We report the synthesis and characterization of cubic NaGdF 4 :Yb/Tm@NaGdF 4 :Mn core-shell structures.Bytaking advantage of energy transfer through Yb!Tm!Gd!Mn in these core-shell nanoparticles,w eh ave realized upconversion emission of Mn 2+ at room temperature in lanthanide tetrafluoride based host lattices.T he upconverted Mn 2+ emission, enabled by trapping the excitation energy through aG d 3+ lattice,was validated by the observation of adecreased lifetime from 941 to 532 msi nt he emission of Gd 3+ at 310 nm ( 6 P 7/2 ! 8 S 7/2 ). This multiphoton upconversion process can be further enhanced under pulsed laser excitation at high power densities. Both experimental and theoretical studies provide evidence for Mn 2+ doping in the lanthanide-based host lattice arising from the formation of F À vacancies around Mn 2+ ions to maintain charge neutrality in the shell layer.Since the discovery of the phenomenon of upconversion in the mid-1960s, [1] tremendous success has been achieved with respect to elucidating fundamental optical mechanisms, identifying optimal host-dopant combinations for efficient upconversion processes,a nd precisely controlling emission profiles.[2] As au nique class of luminescent phosphors, upconversion nanocrystals hold great promise in ab road range of applications spanning from bioimaging through drug delivery to 3D volumetric display.[3] Despite the notable achievements over the past decade,e fficient photon upconversion is almost exclusively restricted to lanthanide activators.Aformidable challenge is the development of upconversion nanocrystal systems dominated by transition-metalactivated emission. Theg eneration of photon upconversion through transition-metal ions is important for expanding the scope of upconversion nanocrystals in favor of diverse applications in lighting, molecular sensing,a nd photovoltaics.[4] Previously, several attempts have been made to realize upconversion emission by using transition-metal ions such as Mn 2+ ,N i 2+ , and Cr 3+ .[5] However, the investigation of optical properties typically has to be carried out at cryogenic temperatures [5, 6] or in perovskite/magnetoplumbite host lattices. [7] Recently,o ur research group has demonstrated efficient anti-Stokes emission by an energy migration process for av ariety of lanthanide activators without long-lived intermediate energy states.[8] Ther ealization of tunable antiStokes emissions by energy migration through Gd sublattice provides insights into the rational design of luminescent materials that display unprecedented properties.W er eason that the effect of the energy migration on long-distance energy transfer can be harnessed to achieve photon upconversion for transition-metal ions with electronic sublevels within the 6 P 7/2 level of Gd 3+ .[9]Thee xperimental design is presented in Figure 1. We intended to synthesize acore-shell nanostructure in the form of NaGdF 4 :Yb/Tm@NaGdF 4 :Mn. As et of lanthanide or ,M n 2+ )a re incorporated into different core/shell layers to effectively elimi...
We report the mechanism on the ultrahigh stability of Na<sub>4</sub>Ag<sub>44</sub>(SR)<sub>30</sub> by uncovering how coordinating solvents interact with the Na<sub>4</sub>Ag<sub>44</sub>(SR)<sub>30</sub> nanocluster at the atomic scale. Through synchrotron X-ray experiments and theoretical calculations, it was found that strongly coordinating aprotic solvents interact with surface Ag atoms, particularly between ligand bundles, which compresses the Ag core and relaxes surface metal-ligand interactions. Furthermore, water was used as a cosolvent to demonstrate that semi-aqueous conditions play an important role in protecting exposed surface regions and can further influence the local structure of the silver nanocluster itself. Notably, under semi-aqueous conditions, aprotic coordinating solvent molecules preferentially remain on the metal surface while water molecules interact with ligands, and ligand bundling persisted across the varied solvation conditions.
We present a spectrophotometer (optical density meter) combined with electromagnets dedicated to the analysis of suspensions of magnetotactic bacteria. The instrument can also be applied to suspensions of other magnetic cells and magnetic particles. We have ensured that our system, called MagOD, can be easily reproduced by providing the source of the 3D prints for the housing, electronic designs, circuit board layouts, and microcontroller software. We compare the performance of our system to existing adapted commercial spectrophotometers. In addition, we demonstrate its use by analyzing the absorbance of magnetotactic bacteria as a function of their orientation with respect to the light path and their speed of reorientation after the field has been rotated by 90°. We continuously monitored the development of a culture of magnetotactic bacteria over a period of 5 days and measured the development of their velocity distribution over a period of one hour. Even though this dedicated spectrophotometer is relatively simple to construct and cost-effective, a range of magnetic field-dependent parameters can be extracted from suspensions of magnetotactic bacteria. Therefore, this instrument will help the magnetotactic research community to understand and apply this intriguing micro-organism.
Metal sulfides are a common group of extracellular bacterial biominerals. Only few cases of intracellular biomineralization have been reported in this group, mostly limited to greigite (Fe3S4) in magnetotactic bacteria. Here, we report the intracellular but periplasmic biomineralization of copper sulfide by the magnetotactic bacterium Desulfamplus magnetovallimortis (strain BW-1) that is known to mineralize greigite and magnetite (Fe3O4) in the cytoplasm. BW-1 produces hundreds of spherical nanoparticles, composed of 1-2 nm substructures of a poorly crystalline hexagonal copper sulfide that remains in a thermodynamically unstable state. Differential proteomics suggests that periplasmic proteins, such as a DegP-like protein and a heavy metal-binding protein, could be involved in this process. The unexpected periplasmic formation of copper sulfide nanoparticles in BW-1 reveals previously unknown possibilities for intracellular biomineralization.
<p>This report demonstrates how scanning X-ray fluorescence microscopy (SXFM) and nanoscale X-ray absorption near-edge structure (nano-XANES) can spatially and chemically identify intracellular iron species at the single-cell level, creating an opportunity to examine the role of iron storage in magnetite biomineralization. Fe K-edge nano-XANES measurements of <i>Magnetospirillum gryphiswaldense</i> in varied iron media conditions and iron storage capacity revealed intracellular iron heterogeneities through a distinction between formed magnetosomes and intracellular iron material. This work highlights the potential of nano-XANES in providing an experimental advantage in the multidisciplinary field of biomineralization.</p>
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