Luminescence Mechanism Research Articles

Emission Tuning of Nonconventional Luminescent Materials via Cluster Engineering.

Nonconventional Luminescent Materials (NLMs) with distinctive optical properties are garnering significant attention. A key challenge in their practical application lies in precisely controlling their emission behavior, particularly achieving excitation wavelength-independent emission, which is paramount for accurate chemical sensing. In this study, NLMs (Y1, Y2, Y3, and Y4) are synthesized via a click reaction, and it is found that excitation wavelength-dependent emission correlates with molecular cluster formation. Rigid NLMs (Y1, Y2) exhibit excitation-independent emission in dilute solutions with nanoscale clusters but become excitation-dependent at higher concentrations due to larger cluster formation. Flexible NLMs (Y3 and Y4) always show excitation-dependent emission, indicating a tendency for larger cluster formation. While these NLMs exhibit high photoluminescence quantum yields (PLQYs) in dilute solutions (0.1 mgmL-1) up to 38.0%, they suffer from significant aggregation-caused quenching (ACQ) in the solid state (as low as 0.5%). These findings provide insights into NLM luminescence mechanisms and offer a new approach for tuning their optical properties. With excellent optical properties, facile synthesis, and biocompatibility, these NLMs hold promise for bioimaging and other applications.

Trap‐induced persistent luminescence in organic light‐emitting diodes

AbstractLuminescence in organics that lasts for seconds to a few hours after light excitation has been reported recently, showcasing significant application potentials in flexible electronics and bioimaging. In contrast, long‐lasting luminescence that can be electrically excited, whether in organics or inorganics, is much rarer and often less efficient. In this study, we report persistent luminescence (PersL) in organic light‐emitting diodes (OLEDs) that lasts over 100 s and an energy storage effect beyond 60 min after charging with a direct‐current electric field. Thermoluminescence studies reveal that the PersL in OLEDs is induced by traps formed in a host‐guest molecular system serving as an emission layer (EML) with a trap depth of approximately 0.24 eV, consistent with the results from the same EML materials under light irradiation. Integrating results from electronic spin resonance, and density functional theory calculations, we propose a model delineating the charge carrier migration responsible for the trap‐induced PersL in OLEDs. This study on trap‐induced PersL in OLEDs may deepen our understanding of the luminescence mechanism in organic semiconductors and pave the way for expanding their applications in optoelectronics, energy storage and biological detection technologies.image

Comparative Study of Gemological and Spectroscopic Features and Coloration Mechanism of Three Types of Spodumene

Spodumene is a characteristic mineral in lithium-rich granitic pegmatites, serving both as a valuable mineral resource and an important gem material. This study incorporates three different color varieties of spodumene—pink to violet, yellow-green, and colorless—into a unified research framework. X-ray powder diffraction (XRD), electron probe microanalyzer (EPMA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), and photoluminescence spectroscopy (PL) were employed to systematically analyze the chemical composition, crystal structure, and spectroscopic properties of spodumene. Furthermore, the coloration mechanism and fluorescence emission of the different color samples were investigated and analyzed. The results indicate that the presence and mixed valence states of the transition metals Fe and Mn primarily influence the color and photoluminescence of the three types of spodumene. Mn3+ is the primary color-causing element in pink to violet spodumene, while Fe3+ is the primary color-causing element in yellow-green spodumene. Photoluminescence in all three color varieties is dominated by Mn2+. These findings contribute to a deeper understanding of the color and luminescence mechanisms of spodumene, expanding its potential applications as both a gem material and a luminescent material.

Ingeniously regulating the conformational equilibrium and ESPT mechanism of HBT-DPI by solvent environment: A novel perspective.

HBT-DPI was a single-molecule multi-conformational fluorescent material and had unique applications for hydrophobic/hydrophilic mapping on large-scale heterogeneous surfaces. In this paper, the different proton transfer processes and luminescence mechanisms of HBT-DPI in Dichloromethane (DCM, no hydrogen bond (HB) receptor) and N, N-Dimethylformamide (DMF, HB receptor) solvents were systematically studied. Using the quantum chemistry method, the stable structures of HBT-DPI in two solvents were determined based on the Boltzmann distribution. The analysis related to HBs parameters and charge distribution confirmed the HBs strength variation and ICT properties of HBT-DPI after photoexcitation. We confirmed that HBT-DPI underwent the stepwise (A→B→C) excited state double proton transfer (ESDPT) process in DCM. Whereas, HBT-DPI underwent the excited state intramolecular proton transfer (ESIPT) process in DMF, with the weakened intramolecular hydrogen bond (IAHB) after photoexcitation. By simulating the fluorescence spectra in the two solvents, we attributed the fluorescence in the experiment of DCM to the S1 state radiation. In DMF, the fluorescence of the S1 and PT states jointly contributed to the fluorescence band at 500nm observed in the experiment. Furthermore, the hole-electron analysis indicated that the fundamental reason for fluorescence quenching of HBT-DPI in DCM was the charge decoupling effect. Our work provided a comprehensive and systematic explanation of the different proton transfer mechanism and luminescence characteristic for HBT-DPI in two kinds of solvents. On this basis, we furnished the theoretical guidance and reference for its application in hydrophobic/hydrophilic monitoring and measurement.

Nonconventional Full-Color Luminescent Polyurethanes: Luminescence Mechanism at the Molecular Orbital Level.

The study of structure-activity relationships is a top priority in the development of nontraditional luminescent materials. In this work, nonconjugated polyurethanes (PUs) with full-color emission (red, green, and blue) are easily obtained by control of the diol monomer structure and the polymerization conditions. Selected diol monomers introduced single, double, or triple bond repeating units into the main chain of the PUs, in order to understand how unsaturated bonds and H-bonds affect their luminescence from a molecular orbital viewpoint. Detailed experimental and theoretical results show that the PUs have different temperature-dependent behaviors related to the interplay of H-bonding, through-space n-π interactions, and aggregation properties. The potential applications of PUs in colorful displays, covert information transmission, and multifunctional bioimaging have been verified. This work provides a new general protocol for the simple preparation of multifunctional nonconventional fluorescent polymers and deepens the understanding of their luminescence mechanisms.

Metal-organic framework-based hybrids with photon upconversion.

Upconversion materials (UCMs) featuring an anti-Stokes type emission establish them as an important category of photoluminescent materials. Metal-organic frameworks (MOFs) are rapidly gaining prominence as a class of versatile materials with favourable physical and chemical properties, including high porosity, controllable pore size, flexible design, and diverse functional sites. To endow MOFs with upconversion capability and improve the properties and performance of UCMs, the hybrids integrating UCMs and MOFs are proven to be successful. This review focuses on the research advancements of upconverting MOF-based hybrids, encompassing classifications, luminescence mechanisms, designs, properties, and applications in energy, catalysis, and biomedical fields. The analyses on the functions of upconversion and MOFs, as well as the advantages and disadvantages of various upconverting MOF-based hybrids, are included. Future research directions spanning from properties and performance to applications are explored. This review will be valuable in highlighting the research accomplishments, inspiring more ideas, facilitating deeper investigations in diverse avenues, and further advancing the research field.

Advances in the syntheses, mechanisms and applications of room-temperature phosphorescent carbon dots

In this review, the structure and luminescence mechanisms of RTP-CDs are clearly demonstrated. Based on the potential strategies to optimize their luminescence performance, the applications and future perspectives of RTP-CD systems are presented.

A linearly polarized AC-driven perovskite light emitting device with nanoscale metal contact.

Electroluminescent (EL) devices consisting of a single metal-semiconductor contact and a gate effect structure have garnered significant attention in the field of perovskite light-emitting devices. This interest is largely due to the thermal stability of the active layer and the simplicity of the device structure. However, the application of these devices in large-area light-emitting applications is hindered by the inherently low carrier mobility in perovskite materials. In our study, we addressed this limitation by optimizing the nanostructure within the electrodes, which resulted in enhanced electroluminescence and linear polarization. To confirm the luminescence mechanism and the observed enhancement, we conducted comprehensive electrical and optical characterization studies. These characterization studies demonstrated the effectiveness of our approach in improving the performance of perovskite-based EL devices, paving the way for their broader application in large-area light-emitting technologies.

Near-infrared downshifting luminescence of Ca2LaTaO6:Nd3+/Yb3+/K+ phosphors and their applications: solar cells and anti-counterfeiting.

A series of Nd3+/Yb3+ co-doped Ca2LaTaO6 (CLTO) phosphors are synthesized by a high temperature solid phase method. Structural characterization confirms the successful incorporation of Nd3+ and Yb3+ ions into the CLTO host lattice. The photoluminescence excitation (PLE) spectra and photoluminescence (PL) spectra of CLTO:Nd3+ and CLTO:Nd3+/Yb3+ are investigated in detail. Under the excitation of ultraviolet (UV) and visible (VIS) light, the CLTO:Nd3+/Yb3+ phosphor emits broadband near infrared (NIR) luminescence. In particular, the luminescence intensity of the Yb3+ ion is increased through an energy transfer (ET) process from Nd3+ to Yb3+. The luminescence mechanism of the CLTO:Nd3+/Yb3+ sample is analyzed based on the decay lifetime and PL spectra. In addition, the NIR emission intensity of Yb3+ ions is also enhanced by doping K+ ions. The broadband luminescence (850-1050 nm) of the CLTO:Nd3+/Yb3+/K+ phosphor has good application in solar cells and anti-counterfeiting.

Preparation and photoelectric properties of Si:B nanowires with thermal evaporation method.

We have successfully prepared a significant number of nanowires from non-toxic silicon sources. Compared to the SiO silicon source used in most other articles, our preparation method is much safer. It provides a simple and harmless new preparation method for the preparation of silicon nanowires. SiNWs (Silicon nanowires), as a novel type of nanomaterial, exhibit many outstanding properties, including the quantum confinement effect, quantum tunneling, Coulomb blocking effect, and exceptional electrical and optical properties. The study of SiNWs is therefore highly significant. In this paper, non-toxic SiO2 powder, Si powder, and B2O3 powder were utilized as raw materials to prepare SiNWs with diameters ranging from 30-60 nm and lengths from several hundred nanometers to tens of microns. The resulting SiNWs have a uniform morphology, smooth surfaces, and are produced in considerable yield. The morphology and structure of the SiNWs were characterized using XRD, SEM, HRTEM, SAED, EDS, and Raman spectroscopy. The results indicate that the prepared SiNWs are pure, uniform, and have a polycrystalline structure. The PL (photoluminescence) spectra show a pronounced UV emission peak at 346 nm, with the optimal excitation wavelength being 234 nm. Measurements with the Keithley 2601B demonstrate that the resistivity of the SiNWs is 4.292 × 108Ω·cm. Further studies reveal that the PL properties of SiNWs are influenced by their size and surface state. These findings have significant implications for understanding the luminescent mechanism of SiNWs and their potential applications in optoelectronics and biomedicine. This paper serves as a reference for the preparation and characterization of SiNWs, highlighting their PL properties and potential use in various applications, including biomedical imaging, sensors, and optoelectronic devices.

Low-potential bionic electrochemiluminescence sensing platform based on SnS2/CuNWs synergistic promotion for highly selective detection of glycocholic acid.

Glycholic acid (GCA) can dynamically reflect the process of liver injury, and can be used for early diagnosis and curative effect evaluation of early hepatitis and cirrhosis. The highly sensitive detection of liver injury markers is conducive to a more accurate and effective auxiliary diagnosis of liver diseases. In addition, the low trigger potential helps to avoid more chemical interference and improve the detection sensitivity. It is of great significance to develop a high sensitive and low potential ECL sensor for GCA detection. In this work, a low trigger potential molecularly imprinted electrochemiluminescence sensor (MIECLS) combining SnS2 and CuNWs was proposed for highly selective and sensitive detection of GCA, a marker of liver injury. The stabilization and enhancement of ECL signal can be attributed to the synergistic promotion strategy of SnS2 and CuNWs. CuNWs not only has good ECL performance, but also serves as a substrate material for loading SnS2 to enhance the film forming performance. In addition, the Sn4+ active site can be regenerated by redox reaction, significantly improving the efficiency of the co-reactant and the stability of the sensor. By studying the ECL luminescence mechanism and specific recognition quenching mechanism of MIECLS in detail, a selective detection method for GCA was established. Under optimal conditions, in the range of 5×10-10 to 5×10-6molL-1, the quenching value of ECL intensity is proportional to LgCGCA, and the limit of detection is 1.30×10-10molL-1. In addition, satisfactory recovery rate was obtained in human serum samples, showing good practical application, providing a new way for clinical detection of GCA. At the same time, it not only broadens the development of CuNWs in the ECL field, but also provides a new way to reduce the triggering potential.

Thermal Enhanced Near-Infrared Upconversion Luminescence in Y2Mo4O15:Yb/Nd with Uniaxial Negative Thermal Expansion.

Thermal quenching (TQ) of luminescence presents a significant barrier to the effective use of optical thermometers in high-temperature applications. Herein, we report a novel uniaxial negative thermal expansion (NTE) phosphor, Y2-2x-2yMo4O15:xYb,yNd, synthesized by a solid-state reaction. Under 980 nm laser excitation, it exhibits excellent thermally enhanced near-infrared (NIR) upconversion luminescence (UCL) performance. The UCL intensities of Nd3+ at 573 K were enhanced by 396-fold (750 nm), 57.6-fold (810 nm), and 7.6-fold (882 nm), respectively, compared with that of room temperature. In situ temperature-dependent X-ray diffraction and steady- and transient-state spectra are used to reveal thermal expansion behavior and luminescence mechanism in detail. The thermal enhancement of NIR UCL is attributed to the synergistic effect of increased radiative transition probability due to the anisotropic thermal expansion of the crystal and the enhanced energy transfer (ET) efficiency resulting from uniaxial shrinkage and the phonon-assisted process. Based on the luminescence intensity ratio (LIR) of the thermally coupled energy levels (4F7/2/4F3/2), the target sample achieved ultrahigh sensitivity (Sr = 3.0% K-1 at 298 K) with high repeatability over the entire temperature range. This study not only provides a fresh perspective for achieving thermal enhancement of NIR UCL phosphors using uniaxial negative thermal expansion materials but also presents a novel approach for developing NIR UCL optical thermometers with outstanding temperature performance.

Low-Dimensional Lead-Free Metal Halides for Efficient Electrically Driven Light-Emitting Diodes.

Electrically driven light-emitting diodes (ED LEDs) based on 3D metal halide perovskites have seen remarkable advancements during the past decade. However, the highest-performing devices are largely based on lead-containing 3D perovskites, presenting two key challenges-toxicity and stability-that must be addressed for commercialization. Reducing structural dimensionality and incorporating non-lead metals present promising pathways to address these issues. Although research on ED LEDs based on low-dimensional, lead-free metal halides (LD LFMHs) is growing, their performance still significantly lags behind that of 3D lead halide perovskites. This review seeks to deliver a comprehensive overview of ED LEDs based on LD LFMHs, covering a brief history of their development, methods for material synthesis, luminescence mechanisms, and applications in electroluminescent devices. It also examines current challenges and proposes practical strategies to enhance device performance, with the goal of inspiring further progress in the field.

Recent advances and design strategies for organic afterglow agents to enhance autofluorescence-free imaging performance.

Long-lasting afterglow luminescence imaging that detects photons slowly being released from chemical defects has emerged, eliminating the need for real-time photoexcitation and enabling autofluorescence-free in vivo imaging with high signal-to-background ratios (SBRs). Organic afterglow nano-systems are notable for their tunability and design versatility. However, challenges such as unsatisfactory afterglow intensity, short emission wavelengths, limited activatable strategies, and shallow tissue penetration depth hinder their widespread biomedical applications and clinical translation. Such contradiction between promising prospects and insufficient properties has spurred researchers' efforts to improve afterglow performance. In this review, we briefly outline the general composition and mechanisms of organic afterglow luminescence, with a focus on design strategies and an in-depth understanding of the structure-property relationship to advance afterglow luminescence imaging. Furthermore, pending issues and future perspectives are discussed.

Excited-State Engineering of Chalcogen-Bridged Chiral Molecules for Efficient OLEDs with Diverse Luminescence Mechanisms.

The exploration of circularly polarized luminescence is important for advancing display and lighting technologies. Herein, by utilizing isomeric molecular engineering, a novel series of chiral molecules are designed to exploit both thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) mechanisms for efficient luminescence. The cooperation of a small singlet-triplet energy gap, moderate spin-orbital coupling (SOC), and large oscillator strength enables efficient TADF emission, with photoluminescence quantum yields exceeding 90%. By altering the symmetry of molecular structures, it is demonstrated that the intrinsic electronic SOC and vibrational SOC effects can be greatly enhanced to facilitate RTP emission. Notably, through modulating simultaneous TADF and RTP emissions, single-molecule white emission is successfully achieved. Accordingly, the TADF-based organic light-emitting diode (OLED) achieves a maximum external quantum efficiency up to 30%, representing exceptional performance of non-aromatic amine-based emitters. Furthermore, the first single-molecule white OLED based on TADF and RTP dual-emissive chiral material is developed, establishing a benchmark for the development of advanced display and lighting technologies.

Recent Advances in Highly Luminescent Carbon Dots

AbstractHighly luminescent carbon dots (CDs) have garnered significant attention and are increasingly utilized in various fields. Despite its importance, there has been a lack of comprehensive reviews focusing specifically on highly luminescent CDs. It is aimed here to fill that gap by exploring CDs with high photoluminescence quantum yield (PLQY), starting with an examination of the luminescent mechanisms underlying highly luminescent CDs. The selection of synthetic raw materials and preparation methods along with the research progress are reviewed and the information on highly luminescent CDs across various luminescent bands is then statistically summarized in several tables. Subsequently, the structural features, synthesis methods, and purification strategies that lead to high PLQY in CDs are summarized based on analyzing collected examples of highly luminescent CDs. Furthermore, the highly luminescent‐based multifunctional applications of CDs in bioimaging, light‐emitting diodes, luminescent solar concentrators, and lasers are introduced. Finally, the current research landscape is evaluated, existing challenges are identified, and feasible directions are proposed for future development.

Enhancing reverse intersystem crossing process of thermally activated delayed fluorescence molecules with through-space charge transfer feature by acceptor engineering strategy

Developing efficient thermally activated delayed fluorescence (TADF) molecule with through-space charge transfer (TSCT) feature remains a great challenge, and theoretical investigation to reveal the inner luminescence mechanisms is highly desired. Herein, the photophysical properties of eight TSCT-type TADF molecules are studied by first-principle calculations. Results show that small S1–T1 energy gaps and large SOC constants are obtained for all molecules, and the transition properties can be adjusted by the acceptor engineering strategy. The ISC and RISC processes can be enhanced by adopting A–D–A configurations. Thus, previous experimental measurements are reasonably explained, and six new TSCT-type TADF molecules are proposed.

An Innovative Food Processing Technology: Microwave Electrodeless Ultraviolet, Luminescence Mechanism, Microbial Inactivation, and Food Application.

Microwave electrodeless ultraviolet (MWUV) technology, as an emerging food processing technique, has garnered growing attention in the realm of food science in recent years. Based on different application requirements, MWUV equipment types are categorized as microwave oven reactor, continuous-flow UV-microwave reactor, coaxially driven MWUV reactor, and complete ultraviolet reactor. The luminescence properties of MWUV equipment depend on their filler gas; mercury is commonly used as a filler gas to produce a wavelength at 253.7 nm for food non-thermal sterilization. The microbial sterilization effect of MWUV is primarily attributed to the synergistic action of microwave and ultraviolet (UV): MWUV enhances reactive oxygen species (ROS) production, disrupts the cell membrane structures of bacteria, leads to bacterial endosome leakage, and induces nucleic acid damage. MWUV extends food shelf-life by eliminating microorganisms without significantly altering food quality compared with traditional thermal sterilization methods. Additionally, MWUV, combined with digestion reagents such as HNO3 and H2O2, can effectively enhance the digestion of food samples to detect essential and toxic elements. Studies on MWUV technology hold broad potential in the food industry, with promising implications for food safety and consumer demand for high-quality food. Future research may focus on optimizing the equipment parameters and integrating with other food processing technologies to facilitate further development and application of MWUV.

Luminescent Tactile Sensor System for Robots: Enhancing Human-Computer Interaction in Complex Dark Environments.

In order to achieve interaction and collaboration with humans, robots need to have the ability for tactile perception of simulating human. Traditional methods use electrically connected sensors with complex arrays, leading to intricate wiring, high manufacturing costs, and demanding current environments. A flexible sensor with simple structure, easy preparation process, and low cost based on triboluminescence effect is proposed in this paper, which avoids the complex array and wiring of traditional sensors. The study discusses the relationship between luminescent intensity and factors such as luminescent particle content, luminescent layer thickness, encapsulation layer thickness, and friction layer thickness. It also analyzes the mechanism of luminescence. A micro charge-coupled device is configured for the luminescent unit to collect optical information and is integrated with the robot's manipulator for testing. A simple sensing system is constructed to demonstrate environmental perception, acquiring, and feeding back shape and size information of contact objects in the dark. The system successfully identifies and judges target objects in complex dark environments, offering insights for applications such as unmanned assembly lines. It overcomes the challenge of intricate electrical connections, paving new avenues for intelligent object recognition research in human-computer interaction.

Integrated analysis of miRNA-mRNA regulatory networks in Anoectochilus roxburghii in response to blue laser light.

Anoectochilus roxburghii (Wall.) Lind. has significant medicinal and economic value, and the social demand for this species is increasing annually. Laser light sources have different luminescent mechanisms compared with ordinary light sources and are also important factors regulating the synthesis of functional metabolites in A. roxburghii. However, the regulatory mechanism through which A. roxburghii responds to blue laser light has not been investigated. Previous studies have shown that blue-laser treatment results in more red leaves than blue- or white-light treatment. Here, the differences in the effects of laser treatment on A. roxburghii were analyzed by transcriptome sequencing. Gene Ontology analysis revealed that the membranes, calcium ion binding, brassinosteroid-mediated signaling pathway and response to salicylic acid play important roles in the response of A. roxburghii to blue laser light. Kyoto Encyclopedia of Genes and Genomes analysis revealed the involvement of multiple pathways in the response to blue-laser treatment, and among these, beta biosynthesis, flavone and flavonol biosynthesis, thiamine metabolism, limonene and pinene biosynthesis, and peroxisomes play core roles. Cytoscape interaction analysis of the differentially expressed miRNA targets indicated that novel_miR_66, novel_miR_78 and novel_miR_212 were most likely involved in the effect of blue laser light on A. roxburghii. Metabolic content measurements showed that blue laser light increased the beet red pigment, thiamine, total flavonoid and limonene contents, and qPCR analysis confirmed that novel_miR_21, novel_miR_66, novel_miR_188 and novel_miR_194 might participate in the blue-laser signaling network through their target genes and thereby regulate the functional metabolite accumulation in A. roxburghii. This study provides a scientific basis for high-yield A. roxburghii production.