Emission Of Nanoparticles Research Articles

Off-Angle Amplified Spontaneous Emission of Upconversion Nanoparticles by Propagating Lattice Plasmons.

Lanthanide-doped upconversion nanoparticles (UCNPs) are appealing for light emitting applications because their high internal conversion efficiency facilitates the amplified spontaneous emission (ASE) under low pumping. In addition, the integration of photonic crystals and microcavities with optical quantum emitters provides a unique opportunity to manipulate their light emissions and generate coherent light sources for quantum photonics. Here, this work describes a two-dimensional (2D) plasmonic lattice of Al nanocone array (Al NCA), which can confine the light at the tip. Light confinement by the enhancement effect supports narrow linewidth resonances as optical feedback for the ASE of UCNPs doped with sensitizer Yb3+ ions/emitter Ho3+ ions/relaxator Ce3+ ions. An off-angle ASE with an enhancement of 19-fold from UCNPs is achieved by propagating lattice plasmons from the Al NCA. Moreover, this upconverting ASE can be switched on or off by adjusting the polarization state of the incident pump light, and photonic band engineering can be used to manipulate it intentionally. This composite plasmonic system opens prospective applications for the ASE as directional emission, real-time tunable wavelengths, controlled multimode lasing, and optical switches.

Multiplexed detection of SARS-CoV-2 based on upconversion luminescence nanoprobe/MXene biosensing platform for COVID-19 point-of-care diagnostics

Multiplexed detection is essential in biomedical sciences since it is more efficient and accurate than single-analyte detection. For an accurate early diagnosis of COVID-19, a multiplexed detection strategy is required to avoid false negatives with the existing gold standard assay. Nb2CTx nanosheets were found to efficiently quench the fluorescence emission of lanthanide-doped upconversion luminescence nanoparticles at wavelengths ranging from visible to near-infrared spectrum. Using this broad-spectrum quencher, we developed a label-free FRET-based biosensor for rapid and accurate detection of SARS-CoV-2 RNA. To target ORF and N genes, two types of oligo-modified lanthanide-doped upconversion nanoparticles can be used simultaneously to identify-two sites in one assay via upconversion fluorescence enhancement intensity measurement with detection limits of 15 pM and 914 pM, respectively. Moreover, with multisite cross-validation, this multiplexed and sensitive biosensor is capable of simultaneous and multicolor analysis of two gene fragments of SARS-CoV-2 Omicron variant within minutes in a single homogeneous solution, which significantly improves the detection efficiency. The diagnosis result via our assay is consistent with the PCR result, demonstrating its application in the rapid and accurate screening of multiple genes of SARS-CoV-2 and other infectious diseases.

(Digital Presentation) Tailored Rare Earth-Doped Nanomaterials Toward Information Storage and Deep Learning Decoding

Lanthanide-doped nanoparticles have been considered as one of the most promising luminescent materials due to their excellent properties such as high photochemical stability, long-lived (μs-ms) luminescence, narrow emission band, and low toxicity.Moreover, benefiting from a unique electronic structure (4fn5s25p6 , n = 0-14), lanthanides have discrete energy levels and exhibit practical wavelength conversion via downshifting and upconversion processes. Hence, their emissions cover the spectral regions from ultraviolet (UV) to near-infrared (NIR).[1,2] Here, my talk is mainly devoted to our recent developments, including (1) recently, we present a new composition of Er3+-based upconversion nanoparticles with color-switchable output under irradiation with 980, 808, or 1535 nm light for information security. The variation of excitation wavelengths changes the intensity ratio of visible (Vis)/near-infrared 1535 nm (NIR-II) emissions. Taking advantage of the Vis/NIR-II multi-modal emissions of upconversion nanoparticles and deep learning, we successfully demonstrated the storage and decoding of visible light information in pork tissue.[3] (2) we construct heterostructured nanocomposites based on upconversion nanoparticles and EuSe semiconductors by using cation exchange method. It is generally considered that epitaxial growth is difficult when the lattice mismatch is large between two materials. In this case, the cation exchange of Eu3+ ions and other rare-earth ions could promote the formation of buffer layers to reduce the lattice mismatch and promote the heterogeneous epitaxial growth of EuSe on the upconversion nanoparticles. The heterostructured nanocomposites can emit tunable multicolor fluorescence under excitation of UV, continuous NIR, and pulsed NIR light. Based on the advantage of multiple tunable luminescence, the nanocomposites are designed as optical modules to load optical information. This work enables multi-dimensional storage of information and provides new insights into the design and fabrication of next-generation storage materials.

Absolute Counting Method with Multiplexing Capability for Estimating the Number Concentration of Nanoparticles Using Anisotropically Collapsed Gels.

Number concentration─the number of nanoparticles in a given volume─is an important characteristic of any nanoparticle dispersion. However, its estimation for small nanoparticles (∼30 nm) is generally challenging. We introduce an absolute and widely applicable method for analyzing aqueous dispersions of nanoparticles. An innovative immobilization of nanomaterials in the anisotropically collapsed agarose gel is pioneered, followed by optical microscopy and nanoparticle counting. The number of counted nanoparticles is inherently coupled with sampled volume (517 pL) and translates to the number concentration. Photon-upconversion, fluorescence, bright-field, and dark-field microscopy techniques have been proven applicable and used for imaging lanthanide-doped photon-upconversion nanoparticles, their bioconjugates with antibodies, silica dye-doped fluorescent nanoparticles, quantum dots, and pure silica submicron particles. The precision and linearity were characterized by constructing a dilution series of photon-upconversion nanoparticles. The limit of detection was 2.0 × 106 mL-1, and the working range was from 4.4 × 107 to 2.2 × 1010 mL-1. The quantification of nanoparticle clusters was achieved by a thorough analysis of the micrographs. The accuracy was confirmed using gravimetric analysis and transmission electron microscopy as a reference. Multiplexed detection of two nanoparticle types in a mixed dispersion was feasibly demonstrated. The low thickness of the collapsed gel (<1 μm) supported extremely sensitive imaging. This was proven by imaging Tm3+-doped photon-upconversion nanoparticles (17 nm hydrodynamic diameter) with a nanoparticle emission rate of only ∼900 photons/s at a wavelength of 800 nm (excitation wavelength 976 nm).

Bioaccumulation of silver nanoparticles in marine copepod Tigriopus japonicus under waterborne and dietary exposure

At present, the emission of silver nanoparticles (AgNPs) will affect a variety of aquatic organisms. AgNPs may be transferred to the food web through the bioaccumulation or biomagnification of the food chain, which is harmful to at higher trophic level organisms, and even threatens human health. Therefore, in this study, we tested the acute toxicity effect of AgNPs to marine copepod Tigriopus japonicus, and analyzed the Ag bioaccumulation in T. japonicus under short-term waterborne (exposure of AgNPs to T. japonicus) and dietary exposure (AgNP-accumulated algae cells of Isochrysis galbana are used to feed T. japonicus). The results showed that, after 48 h exposure, significant effects of AgNPs on the mortalities were observed (LC50=6.330 mg·L−1). The bioaccumulation of Ag by T. japonicus under different exposure modes was positively correlated with exposure concentration and time, and the bioaccumulation level under waterborne exposure was significantly higher. The biomagnification of T. japonicus was not observed under 24 h dietary exposure of different AgNP concentrations (BMFs<1), but the transfer efficiency was higher under low exposure concentration (BMFlow concentration>BMFhigh concentration). This study is helpful to understand the toxicity mechanism and effect of AgNPs on aquatic organisms.

Clustering-Triggered Emission of EPS-605 Nanoparticles and Their Application in Biosensing.

Natural carbohydrates with intrinsic luminescent properties have drawn increasing attention thanks to their fundamental importance and promising applications. To expand the range of natural nonconventional biomacromolecule luminogens and to gain deep insights into their emission mechanism, we prepared EPS-605, a naturally occurring spherical nanoparticle based on negatively charged exopolysaccharides (EPS), and studied its emission behavior. It was found that EPS-605 was highly emissive in the aggregate state, such as powder and film. Furthermore, EPS-605 aqueous solutions exhibited concentration-enhanced emission characteristics. According to fluorescence spectra and confocal images, the fluorescence phenomenon of EPS-605 was not affected by the pH value and the carbon sources. The emission behavior of EPS-605 was attributed to the clustering-triggered emission (CTE) mechanism. Moreover, EPS-605 was successfully utilized for Fe3+ detection since its fluorescence could be selectively quenched by Fe3+. It could be used to detect Fe3+ with a low limit of detection (0.06 μM) and a wide detection range from 0.05 to 250 μM. Overall, these findings not only benefit the exploitation of EPS-based nonconventional biomacromolecule luminogens, but also reveal the potential applications of EPS-605 in biosensing/bioimaging, anticounterfeiting, and encryption owing to its excellent biocompatibility, environmental friendliness, and intrinsic photoluminescence property.

Slow thermal decomposition of lignocelluloses compared to numerical model: Fine particle emission, gaseous products analysis

This paper is focused on aerosol fine particle release during the thermal decomposition of beech wood samples with identical mass under an oxidizing and inert atmosphere. This thermal degradation of wood is a significant part of the biomass combustion and pyrolytic process. This contribution focuses on nanoparticles emission with specifying sizes and concentrations in the range of 18–545 nm during thermal degradation processes and determining correlations between individual thermal degradation processes of a wood sample with the same weights but with different heating rates. The flue gases' chemical composition was simultaneously analyzed using a quadrupole mass spectrometer during the thermal degradation process. The weight loss of the sample and its derivation were monitored using a thermogravimeter. This combination made it possible to identify the ranges with the highest particle emission concerning the wood sample and the sample's heating rate. The fine particle identification apparatus uses a Scanning Mobility Particle Sizer and a condensation particle counter. This experimentally obtained data were then compared with the numerical model CPD-Bio. In this case, the comparison was focused on the prediction of the temperatures of the individual pyrolysis stages, at which gaseous products and especially tars are formed.

Cellular and molecular mechanisms of NiONPs toxicity on eel hepatocytes HEPA-E1: An illustration of the impact of Ni release from mining activity in New Caledonia.

Anthropic activities such as open pit mining, amplify the natural erosion of metals contained in the soils, particularly in New Caledonia, leading to atmospheric emission of nickel oxide nanoparticles (NiONPs). These particles are produced during extraction end up in aquatic ecosystems through deposition or leaching in the rivers. Despite alarming freshwater Ni concentrations, only few studies have focused on the cellular and molecular mechanisms of NiONPs toxicity on aquatic organisms and particularly on eels. Those fish are known to be sensitive to metal contamination, especially their liver, which is a key organ for lipid metabolism, detoxification and reproduction. The objective of this study was to assess in vitro the cytotoxic effects of NiONPs on Anguilla japonica hepatocytes, HEPA-E1. HEPA-E1 were exposed to NiONPs (0.5-5μg/cm2) for 4 or 24h. Several endpoints were studied: (i) viability, (ii) ROS production, SOD activity and selected anti-oxidant genes expression, (iii) inflammation, (iv) calcium signalling, (v) mitochondrial function and (vi) apoptosis. The results evidenced that NiONPs induce a decrease of cell viability and an increase in oxidative stress with a significant superoxide anion production. An increase of mitochondrial calcium concentration and a decrease of mitochondrial membrane potential were observed, leading to apoptosis. These results underline the potential toxic impact of NiONPs on eels living in mining areas. Therefore, eel exposure to NiONPs can affect their migration and reproduction in New Caledonia.

Chitosan coated fluorescent mesoporous silica for the sensitive and selective detection of H2O2

A novel turn-on fluorescent sensor for hydrogen peroxide (H2O2) was prepared from chitosan (CS) coating mesoporous silica nanoparticles (MSNs) loaded with 1-(4-Aminophenyl)-1,2,2-triphenylethene (TPE-NH2) and silver nanoparticles (AgNCs). The surface of MSNs was coated by CS as the gatekeeper and the template for loading of AgNCs. Because of the surface plasmon-enhanced energy transfer (SPEET), AgNCs effectively quenched the fluorescence emission of nanoparticles. In the presence of H2O2, AgNCs can be oxidized to Ag+, resulting in the recovery of fluorescence. This fluorescent sensor was characterized with respect to its chemical composition, morphological features and optical properties by means of FTIR, XRD, TGA, SEM, TEM, XPS, UV–Vis and fluorescence spectroscopy. The MSN/TPE-CS@Ag nanoparticles showed good sensitivity and selectivity for H2O2 even with various interfering ions and agents. Under optimized conditions, the detection limit for H2O2 was 0.64 μM in the rage of 1–300 μM. The feasibility of the practical application of this probe was confirmed by accurate quantitative of H2O2 in practical samples.

Nucleation-accumulation mode trade-off in non-volatile particle emissions from a small non-road small diesel engine.

Small (< 8kW) non-road engines are a significant source of pollutants such as particle number (PN) emissions. Many small non-road engines do not have diesel particulate filters (DPFs). They are so designed that air-fuel ratio (AFR) can be adjusted to control visible diesel smoke and particulate matter (PM) resulting from larger accumulation mode particles. However, the effect of AFR variation on smaller nucleation mode nanoparticle emissions is not well understood. Several studies on larger engines have reported a trade-off between smaller and larger particles. In this study, AFR was independently varied over the entire engine map of a naturally aspirated (NA) non-road small diesel engine using forced induction (FI) of externally compressed air. AFR's ranged from 57 to 239 compared to the design range of 23-92 for the engine, including unusually high AFR's at full-load operation, not previously reported for conventional combustion. As expected, larger accumulation mode particles were lowered (up to 15 times) for FI operation. However, the smaller nucleation mode nanoparticles increased up to 15 times. Accumulation mode particles stopped decreasing above an AFR threshold while nucleation particles continuously increased. In-cylinder combustion analysis showed a slightly smaller ignition delay and higher burn rate for FI cases relative to NA operation. Much higher peak cylinder pressures were accompanied by much lower combustion and exhaust gas temperatures (EGT), due to higher in-cylinder mass during FI operation. Peak nucleation mode emissions were shown to be negatively correlated to EGT for all the data, collapsing on a single curve. This is consistent with some other studies reporting increased nucleation mode emissions (and higher accumulation mode particles) with decreased load, lower speed, lower EGR, advanced combustion phasing, and higher injection pressure, all of which reduce EGT. The nucleation-accumulation trade-off has been explained by the 'adsorption hypothesis' by some investigators. In the current work, an alternative/supplemental argument has been made for the possibility that lower cylinder temperatures during the late-burning phase (correlated to lower EGT) phase hampers oxidation of nucleation mode particles and increases nucleation mode emissions.

Radial distribution of the carbonaceous nano-grains in the protoplanetary disk around HD 169142

Context. HD 169142 is part of the class of (pre-)transitional protoplanetary disks showing multiple carbon nanodust spectroscopic signatures (aromatic, aliphatic) dominating the infrared spectrum. Precise constraints on the spatial distribution and properties of carbonaceous dust particles are essential to understanding the physics, radiative transfer processes, and chemistry of the disk. The HD 169142 disk is seen almost face-on and thus it offers a unique opportunity to study the dust radial evolution in disks. Aims. We investigate the spatial distribution of the carriers of several dust aromatic emission features of the disk across a broad spatial range (10–200 AU) as well as their properties. Methods. We analysed imaging and spectroscopic observations in the 8–12 µm range from the VLT Imager and Spectrometer for mid-Infrared (VISIR) at the Very Large Telescope (VLT), as well as adaptive optics spectroscopic observations in the 3–4 µm range from the Nasmyth Adaptive Optics System – Near-Infrared Imager and Spectrograph (NACO) at VLT. The data probe the spatial variation of the flux in the 3.3 µm, 8.6 µm, and 11.3 µm aromatic bands. To constrain the radial distribution of carbonaceous nano-grains, the observations were compared to model predictions using The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), which is integrated into the POLARIS radiative transfer code by calculating the thermal and stochastic heating of micro-and nanometer-sized dust grains for a given disk structure. Results. Our data show predominant nano-particle emission at all radii (accessible with our resolution of about 0.1″ or ~12 AU at 3 µm and ~0.3″, 35 AU at 10 µm) in the HD 169142 disk. This unambiguously shows that carbonaceous nano-grains dominate radiatively the infrared spectrum in most of the disk, a finding that has been suggested in previous studies. In order to account for both VISIR and NACO emission maps, we show the need for aromatic particles distributed within the disk from the outermost regions to a radius of 20 AU, corresponding to the outer limit of the inner cavity derived from previous observations. In the inner cavity, these aromatic particles might be present but their abundance would then be significantly decreased.

Influence of fuel injection pressure and RME on combustion, NOx emissions and soot nanoparticles characteristics in common-rail HSDI diesel engine

‏ Manipulating in fuel injection strategies and introduce renewable fuel in diesel engine can provide clean combustion and lower pollutant emissions. The effect of fuel injection pressures (FIPs) and RME on combustion characteristics, NOx emissions and soot nanoparticle emissions when rapeseed methyl esters was used have been investigated at 1500 rpm and two brake mean effective pressure of 2.5 and 5 bar. A calibrated electrostatic mobility spectrometer (EMS) was used to measure the soot nanoparticle number size distributions. The peak cylinder pressure and heat release rates were evaluated when the FIP increased for all fuels studied. The results showed that further advanced in combustion with RME, meanwhile a shorter ignition delay from the fuel was exhibited in comparison with diesel fuel combustion under various FIP. Furthermore, the values of BSFC decreased by 3.7% and 17.8% from the RME combustion at high and low engine load, respectively. The reduction in NOx emissions was obtained when FIP increased during RME combustion in comparison with ULSD under low engine load. In contrast, RME generated higher NOx by 7% and lower soot nanoparticles by 27% compared to the ULSD under high engine load. RME combustion produced lower nucleation particle numbers in comparison with those emitted from ULSD under all engine operating conditions as well as the accumulation mode particles was higher for ULSD.

Three-Pronged Attack by Hybrid Nanoplatform Involving MXenes, Upconversion Nanoparticle and Aggregation-Induced Emission Photosensitizer for Potent Cancer Theranostics.

Inspired by the excellent photothermal conversion ability and inherent nanomedicine platform property of MXenes, efficient reactive oxygen species production and prominent fluorescence emission feature of aggregation-induced emission (AIE)-active photosensitizers (PSs), as well as the extending excitation wavelength capability of upconversion nanoparticles (UCNPs), a versatile nanoplatform comprised of Ti3 C2 nanosheets (NSs), AIE-active PSs and UCNPs is intelligently fabricated. This three-pronged strategy takes advantages of each component simultaneously, and realizes fluorescence imaging/photoacoustic imaging/photothermal imaging triple-modal imaging-guided photothermal/photodynamic synergetic therapy under 808nm laser irradiation. The introduction of UCNPs actualizes the long wavelength-activation of AIE-active PSs, which significantly increases the tissue penetration depth. Spatially isolation of AIE-active PSs and Ti3 C2 NSs is beneficial for suppressing the fluorescence quenching effect of Ti3 C2 NSs, bringing about ultimately brilliant fluorescence. The covalently bonded polymer surface endows the nanoplatform with excellent physiological stability and efficient tumor accumulation. These outputs reveal a win-win cooperation of multiple inorganic/organic nanocomposites for phototheranostics, and present great potential for future clinical translations.

Aggregation-induced emission of active nanoparticles based on konjac glucomannan: Fabrication, properties, and applications

Recently, the design of aggregation-induced emission (AIE) materials with good water-solubility and biocompatibility has attracted much attention. In this work, amphiphilic AIE-active nanoparticles (KGM-TPE) were synthesized by a facile Schiff base condensation of oxidized konjac glucomannan with amino-tetraphenylethylene. The final KGM-TPE had good water dispersibility and could self-assemble into nanoparticles with average diameters ranging from 100 to 200 nm. A cytotoxicity test showed that the cell survival was approximately 90% even when the concentration of KGM-TPE reached 150 μg/mL, indicating that KGM-TPE possessed good biocompatibility. In addition, the excellent cell imaging and good anti-counterfeiting function results of KGM-TPE indicated that this material has great potential in the fields of biomedicine and anti-counterfeiting.

Generalized coupled dipole method for thermal far-field radiation

We introduce a many-body theory for thermal far-field emission of dipolar dielectric and metallic nanoparticles in the vicinity of a substrate within the framework of fluctuational electrodynamics. Our theoretical model includes the possibility to define the temperatures of each nanoparticle, the substrate temperature, and the temperature of the background thermal radiation, separately. To demonstrate the versatility of our method, we apply it in an exemplary way by discussing the thermal radiation of four particle assemblies of SiC and Ag nanoparticles above a planar SiC and Ag substrate. Furthermore, we use discrete dipole approximation to determine the thermal emission of a spherical nanoparticle in free space and close to a substrate. Finally, the calculation of the thermal far-field radiation of a sharp Si tip close to a SiC substrate using the discrete dipole approximation including the near-field scattering by the tip as well as the thermal emission of the tip and the contribution of the substrate which is partially blocked by the tip serves as another example.

Vast emission of Fe- and Ti-containing nanoparticles from representative coal-fired power plants in China and environmental implications

Coal combustion is considered an important source of atmospheric nanoparticles (NPs). However, the underlying information on the emission of NPs from coal-fired power plants (CFPPs) is still lacking. Along these lines, in this study, coal fly ashes (CFAs) were collected from different multi-stage particulate emission control devices (PECDs) in three representative CFPPs in China. The particle size and particle number concentration (PNC) of typical metal-containing NPs (Fe- and Ti-containing NPs) were analyzed by using the single-particle inductively coupled plasma mass (SP-ICP-MS) technology. By increasing the stage of PECDs, the mean particle sizes of NPs gradually declined and the PNCs of Fe- and Ti-containing NPs increased significantly. Specifically, the PNC of final-stage CFA was 3 - 8 times that of the first-stage CFA. A comparison of the electrostatic precipitators (ESPs), fabric filters (FFs), and electrostatic-fabric-integrated precipitators (EFIPs) showed that the state-of-the-art EFIPs exhibited a relatively good NP-removal efficiency with the highest PNCs. In addition, NP hourly emissions in all coal combustion by-products (CCPs) were further calculated in a typical CFPP. The total emissions of Fe- and Ti-containing NPs in all CCPs were 1.87 × 1018 and 1.57 × 1018 particles/h, respectively. NPs were mainly enriched in CFA trapped by PECDs (80% of total emissions). Although the mass of the CFA that escaped through the stack was extremely low, it contained the highest PNCs of Fe- and Ti-containing NPs of all CCPs, accounting for 3.41% and 1.67% of the corresponding total NP emissions. These NPs may also coexist with various toxic metals, such as Zn and Pb, and be released directly into the atmosphere, where they pose a potential risk to human health.

Emission of nanoparticles from coal and diesel fired power plants on Svalbard: An electron microscopy study

Sub-micrometer aerosol particles were collected at the stack of two coal power plants (Barentsburg, Longyearbyen), two diesel power plants (Pyramiden, Sveagruva) and one small-scale coal-burning boiler (Pyramiden) on the Arctic archipelago of Svalbard (Norway). Primary particles (n = 5752) in the size range of 100–1000 nm were investigated by operator-controlled high-resolution scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX). Based on morphology and chemical composition primary particles were assigned to one of the following groups: soot, carbonaceous, fly ash spheres, Hg-containing particles, and mineral particles. Soot is the dominating particle group in most samples with a relative number abundance between 69 and 98%. Two coal burning samples have significantly lower soot contents of about 12 and 31%. The relative number abundance of the other particle groups is highly variable.The chemical composition of soot, fly ash spheres and mineral particles was studied in more detail. Soot particles from coal burning are significantly enriched in the elements S, Na, and K compared to diesel soot. The P contents of soot, fly ash spheres, and mineral particles reflect the variable concentration of this element in the different coal seams. Fly ash spheres from coal burning consist of a Si-rich component (quartz or silica glass), alumosilicates or alumosilicate glass, Fe oxides and a Fe, Ca, Al component (most likely a mechanical mixture of spinel and gypsum or lime). Fly ash spheres from diesel burning have a similar composition except that the Fe, Ca, Al component does not occur. Mineral particles from coal burning may be divided into Si-rich (quartz or silica glass), Pb-rich, Fe oxides, alumosilicates or alumosilicate glass and Na-rich particles (most likely a mechanical mixture of Si-rich particles with aged sea salt). The relative number abundance of these subgroups of mineral particles is highly variable. Mineral particles are rare in diesel burning, and seem to be mostly Fe oxides.The observed differences in minor element contents can be used in source apportionment studies for discrimination of individual soot particles as well as fly ash spheres from coal and diesel burning. The highly variable abundance of soot and of mineral particles (especially those consisting predominantly of toxic metals as for example Pb) should be taken into account in exposure assessment.

Tailoring of polychromatic emissions in Tb3+/Eu3+ codoped NaYbF4 nanoparticles via energy transfer strategy for white light-emitting diodes

The polychromatic emission and wide-range color tuning in the luminescent nanoparticles are currently of crucial importance, due to the development of color and white light-emitting diode (LED) devices, based on such lanthanide-doped nanostructured materials. By utilization of precipitation method, Tb3+-doped and Tb3+/Eu3+-codoped NaYbF4 nanoparticles (i.e. NPs) are synthesized. For Tb3+-doped NaYbF4 NPs excited by 377 nm, green emission originating from Tb3+ is observed, where its optimum state is obtained when Tb3+ content is 25 mol% and the concentration quenching mechanism is found by electric dipole-dipole interaction. Moreover, due to the existence of energy transfer between Tb3+ and Eu3+, polychromatic emissions are realized in Tb3+/Eu3+-codoped NaYbF4 NPs as Eu3+ content increases. Through analyzing emission decay times and emission spectra, it was confirmed that the energy transfer mechanism in the synthesized NPs is governed mainly by electric dipole-dipole interaction. Furthermore, the resultant NPs also own strong resistance to temperature, which is verified by temperature-dependent emission spectra, and the activation energies of Tb3+ and Eu3+ are 0.206 and 0.207 eV, respectively. In addition, by employing designed NPs as yellow-emitting components, the fabricated white-LED emits brightness warm white light with color coordinate of (0.385, 0.380), high color rendering index of 84.3 and low correlated color temperature of 3903 K. This work does not only offer an available route to develop NPs with polychromatic emissions but also devise promising luminescent materials for improving the performance of the phosphor-converted white-LED.

Health and safety in 3D printing

Fused deposition modelling, or 3D printing, is an additive manufacturing technique that is quickly gaining popularity because of its ability to produce usable parts with several geometries. It provides multiple advantages in everyday life. However, the emerging risks of using 3D printers at home is an issue that needs to be addressed. It is estimated that a person spends, on average, 80-90% of their time inside a building, up to 60% of that time is at home. Therefore it is essential to control the pollutants in the indoor environment. This paper evaluated the Volatile Organic Compounds (VOCs) and nanoparticle emissions during 3D printing with the most common Poly-Lactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS) materials. Real-time aerosol monitors were used to characterise particulate emission, and laboratory analysis was used to check the VOCs levels. During printing, an increase of VOCs and nanoparticles was observed. This increase was more significant during printing with ABS filaments than during printing with PLA filaments. The nanoparticles size emitted for the ABS filament was smaller than the particles emitted for the PLA filament. A carcinogen substance like benzene was found during printing. The pollutants levels observed may cause health problems, and it is recommended that printing be avoided without engineering controls in place, e.g. a good ventilation and extraction system.

Sampling and characterization of particle emission from the 3D FDM printing

Fused deposition modeling (FDM) printers dominate the consumer market because of their low cost and high efficiency, resulting in an annual market growth rate of 40%. However, undesired emission of nanoparticles during the printing is accompanied, which can cause adverse health effects. It is very desirable to quantify these nanoparticles. However, the size and concentration (or size distribution) of these nanoparticles change dynamically due to ongoing nucleation, condensation and coagulation and these mechanisms are sensitively affected by printing and environmental conditions. An accurate size distribution of the emitted nanoparticles can only be obtained by a rigorous experimental design. This study designed a sampler to reduce the influences from sampling and environmental conditions and to help accurately characterize the instantaneous emitted nanoparticles. Using the sampler, the emissions from six different filaments, including an original poly-lactic acid (PLA-O), a carbon-fiber-filled PLA (PLA-C), an iron-additive PLA (PLA-Fe), an original white acrylonitrile butadiene styrene (ABS-W), a florescent ABS (ABS-F) and a glow-in-dark ABS (ABS-G) filament were characterized and compared. The results showed that the sampler method detected the particle emissions earlier than traditional methods, which had a majority size less than 20 nm. The ABS-W had the highest emission rate of 4.3 × 1010 #/g which was about one order of magnitude higher than that of ABS-F, ABS-G and PLA-Fe (∼109 #/g) and three orders of magnitude higher than PLA-O and PLA-C filaments (∼107 #/g). A new metric, dynamic emission index (DEI), was proposed to characterize the dynamic changes of emitted nanoparticles during the printing. With the DEI, one can clearly identify the emission intensity for different sizes of particles along the printing time for different filaments and take required precautions if needed.