Angle-dispersive x -ray diffraction (ADXRD) and x -ray absorption near-edge structure (XANES) measurements have been performed on CaWO 4 and SrWO 4 up to pressures of approximately 20 GPa. Both materials display similar behavior in the range of pressures investigated in our experiments. As in the previously reported case of CaWO 4 , under hydrostatic conditions SrWO 4 undergoes a pressure-induced scheelite-to-fergusonite transition around 10 GPa. Our experimental results are compared to those found in the literature and are further supported by ab initio total energy calculations, from which we also predict the instability at larger pressures of the fergusonite phases against an orthorhombic structure with space group Cmca. Finally, a linear relationship between the charge density in the AO 8 polyhedra of ABO 4 scheelite-related structures and their bulk modulus is discussed and used to predict the bulk modulus of other materials, like hafnon.

Manipulating properties of matter at the nanoscale is the essence of nanotechnology, which has enabled the realization of quantum dots, nanotubes, metamaterials, and two-dimensional materials with tailored electronic and optical properties. Two-dimensional semiconductors have revealed promising perspectives in nanotechnology. However, the tunability of their physical properties is challenging for semiconductors studied until now. Here we show the ability of morphological manipulation strategies, such as nanotexturing or, at the limit, important surface roughness, to enhance light absorption and the luminescent response of atomically thin indium selenide nanosheets. Besides, quantum-size confinement effects make this two-dimensional semiconductor to exhibit one of the largest band gap tunability ranges observed in a two-dimensional semiconductor: from infrared, in bulk material, to visible wavelengths, at the single layer. These results are relevant for the design of new optoelectronic devices, including heterostructures of two-dimensional materials with optimized band gap functionalities and in-plane heterojunctions with minimal junction defect density.

We have carried out optical-absorption and reflectance measurements at room temperature in single crystals of AWO 4 tungstates (A = Ba, Ca, Cd, Cu, Pb, Sr, and Zn).

The electronic structure of four ternary-metal oxides containing isolated vanadate ions is studied. Zircon-type YVO 4 , YbVO 4 , LuVO 4 , and NdVO 4 are investigated by high-pressure optical-absorption measurements up to 20 GPa. Firstprinciples calculations based on density-functional theory were also performed to analyze the electronic band structure as a function of pressure. The electronic structure near the Fermi level originates largely from molecular orbitals of the vanadate ion, but cation substitution influence these electronic states. The studied ortovanadates, with the exception of NdVO 4 , undergo a zircon-scheelite structural phase transition that causes a collapse of the band-gap energy. The pressure coefficient dE g /dP show positive values for the zircon phase and negative values for the scheelite phase. NdVO 4 undergoes a zircon-monazite-scheelite structural sequence with two associated band-gap collapses.

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