Luminescent Particles Research Articles

Molten Salt Synthesis of Persistent Luminescent/Magnetic Cr3+-Doped Zinc Gallogermanate Particles

Near-infrared persistent luminescent particles are appealing materials for a diverse range of optoelectronic and biomedical applications. Thermal treatment at high temperature (e.g., solid-state annealing process) has been shown to enhance the luminescence intensity of these particles, while it remains a challenge to manipulate the morphology and solution dispersibility. Herein, molten salt in situ synthesis of Cr3+-doped zinc gallogermanate (ZGGO) with well-defined morphology and solution dispersibility is developed in combination with citric acid. In the absence of the physical grinding treatment (e.g., mechanically milling), the resulting ZGGO particles are not only readily dispersible in the aqueous solution but also exhibit enhanced persistent luminescence. The synergetic effects of salt and citric acid on the particle formation process as well as the optical properties are elucidated. Interestingly, these particles also exhibit enhanced ferromagnetism properties, showing promise for multiple optical/magnetic applications. The molten salt synthesis approach demonstrated in this work offers an alternative pathway for producing persistent luminescent particles, and the method may help to improve the synthesis of other complex metal oxide particles.

Subclinical signs of podocyte injury associated with Circulating Anodic Antigen (CAA) in Schistosoma mansoni-infected patients in Brazil

The long-term effects of schistosomiasis on the glomerulus may contribute to the development of chronic kidney disease. This study aimed to investigate baseline Schistosoma mansoni-Circulating Anodic Antigen (CAA) levels and their association with kidney biomarkers related to podocyte injury and inflammation in long-term follow-up after praziquantel (PZQ) treatment. Schistosoma infection was diagnosed by detecting CAA in urine using a quantitative assay based on lateral flow using luminescent up-converting phosphor reporter particles. A cutoff threshold of 0.1 pg/mL CAA was used to diagnose Schistosoma infection (baseline) in a low-prevalence area in Ceará, Northeast, Brazil. Two groups were included: CAA-positive and CAA-negative individuals, both of which received a single dose of PZQ at baseline. Urinary samples from 55 individuals were evaluated before (baseline) and at 1, 2, and 3 years after PZQ treatment. At all time points, kidney biomarkers were quantified in urine and adjusted for urinary creatinine levels. CAA-positive patients had increased baseline albuminuria and proteinuria and showed greater associations between kidney biomarkers. CAA levels correlated only with Vascular Endothelial Growth Factor (VEGF) (podocyte injury) levels. Increasing trends were observed for malondialdehyde (oxidative stress), monocyte chemoattractant protein-1 (inflammation marker), and VEGF. In the follow-up analysis, no relevant differences were observed in kidney biomarkers between the groups and different periods. S. mansoni-infected individuals presented subclinical signs of glomerular damage that may reflect podocyte injury. However, no causal effect on long-term renal function was observed after PZQ treatment.

Green chemistry synthesis of wolframites: An investigation about stoichiometric ratios, optical, structural, vibrational, and physico-chemical properties

This work aims to use a new route to synthesize nanostructured materials. The method has an eco-frendly perspective, which seeks to produce materials with dual characteristics (fluorescence and/or plasmon band) with various applications in luminescent sensors or particles for spectral optimization. Cobalt tungstate nanoparticles (CoWO4 - wolframite), with non-stoichiometric ratios of 2:1 and 1:2 of the precursor materials (ammonium paratungstate and cobalt nitrate), were prepared by the proteic sol-gel method. For the synthesis of the nanoparticles, two types of polymerizing agents were used: animal gelatin (collagen) and vegetal gelatin extracted from red algae (Rhodophyta). The prepared materials were calcined between 773 and 1073 K for 2 h. XRD results evidenced a variation of the lattice parameters and a monoclinic symmetry of the P21/c type for CoWO4 and of the P21/n type for WO3. Particle sizes, evaluated by the Scherrer equation, ranged from 13 to 30 nm for specimens synthesized at 773 K and from 20 to 51 nm for specimens synthesized at 1073 K. Raman spectroscopy revealed anharmonicity in the vibrational system and its damping according to the presence of distinct symmetries. The experiment was successful in obtaining a reproducible sol-gel procedure for the synthesis of the CoWO4 nanosystem. The procedure allowed the obtaining of plasmonic and photoluminescent properties only by stoichiometric modification of the precursors. Finally, the process was optimized, and the best synthesis conditions were defined. Furthermore, fluorescence and plasmon band investigation revealed that the nanostructures have maximum emission and absorption at 468 and 410 nm, respectively.

Preparation and Characterization of Gd2O3: Er3+ Nanosphere Particles Combinated with Chitosan Gd2O3: Er3+@CS

Nanospherical upconversion luminescence particles (UCLPs) Gd2O3:Er3+ and Gd2O3:Er3+@ chitosan (CS) were prepared by step-by-step precipitation and calcination of the available nitrate rare Earth sales and chitosan. The morphology and composition of as-prepared samples were characterized by field emission electron spectroscopy (FESEM) and Fourier transform infrared (FT-IR) spectroscopy. The synthesized UCLPs were non-agglomerate spheres in uniform nanoscale. The quantitative amount of chitosan was well coated with the gain surface of the UCLPs Gd2O3:Er3+ to obtain Gd2O3:Er3+@CS nanocomposite. The down-conversion luminescent intensity of Gd2O3:Er3+ NSP is lower than Gd2O3:Er3+@CS NSP samples, but luminescent characterizations were non-change. The photoluminescence (PL) of the green emission range of all UCLPs samples with chitosan-coated and -uncoated took the leading position. By using a diode laser excitation with 975 nm of wavelength, the detected intensity of red emission is more remarkably detected than green emissions. The two-photon mechanism for both green and red emissions of nanophosphor was observed. As a result, these might be promising opportunities to conjugate with various bio subjects that could be used in medical applications.

Single-Particle Optical Imaging for Ultrasensitive Bioanalysis.

The quantitative detection of critical biomolecules and in particular low-abundance biomarkers in biofluids is crucial for early-stage diagnosis and management but remains a challenge largely owing to the insufficient sensitivity of existing ensemble-sensing methods. The single-particle imaging technique has emerged as an important tool to analyze ultralow-abundance biomolecules by engineering and exploiting the distinct physical and chemical property of individual luminescent particles. In this review, we focus and survey the latest advances in single-particle optical imaging (OSPI) for ultrasensitive bioanalysis pertaining to basic biological studies and clinical applications. We first introduce state-of-the-art OSPI techniques, including fluorescence, surface-enhanced Raman scattering, electrochemiluminescence, and dark-field scattering, with emphasis on the contributions of various metal and nonmetal nano-labels to the improvement of the signal-to-noise ratio. During the discussion of individual techniques, we also highlight their applications in spatial-temporal measurement of key biomarkers such as proteins, nucleic acids and extracellular vesicles with single-entity sensitivity. To that end, we discuss the current challenges and prospective trends of single-particle optical-imaging-based bioanalysis.

Synthesis and Structural Characterization of an Amorphous and Photoluminescent Mixed Eu/Zr Coordination Compound, a Potential Marker for Gunshot Residues

Hydrogels based on mixed zirconium/europium ions and benzene tricarboxylic acid were synthesized by hydrothermal reaction. A solid glass-like material is formed upon drying, showing strong reddish luminescence. The system was characterized by solid-state nuclear magnetic resonance, thermal analyses, and infrared spectroscopy. The results reveal the amorphous character of the structure and the presence of at least four types of binding modes between the metal oxide clusters and benzene tricarboxylic acid. On the other hand, thermogravimetric analysis (TGA) showed high thermal stability, with the material decomposing at temperatures higher than 500 °C. The combination of intense Eu3+ luminescence with large thermal stability makes this material a strong candidate for application as a luminescent red marker for gunshot residue (GSR). As proof of concept, we show the feasibility of this application by performing shooting tests using our compound as a GSR marker. After the shots, the residual luminescent particles could be visualized in the triggered cartridge, inner the muzzle of the firearm, and a lower amount on the hands of the shooter, using a UV lamp (λ = 254 nm). Remarkably, our results also show that the Eu3+ emission for the GSR is very similar to that observed for the original solid material. These characteristics are of huge importance since they provide a chance to use smaller amounts of the marker in the ammunition, lowering the costs of potential industrial manufacturing processes.

Controlled afterglow luminescent particles for photochemical tissue bonding

Upconversion materials (UCMs) have been developed to convert tissue-penetrating near-infrared (NIR) light into visible light. However, the low energy conversion efficiency of UCMs has limited their further biophotonic applications. Here, we developed controlled afterglow luminescent particles (ALPs) of ZnS:Ag,Co with strong and persistent green luminescence for photochemical tissue bonding (PTB). The co-doping of Ag+ and Co2+ ions into ZnS:Ag,Co particles with the proper vacancy formation of host ions resulted in high luminescence intensity and long-term afterglow. In addition, the ALPs of ZnS:Ag,Co could be recharged rapidly under short ultraviolet (UV) irradiation, which effectively activated rose bengal (RB) in hyaluronate-RB (HA-RB) conjugates for the crosslinking of dissected collagen layers without additional light irradiation. The remarkable PTB of ZnS:Ag,Co particles with HA-RB conjugates was confirmed by in vitro collagen fibrillogenesis assay, in vivo animal wound closure rate analysis, and in vivo tensile strength evaluation of incised skin tissues. Taken together, we could confirm the feasibility of controlled ALPs for various biophotonic applications.

Light emission of Zr-based bulk metallic glass during high-speed cutting: From generation mechanism to control strategies

Light emission is a unique machining feature during high-speed cutting of Zr-based bulk metallic glass (BMG), which significantly deteriorates the machining quality and efficiency. However, its generation mechanism is still unclear. In this study, the light emission of Zr-based BMG during high-speed cutting was quantified photometrically, and its correlation with cutting energy was investigated. The chemical composition change and the formation process of luminescent particles were analyzed. The generation mechanism of light emission was subsequently revealed. It was found that the light emission is due to the spontaneous ignition in air of Zr-based BMG particles with large specific surface area, produced by ductile tearing of the bottom of the chip. The friction energy of the tool-chip interface flowing into the chips is the dominant factor that triggers particle combustion. Therefore, from the perspective of controlling tool wear, machining strategies with controllable light emission were proposed. In order to suppress light emission, the primary method is to decrease the cutting speed and feed. The second is to improve the chip removal ability and the wear resistance of the tool. Cutting oil is only effective for suppressing light emission at low cutting speeds, while liquid nitrogen is not suitable for cutting Zr-based BMG due to increased tool wear. The findings of this work contribute to a deeper understanding of the generation mechanism of cutting features in glassy metals, and provide guidance for high-speed cutting process optimization of Zr-based BMG.

Modulation of inner filter effect between persistent luminescent particles and 2, 3-diaminophenazine for ratiometric fluorescent assay of ascorbic acid and ascorbate oxidase activity

Ascorbate oxidase (AAO) and ascorbic acid (AA) play an important role in delaying lives senescence and metabolism. In this study, a sensitive ratiometric fluorescence sensing system based on the inner filter effect (IFE) between persistent luminescent particles (PLPs) and 2, 3-diaminophenazine (DAP), was designed for the detection of AA and AAO activity. Wherein, PLPs emit blue fluorescence at 475 nm with an excitation wavelength of 370 nm. CoOOH nanosheets with oxidase-like activity can oxidize o-phenylenediamine (OPD) to produce 2, 3-diaminophenazine (DAP) with orange fluorescence at 558 nm. The generated DAP quenched the fluorescence of PLPs by an inner filter effect (IFE). When AA was introduced to the system, CoOOH nanosheets were destroyed and reduced to Co2+, thereby inhibiting the oxidization of OPD and effectively preserving the blue fluorescence of PLPs at 475 nm. Besides, AAO can catalyse AA to produce the oxided dehydroascorbic acid (DHA). The dissipative AA can recover orange fluorescence of DAP with weakening the blue fluorescence of PLPs. Therefore, a sensitive ratio fluorescence sensing strategy was established by using PLPs as the reference signal and DAP as a reported signal for the detection of AA and AAO activity. Under optimal conditions, the obtained linear ranges were 1–45 μM and 1–20 mU/mL, and detection limits were 0.2 μM and 0.25 mU/mL, respectively. Finally, this proposed ratiometric fluorescent analytical strategy was used to detect AA in real samples (lemon, orange, tomato), which exhibited satisfactory results comparing with commercial kit.

Luminescent Composite Carbon/SiO2 Structures: Synthesis and Applications.

Luminescent carbon nanostructures (CNSs) have attracted great interest from the scientific community due to their photoluminescent properties, structural features, low toxicity, and a great variety of possible applications. Unfortunately, a few problems hinder their further development. These include the difficulties of separating a mixture of nanostructures after synthesis and the dependence of their properties on the environment and the aggregate state. The application of a silica matrix to obtain luminescent composite particles minimizes these problems and improves optical properties, reduces photoluminescence quenching, and leads to wider applications. We describe two methods for the formation of silica composites containing CNSs: inclusion of CNSs into silica particles and their grafting onto the silica surface. Moreover, we present approaches to the synthesis of multifunctional particles. They combine the unique properties of silica and fluorescent CNSs, as well as magnetic, photosensitizing, and luminescent properties via the combination of functional nanoparticles such as iron oxide nanoparticles, titanium dioxide nanoparticles, quantum dots (QDs), and gold nanoclusters (AuNCs). Lastly, we discuss the advantages and challenges of these structures and their applications. The novelty of this review involves the detailed description of the approaches for the silica application as a matrix for the CNSs. This will support researchers in solving fundamental and applied problems of this type of carbon-based nanoobjects.

Brightness-enhanced electroluminescence driven by triboelectric nanogenerators through permittivity manipulation and impedance matching

Triboelectric nanogenerator-driven electroluminescence (TDEL) that can convert human kinetic energy into visible light has attracted extensive attention in wearable electronics. However, the brightness is usually low due to the low electric field strength on the phosphors caused by impedance mismatch. In this work, a TDEL system with optimal brightness has been proposed by adjusting the dielectric constant of nanocomposite and matching impedance. The circuit model of the TDEL system is established and the voltage of the EL layer is predicted through simulation with an error below 4.7%. Finite element simulation is used to simulate the optimal field strength of phosphors under the dual effects of voltage drop and polarization enhancement of the EL layer caused by the increase of dielectric constant of nanocomposites. When the volume ratio of ZnS:Cu is 40% and the dielectric constant of the composite increases from 12 to 22.8, the optimal brightness value increases by 172%. Finally, a patterned TDEL system driven by walking or running to realize night alarm and information exchange is demonstrated. This study opens the window to improve the brightness of TDEL system through permittivity manipulation and impedance matching, which applies to different types of TENG, luminescent particles, and dielectric nanocomposites.

Preparation and Luminescence Properties of PVDF/ZnS:Mn Flexible Thin-Film Sensors

Flexible luminescent thin-film sensors have attracted widespread attention for their potential applications in biomedical detection, structural health detection, and smart wear. In this work, PVDF/ZnS:Mn flexible luminescent thin-film sensors were fabricated using electro-assisted 3D-printing techniques. The interaction and influence of PVDF thin film and ZnS:Mn were studied. The mechanism through which the PVDF matrix and ZnS:Mn particles affects the luminescence of the flexible thin-film sensor were investigated. The results demonstrate that the ZnS:Mn luminescent particles in PVDF thin films can promote the formation of the β-phase in the PVDF thin films. The mechano-luminesce spectra of the PVDF/ZnS:Mn composite thin film is consistent with the photoluminescence spectra, both of which exhibit yellow light with a wavelength of 580 nm. Mn entering the ZnS lattice increases the number of effective luminescent centres. Because of the double piezoelectric field, when the Mn content of ZnS:Mn is 4 at.% and PVDF films contain 3 wt.% ZnS:Mn particles, the PVDF/ZnS:Mn flexible thin-film sensors demonstrate excellent mechano-luminescence performance.

Reusable and pH-Stable Luminescent Sensors for Highly Selective Detection of Phosphate.

Phosphate sensors have been actively studied owing to their importance in water environment monitoring because phosphate is one of the nutrients that result in algal blooms. As with other nutrients, seamless monitoring of phosphate is important for understanding and evaluating eutrophication. However, field-deployable phosphate sensors have not been well developed yet due to the chemical characteristics of phosphate. In this paper, we report on a luminescent coordination polymer particle (CPP) that can respond selectively and sensitively to a phosphate ion against other ions in an aquatic ecosystem. The CPPs with an average size of 88.1 ± 12.2 nm are embedded into membranes for reusable purpose. Due to the specific binding of phosphates to europium ions, the luminescence quenching behavior of CPPs embedded into membranes shows a linear relationship with phosphate concentrations (3–500 μM) and detection limit of 1.52 μM. Consistent luminescence signals were also observed during repeated measurements in the pH range of 3–10. Moreover, the practical application was confirmed by sensing phosphate in actual environmental samples such as tap water and lake water.

Polarized luminescence of MoS-=SUB=-2-=/SUB=- nanodots

The effect of temperature on the polarization of the luminescence of the colloidal system of MoS2 nanodots in n-methylpyrrolidone is studied under the condition of linearly polarized excitation. Nanodots are obtained by chemical exfoliation and dispersion of MoS2 microcrystals in a liquid medium under the action of ultrasound. The photoluminescence spectrum of the ensemble of MoS2 nanodots is significantly shifted towards shorter wavelengths with respect to the luminescence spectrum of bulk crystals, which is explained by the quantum-size effect in the electronic spectrum of MoS2 nanocrystals. It is shown that the temperature dependence of the anisotropy of the radiation of nanodots is described by the Levshin-Perrin equation, which takes into account the rotational diffusion of luminescent particles in the liquid matrix. The size of photoexcited nanodots in the framework of the Levshin-Perrin model turns out to be ≥ 1.5 nm and increases with increasing the emission wavelength. It is shown that the sizes of MoS2 nanodots obtained by analyzing the temperature dependence of the emission anisotropy are in satisfactory agreement with the data obtained by analyzing the quantum-size effect in the electronic spectrum of nanodots. Keywords: polarized luminescence, molybdenum disulfide, nanodots, colloidal systems.

Optical Properties and Applications of Crystalline Materials

Optical Properties and Applications of Crystalline Materials

Purcell enhancement of fluorescence from silicon-vacancy color centers in Mie-resonant luminescent diamond particles

Over the past two decades, nanosized diamond particles with various luminescent defects have found numerous applications in many areas from quantum technologies to medical science. The size and shape of diamond particles can affect drastically the luminescence of embedded color centers. Here we study diamond particles of 250–450 nm in size containing silicon-vacancy (SiV) centers. Using dark-field scattering spectroscopy, we found that fundamental Mie resonances are excited in the spectral range of interest. We then measured the fluorescence saturation curves under continuous excitation to estimate the effects of the excitation and Purcell factor enhancement on the luminescent properties of the studied particles. The results show that the saturation excitation intensity differs by several times for particles of different sizes which is well explained by the numerical model that takes into account both the Parcell factor enhancement and resonant excitation.

Prediction of Ln3+[formula omitted]4f energy levels in β-NaYF4:Ln3+ and understanding of absorption behaviors

In lanthanide ion (Ln)-doped luminescent systems, electron transfer between 4f−4f states in Ln3+ ions is critical for luminescing specific colors. Therefore, understanding the 4f orbital energy levels of Ln3+ ions is a prerequisite for elucidating the specific light absorption−emission process in luminescent particles and for designing superior luminescent materials. In this study, we first predict the ground energy states of Ln3+−4f (E(Ln3+−4f)) in hexagonal (β)-NaYF4:Ln3+ model system relative to the valence band maximum of the host material using first-principles density functional theory calculations. We obtain E(Ln3+−4f) values comparable to the empirical values and find that they are dependent on both the dopant and host material, which directly affect the optical absorption behaviors. Based on the absorption behaviors of the singly Ln3+-doped system, we discuss the mechanism by which lanthanide-codoped systems (e.g., β-NaYF4:Ln(1)3+,Ln(2)3+) react to incident near infrared light with respect to the dopant distribution. This study can serve as a guideline for designing efficient luminescent systems that absorb light in the desired energy range and finely tune the luminescence color of the systems.

Effects of Scattering of Luminescent Down-Shifting Particles Inside Ethylene-Vinyl Acetate Films on Reflection of Light

Silicon solar cells are suffering from a poor spectral response in short wavelength ranges due to the loss of higher energy photons. The luminescent down-shifting (LDS) materials have the ability to convert shorter wavelength photons into longer wavelength photons and improve the performance of the solar cells. However, besides the down-shifting effects, the introduction of LDS particles into ethylene-vinyl acetate (EVA) films on the solar cells also increases surface reflection, which will negatively influence the performance of the solar cells. In this study, the influence of the size of LDS particles inside EVA films on reflection is investigated theoretically. The results showed that the reflection results from the scattering by LDS particles, which depends on the particle’s size. The total reflection caused by LDS particles can be calculated according to the size distribution of LDS particles. This study is helpful in selecting LDS particles that can be applied to solar cells.

Lanthanide-Doped Luminescent Nanophosphors via Ionic Liquids.

Lanthanide (Ln3+) ion(s)-doped or rare-earth ion(s)-doped nanomaterials have been considered a very important class of nanophosphors for various photonic and biophotonic applications. Unlike semiconductors and organic-based luminescent particles, the optical properties of Ln3+-doped nanophosphors are independent of the size of the nanoparticles. However, by varying the crystal phase, morphology, and lattice strain of the host materials along with making core-shell structure, the relaxation dynamics of dopant Ln3+ ions can be effectively tuned. Interestingly, a judicious choice of dopant ions leads to unparallel photophysical dynamics, such as quantum cutting, upconversion, and energy transfer. Recently, ionic liquids (ILs) have drawn tremendous attention in the field of nanomaterials synthesis due to their unique properties like negligible vapor pressure, nonflammability, and, most importantly, tunability; thus, they are often called “green” and “designer” solvents. This review article provides a critical overview of the latest developments in the ILs-assisted synthesis of rare-earth-doped nanomaterials and their subsequent photonic/biophotonic applications, such as energy-efficient lighting and solar cell applications, photodynamic therapy, and in vivo and in vitro bioimaging. This article will emphasize how luminescence dynamics of dopant rare-earth ions can be tuned by changing the basic properties of the host materials like crystal phase, morphology, and lattice strain, which can be eventually tuned by various properties of ILs such as cation/anion combination, alkyl chain length, and viscosity. Last but not least, different aspects of ILs like their ability to act as templating agents, solvents, and reaction partners and sometimes their “three-in-one” use in nanomaterials synthesis are highlighted along with various photoluminescence mechanisms of Ln3+ ion like up- and downconversion (UC and DC).

Preparation of glass-based composites with green upconversion and persistent luminescence using modified direct doping method

New oxyfluorophosphate glass-based composites which exhibit not only green upconversion under 980 nm pumping but also green persistent luminescence (PeL) after being UV charged were successfully prepared using the direct doping method. The composites are composed of a glass-ceramic with Er3+ doped CaF2 crystals and of the persistent luminescent particles with the SrAl2O4:Eu,Dy composition. In the standard direct doping method, the glass melt is quenched few minutes after adding the PeL particles in the melt held at a temperature lower than the melting temperature. It is demonstrated that the direct doping method should be modified when preparing oxyfluoride glasses with PeL particles to limit not only the decomposition of the PeL particles in the glass but also the fluorine evaporation occurring during the glass preparation. Here, the composites were prepared by quenching the melt right after adding the PeL particles. The modified direct doping method allows the preparation of glass-based composites with strong green upconversion and homogeneous green persistent luminescence.