ZnO-AuxCu1−x Alloy and ZnO-AuxAl1−x Alloy Vertically Aligned Nanocomposites for Low-Loss Plasmonic Metamaterials

Hyperbolic metamaterials are a class of materials exhibiting anisotropic dielectric function owing to the morphology of the nanostructures. In these structures, one direction behaves as a metal, and the orthogonal direction behaves as a dielectric material. Applications include subdiffraction imaging and hyperlenses. However, key limiting factors include energy losses of noble metals and challenging fabrication methods. In this work, self-assembled plasmonic metamaterials consisting of anisotropic nanoalloy pillars embedded into the ZnO matrix are developed using a seed-layer approach. Alloys of Au_xAl_1−x or Au_xCu_1−x are explored due to their lower losses and higher stability. Optical and microstructural properties were explored. The ZnO-Au_xCu_1−x system demonstrated excellent epitaxial quality and optical properties compared with the ZnO-Au_xAl_1−x system. Both nanocomposite systems demonstrate plasmonic resonance, hyperbolic dispersion, low losses, and epsilon-near-zero permittivity, making them promising candidates towards direct photonic integration.     

过渡金属元素Sc、Cr和Mn对Mg2Ge掺杂的第一性原理研究

基于密度泛函理论(DFT)的第一性原理计算,研究了过渡金属元素Sc、Cr和Mn掺杂对Mg₂Ge晶体光、电、磁性质的影响。结果表明,Sc掺杂能使Mg₂Ge的费米能级进入导带,呈n型简并半导体;Cr和Mn掺杂能使Mg₂Ge能带结构和态密度在费米能级附近产生自旋劈裂而形成净磁矩,表现为半金属磁体和稀磁半导体,体系净磁矩均来自杂质原子3d轨道电子及其诱导极化的Ge4p态和Mg2p态自旋电子。与本征Mg₂Ge相比,掺杂体系静态介电常数增大,扩展了吸收光谱,提升了近红外光波段吸收能力。     

Transient photothermal spectra of plasmonic nanobubbles

The photothermal efficacy of near-infrared gold nanoparticles (NP), nanoshells, and nanorods was studied under pulsed high-energy optical excitation in plasmonic nanobubble (PNB) mode as a function of the wavelength and duration of the excitation laser pulse. PNBs, transient vapor nanobubbles, were generated around individual and clustered overheated NPs in water and living cells. Transient PNBs showed two photothermal features not previously observed for NPs: the narrowing of the spectral peaks to 1 nm and the strong dependence of the photothermal efficacy upon the duration of the laser pulse. Narrow red-shifted (relative to those of NPs) near-infrared spectral peaks were observed for 70 ps excitation laser pulses, while longer sub- and nanosecond pulses completely suppressed near-infrared peaks and blue shifted the PNB generation to the visual range. Thus, PNBs can provide superior spectral selectivity over gold NPs under specific optical excitation conditions.     

Plasmonic resonance instigated enhanced photoluminescence in quantum dot dispersed nematic liquid crystal

In the present investigation, the optical property of the nematic sample p-methoxybenzylidene p-decylaniline, dispersed with SiO₂ quantum dot (QD), has been reported. Enhanced luminescence has been observed from nematic-QD composites. Surface plasmonic effect along with QD exciton has been highlighted to discuss the observed intensification in photoluminescence. The intensified photoemission from the nematic composites can also be inferred from improved orientational behaviour of the liquid crystal molecules due to dispersion of QDs. Variation in the intensity of photoabsorption can be harnessed for development of luminescent display devices and optical parameter-driven scientific applications.     

Molecular design, characterization, and application of multiinformation dyes for optical chemical sensing: IV. Multiinformation dyes with extended spectral sensitivity in the near-infrared spectral range

In this paper, new “multiinformation dyes” (MIDs) with extended spectral sensitivity reporting on both changes in solvent polarity (solvatochromism) and in pH (halochromism) by changes in their visible absorption spectra, are presented. The merocyanine dyes 2,6-dibromo-4-[4-(1-dodecyl-4(1H)-pyridinylidene)-2-butenylidene]-2,5-cyclohexadien-1-one (KD-M301) and 2,6-dibromo-4-[4-(1-dodecyl-4(1H)-quinolinylidene)-2-butenylidene]-2,5-cyclohexadien-1-one (KD-M402) were designed, synthesized, and characterized regarding analytical applications. The spectral sensitivity for the MIDs was extended into the near-infrared (NIR) wavelength range (λ_max=800 nm in CHCl₃ for KD-M402) and at the same time, the degree of solvent polarity-induced spectral shifts was strongly enhanced (Δλ_max=202 nm for KD-M402 between tetrahydrofuran (THF) and methanol), reaching similar values to the standard solvatochromic dye Dimroth-Reichardt’s betaine on which the empirical E_T(30) classification of solvent polarity is based. Compared to Dimroth-Reichardt’s betaine dye, the molar absorption coefficient ε, is increased more than 10-fold (ε of KD-M402 in THF: 7.7×10⁴ M⁻¹ cm⁻¹), allowing sensitive measurements at low concentrations of the dye. The dodecyl-substituted KD-M402 is suitable as a lipophilic pH indicator in ion-exchange type optical sensors (optodes) with optical detection in the near-infrared wavelength range.     

Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: applications in biological imaging and biomedicine

The selection of nanoparticles for achieving efficient contrast for biological and cell imaging applications, as well as for photothermal therapeutic applications, is based on the optical properties of the nanoparticles. We use Mie theory and discrete dipole approximation method to calculate absorption and scattering efficiencies and optical resonance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica-gold nanoshells, and gold nanorods. The calculated spectra clearly reflect the well-known dependence of nanoparticle optical properties viz. the resonance wavelength, the extinction cross-section, and the ratio of scattering to absorption, on the nanoparticle dimensions. A systematic quantitative study of the various trends is presented. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range commonly employed ( approximately 40 nm) show an absorption cross-section 5 orders higher than conventional absorbing dyes, while the magnitude of light scattering by 80-nm gold nanospheres is 5 orders higher than the light emission from strongly fluorescing dyes. The variation in the plasmon wavelength maximum of nanospheres, i.e., from approximately 520 to 550 nm, is however too limited to be useful for in vivo applications. Gold nanoshells are found to have optical cross-sections comparable to and even higher than the nanospheres. Additionally, their optical resonances lie favorably in the near-infrared region. The resonance wavelength can be rapidly increased by either increasing the total nanoshell size or increasing the ratio of the core-to-shell radius. The total extinction of nanoshells shows a linear dependence on their total size, however, it is independent of the core/shell radius ratio. The relative scattering contribution to the extinction can be rapidly increased by increasing the nanoshell size or decreasing the ratio of the core/shell radius. Gold nanorods show optical cross-sections comparable to nanospheres and nanoshells, however, at much smaller effective size. Their optical resonance can be linearly tuned across the near-infrared region by changing either the effective size or the aspect ratio of the nanorods. The total extinction as well as the relative scattering contribution increases rapidly with the effective size, however, they are independent of the aspect ratio. To compare the effectiveness of nanoparticles of different sizes for real biomedical applications, size-normalized optical cross-sections or per micron coefficients are calculated. Gold nanorods show per micron absorption and scattering coefficients that are an order of magnitude higher than those for nanoshells and nanospheres. While nanorods with a higher aspect ratio along with a smaller effective radius are the best photoabsorbing nanoparticles, the highest scattering contrast for imaging applications is obtained from nanorods of high aspect ratio with a larger effective radius.     

Nanostructured materials with localized surface plasmon resonance for photocatalysis

Localized surface plasmon resonance（LSPR） enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts.In the past decades,noble metal nanoparticles（Au and Ag） with LSPR feature have found wide applications in solar energy conversion.Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures.However,high cost and...     

Dual Plasmonic Au−Cu2−xS Nanocomposites: Design Strategies and Photothermal Properties

Coupling two different materials to create a hybrid nanostructured system is a powerful strategy for achieving synergistically enhanced properties and advanced functionalities. In the case of Au and Cu_2−xS, their combination on the nanoscale results in dual plasmonic Au−Cu_2−xS nanocomposites that exhibit intense photon absorption in both the visible and the near-infrared spectral ranges. Their strong light-absorbing properties translate to superior photothermal transduction efficiency, making them attractive in photothermal-based applications. There are several nanostructure configurations that are possible for the Au−Cu_2−xS system, and the successful fabrication of a particular architecture often requires a carefully planned synthetic strategy. In this Minireview, the different synthetic approaches that can be employed to produce rationally designed Au−Cu_2−xS nanocomposites are presented, with a focus on the experimental protocols that can lead to heterodimer, core–shell, reverse core–shell, and yolk–shell configurations. The photothermal behavior of these materials is also discussed, providing a glimpse of their potential use as photothermally active agents in therapeutic and theranostic applications.     

Electrochemical Proton Intercalation in Vanadium Pentoxide Thin Films and its Electrochromic Behavior in the near-IR Region

This work examines the proton intercalation in vanadium pentoxide (V₂O₅) thin films and its optical properties in the near-infrared (near-IR) region. Samples were prepared via direct current magnetron sputter deposition and cyclic voltammetry was used to characterize the insertion and extraction behavior of protons in V₂O₅ in a trifluoroacetic acid containing electrolyte. With the same setup chronopotentiometry was done to intercalate a well-defined number of protons in the H_xV₂O₅ system in the range of x=0 and x=1. These films were characterized with optical reflectometry in the near-IR region (between 700 and 1700 nm wavelength) and the refractive index n and extinction coefficient k were determined using Cauchy ’s dispersion model. The results show a clear correlation between proton concentration and n and k.     

Optical Temperature-Sensing Performance of Nd3+:MF2 (M=Ba,Ca, Sr) Crystalline Powders Prepared by Combustion Synthesis

There is a large interest in luminescent materials for application as temperature sensors. In this scenario, we investigate the performance of neodymium-doped alkaline-earth fluoride (Nd³⁺:MF₂; M=Ba, Ca, Sr) crystalline powders prepared by combustion synthesis for optical temperature-sensing applications based on the luminescence intensity ratio (LIR) technique. We observe that the near-infrared luminescence spectral profile of Nd³⁺ changes with the temperature in a way that its behavior is suitable for optical thermometry operation within the first biological window. We also observe that the thermometric sensitivities of all studied samples change depending on the spectral integration range used in the LIR analysis. Nd³⁺:CaF₂ presents the largest sensitivity values, with a maximum absolute sensitivity of 6.5×10⁻³/K at 824 K and a relative sensitivity of 1.71 %/K at human-body temperature (310 K). The performance of CaF₂ for optical thermometry is superior to that of β-NaYF₄, a standard material commonly used for optical bioimaging and temperature sensing, and on par with the most efficient oxide nanostructured materials. The use of thermometry data to help understand structural properties via Judd-Ofelt intensity standard parameters is also discussed.     

Size- and Emission-Controlled Synthesis of Full-Color Luminescent Metal-Organic Frameworks for Tryptophan Detection

The development of nanoscaled luminescent metal–organic frameworks (nano-LMOFs) with organic linker-based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano-LMOFs with customized linker design. Herein two series of fcu - and csq -type nano-LMOFs, with precise size control in a broad range and emission colors from blue to near-infrared, were prepared using 2,1,3-benzothiadiazole and its derivative based ditopic- and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH₂ as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non-substituted and NH₂-substituted nano-LMOFs exhibit turn-off and turn-on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano-LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.     

Wavelength dependence of the suppressed ionization of molecules in strong laser fields

We study ionization of molecules by an intense laser field over a broad wavelength regime, ranging from 0.8 to 1.5 μm experimentally and from 0.6 to 10 μm theoretically. A reaction microscope is combined with an optical parametric amplifier to achieve ionization yields in the near-infrared wavelength regime. Calculations are done using the strong-field S-matrix theory and agreement is found between experiment and theory, showing that ionization of many molecules is suppressed compared to the ionization of atoms with identical ionization potentials at near-infrared wavelengths at around 0.8 μm, but not at longest wavelengths (10 μm). This is due to interference effects in the electron emission that are effective at low photoelectron energies but tend to average out at higher energies. We observe the transition between suppression and nonsuppression of molecular ionization in the near-infrared wavelength regime (1-5 μm).     

Improved synthesis of porous C2N for CO2 conversion

Since the initial introduction of porous C₂N-h2D materials by the Baek group in 2015, these materials have exhibited highly promising applications in fields such as semiconductor devices, heterogeneous catalysis, gas storage and separation, biomedicine, and more. However, much of the existing research on C₂N materials has been based on theoretical calculations due to the challenges associated with their synthesis. In this study, an enhanced synthesis method for porous C₂N materials has been successfully developed, involving the innovative and nonexplosive synthesis of hexaaminobenzene trihydrochloride (HAB·3HCl) as a crucial intermediate, as well as a time-efficient synthesis of C₂N. Rigorous structural characterizations have been conducted, including solid-state NMR analysis, among others. The resultant C₂N material has been effectively employed to improve the efficiency of CO₂ conversion reactions. This straightforward protocol for synthesizing C₂N materials is poised to stimulate further exploration and application of this promising 2D material in the near future.     

The Two-Dimensional Electrides XONa (X=Mg,Ca) as Novel Natural Hyperbolic Materials

In two-dimensional electrides, anionic electrons are spatially confined in interlayer regions with high density, comparable to metals, and they are highly mobile, just as free electrons, resembling hyperbolic metamaterials with metal-dielectric multilayered structures. In this work, two-dimensional electride materials MgONa and CaONa are proposed as good natural hyperbolic materials. By using the first-principles calculations based on density functional theory (DFT), the electronic structures, stabilities, and optical properties of two-dimensional electride materials XONa (X=Mg, Ca) are investigated. Our results show that they are stable in 1-monolayer (1-ML) structures as well as in bulk states. They exhibit hyperbolic dispersions from visible to near infrared spectral range with high qualities up to about 700, which is two orders-of-magnitude larger than the preceding bulk hyperbolic materials. Numerical results reveal that they exhibit negative refraction with low losses. Their high-quality hyperbolic responses over a wide spectral range pave the way of broad photonic applications as natural hyperbolic materials.     

Chemical short range order in MgPb alloys

Magnesium and its alloys are the ideal materials for the automotive and aerospace applications due to their light weight, excellent physical and mechanical properties. In recent years, great effort is being made to synthesise Mg-alloys which are superior in corrosion performance and endowed with required thermal and mechanical properties. Despite of the growing interest in such alloys, very little studies exist which analyse the microscopic level bonding and the atomic order which are ultimately responsible for their thermal stability and synthesisation. In the present work, we have used the compound formation model (2Mg + Pb?Mg₂Pb) to establish the interconnection between the microscopic interactions to the observed thermodynamic properties. It has been used to compute the concentration and the temperature dependence of the excess free energy, concentration fluctuations and chemical short range order which suggests that a reasonable degree of chemical order exist in the alloys.     

Understanding plasmonic catalysis with controlled nanomaterials based on catalytic and plasmonic metals

Recently, it has been established that the localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can be put toward the acceleration and control of molecular transformations. This field, named plasmonic catalysis, has emerged as a new frontier in nanocatalysis. For metals such as silver (Ag), gold (Au), and copper (Cu), the LSPR excitation can take place in the visible and near-infrared ranges, opening possibilities for the conversion of solar to chemical energy and new/alternative reaction pathways not accessible via conventional, thermally activated catalytic processes. As both catalytic and optical properties can be tuned by controlling several physical and chemical parameters at the nanoscale, design-controlled nanomaterials open the door to unlock the potential of plasmonic catalysis both in terms of fundamental understanding and optimization of performances. In this context, after introducing the fundamentals of plasmonic catalysis, we provide an overview on the current understanding of this field enabled by the utilization of designed-controlled nanostructures based on plasmonic and catalytic metals as model systems. We start by discussing trends in plasmonic catalytic performances and their correlation with nanoparticle size, shape, composition, and structure. Then, we highlight how multimetallic compositions and morphologies containing both catalytic and plasmonic components enables one to extend the use of plasmonic catalysis to metals that are important in catalysis but do not support LSPR excitation in the visible range. Finally, we focus on key challenges and perspectives that are critically important to assist us in designing future energy-efficient plasmonic-catalytic materials.     

The optical and gas-sensitive properties of opal-like structures based on SnO<Subscript>2</Subscript>

Opal-like materials based on tin dioxide were prepared, and their structural and sensor characteristics were studied. The optical transmission spectra of opal-like structures based on SnO₂ were recorded, and the volume fraction occupied in them by tin dioxide was estimated. It was shown that structures based on SnO₂ contained a photon stop-zone in the visible spectrum range. The sensor properties of the materials toward CO and H₂ were studied over the temperature range 375−425°C. The SnO₂ samples studied had much higher sensitivity to CO compared with SnO₂ materials without opal-like structures.     

Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions

The family of polyoxometalate (POM) intercalated layered double hydroxide (LDH) composite materials has shown great promise for the design of functional materials with numerous applications. It is known that intercalation of the classical Keggin polyoxometalate (POM) of [PW₁₂O₄₀]^3? (PW₁₂) into layered double hydroxides (LDHs) is very unlikely to take place by conventional ion exchange methods due to spatial and geometrical restrictions. In this paper, such an intercalated compound of Mg_0.73Al_0.22(OH)₂ [PW₁₂O₄₀]_0.04?0.98 H₂O (Mg₃Al‐PW₁₂) has been successfully obtained by applying a spontaneous flocculation method. The Mg₃Al‐PW₁₂ has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT‐IR, NMR, BET). XRD patterns of Mg₃Al‐PW₁₂ exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg₃Al‐PW₁₂ as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z‐CH₂‐Z′ type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents (V_2‐propanol:V_water=2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg₃Al‐PW₁₂ composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg₃Al‐PW₁₂‐catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction.     

帽状锑纳米粒子的制备及表面等离子共振特性的研究

采用热蒸发法在SiO₂自组装单层膜上制备了帽状锑纳米粒子,通过扫描电镜(SEM)、原子力显微镜(AFM)、X射线衍射仪(XRD)和紫外-可见-近红外(UV-Vis-NIR)分光光度计对帽状复合纳米粒子的表面形貌、结构以及表面等离子共振特性进行了研究和表征。结果表明,制备的复合纳米粒子呈帽状,表面等离子共振峰具有明显的可调谐性,当二氧化硅粒径增大或锑帽层厚度增加时,等离子共振吸收峰位置红移。     

Enhancing the photothermal conversion of tetrathiafulvalene-based MOFs by redox doping and plasmon resonance

Near-infrared (NIR) photothermal materials hold great promise for use in several applications, particularly in photothermal therapy, diagnosis, and imaging. However, current NIR responsive materials often show narrow absorption bands and low absorption efficiency, and have long response times. Herein, we demonstrate that the NIR absorption of tetrathiafulvalene-based metal–organic frameworks (MOFs) can be tuned by redox doping and using plasmonic nanoparticles. In this work, a MOF containing redox-active tetrathiafulvalene (TTF) units and Dy-carboxylate chains was constructed, Dy-m-TTFTB. The NIR absorption of the as-synthesized Dy-m-TTFTB was further enhanced by Ag⁺ or I₂ oxidation, transforming the neutral TTF into a TTF˙⁺ radical state. Interestingly, treatment with Ag⁺ not only generated TTF˙⁺ radicals, but it also formed Ag nanoparticles (NPs) in situ within the MOF pores. With both TTF˙⁺ radicals and Ag NPs, Ag NPs@Dy-m-TTFTB was shown to exhibit a wide range of absorption wavelengths (200–1000 nm) and also a high NIR photothermal conversion. When the system was irradiated with an 808 nm laser (energy power of 0.7 W cm⁻²), Ag NPs@Dy-m-TTFTB showed a sharp temperature increase of 239.8 °C. This increase was higher than that of pristine Dy-m-TTFTB (90.1 °C) or I₂ treated I₃⁻@Dy-m-TTFTB (213.0 °C).

The photo-response of the redox-active metal–organic framework has been systematically tuned by incorporating plasmonic Ag nanoparticles and tetrathiafulvalene radicals, resulting in efficient near-infrared photothermal conversion materials.