Two new non-centrosymmetric ternary compounds, MgSiAs 2 and Mg 3 Si 6 As 8 , are discovered via metal flux and solid-state synthetic methods. MgSiAs 2 belongs to the well-known II-IV-V 2 family, which is extensively studied experimentally and computationally for their optical properties. MgSiAs 2 is computationally predicted but not experimentally known prior to this work. Mg 3 Si 6 As 8 crystallizes in a new non-centrosymmetric cubic chiral structure type with the Pearson symbol cP68. The syntheses, crystal structure, thermal and chemical stabilities, electronic structures, and optical properties of these two new compounds are investigated in this work. Optical absorption measurements and electronic structure calculations reveal the two compounds to be direct or pseudo-direct bandgap semiconductors (1.8-2 eV). The crystal structures of both compounds are non-centrosymmetric, though Mg 3 Si 6 As 8 belongs to the 432 chiral crystal class, which is optically active but does not exhibit second harmonic generation (SHG) behavior. The SHG response of MgSiAs 2 is 60% of that for AgGaS 2 , but MgSiAs 2 exhibits a higher laser damage threshold than AgGaS 2 at 33.2 MW cm −2 .

The discovery of atomically thin van der Waals magnets (e.g., CrI3 and Cr2Ge2Te6) has triggered a renaissance in the study of two-dimensional (2D) magnetism. Most of the 2D magnetic compounds discovered so far host only one single magnetic phase unless the system is at a phase boundary. In this work, we report the near degeneracy of magnetic phases in ultrathin chromium telluride (Cr2Te3) layers with strong perpendicular magnetic anisotropy highly desired for stabilizing 2D magnetic order. Single-crystalline Cr2Te3 nanoplates with a trigonal structure (space group P3̅1c) were grown by chemical vapor deposition. The bulk magnetization measurements suggest a ferromagnetic (FM) order with an enhanced perpendicular magnetic anisotropy, as evidenced by a coercive field as large as ∼14 kOe when the field is applied perpendicular to the basal plane of the thin nanoplates. Magneto-optical Kerr effect studies confirm the intrinsic ferromagnetism and characterize the magnetic ordering temperature of individual nanoplates. First-principles density functional theory calculations suggest the near degeneracy of magnetic orderings with a continuously varying canting from the c-axis FM due to their comparable energy scales, explaining the zero-field kink observed in the magnetic hysteresis loops. Our work highlights Cr2Te3 as a promising 2D Ising system to study magnetic phase coexistence and switches for ultracompact information storage and processing.

No abstract

A comprehensive and concrete exploration into the deactivation mechanisms of luminescent materials is imperative, with the improvement of simulating and computing technology. In this study, an integrated calculation scheme is employed on five Ir(III) complexes for thorough investigation of their photophysical properties, including radiative ( k) and nonradiative ( k) decay rates. As a most famous Ir(III) complex with superior quantum efficiency, fac-Ir(ppy) herein serves as a reference relative to the other four β-diketonate complexes. Both temperature-independent and temperature-dependent k are taken into account quantitatively for the first time, to unearth the role of different ancillary ligands in the determination of luminescent properties. Since the validated calculations of k for the five complexes are of the same order of magnitude, the nonemissive peculiarity of 4 is caused by large k. The newly designed compound 5, which simply has two more -CH groups than 4 in the ancillary ligand, further manifests that the reason for large k in molecule 4 should be attributed to the ligand resonance caused by great π conjugation.

Quantum chemical calculations of a set of valid photoswitches of azobenzene compounds, with the aim of describing their thermal isomerization.

We report, from a theoretical point of view, the first comparative study between the highly water-stable hydroxamate and the widely used carboxylate, in addition to the robust phosphate anchors. Theoretical calculations reveal that hydroxamate would be better for photoabsorption. A quantum dynamics description of the interfacial electron transfer (IET), including the underlying nuclear motion effect, is presented. We find that both hydroxamate and carboxylate would have efficient IET character; for phosphate the injection time is significantly longer (several hundred femtoseconds). We also verified that the symmetry of the geometry of the anchoring group plays important roles in the electronic charge delocalization. We conclude that hydroxamate can be a promising anchoring group, as compared to carboxylate and phosphate, due to its better photoabsorption and comparable IET time scale as well as the experimental advantage of water stability. We expect the implications of these findings to be relevant for the design of more efficient anchoring groups for dye-sensitized solar cell (DSSC) application.

No abstract

No abstract