A platform of recent interest and large application potential is one in which the light emitters are directly integrated with an optical metasurface. Plasmonic metals and high-refractive-index, dielectric Mie metasurfaces have been explored in this connection but have their challenges. We propose low-refractive-index, contrast nanostructured thin films for studying metasurface-emitter systems, specifically focusing on two configurations of practical importance: LED white light generation using color converting polymers and fluorescence-based sensing in aqueous media. To achieve light emission enhancement in a low-index contrast, low optical absorption setting, we exploit the excitation of quasi-bound states in the continuum modes in a mirror-symmetry broken grating. Our numerical study predicts widely tuneable sharp-linewidth emission enhancements, near-zero quenching, and large and controllable active volume in the grating vicinity, which are significant improvements in comparison with both plasmonic and high-index contrast, all-dielectric platforms. When compared with simple gratings, mirror-symmetry broken gratings give four times larger radiative enhancement. Our results are of interest in furthering experimental activity and realizing applications such as light converter for efficient white LEDs and smart detection electronics-integrated substrates for sensing.

Considerable details in the sampling procedure for the detection of the pesticide carbendazim by surface-enhanced Raman scattering (SERS) were developed. Experimental parameters and recommendations were selected to minimize side processes of carbendazim photodestruction as well as to reduce the background signal from the silver substrate. It was found from the comparison of experimental and density functional theory calculations data that the position of the SERS bands in the carbendazim spectrum depends on the nature of the applied solvent due to different orientations of carbendazim with respect to the surface of silver nanoparticle film. Adsorption from a chloroform solution is preferable to form an aqueous solution for SERS because random adsorption of molecules on a silver surface provides robust carbendazim identification, displaying a larger number of bands in the SERS spectrum, a higher “signal-to-noise” ratio, and then the processes of carbendazim photodestruction slow down.

We study asymmetric excitations of toroidal dipole resonance and magnetic dipole quasi-bound state in the continuum (BIC) in hybrid graphene-dielectric metasurface consisting of a nanoring and a Y-shaped nanobar. Through reducing or increasing inner radius of nanoring, the quasi-BIC dominated by magnetic dipole moment can be excited and effectively modulated via adjusting the Fermi energy and layer numbers of the graphene. The proposed metasurface can not only produce a symmetric localized magnetic field distribution but also create two asymmetric localized magnetic field distributions in near-infrared wavelength, providing a new way of indirectly manipulating the localized magnetic field enhancement. Our results can be of practical interest for a variety of applications including optical modulator, filter, switches and light trapping.

Equichiral sculptured thin films (ECSTFs) with unit cells comprising a sequence of four identical columnar thin films were fabricated using asymmetric serial bideposition to exhibit the polarization-universal Bragg phenomenon. Oblique-angle optical transmission measurements of the ECSTFs showed bands of total transmittance values under 20%, regardless of the polarization state of the incident plane wave. These polarization-universal bandgaps can be tuned by adjusting the angle of incidence.

Inspired by the surface structure of Morpho butterfly wings, we theoretically propose a biomimetic nanosphere structure with high optical reflectivity. By adjusting the geometric parameters and material parameters of the nanostructure, we obtain reflectivity >99 % in a certain band; the high-reflection bandwidth depends on the period width, filling factor, and number of nanospheres. Its high-reflectivity bandwidth is less dependent on the incidental light angle compared with general single-layer or multilayer coatings for reflection enhancement. Unlike the biomimetic structures that are completely the same as the Morpho butterfly surface, this simplified structure can be assembled in ways other than photolithography and electron-beam lithography. We also analyzed several deviations of the structure, and the results show that our design allowed these deviations, which is helpful to achieving the effect of the structure in the preparation process. At the same time, the equivalent medium theory was used to analyze the nanostructure. The nanosphere structure has excellent potential applications in optical devices that require high reflectivity, such as laser resonant cavity and optical filters.

In this study, we designed a plasmonic system containing an array of nanoparticles (NPs) coupled to a quantum dot (QD) to generate entangled photons. The interaction of incoming light with the array of NPs generates a modified plasmon resonance, so-called lattice-plasmon (interaction of the NPs near-field with the photonic mode). Due to its unique optical properties, the lattice-plasmon strongly manipulates the output modes’ entanglement behavior. This is mainly because of the influence of the lattice-plasmon on the transition and dephasing rates of the quantum dot. It is shown that it can be possible to manipulate the QD decay rates via the optical properties of the lattice-plasmon. Also, to manage the output modes entanglement, the emphasis is put on the retarded field effect, which dramatically impacts the lattice-plasmon optical properties. It is theoretically found that engineering the optical properties of the lattice-plasmon facilitates the manipulation of the entanglement behavior.

A disordered photonic crystal (D-PhC) structure is analyzed to study the interface mode localization characteristics. The design comprises a bilayer-disordered PhC structure, where layers are arranged in Thue–Morse sequence (TMS). The impact of local symmetric substructures on eigenstates coupling is also considered over a wider wavelength range. The mode hybridization study is carried out for varying refractive index contrast values of TMS structures at an operating wavelength of 550, 632.8, and 750 nm, respectively. The dispersion analysis confirms the localization of bulk guided, and edge-guided modes for different incidence angles at the structural local resonators. Further, increasing the RI contrast value leads to generation of hybrid interface modes of very high electric field intensity. Thus, showing its potential applications in both sensing and light guiding applications. Moreover, because of the higher surface electric field intensity this structure can also be used for fluorescence-based detection and surface-enhanced Raman spectroscopy as well.

The quantum dot light-emitting devices (QLEDs) have emerged as a promising candidate for electroluminescent devices due to their excellent optical properties, high efficiency, and tunable bandgaps. The QLEDs with increased and prolonged brightness have potential applications in lighting and display devices. However, the stability of these devices is still a matter of concern, and some factors that affect the luminescence from the device involve electric field and temperature-dependent conduction mechanism. Thermal degradation, quenching within the quantum dots, the design of charge transport layers and the charge balance between them are also some factors that affect the efficacy of these devices. The high working temperature of QLEDs is among the most challenging degradation mechanisms, thus an analysis has been carried out regarding the working temperature within the QLEDs, and the methods to minimize these effects have been studied. Another challenge is achieving charge balance within the device and different device structures have been analyzed to achieve the best results regarding charge balance within the device. A few potential strategies have been suggested to reduce the constraints faced in these electroluminescent devices.

Fluorescent bioimaging technology has been widely used in clinic because of its high sensitivity, quick feedback, and no radiation. Among them, NIR-II imaging has lower absorption, tissue scattering, self-fluorescence, and higher signal-to-noise ratio. As a precursor of nanoprobe, BaYF₅ is an excellent material due to its low phonon energy, which makes it easy to achieve rare earth ion energy level transition and obtain strong upconversion luminescence. A near-infrared II (NIR-II) rare earth fluoride nanoparticle (NP) BaYF₅ : Yb^{3 +} , Er^{3 +} @ BaYF₅ has been constructed. The luminescence principle of the material was deeply analyzed, and the influence of different doping ion ratio on fluorescence intensity was explored. Finally, the optimal doping ratio for this matrix material was obtained. In addition, according to the surface properties of the materials, the water solubility and biocompatibility of the NPs were significantly improved by the modification. Our work also systematically tested and analyzed the cytotoxicity, hematotoxicity, and tissue toxicity of the NPs and finally realized the high-resolution fluorescence imaging in living mice. This NP can be used as an effective and safe NIR-II contrastive agent, which provides the possibility for the detection and monitoring of physiological activity under deep tissue in vivo.