Unique Emission Research Articles

Grafting Carbon Dots on Persistent Luminescence Phosphors to Generate Remarkably Improved NIR Afterglow for Microenvironment Fluorescence Detection

AbstractRecently, combining long afterglow materials with organic fluorescent dyes, particularly carbon dots (CDs) to produce heterojunction and improve its luminescence and persistence properties became an important research direction. However, the precise role of these internal defects in the energy transfer process of CD@inorganic matrix composite fluorescent materials has not been thoroughly discussed. Establishing matching trap level to promote the energy transfer between the trap level and CDs level not only helps to enhance the afterglow performance, but also can explain the heterogeneous structure interaction between organic–inorganic fluorescent materials. Herein, ZLAGC@CDs luminescent composite is successfully synthesized via coating CDs on Zn1‐x(Li/Al)xGa2xO4:0.005Cr3+ (ZLAGC, x = 0–1), which exhibits a unique double emission at ≈430 nm (the defect luminescence of CDs) and 718 nm (the 2E→4A2 transition of Cr3+). After coating, the energy transfer from the defect level of CDs to the excited state of Cr3+ enhanced the NIR emission. The electron transfer between the defect level of CDs and the split deeper trap level of ZLAGC also improved the visible and near‐infrared (NIR) afterglow. The fluorescence and afterglow signals of ZLAGC@CDs are highly sensitive to solution pH under acidic conditions, indicating that the prepared fluorescent composite has potential application in acid microenvironment fluorescence detection.

Enhancing biodiesel stability and performance: synthesis and extraction of macauba biodiesel for sustainable engine applications

The demand for sustainable fuels has driven research on biodiesel blends’ combustion characteristics and emissions. The study evaluates the performance of macauba and soybean biodiesel blends by analyzing torque, power, and fuel consumption indicators. The effects of leaf extract additives on engine performance are also assessed. Comparing macauba and soybean blends show similar load, brake power, and engine speed trends on response variables. However, slight variations in coefficients and significance levels indicate unique combustion and emission profiles for each blend. Understanding these distinctions is crucial for optimizing engine performance and emission control strategies. Parameters analyzed include brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), exhaust gas temperature (EGT), carbon monoxide (CO) emissions, hydrocarbon (HC) emissions, oxides of nitrogen (NOx) emissions, smoke opacity, cylinder pressure, heat release rate, and ignition delay. Blends 80% Soy Methyl and 20% Macauba Methyl Biodiesel (BSM20) demonstrates 5–10% superior fuel efficiency, 8–12% higher energy conversion capability, 3–5% lower exhaust temperatures, 10–15% reduced emissions, and 5–8% enhanced efficiency versus other blends and Diesel. It also shows 10–20% lower hydrocarbon and CO emissions, 15–25% reduced NOx, 20–30% lower particulate matter, and more efficient energy release during combustion. Optimizing heat release rate and ignition delay is crucial; BSM20 shows a 10–15% shorter ignition delay. Understanding blend distinctions is key for optimizing performance and emissions. BSM20 blend demonstrates superior fuel efficiency, energy conversion capability, lower exhaust gas temperatures, reduced emissions, and enhanced engine efficiency compared to other blends and Diesel. It also shows lower hydrocarbon, CO, and NOx emissions, reduced particulate matter emissions, and more efficient energy release during combustion. Optimizing heat release rate and ignition delay is crucial for cleaner combustion and improved engine performance.

Understanding the AIE phenomenon of nonconjugated rhodamine derivatives via aggregation-induced molecular conformation change

The bottom-up molecular science research paradigm has greatly propelled the advancement of materials science. However, some organic molecules can exhibit markedly different properties upon aggregation. Understanding the emergence of these properties and structure-property relationship has become a new research hotspot. In this work, by taking the unique closed-form rhodamines-based aggregation-induced emission (AIE) system as model compounds, we investigated their luminescent properties and the underlying mechanism deeply from a top-down viewpoint. Interestingly, the closed-form rhodamine-based AIE system did not display the expected emission behavior under high-viscosity or low-temperature conditions. Alternatively, we finally found that the molecular conformation change upon aggregation induced intramolecular charge transfer emission and played a significant role for the AIE phenomenon of these closed-form rhodamine derivatives. The application of these closed-form rhodamine-based AIE probe in food spoilage detection was also explored.

Recent Advances in Optical Properties and Light‐Emitting Diode Applications for 2D Tin Halide Perovskites

AbstractLead halide perovskites are widely used and intensively studied in optoelectronic devices due to their superior properties. However, the toxicity of Pb hinders the industrialization of perovskite optoelectronic devices. Sn has a similar electronic structure to Pb, thus has been widely studied as an alternative to Pb‐based perovskite optoelectronics in recent years. In this review, the research progress in luminescent properties and synthesis methods of 2D tin halide perovskites are summarized. It is also highlight a unique dual emission phenomenon in 2D tin halide perovskites and summarize several types of possible luminous mechanisms. At last, the recent development of 2D tin halide perovskites based light‐emitting diodes are also overviewed, and the challenges of oxidative inhibition and efficiency improvement in 2D tin halide perovskites are discussed. This review is expected to provide a comprehensive perspective on luminescent properties and light‐emitting diode applications of 2D tin halide perovskites.

Atomic insights into the optoelectronic properties of vacancy-ordered double perovskite halide semiconductors

Vacancy-ordered halide perovskite Cs2BX6 semiconductors are attracting an increasing level of interest for optoelectronic applications due to their high chemical stability and unique light emission properties. Here, we performed first-principles calculations to determine the energy positions and atomic orbital hybridization features of band edge states in Cs2BX6 (B = Ge, Sn, Te, Ti, Zr, Hf; X = Cl, Br, I). Our results revealed that all the Cs2BX6 perovskites, except for Cs2TeX6, have direct bandgaps at the Γ point. The indirect bandgaps of Cs2TeX6 originate from the symmetry-forbidden Te p–X p coupling at the Γ point. Both energy positions and dispersions of the band edge states of Cs2BX6 can be well modulated by varying X- and B-site ions. Our work provides a comprehensive understanding of electronic structures and optoelectronic properties of Cs2BX6 perovskites, shedding light on the design rules for high-performance perovskite optoelectronics.

Chemical Ecology, Detection and Identification of Subterranean Termites Based on Electronic-Nose Volatile Emissions Analysis

The effective monitoring and identification of existing subterranean termite populations within coarse woody debris and infested wood in service depend on accurate detection. These insects are often concealed within logs, wooden support structures, walls, and floorboards of buildings. In the absence of external mud tubes, termite infestations normally must be discovered through the destructive exploration of wooden structures to reveal the physical presence of these insect pests. Subterranean termite species are difficult to identify due to similarities in morphological features, but they may be readily distinguished by differences in volatile emissions from which they are divided into chemotaxonomic groups. Consequently, a more effective and nondestructive approach for detection and identification is to take advantage of unique species-specific emissions of volatile organic compounds (VOCs) from termite bodies which easily pass through wooden structures, allowing for detection without physical damage to wood and avoiding expensive DNA analysis. Electronic aroma detection analyses were conducted with an Aromascan A32S electronic-nose (e-nose) instrument, fitted with a 32-sensor conducting polymer (CP) sensor array, for discrimination between four common subterranean termite species based on differences in volatile emissions. Principal component analysis (PCA) of whole-body volatiles effectively distinguished between four termite species with the first two principal components accounting for more than 98% of sample variance (p < 0.01). Unique electronic aroma signature patterns (smellprints) were produced from e-nose sensor array outputs that allowed for the effective identification of termite species based on distinct differences in volatile metabolites released from their bodies. The e-nose methods were determined to be an improved means for rapidly detecting and monitoring termite species in wood. The method is cheaper than conventional detection methods and allows for the timelier discovery of species-specific termite infestations necessary for better management. The e-nose capability of detecting the Formosan termite in indoor living spaces was particularly significant due to the production of naphthalene, a volatile hazardous gas causing many adverse human health effects in enclosed environments.

Substantial enhancement of optoelectronics and piezoelectric properties of novel hollow ZnO nanorods towards efficient flexible touch and bending sensor

The novel solid and hollow ZnO nanorods were prepared by chemical synthesis approach. The hollow ZnO NRs show a large optical band gap as compared to the solid ZnO NRs which is attributed to quantum confinement effect. The unique emission spectra of hollow ZnO NRs show an exceptional ability for visible emission as compared to solid ZnO NRs owing to unique hollow structure, which enhanced multiple scattering. The piezoelectric potential of hollow nanorod shows about 3.75 times higher peizopotential than the solid nanorods with length (a = 200 nm) and height (h = 1000 nm). The piezoelectric potential was found to be increased with the height of nanorod with a fixed length. Interestingly, the piezoelectric potential increases with decreasing wall thickness in hollow nanorod. The hollow ZnO NRs-based touch sensor shows five times higher piezoelectric response as compared to the solid ZnO NRs. These results provide valuable information for future studies aimed at improving the piezoelectric properties of hollow nanostructures for potential applications in energy harvesting and sensing.

Going green while getting lean: Decomposing carbon and green total factor productivity

While research on carbon productivity is growing rapidly, the role of structural change in green transition remains unexplored due to the scarcity of firm-level emission data. This study addresses this gap by utilizing unique register-based greenhouse gas emission data from Finland’s energy-intensive manufacturing firms for 2000–2019. Applying a structural change productivity decomposition, we break down the sector’s carbon productivity and green total factor productivity into four components: contributions from non-switching continuing firms, industry-switching continuing firms, the effects of entry and exit, and resource allocation. The findings highlight the important role of structural change in the sector’s productivity. Non-switching continuing firms emerged as the key drivers of both carbon and green total factor productivity growth. The contribution of entry and exit was negative during the financial crisis, while inefficient resource allocation significantly hindered productivity growth throughout the study period. These findings emphasize the importance of public subsidies targeted at environmentally efficient firms to enhance their competitiveness under challenging market conditions. Furthermore, the establishment of a stable yet positive carbon price would incentivize less-productive firms to adopt environmentally friendly technologies.

Significant enhancement of the photon upconversion of a single fluorescent microsphere via annular near-field localization

Fluorescent microspheres exhibit unique emissions at the microscale and have been widely used as probes for immunoassays and advanced micro-sensors.

Observation of Multi-Phonon Emission in Monolayer WS2 on Various Substrates.

Transition metal dichalcogenides (TMDs) have unique absorption and emission properties that stem from their large excitonic binding energies, reduced-dielectric screening, and strong spin-orbit coupling. However, the role of substrates, phonons, and material defects in the excitonic scattering processes remains elusive. In tungsten-based TMDs, it is known that the excitons formed from electrons in the lower-energy conduction bands are dark in nature, whereas low-energy emissions in the photoluminescence spectrum have been linked to the brightening of these transitions, either via defect scattering or via phonon scattering with first-order phonon replicas. Through temperature and incident-power-dependent studies of WS2 grown by CVD or exfoliated from high-purity bulk crystal on different substrates, we demonstrate that the strong exciton-phonon coupling yields brightening of dark transitions up to sixth-order phonon replicas. We discuss the critical role of defects in the brightening pathways of dark excitons and their phonon replicas, and we elucidate that these emissions are intrinsic to the material and independent of substrate, encapsulation, growth method, and transfer approach.

Capturing Doublet Intermediate Emitters by Chemically Crosslinking Confinement towards Spatiotemporal Encryption.

Photoluminescence is one of the most meticulous ways to manipulate light energy. Typical photoluminescent emitters are mostly stable substances with a pure photophysical process of spontaneous photon-emission from their excited states. Intermediate emitters are elusive attributing to their synchronous energy transfer process including photophysical and incomplete photochemical pathways. An intermediate emitter containing radicals is more difficult to be observed due to its inherent chemical reactivity. Here, these challenges are overcome by spontaneously formed space limitations in polymer crosslinking networks meanwhile chemically active intermediates are captured. These doublet intermediates exhibit unique long-wavelength emissions under chemically crosslinking confinement conditions, and their luminous mechanism provides a novel perspective for designing intermediate emitters with liquid-crystal character and photoresponsive features towards spatiotemporal encryption, promising for the detection of photochemical reactions and the development of fascinating luminescent systems.

Highly Efficient Stable Luminescent Radical-Based X-ray Scintillator.

Stable luminescent radicals are open-shell emitters with unique doublet emission characteristics. This feature makes stable luminescent radicals exhibit widespread application prospects in constructing optical, electrical, and magnetic materials. In this work, a stable luminescent radical-based X-ray scintillator of AuPP-1.0 was prepared, which exhibited a high X-ray excited luminescence (XEL) efficiency as well as excellent stability. A mechanism study showed that the heavy atom of Au in AuPP-1.0 endowed it with effective absorption of X-rays, and the doublet emission characteristics of AuPP-1.0 significantly increased its exciton utilization rate in the radioluminescence process. Moreover, AuPP-1.0 has good processability to fabricate a flexible screen for high-quality X-ray imaging, whose resolution can reach 20 LP mm-1. This work demonstrates that the doublet emission is beneficial for improving the exciton utilization rate of radioluminescence, providing a brand-new strategy for the construction of high-performance X-ray scintillators.

Broadband near-infrared emission in Bi-Er co-doped germanosilicate glasses

Broadband gain materials have garnered considerable attention on account of their practical utilization in optical amplifiers. Among them, Bi-doped glasses depict tremendous potential due to their unique broadband emission. In this paper, we report a series of Bi-Er co-doped germanosilicate glasses exhibiting broadband and tunable near-infrared (NIR) emission. By the strategy of Bi-Er co-doping, the luminescence bandwidth is effectively expanded in two ways: co-excitation and energy transfer between two active centers. Importantly, broadband luminescence covering O-E-S-C-L bands with full width at half maximum (FWHM) more than 320 nm is realized via the way of energy transfer. In addition, ultrabroadband emission covering C-L-U bands with FWHM of ∼370 nm and relatively flat emission of ∼170 nm is achieved via the way of co-excitation. Furthermore, the mechanism of energy transfer is discussed. These results indicate that Bi-Er co-doped germanosilicate glasses are the promising candidates in the field of optical fiber amplifiers.

Reblooming of the cis-Bis(2-phenylpyridine) Platinum(II) Complex: Synthesis Updating, Aggregation-Induced Emission, Electroluminescence, and Cell Imaging.

Studies on the syntheses, photophysical properties, and applications of cis-bis(2-phenylpyridine) platinum(II) complex (Pt(ppy)2) family are of great importance, but very limited progress has been achieved to date. Herein, a one-pot method was established for the syntheses of Pt(ppy)2-type complexes Pt-ppy and Pt-tBu. These two compounds were nonemissive in dilute solutions. However, they produced intense red and deep-red phosphorescence in the aggregation and film states, with lifetimes and quantum yields up to 1.92 μs and 70%, respectively, exhibiting unique aggregation-induced emission (AIE) characteristics. According to the experimental and theoretical studies, molecular configuration transformation (MCT) in the excited state may occur because of the d-d transition from the Pt center, causing nonradiative transitions in the solution. Nevertheless, the MCT would be largely restricted by the intermolecular interactions or rigid matrix, thereby enabling efficient phosphorescence in the aggregation state and in the PMMA films. Consequently, the AIE characteristics of Pt-ppy and Pt-tBu probably result from the restriction of molecular configuration transformation (RMCT). Due to the π-π and/or weak Pt-Pt interactions and the concentration-dependent emission characteristics, they emit deep-red and NIR emissions generated by excimer and/or MMLCT emitting species. Inspired by their AIE features, electroluminescence and cell imaging applications are explored. To the best of our knowledge, this is the first comprehensive study on the synthesis optimization, photophysical properties, AIE characteristics, and applications of the Pt(ppy)2-type complexes, which may rebloom the research studies on this type of Pt(II) complex family and provide valuable insights on the development of phosphorescent AIE metal-organic complexes.

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.

Covalent organic framework enhanced aggregation-induced emission of berberine and the application for detection

In this work, we prepared TaTp-COF, a covalent organic framework material with porous and uniform spheres, by hydrothermally reacting 1,3,5-tris (4-aminophenyl) benzene (TaPb) with terephthalaldehyde (TpTa). TaTp-COF could significantly enhance the aggregation-induced emission (AIE) of berberine (BBR), a natural plant medicine, which was related to the porous structure, the suitable voids, and the hydrogen bonding between TaTp-COF and BBR that could limit the free movement of BBR. The unique emission properties of BBR on TaTp-COF were investigated and used for the sensitive detection of BBR based on the fluorescence intensity of AIE, with a linear range of 10–100 μ mol/L (R2 = 0.9991) and a detection limit of 0.0453 μ;mol/L. Finally, the TaTp-COF was successfully applied to the detection of BBR in real samples, achieving good recoveries and satisfactory relative standard deviations.

Evaluating provincial carbon emission characteristics under China’s carbon peaking and carbon neutrality goals

This study defines Provincial Carbon Emission Characteristics (PCEC) as the socioeconomic conditions influencing provincial carbon emissions, the potential for carbon neutrality, and carbon management strategies. Given China’s commitment to peak carbon emissions and to achieve carbon neutrality, the development of a robust and versatile PCEC evaluation system is imperative. However, previous studies that rely on single-objective evaluation models are limited. To address this gap, we propose a multi-objective PCEC evaluation system using a novel three-layer approach. This approach enhances the scientific rigor, comprehensiveness, and comparability of PCEC evaluation indicators (PCEC-EIs) by segregating the extraction process into three layers: (1) a factor layer, which identifies critical socioeconomic conditions; (2) a quantitative layer, which selects optimal quantitative indicators for each identified condition; and (3) a standardized layer, which standardizes these indicators, thereby improving their comparability. By applying hierarchical cluster analysis, our study classified 30 Chinese provinces into 7 distinct clusters, each with unique carbon emission characteristics. Further investigation of these clusters across various climate governance issues revealed the versatility of our multi-objective PCEC evaluation system. Our system supports the identification of provinces qualified to reach the emission peak earlier than 2030, differentiation of carbon intensity reduction efforts during the carbon peaking stage, and exploration of various emission reduction pathways to achieve carbon neutrality. Hence, our findings can guide the creation of bespoke emission-reduction strategies for each province; thus, aiding China’s national ambition to achieve peak carbon emissions and carbon neutrality. Importantly, our three-layered approach has broader implications beyond China, potentially assisting other regions or countries in grappling with similar climate-mitigation challenges.

Effect of TiO2/ZnO nanofillers on structural, optical and nonlinear optical properties of PVA

Polyvinyl alcohol (PVA)/(x)Titanium dioxide (TiO2) (15-x) Zinc oxide (ZnO) nanocomposites for x = 0, 1, 5, 7.5, 10, 14 and 15 wt% concentration was prepared using solution casting method with the help of an ultrasonicator. The XRD spectra of films validate the formation of nanocomposites, as evidenced by the presence of peaks corresponding to both PVA and TiO2/ZnO nanoparticles. FTIR spectroscopy reveals the formulation of complexes between the PVA main chain and nano fillers. The homogeneous distribution of nano fillers in PVA nanocomposites was observed using SEM and EDAX. The optical studies conducted using an ultraviolet–visible spectrometer reveals that PVA/(x)TiO2(15-x) ZnO shows minimum energy gap of 2.66 eV at x = 15 wt%. The photoluminescence measurements carried out at an excitation wavelength of 370 nm using spectrophotometer exhibits unique strong emission band at 680 nm in the visible region for all the films. The open aperture (OA) Z-scan traces of PVA filled TiO2–ZnO nanocomposites at various filling levels were explored by means of Z-scan technique with DPSS continuous wave laser at 532 nm wavelength and 200 mW output power reveals that the absorption coefficient (β) of PVA nanofilms rises from 3.19 × 10−5 cm/W (for pure) to 1.17 × 10−3 cm/W (for x = 14 wt %) with rise in filling level. The closed-aperture (CA) z-scan analysis gives the nature of third order nonlinear refractive index (NRI) (n2) of PVA nanofilms. The value of nonlinear refractive index (NRI) increases from −1.57 × 10−9cm2/W (pure PVA) to −3.24 × 10−8 cm2/W for x = 14 wt% filling level. The observed enhancement in Nonlinear absorption (NLA) coefficient (β), NRI (n2) and third order nonlinear susceptibility (χ3) of prepared nanocomposites is due to added nanofillers to the PVA matrix. The improved third order nonlinear optical properties make these PVA nanocomposites as good candidates for optical switching device and optoelectronic device applications.

Plants' emission behaviors under dual control of pollutant concentration and quantity

Quantity-based and concentration-based limits are two common environmental permitting approaches utilized by government worldwide in environmental management. While existing literature is still unambiguous about roles played by quantity-based versus concentration-based limits in environmental management, it becomes evident that relying exclusively on concentration-based or quantity-based limits to control plant emissions may not necessarily result in improved environmental quality. This paper leverages a unique opportunity arising from a recent reform in China's Pollutant Emission Permit System (PEPS) initiated in 2016 to analyze how the introduction of quantity-based limits in addition to concentration-based limits through the PEPS reform impact emissions at the plant level. Utilizing a unique plant-level continuous emission monitoring system data collected from Shaanxi Province (located in western China), the paper finds a significant reduction in air pollutant emissions as a result of the PEPS reform (nitrogen oxides (NOx) by 39%, sulfur dioxide (SO2) by 15% and particulate matter (PM) by 13%). The heterogeneity analyses show emission reductions in plants differ across those with varying quantity limits specified in their permits, distinct emission ratios and diverse ownership structures. Furthermore, plants that fall under the classified management system with more stringent regulations imposed, especially those operating in high-pollution sectors, situated within industrial parks, or classified as large-sized plants, attain higher pollutant quantity limits. Findings of the paper carry important implications for effective environmental management, particularly within developing countries, and shed some light on carbon emission reduction policies in China.

Quantitative attribution framework for urban air pollutant: Investigating policy impact on NO2 emissions of megacities in China and Japan

This comparison study deciphered the intricate dynamics of policy impacts on NO2 air pollution emissions across five populous megacities – Tokyo and Osaka in Japan, Shanghai, Beijing, and Tianjin in China. Utilizing spatiotemporal mapping and time series analysis, we traced pollution trends from 2015 to 2022, underlining the profound influence of rapidly enacted policy measures on these densely populated urban areas. Leveraging daily policy data coupled with NO2 emission records, we developed a quantitative attribution framework to measure policy impacts. The results showed that 'School Closure' emerged as a dominant factor in four out of five cities. Besides, 'International Travel Controls' played a pivotal role in coastal megacities like Tokyo, Osaka, and Tianjin, revealing their unique emission characteristics. The insights demonstrated the essential need for targeted, city-specific policy interventions, cautioning against the over-simplified approach of one-size-fits-all strategies.