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Dielectric metasurfaces have made significant advancements in the past decade for enhancing light–matter interaction at the nanoscale. Particularly, bound states in the continuum (BICs) based on dielectric metasurfaces have been employed to enhance nonlinear harmonic generation. However, conventional nonlinear metasurfaces are typically fixed in their operating wavelength after fabrication. In this work, we numerically demonstrate tunable third harmonic generation (THG) by integrating a dielectric metasurface with the phase-change material Ge2Sb2Te5 (GST). The hybrid phase-change metasurface can support two BICs with different electromagnetic origins, which are transformed into two high-Q quasi-BICs through the introduction of structural asymmetry. The two quasi-BICs are selectively excited by controlling the polarization of incident light, and their wavelengths are tunable due to the phase transition of GST. Notably, the efficiency of THG is significantly enhanced at the fundamental wavelengths corresponding to the two quasi-BICs, and the operating wavelength for THG enhancement can be dynamically tuned through the GST phase transition. Furthermore, the wavelength of THG enhancement can be further tuned by manipulating the polarization of pump light. Additionally, a high-Q analog of electromagnetically induced transparency is numerically achieved through the interaction between a low-Q Mie resonance and a quasi-BIC mode, which also improves the THG efficiency. The high-Q polarization-controlled hybrid phase-change metasurface holds promise for applications in dynamically tunable nonlinear optical devices.

Dielectric metasurfaces have made great progress over the past decade to enhance light-matter interaction. Recently, dielectric nanohole structures have been employed for the creation of dielectric metasurfaces. However, the optical characteristics of most dielectric nanohole structures remain fixed once they are manufactured. This study investigates the optical properties of Ge2Sb2Te5 (GST) film perforated with a periodic dual nanohole array. The GST dual nanohole array is capable of supporting multiple guided resonances and bound states in the continuum (BICs). By introducing asymmetry in the radius, BICs can be transformed into quasi-BICs with high- Q resonances. The wavelengths of guided resonances and quasi-BICs can be dynamically controlled through the phase transition of GST. Furthermore, modifying the gap allows for the achievement of active high- Q electromagnetically induced transparency, resulting from the interaction between one guided resonance and one quasi-BIC mode. The GST asymmetric nanohole array holds potential for applications in optical modulators, slow-light devices, and nonlinear optical devices. [ABSTRACT FROM AUTHOR]

Abstract Mimicking biological proton pump phenomenon to achieve stimulus‐responsive proton conduction behavior has received long‐term attention. The Pa@Zn‐MOF (Pa = photoacids) composites are successfully prepared through adsorption photoacid in Zn‐MOF, then, the composites are mixed into poly(vinyl alcohol) (PVA) to fabricate hybrid membranes Pa@Zn‐MOF‐PVA. When the hybrid membrane is activated through 375 nm violet light at room temperature, the value of proton conductivity after illumination is always superior to that before light irradiation. This phenomenon is attributed to the light‐induced ring‐closing reaction of the photoacid molecules to give the spiro‐forms (SPs) along with an abundant release of protons. The released protons jump into hydrogen bond networks and conveniently accelerate proton transport, resulting in higher proton conductivity. This is a noteworthy demonstration of dynamic control over proton conduction in composite membrane materials by adsorption of photoacid molecules in metal–organic framework.

Broadband tuning of polarization states is pivotal yet challenging in modern photonics technologies, especially for miniaturized or integrated systems. Metasurfaces potentially provide an effective approach to resolve this challenge. However, once a metadevice is fabricated, its functionalities are determined, and it is hard to actively tune the polarization states. Here, the electrically tunable broadband polarization states by combining phase‐change material (vanadium dioxide) and dispersion‐free metasurface are demonstrated for the first time. The polarization states are modulated through the electrically driven, Joule‐heat‐induced phase transition of vanadium dioxide, where the output polarization state can be continuously tuned from horizontal one to vertical one, or from circular polarization to linear polarization. With accurate on‐chip control of the phase transition, continuous and reversible modulation of polarization is verified in a scanning display. Moreover, a proof‐of‐concept demonstration for dynamically independent control of multiple polarization display is carried out. Different images are produced by applying electrical currents in N separate channels to generate a dynamic multiplexing polarization display with 2N encoding states. Such an active metasurface can be readily integrated with electronics and has potential applications in display, encryption, camouflage, and information processing. [ABSTRACT FROM AUTHOR]

Abstract: Plasmonic color filtering and color printing have attracted considerable attention in recent years due to their supreme performance in display and imaging technologies. Although various color‐related devices are designed, so far very few studies have touched the topic of dynamic color generation. In this article, dynamic color generation is demonstrated by integrating plasmonic nanostructures with vanadium dioxide based on its tunable optical properties through insulator–metal transition. Periodic arrays of silver nanodisks on a vanadium dioxide film are fabricated to realize different colors, relying on the excitation of localized and propagating surface plasmons, and Wood's anomaly. By tuning spatial periodicity of the arrays and diameter of the silver nanodisks, various colors can be achieved across the entire visible spectrum. Further, using insulator–metal transition of vanadium dioxide, the colors can be actively tuned by varying temperature. The approach of dynamic color generation based on the phase transition of vanadium dioxide can easily realize diverse color patterns, which makes it beneficial for display and imaging technology with distinct advantages of multifunctionality, flexibility, and high efficiency. [ABSTRACT FROM AUTHOR]

Abstract A novel oxovanadium(IV) complex with tridentate schiff base and bidentate phenanthroline ligands, VO(o-van)(phen) ·2H2O[o-van-gly: o-vanillin-glycine; phen: phenanthroline], was synthesized and characterized by elemental analysis, IR and UV-vis spectra. The crystal structure was determined by X-ray single crystal diffraction analysis. The crystal of title complex (C22H21N3O7V, Mw = 490.36) belongs to triclinic, space group P-1 with the following crystallographic parameters: a = 9.247(3) Å, b = 10.125(4) Å, c = 13.100(5) Å, a = 106.343(6)°, ß = 96.042(7)°, ? = 101.726(7)°, V = 1135.0(7) Å3, Z = 2, Dc = 1.435 Mg · m-3, µ(MoK a = 0.485 mm-1, F(000) = 506, and final R1 = 0.0779, wR2 = 0.1598 for observed reflections 1606 (I > 2s(I)). V(IV) is six-coordinate with three oxygen atoms and three nitrogen atoms in a distorted octahedral geometry. The complex forms a 3-D network via p–p stacking and hydrogen bonds. [ABSTRACT FROM AUTHOR]