Due to their low‐symmetry lattice characteristics and intrinsic in‐plane anisotropy, 2D pentagonal materials, a new class of 2D materials composed entirely of pentagonal atomic rings, are attracting increasing research attention. However, the existence of these 2D materials has not been proven experimentally until the recent discovery of PdSe2. Herein, penta‐PdPSe, a new 2D pentagonal material with a novel low‐symmetry puckered pentagonal structure, is introduced to the 2D family. Interestingly, a peculiar polyanion of [SePPSe]4− is discovered in this material, which is the biggest polyanion in 2D materials yet discovered. Strong intrinsic in‐plane anisotropic behavior endows penta‐PdPSe with highly anisotropic optical, electronic, and optoelectronic properties. Impressively, few‐layer penta‐PdPSe‐based phototransistor not only achieves excellent electronic performances, a moderate electron mobility of 21.37 cm2 V−1 s−1 and a high on/off ratio of up to 108, but it also has a high photoresponsivity of ≈5.07 × 103 A W−1 at 635 nm, which is ascribed to the photogating effect. More importantly, penta‐PdPSe also exhibits a large anisotropic conductance (σmax/σmax = 3.85) and responsivity (Rmax/Rmin = 6.17 at 808 nm), superior to most 2D anisotropic materials. These findings make penta‐PdPSe an ideal material for the design of next‐generation anisotropic devices.

Second harmonic generation (SHG) of two-dimensional (2D) layered materials has attracted immense research interests due to the abilities of photon generation, manipulation, transmission, detection, and imaging for the applications of modern on-chip nanophotonic devices. Some layered materials with broken inversion symmetry associated with their 2D nature enable the development of nanophotonic and nanooptoelectronic devices based on the second harmonic generation effect. Recently, many 2D materials with broken inversion symmetry have been discovered, which not only exhibit SHG quantum effects but also greatly promote the development of nanophotonics. In this review, we review the recent developments of all 2D SHG materials, including the graphene-like family, transition metal dichalcogenides, IIIA-VIA compounds and others. We focus on their fabrication, structural characteristics, and generating mechanism and basic characteristics of SHG, associated with the main strategies to tune, modulate, and enhance the SHG of 2D materials. Additionally, several practical applications and possible future research directions of 2D material-based SHG are discussed.

The electromagnetic spectrum between microwave and infrared light is termed the “terahertz (THz) gap,” of which there is an urgent lack of feasible and efficient room‐temperature (RT) THz detectors. Type‐II Weyl semimetals (WSMs) have been predicted to host significant RT topological photoresponses in low‐frequency regions, especially in the THz gap, well addressing the shortcomings of THz detectors. However, such devices have not been experimentally realized yet. Herein, a type‐II WSM (NbIrTe4) is selected to fabricate THz detector, which exhibits a photoresponsivity of 5.7 × 104 V W−1 and a one‐year air stability at RT. Such excellent THz‐detection performance can be attributed to the topological effect of type‐II WSM in which the effective mass of photogenerated electrons can be reduced by the large tilting angle of Weyl nodes to further improve mobility and photoresponsivity. Impressively, this device shows a giant intrinsic anisotropic conductance (σmax/σmin = 339) and THz response (Iph‐max/Iph‐min = 40.9), both of which are record values known. The findings open a new avenue for the realization of uncooled and highly sensitive THz detectors by exploring type‐II WSM‐based devices.

Band engineering is an effective way to tune the physical and chemical properties of materials, leading to significant performance improvement. Herein, the first two-dimensional (2D) quaternary quantum dots (QDs), CuInP2S6 (CIPS) QDs, were successfully fabricated by the lithium intercalation method with a high yield of ∼29%. Importantly, the tuned band structure of CIPS was achieved by forming colossal lithium-induced phosphorus and sulfur vacancies, endowing CIPS QDs with stronger and broader optical absorbance, as well as higher conductivity. Therefore, CIPS QDs exhibit outstanding intrinsic optoelectronic performances toward broadband photodetection with a broadband photoresponse from 405 to 1550 nm, a photoresponsivity of 22.9 A/W, a detectivity of 3.65 × 108 Jones, and a response speed of 60 ms. Especially, such excellent performances can be realized in a simple device structure and ambient air, exceptionally different from most 2D QD-based photodetectors requiring a heterostructure, gate voltage, or vacuum condition. In addition, CIPS QDs retain outstanding photoresponse on curving flexible substrates and in imaging applications. This work provides a unique venue for band structure tuning to effectively manipulate materials’ optoelectronic properties and functionalities.

An optical refractive index (RI) nanosensor with a high sensitivity and figure of merit (FOM), good stability, and biocompatibility is of great significance for biological detection and sensing in narrow spaces. However, the current optical RI nanosensors are mainly fabricated using metals, semiconductors, and quartz, which are not biocompatible and are even biotoxic, and often face a trade-off between a high sensitivity and a high FOM. Moreover, the sensors are mainly based on surface plasmon resonance, photonic crystals, fiber grating, etc., and, thus, most of them usually require a laser source with a specific optical wavelength or harsh excitation conditions, which are likely to cause photodamage and are unfavorable for biological applications. Hence, polylactic acid (PLA), a flexible dielectric material with good biocompatibility, is functioned by doping high refractive index quantum dots (QDs) and fabricated as a nanowire RI sensor. Doping the QDs into a PLA nanowire can improve the light confinement ability and then enhance Mie resonant scattering of the PLA nanowire, which is very beneficial to obtain a higher quality factor and then a higher-performance nanowire sensor. Under irradiation of a white light source, a high sensitivity with 833.78 nm/RIU (per refractive index unit) and the highest FOM of 9.64 RIU−1 are obtained. The good reliability and reproducibility of the sensors are further demonstrated. By choosing a proper diameter, the scattering peak of the nanosensor can be tuned into a biofriendly spectral range (600–900 nm), which predicts that the PLA nanowire RI sensors have a great potential in biological microenvironment monitoring, biosensing, and biomedical treatment.