No abstract

Organic-inorganic perovskites have attracted great attentions driven by exceptional progress in photovoltaics, photonics and optoelectronics. Different from the corner sharing framework of three-dimensional (3D) perovskite, two-dimensional (2D) organic-inorganic perovskites possess a layered staking structure composed of alternative organic and inorganic components.Due to the inherent multi-quantum-well-like structure, it is intriguing to explore the optical properties of 2D perovskites enabled by spatial and dielectric confinement. Herein, the twophoton absorption (TPA) properties of 2D perovskite phenylethylamine lead iodide ((PEA)2PbI4) are systematically studied. The 2D perovskite exhibits a giant TPA and saturation effect under excitation of 800 nm femtosecond laser. The TPA coefficient of a (PEA)2PbI4 flake is measured to be about 211.5 cm/MW, which is at least one order of magnitude larger than those of 3D perovskite films and some typical semiconductor Submitted to 2 2 nanostructures. The giant TPA can be attributed to the enhanced quantum and dielectric confinement in the organic-inorganic multi-quantum-well structure. In addition, a highly thickness-dependent TPA is observed for the 2D perovskite flakes. The result advocates a great promise of 2D organic-inorganic perovskites for nonlinear optical absorption related optoelectronic devices.

Nonlinear optics (NLO) of transition metal dichalcogenides (TMDs) is promising for the on‐chip photonic and optoelectronic applications. In this review, we will survey the current progress of NLO in TMDs. First, we will brief the basic theory of the NLO in TMDs. Second, several important nonlinear processes in TMDs such as harmonic generation, four‐wave mixing, saturable absorption, and two‐photon absorption will be presented and their potential applications are also discussed. Third, the main strategies to tune, modulate, and enhance the NLO in TMDs are reviewed, including the excitonic effect, symmetry modulation, optical cavity enhancement, valley selection, edge state, and material phase. Finally, we give an outlook regarding some important issues and directions of NLO in TMDs.

A universal approach to develop various two-dimensional ordered nanostructures, namely nanoparticle, nanonet and nanodome arrays with controllable periodicity, ranging from 100 nm to 1 μm, has been developed in centimeter-scale by nanosphere lithography technique. Hexagonally patterned vanadium dioxide (VO) nanoparticle array with average diameter down to sub-100 nm as well as 160 nm of periodicity is fabricated, exhibiting distinct size-, media-, and temperature-dependent localized surface plasmon resonance switching behaviors, which fits well with the predication of simulations. We specifically explore their decent thermochromic performance in an energy saving smart window and develop a proof-of-concept demo which proves the effectiveness of patterned VO film to serve as a smart thermal radiation control. This versatile and facile approach to fabricate various ordered nanostructures integrated with attractive phase change characteristics of VO may inspire the study of temperature-dependent physical responses and the development of smart devices in extensive areas.

Thermochromic windows can smartly modulate the indoor solar irradiation, leading to energy saving for architectural heating and cooling systems. Herein, we integrate the active plasmonic VO 2 nanoparticles in kirigami-inspired reconfigurable elastomers to achieve adaptive, broadband, and highly efficient solar modulation. The smart window promises a UV-visible-NIR traverse state in cold days and a UV-visible-NIR blocked state in hot days to reduce the architectural heating and cooling energy consumption.

Modulating second harmonic generation (SHG) by a static electric field through either electric-field-induced SHG or charge-induced SHG has been well documented. Nonetheless, it is essential to develop the ability to dynamically control and manipulate the nonlinear properties, preferably at high speed. Plasmonic hot carriers can be resonantly excited in metal nanoparticles and then injected into semiconductors within 10-100 fs, where they eventually decay on a comparable time scale. This allows one to rapidly manipulate all kinds of characteristics of semiconductors, including their nonlinear properties. Here we demonstrate that plasmonically generated hot electrons can be injected from plasmonic nanostructure into bilayer (2L) tungsten diselenide (WSe), breaking the material inversion symmetry and thus inducing an SHG. With a set of pump-probe experiments we confirm that it is the dynamic separation electric field resulting from the hot carrier injection (rather than a simple optical field enhancement) that is the cause of SHG. Transient absorption measurement further substantiate the plasmonic hot electrons injection and allow us to measure a rise time of ∼120 fs and a fall time of 1.9 ps. Our study creates opportunity for the ultrafast all-optical control of SHG in an all-optical manner that may enable a variety of applications.

2D layered halide perovskites have attracted significant attention. Apart from the linear optical properties, it is also intriguing to explore the nonlinear optics of 2D layered halide perovskites and their heterostructures. Previous nonlinear optical (NLO) studies of 2D perovskites primarily focus on the thin films or microplates. Herein, the NLO properties of (n‐C4H9NH3)2PbI4/(n‐C4H9NH3)2(CH3NH3)Pb2I7 heterostructures with centimeter size are systematically studied. The NLO properties can be continuously tuned by changing the thickness. A giant two‐photon absorption (2PA) coefficient up to 44 cm MW−1 is obtained for the heterostructures with a total thickness of 20 µm based on the nonlinear transmittance measurement. Additionally, strong multiphoton‐induced photoluminescence is observed in the heterostructures. It is proposed that the giant 2PA coefficient might arise from the small thickness (≈1 µm) of (n‐C4H9NH3)2(CH3NH3)Pb2I7 layer and possibly the nonradiative energy transfer between the different constituting layers within the heterostructures through an antenna‐like effect. Finally, benefiting from the giant 2PA coefficient, direct detection of 980 nm light is demonstrated with a responsivity of 10−7 A W−1 in the heterostructures. The findings suggest the promising applications of 2D perovskite heterostructures in the infrared photodetection and some other nonlinear absorption related optoelectronic devices.

Analysis of molecular interaction and conformational dynamics of biomolecules is of paramount importance in understanding their vital functions in complex biological systems, disease detection, and new drug development. Plasmonic biosensors based upon surface plasmon resonance and localized surface plasmon resonance have become the predominant workhorse for detecting accumulated biomass caused by molecular binding events. However, unlike surface-enhanced Raman spectroscopy (SERS), the plasmonic biosensors indeed are not suitable tools to interrogate vibrational signatures of conformational transitions required for biomolecules to interact. Here, we show that highly tunable plasmonic metamaterials can offer two transducing channels for parallel acquisition of optical transmission and sensitive SERS spectra at the biointerface, simultaneously probing the conformational states and binding affinity of biomolecules, e.g., G-quadruplexes, in different environments. We further demonstrate the use of the metamaterials for fingerprinting and detection of the arginine-glycine-glycine domain of nucleolin, a cancer biomarker that specifically binds to a G-quadruplex, with the picomolar sensitivity.