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A photon avalanche (PA) effect that occurs in lanthanide-doped solids gives rise to a giant nonlinear response in the luminescence intensity to the excitation light intensity. As a result, much weaker lasers are needed to evoke such PAs than for other nonlinear optical processes. Photon avalanches are mostly restricted to bulk materials and conventionally rely on sophisticated excitation schemes, specific for each individual system. Here we show a universal strategy, based on a migrating photon avalanche (MPA) mechanism, to generate huge optical nonlinearities from various lanthanide emitters located in multilayer core/shell nanostructrues. The core of the MPA nanoparticle, composed of Yb3+ and Pr3+ ions, activates avalanche looping cycles, where PAs are synchronously achieved for both Yb3+ and Pr3+ ions under 852 nm laser excitation. These nanocrystals exhibit a 26th-order nonlinearity and a clear pumping threshold of 60 kW cm−2. In addition, we demonstrate that the avalanching Yb3+ ions can migrate their optical nonlinear response to other emitters (for example, Ho3+ and Tm3+) located in the outer shell layer, resulting in an even higher-order nonlinearity (up to the 46th for Tm3+) due to further cascading multiplicative effects. Our strategy therefore provides a facile route to achieve giant optical nonlinearity in different emitters. Finally, we also demonstrate applicability of MPA emitters to bioimaging, achieving a lateral resolution of ~62 nm using one low-power 852 nm continuous-wave laser beam.A general mechanism, migrating photon avalanche, can generate large optical nonlinearity from various lanthanides emitters at the nanoscale.

The Ca2+-sensing protein calmodulin (CaM) is a popular model of biological ion binding since it is both experimentally tractable and essential to survival in all eukaryotic cells. CaM modulates hundreds of target proteins and is sensitive to complex patterns of Ca2+ exposure, indicating that it functions as a sophisticated dynamic transducer rather than a simple on/off switch. Many details of this transduction function are not well understood. Fourier transform infrared (FTIR) spectroscopy, ultrafast 2D infrared (2D IR) spectroscopy, and electronic structure calculations were used to probe interactions between bound metal ions (Ca2+ and several trivalent lanthanide ions) and the carboxylate groups in CaM’s EF-hand ion-coordinating sites. Since Tb3+ is commonly used as a luminescent Ca2+ analog in studies of protein−ion binding, it is important to characterize distinctions between the coordination of Ca2+ and the lanthanides in CaM. Although functional assays indicate that Tb3+ fully activates many Ca2+-dependent proteins, our FTIR spectra indicate that Tb3+, La3+, and Lu3+ disrupt the bidentate coordination geometry characteristic of the CaM binding sites’ strongly conserved position 12 glutamate residue. The 2D IR spectra indicate that, relative to the Ca2+-bound form, lanthanide-bound CaM exhibits greater conformational flexibility and larger structural fluctuations within its binding sites. Time-dependent 2D IR lineshapes indicate that binding sites in Ca2+−CaM occupy well-defined configurations, whereas binding sites in lanthanide-bound-CaM are more disordered. Overall, the results show that binding to lanthanide ions significantly alters the conformation and dynamics of CaM’s binding sites.

The controlled, self-assembled synthesis of multinuclear coordination compounds can be performed via different approaches. Frequently, steric, geometric and/or electronic factors located at the ligand systems predefine the way in which metal ions can assemble them to large aggregates. For the compounds in the present paper, also the Pearson’s acidities and preferred coordination geometries of the metal ions were used as organization principles. The ligand under study, 2,6-dipicolinoylbis(N,N-diethylthiourea), H[sub.2]L1[sup.ethyl], possesses ‘soft’ sulfur and ‘hard’ nitrogen and oxygen donors. One-pot reactions of this compound with [AuCl(tht)] (tht = tetrahydrothiophene) and M[sup.3+] salts (M = Sc, Y, La, Ln, Ga, In) give products with gold-based Au[sub.3](L1[sup.ethyl])[sub.3][sup.3+] or Au[sub.2](L1[sup.ethyl])[sub.2][sup.2+] coronands, which host central M[sup.3+] ions. The formation of such units is templated by the M[sup.3+] ions and the individual size of the coronand rings is dependent on the ionic radii of the central ions in a way that small ions such as Ga[sup.3+] form a [Ga⊂Au[sub.2](L1[sup.ethyl])[sub.2]][sup.+] assembly, while larger ions (starting from Sc[sup.3+]/In[sup.3+]) establish neutral [M⊂Au[sub.3](L1[sup.ethyl])[sub.3]] units with nine-coordinate central ions.

Smart control of photon upconversion is a key strategy for lanthanide-based materials used in biological and photonic applications. However, this has remained a challenge for the upconversion luminescence of lanthanides under excitation in the second near-infrared (NIR II) biowindow instead of at the conventional 980 and 808 nm wavelengths. Here, we report a conceptual design for an energy-migratory ytterbium sublattice in an erbium-sensitized multilayer core–shell nanostructure that is able to achieve photon upconversion from a broad range of lanthanide ions (Yb3+, Tm3+, Ho3+, Gd3+, Eu3+ and Tb3+) under 1,530 nm irradiation. The quasi-single-band upconversion in the first near-infrared (NIR I) biowindow is also realized through fine manipulation of the introduced cross-relaxations. By establishing an interfacial energy-transfer-mediated nanostructure, we also gain a deep insight into the mechanistic features of the energy migration. These results open new opportunities in a variety of frontier applications, such as information security.An ytterbium sublattice in an erbium-sensitized multilayer core–shell structure enables photon upconversion from lanthanide ions under 1,530 nm irradiation.

Six new complexes of the ligand HQ[sup.cy] (-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) and Ln[sup.3+] ions with emission in the near-infrared (Nd[sup.3+]) or visible and near-infrared (Sm[sup.3+], Pr[sup.3+]) spectral regions were synthesized and characterized using various methods, including single crystal X-ray diffraction. The study demonstrated that both tris complexes [LnQ[sup.cy] [sub.3](H[sub.2]O)(EtOH)] and tetrakis-acids [H[sub.3]O][LnQ[sup.cy] [sub.4]] can be synthesized by varying the synthetic conditions. The photochemical properties of the complexes were investigated experimentally and theoretically using various molecular spectroscopy techniques and Judd–Ofelt theory. The objective was to quantitatively and qualitatively disclose the influence of complex stoichiometry on its luminescence properties. The study showed that the addition of an extra ligand molecule (in the tetrakis species) increased molar extinction by up to 2 times, affected the shape of photoluminescence spectra, especially of the Pr[sup.3+] complex, and increased the quantum yield of the Sm[sup.3+] complex by up to 2 times. The results obtained from this study provide insights into the luminescent properties of lanthanide coordination compounds, which are crucial for the design and development of novel photonic materials with tailored photophysical properties.

Partitioning of americium from lanthanides (Ln) present in used nuclear fuel plays a key role in the sustainable development of nuclear energy 1 – 3 . This task is extremely challenging because thermodynamically stable Am(III) and Ln(III) ions have nearly identical ionic radii and coordination chemistry. Oxidization of Am(III) to Am(VI) produces AmO 2 2+ ions distinct with Ln(III) ions, which has the potential to facilitate separations in principle. However, the rapid reduction of Am(VI) back to Am(III) by radiolysis products and organic reagents required for the traditional separation protocols including solvent and solid extractions hampers practical redox-based separations. Herein, we report a nanoscale polyoxometalate (POM) cluster with a vacancy site compatible with the selective coordination of hexavalent actinides ( 238 U, 237 Np, 242 Pu and 243 Am) over trivalent lanthanides in nitric acid media. To our knowledge, this cluster is the most stable Am(VI) species in aqueous media observed so far. Ultrafiltration-based separation of nanoscale Am(VI)-POM clusters from hydrated lanthanide ions by commercially available, fine-pored membranes enables the development of a once-through americium/lanthanide separation strategy that is highly efficient and rapid, does not involve any organic components and requires minimal energy input. A new strategy to separate radioactive americium from lanthanides based on complexation with polyoxometalates and ultrafiltration technique is highly efficient and rapid, does not involve any organic components and requires minimal energy input.

Single-molecule magnets display magnetic bistability of molecular origin, which may one day be exploited in magnetic data storage devices. Recently it was realised that increasing the magnetic moment of polynuclear molecules does not automatically lead to a substantial increase in magnetic bistability. Attention has thus increasingly focussed on ions with large magnetic anisotropies, especially lanthanides. In spite of large effective energy barriers towards relaxation of the magnetic moment, this has so far not led to a big increase in magnetic bistability. Here we present a comprehensive study of a mononuclear, tetrahedrally coordinated cobalt(II) single-molecule magnet, which has a very high effective energy barrier and displays pronounced magnetic bistability. The combined experimental-theoretical approach enables an in-depth understanding of the origin of these favourable properties, which are shown to arise from a strong ligand field in combination with axial distortion. Our findings allow formulation of clear design principles for improved materials. Bistable single-molecule magnets potentially allow information storage at extremely high densities. Here, the authors study an air- and moisture-stable mononuclear tetrahedral cobalt(II) complex, elucidating the origin of its pronounced magnetic bistability.

Observations of the transient associated with the gravitational-wave event GW170817 and γ-ray burst GRB 170817A reveal a bright kilonova with fast-moving ejecta, including lanthanides synthesized by rapid neutron capture. When neutron stars collide Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim. The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical–near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process) 1 , 2 , 3 . Such transients, named ‘macronovae’ or ‘kilonovae’ 4 , 5 , 6 , 7 , are believed to be centres of production of rare elements such as gold and platinum 8 . The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst 9 , 10 at redshift z  = 0.356, although findings indicating bluer events have been reported 11 . Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source 12 GW170817 and γ-ray burst 13 , 14 GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features similar to those predicted by current models 15 , 16 . The ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. As the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. Comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides.

The high platinum loadings required to compensate for the slow kinetics of the oxygen reduction reaction (ORR) impede the widespread uptake of low-temperature fuel cells in automotive vehicles. We have studied the ORR on eight platinum (Pt)–lanthanide and Pt-alkaline earth electrodes, Pt₅M, where M is lanthanum, cerium, samarium, gadolinium, terbium, dysprosium, thulium, or calcium. The materials are among the most active polycrystalline Pt-based catalysts reported, presenting activity enhancement by a factor of 3 to 6 over Pt. The active phase consists of a Pt overlayer formed by acid leaching. The ORR activity versus the bulk lattice parameter follows a high peaked \"volcano\" relation. We demonstrate how the lanthanide contraction can be used to control strain effects and tune the activity, stability, and reactivity of these materials.

A two-bit magnetic memory is demonstrated, based on the magnetic states of individual holmium atoms, which are read and written in a scanning tunnelling microscope set-up and are stable over many hours. Reading and writing of single atoms (Natterer, Physics Letter, Liesbeth Venema) The ultimate limit of miniaturized classical data storage would be to use single-atom magnetic bits. Holmium atoms are seen as promising candidates because they have long magnetic relaxation times, so they do not easily lose their information. Fabian Natterer et al . now achieve the reading and writing of the magnetism of single holmium atoms, using a scanning tunnelling microscope, and show that individual atoms keep their state for many hours. They use these atoms to make a two-bit memory, to which they write the four possible states. They then use nearby magnetic iron atoms as sensors to confirm the magnetic states. This work suggests that single-atom magnetic memory should be possible. The single-atom bit represents the ultimate limit of the classical approach to high-density magnetic storage media. So far, the smallest individually addressable bistable magnetic bits have consisted of 3–12 atoms 1 , 2 , 3 . Long magnetic relaxation times have been demonstrated for single lanthanide atoms in molecular magnets 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , for lanthanides diluted in bulk crystals 13 , and recently for ensembles of holmium (Ho) atoms supported on magnesium oxide (MgO) 14 . These experiments suggest a path towards data storage at the atomic limit, but the way in which individual magnetic centres are accessed remains unclear. Here we demonstrate the reading and writing of the magnetism of individual Ho atoms on MgO, and show that they independently retain their magnetic information over many hours. We read the Ho states using tunnel magnetoresistance 15 , 16 and write the states with current pulses using a scanning tunnelling microscope. The magnetic origin of the long-lived states is confirmed by single-atom electron spin resonance 17 on a nearby iron sensor atom, which also shows that Ho has a large out-of-plane moment of 10.1 ± 0.1 Bohr magnetons on this surface. To demonstrate independent reading and writing, we built an atomic-scale structure with two Ho bits, to which we write the four possible states and which we read out both magnetoresistively and remotely by electron spin resonance. The high magnetic stability combined with electrical reading and writing shows that single-atom magnetic memory is indeed possible.