In recent years, ternary layered carbide/nitride MAX phases and their derived two-dimensional nanolaminates MXenes have attracted extensive attention. The crystal structure of MAX phase is composed of M_n+1X_n unit interleaved with layers of A element. MAX phases combine good properties of metal and ceramic, which makes them promising candidates for high temperature structural materials, friction and wear devices, nuclear structural materials, etc. When etching the A-layer atoms of the MAX phase, the two-dimensional nanolaminates with the composition of M_n+1X_nT_x (T_x is surface termination), i.e. MXene, is obtained. MXenes have wide range of composition, and tunable physical and chemical properties, which endow them great potential in the applications of energy storage devices, electromagnetic shielding materials, and electronic devices, etc. In this paper, the research progress of MAX phase and MXene was introduced in terms of composition and structure, synthesis methods, and properties and application. Furthermore, the research prospects of this large family of materials were discussed.

Using Ti₃AlC₂ as the precursor, a new MAX phase Ti₃ZnC₂ was synthesized via an A-elemental substitution reaction in a molten salts bath. Composition and crystal structure of Ti₃ZnC₂ were confirmed by XRD, SEM and TEM analysis. Its structure stability and lattice parameter of Ti₃ZnC₂ were further proved by a theoretical calculation based on density function theory (DFT). Moreover, thermodynamics of A-elemental substitution reactions based on Fe, Co, Ni, and Cu were investigated. All results indicated that the similar substitution reactions are feasible to form series of MAX phases whose A sites are Fe, Co, Ni, and Cu elements. The substitution reaction was achieved by diffusion of Zn atoms into A-layers of Ti₃AlC₂, which requires Al-Zn eutectic formation at high temperatures. The molten salts provided a moderate environment for substitution reaction and accelerated reaction dynamics. The major advantage of this substitution reaction is that MAX phase keeps individual metal carbide layers intact, thus the formation of competitive phases, such as MA alloys, was avoided. The proposed A-elemental substitution reactions approach opens a new door to design and synthesize novel MAX phases which could not be synthesized by the traditional methods.

All-inorganic cesium lead halide CsPbX₃ (X = Cl, Br, I) perovskite materials emerged as a rising star in the area of optoelectronics since 2015, due to its excellent photoelectric properties and environmental stability. Substantial progresses were made in the application of many electronic and optoelectronic devices, which attracted wide attention from the scientific community. This paper mainly reviews the latest research progress of cesium lead halide perovskite based planar heterojunction LED, where the structure and working principle of LED devices are briefly introduced. In addition, the classification and summarization of some optimization strategies for improving luminescence performance and working stability of LED devices are emphatically suggested, and the development trend of stable and efficient inorganic perovskite based planar heterojunction LED is finally prospected.

Two dimensional (2D) materials have attracted wide attention due to their ultrathin atomic structure, large specific surface area and quantum confinement effect which are remarkably different from their bulk counterparts. Anisotropic materials are unique among reported 2D materials. Their orientation-dependent physical and chemical properties make it possible to selectively improve the performance of materials. As representative examples, Re-based transition metal dichalcogenides (Re-TMDs) have tunable bandgaps in visible spectrum, extremely weak interlayer coupling, and anisotropic properties in optics and electronics, which make them attractive in the application areas of electronics and optoelectronics. In this riviev, the unique crystal structures and intrinsic properties of the Re-based TMDs semiconductors are introduced firstly, and then the synthetic method is introduced, followed by discussion on the unique physical characterizations and optimized means. Finally, prospects and suggestions are put forward for the preparation and research of ReX₂.

Magneto-optical material is a kind of optical functional material which has the magneto-optical effect from ultraviolet to infrared band. According to the type of material, magneto-optical materials can be classified into magneto-optical glass, magneto-optical crystals, magneto-optical transparent ceramics, etc. As a new type of magneto- optical material which has emerged in recent years, magneto-optical transparent ceramics are considered as one of the most promising candidates for Faraday isolators used in high power lasers due to its high Verdet constant, large size, high thermal conductivity, and high laser-induced-damage threshold. Up to now, the magneto-optical transparent ceramics reported mainly include terbium gallium garnet (Tb₃Ga₅O₁₂, TGG), terbium aluminum garnet (Tb₃Al₅O₁₂, TAG) and some sesquioxide ceramics such as terbium oxide (Tb₂O₃), holmium oxide (Ho₂O₃), dysprosium oxide (Dy₂O₃), etc. In this paper, several common magneto-optical effects were briefly introduced, and the basic principles of Faraday effect and Kerr effect were illustrated in detail. In addition, the research progress, all-sides properties and application prospects of magneto-optical transparent ceramics were mainly reviewed. The properties of different kinds of magneto-optical transparent ceramics were compared and analyzed, and the existing problems as well as the research prospects were also proposed.

Terbium gallium garnet (TGG) ceramics were successfully fabricated by air sintering at 1500 ℃ for 3 h combined with HIP post-treating at 1550 ℃ for 3 h under 150 MPa argon gas, where the TGG powders were synthesized by the co-precipitation method employing ammonium hydrogen carbonate (AHC) as precipitant. The influences of ammonium hydrogen carbonate to metal ions molar ratio (R value) on phase composition and morphology of the resultant powders as well as optical transmittance and Verdet constant of the TGG ceramics were investigated systematically. The precursors with R=3.6, 4.0 and 4.4 calcined at 1100 ℃ form pure TGG phase, whereas the precursor with R=3.2 treated at the same temperature yields the mixed phases of TGG and Ga₂O₃. The TGG powder with R=4.0 shows the best dispersity and homogeneity, giving rise to ceramic with the best optical quality. On the contrary, the powder with R=4.4 exhibits a strong agglomeration, which is closely related to the morphology of its precursor. High quality TGG transparent ceramics with the transmittance of 80.1% at 1064 nm can be fabricated by the nanopowder with R=4.0, and the Verdet constant of the TGG ceramics at 633 nm is rather close to that of the commercial TGG single crystals (-134 rad·T ^-1·m ^-1).

Transparent ytterbium doped calcium fluoride ceramics (Yb:CaF₂) were successfully fabricated by vacuum sintering and hot pressing post-treatment from coprecipitated powders. In-line transmittance of 5at% Yb:CaF₂ transparent ceramics fabricated by pre-sintering at 600 ℃ for 1 h and hot pressing post-treatment at 700 ℃ for 2 h, reaches 92.0% at the wavelength of 1200 nm. Microstructure, spectroscopic characteristics and laser performance of the ceramics were measured and discussed. The sample shows a homogeneous microstructure with average grain size of 360 nm. Furthermore, the absorption cross section at 977 nm and the emission cross section at the 1030 nm of the ceramics are calculated to 0.39×10 ^-20 cm ²and 0.26×10 ^-20 cm ², respectively. Finally, the laser behavior was tested, finding a maximum output power of 0.9 W while the highest slope efficiency was 23.6%.

Heterojunction-type nanostructures based on ZnO nanomaterials are one of the important candidates for constructing high-performance ultraviolet (UV) photodetectors. In this work, a novel ZnO nanorods/ZnCo₂O₄ nanoplates heterojunction was designed and prepared, and the electrical properties and photodetection properties of the as-prepared heterojunction were investigated. ZnCo₂O₄ nanoplates were constructed into uniform thin film on ITO glass substrate using oil/water interface self-assembly. Next, ZnO nanorod arrays with uniform orientation and proper density were grown on ZnCo₂O₄ nanoplates thin film using hydrothermal method with the help from ZnO seed layer. As a result, high-quality ZnO nanorods/ZnCo₂O₄ nanoplates heterojunction was achieved. This heterojunction has a high rectification ratio of 673.7. Under reverse bias, this heterojunction has a light-dark current ration of more than two orders of magnitude. The UV-visible rejection ratio of this heterojunction is 29.4, which indicates its selective detection of UV light. These results effectively prove the potential of this ZnO nanorods/ZnCo₂O₄ nanoplates heterojunction in constructing high-performance UV photodetectors.