With growing public awareness of food safety, the high-sensitivity and rapid detection of hazardous substances in food has become increasingly important. Surface-enhanced Raman spectroscopy (SERS) offers significant advantages in food detection due to its high sensitivity and fast response. In this study, gold microflakes (GMFs) and bimetallic Au-Ag alloy nanostars (Au-AgNSts) were synthesized via wet chemical and seed-mediated growth methods, respectively. A liquid-liquid three-phase self-assembly technique was employed to construct a three-dimensional GMFs/Au-AgNSts substrate, where Au-AgNSts were assembled on top of GMFs. By adjusting the Au-to-Ag ratio and the molar quantity of AgNO 3 during nanostar synthesis, the influence of plasmonic “hot spot” distribution among in the Au-AgNSts and GMFs on SERS enhancement was systematically investigated. The results indicate that the optimal SERS enhancement was achieved at a 1:1 Au-to-Ag ratio with 250 μL of AgNO 3 (2 mM). The detection limits for probe molecules Rhodamine 6G (R6G) and crystal violet (CV) as low as 10 −11 M and 10 −10 M, respectively. Additionally, the substrate demonstrated a low detection limit of 0.0313 g/L for aspartame and exhibited excellent stability and uniformity. These findings highlight the substrate’s high sensitivity, uniformity, and stability, suggesting its strong potential for applications in food safety monitoring and related fields.

Surface-enhanced Raman scattering (SERS) has emerged as a powerful tool for food safety analysis. We present a three-dimensional particle-in-cavity substrate that utilizes plasmonic cavity resonances for highly sensitive detection. Fabricated by a convenient transfer of AuNPs onto an anodic aluminum oxide (AAO) template, this design facilitates scalable production. The synergistic cavity-particle interplay yields a 4.24-fold SERS enhancement over a conventional flat Si substrate. The substrate demonstrated high sensitivity with a Rh6G enhancement factor of 1.77 × 109, excellent uniformity showcasing relative standard deviations of 9.17% for Rh6G and 8.54% for crystal violet, and strong log-concentration linearity with correlation coefficients reaching 0.988 for Rh6G and 0.989 for Crystal Violet. It maintained 60% of its initial signal intensity after 30 days of storage and achieved an aspartame detection limit as low as 0.0078 g/L, demonstrating its excellent detection capability.

Constructing rare-earth-doped core-shell nanostructures and rationally co-doping with ions is an effective strategy to tailor upconversion luminescence, especially for enhancing Er3+-based red emission. Here, we synthesize NaErF4:0.5 % Tm3+@NaYF4 core-shell nanoparticles and systematically tune their red emission by codoping with Ce3+ and Yb3+ ions. Under 980 nm excitation, introducing 0.1 % Ce3+ increases the red-to-green intensity ratio (R/G) from 19.1 to 21.6. Upon further Yb3+ sensitization, the red emission intensity is maximized at 15 % Yb3+ (R/G = 24.4), whereas the R/G ratio reaches its highest value (33.6) at 20 % Yb3+, indicating distinct optima for brightness and color balance. Power-dependent emission measurements confirm predominantly two-photon-driven red upconversion, with slight variations in the slopes reflecting a redistribution of Er3+ level populations. Time-resolved luminescence reveals that Ce3+-induced cross-relaxation shortens the 4F9/2 lifetime of Er3+. Introducing 15 % Yb3+ compensates this effect by sustaining the population in the 4I11/2/4I13/2 intermediate states, which lengthens the 4F9/2 lifetime while recovering the red emission intensity. These results reveal that Ce3+-mediated cross-relaxation channels the Er3+ population into the 4I13/2 state, thereby promoting red emission from the 4F9/2 manifold, whereas Yb3+ acts as a 980 nm energy reservoir that recycles excitation energy to maintain this population, thereby boosting the R/G ratio. The inert NaYF4 shell combined with rational Ce3+/Yb3+ co-doping provides an efficient route to red-enhanced upconversion core-shell nanoparticles, which are promising for bioimaging, anti-counterfeiting, and display applications.

Surface-Enhanced Raman Scattering (SERS), with the exceptional single-molecule detection capability and high sensitivity, has become an advanced spectroscopic analysis method in fields such as chemical analysis and biosensing. Three-dimensional (3D) sandwich substrates, due to their unique structural characteristics, have attracted considerable attention for their ability to enhance SERS detection sensitivity. However, the controlled assembly of 3D sandwich substrates with bimetallic nanoparticles remains a challenge. In this paper, a fabrication method for constructing 3D sandwich substrates via a bottom-up approach is proposed. Using a liquid--liquid phase self-assembly method, Au@Ag nanocubes (Au@Ag NCs) were assembled on a polystyrene (PS) microsphere array with monolayer MXene (Ti3C2TX) adsorption, successfully constructed an Au@Ag NCs/ MXene/PS microsphere substrate. Furthermore, the SERS sensitivity of the substrate was evaluated using Rhodamine 6G (R6G), Crystal Violet (CV), and Aspartame (APM) molecules, and experimental results show that the detection limits are 10-12 M, 10-11 M, and 0.0313 g/L (1.06 x 10-4 M), respectively, with excellent uniformity and stability of the substrate. These findings demonstrate that the constructed 3D substrate exhibits outstanding SERS performance and holds significant potential for applications in environmental pollutant detection and food safety.

Abstract Surface plasmons modulate rare-earth luminescence via local field enhancement and photothermal effects, yet the synergy-competition between these inherently coupled effects remains to be decoded, impeding precise level-selective control. Herein, we construct a Yb3+, Er3+ upconversion system with different metals (Au/Ag nanoislands) and host morphologies (prism/plate), and combine steady-state spectroscopy, fluorescence lifetime dynamics, and multiphysics simulations to decode their interplay. We unveil pronounced level selectivity: the 2H11/2→4I15/2 transition is dominated by field enhancement, whereas the 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions exhibit a synergy-competition between field enhancement and nonradiative processes. Ag nanoislands, owing to dense coverage, create strong near-field coupling that boosts 520 nm emission but simultaneously introduce additional nonradiative decay channels, limiting lifetime extension. Dispersed Au nanoparticles, by contrast, form weaker coupling that suppresses nonradiative losses, resulting in a markedly prolonged excited-state lifetime. Host morphology further governs the field–thermal balance: plate-like crystals realize tighter plasmon coupling and higher enhancement under single-wavelength excitation, yet their smaller volume and reduced heat capacity lead to more pronounced thermal quenching under dual-wavelength coexcitation. Prism-like crystals, benefiting from larger metal-ion separation and greater thermal mass, achieve superior net enhancement at 520 nm. Simulations corroborate the near-field and thermal origins of these behaviors. This work decodes the synergy-competition landscape, establishing a design framework for level-selective rare-earth luminescence and tunable photonic devices.

This erratum corrected Fig. 10(a) errors in our paper [Opt. Express34, 104 (2026)10.1364/OE.578647]. The corrections have no influence on the results and conclusions of the original paper.

Chiral metasurfaces typically exhibit strong circular dichroism (CD), demonstrating immense application potential in fields such as optical polarization conversion, chiral molecular detection, and negative refraction materials. However, designing chiral metasurfaces with outstanding sensing performance and dynamic tunability remains a challenging task. This study introduces bound states in the continuum (BICs) and electrically controllable lithium niobate into chiral nanorod metasurfaces, forming a multilayer complementary chiral metasurface (MCCMs) structure. Notably, this structure can be fabricated using a single electron beam exposure and LiNbO3 deposition. The simulation results demonstrated that the MCCMs generated three ultra-narrowband transmission CD signals in the near-infrared band. The near-field electric field distributions revealed that these three CD signals primarily originated from the guided-mode and quasi-BIC resonances. The three CD signals were strongly dependent on the geometric parameters of the MCCMs and could be dynamically controlled by varying the applied uniform electric field strength. Additionally, the sensing performance of the MCCMs was analyzed under various ambient refractive indices, applied electric field strengths, and chiral environments, achieving a maximum figure-of-merit (FOM) of 3158.83 for refractive-index sensing. This work contributes to the design of complementary chiral metasurfaces and provides a feasible strategy for generating and controlling ultra-narrowband CD, as well as for high-performance chiral molecular sensing.

Chiral micro- and nanostructures exhibit strong circular dichroism (CD), demonstrating significant research and engineering potential in chiral molecular recognition, negative refraction material design, and polarization-selective imaging techniques. However, designing chiral structures with powerful CD, extremely narrow bandwidth, and dynamically adjustable performance remains challenging. This work introduces bound states in the continuum (BIC) and magneto-optical effects into achiral hexagonal nanopore arrays (AHNAs), investigating their CD properties under external magnetic fields. Under an applied magnetic field, the symmetric protected BICs within AHNAs are excited into Q-BICs, inducing two remarkably narrow and distinct CD signal responses in the near-infrared region. These signals exhibit a minimum full width at half-maximum of only 1.83 × 10-5 nm and a maximum Q-factor of 107. Tilting the structure along the x-axis further significantly enhances the CD signal (approaching 1). The formation mechanism of the magnetically induced CD signal is elucidated by combining quantum optical models with analyses of magnetic field and current distributions. The CD response of AHNAs is highly sensitive to structural geometry and can be dynamically modulated by varying the applied magnetic field strength. Additionally, the AHNAs achieve a maximum figure of merit of 106 in different refractive index environments and a CD enhancement factor of 106 in chiral molecules. These findings not only provide valuable insights for designing ultranarrowband chiral micro- and nanostructures but will also advance their applications in chiral sensing, asymmetric catalysis, and polarization conversion.

Surface-enhanced Raman scattering (SERS) was extensively employed in the domains of target analysis and detection owing to its benefits of high sensitivity and nondestructive detection. In this study, polystyrene (PS) microspheres served as templates. PS microspheres were systematically assembled on silicon wafer surfaces using air-liquid interfacial self-assembly. Subsequently, a PMMA-anisole solution was spin-coated to fill the interstices of the microspheres. Following the removal of the templates using cyclohexane ultrasonication method, gold nanoparticles were deposited onto the substrates utilizing the three-phase self-assembly procedure to construct the AuNPs@PMMA sphere-cavity array substrate. When the PMMA-anisole solution concentration was 1 %, the spinning speed was 5500 r/min, and the annealing temperature was 120 degrees C, the most regular nanostructure of the spherical cavity substrate was achieved. The Raman activity of the fabricated substrates was investigated with the selection of Rhodamine (R6G), Crystal Violet (CV) and Aspartame (APM) as target molecules. The experimental results indicated that AuNPs@PMMA sphere-cavity array substrate exhibiting high sensitivity, excellent uniformity, and stability, and the detection limits for R6G and CV were 10- 11 M and 10-10 M, respectively. In addition, the substrate achieved a low detection limit of 0.0313 g/L for aspartame (APM), demonstrating the potential application of the substrate in food safety testing.

Achieving multispectral camouflage compatible across laser, infrared (IR), and microwave bands is a pivotal challenge for advanced optoelectronic systems, yet its development has been fundamentally hindered by a longstanding paradox: severe heat accumulation caused by essential electromagnetic absorption inevitably compromises infrared stealth. Current strategies often suffer from performance trade-offs or structural complexity. Here, we propose and numerically demonstrate a hierarchical metasurface that resolves this conflict via a mechanism-decoupling strategy, enabling synergistic laser-IR-microwave stealth with built-in thermal management. The upper laser-IR layer employs coupled plasmonic resonances to achieve >0.99 absorption at 1.064 μm, maintain low emissivity (<0.2) within the 3-5 μm and 8-14 μm atmospheric windows, and simultaneously provide selective high emission (>0.8) in the 5-8 μm non-atmospheric window for radiative cooling. The lower radar layer incorporates genetically-optimized, polarization-insensitive Pancharatnam-Berry phase coding elements, delivering >10 dB monostatic radar cross-section reduction from 12 to 20 GHz. Full-wave simulations confirm that this integrated design effectively tackles the "absorption-heating" paradox endemic to conventional stealth materials. The microwave stealth performance is experimentally validated using fabricated prototypes. This work provides a scalable platform to overcome the thermal management bottleneck in multispectral camouflage and offers new insights into the design of integrated photonic devices requiring multifunctional electromagnetic and thermal control.

Balancing red-emission intensity and the red-to-green (R/G) emission ratio remains an important challenge in Er3+-based upconversion nanoparticles. Herein, a multilayer core–shell architecture was developed to achieve differential regulation of red-emission intensity and the red-to-green (R/G) emission ratio in Er3+-based upconversion nanoparticles. After screening NaYbF4:x%Er3+@NaYF4 core–shell nanoparticles, the sample containing 2% Er3+ exhibited a favorable balance between overall emission intensity and the R/G ratio and was therefore selected as the precursor for constructing NaYbF4:2%Er3+@NaYF4@NaErF4:y%M3+@NaYF4 (M = Yb or Tm) multilayer nanoparticles. In this architecture, the Yb-rich core, intermediate NaYF4 layer, compositionally tunable Er-rich shell, and outer NaYF4 shell were designed to provide spatially differentiated excitation harvesting, interfacial modulation, spectral regulation, and surface passivation, respectively. Under identical 980 nm excitation and collection conditions, incorporation of 15%Yb3+ into the Er-rich shell increased the integrated red-emission intensity to 2.40 times that of the undoped multilayer counterpart, whereas incorporation of 0.5%Tm3+ produced the highest R/G ratio of 17.1 while retaining comparatively strong emission. Power-dependent and time-resolved luminescence measurements, together with the proposed energy-transfer model, indicate that Yb3+ incorporation is predominantly associated with enhanced local excitation sensitization and energy utilization within the Er-rich region, whereas trace Tm3+ incorporation is more closely associated with excited-state population redistribution toward the red-emitting pathway. These results demonstrate that red-emission intensity and the R/G ratio can be differentially regulated within the same multilayer platform through Yb3+ or Tm3+ incorporation into the Er-rich shell. This work provides a spatially organized and compositionally tunable strategy for tailoring red upconversion emission in Er3+-based multilayer nanoparticles.

Raman spectroscopy is a pivotal tool in analytical and physical chemistry, yet its application in complex systems is hindered by spectral superposition and analysis challenges. The development of deep learning technology has provided new ideas for the component analysis of complex mixtures. This study proposes a mixture component identification method named MCI, which is based on the masked autoencoder and convolutional neural network. The aim is to effectively solve the problems of qualitative recognition and quantitative analysis in the Raman spectra of mixtures. The MCI method adopts a multi-stage framework: First, the Voigt function is used to accurately extract the characteristic peaks of the mixture. Second, the MAE model is employed to reconstruct the corresponding pure-substance spectra. Then, the CNN model is combined to conduct qualitative and quantitative analyses on the reconstructed spectra. Finally, the spectrum of the remaining components is obtained by subtracting the reconstructed spectrum from the mixture spectrum. By iterating the above process, the step-by-step unmixing of complex mixtures is achieved. In the generated mixed sample test data, the MCI outperforms the other three comparative models in terms of complete recognition accuracy in qualitative analysis and the evaluation indicators of each substance, while maintaining a lower average concentration error in quantitative analysis. Moreover, for complex mixtures containing interfering substances, the MCI shows strong anti-interference ability and maintains a high Identification accuracy. In the actual measurement of mixed sample Raman spectral identification detection, The MCI model achieved an average accuracy and F1_Score of 97% in all test samples, further verifying its reliability and practicality in detecting the main components of real and complex mixtures. In summary, this study provides a new technical method for Raman spectral analysis of complex mixtures, which holds certain theoretical significance and practical value.

In the era of the Internet of Things (IoT), droplet-based nanogenerators offer a promising solution for self-powered environmental monitoring. However, conventional displacement-current-driven devices are constrained by fluid-solid interface coupling, which results in low carrier transport efficiency and limits both output performance and sensing sensitivity. To address the need for acid rain monitoring, this study introduces a novel total-current nanogenerator (TCNG) optimized through curvature engineering, enabling an intelligent real-time acid rain sensing platform. By optimizing fluid-solid coupling dynamics and regulating the interfacial electric field gradient, the TCNG enhances spatiotemporal separation and pump accumulation of charge carriers at the solid-liquid interface, thereby improving charge transfer efficiency in the droplet-based nanogenerator platform. The platform exhibits high sensitivity and rapid response for acid rain monitoring, and it incorporates a ResNet18-1D deep learning algorithm to analyze the time-frequency features of the current signals, achieving 99.86% accuracy in identifying the pH values of acid rain. Furthermore, the TCNG delivers a peak voltage of 4500 V, sufficient to power electronic devices. By integrating multiphysics coupling design with artificial intelligence, this work provides a novel strategy for advancing the next-generation IoT-based environmental monitoring platform.

Transition metal dichalcogenides(TMDs)and their heterostructures exhibit excellent optoelectronic properties,thus rendering them promising candidates for next-generation electronic and optoelectronic devices.Investigating the ultrafast carrier dynamics in these materials not only allows for the exploration of ultrafast optoelectronic conversion processes within new materials but also provides a theoretical foundation for the development of high-speed optoelectronic devices.This review focuses on the latest advancements in carrier-dynamics behavior in TMDs and their heterojunctions.An optical pump-terahertz probe(OPTP)system and optimization methods were introduced to achieve OPTP signals with large signal-to-noise ratios in nanomaterials.Based on analysis using the OPTP,we summarized the different physical processes involved in the relaxation of TMDs,including exciton dynamics,phonon-assisted recombination,Auger recombination,and defect-induced relaxation processes.Aditionally,we discussed charge transfer via the OPTP in TMD heterostructures tuned by the pump wavelengths and stacking orders.This review summarized the recent progress of ultrafast dynamics in TMDs based on an OPTP and indentified some potential directions in condensed matter physics.

Next-generation optical data storage demands materials that support reversible and high-contrast luminescence switching across multiple wavelengths. In this study, we developed hybrid systems integrating rare-earth-doped nanocrystals (Eu3+ or Yb3+/Er3+) with tunable silver nano-islands films designed to exhibit either narrowband or broadband plasmonic absorption. The plasmon-driven photothermal effect facilitates reversible phase transitions in the host matrix and enables efficient modulation of luminescence, demonstrating wavelength-selective switching with narrowband absorbers and broad-wavelength response with broadband absorbers. Notably, we achieved cross-wavelength optical information storage using near-infrared light (800/980 nm) for writing and visible light (532 nm) for reading. Finite element simulations provide insight into the photothermal mechanisms and spatial temperature distributions, indicating that narrowband absorption induces localized hot spots, while broadband absorption results in spatially distributed heating. This work establishes a material platform and mechanistic foundation for high-security optical storage, anti-counterfeiting technologies, and multiplexed photonic devices.

Localized surface plasmon resonance (LSPR) in noble-metal nanostructures is a powerful strategy for enhancing upconversion (UC) emission from rare-earth-dopants. Herein, we present a distance-engineered Au-NaYF4 core shell (CS) platform that selectively amplifies multicolor UC emission by jointly tuning the diameter of Au nanoparticles (NPs) and the thickness of an inert NaYF4 spacer. Under 980 nm excitation, 56 nm Au NPs generate optimal near-field enhancement, yielding 6.82-fold (Er3 +, 654 nm) and 5.61-fold (Tm3+, 450 nm) increases, respectively, in comparison to NaYF4: 20 %Yb3+/2 %Ho3+@NaYbF4: 2 %Er3+ and NaYF4: 20 %Yb3+/2 % Ho3+@NaYbF4: 2 %Er3+@NaYF4: 20 %Yb3+/2 %Tm3+ CS NPs. Power- dependent and time-resolved measurements attribute the gain to excitation-rate enhancement-an increased Yb3+ absorption cross section-with negligible modulation of radiative rates. Finite-element simulations reveal intense gap "hot spots" for 56 nm Au NPs that account for the optimum. These results establish a simple distance-size design rule for spectrally selective, intensity-tunable UC emission, enabling compact plasmonic platforms for bioimaging, anti-counterfeiting and nanoscale optoelectronics.

In this paper, Au-Ag alloy nanostar (Au-Ag NSt) substrates were prepared by liquid-liquid three-phase self-assembly method, and the influence of preparation conditions on their Raman activity of the substrate was explored. By adjusting the gold-silver ratios of alloy seeds and the concentration of AgNO3 in the growth solution, it was found that the LSPR peak can be adjusted. Under the conditions of Au1-Ag3 nanoparticles as seeds and 200 μL AgNO3 solution (2 mM) as epitaxial growth solution, the prepared Au1-Ag3 NSt substrate exhibits excellent SERS activity. The substrate can detect R6G and CV probe molecules with detection limits as low as 10-11 M and 10-10 M, respectively. Experiments have confirmed that the substrate has the characteristics of high sensitivity, good uniformity and strong stability. In addition, the substrate can detect APM molecules far below the safety standard, which further proves that the structure has excellent practical application potential as a SERS substrate.