Facile and Chemically Pure Preparation of YVO4:Eu(3+) Colloid with Novel Nanostructure via Laser Ablation in Water

Tuning morphology, surface, and nanocrystallinity of rare earth vanadates by one-pot colloidal conversion of hydroxycarbonates

We show that particle size, morphology, nanocrystallinity, surface area, and defect density of (Y,Eu)VO₄ structures can be tuned by one-pot colloidal conversion of rare earth hydroxycarbonates in water/ethylene glycol (EG) suspensions. Using small angle X-ray scattering, transmission electron microscopy and dynamic light scattering, we show how volume fractions of EG direct the amorphous to crystalline conversion at 1 atm/95 °C by controlling size and aggregation of hydroxycarbonate precursors. A template effect due to a Kirkendall-type conversion occurs for low EG contents, yielding solids with high densities of oxygen defects, as demonstrated by O₂ uptakes in thermogravimetry and X-ray photoelectron spectroscopy profiles. Starting from small and aggregated hydroxycarbonates high-porosity (Y,Eu)VO₄ nanoparticles were produced with expanded unit cells and short-range (<100 Å) crystalline ordering. We explored the effects of synthesis on the textural, microstructure, and defects of (Y,Eu)VO₄ solids, which were further correlated to the spectroscopic profiles of Eu³⁺-activated samples. We show that the ratios between Eu^{3+ 5}D₀ internal quantum yields and particle diameters can be directly correlated to the particle surface areas, opening new perspectives for theoretical detailing of f-f luminescence in YVO₄ solids, and enabling accurate tuning of structure and applicability of colloidal vanadate nanoparticles for sensing and catalysis applications.

In situ immobilization of YVO4:Eu phosphor particles on a film of vertically oriented Y2(OH)5Cl·nH2O nanosheets

A heterostructured photoluminescence 'turn-off' film was developed using vertically oriented LYH:Eu nanosheets as a partial sacrificial layer for isolated YVO₄:Eu³⁺ nanophosphor layers and was used for the convenient detection and removal of Cu²⁺ ions with excellent sensitivity and recyclability.

Manipulation of the Size and Phase Composition of Yttrium Iron Garnet Nanoparticles by Pulsed Laser Post-Processing in Liquid

Modification of the size and phase composition of magnetic oxide nanomaterials dispersed in liquids by laser synthesis and processing of colloids has high implications for applications in biomedicine, catalysis and for nanoparticle-polymer composites. Controlling these properties for ternary oxides, however, is challenging with typical additives like salts and ligands and can lead to unwanted byproducts and various phases. In our study, we demonstrate how additive-free pulsed laser post-processing (LPP) of colloidal yttrium iron oxide nanoparticles using high repetition rates and power at 355 nm laser wavelength can be used for phase transformation and phase purification of the garnet structure by variation of the laser fluence as well as the applied energy dose. Furthermore, LPP allows particle size modification between 5 nm (ps laser) and 20 nm (ns laser) and significant increase of the monodispersity. Resulting colloidal nanoparticles are investigated regarding their size, structure and temperature-dependent magnetic properties.

Synthesis and Research of Rare Earth Nanocrystal Luminescent Properties for Security Labels Using the Electrohydrodynamic Printing Technique

YVO4:Eu3+ nanoparticles were successfully synthesized by two methods, namely the sonochemical method and hydrothermal method. The X-ray diffraction (XRD) patterns showed the tetragonal phase of YVO4 (JCPDS 17-0341) was indexed in the diffraction peaks of all samples. The samples synthesized by the sonochemical method had a highly crystalline structure (X-ray diffraction results) and luminescence intensity (photoluminescence results) than those synthesized by the hydrothermal method. According to the results of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), the average size of YVO4:Eu3+ nanoparticles was around 25–30 nm for the sonochemical method and 15–20 nm for the hydrothermal method. YVO4:Eu3+ nanoparticles in the case of the sonochemical method had a better crystalline structure and stronger emissivity at 618 nm. The Eu3+ ions’ average lifetime in YVO4:Eu3+ at 618 nm emission under 275 nm excitation were at 0.955 ms for the sonochemical method and 0.723 ms for the hydrothermal method. The security ink for inkjet devices contained YVO4:Eu3+ nanoparticles, the binding agent as polyethylene oxide or ethyl cellulose and other necessary solvents. The device used for security label printing was an inkjet printer with an electrohydrodynamic printing technique (EHD). In the 3D optical profilometer results, the width of the printed line was ~97–167 µm and the thickness at ~9.1–9.6 µm. The printed security label obtained a well-marked shape, with a size at 1.98 × 1.98 mm.

Laser-Ablative Synthesis of Isotope-Enriched Samarium Oxide Nanoparticles for Nuclear Nanomedicine

Nuclear nanomedicine is an emerging field, which utilizes nanoformulations of nuclear agents to increase their local concentration at targeted sites for a more effective nuclear therapy at a considerably reduced radiation dosage. This field needs the development of methods for controlled fabrication of nuclear agents carrying nanoparticles with low polydispersity and with high colloidal stability in aqueous dispersions. In this paper, we apply methods of femtosecond (fs) laser ablation in deionized water to fabricate stable aqueous dispersion of ¹⁵²Sm-enriched samarium oxide nanoparticles (NPs), which can capture neutrons to become ¹⁵³Sm beta-emitters for nuclear therapy. We show that direct ablation of a ¹⁵²Sm-enriched samarium oxide target leads to widely size- and shape-dispersed populations of NPs with low colloidal stability. However, by applying a second fs laser fragmentation step to the dispersion of initially formed colloids, we achieve full homogenization of NPs size characteristics, while keeping the same composition. We also demonstrate the possibility for wide-range tuning of the mean size of Sm-based NPs by varying laser energy during the ablation or fragmentation step. The final product presents dispersed solutions of samarium oxide NPs with relatively narrow size distribution, having spherical shape, a controlled mean size between 7 and 70 nm and high colloidal stability. The formed NPs can also be of importance for catalytic and biomedical applications.

Sonochemical Synthesis and Properties of YVO4:Eu3+ Nanocrystals for Luminescent Security Ink Applications

Solutions and redispersible powders of nanocrystalline, europium-doped YVO4, are prepared via a wet chemical method using the ultrasonic processor (sonochemical) and microwave and thermal stirring. From X-ray diffraction (XRD) results, YVO4:Eu3+ nanoparticles synthesized using sonochemical method have better crystallinity than those prepared using thermal stirring and microwave methods exhibiting the tetragonal structure known for bulk material. From field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results, it is found that the size of nanoparticles is around 25 nm and increasing after annealing at 900°C. From UV-Vis result, there is a peak at 270 nm corresponding to the absorption of VO43− groups. The photoluminescence (PL) results clearly show the strongest red emission peak at the wavelength around 618 nm. The highest luminescent intensity is obtained for the sample prepared by the sonochemical method at pH = 12 and annealing temperature at 900°C for 4 h. The average lifetimes of the Eu3+ ions in the samples annealed at 300, 600, and 900°C for 1 h at 618 nm emission under 275 nm excitation are 0.36, 0.62, and 0.64 ms, whereas sample annealed at 900°C for 4 h has lifetime of 0.70 ms. The security ink, containing synthesized YVO4:Eu3+ nanoparticles, is dispersed in glycerol and other necessary solvents. The experimental security labels are printed by inkjet using the electrohydrodynamic printing technique. The resulting lines represented to the security labels are analyzed by the 3D microscope equipment and UV 20 W mercury lamp with a wavelength of ∼254 nm. The seamless line of the printed security label has the value of the width at ∼230 μm, thickness at ∼0.68 μm, and distance between two adjacent lines at 800 μm. This result is compatible for producing security labels in small size (millimeter) in order to increase security property.

Spontaneous Shape Alteration and Size Separation of Surfactant-Free Silver Particles Synthesized by Laser Ablation in Acetone during Long-Period Storage

The technique of laser ablation in liquids (LAL) has already demonstrated its flexibility and capability for the synthesis of a large variety of surfactant-free nanomaterials with a high purity. However, high purity can cause trouble for nanomaterial synthesis, because active high-purity particles can spontaneously grow into different nanocrystals, which makes it difficult to accurately tailor the size and shape of the synthesized nanomaterials. Therefore, a series of questions arise with regards to whether particle growth occurs during colloid storage, how large the particle size increases to, and into which shape the particles evolve. To obtain answers to these questions, here, Ag particles that are synthesized by femtosecond (fs) laser ablation of Ag in acetone are used as precursors to witness the spontaneous growth behavior of the LAL-generated surfactant-free Ag dots (2–10 nm) into different polygonal particles (5–50 nm), and the spontaneous size separation phenomenon by the carbon-encapsulation induced precipitation of large particles, after six months of colloid storage. The colloids obtained by LAL at a higher power (600 mW) possess a greater ability and higher efficiency to yield colloids with sizes of <40 nm than the colloids obtained at lower power (300 mW), because of the generation of a larger amount of carbon ‘captors’ by the decomposition of acetone and the stronger particle fragmentation. Both the size increase and the shape alteration lead to a redshift of the surface plasmon resonance (SPR) band of the Ag colloid from 404 nm to 414 nm, after storage. The Fourier transform infrared spectroscopy (FTIR) analysis shows that the Ag particles are conjugated with COO– and OH– groups, both of which may lead to the growth of polygonal particles. The CO and CO₂ molecules are adsorbed on the particle surfaces to form Ag(CO)_x and Ag(CO₂)_x complexes. Complementary nanosecond LAL experiments confirmed that the particle growth was inherent to LAL in acetone, and independent of pulse duration, although some differences in the final particle sizes were observed. The nanosecond-LAL yields monomodal colloids, whereas the size-separated, initially bimodal colloids from the fs-LAL provide a higher fraction of very small particles that are <5 nm. The spontaneous growth of the LAL-generated metallic particles presented in this work should arouse the special attention of academia, especially regarding the detailed discussion on how long the colloids can be preserved for particle characterization and applications, without causing a mismatch between the colloid properties and their performance. The spontaneous size separation phenomenon may help researchers to realize a more reproducible synthesis for small metallic colloids, without concern for the generation of large particles.

Photonic structuring improves the colour purity of rare-earth nanophosphors

Nanophosphor integration in an optical cavity allows unprecedented control over both the chromaticity and the directionality of the emitted light, without modifying the chemical composition of the emitters or compromising their efficiency. Our approach opens a route towards the development of nanoscale photonics based solid state lighting.

Combustion Synthesis Technology for a Sustainable Settlement Overnight

Space technology has been developed for frontier exploration not only in low-earth orbit environment but also beyond the earth orbit to the Moon and Mars, where material resources might be strongly restricted and almost impossible to be resupplied from the earth for distant and long-term missions performance toward “long-stays of humans in space”. For performing such long-term space explorations, none would be enough to develop technologies with resources only from the earth; it should be required to utilize resources on other places with different nature of the earth, i.e., in-situ resource utilization. One of important challenges of lunar in-situ resource utilization is thermal control of spacecraft on lunar surface for long-lunar durations. Such thermal control under “long-term field operation” would be solved by “thermal wadis” studied as a part of sustainable researches on overnight survivals such as lunar-night. The resources such as metal oxides that exist on planets or satellites could be refined, and utilized as a supply of heat energy, where combustion synthesis can stand as a hopeful technology for such requirements. The combustion synthesis technology is mainly characterized with generation of high-temperature, spontaneous propagation of reaction, rapid synthesis and high operability under various influences with centrifugal-force, low-gravity and high vacuum. These concepts, technologies and hardware would be applicable to both the Moon and Mars, and these capabilities might achieve the maximum benefits of in-situ resource utilization with the aid of combustion synthesis applications. The present paper mainly concerns the combustion synthesis technologies for sustainable lunar overnight survivals by focusing on “potential precursor synthesis and formation”, “in-situ resource utilization in extreme environments” and “exergy loss minimization with efficient energy conversion”.

Ultrasmall Yttrium Iron Garnet Nanoparticles with High Coercivity at Low Temperature Synthesized by Laser Ablation and Fragmentation of Pressed Powders

Pulsed laser ablation of pressed yttrium iron garnet powders in water is studied and compared to the ablation of a single-crystal target. We find that target porosity is a crucial factor, which has far-reaching implications on nanoparticle productivity. Although nanoparticle size distributions obtained by analytical disc centrifugation and transmission electron microscopy (TEM) are in agreement, X-ray diffraction and energy dispersive X-ray analysis show that only nanoparticles obtained from targets with densities close to that of a bulk target lead to comparable properties. Our findings also show why the gravimetrical measurement of nanoparticle productivity is often flawed and needs to be complemented by colloidal productivity measurements. The synthesized YIG nanoparticles are further reduced in size by laser fragmentation to obtain sizes smaller than 3 nm. Since the particle diameters are close to the YIG lattice constant, these ultrasmall nanoparticles reveal an immense change of the magnetic properties, exhibiting huge coercivity (0.11 T) and irreversibility fields (8 T) at low temperatures.

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials, thereby enabling the fabrication of bioconjugates and heterogeneous catalysts. Accurate size control of LSPC-synthesized materials ranging from quantum dots to submicrometer spheres and recent upscaling advancement toward the multiple-gram scale are helpful for extending the applicability of LSPC-synthesized nanomaterials to various fields. By discussing key reports on both the fundamentals and the applications related to laser ablation, fragmentation, and melting in liquids, this Article presents a timely and critical review of this emerging topic.

Germanium Sub-Microspheres Synthesized by Picosecond Pulsed Laser Melting in Liquids: Educt Size Effects

Pulsed laser melting in liquid (PLML) has emerged as a facile approach to synthesize submicron spheres (SMSs) for various applications. Typically lasers with long pulse durations in the nanosecond regime are used. However, recent findings show that during melting the energy absorbed by the particle will be dissipated promptly after laser-matter interaction following the temperature decrease within tens of nanoseconds and hence limiting the efficiency of longer pulse widths. Here, the feasibility to utilize a picosecond laser to synthesize Ge SMSs (200~1000 nm in diameter) is demonstrated by irradiating polydisperse Ge powders in water and isopropanol. Through analyzing the educt size dependent SMSs formation mechanism, we find that Ge powders (200~1000 nm) are directly transformed into SMSs during PLML via reshaping, while comparatively larger powders (1000~2000 nm) are split into daughter SMSs via liquid droplet bisection. Furthermore, the contribution of powders larger than 2000 nm and smaller than 200 nm to form SMSs is discussed. This work shows that compared to nanosecond lasers, picosecond lasers are also suitable to produce SMSs if the pulse duration is longer than the material electron-phonon coupling period to allow thermal relaxation.

Laser-induced growth of YVO4:Eu3+ nanoparticles from sequential flowing aqueous suspension

Ligand-free lanthanide ion-doped oxide nanoparticles have critical biological applications.