Synthesis of Mixed-Valent Lanthanide Sulfide Nanoparticles

Metallic Re3O2 with mixed-valence states

Rhenium (Re) shows the richest valence states from +2 to +7 in compounds, but its mixed-valence states are still missing thus far. In this work, we have explored the Re-O phase diagram with a wide range of stoichiometric compositions under high pressure through first-principles structural search calculations. Besides identifying two novel high-pressure phases of ReO2 and ReO3, we reveal two hitherto unknown Re-rich Re3O2 and O-rich ReO4 compounds. Re atoms in Re3O2 show mixed-valence states due to their inequivalent coordination environments, the first example in Re-based compounds. Electronic structure calculations demonstrate that the four discovered Re-O phases exhibit metallicity contributed by Re 5d electrons. Among them, ReO3 has a predicted critical temperature of up to 12 K at 50 GPa, derived from the interaction between Re 5d electrons and Re-derived low-frequency phonons. Our study points to new opportunities to disclose novel transition metal compounds with mixed-valence states.

A Universal Synthesis Strategy for Lanthanide Sulfide Nanocrystals with Efficient Photocatalytic Hydrogen Production

As an important lanthanide (Ln)-based functional materials, the Ln chalcogenides possess unique properties and various applications. However, the controllable synthesis of Ln chalcogenide nanocrystals still faces great challenges because of the rather poor affinity between Ln and chalcogenide ions (S, Se, Te) as well as strong preference of combination with existed oxygen. Herein, a facile but general heterogeneous nucleation synthetic strategy is established toward a series of colloidal ternary Cu Ln sulfides nanocrystals using the Ln dithiocarbamates and CuI as precursors. To extend this synthetic protocol, similar strategy is used to prepare six kinds of high quality CuLnS2 nanocrystals, while the bulk ones are only obtained by the traditional solid-state reaction at rigorous condition. Importantly, high-entropy nanocrystals CuLnS2 and CuEux Ln2-x S3 which contain six Ln elements (Nd, Sm, Gd, Tb, Dy) are readily obtained by the co-decomposed process attributed to their similar diffusion speed. As a proof-of-concept application, CuEu2 S3 nanocrystals showed efficient photocatalytic hydrogen production properties.

Strain-Negligible Eu2+ Doping Enabled Color-Tunable Harsh Condition-Resistant Perovskite Nanocrystals for Superior Light-Emitting Diodes

Cesium lead halide (CsPbX₃, X = Br, Cl, I) perovskite nanocrystals (NCs) possess tunable band gaps across the entire visible spectral range and are promising for various optoelectronic device applications. However, poor performance in adverse conditions limits their further development in practical optoelectronics. Herein, highly stable perovskite NCs are developed by doping europium(II) (Eu²⁺) into the B-site of CsPbBr₃ with negligible lattice distortion/strain. Eu²⁺-doped CsPbBr₃ NCs exhibit tunable green-to-cyan emissions, high photoluminescence quantum yield, and good resistance to harsh conditions, including ultraviolet irradiation, erosion of moisture, and corrosion of polar solvent molecules. In particular, the thermal stability of CsPbBr₃ NCs after Eu²⁺ doping is greatly enhanced under continuous heating in air, while exhibiting the emissions of Eu²⁺. Furthermore, a Eu²⁺-doped CsPbBr₃ NC-based cyan light-emitting diode is fabricated, which exhibits narrow exciton emission driven under different current densities. This work would open the avenue to develop the rational lanthanide ion doping strategy for further advancing perovskite nanomaterials toward practical applications.

The Influence of Yb Doping and Sintering Conditions on the Magnetocaloric and Mechanical Properties of EuS

For this work, europium monosulfide (EuS) powders were prepared by sulfurizing Eu₂O₃ powder with CS₂ gas. The synthesized EuS powders were sintered by SPS at temperatures in the 800-1600 °C range for 0.33-1 h at 50 MPa under vacuum conditions. The influences of Yb doping and sintering conditions on the magnetocaloric and mechanical properties of EuS were investigated systematically. An increase in sintering temperature caused the rise of lattice parameters of EuS, whereas Yb doping caused them to drop. SEM showed that the grain size of the EuS increased with sintering temperatures in the 1000-1400 °C range. Higher sintering temperatures can enlarge the magnetizability and saturation magnetization of EuS compact. On the contrary, Yb doping can weaken the magnetizability and saturation magnetization of EuS compact. All sintered polycrystalline EuS compacts had weaker thermomagnetic irreversibility and lower magnetic anisotropy.

Ultra-mild synthesis of nanometric metal chalcogenides using organyl chalcogenide precursors

Bis(trialkylsilyl) monochalcogenides and diorganyl dichalcogenides, (R₃Si)₂E and R₂E₂ (E = S, Se or Te and R = alkyl, aryl or allyl group), have emerged in the past decade as excellent reagents for the synthesis of metal chalcogenide nanoparticles (NPs) and clusters owing to their ability to transfer the chalcogenide anion (E^2-) under ultra-mild conditions and versatility in reacting even with non-conventional metal reagents or being employed in a variety of synthetic methods. In comparison, the related non-silylated diorganyl monochalcogenides R₂E have received attention only recently for the solution phase synthesis of metal chalcogenide NPs. In spite of sharing many similarities, these three families of organyl chalcogenides are different in their coordination ability and decomposition behavior, and therefore in reactivities towards metal reagents. This feature article provides a concise overview on the use of these three families as synthons for the ultralow-temperature synthesis of metal chalcogenide nanomaterials, deliberating their different decomposition mechanisms and critically assessing their advantages for certain applications. More specifically, it discusses their usefulness in (i) affording molecular precursors with different kinetic and thermal stabilities, (ii) isolating reactive intermediates for comprehending the mechanism of molecule-to-nanoparticle transformation and, therefore, achieving fine control over the synthesis, (iii) stabilizing isolable metastable or difficult-to-achieve phases, and (iv) yielding complex ternary nanoparticles with controlled stoichiometry or composites with sensitive materials without modifying the characteristics of the latter. Besides providing a perspective on the low-temperature synthesis of nanomaterials, this overview is expected to assist further progress, particularly in the field of R₂E, leading to interesting materials including metastable ones for new applications.