Multipole Interactions Research Articles

Ab initio calculation of the interaction between neutral and charged silicon nanoclusters

In dusty plasmas, the formation of nanoclusters marks the beginning of the coagulation stage, leading to the rapid generation of larger particles. In this work, we present an overview of the interaction between silicon nanoclusters (SNCs) of about 1 nm diameter within the framework of density functional theory (DFT), taking into account chemical, van der Waals, and multipolar electrostatic interactions. Two types of SNCs are considered: particles composed entirely of silicon (Si30, Si40, Si50, Si60) and a particle whose dangling bonds are occupied by hydrogen atoms (Si29H24). The interaction energies obtained between two neutral or weakly charged SNCs all have a repulsive part at a short separation distance, followed by a minimum corresponding to a stable state of coagulation due to chemical bonds between the particles. In particular, our calculations show that: (1) the Hamaker constant (which characterizes the London-type van der Waals interaction) depends on the pair of identical SNCs, (2) the multipolar electrostatic contribution at large separation distances allows the extraction of the charged SNC polarization coefficient, and (3) the coagulation rates between SNCs are significantly higher than previously estimated.

On boundedness of isomerization paths for non- and semirelativistic molecules

This article focuses on isomerizations of molecules, i.e. chemical reactions during which a molecule is transformed into another one with atoms in a different spatial configuration. We consider the special case in which the system breaks into two submolecules whose internal geometry is solid during the whole procedure. We prove, under some conditions, that the distance between the two submolecules stays bounded during the reaction. This paper extends [Anapolitanos-Lewin, 2020] in two directions. The first one is that we relax assumptions that the ground state eigenspaces of the submolecules have to fulfill. The second one is that we allow semirelativistic kinetic energy as well. We provide an asymptotic expansion of the interaction energy between two molecules, including multipolar interactions and the van der Waals attraction. In addition to this static result, we proceed to a quasistatic analysis to investigate the variation of the energy when the nuclei move.

Enhanced hypersensitive (5D0→7F2) transition characteristics of Eu3+ doped β-Ga2O3 microrods

Exploring and realizing the luminescence characteristics of rare earth metal (RE) ions doped gallium oxide (Ga2O3) is crucial for developing optoelectronic device applications. The current research used the solid-state reaction approach to synthesize Ga2O3 microrods doped with various europium (Eu3+) concentrations (0.1, 0.2, 0.3, 0.5, 0.75, and 1 mol). X-ray diffraction (XRD) and Raman spectral analyses confirm the monoclinic structure of β-Ga2O3. The intensity of the Raman phonon modes decreased and a peak shift was observed for Eu:β-Ga2O3. The electron microscopy (SEM, TEM) images depicted a nearly uniform distribution of microrods for undoped and Eu:β-Ga2O3 samples. The interplanar distance (d = 0.290 nm, 0.561 nm, and 0.433 nm), from HR-TEM images, corresponding to (0 0 4), (1 0 0), and (1 0 2) crystallographic orientations confirm the monoclinic structure of β-Ga2O3. The elemental mapping images showed a nearly homogeneous Ga, O, and Eu distribution. The UV–visible diffuse reflectance spectroscopy (UV-DRS) showed a notable reduction in the bandgap as the Eu3+ concentration increased. The emission spectra of Eu: β-Ga2O3 microrods showed a narrow red emission at 612 nm (5D0 → 7F2), which relates to the 5D0 → 7Fj (j = 0, 1, 2, 3) energy level arising from an intra-4f transition of Eu3+ ions upon 394 and 465 nm excitation. The red emission was found to increase with Eu content up to 0.5 mol.%. A quenching of emission due to the multipole–multipole interactions was obtained beyond 0.5 mol.% of Eu. The absolute quantum yield (η) calculated for Eu: β-Ga2O3 (0.5 mol.%) was 3.82 %. The luminescence decay curve using the bi-exponential fit and the average lifetime (τ) of the Eu: β-Ga2O3 (0.5 mol.%) was found to be ∼0.172 ms. CIE chromaticity and correlated color temperature analyses of Eu:β-Ga2O3 microrods yielded a red emission with a superior color purity (93 %). The obtained results suggest that Eu:β-Ga2O3 (0.5 wt.%) microrods could be one of the potential candidates for red light sources.

Luminescence and dosimetry investigations of Eu(III) doped Ca2CeVO6 novel double perovskite

A novel composition of vanadate double perovskite Ca2CeVO6 doped with Eu3+ was successfully synthesized using combustion synthesis, wherein the doping levels of Eu3+ ranged from 1 to 6 mol%. The Rietveld refinement of the powder X-ray diffraction (XRD) data confirmed the orthorhombic structure of the phosphors. Scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX) were employed to investigate the surface morphology and elemental distribution in the phosphor, respectively. Under the excitation at 280 nm and 467 nm, the phosphor exhibited strong down-conversion red photoluminescence (PL) emission, attributed to Eu3+ transitions (5D0-7FJ, where J = 0–3) originating from its 4f states. The intensity of PL emission shows increasing trend with increasing doping concentration. However, exceeding the threshold doping concentrations led reduction in PL intensity due to multipolar interaction effects. Additionally, the Eu3+ doped Ca2CeVO6 phosphors were subjected to irradiation with a radioactive 90Sr/90Y beta source to explore their thermoluminescence (TL) properties. Post-irradiation, the phosphors displayed prominent TL glow curves, with the most intense peak at around 94 °C, followed by peaks at 160 °C and 288 °C. The TL intensity of these peaks exhibited a linear dose response within the dose range of 1 Gy–50 Gy. Besides, the TL fading and reproducibility tests showed satisfactory results. Furthermore, Tmax-Tstop experiments revealed the presence of three trap centres within the trap depth range of 0.7–2.1 eV in the Ca2CeVO6:Eu3+ phosphor. Additionally, the glow curve deconvolution (GCD) was employed to determine trapping parameters, providing valuable insights into the TL behaviour of the phosphor. Overall, the results suggest that the novel phosphor under study holds promise for its applications in lighting devices and TL dosimetry (TLD).

Photoluminescence and beta-ray irradiation induced thermoluminescence of Er(III) doped tungstate double perovskite

A luminescent double perovskite Ca3WO6 doped with Er3+ was successfully synthesized via traditional solid-state reaction. Structural analysis was performed through X-ray diffraction (XRD) patterns utilizing Rietveld refinement. When excited at 380 nm, the Ca3WO6:Er3+ phosphors displayed green spectral emission, corresponds to 2H11/2, 4S3/2 to 4I15/2 transitions of Er3+. The influence of Er3+ concentrations on photoluminescence (PL) intensity and concentration quenching was discussed, ascribing multipolar interaction as a cause of intensity quenching. The temperature-dependent PL analysis revealed the phosphor's excellent thermal stability, retaining approximately 79.6 % of its PL intensity at 150 °C. Furthermore, the Ca3WO6:Er3+ phosphors exhibited high-quality thermoluminescence (TL) after beta irradiation. The impact of Er3+ concentrations and beta dose on TL intensity was investigated comprehensively. The reproducibility of the phosphor was checked after several TL readouts. The various heating rate (VHR) experiments were conducted to examine the effect of HR and to determine the trapping parameters.

In-situ synthesis of samarium activated MgO–LaAlO3 nanocomposite for enhanced and prolonged phosphorescence

A series of MgO–La1-xAlO3:xSm (x = 0–5 mol.%) nanocomposite phosphors have been synthesized in-situ using Pechini sol-gel method. The rhombohedral and face-centered crystal structures of LaAlO3 and MgO, respectively, were corroborated utilizing X-Ray Diffractograms and their Rietveld refinement. The optical band gaps of these nanocomposites have been observed in the range of 5.20–5.63 eV. Upon excitation by n-UV 405 nm radiation, the emission characteristics of these phosphors spanning 450–750 nm have been thoroughly investigated. The most notable emission occurred at 599 nm in the orange region, confirmed by CIE-1931 chromaticity coordinates. The MgO–La1-xAlO3:xSm (x = 2 mol.%) is found to be the optimum concentration exhibiting maximum luminescence with a high color purity of 90 %. Insights from Riesfeld's theory pointed towards d-q multipolar interactions as the underlying mechanism behind concentration quenching observed beyond this optimum concentration. Bi-exponential decay behavior was observed via Time-Resolved Photoluminescence (TRPL) technique, with an Internal Quantum Efficiency of 63 % calculated utilizing Auzel's formalism. The study extensively explored the impact of MgO addition on the crystallite size, band-gap, luminescence, and life-time properties, attributing the enhanced and prolonged luminescence behavior to the MgO–La1-xAlO3:xSm (x = 2 mol.%) nanocomposite. Assessment of additional parameters such as CCT (Correlated Color Temperature) and energy transfer efficiencies further reinforced the suitability of these orange emissive phosphors for potential applications in photonics and forensics, underlining their promising prospects in various technological domains.

Manipulating ultrafast even-order nonlinear chiral responses of L-tryptophan by polarization pulse shaping

Molecular chirality has long been monitored in the frequency domain in the ultraviolet, visible, and infrared regimes. Recently developed time-domain approaches can detect time-dependent chiral dynamics by enhancing intrinsically weak chiral signals. Even-order nonlinear signals in chiral molecules have gained attention thanks to their existence in the electric dipole approximation, without relying on the weaker higher-order multipole interactions. We illustrate the optimization of temporal polarization pulse-shaping in various frequency ranges (infrared/optical and optical/X ray) to enhance chiral nonlinear signals. These signals can be recast as an overlap integral of matter and field pseudoscalars which contain the relevant chiral information. Simulations are carried out for second- and fourth-order nonlinear spectroscopies in L-tryptophan.

Visible emission studies by UV light conversion in (Dy3+/Tb3+) ions pair activated zinc-bismuth-barium borotellurite glasses for achieving intense green and white light

Both white light and green emission properties of (Dy3+/Tb3+) ions pair activated zinc-bismuth-barium borotellurite glasses were studied by ultraviolet light (UV:388 and 366 nm) conversion with a focus on down-conversion process. On the dependences of Tb3+ amounts with co-doping of Dy3+, densities of glasses, excitation, emission, area of the integration in percent, decay times, multipolar interactions, and most responsible photometric parameters are investigated in the current work. These co-activated glasses show a broad color production range (450–700 nm) covering of red (∼622 nm), green (∼545 nm), and blue (∼488 nm) colors under the stimulation of UV light wavelengths. The ratio from Yellow to blue emission was analyzed to study the site symmetry of Dy3+ surrounds. With 388 nm of UV radiation, the area of the integrated intensity under the green (Tb3+:545 nm) peak reaches a maximum of 87 %, while it falls under the yellow (Dy3+:575 nm) peak at about 13 %. The decay times of co-activated glasses were found in decreasing order, followed by fitting with a double-exponential function. The Reisfeld and Dexter's energy transfer mechanism confirmed the reduction in Dy3+ emission and its lifetime values through quadrupole-quadrupole interaction (f = 10). Moreover, photometric properties such as relative color temperatures, color coordinates, and color purity were also discussed and compared to discriminate the potentiality of the present fabricated glasses for use in both white light and green-emitting devices.

Highly thermally stable SrLaMgTaO6: Cr3+ double-perovskite phosphors for night-vision applications

In this study, a novel thermally stability broad-band near-infrared (NIR) phosphor SrLaMgTaO6 (SLMT): Cr3+ was research, along with investigations into its structure, morphology, PL spectra and crystal field strengths. Additionally, the mechanism of concentration quenching in these samples was investigated, which primarily attributed to electric multipolar interactions notably. Surprisingly, the NIR emission intensity at 423 K remains 80.4 % of its room temperature intensity, which shows its outstanding thermal stability. To comprehend the mechanism behind the exceptional thermal stability of luminescence, a comprehensive analysis in this material was conducted, focusing on factors such as the crystal field strength of the host material and the electron-phonon coupling (EPC) effect. Subsequently, an optimized phosphor coating was applied to a 470 nm LED chip to get a NIR pc-LED device, which was evaluated for its performance. The research demonstrate that SLMT: Cr3+ phosphor is a promising NIR pc-LED.

Photoluminescence and supercapacitor applications of dysprosium doped rhombohedral silver gallium oxide nanoparticles

Dy3+ doped Silver Gallium Oxide (AgGaO2) nanoparticles (NPs) (AGO:Dy3+) are effectively synthesized via a green mediated route using Aloe vera gel extract as a reducing agent, followed by calcination at 600 °C for 3 h. Powder X-ray diffraction (PXRD), Fourier transformation infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), photoluminescence (PL), and electrochemical studies were employed to confirm the synthesis, structural, luminescence, and supercapacitor properties of the NPs. The diffraction peaks of the synthesized samples possess a trigonal structure within a rhombohedral system. The surface morphology consists of a few irregular, a few hexagonal, and a few rice grain-structured NPs. The changes in the agglomeration were observed with variations in the dopant concentration. The direct energy band gap increases from 3.11 to 3.13 eV with an increase in the dopant concentration. Under 276 nm excitation, the PL spectra of AGO:Dy3+ nanophosphors reveal robust emission peaks attributed to 4F9/2→6F15/2 (480 nm) and 4F9/2→6F13/2 (565 nm). The confirmed critical distance signifies that energy transfer occurs through a multipolar interaction mechanism. The CIE chromaticity diagram illustrates the emission of yellowish green light from the phosphors. These investigations indicate the potential applications of AGO:Dy3+ nanocrystals in a light-emitting diode as a nanophosphor material. Nanocrystals in light-emitting diodes as a nanophosphor material. Thorough electrochemical investigations, encompassing cyclic voltammetry, were conducted to decipher redox reactions, electrode kinetics, and electrochemical behavior. The precise elucidation of ion transport kinetics was achieved through Electrochemical Impedance Spectroscopy (EIS), while the determination of supercapacitance values was accomplished via Galvanostatic Charge-Discharge (GCD) analysis. The supercapacitance values exhibited a remarkable range from 76.177 to 111.53 F/g, underscoring their sensitivity to dopant concentration. Consequently, the material synthesized in this groundbreaking study exhibits substantial promise for diverse applications, spanning from energy storage materials to the dynamic landscape of display technology. Electrochemical studies.

Quantum-classical rate coefficient datasets of vibrational energy transfer in carbon monoxide based on highly accurate potential energy surface.

A merged potential energy surface (PES) is introduced for CO + CO collisions by combining a recent full-dimensional abinitio PES [Chen et al. J. Chem. Phys. 153, 054310 (2020)] and analytical long-range multipolar interactions. This merged PES offers a double advantage: it retains the precision of the abinitio PES in describing the van der Waals well and repulsive short range while providing an accurate physical description of long-range interaction; it significantly reduces the computational time required for trajectory integration since the long-range portion of the abinitio PES (involving numerous neural network fitting parameters) is now replaced by the analytical model potential. Based on the present merged PES, mixed Quantum-Classical (MQC) calculations, which capture quantum effects related to vibrational motion, align with a range of experimental data, including transport properties, vibrational energy transfer between CO and its isotoplogues, as well as rate coefficients for V-V and V-T/R processes. Notably, the original abinitio PES yields V-T/R rate coefficients at low temperatures that are significantly higher than the experimental data due to the artificial contribution of its unphysical long-range potential. In addition to conducting extensive MQC calculations to obtain raw data for V-V and V-T/R rate coefficients, we employ Gaussian process regression to predict processes lacking computed MQC data, thereby completing the considered V-V and V-T/R datasets. These extensive rate coefficient datasets, particularly for V-T/R processes, are unprecedented and reveal the significant role played by V-T/R processes at high temperatures, emphasizing the necessity of incorporating both V-V and V-T/R processes in the applications.

The significance of multipole interactions for the stability of regular structures composed from charged particles

Identifying the forces responsible for stabilising binary particle lattices is key to the controlled fabrication of many new materials. Experiments have shown that the presence of charge can be integral to the formation of ordered arrays; however, a complete analysis of the forces responsible has not included many of the significant lattice types that may form during fabrication. A theory of many-body electrostatic interactions has been applied to six lattice stoichiometries, AB, AB2, AB3, AB4, AB5 and AB6, to show that induced multipole interactions can make a very significant (>80 %) contribution to the total lattice energy of arrays of charged particles. Particle radii ratios which favour global minima in electrostatic energy are found to be the same or a close match to those observed by experiment. Although certain lattice types exhibit local energy minima, the calculations show that many-body rather than two-body interactions are ultimately responsible for the structures observed by experiment. For a lattice isostructural with CFe4, a particle size ratio not previously observed is found to be particularly stable due to many-body effects.

Efficient near-infrared emission at 1070 nm in (Eu3+/Nd3+) ions pair activated NAFBT glasses by CET process for improving the silicon solar cell efficiency

Present work reveals the luminescent downconversion (LDC) process in a series of new sodium-aluminumfluoro borotellurite (NAFBT) glasses by co-doping Nd3+ concentrations (0.1, 0.5, 1.5, and 2.0 mol%) with a constant (2.0 mol%) Eu3+ content. The X-ray diffractogram and IR spectral studies have shown the amorphous like structure and functional groups of the fabricated NAFBT glasses. The fabricated glasses’ physical properties like density and molar volume, and their absorption in the 300–780 nm (UV-Visible) and 800–2300 nm (NIR) ranges were studied. The LDC effect via co-operative type energy transfer (CET) in NAFBT:(Eu3+/Nd3+) glasses was tested with the stimulation at 463 nm of Eu3+, showing a prominent 614 nm (visible) photon of Eu3+ and 907, 1070, and 1339 nm photons (NIR) of Nd3+ ions. The variation in percentage (%) of the integrated intensity at 1070 nm (Nd3+) and 614 nm (Eu3+) was studied as a function of Nd3+ concentration at a fixed Eu3+ content. The multipolar interactions between Nd3+ and Eu3+ ions in NAFBT glasses were studied by Reisfeld and Dexter energy transfer (ET) process. The decline of PL decay from 1.91 to 0.38 ms was represented by dipole-quadrupole interaction in NAFBT glasses. Asymmetric ratio and photometric parameters such as correlated color temperatures (∼1020 K), and (x, y) color coordinates nearly (0.65, 0.34) of red emission were also evaluated for NAFBT glasses. The intense NIR (1070 nm) emission matches well with the silicon solar spectrum and an increase of conversion efficiency (ηQE) from 125% to 199% demonstrate the potential application of NAFBT glass materials in crystalline silicon (c-Si) solar cells.

Temperature-responsive insights: Investigating Eu3+ and Dy3+ activated yttrium calcium oxyborate phosphors for structure and luminescence

An investigation into the luminescent behavior of YCOB (Yttrium Calcium Oxyborate) doped with Eu3+ and Dy3+ ions, synthesized via the combustion method, is presented. The study, employing X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Energy-Dispersive X-ray Spectroscopy (EDS) analyses, confirms the structural integrity and purity of the synthesized nanophosphors. An XRD pattern exhibiting distinct crystalline peaks indicates that the dopant ions were successfully integrated into the YCOB lattice. The photoluminescence (PL) response of YCOB with Eu3+ and Dy3+ ions is thoroughly examined, uncovering distinct excitation and emission spectra. In the case of Eu3+ doping, excitation spectra reveal a significant charge transfer (CT) band at 254 nm, indicative of electron transfer between oxygen and europium ions. This CT transition enhances our understanding of the excitation behavior, with the dominant and Laporte-forbidden 5D0 → 7F2 transition. Characteristic peaks at 345 nm in the excitation spectra efficiently stimulate YCOB:Dy3+ when Dy3+ is used as a dopant. The primary emission peak at 585 nm corresponds to the hypersensitive electric dipole transition 4F9/2–6H13/2. Concentration quenching phenomena are observed, with a maximum Eu3+ concentration of 7 wt % attributed to the dipole-quadrupole interaction. Dy3+ doping, with a maximum concentration of 2 wt % primarily shows multipolar interactions, especially dipole-dipole interactions. The study extends to CIE chromaticity analysis, emphasizing Eu3+ doping's suitability for white light-emitting diode (WLED) applications and ensuring color stability. Conversely, varying Dy3+ concentrations do not yield consistent chromaticity coordinates. These findings have significant implications for the development of advanced phosphor materials across diverse applications, offering a roadmap for optimizing their optical performance.

Non-collinear magnetism driven by a hidden multipolar order in PrO2

Standard microscopic approach to magnetic orders is based on assuming a Heisenberg form for inter-atomic exchange interactions. These interactions are considered as the driving force for the ordering transition with magnetic moments serving as the primary order parameter. Any higher-rank multipoles appearing simultaneously with such magnetic order are typically treated as auxiliary order parameters rather than a principal cause of the transition. In this study, we show that these traditional assumptions are violated in the case of PrO2. Evaluating a full set of Pr-Pr superexchange interactions from a first-principles many-body technique we find that its unusual non-collinear 2k magnetic structure stems from high-rank multipolar interactions, and that the corresponding contribution of the Heisenberg interactions is negligible. The observed magnetic order in PrO2 is thus auxiliary to high-rank “hidden” multipoles. Within this picture we consistently account for previously unexplained experimental observations like the magnitude of exchange splitting and the evolution of magnetic structure in external field. Our findings challenge the standard paradigm of observable magnetic moments being the driving force for magnetic transitions.

Comprehension of the photoinduced charge transfer assisted energy transfer in Gd3+-based host sensitized tellurate phosphors for thermal sensing and anticounterfeiting labels.

A series of novel Eu3+-activated Ba2Gd2/3TeO6 (BGT) phosphors were successfully synthesised via a high temperature solid state reaction method. The crystal structure analysis showed that Eu3+-doped Ba2Gd2/3TeO6 double perovskite phosphors possess monoclinic symmetry with space group P21/n. The as-prepared phosphors can be efficiently excited by far-ultraviolet light to generate reddish orange luminescence of around 593 nm corresponding to the 5D0 → 7F1 transitions of Eu3+ ions. Gd3+ acts as a sensitizer for luminescence enhancement. The highest luminescence intensity corresponded to x = 0.11 Eu3+ concentration, and the critical distance was calculated to be 9.61 Å, indicating that multipolar interaction is behind the concentration quenching mechanism. Besides, the optimum concentration Eu3+-activated Ba2Gd2/3TeO6 phosphor exhibited color co-ordinates of (0.63, 0.36), a high color purity of 94.21% and a quantum efficiency of 18%. JO intensity parameters reveal the slight distortion of the crystal field around the activator ion. Notably, the maximum relative sensitivities of the BGT:0.11Eu3+ phosphor were found to be 0.19% K-1 within the temperature range of 300-500 K and 2.07% K-1 within 80-300 K, and it can potentially be used as a promising thermometer in high and low temperature regions, respectively. The luminescent labels based on fluorescent ink and PL chalk demonstrate the potential application of synthesized phosphors in anti-counterfeiting and security labeling.

Characterization of Sm3+-activated carbonated calcium chlorapatite phosphors for theranostic applications: a comparative study of co-precipitation and hydrothermal methods.

Continuous efforts are ongoing to discover new luminescent materials with appropriate properties for applications in medicine, serving as theranostic agents for healing and bioimaging. In this paper, novel single-phase carbonated calcium chlorapatite (Ca10(PO4)5(CO3)Cl2, abbreviated as CaClAp-CO3) phosphors activated with varying concentrations of Sm3+ ions were successfully fabricated using both co-precipitation and hydrothermal methods to investigate the influence of the synthesis techniques on the physicochemical properties of these materials. The effects of doping concentration of Sm3+ ions and synthesis techniques on the structure, photoluminescence (PL), energy transfer, substitute sites, fluorescence lifetime and luminescence colour of phosphors were investigated. The synthesized phosphors were characterized by X-ray diffraction (XRD) to confirm their crystal phase structure and purity. Vibrational features and the incorporation of carbonate ions were verified using Fourier-transform infrared (FTIR) spectroscopy. The obtained materials emit reddish-orange light, primarily from the most intense 4G5/2 → 6H7/2 transition. The electric dipole to magnetic dipole transition ratio (ED/MD), CIE colour coordinates and colour purity were determined to provide additional insights into the spectroscopic attributes of the obtained phosphors. In addition, the concentration quenching was also observed, and its mechanism was proposed based on theoretical calculations showing the multipolar interactions.

Schrödinger's Red Beyond 65,000Pixel-Per-Inch by Multipolar Interaction in Freeform Meta-Atom through Efficient Neural Optimizer.

Freeform nanostructures have the potential to support complex resonances and their interactions, which are crucial for achieving desired spectral responses. However, the design optimization of such structures is nontrivial and computationally intensive. Furthermore, the current "black box" design approaches for freeform nanostructures often neglect the underlying physics. Here, a hybrid data-efficient neural optimizer for resonant nanostructures by combining a reinforcement learning algorithm and Powell's local optimization technique is presented. As a case study, silicon nanostructures with a highly-saturated red color are designed and experimentally demonstrated. Specifically, color coordinates of (0.677, 0.304) in the International Commission on Illumination (CIE) chromaticity diagram- close to the ideal Schrödinger's red, with polarization independence, high reflectance (>85%), and a large viewing angle (i.e., up to ± 25°) is achieved. The remarkable performance is attributed to underlying generalized multipolar interferences within each nanostructure rather than the collective array effects. Based on that, pixel size down to ≈400nm, corresponding to a printing resolution of 65000 pixels per inch is demonstrated. Moreover, the proposed design model requires only ≈300 iterations to effectively search a thirteen-dimensional (13D) design space - an order of magnitude more efficient than the previously reported approaches. The work significantly extends the free-form optical design toolbox for high-performance flat-optical components and metadevices.

Probing chiral discrimination in biological systems using atomic force microscopy: The role of van der Waals and exchange interactions

We analyze from a theoretical perspective recent experiments where chiral discrimination in biological systems was established using Atomic Force Microscopy (AFM). Even though intermolecular forces involved in AFM measurements have different origins, i.e., electrostatic, bonding, exchange, and multipole interactions, the key molecular forces involved in enantiospecific biorecognition are electronic spin exchange and van der Waals (vdW) dispersion forces, which are sensitive to spin–orbit interaction (SOI) and space-inversion symmetry breaking in chiral molecules. The vdW contribution to chiral discrimination emerges from the inclusion of SOI and spin fluctuations due to the chiral-induced selectivity effect, a result we have recently demonstrated theoretically. Considering these two enantiospecific contributions, we show that the AFM results regarding chiral recognition can be understood in terms of a simple physical model that describes the different adhesion forces associated with different electron spin polarization generated in the (DD), (LL), and (DL) enantiomeric pairs, as arising from the spin part of the exchange and vdW contributions. The model can successfully produce physically reasonable parameters accounting for the vdW and exchange interaction strength, accounting for the chiral discrimination effect. This fact has profound implications in biorecognition where the relevant intermolecular interactions in the intermediate-distance regime are clearly connected to vdW forces.

Higher-order multipoles in metaphotonic structures: reviewing symmetric approaches and constructing a comprehensive theoretical method

This research explores localized electric fields in two-dimensional (2D) photonic crystals, focusing on higher-order multipoles. Novel formulas are developed to accurately describe and analyze these complex electromagnetic modes. By considering various crystal element arrangements, we investigate the formation and interactions of electric, magnetic, and toroidal moments. We examine the effects of symmetry on the localized electromagnetic fields in 2D periodic structures and explain how bound states in the continuum (BICs) arise and behave in different symmetry classes. It is important to point out that every singularity point that occurs in multipolar series expansions depends on a BIC point, and it inspires us to study the characteristics of them. Furthermore, we analyze a variety of BICs and use perturbed and degeneracy breaking to investigate high-Q-factor quasi-BICs. The results provide a thorough understanding of how symmetry and multipolar interactions affect potential applications in cutting-edge metasurfaces and photonic devices (metaphotonic).