Two-dimensional (2D) materials are promising candidates for next-generation electronic devices. In this regime, insulating 2D ferromagnets, which remain rare, are of special importance due to their potential for enabling new device architectures. Here we report the discovery of ferromagnetism in a layered van der Waals semiconductor, VI 3 , which is based on honeycomb vanadium layers separated by an iodine-iodine van der Waals gap. It has a BiI 3 -type structure (R-3, No.148) at room temperature, and our experimental evidence suggests that it may undergo a subtle structural phase transition at 78 K. VI 3 becomes ferromagnetic at 49 K, below which magneto-optical Kerr effect imaging clearly shows ferromagnetic domains, which can be manipulated by the applied external magnetic field. The optical band gap determined by reflectance measurements is 0.6 eV, and the material is highly resistive.

The development of rare-earth doped upconversion nanoparticles (RE-UCNPs) in various applications is fuelling the demand for nanoparticles with highly enhanced upconversion luminescence (UCL). Although the core/shell structure is proved to enhance the UCL effectively, there is still plenty of room to further improve the UCL by optimizing the doping ratio of the materials. In this article, a general strategy is demonstrated to achieve highly-enhanced visible UCL in core/shell nanostructured NaREF by increasing the doping ratio of Yb in the core region. The energy transfer from RE-UCNPs to surface quenching sites through Yb-Yb energy migration is demonstrated to be the main reason for restricting the doping ratio of Yb. Notable UCL enhancement (ca. 15 times) of core/shell structured α-NaYF:Yb,Er@CaF nanoparticles is observed by increasing the concentration of Yb to 98 mol%. The highly-enhanced visible UCL signal is used to guide the lymphatic vessel resection with the naked eye.

The layered honeycomb lattice material α‐RuCl3 has emerged as a prime candidate for displaying the Kitaev quantum spin liquid state, and as such has attracted much research interest. Here a new layered honeycomb lattice polymorph of RuI3, a material that is strongly chemically and structurally related to α‐RuCl3 is described. The material is synthesized at moderately elevated pressures and is stable under ambient conditions. Preliminary characterization reveals that it is a metallic conductor, with the absence of long‐range magnetic order down to 0.35 K and an unusually large T‐linear contribution to the heat capacity. It is proposed that this phase, with a layered honeycomb lattice and strong spin–orbit coupling, provides a new route for the characterization of quantum materials.

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