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2D materials and the associated heterostructures define an ideal material platform for investigating physical and chemical properties, and exhibiting new functional applications in (opto)electronic devices, electrocatalysis, and energy storage. 2D transition metal dichalcogenides (2D TMDs), as a member of the 2D materials family including 2D semiconducting TMDs (s-TMDs) and 2D metallic/semimetallic TMDs (m-TMDs) have attracted considerable attention in the scientific community. Over the past decade, the 2D s-TMDs have been extensively researched and reviewed elsewhere. Because of their distinctive physical properties including intrinsic magnetism, chargedensity-wave order and superconductivity, and potential applications, such as high-performance electronic devices, catalysis, and as metal electrode contacts, 2D m-TMDs have grabbed widespread attention in recent years. However, reviews demonstrating the m-TMDs systematically and comprehensively have been rarely reported. Here, the recent advances in 2D m-TMDs in the aspects of their unique structures, synthetic approaches, distinctive physical properties, and functional applications are highlighted. Finally, the current challenges and perspectives are discussed.

The limitation on the spintronic applications of van der Waals layered transition-metal dichalcogenide semiconductors is ascribed to the intrinsic nonmagnetic feature. Recent studies have proved that substitutional doping is an effective route to alter the magnetic properties of two-dimensional transition-metal dichalcogenides (TMDs). However, highly valid and repeatable substitutional doping of TMDs remains to be developed. Herein, we report group VIII magnetic transition metal-doped molybdenum diselenide (MoSe2) single crystals via a one-pot mixed-salt-intermediated chemical vapor deposition method with high controllability and reproducibility. The high-angle annular dark-field scanning transmission electron microscopy studies further confirm that the sites of Fe are indeed substitutionally incorporated into the MoSe2 monolayer. The Fe-doped MoSe2 monolayer with a concentration from 0.93% to 6.10% could be obtained by controlling the ratios of FeCl3/Na2MoO4. Moreover, this strategy can be extended to create Co­(Ni)-doped MoSe2 monolayers. The magnetic hysteresis (M–H) measurements demonstrate that group VIII magnetic transition-metal-doped MoSe2 samples exhibit room-temperature ferromagnetism. Additionally, the Fe-doped MoSe2 field effect transistor shows n-type semiconductor characteristics, indicating the obtainment of a room-temperature dilute magnetic semiconductor. Our approach is universal in magnetic transition-metal substitutional doping of TMDs, and it inspires further research interest in the study of related spintronic and magnetoelectric applications.

Numerous efforts have been made to synthesize 2D atomic semiconductor materials and their heterojunctions because of the diverse novel properties and potential applications in constructing next‐generation highly compact electronic and optoelectronic devices. However, intrinsic 2D p‐type semiconductor materials are still scarce. Herein, to enrich the p‐type 2D semiconductor family, epitaxial growth of a large‐area, ultrathin 2D nonlayered p‐type semiconductor α‐MnSe on mica with the thickness down to one unit crystal cell (0.9 nm) is reported. Moreover, the thickness of the α‐MnSe nanosheets can be systematically tailored from over 150 to 0.9 nm by increasing the flow rate of the carrier gas. X‐ray‐diffraction, transmission electron microscopy, and electron diffraction studies confirm that the resulting 2D nanosheets are high‐quality single crystals. The photodetector based on the p‐type α‐MnSe nanosheet shows a fast response time of 4 ms. Furthermore, α‐MnSe/WS2 heterojunctions are synthesized and a diode based on p‐type α‐MnSe and n‐type WS2 displays outstanding photodetectivity (1.00 × 1013 Jones), high photoresponsivity (49.1 A W−1), and an obvious rectification ratio (283). Together, the synthesis of α‐MnSe and the α‐MnSe/WS2 p–n heterojunction provides opportunities for next‐generation electronics and optoelectronics.

Sr2ScF7 micro/nanocrystals with various morphologies were firstly synthesized via a one-step surfactant-free hydrothermal route. Sr2ScF7:Yb3+/Er3+/Tm3+ phosphors show tunable RGB and white emissions.

A series of color-tunable emitting Na3Sc2(PO4)3:Ce3+/Tb3+/Eu3+ (NSPO) phosphors were prepared by a combination of hydrothermal synthesis and low temperature calcination.

Two-dimensional (2D) materials have attracted extensive attention due to their important prospects in electronics and optoelectronics. Synthesizing new 2D materials, characterizing their properties, and developing their applications are still important topics. Herein, the synthesis of α-GeTe nanoplates on different substrates via the chemical vapor deposition process and the systematical investigation of their structure and electrical properties, is reported. By controlling the synthesis temperature and carrier gas, α-GeTe nanoplates, with a lateral dimension up to 30 µm and a thickness down to 1.2 nm, which corresponds to the thickness of one unit cell, can be obtained on 2D WSe 2 substrate. Electrical transport studies show 2D α-GeTe nanoplates have an excellent conductivity (9.33 × 10 5 S m −1 ) and an extraordinary breakdown current density (6.1× 10 7 A cm −2 ). Compared with traditional WSe 2 transistors with deposited metal electrodes, the WSe 2 transistors with the metallic α-GeTe nanoplates as van der Waals metal electrodes achieved much better performance, such as higher on-state current (from 7.83 to 23.23 µA µm −1 ) and electron mobility (from 16.5 to 75.0 cm 2 V 1 S 1 ). This study demonstrates an effective pathway to achieve ultrathin 2D materials and provides an accessible strategy to improve the performance of 2D electronic devices.

Well-crystallized and uniform ScPO 4 •2H 2 O and ScPO 4 •2H 2 O:Ln 3+ (Ln = Ce, Eu, Tb, Lu) nano/micro-crystals with multiform morphologies, such as sphere, hexagonal plate, diamond, four-angle star, butterfly-shaped and cuboid, have been successfully synthesized by a facile hydrothermal route without any surfactant molecules. XRD, FE-SEM, TEM, PL and kinetic decay were used to characterize the as-prepared products. The size and morphology of ScPO 4 •2H 2 O can be determined by the pH value, reaction time, reaction temperature, additive and doping of lanthanide ions. In particular, Ln 3+ doping not only has a crucial role in the morphology of ScPO 4 •2H 2 O, but also affects its luminescence properties. The ScPO 4 •2H 2 O:Tb 3+ and ScPO 4 •2H 2 O:Ce 3+ samples display intense green and blue emissions, respectively. More importantly, the luminescence properties are closely related to morphologies and crystallinity. It can be found that the ScPO 4 •2H 2 O:Tb 3+ sample with a hexagonal plate-like morphology possesses much higher emission intensity than those with other morphologies because of its larger anisotropic geometry. ScPO 4 :Ln 3+ crystals will become promising candidates for a variety of applications in down/up-conversion luminescence, magnets, lasers, and bio-labeling.