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Abstract Dual‐band photodetectors exhibit considerable advantages in target discrimination and navigation compared to single‐band devices in complex circumstances. However, it remains a major challenge to overcome the limitations of traditional devices in terms of their integration with multiple light‐absorbing layers and complicated optical components. In this study, a visible and near‐infrared (NIR) dual‐band polarimetric photodetector with a single light‐absorbing layer is constructed by utilizing the distinctive conversion of linear dichroism (LD) polarity in two‐dimensional niobium trisulfide (NbS3). The NbS3 photodetector exhibits selective detection behaviors in the visible and NIR bands, in which by switching the polarization angle of the incident light from 0° to 90°, photocurrent decreases in the visible region, and increases in the NIR region. Specifically, the degrees of linear polarization of photocurrent are 0.59 at 450 nm and −0.47 at 1300 nm, respectively. The opposite photoresponse in the visible and NIR bands of the photodetector significantly enhances the dual‐band information recognition. Therefore, clear visible and NIR dual‐band polarimetric imaging is accurately realized based on the NbS3 photodetector taking advantage of its fast response speed of 28 μs. Such anisotropic materials, with unique LD conversion features, can facilitate selective modulation between the visible and NIR spectral ranges and promote the development of next‐generation multi‐dimensional photodetection for various applications, including com/puter vision, surveillance, and biomedical imaging.

Abstract Photonic crystals (PhCs) are a kind of artificial structures that can mold the flow of light at will. Polaritonic crystals (PoCs) made from polaritonic media offer a promising route to controlling nano-light at the subwavelength scale. Conventional bulk PhCs and recent van der Waals PoCs mainly show highly symmetric excitation of Bloch modes that closely rely on lattice orders. Here, we experimentally demonstrate a type of hyperbolic PoCs with configurable and low-symmetry deep-subwavelength Bloch modes that are robust against lattice rearrangement in certain directions. This is achieved by periodically perforating a natural crystal α-MoO3 that hosts in-plane hyperbolic phonon polaritons. The mode excitation and symmetry are controlled by the momentum matching between reciprocal lattice vectors and hyperbolic dispersions. We show that the Bloch modes and Bragg resonances of hyperbolic PoCs can be tuned through lattice scales and orientations while exhibiting robust properties immune to lattice rearrangement in the hyperbolic forbidden directions. Our findings provide insights into the physics of hyperbolic PoCs and expand the categories of PhCs, with potential applications in waveguiding, energy transfer, biosensing and quantum nano-optics.

Owing to their broad operational bandwidth, broadband absorbers are extensively used in various applications, such as solar cells, microbolometers, and light modulators. To enhance energy harvesting, it is essential to achieve insensitivity to wide incident angles and polarization-independent absorption. α-MoO3 is a natural polar van der Waals crystal that hosts phonon polaritons in the mid-infrared spectral region. These polaritons can manipulate the infrared light at the nanoscale and break the diffraction limit, offering a great opportunity for the design of broadband absorbers. In this study, we propose a strategy based on an array of crossed the permittivity of α-MoO3 in [100] and [001] crystallographic axes to expand its broadband absorption. Triangular one-dimensional grating pattern is initially considered, which shows an ultra-broadband and wide-angle insensitive absorption within the range of 10.23–18.07 μm. Subsequently, square pyramidal two-dimensional arrays are investigated, which not only show ultra-broadband absorption and wide-angle insensitivity, but also exhibit polarization independence within the range of 10.46–18.32 μm. This remarkable broadband absorption is elucidated by the effective medium theory and the local power dissipation density. These results demonstrate an effective strategy for constructing ultra-broadband absorbers based on α-MoO3 for applications in solar thermal and photovoltaic systems.

All-optical devices without external electronic components have drawn extraordinary attentions in all-optical communication. In this work, boron quantum dots (BQDs) were synthesized by a facile liquid-phase exfoliation method. The as-prepared BQDs showed good structural homogeneity and crystallinity, broadband optical absorption as well as excellent photothermal properties. Femtosecond-resolved transient absorption further revealed the short carrier relaxation time of BQDs. Inspired by the outstanding photothermal properties and ultrafast carrier dynamic of BQDs, we fabricated BQDs-based all-optical modulator. The phase shift with a slope efficiency of 0.032 π/mW and response time of 0.97 ms can be achieved. The modulator was used in laser resonance cavity to achieve all-optical actively Q-switched laser operation with control repetition rate. This prototypical BQDs-based all-optical modulator shows a great potential to be applied in all-optical information processing and communication.

Abstract In recent years, emerging two-dimensional (2D) platinum diselenide (PtSe2) has quickly attracted the attention of the research community due to its novel physical and chemical properties. For the past few years, increasing research achievements on 2D PtSe2 have been reported toward the fundamental science and various potential applications of PtSe2. In this review, the properties and structure characteristics of 2D PtSe2 are discussed at first. Then, the recent advances in synthesis of PtSe2 as well as their applications are reviewed. At last, potential perspectives in exploring the application of 2D PtSe2 are reviewed.

Abstract Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power. Moreover, the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades. Among these compounds, layered two-dimensional (2D) materials, such as graphene, black phosphorus, transition metal dichalcogenides, IVA–VIA compounds, and MXenes, have generated a large research attention as a group of potentially high-performance thermoelectric materials. Due to their unique electronic, mechanical, thermal, and optoelectronic properties, thermoelectric devices based on such materials can be applied in a variety of applications. Herein, a comprehensive review on the development of 2D materials for thermoelectric applications, as well as theoretical simulations and experimental preparation, is presented. In addition, nanodevice and new applications of 2D thermoelectric materials are also introduced. At last, current challenges are discussed and several prospects in this field are proposed.

A simple and effective approach based on the liquid phase exfoliation (LPE) method has been put forward for synthesizing boron quantum dots (BQDs). By adjusting the interactions between bulk boron and various solvents, the average diameter of produced BQDs is about 7 nm. The nonlinear absorption (NLA) responses of as-prepared BQDs have been systematically studied at 515 nm and 1030 nm. Experimental results prove that BQDs possess broadband saturable absorption (SA) and good third-order nonlinear optical susceptibility, which are comparable to graphene. The fast relaxation time and slow relaxation time of BQDs at 515 nm and 1030 nm are about 0.394–5.34 ps and 4.45–115 ps, respectively. The significant ultrafast nonlinear optical properties can be used in optical devices. Here, we successfully demonstrate all-optical diode application based on BQDs/ReS2 tandem structure. The findings are essential for understanding the nonlinear optical properties in BQDs and open a new pathway for their applications in optical devices.