Tunable Luminescence Properties Research Articles

Preparation and application of wormlike micelles generated from a rosin-based aggregation-induced emission surfactant through coordinating aggregation

Fluorescent nanomaterials have drawn considerable attentions due to their high fluorescence sensitivity, excellent signal stability and tunable luminescent properties. A bio-based aggregation-induced emission (AIE) surfactant (Sodium 4-(tetraphenylstyrene)maleate, MPA-TPE-Na) was prepared from rosin, which showed typical AIE characteristic, obvious solvatochromism and a large Stokes shift (>100 nm). AIE viscoelastic solutions were further prepared by complexing MPA-TPE-Na and cetyltrimethylammonium bromide (CTAB) through coordinating aggregation and their microstructure, fluorescence properties and viscoelasticities were investigated. The aggregates in the viscoelastic solutions were wormlike micelles. As the concentration of MPA-TPE-Na increased, the fluorescence intensity of the viscoelastic solutions increased, and their viscosity increased at first and then decreased. The fluorescence emission intensity of the viscoelastic solutions was barely affected by the change in pH. But reducing the pH could increase its viscosity. This system can specifically recognize Fe3+ without any organic solvent and has anti-interference ability. The present work provided a bio-based fluorescent nanomaterial and verified the feasibility of preparing aqueous AIE nanomaterials by modifying AIE groups with rosin skeleton.

Tunable luminescent properties and structure of Sn2+-doped boroaluminate glasses

A series of novel Sn2+ doped boroaluminate glasses were prepared by the traditional melt quenching method in this work. Their glass network structure, luminescent properties, and mechanisms were studied in detail. The main framework of the glass network was dependent on the glass network former (B2O3) and intermediate (Al2O3), and was characterized by the 11B and 27Al NMR spectra. Broadband tunable blue-violet emissions ranging from 320 to 550 nm were realized by regulating the glass network structure through optical basicity. The quantitative relationship between optical basicity and emission/excitation peak positions and intensities, FWHM, and Stokes-Shift of this Sn2+-doped glass were revealed, according to which the luminescent properties of Sn2+ could be modulated and even predicted in the future. This work will enrich our understanding of the luminescent properties of Sn2+ ions and the variations of glass network structure, guiding the design of efficient and tunable luminescent boroaluminate glass.

Eu3+-Directed Supramolecular Metallogels with Reversible Quadruple-Stimuli Response Behaviors.

Smart luminescent materials that have the ability to reversibly adapt to external environmental stimuli and possess a wide range of responses are continually emerging, which place higher demands on the means of regulation and response sites. Here, europium ions (Eu3+)-directed supramolecular metallogels are constructed by orthogonal self-assembly of Eu3+ based coordination interactions and hydrogen bonding. A new organic ligand (L) is synthesized, consisting of crown ethers and two flexible amide bonds-linked 1,10-phenanthroline moieties to coordinate with Eu3+. Synergistic intermolecular hydrogen bonding in L and Eu3+-L coordination bonding enable Eu3+ and L to self-assemble into shape-persistent 3D coordination metallogels in MeOH solution. The key to success is the utilization of crown ethers, playing dual roles of acting both as building blocks to build L with C2-symmetrical structure, and as the ideal monomer for increasing the energy transfer from L to Eu3+'s excited state, thus maintaining the excellent luminescence of metallogels. Interestingly, such assemblies show K+, pH, F-, and mechano-induced reversible gel-sol transitions and tunable luminescence properties. Above findings are useful in the studies of molecular switches, dynamic assemblies, and smart luminescent materials.

Stimuli‐responsive fluorescent hydrogels: Strategies and applications

AbstractStimuli‐responsive fluorescent hydrogels are three‐dimensional networked polymeric materials with tunable luminescence and dynamic properties, which play an important role as a water‐rich soft material in the fields of information encryption, bionic actuation, bioimaging, environmental monitoring, and luminescent materials. Compared with conventional hydrogels, their unique luminescent properties allow the visualization of microscopic dynamics within the polymer network. By rational inclusion of dynamic motifs, such as photoswitches, AIEgens, lanthanide complexes, and host–guest complexes, these materials are endowed with tunability of emission, shape, and phase in time and space in response to environmental effectors. In this review, we summarize the fabrication strategies that are mainly used by recently reported stimuli‐responsive fluorescent hydrogels and the applications of these materials.

Assessment of the correlation between optical properties and CQD preparation approaches

Various production procedures, for carbon quantum dots (CQDs), are still being extensively researched to understand the nature of CQD luminescence. This study compares and examines the impact of chemical as well as green methods on the structural and optical properties of CQDs. We present a straightforward, cost-effective bottom-up method for producing fluorescent CQDs from lemon peels (L-CQDs), orange juice (O-CQDs), and citric acid (C-CQDs) without having to deal with time-consuming or ineffective post-processing processes. The proposed green synthesis has no toxic by-products, and the residual resources utilized promote the large-scale production of CQDs. X-ray diffraction, high-resolution transmission electron microscopy, FTIR, Raman, DLS, and UV–Vis spectroscopy are utilized to investigate the structure and optical characteristics of the prepared CQDs. The as-prepared CQDS possess small particle sizes of 5.6 nm, 6.2 nm, and 1.1 nm for L-CQDs, O-CQDs, and C-CQDs samples, respectively. FTIR results reveal the coexistence of carboxylic and hydroxyl groups on the surface of the CQDs, as also supported by zeta-potential values. Maximal fluorescence intensity was reached at excitation wavelengths of 365, 250, and 280 nm with an emission color of blue, indigo, and light blue for L-CQDs, O-CQDs, and C-CQDs, respectively. The presented approaches show a high quantum yield of 88% for O-CQDs, 49% for L-CQDs, and 37% for C-CQDs. Due to their minuscule particle size, perfect water solubility, high stability, and tunable luminescence properties, the prepared CQDs are preferred for potential applications in multicolor imaging, metal ion sensing, and wastewater technologies.

Assembly of two new self-interpenetrating metal-organic frameworks with tunable luminescent properties

Two newly isostructural Zn-MOFs, namely [Zn2(DMTDC)2(H2O)(TPT)]·4H2O (JOU-8) and [Zn2(DMTDC)2(H2O)(TPY)]·4H2O (JOU-9), have been solvothermally synthesized and characterized (H2DMTDC = 3,4-DiMethylthieno(2,3-b)thiophene-2,5-dicarboxylic acid, TPT = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine, TPY = 2,4,6-tri(pyridin-4-yl)pyridine). Single-crystal X-ray diffraction revealed that JOU-8 and JOU-9 displayed three-dimensional self-interpenetrating structure with a new type of (6,6)-connected topology. Further studies revealed that strong π-π interactions between conjugated ligand DMTDC and TPT/TPY leaded to the formation of ligand-to-ligand charge transfer, which not only extended the absorption band edge of MOFs but also induced new emission peaks. The emission peaks at 401 nm for JOU-8 and 402 nm for JOU-9 were derived from the ligands, while the emission peaks at 489 nm for JOU-8 and 499 nm for JOU-9 may be derived from the π-π interactions between DMTDC and TPT/TPY. Moreover, the emission peak intensity of JOU-8 and JOU-9 are tunable depending upon the excitation wavelength. Thus, both JOU-8 and JOU-9 were potential dual-emission materials. This work provides new clues for the preparation of entangled MOFs with tunable luminescent properties.

Wide-Range Color-Tunable Organic Scintillators for X-Ray Imaging Through Host-Guest Doping.

With the increasing demands of X-ray detection and medical diagnosis, organic scintillators with intense and tunable X-ray excited emission have been becoming important. To guarantee the X-ray absorption, heavy atoms were widely added in reported organic scintillators, which led to emission quenching. In this work, we propose a new strategy to realize organic scintillators through the host-guest doping strategy. Then the X-ray absorption centers (host) and emission centers (guest) are separated. Under X-ray excitation, these materials displayed intense and readily tunable emissions ranging from green (520 nm) to near infrared (NIR) regions (682 nm). Besides, the relationship between the X-ray absorption and spatial arrangement of the heavy atoms in the host matrix was also revealed. The potential application of these wide-range color tunable organic host-guest scintillators in X-ray imaging were demonstrated. This work provides a new feasible strategy for constructing high-performance organic scintillators with tunable luminescence properties.

Wide‐Range Color‐Tunable Organic Scintillators for X‐Ray Imaging Through Host‐Guest Doping

AbstractWith the increasing demands of X‐ray detection and medical diagnosis, organic scintillators with intense and tunable X‐ray excited emission have been becoming important. To guarantee the X‐ray absorption, heavy atoms were widely added in reported organic scintillators, which led to emission quenching. In this work, we propose a new strategy to realize organic scintillators through the host‐guest doping strategy. Then the X‐ray absorption centers (host) and emission centers (guest) are separated. Under X‐ray excitation, these materials displayed intense and readily tunable emissions ranging from green (520 nm) to near infrared (NIR) regions (682 nm). Besides, the relationship between the X‐ray absorption and spatial arrangement of the heavy atoms in the host matrix was also revealed. The potential application of these wide‐range color tunable organic host‐guest scintillators in X‐ray imaging were demonstrated. This work provides a new feasible strategy for constructing high‐performance organic scintillators with tunable luminescence properties.

Tunable luminescence properties of the Ca3-xLuxSc2-xMgxSi3O12:Ce3+ phosphor based LD lighting

In white-light laser diodes (LD) illumination, the full width at half maximum (FWHM) of the emission spectrum of blue LD is too narrow, leading to the cyan light deficiency, while the emitting color of the material limits the red component of the device. Therefore, in this paper, Ca3-xLuxSc2-xMgxSi3O12:Ce3+ (CLSMS:Ce3+, x = 0, 0.5, 1, 1.5, 2) phosphor samples were successfully prepared based on Ca3Sc2Si3O12 (CSS) cyan-green fluorescent materials with different concentrations of Lu–Mg ions introduced in the matrix instead of Ca–Sc ions. And their luminescence properties were systematically investigated. The peak of the sample was shifted from 508 nm to 590 nm as the concentration of Lu–Mg increased. The thermal stability of the series phosphors gradually deteriorated with increasing Lu–Mg concentration. At 423 K, the emission intensity of the samples was 98.11 %, 94.13 %, 92.18 %, 81.96 % and 77.60 % of that at 298 K, respectively. And the thermal quenching activation energy also gradually decreases. The CLSMS:Ce3+ fluorescent materials were prepared into LD devices and tested. It was found that the series of samples showed a gradual decrease in cyan-green light and a gradual increase in red light with increasing Lu–Mg concentration. The CSS compounded with CaLu2Mg2Si3O12 (CLMS) obtained a white LD device with color coordinates of (0.3440, 0.3455), and the cyan and red components of the samples were compensated. In summary, this study demonstrates that CLSMS:Ce3+ is a very promising fluorescent material to extend the color gamut coverage of fluorescent materials. And it has a potential reference value for the field of white-light LD lighting.

Heteroatom-engineered multicolor lignin carbon dots enabling bimodal fluorescent off-on detection of metal-ions and glutathione

Carbon dots (CDs) have emerged as a promising subclass of optical nanomaterials with versatile functions in multimodal biosensing. Howbeit the rapid, reliable and reproducible fabrication of multicolor CDs from renewable lignin with unique groups (e.g., –OCH3, –OH and –COOH) and alterable moieties (e.g., β-O-4, phenylpropanoid structure) remains challenging due to difficult-to-control molecular behavior. Herein we proposed a scalable acid-reagent strategy to engineer a family of heteroatom-doped multicolor lignin carbon dots (LCDs) that are functioned as the bimodal fluorescent off-on sensing of metal-ions and glutathione (GSH). Benefiting from the modifiable photophysical structure via heteroatom-doping (N, S, W, P and B), the multicolor LCDs (blue, green and yellow) with a controllable size distribution of 2.06–2.22 nm deliver the sensing competences to fluorometric probing the distinctive metal-ion systems (Fe3+, Al3+ and Cu2+) under a broad response interval (0–500 μM) with excellent sensitivity and limit of detection (LOD, 0.45–3.90 μM). Meanwhile, we found that the addition of GSH can efficiently restore the fluorescence of LCDs by forming a stable Fe3+-GSH complex with a LOD of 0.97 μM. This work not only sheds light on evolving lignin macromolecular interactions with tunable luminescent properties, but also provides a facile approach to synthesize multicolor CDs with advanced functionalities.

Multicolor Mechanoluminescence in Sr2Ga2GeO7: Pr3+ for Stress Sensing and Anticounterfeiting

AbstractMechanical luminescence (ML) is the conversion of mechanical energy into light energy when a material is subjected to a force. It is challenging to develop ML materials with tunable luminescent properties by single ion doping, which have broad application prospects in the fields of stress sensing and dynamic signature anticounterfeiting. In this study, a Pr3+ doped Sr2Ga2GeO7 tunable ML material is reported. Due to the traps resulting from unequal substitution of Pr3+–Sr2+ in [SrO6] heptahedra, the deep/shallow traps redistribution occurs towards a multicolor ML from red to green. In addition, even after continuous friction sliding force (15 N), the ML intensities can be recovered after ultraviolet pre‐irradiation, indicating that Sr2Ga2GeO7: Pr3+ has excellent ML emission stability. Based on thermoluminescence analysis, potential PersL and ML mechanisms are further elaborated by a lattice engineering (trap regulation) strategy. In all, the development of single‐ion doped multicolor ML materials may have crucial research value and show a variety of potential applications in the fields of anticounterfeiting and information encryption.

Luminescent materials with dual-mode excitation and tunable emission color for anti-counterfeiting applications

GdVO4-based dual-mode phosphors were successfully synthesized via a hydrothermal approach. The X-ray diffraction analysis determined the tetragonal structure as well as I41/amd space group of products by comparing with a reference pattern no. ICDD #01-072-0277. The morphology of yielded phosphors was confirmed by transmission electron microscopy and scanning electron microscopy. Detailed spectroscopy analysis revealed tunable luminescence properties with an increasing Yb3+ content in series of GdVO4: x% Yb3+, y% Tm3+, 5% Eu3+ (x = 5, 10, 15, 20; y = 0.1, 0.5, 1) phosphors. For Yb3+, Tm3+, and Eu3+- codoped phosphors we observed bands related to the 1G4 → 3H6 and 1G4 → 3F4 transitions of Tm3+ ions, occurred through the cooperative up-conversion mechanism, where two nearby Yb3+ ions were involved in near-infrared absorption. Moreover, the GdVO4: 20% Yb3+, 0.5% Tm3+, 5% Eu3+ showed the most outstanding color tunability from red color (x = 0.6338, y = 0.3172) under UV to blue color (x = 0.2640, y = 0.1988) under NIR excitation, which can be applied in anti-counterfeiting activity.

Arene-Perfluoroarene Force Driven Sublimation-Removable Chiral Coassemblies.

Multiple constituent coassembly is an emerging strategy to manipulate supramolecular chirality and chiroptical properties such as circularly polarized luminescence (CPL). However, the second or third constituent could not be removed from pristine self-assembly. Here we developed a constitute-removable chiral coassembly using sublimation that could realize coassembly with tunable supramolecular chirality, luminescence and CPL properties. Octafluoronapthalene (OFN) with small sublimation enthalpy formed coassemblies with perylene-conjugated peptoids via arene-perfluoroarene (AP) interaction that induced the emergence of macroscopic chirality and hypochromic luminescence from yellow to green. Coassembly with OFN accelerated one-dimensional growth and induced the emergence of macroscopic chirality and CPL. Despite the stability at ambient conditions, vacuum-treatment triggered fast sublimation of OFN, which behaved as a sacrificial template. Physical removal of OFN retained the helical nanoarchitectures as well as the basic features of Cotton effects and CPL activities. X-ray diffraction suggested the back-fill consolidation occurred on the molecular voids by OFN removal that slightly varied the templated molecular arrangements. Sublimation of perfluorinated building units is green and efficient and non-destructive, which is potentially applicable in constructing template-directed chiroptical materials and devices.

Arene‐Perfluoroarene Force Driven Sublimation‐Removable Chiral Coassemblies

AbstractMultiple constituent coassembly is an emerging strategy to manipulate supramolecular chirality and chiroptical properties such as circularly polarized luminescence (CPL). However, the second or third constituent could not be removed from pristine self‐assembly. Here we developed a constitute‐removable chiral coassembly using sublimation that could realize coassembly with tunable supramolecular chirality, luminescence and CPL properties. Octafluoronapthalene (OFN) with small sublimation enthalpy formed coassemblies with perylene‐conjugated peptoids via arene‐perfluoroarene (AP) interaction that induced the emergence of macroscopic chirality and hypsochromic luminescence from yellow to green. Coassembly with OFN accelerated one‐dimensional growth and induced the emergence of macroscopic chirality and CPL. Despite the stability at ambient conditions, vacuum‐treatment triggered fast sublimation of OFN, which behaved as a sacrificial template. Physical removal of OFN retained the helical nanoarchitectures as well as the basic features of Cotton effects and CPL activities. X‐ray diffraction suggested the back‐fill consolidation occurred on the molecular voids by OFN removal that slightly varied the templated molecular arrangements. Sublimation of perfluorinated building units is green and efficient and non‐destructive, which is potentially applicable in constructing template‐directed chiroptical materials and devices.

Efficient luminescence emission in both visible and NIR-II regions by Er3+ partitioning doping and interfacial energy transfer

Lanthanide-doped nanoparticles (LDNPs) are widely used in biophotonics due to their narrow emission band, long lifetime and broad-spectrum tunable luminescence properties. Usually, photosensitizers for biotherapeutic applications need to be triggered by visible light, while bioimaging requires near-infrared (NIR) light with better penetration. However, it is still challenging to achieve efficient luminescence emission in the visible to second near-infrared (NIR-II, 1000–1700 nm) range simultaneously for multifunctional nanoparticles excited at a single NIR wavelength. Here, a simple NaYF4:Er/Ce@NaYbF4:Er@NaYF4:Nd core-shell-shell nanoparticle with interfacial energy transfer by the Yb-sensitized shell and partition doping of Er3+ under 808 nm excitation, which allows the system to achieve visible and NIR-II luminescence emission from different partitions of Er3+. When Ce3+ is introduced into the core, the Er3+ in the Yb-sensitized shell is responsible for the emission in the visible region, while the core-doped Er3+ is mainly responsible for the emission at 1550 nm in the NIR-II. In addition, this core-shell-shell nanostructure has a long luminescence emission lifetime in the visible and NIR-II regions, especially the luminescence lifetime of Er3+ at 1550 nm is extended to 6.4 ms. More importantly, efficient 1O2 generation can be achieved by coupling core-shell-shell nanoparticles with photosensitizer. These results will provide previously unattainable opportunities for LDNPs in biotherapeutic and imaging applications.

Tetraphenylethene-based macrocycles: Visualized monitoring the hydrolysis of silicon-oxygen bond and their tunable luminescent properties

The preparation of silicone material is generally carried out by hydrolytic condensation, and various methods have been tried so far to study the kinetics of silicon-oxygen bond hydrolysis. However, the process and kinetics of silicon-oxygen bond hydrolysis cannot be efficiently monitored in real-time due to the limitations of traditional testing methods. In the present study, we have successfully designed and synthesized a series of circular tetraphenylethylene (TPE) derivatives connected with different lengths of the siloxanes chain. As the chain length gets longer, the restriction on phenyl rotation in TPE derivatives becomes weaker, which induced fluorescence quenching gradually at the molecular level. Hence, it provides the most direct and convincing evidence for the effect of chain lengths in the popular restricted intramolecular rotation (RIR) mechanism with aggregation-induced emission (AIE) phenomenon. The strong fluorescent molecule was used to monitor the kinetics of silicon-oxygen bond hydrolysis in real-time successfully by the AIE method with the RIR mechanism. The high sensitivity and efficiency of fluorescence provide an unparalleled “visualization” window for real-time monitoring of the kinetic control of Si-O bond hydrolysis. Furthermore, the half-life and reaction kinetic data of Si-O bond-breaking reaction by different pH are obtained to provide a reference for scientists and engineers not only in fundamental research but also in industrial production. Finally, the aggregation-induced color-tunable emission was obtained with the different aggregation forms of molecules, exhibiting a promising potential for intelligent luminescent materials.

Facile synthesis, novel structure, and tunable luminescence properties of K6Bi13(PO4)15:Dy3+,Eu3+ phosphors for ultraviolet converted white light-emitting diodes

A variety of novel Dy3+/Eu3+ mono- and co-doped K6Bi13(PO4)15 (KBPO) luminescent materials have been fabricated by a simple solid-state method for the first time. Both experimental studies and theoretical calculations verify that the K6Bi13(PO4)15 crystals are suitable to be utilized as host materials for the lanthanide activator ions. The XRD, EDS, and XPS results reveal that the Dy3+ and Eu3+ have been effectively incorporated into the KBPO host matrix and do not damage the structure of KBPO. The Dy3+ or Eu3+ mono-doped phosphors display the characteristic spectral patterns of the activator ions upon UV excitation whereas an energy transfer between Dy3+ and Eu3+ occurs which helps to obtain the tunable luminescence of the KBPO:Dy3+,Eu3+ phosphors. The emission colors of the KBPO:Dy3+,Eu3+ regularly shift from green-blue, through white, and finally toward yellow and orange-red by varying the activator doping concentrations under a fixed excitation wavelength. Interestingly, the single-phase white light emitting phosphors with CIE chromaticity coordinates of (0.3122, 0.3106) and (0.3602, 0.3246) are obtained by doping appropriate concentrations of Dy3+ and Eu3+, which match well with the standard white light illuminate of (0.333, 0.333). Moreover, the annealing conditions are optimized and the luminescent mechanisms and temperature-dependent luminescence performance are systematically investigated. Finally, the WLEDs device prepared by KBPO:Dy3+,Eu3+ phosphor and UV chip displays a dazzling white light with favorable CIE (Commission Internationale de I'Eclairage 1931 chromaticity) coordinates, color rendering index (Ra), correlated color temperature (CCT), and thermal stability, which provides direct evidence that the as-prepared inorganic luminescent materials may have prospects as an eminent single-phase white light emitting materials for white light-emitting diodes (WLEDs) and optoelectronic devices.

Recent Advances in Luminescent Metal-Organic Frameworks for Detection of Gas and Volatile Organic Molecules

Gas molecules and volatile compounds in the air affect product purity and health. Because of increasing demand for better quality of life and health in industrial and general environments, timely detection of abnormal gas releases and poisonous compound volatilization is essential. Luminescence metal-organic frameworks (LMOFs) are materials with tunable pore sizes, defined structures, and luminescence properties, which have been widely reported as sensor materials for detecting various compounds. Here, luminescence mechanisms of LMOFs are reviewed and interactions between the host and guest molecules are explained at the molecular level. On the basis of these relationships, the state-of-the-art LMOF-based sensors for various common gas molecules (including H2O, O2, COx, and NOx) and volatile organic compounds (VOCs) are further described in depth. This review may benefit the further development of LMOFs and accelerate their practical application in various sensor combinations.

Chiral Naphthalenediimides with High-Efficiency Fluorescence and Circularly Polarized Luminescence in the Solid State for the Application in Organic Optoelectronics.

Naphthalenediimides (NDIs) have been extensively studied due to their tunable luminescent properties. However, generally, the monomers or aggregates of non-core substituted NDIs exhibit low fluorescence quantum yields (ΦFL <10 %) in the solid state, which limit their applications as light-emitting materials and render their chiral species unsuitable for circularly polarized luminescence (CPL). Herein, a series of non-core substituted chiral NDIs that exhibit high luminous efficiencies (ΦFL up to 56.8 % for racemate and 36.5 % for enantiomer) and a strong CPL behavior in the solid state is reported. These significant improvements are attributed to the unique molecular conformation of the chiral NDIs and the formation of distinctive discrete dimers. The structures of the NDIs were significantly simpler and more accessible than those of other NDIs. The findings evidence that non-core substituted NDIs can exhibit strong fluorescence in the solid state and provide a new pathway to improve photophysical properties of NDIs.

Lanthanide ions doped rare earth-based double perovskite single crystals for light-emitting diodes

Lead-free double perovskites have become the research hotspot in the optoelectronic fields. Then, it is a challenge to utilize the lattice doping by different rare earth ions with rich energy level and unique luminescence for emerging photonic applications. Here, we successfully prepared Sb3+ and Ln3+ ions doped Cs2NaYCl6 single crystals (SCs), bringing tunable bright luminescent emissions of blue, red, and white light, the highest photoluminescence quantum yield (PLQY) is up to 58.33%. Based on excellent and tunable luminescent properties, the multicolor light-emitting diodes (LEDs) applications for the rare earth-based double perovskite SCs were designed. These findings indicate that rare earth-based double perovskite will provide a broader application space for lighting.