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A core/shell nanoparticle with enhanced emission comprises a fluorescent conjugated polymer core that is encapsulated by an amphiphilic block copolymer shell. The core/shell nanoparticle structure confines the electronic charge to improve quantum yield and is water soluble to enable low-cost and environmentally friendly processing.
The disorder-order phase transition of FePt/SiO{sub 2} core/shell nanoparticles (NPs) induced by rapid thermal annealing was investigated. The FePt/SiO{sub 2} NPs were synthesized using FePt cores as seeds. For as-prepared FePt/SiO{sub 2} NPs, the average size of the FePt core and the thickness of the SiO{sub 2} shell are about 4.8 and 1.2 nm respectively, and the FePt NPs exhibit a disordered fcc structure. The FePt core NPs show obvious phase transformation from a disordered to an ordered structure after they were annealed at 600 °C for 2 min. Moreover, increasing annealing time can promote effectively the formation of the ordered fct-FePt phase. The relatively large coercivity H{sub c} is obtained for FePt NPs with a thicker SiO{sub 2} shell. The H{sub c} decreases firstly with decreasing temperature from 300 to 100 K and then increases from 100 to 10 K, which is ascribed to the coexistence of magnetically hard fct-FePt and magnetically soft fcc-FePt in the sample, and the incomplete exchange coupling between the hard and soft magnetic phases.
Here, suspended particle devices (SPDs) adapted for controlling the transmission of electromagnetic radiation have become an area of considerable focus for smart window technology due to their desirable properties, such as instant and precise light control and cost-effectiveness. Here, we demonstrate a SPD with tunable transparency in the visible regime using colloidal assemblies of nanoparticles. The observed transparency using ZnS/SiO 2 core/shell colloidal nanoparticles is dynamically tunable in response to an external electric field with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby modifies the photonic band structures, as confirmed by the finite-difference time-domain simulations of Maxwell’s equations. The transparency of the device can also be manipulated by changing the particle size and the device thickness. In addition to transparency, structural colorations and their dynamic tunability are demonstrated using α-Fe 2 O 3 /SiO 2 core/shell nanomaterials, resulting from the combination of inherent optical properties of α-Fe 2 O 3 /SiO 2 nanomaterials and coloration due to their tunable structural particle assemblies in response to electric stimuli.
The optical efficiency of lanthanide-based upconversion is intricately related to the crystalline host lattice. Different crystal fields interacting with the electron clouds of the lanthanides can significantly affect transition probabilities between the energy levels. Here, we investigate six distinct alkaline-earth rare-earth fluoride host materials (M 1- x Ln x F 2+ x , MLnF) for infrared-to-visible upconversion, focusing on nanoparticles of CaYF, CaLuF, SrYF, SrLuF, BaYF, and BaLuF doped with Yb 3+ and Er 3+ . We first synthesize ~5 nm upconverting cores of each material via a thermal decomposition method. Then we introduce a dropwise hot-injection method to grow optically inert MYF shell layers around the active cores. Five distinct shell thicknesses are considered for each host material, resulting in 36 unique, monodisperse upconverting nanomaterials each with size below ~15 nm. The upconversion quantum yield (UCQY) is measured for all core/shell nanoparticles as a function of shell thickness and compared with hexagonal (β-phase) NaGdF 4 , a traditional upconverting host lattice. While the UCQY of core nanoparticles is below the detection limit (<10-5%), it increases by 4 to 5 orders of magnitude as the shell thickness approaches 4-6 nm. The UCQY values of our cubic MLnF nanoparticles meet or exceed the β-NaGdF 4 reference sample. Across all core/shell samples, SrLuF nanoparticles are the most efficient, with UCQY values of 0.53% at 80 W/cm 2 for cubic nanoparticles with ~11 nm edge length. This efficiency is 5 times higher than our β-NaGdF 4 reference material with comparable core size and shell thickness. Our work demonstrates efficient and bright upconversion in ultrasmall alkaline-earth-based nanoparticles, with applications spanning biological imaging and optical sensing.
Hybrid nanoparticles allow exploiting the interplay of confinement, proximity between different materials and interfacial effects. However, to harness their properties an in-depth understanding of their (meta)stability and interfacial characteristics is crucial. This is especially the case of nanosystems based on functional oxides working under reducing conditions, which may severely impact their properties. Here, the in-situ electron-induced selective reduction of Mn 3 O 4 to MnO is studied in magnetic Fe 3 O 4 /Mn 3 O 4 and Mn 3 O 4 /Fe 3 O 4 core/shell nanoparticles by means of high-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Such in-situ transformation allows mimicking the actual processes in operando environments. A multi-stage image analysis using geometric phase analysis combined with particle image velocity enables direct monitoring of the relationship between structure, chemical composition and strain relaxation during the Mn 3 O 4 reduction. In the case of Fe 3 O 4 /Mn 3 O 4 core/shell the transformation occurs smoothly without the formation of defects. However, for the inverse Mn 3 O 4 /Fe 3 O 4 core/shell configuration the electron beam-induced transformation occurs in different stages that include redox reactions and void formation followed by strain field relaxation via formation of defects. This study highlights the relevance of understanding the local dynamics responsible for changes in the particle composition in order to control stability and, ultimately, macroscopic functionality.
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Here, nanoparticles with low-Pt content core and a few-layer Pt skin are attractive catalysts toward the oxygen reduction reaction (ORR) not only for its low cost, but also because its activity can be enhanced by judiciously choosing the core alloy. Achieving optimal ORR performance would require fine tuning of the core composition and structure. Previous work studying the enhancement effects has primarily focused on core alloys with a cubic structure, (i.e. disordered alloy or L12 ordered structure) which limits the tuning to composition alone. In this work, using ab initio calculations, we have systemically investigated a new class of Pt0.5M0.5 (M=V, Cr, Fe, Co, Ni and Cu) core alloy that has a face-centered tetragonal L10 intermetallic structure. We have calculated the adsorption energies of O, OH, and OOH on various Pt skins and the underlying tetragonal structured alloys, which allows us to not only predict the optimal number of pure Pt skin layers but also tune the activity of the catalysts toward the peak of the ORR volcano plot. More importantly, using adsorption energies on intermediate structures, we are able to decompose the enhancement factor into ligand, normal and shear strain effects, and reveal the significant contribution of the shear strain that is only possible with a tetragonal core but not a cubic one. Our results point to a new direction in designing tetragonal structured intermetallic core-shell nanoparticles for ORR applications.
Exchange coupling in a model core–shell system is demonstrated as a step on the path to 3d exchange spring magnets.
Nitride stabilized metal nanoparticles and methods for their manufacture are disclosed. In one embodiment the metal nanoparticles have a continuous and nonporous noble metal shell with a nitride-stabilized non-noble metal core. The nitride-stabilized core provides a stabilizing effect under high oxidizing conditions suppressing the noble metal dissolution during potential cycling. The nitride stabilized nanoparticles may be fabricated by a process in which a core is coated with a shell layer that encapsulates the entire core. Introduction of nitrogen into the core by annealing produces metal nitride(s) that are less susceptible to dissolution during potential cycling under high oxidizing conditions.
Abstract not provided.
Nitride stabilized metal nanoparticles and methods for their manufacture are disclosed. In one embodiment the metal nanoparticles have a continuous and nonporous noble metal shell with a nitride-stabilized non-noble metal core. The nitride-stabilized core provides a stabilizing effect under high oxidizing conditions suppressing the noble metal dissolution during potential cycling.
Nitride stabilized metal (M or Pt(M)) nanoparticles and methods for their manufacture are disclosed. In one embodiment the metal nanoparticles have a nonporous noble metal shell with a nitride-stabilized non-noble metal core. The nitride-stabilized core provides a stabilizing effect under high oxidizing conditions suppressing the noble metal dissolution during potential cycling. Introduction of nitrogen into the core by annealing produces metal nitride(s) that are less susceptible to dissolution during potential cycling under high oxidizing conditions.
According to one embodiment, a product is a mixture including a solvent and generally spherical colloidal nanoparticles, the colloidal nanoparticles each having a core and a shell surrounding the core, and an electrode. In addition, the mixture is characterized as having a transparency to light in a predetermined wavelength range, where the transparency increases as a voltage of the electrode increases.
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Magnetite (Fe 3 O 4 ) nanoparticles are one of the most studied nanomaterials for different nanotechnological and biomedical applications. However, Fe 3 O 4 nanomaterials gradually oxidize to maghemite (γ-Fe 2 O 3 ) under conventional environmental conditions leading to changes in their functional properties that determine their performance in many applications. Here we propose a novel strategy to control the surface chemistry of monodisperse 12 nm magnetite nanoparticles by means of a 3 nm-thick Zn-ferrite epitaxial coating in core/shell nanostructures. We have carried out a combined Mössbauer spectroscopy, dc magnetometry, X-ray photoelectron spectroscopy and spatially resolved electron energy loss spectroscopy study on iron oxide and Fe 3 O 4 /Zn 0.6 Fe 2.4 O 4 core/shell nanoparticles aged under ambient conditions for 6 months. Our results reveal that while the aged iron oxide nanoparticles consist of a mixture of γ-Fe 2 O 3 and Fe 3 O 4 , the Zn-ferrite-coating preserves a highly stoichiometric Fe 3 O 4 core. Therefore, the aged core/shell nanoparticles present a sharp Verwey transition, an increased saturation magnetization and the possibility of tuning the effective anisotropy through exchange-coupling at the core/shell interface. The inhibition of the oxidation of the Fe 3 O 4 cores can be accounted for in terms of the chemical nature of the shell layer and an epitaxial crystal symmetry matching between the core and the shell.
We report a systematic study of the effects of core and shell size on the magnetic properties and heating efficiency of exchange-coupled Fe 3 O 4 /CoFe 2 O 4 core/shell nanoparticles. The nanoparticles were synthesized using thermal decomposition of organometallic precursors. Transmission electron microscopy (TEM) confirmed the formation of spherical Fe 3 O 4 and Fe 3 O 4 /CoFe 2 O 4 nanoparticles. Magnetic measurements showed high saturation magnetization for the nanoparticles at room temperature. Increasing core diameter (6.4±0.7, 7.8±0.1, 9.6±1.2 nm) and/or shell thickness (~1, 2, 4 nm) increased the coercive field (H C ), while an optimal value of saturation magnetization (M S ) was achieved for the Fe 3 O 4 (7.8±0.1nm)/CoFe 2 O 4 (2.1±0.1nm) nanoparticles. Magnetic hyperthermia measurements indicated a large increase in specific absorption rate (SAR) for 8.2±1.1 nm Fe 3 O 4 /CoFe 2 O 4 compared to Fe 3 O 4 nanoparticles of same size. The SAR of the Fe 3 O 4 /CoFe 2 O 4 nanoparticles increased from 199 to 461 W/g for 800 Oe as the thickness of the CoFe 2 O 4 shell was increased from 0.9±0.5 to 2.1±0.1 nm. The SAR enhancement is attributed to a combination of the large M S and the large H C . Therefore, these Fe 3 O 4 /CoFe 2 O 4 core/shell nanoparticles can be a good candidate for advanced hyperthermia application.