Luminescent Composites Research Articles

Studying the Spectral Properties of Luminescent Polymer Composites Doped with Boron Difluoride Curcuminoids

Studying the Spectral Properties of Luminescent Polymer Composites Doped with Boron Difluoride Curcuminoids

Photoluminescent Y2O3:Eu3+@PVA composite dispersions and films for anti-counterfeiting ink applications

The development of high-tech anti-counterfeiting inks to detect counterfeit products is a crucial task for almost every aspect of modern life around the world. Herein, we report the synthesis of photoluminescent xY2O3:Eu3+@PVA (x = 0, 1, 2.5, 5, 10, 15, and 20 wt%) composite dispersions and films and demonstrate their potential for anti-counterfeiting inks applications. Laser-synthesized m-Y2O3:Eu3+ nanoparticles (daver = 20.3 ± 6.9 nm) with strong red luminescence due to 5D0 → 7F0-4 transitions of Eu3+ were used as a pigment to create luminescent composites. Detailed photoluminescence properties of the obtained composite dispersions and films as a function of m-Y2O3:Eu3+ content were investigated in combination with SEM, EDX, UV–Vis and IR spectroscopy data. Tuning of the CIE coordinates of xY2O3:Eu3+@PVA is observed by changing the excitation wavelength. The results of SEM showed that the photoluminescent nanoparticles were uniformly distributed in the PVA film. Photoluminescent m-Y2O3:Eu3+-doped PVA composite inks can be applied via spray, brush, and screen-printing techniques to create security features on various surfaces, including glass, ceramics, paper, plastics, and currency notes. These inks remain stable for at least four months and offer a distinctive luminescent signature that is challenging to replicate, owing to the unique photoluminescence spectrum of Eu3+ in the monoclinic Y2O3 polymorph.

White light-emitting Ag+-doped H-SSZ-13 zeolite

Ag+-exchanged SSZ-13 zeolites with single-phase white-emitting, especially obtained in a mild temperature (400 °C), are highly desirable for the construction of white LEDs, but rarely reported. Herein, luminescent silver nanoclusters composites were synthesized though treating H-SSZ-13 zeolites in the presence of a moderate amount of sodium hydroxide solutions, by assembling the silver nanoclusters in the modified SSZ-13 zeolites, followed by heating under mild conditions, which it bright white light emission phenomena under a 365 nm UV light. This white emitting may be ascribed to the collapse of the zeolite skeleton due to the etching of the zeolites by NaOH, thereby formation and stabilization of silver nanoclusters within modified Na-SSZ-13 zeolites. For the first time, the white-emitting Ag@Na-SSZ-13-400 zeolites phosphors were obtained at a mild temperature (400 °C) with a photoluminescence quantum yield (PLQY) of 24.45 % and the CIE chromaticity coordinate were (0.26, 0.33) under the 360 nm excitation. We believe that this work may provide a prospect for application of SSZ-13 zeolites and the preparation of luminescent AgNCs.

Thermally enhanced luminescence and photoluminescence properties of green-emitting Lu2(1-x)Tb2x(WO4)3 phosphors

A series of Lu2(1-x)Tb2x(WO4)3 (x = 0.00–1.00) white powder materials were prepared by a high-temperature solid-phase method. The crystal structure, microscopic morphology, elemental composition, bandgap energy, photoluminescence properties, and thermal stability of luminescence of the prepared materials were analyzed and studied through room and high temperature X-ray diffraction patterns, field emission scanning electron microscopy images, energy energy-dispersive spectra and X-ray photoelectron spectra, diffuse reflectance spectra, room and high temperature photoluminescence spectra. Under 260 nm excitation, the green emitting Lu2(1-x)Tb2x(WO4)3 samples exhibited an optimum Tb3+ doping concentration at x = 0.30. Calculated results illustrate that the concentration quenching was mainly caused by dipole-dipole interaction. Lu1.98Tb0.02(WO4)3 phosphor exhibited thermally enhanced luminescence at 120 °C, with a maximum luminescence intensity of 254 % of the initial room temperature intensity. Lu1.4Tb0.6(WO4)3 phosphor exhibited thermally enhanced luminescence at 150 °C, with a maximum luminescence intensity of 109 % of the initial room temperature intensity. The mechanism of the thermally enhanced luminescence phenomenon is further discussed to be the adsorbed crystal water and the negative thermal expansion of the material. Thermally enhanced luminescence is of great significance in overcoming luminescent thermal quenching phenomenon, improving the luminescence efficiency, optimizing the material design, and so forth. It has potential applications in high-temperature lighting, display technology, temperature sensing, and optical anti-counterfeiting.

Polyvinylalcohol Composite Filled with Carbon Dots Produced by Laser Ablation in Liquids.

Carbon dots (CDs), owing to their excellent photoluminescent features, have been extensively studied for physics preparation methods and for biomedical and optoelectronic device applications. The assessment of the applicability of CDs in the production of luminescent polymeric composites used in LEDs, displays, sensors, and wearable devices is being pursued. The present study reports on an original, environmentally friendly, and low-cost route for the production of carbon dots with an average size of 4 nm by laser ablation in liquid. Jointly, to prove the significance of the study for a wide range of applications, a free-standing flexible polyvinyl alcohol (PVA) composite containing photoluminescent carbon dots was manufactured. CDs were prepared using targets of porose charcoal with a density of 0.271 g/cm3 placed in phosphate-buffered saline (PBS) liquid solution and irradiated for 30 min by pulsed IR diode laser. The optical properties of the obtained suspension containing carbon dots were studied with UV-ViS and FTIR spectroscopies. The photoluminescence of the produced carbon dots was confirmed by the emission peak at 480 nm in the luminescence spectrum. A narrow luminescence band with a full width at half-maximum (FWHM) of less than 40 nm could be an asset in spectral emission analysis in different applications. Atomic force microscopy confirms the feasibility of manufacturing CDs in clean and biocompatible environments, paving the way for an easier and faster production route, crucial for their wider applicability.

Diamond seed dependent luminescence properties of CVD diamond composite

Diamond-based X-ray luminescent composites are robust materials to be used in synchrotrons and free-electron lasers to detect and visualize high-intensity X-ray beams. Such composites consist of luminescent rare-earth (RE) particles embedded into an X-ray transparent diamond matrix. In this work, polycrystalline diamond composites with embedded particles of EuF3, SrF2:Eu and YAG:Ce were grown by microwave plasma CVD using diamond seeds with an average particle size difference of two orders of magnitude: from 5 nm up to 500 nm, with positive and negative zeta potentials. The structure, phase composition, and luminescent characteristics of the resulting composite films were investigated and analyzed. We found that various particle types can be better-suited for different composites, and the exact seeding should be selected on the case-by-case basis. The direct comparison of various diamond-based composites, grown in the identical CVD conditions but with various luminescent powders, show that YAG:Ce particles in diamond allow achieving a brighter photoluminescence (PL) in comparison to Eu-based fluorides. However, the set of fluoride powders doped with Eu3+ ions allow obtaining unusually narrow (FWHM = 0.9 nm) and intensive line near 611 nm in PL spectra, which might be better-suited for detection and characterization applications rather than a broad peak of Ce with FWHM ≈ 120 nm.

Carboxymethylcellulose modified Fe3O4@SiO2@GdPO4:Tb3+,Ce3+ nanocomposites for combined optical and magnetic fluid hyperthermia in cancer therapy

A stepwise synthetic method is reported for the synthesis of multifunctional, magnetic and luminescent composites with silica-coated Fe3O4 as the core and Ce3+ sensitized Tb3+ doped GdPO4 embedded in carboxymethylcellulose.

Preparation of Zn2GeO4:Mn,In persistent luminescence nanoparticle composites for the detection of copper ions

Preparation of persistent luminescent nanoparticle composites for the detection of copper ions using the aggregation-induced quenching principle.

Chiroptically Active Multi-Modal Calcium Carbonate-Based Nanocomposites.

The development of multimodal nano- and micro-structures has become an increasingly popular area of research in recent years. In particular, the combination of two or more desirable properties within a single structure opens multiple opportunities from biomedicine, sensing, and catalysis, to a variety of optical applications. Here, for the first time, we report the synthesis and characterization of multimodal chiroptically active CaCO3 nanocomposites. These composites have been prepared by a modified microemulsion method in the presence of an amino acid (cysteine). Following this, additional modalities have been introduced by loading the composites with luminescent nanoparticles or doping with Eu3+ ions. The luminescent composites have been produced by the incorporation of CuInZnS/ZnS or CdSe@ZnS/ZnS core/shell quantum dots, or via doping with trivalent europium. In this manner, we have produced chiroptically active composites with orange, green, and red luminescence. Overall, this work demonstrates the unique advantage and potential of our approach and new class of chiroptically active CaCO3 nanocomposites, which display tunable functionality to specific requirements via the incorporation of desired ions, nanoparticles, and chirality of the structure.

NATURE OF ZINC OXIDE COLLOIDAL NANOCRYSTALS PHOTOLUMINESCENCE

The purpose of the study is to determine the nature of the radiative transitions responsible for the visible radiation of zinc oxide nanocrystals. Show that the size of nanocrystallites does not affect the spectral composition and location of long-wave luminescence. ZnO nanocrystals obtained by the method of colloidal synthesis with or without gelatin stabilization were investigated in the paper. The size of the nanocrystallites was determined in the approximation of the effective masses by the magnitude of the fundamental absorption edge shift. The results of calculating the size of nanocrystallites agree well with the results of SEM studies. It is shown that the main factor affecting the size of nanocrystallites is the concentration of precursors. Photoluminescence spectra of colloidal ZnO nanocrystals were studied in two spectral regions – ultraviolet and visible. Photoluminescence spectra in the ultraviolet region are characterized by three emission lines, the location of which depends on the concentration of precursors, that is, on the width of the band gap. Analysis of the energy states of intrinsic defects in nanostructured zinc oxide showed that the first two emission lines are associated with radiative transitions of excitons bound on neutral interstitial zinc atoms and on neutral zinc vacancies. The third line of ultraviolet radiation is caused by radiative transitions with the participation of deep donors, which are interstitial zinc atoms in the +2 charge state. The visible radiation spectra of colloidal ZnO nanocrystals are characterized by broad non-elemental emission bands in the blue-green and yellow-red regions of the spectrum. A detailed analysis of the spectra at different concentrations of precursors showed that the change in concentrations of precursors does not affect the spectral location of elementary emission lines. The absence of impurity absorption lines indicates that the centers responsible for visible radiation are donor-acceptor pairs. The analysis of the ratio of the emission lines intensities with increasing concentrations of the precursors shows that interstitial zinc and oxygen atoms dominate in the studied nanocrystals at high concentrations. As a result, in samples with a high concentration of precursors, blue radiation dominates over yellow and green. Thus, the study shows that by changing the concentrations of precursors, it is possible to influence both the spectral location of the edge ultraviolet luminescence and the intensity of individual long-wave luminescence components. The resulting colloidal ZnO nanocrystals can be used as luminescent sensors.

Construction of Naphthalenediimide Lanthanide(III)‐MOFs and Composites Incorporated Electron‐Rich Pyrene Derivative as Multifunctional Fluorescence Sensing for Nitro Aromatic Compounds and Aldehydes

Comprehensive SummaryThe development of host‐guest MOF luminescent composites has attracted considerable attention. However, it is still a challenge to reasonably design large scale conjugated polycarboxylic acids metal‐organic framework (MOF) and modulate donor‐acceptor interaction. Herein, a series of isostructural 3D porous lanthanide MOF [Ln2(BINDI)0.5(NO3)(DMA)(H2O)]∙DMA∙2.5H2O (Ln = La (1), Ce (2), Pr (3) and Nd (4); H4BINDI (N,N’‐bis(5‐isophthalic acid)‐1,4,5,8‐naphthalenediimide) were synthesized. Considering the electron‐deficient performances of Ln‐BINDI MOFs, D‐A type composites Ln‐MOFs (1—4@H4TBAPy) were prepared via the incorporation of electron‐rich H4TBAPy (1,3,6,8‐tetrakis(p‐benzoic acid) pyrene), which more improved the luminescence performance of complexes 1—4 and can be used as fluorescence sensors for the detection of nitro compounds and aldehydes. High sensitivity of 1@H4TBAPy towards pNBA, pNA PNP, DNP, and TNP could be achieved through hydrogen bond interactions between MOF and analytes, as well as the π‐π interaction between H4TBAPy and the naphthalene ring of BINDI, thus the fluorescence quenching efficiency of 1@H4TBAPy was better than that of the complex 1. In addition, it is found that 1@H4TBAPy has high selectivity and sensitivity to aromatic aldehyde SA, 5‐Mesal and HMBA. Such strategy to enhance the emission of NDI based Ln‐BINDI MOFs, will open up an avenue to obtain more fluorescent MOFs for sensing.

From synthesis to fabrication: Engineering thin translucent films with green persistent luminescent nanoparticles

Green-emitting ZnGa2O4:Mn2+ persistent luminescent nanoparticles were synthesized via a solvothermal method followed by a microwave-assisted sintering at 1150 °C. The obtained cubic-like particles averaged 62 ± 16 nm by Transmission Electron Microscopy (TEM) and presented afterglow for up to 2 h after a 5 min excitation in the UV. By Electron Paramagnetic Resonance (EPR), it was observed that the Mn2+ dopant replaces uniquely Zn2+ sites during synthesis. The obtained particles were dispersed with hydroxypropyl methylcellulose (HPMC) in water to create thin films by drop-casting. The films with different concentrations of nanoparticles (1 g/m2, 10 g/m2 and 100 g/m2) had average visible transmittances between 20% and 24%, and presented persistent luminescence after UV excitation, with longer duration by increasing nanoparticle concentration. By synchrotron X-ray Fluorescence (XRF) nanomapping of these films it is possible to see clusters of up to 6 μm of the nanoparticles in the film due to water pockets during film-casting. The X-ray Excited Optical Luminescence (XEOL) showed only Mn2+ emission and the XEOL-XRF mapping proved the integrity of the nanoparticles after film fabrication. By combining the solvothermal method, microwave-assisted sintering, and drop casting, this study establishes a promising pathway for the development of advanced flexible and translucent persistent luminescent composites.

The mineral composition and gemological characteristics of decorative-interior and jewelry-ornamental ammonites from the Republic of Kabardino-Balkaria

The article first presents results of a study of fossil ammonites from the Republic of Kabardino-Balkaria as a mineral resource – a jewelry and ornamental raw material. The ammonites are associated with Lower Aptian deposits and are encountered within marly concretions. 
 The complex of the study of the ammonites included determination of the density, microhardness, luminescence, and mineral and chemical composition; the optical-petrographic and electron-probe investigations. The ammonites mainly consist of calcite (about 85 % by weight). They contain mineral impurities: aragonite, quartz, illite, kaolinite, microcline, albite, chlorite, anatase, pyrite, dolomite, and apatite. Their impurity elements are represents by Sr and Ba in increased concentration. The walls and septa of the shells are made mainly of calcite, aragonite partly preserved as well. 
 The ammonites are characterized by a wide range of the sizes, high decorativeness, good technological and environmental characteristics, which make it possible to manufactor a diverse range of interior articles and jewelry. The ammonite collecting is carried out in river valleys without mining workings, which does not require significant financial costs and does not violate the environment.

Hydrothermal deposition synthesis of dual-mode luminescent material GdVO4 :Eu3+ /carbon dots with optimal luminescence and its application in anti-counterfeiting.

To obtain optimal luminescence, 0.12 g of GdVO4 : 3% Eu3+ nanocrystals (NCs) and different volumes of nitrogen-doped carbon dots (N-CDs) crude solution were used as precursors, and the composite synthesized by hydrothermal deposition method shows optimal luminescence when 11 mL(2.45 mmol) crude solution was used. Besides, similar composites with the same molar ratio as GVE/cCDs(11) were also prepared with hydrothermal and physical mixing process, respectively. Based on the test results of XRD, XPS and PL spectra, one can find that for the composite GVE/cCDs(11), the highest (lowest) peak intensity of C-C/C=C (C=O/C=N) bond, which is 1.18 (0.75) times that of GVE/cCDs-m, indicates the most N-CDs deposition, and lead to their highest emission intensity under 365 nm excitation though nitrogen atoms in the composite are shed off slightly during the deposition process. Finally, as can be seen from the designable patterns for security application, the optimally luminescent composite is one of the most promising candidates in the anti-counterfeiting field.

Characterization of carbon quantum dots obtained through citric acid pyrolysis

Carbon quantum dots (CQDs) were produced through citric acid (CA) pyrolysis. For the first time, we searched for the optimum CA pyrolysis duration and temperature. As a basic quality criterion of quantum dots, photoluminescence quantum yield (QY) was chosen. For this purpose, the pyrolysis products were analysed with UV–Vis spectroscopy and fluorescence (FL) spectroscopy. The optimum pyrolysis time was accepted to be 240 min, whereas the optimum pyrolysis temperature was approved as 200 °C. The pyrolysis products obtained at the optimum conditions were further subjected to dialysis. Finally, the purified CQDs were characterised with FL spectroscopy, transmission electron microscopy, dynamic light scattering, Raman spectroscopy, and Fourier transform infra-red spectroscopy. The produced CQDs were shown to be stable in water solution. Their PL QY (6.1%) was decreased to 1.2% after CQDs exposure to daylight for 90 days. Luminescent polymer composites were produced when CQDs were embedded in the poly(vinyl alcohol) and bacterial cellulose matrices. The prepared composites can be used for fabrication of transparent, flexible, and luminescent films and for production of anti-counterfeiting paper for confidential documents, labels, and banknotes.

Development of a red persistent luminescent composite: Electrospun nanofiber polymer coating prevents emission quenching by water

Sulfide persistent luminescent materials are known for their efficient luminescence, although a limitation in application of these materials is their susceptibility to hydrolysis. In this work, the electrospinning technique was used to encapsulate polycrystalline SrS:Eu2+,Sm3+ within PVDF-co-HFP nanofibers, after which thermostimulated luminescence could be observed with the naked eye following treatment with boiling water, confirming that the storage capacity of the powder was maintained after encapsulation. The composite material presented high levels of flexibility, hydrophobicity, and thermal and chemical stability. The structural characteristics of the synthesized SrS:Eu2+,Sm3+ were elucidated using X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The morphologies of the SrS:Eu2+,Sm3+ grains and the electrospun nanofibers were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray fluorescence (XRF) mapping, and scanning transmission X-ray microscopy (STXM). Mechanical properties including elastic modulus and deformation degree were evaluated by PeakForce quantitative nanomechanical mapping (PF-QNM). The luminescent properties were investigated using photoluminescence spectroscopy (PLS), diffuse reflectance spectroscopy (DRS), and X-ray excited optical luminescence (XEOL), which showed that the photonic functionality of the material in the nanofibers was preserved, even after severe treatment with boiling water.

Composites of Silk Nanofibrils and Metal–Organic Framework Nanosheets for Fluorescence-Based Sensing and UV Shielding

Silk fibroin, a widely used natural biopolymer, presents remarkable flexibility and biodegradability, making it of great interest as a polymer matrix for functional composite materials. Herein, composites of silk nanofibrils and metal–organic framework (MOF) nanosheets were successfully fabricated by a coincubation and coassembly process. Under heat incubation, silk fibroin self-assembled into one-dimensional nanofibrils, while MOF nanosheets simultaneously covered or wrapped on the silk nanofibrils in a water suspension. Transparent composite membranes were obtained from their water suspensions by the solution casting method. The regenerated silk nanofibrils formed a network structure, and the integrated MOF nanosheets (0.1 to 3.0 wt %) endowed the composites with aggregation-induced emission luminogen (AIEgen)-based fluorescence. The fluorescence intensity of the composites was significantly enhanced owing to the interfacial interactions between silk nanofibrils and MOF nanosheets. The composite membranes also offer excellent UV shielding while maintaining optical transparency in the visible spectrum. This work provides an efficient pathway to fabricate luminescent silk protein-based composites for functional materials such as fluorescence sensing and anticounterfeiting.

Boosting the optical properties of polylactic acid/ lanthanide-based metal-organic framework composites

Luminescent lanthanide metal-organic frameworks (LnMOF) are gathering much interest in the scientific community due to their exceptional optical properties, which have the potential to revolutionize several application fields, including anti-counterfeiting. The traceability of the original products is an ever-growing demand for producers and end-users to verify the authenticity of produced goods. Following this newfound need, we propose an anti-counterfeiting method based on a quick-response (QR) code, with a very specific verification procedure, using a luminescent LnMOF-based composite. The embedded code will only react to certain stimulation, hence it can only be unlocked using the sequence that is programmed to respond to. For that purpose, we explored the incorporation of fresh LnMOFs, with europium (EuMOF) and terbium (TbMOF), on a biodegradable polymer matrix of polylactic acid (PLA). A homogeneous mixture of PLA/LnMOF was produced via a two-step process including solvent casting followed by thermal mixing, after achieving the optimized concentration for each filler. The optical characterization of the fresh composites showed an excellent response to selective excitation, with well-defined intraionic lines for TbMOF @ 542 nm (5D4→7F5) and for EuMOF @ 615 nm (5D0→7F2). PLA/Eu, TbMOF composites were also explored to create an additional level of encryption by tuning the emitted color with the appropriate excitation stimuli. Hence, these new luminescent composite materials can be used as traceable optical tags for a wide variety of polymeric products, capable to respond to a very specific excitation wavelength and act as a level three luminescent security marker, whose decoding demands the assessment of more than one factor, with near-impossible replication. Additionally, this technology has a high potential for scalability since the applied processing techniques used for the production of the optically active QR code are commonly employed in the polymer industry. Nevertheless, the analysis of the aged effects clearly indicates the need for a definition of new strategies to enhance the efficiency of the sensitization process of the Ln3+ intraionic emission.

Tenon effects at drilled multi-walled carbon nanotubes to strongly enhance mechanical and luminescent properties of epoxy resin composites

The effectiveness of mechanical enhancement of carbon nanotubes-polymer matrices, particularly, epoxy resin (EP), depends strongly on the interface interaction between constituents. Providing rough surface and chemical activity of CNTs is the effective way to reach that. To explore both approaches, in this study, unzipped CNTs (uCNTs) and drilled CNTs (dCNTs)were prepared by Hummers methods and chemical etching. The structure of uCNTs and dCNTs were characterized by FT-IR, TG and XPS. The Eu3+ complexes were anchored to CNTs, uCNTs, and dCNTs via strong interaction to form a stable “tenon” structure. That materials were found useful to fabricate the composite with EP. Our study reveals that the ultimate tensile and flexural strengths of Eu-dCNTs/EP increases by 161% and 226%, indicating that Eu-dCNTs improves significantly the mechanical properties of EP. The drilling treatment and the “tenon” structure of the Eu-dCNTs hybrid play a key role in improving the mechanical properties of EP. Fracture morphology and the strengthening mechanism were discussed. Our study shows an effectiveness of using dCNTs and uCNTs to fabricate luminescent polymer composites with enhanced properties.

Luminescent polymer films based on blocksil siloxane copolymers and phenyleuropiumsiloxane molecular filler

In the present work, a method for the preparation of the new luminescent polymer compositions was described. A series of polymer films based on organosilicon dimethylsiloxane-phenylsilsesquioxane block-copolymer containing flexible linear dimethylsiloxane and rigid polycyclic phenylsilsesquioxane blocks in the structure of the macromolecule and polyfunctional phenyleuropiumethoxysiloxane [C6H5Si(OC2H5)2O]3Eu, as a molecular luminescent filler, was prepared and fully characterized. Physicochemical, mechanical, optical, and thermal properties all the polymer films were investigated. The polymer films form stable 3D networks and demonstrate a high thermal and thermo-oxidative stability. The study of mechanical properties showed that the tensile strength is in the range of 14–19 MPa, elongation at break is in the range of 5–8% and the Young's modulus is in the range of 380–560 MPa for the investigated polymers. The optical properties of the polymers were studied in the solid state at room temperature. It was shown, that upon excitation with 310 nm UV light the emission spectra of all samples show the five emission peaks that are characteristic for the Eu3+ ion arising from the 5D0→7FJ (J = 0–4) transitions.