaluate the hydrodynamic diameter of NPs in different waters. The results indicated the stability of PS NPs in natural aquatic environments and their potential for long-term transport.

Molecular Radiative Energy Shifts under Strong Oscillating Fields

Coherent manipulation of light-matter interactions is pivotal to the advancement of nanophotonics. Conventionally, the non-resonant optical Stark effect is harnessed for band engineering by intense laser pumping. However, this method is hindered by the transient Stark shifts and the high-energy laser pumping which, by itself, is precluded as a nanoscale optical source due to light diffraction. As an analog of photons in a laser, surface plasmons are uniquely positioned to coherently interact with matter through near-field coupling, thereby, providing a potential source of electric fields. Herein, the first demonstration of plasmonic Stark effect is reported and attributed to a newly uncovered energy-bending mechanism. As a complementary approach to the optical Stark effect, it is envisioned that the plasmonic Stark effect will advance fundamental understanding of coherent light-matter interactions and will also provide new opportunities for advanced optoelectronic tools, such as ultrafast all-optical switches and biological nanoprobes at lower light power levels.

Theoretical study on the sensing mechanism of chalcone-based fluorescence probe for detecting hydrogen sulfide and biothiols

The single fluorescence phenomenon of Comp2 experimentally is explained by the Boltzmann distribution. Pr1 has three distorted dihedral angles under photo-excitation.