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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.