Structural symmetry plays a crucial role in the electronic band structure and properties of two-dimensional materials. In contrast to graphene, monolayer transition metal dichalcogenides exhibit intrinsic in-plane asymmetry with suitable direct bandgaps and distinctive optical properties. Efforts have been devoted to breaking their out-of-plane mirror symmetry by applying external electric fields, vertical stacking, or functionalization. The successful fabrication of Janus transition metal dichalcogenides offers a synthetic strategy to breaking the vertical mirror symmetry, leading to a variety of novel properties, such as vertical piezoelectricity, Rashba spin splitting, and excellent exciton properties. Here, we discuss the universal fabrication approaches and unique properties of Janus transition metal dichalcogenides and further present a brief perspective on their potential applications and challenges.

All-inorganic lead halides, including CsPbX₃ (X = Cl, Br, I), have become important candidate materials in the field of optoelectronics. However, the inherent toxicity of metal lead and poor material stability have hindered further applications of traditional metal halides, CsPbX₃. Therefore, copper(I)-based ternary metal halides are expected to become promising substitutes for traditional metal halides because of their nontoxicity, excellent optical properties and good stability under ambient conditions. This article reviews the recent development of all-inorganic low-dimensional copper(I)-based ternary metal halides by introducing their various synthesis methods, crystal structures, properties and their optoelectronic applications. In addition, the prospects for future challenges and the potential significance of copper(I)-based ternary metal halides in optoelectronic fields are presented.

Two kinds of all-inorganic lead-free cesium copper iodide (CsCu₂I₃ and Cs₃Cu₂I₅) single crystals (SCs) are synthesized and their multiphoton absorption (MPA) properties are comparatively investigated for the first time.

Samples of As18SxSe82-x glasses were prepared by conventional melt-quenching techniques with As, S and Se of 99.99% purity. Raman spectra of samples were obtained by a Fourier transform Raman spectrometer. In addition, all calculations based on Hartree-Fork theory have been used to investigate the Raman-active modes of AsSnSe3-n clusters. It can be found that the calculated data of basic cluster models are in excellent agreement with observed Raman spectra. We give an explanation about the Raman shift of main vibrational modes in AsSnSe3-n clusters