Electronic and optical properties of GeS and GeS:Gd

In this paper, the results of the first principles calculations within the framework of the density functional theory of the electronic spectrum of a GeS crystal are presented. The density of states and interband optical transitions are investigated. It was found that GeS compounds have semiconducting properties with a bandgap of 1.52 eV. The main contribution of the bands in the vicinity of the Fermi level is from the 3[Formula: see text] and 3[Formula: see text] states of the S and Ge atoms, respectively. The highest amplitude, about 2.3 eV ([Formula: see text], is mainly associated with the interband optical transitions between the states [Formula: see text]. The results of the luminescence studies of GeS and GeS:Gd layered crystals at room-temperature are presented. A noticeable increase in the intensity of the luminescence radiation in GeS:Gd has been established. The reason for the increase in the effectiveness of photoluminescence is due to the overlapping of optical transitions of GeS at 695 nm wavelength with the radiation lines of Gd[Formula: see text]ion at that same energy.

Mixed-cation driven magnetic interaction of interstitial electrons for ferrimagnetic two-dimensional electride

Magnetism of pure electrons is fundamental for understanding diverse magnetic phenomena in condensed matters but has not been fully investigated in experiments due to the lack of a tractable model system. Such an exotic material necessitates an exclusive magnetic interaction of electrons being devoid of orbital and lattice degrees of freedom. Here, we report the two-dimensional mixed-cation [YGdC]2+∙2e− electride, showing ferrimagnetic nature from the direct exchange interaction of magnetic interstitial electrons in interlayer space. We identify that magnetic interstitial electrons are periodically localized in octahedral and tetrahedral cavities between 2D cationic Y2−xGdx arrays. The mixed configuration of non-magnetic and magnetic cations in cavities induces divergent spin states and interactions of magnetic interstitial electrons, in which their direct exchange interaction overwhelms the interactions with magnetic cations, triggering the ferrimagnetic spin-alignment. This discovery facilitates further exploration of magnetic electrides and nurtures the study of two-dimensional magnetism of layered crystals and electron phases.

Programmable hyperbolic polaritons in van der Waals semiconductors

Collective electronic modes or lattice vibrations usually prohibit propagation of electromagnetic radiation through the bulk of common materials over a frequency range associated with these oscillations. However, this textbook tenet does not necessarily apply to layered crystals. Highly anisotropic materials often display nonintuitive optical properties and can permit propagation of subdiffractional waveguide modes, with hyperbolic dispersion, throughout their bulk. Here, we report on the observation of optically induced electronic hyperbolicity in the layered transition metal dichalcogenide tungsten diselenide (WSe2). We used photoexcitation to inject electron-hole pairs in WSe2 and then visualized, by transient nanoimaging, the hyperbolic rays that traveled along conical trajectories inside of the crystal. We establish here the signatures of programmable hyperbolic electrodynamics and assess the role of quantum transitions of excitons within the Rydberg series in the observed polaritonic response.

Simulation of the Distribution of Nanoplates in a Liquid

The general regularities of exfoliation of layered crystals are considered. A physical model based on the analogy of the spatial packing of polydisperse spherical solid particles is proposed to simulate the distribution of nanoplates in a liquid. Mathematical dependences have been obtained for calculating the critical concentration of aggregation of nanoplates, using graphene as an example. The verification of the adequacy of the mathematical model to the real process was carried out.