Abstract Three-dimensional (3D) images have become important information carriers in multimedia, medical treatment, and entertainment. However, existing 3D image hiding and watermarking schemes are mostly limited to single 3D image encryption, resulting in insufficient capacity, low security, and optimizable concealment. To address these issues, this paper proposes a highcapacity multi-3D image watermarking method based on multi-dimensional multiplexing holography and QZ embedding. Multiple 3D images are grouped and encoded into holographic watermarks using a multi-dimensional multiplexing hologram generation algorithm, where chaotic phase masks and spiral phase masks are adopted to expand the key space and enhance security. A contrast-guided embedding strategy is used to locate visually insensitive highcontrast regions in the two-dimensional host image, and the holographic watermarks are embedded into different wavelet sub-bands by combining discrete wavelet transform, singular value decomposition, and QZ embedding to achieve low distortion and strong robustness. Simulation results demonstrate that the proposed method can simultaneously embed sixteen 3D images with high imperceptibility proved by ultrahigh correlation coefficient and negligible entropy variation, good key sensitivity, and reliable robustness against noise and occlusion attacks. Compared with state-of-the-art hologram-based encryption schemes, the proposed method exhibits significant advantages in capacity, security, and concealment, showing potential for secure optical information hiding and copyright protection of 3D visual data.

The size of lanthanide upconversion nanocrystals has a considerable impact on their luminous characteristics, but the underlying mechanism is yet unknown. Six typical samples were chosen for systematic size effect experiments after we manufactured monodisperse Y2O2S: Er3+/Yb3+ microspheres. Our results establish surface defects induced by specific surface area as the fundamental mechanism governing nanoscale structure-property correlations, showing that phosphor particle size can be directionally controlled to maximize both luminescent performance and temperature-sensing capabilities. We have identified the mechanism behind size-dependent optical properties: larger particles alter the emission color and significantly enhance the luminescence intensity. Temperature-sensing behavior also exhibits strong size dependence: absolute sensitivity (Sa) correlates negatively with size and positively with temperature at the thermally coupled level (TCL); at the non-thermally coupled level (NTCL), Sa correlates negatively with both size and temperature. It's interesting to note that the Sa value for the smallest sample is 17 times higher at TCLs, reaching 0.0866 K-1. Our findings provide a clear fundamental understanding of size effects in nanoscale lanthanide upconversion luminescence and offer important insights for nanoscale temperature sensing.

The characteristics of the phosphors used play a crucial role in determining the performance of near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs). The development of phosphors with broadband NIR emission and effective excitation by blue light chips has become a challenge. Herein, Cr3+, Ni2+ co-doped LiMg6AlO8 NIR-emitting phosphors were synthesized. Under 449 nm excitation, the LiMg6AlO8: Cr3+,Ni2+ phosphors exhibits an ultra-broadband emission spanning 600 nm to 1600 nm, with a full width at half maximum (FWHM) of 305 nm. Effective energy transfer (ET) of Ni2+ ions from isolated Cr3+, Cr3+-Cr3+ pairs, and Cr3+ clusters resulted in a 5.3-fold increase in NIR emission peak at 1300 nm, with the ET efficiency of up to 64.3%. Meanwhile, the optimal excitation wavelength was observed to shift gradually from 402 nm in the ultraviolet range to 449 nm in the blue region, effectively addressing the limitation of insufficient blue-light absorption. Furthermore, at 373 K, the material preserves 60.8% of its emission intensity, confirming its moderate thermal stability. The synthesized LiMg6AlO8: Cr3+,Ni2+ phosphor shows potential for applications in nightvision technology, organic compound identification and bioimaging.

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have been widely explored for applications such as night-vision imaging, biomedical analysis, and horticultural illumination. Nevertheless, their broader implementation remains constrained by the insufficient emission intensity and spectral coverage in the long-wavelength NIR region provided by existing phosphor systems. In this work, a ZnWO4 host co-activated with Cr3+ and Yb3+ ions was synthesized, exhibiting strong and continuous NIR luminescence extending from approximately 850 to 1150 nm under ultraviolet (UV) excitation at 345 nm. Relative to the Cr3+-only counterpart, the co-doped phosphor demonstrates a marked enhancement in internal quantum efficiency (IQE), increasing from 55.36% to 78.43%, together with improved thermal robustness, with emission retention rising from 17.35% to 25.22% at 150 degrees C. These improvements are primarily ascribed to efficient non-radiative energy migration from Cr3+ sensitizers to adjacent Yb3+ activators, as well as the favorable energy-level configuration of Yb3+ ions. Furthermore, pc-LED devices fabricated by integrating the ZnWO4: Cr3+, Yb3+ phosphor with commercial 450 nm blue chips were systematically evaluated, confirming stable NIR output. Overall, these results indicate that the proposed ZnWO4: Cr3+, Yb3+ material is a promising candidate for practical long-wavelength NIR pc-LED applications.

This paper proposes a three-dimensional image hierarchical encryption method based on structured light holography and chained iris keys, aiming to address issues in the existing 3D image encryption techniques, such as low decryption quality, insufficient key security, inconvenient key management, and lack of hierarchical access control. The method first divides the 3D image into equidistant slices along the depth direction, generates encrypted structured light using a custom-designed structured light phase mask, and computes the structured light hologram for each slice layer via an iterative angular spectrum algorithm. Subsequently, user iris images are captured, and after preprocessing and feature extraction, user-specific chaotic phase masks are generated through a piecewise linear chaotic map, serving as keys for the hierarchical encryption. On this basis, a chained hierarchical encryption strategy is adopted, where the hologram of each level is coupled with the corresponding user's chaotic mask and the hologram from the previous level for the encryption, forming a dependent ciphertext sequence. During decryption, users must undergo iris authentication to obtain the chaotic key corresponding to their access level, followed by sequential chained decryption and optical reconstruction, thereby achieving identity- and authority-based hierarchical information access. Simulation experiments demonstrate that the method ensures high-quality 3D reconstruction while exhibiting high key sensitivity and robustness against noise, occlusion, and statistical attacks. Furthermore, the multi-parameter design in the structured light phase mask further expands the key space and enhances system security. This study provides a secure, practical, and manageable solution for the confidential transmission and hierarchical management of sensitive 3D visual data, with potential applications in fields such as medical imaging, military simulation, and virtual reality.

To address the challenges of low efficiency and insufficient polarization control in generating cylindrical vector beams (CVBs) using single-layer metasurfaces, this study proposes an efficient CVB generation scheme based on a double-layer metallic metasurface. At 0.1 THz, the structure achieves high co-polarized transmission coefficients ( T_xx = 0.782, T_yy = 0.863) and a near- π phase delay (188.156°), successfully constructing a half-wave-plate functional unit. Full-wave simulations demonstrate that the structure maintains stable polarization conversion characteristics across the 0.08–0.12 THz band. Based on the Pancharatnam–Berry (PB) phase principle, a 31 × 31 metasurface array converts X- and Y-polarized incident plane waves into radially and azimuthally polarized CVBs, respectively, with clearly observed near-field polarization singularities. A comparative study under plane-wave and spherical-wave illumination reveals consistent polarization distribution at the center, while edge regions exhibit polarization scrambling due to wavefront curvature, nonuniform phase modulation, and limitations of the horn antenna model. Furthermore, leveraging the polarization-sensitive properties of the unit cell, vortex beams with topological charges l = ± 1 are generated under circularly polarized incidence. The metasurface was fabricated using standard printed circuit board (PCB) technology and validated via a terahertz imaging system. The measured field intensity distributions agree well with theoretical simulations, confirming the efficient generation and control of CVBs.

This paper introduces a color image encryption technique based on phase-only hologram (POH) encoding with dynamic constraint and phase retrieval under structured light illumination (SLI). During encryption, the color plaintext is first encoded into a POH. This hologram is then transformed into an amplitude distribution through phase-amplitude conversion. Subsequently, using an iterative phase retrieval algorithm under structured light, the amplitude is encrypted into a visible ciphertext image, while a POM set is produced. The resulting ciphertext exhibits a visible image pattern, rather than noise-like appearance, providing ultrahigh imperceptibility. Moreover, the dynamic constraint in hologram encoding ensures balanced quality across color channels, leading to high-quality decrypted images with correct keys. The incorporation of a structured phase mask and the POM set expands the key space and boosts security. In decryption, the decryption structured light (DSL) illuminates the ciphertext and the neural network sequentially to generate a reconstructed amplitude. This amplitude is converted into a phase distribution via amplitude-phase conversion, which then acts as the POH for color holographic reconstruction, yielding the decrypted image. Numerical simulations demonstrate the method’s feasibility, high security, and strong robustness.

Oxysulfides have emerged as promising hosts for advanced optical materials due to their non-toxicity, excellent chemical stability, and high phonon energy matching, making them particularly suitable for fluorescence thermometry and anti-counterfeiting applications. However, despite these advantages, research on constructing welldefined core-shell architectures based on oxysulfide hosts remains scarce, largely due to the challenges in controlling lattice matching and dopant migration. This gap limits the ability to tailor their complex emission processes for multifunctional applications. In this work, we successfully synthesized multicolor, multifunctional up-conversion phosphors Y2O2S: Er3+@Y2O2S: Tm3+ via an improved homogeneous precipitation method. Compared with a conventionally co-doped system, the core-shell structure provides surface passivation and regulates the energy transfer pathway between Er3+ and Tm3+, significantly enhancing spectral emission tunability. Benefiting from the optimized energy transfer in the core-shell design, the phosphors function as highly sensitive fluorescence thermometers, delivering a maximum relative sensitivity of 4.18% K-1 over a wide temperature range (303-583 K). Moreover, under different laser excitations, the materials show remarkable multicolor switching, generating large chromaticity variations, enabling robust visual anti-counterfeiting and optical encryption. This study provides a new paradigm for engineering sulfoxide hosts with core-shell structures.

Rare-earth-doped materials have been widely utilized in optical thermometry and information anti-counterfeiting owing to their high stability and tunable spectral response. In this work, a series of Ca2GdTaO6 (CGTO): Bi3+, Ln3+ (Ln = Eu, Sm, Dy) phosphors were synthesized. The temperature-dependent luminescent behaviors and energy transfer mechanisms of the samples were systematically investigated by precisely regulating the doping ratios of Bi3+ and different Ln3+ ions. In the CGTO host lattice, Bi3+ ions can generate stable blue emission under 316 nm excitation, and subsequently transfer energy efficiently to the excited states of rareearth ions through non-radiative energy transfer (ET) processes. A series of novel optical thermometers with an optimal relative sensitivity of 1.31 % K-1 were designed based on the luminescence of the Bi3+ and Ln3+ ions with different temperature sensitivities. Furthermore, the present investigation explored the multimodal anti-counterfeiting functionality and temperature-dependent color-changing phenomena of CGTO: Bi3+, Ln3+ phosphors. When the doping concentration and excitation wavelength are varied, the material exhibits tunable emission colors and diverse luminescence modes. These results demonstrate the vast potential of CGTO: Bi3+, Ln3+ phosphors in optical thermometry and anti-counterfeiting.

ABSTRACT Investigating the mechanism of persistent luminescence (PersL) enhancement is crucial for designing PersL materials and their applications. In this work, a remarkable green PersL enhancement in Zn 2 GeO 4 :Mn 2+ (ZGO:Mn) via cation engineering using Sb 3+ co‐doping is achieved. After UV excitation, the initial and 500 s PersL intensities of ZGO:Mn/Sb are 6.9–19.2 times higher than those of ZGO:Mn, with a PersL duration exceeding 100 h. The improved PersL originates from Sb 3+ co‐doping, which generates new traps at 0.759 eV and raises the intrinsic defect density of ZGO, leading to enhanced PersL intensity and extended PersL duration. Besides, the ZGO:Mn/Sb sample shows negligible luminescence intensity degradation after 6 months of storage in air and unchanged performance over 100 charge‐decay cycles, and can be effectively excited by natural light at different times of day and various weather conditions. Besides, the scintillation intensity of the sample reaches 47.47 times that of a commercial Bi 4 Ge 3 O 12 crystal, achieves resolution exceeding 16.6 LP/mm in X‐ray imaging, and supports delayed X‐ray imaging up to 10 min. This work not only develops a green PersL phosphor for information storage, safety indication, and X‐ray imaging, but also offers an effective strategy for designing and optimizing PersL materials.

Flexible wearable pressure sensors still face the challenges of complex structure and high manufacturing costs. In this article, we present a simple method for preparing a highly sensitive, flexible wearable pressure sensor based on candle soot and porous PDMS foam. Meanwhile, to enhance the sensor’s robustness and practicality, a fully enclosed packaging design based on PDMS film was developed. The resulting sensor demonstrates excellent sensitivity, attributed to its porous structure, rough surface, and the unique properties of candle soot. Furthermore, the developed sensor can accurately detect movements in various parts of the human body and measure the force applied during finger pressing. This innovative porous PDMS/candle soot pressure sensor shows great potential for applications in wearable electronics.

Ceramic-composite phosphor-in-glass films (PiGFs) are excellent candidates for high-power and stable Laserdriven (LD) lighting due to their excellent thermal management. However, the high temperatures in existing PiGF in-situ crystallization processes can damage the phosphor structure, limiting their development for high color rendering index (Ra) applications. In this study, a novel ceramic-composite tricolor PiGF system is cosintered at a low temperature of 600 degrees C using a ZnO-Li2O-SiO2 (ZLS) sintering matrix and incorporates beta-Zn2SiO4 glass-ceramic as a functional phase. This process achieves enhanced light scattering and thermal management while preserving the integrity of the tricolor phosphors. Through process optimization, the PiGF achieved bright white light with a luminous flux (LF) of 1361 lm @7.08 W and an Ra of 84.5. Finally, the PiGF was assembled into a laser lighting prototype, exhibiting an optimal balance between luminous intensity and color quality, rendering this color converter highly promising for high-quality laser lighting applications.

Terahertz (THz) imaging technology utilises the unique advantages of terahertz waves, such as non-ionising radiation, penetration of non-polar materials and high sensitivity to polar molecules, and shows great potential in various fields including device detection, biomedical diagnostics and security screening. Despite its promise, the technology’s full potential is limited by challenges in power output, stability, resolution, and real-time imaging. This review addresses these challenges by providing an in-depth analysis of the current status and future directions of terahertz imaging. First, this paper compares terahertz imaging techniques to different imaging principles. Besides, the characteristics of various imaging techniques are summarised in a table. This paper then discusses the significant applications of terahertz imaging technology in fields such as device detection and biomedicine. Finally, considering the latest advances in hardware innovation, mechanism exploration, and algorithm enhancement, this paper suggests possible future directions for terahertz imaging technology. Focusing on advances from approximately 2018 onward, this review provides a timely analysis of the field’s evolution beyond its foundational period. It offers a restructured technical taxonomy, highlights emerging applications driven by interdisciplinary convergence, and presents a forward-looking roadmap based on the latest breakthroughs in hardware, mechanisms, and algorithms. This work aims to serve as a comprehensive reference for guiding the next phase of terahertz imaging technology toward practical implementation.

Phosphor-in-glass-ceramic (PiGC) is regarded as promising material for high-power laser-driven lighting. However, the low crystallinity and excessively large grain size of current PiGC materials lead to limited improvement in both luminous flux (LF) and luminous efficacy (LE). Here, we report a preparation of transparent, highly crystalline nanocrystalline glass-ceramic with tunable crystallinity via a low temperature spark plasma sintering (SPS) and heat-treatment process. The nano-crystals perform a dual functional role by acting as light-scattering centers to enhance light conversion efficiency and simultaneously forming a secondary phase that establishes localized thermal dissipation networks for rapid cooling of the PiGC. The optimized sample exhibits superior optical performances with an LE of 347 lm W- 1 and an LF of 1633 lm under 7.08 W. Compared to phosphor-inglass (PiG) sample, the best PiGC sample exhibits an LF reaching 216% of the original value, demonstrating that Zn2SiO4 precipitation significantly enhances the material's luminescent properties. This result shows that the designed PiGC has an important application prospect in high-brightness, long-range laser-driven lighting systems.

Cr3+-activated near-infrared (NIR) phosphors have attracted significant attention in recent years owing to their potential applications in nondestructive testing, bioimaging, and night vision technologies. However, the development of high-performance NIR phosphors remains a considerable challenge. In this work, a novel broadband NIR-emitting phosphor, YGdScSbO7: Cr3+, was successfully synthesized via a high-temperature solidstate reaction. The obtained phosphor exhibits a strong emission centered at 763 nm with a full width at half maximum (FWHM) of 142 nm. Inspired by the cation substitution strategy, the partial substitution of Sc3+ with Ga3+ ions significantly improves the emission intensity and quantum efficiency. The optimized sample, YGdScSbO7: 0.03Cr3+, 0.8Ga3+, shows a broadband NIR emission covering the 600-950 nm region with a FWHM of 117 nm and an internal quantum efficiency as high as 73.89%. Furthermore, the sample maintains approximately 56.64% of its initial emission intensity at 363 K, indicating great thermal stability. A NIR phosphorconverted LED (pc-LED) fabricated by the optimized phosphor with a 450 nm blue LED chip delivers an output power of 8 mW under the 180 mA driving current, demonstrating promising potential for applications in night vision illumination, nondestructive inspection, and biomedical imaging.

As a popular artificial composite material emerging in recent years, metasurfaces are one of the most likely devices to break through the volume limitation of conventional optical components due to their compact structure, flexible materials, and high modulation resolution of the beam. With a unique arrangement of units or made of special materials, the metasurface can effectively modulate the incident light's amplitude, phase, polarization, and frequency, thus realizing applications such as communication, imaging, sensing, and beam steering. The interaction of high‐resolution structure, periodic arrangement, and unique constituent materials makes it possible to realize these applications, so researchers should choose the appropriate micro‐nano processing technologies when designing and preparing the metasurface. This review will present micro‐nano processing technologies related to the preparation of metasurfaces, such as electron beam lithography (EBL), femtosecond laser processing, focused ion beam lithography (FIB), additive manufacturing, nanoimprinting, and self‐assembly, respectively. In addition, classical lithography techniques such as wet lithography, plasma lithography, deep reactive ion etching (DRIE), and photolithography will be introduced. Their development history and functions are described in detail, and examples of these techniques in preparing micro‐nano‐structures in different branches are presented, as well as some examples of metasurface preparation using these techniques. In addition, this paper has produced several tables describing these technologies, outlining their resolution, processing materials, advantages and disadvantages, and so on. Hopefully, this review will provide researchers with options and ideas for preparing metasurfaces.

In complex electromagnetic environments, traditional static absorbers struggle to meet dynamic control requirements. Tunable absorbers based on metasurfaces have emerged as a research hotspot due to their ability to flexibly control electromagnetic wave properties. This paper provides a systematic review of research progress in tunable absorbers across the microwave, terahertz, and infrared bands, with a focus on analyzing the physical mechanisms, material systems, and performance characteristics of five dynamic control methods: electrical control, magnetic control, optical control, temperature control, and mechanical control. Electrical control achieves rapid response through materials such as graphene and varactor diodes; magnetic control utilizes ferrites and other materials for stable tuning; optical control relies on photosensitive materials for ultrafast switching; temperature control employs phase-change materials for large-range reversible regulation; and mechanical control expands tuning freedom through structural deformation. Research indicates that multi-band compatibility faces challenges due to differences in structural scale and physical mechanisms, necessitating the integration of emerging materials and synergistic control strategies. This paper summarizes the core performance metrics and typical applications of absorbers across various bands and outlines future development directions such as multi-field synergistic control and low-power design, providing theoretical references and technical pathways for the development of intelligent tunable absorber devices.

A series of Y2O2S: 0.25 % Ho3+/x%Yb3+ (where x = 4, 6, 8, and 10) phosphors were synthesized by using a chemical co-precipitation method, and their temperature sensing properties were systematically investigated. The upconversion luminescence (UCL) spectra of the samples were recorded under 980 nm laser excitation. The Y2O2S: Ho3+/Yb3+ system exhibits three distinct UC emission bands in the green, red, and near-infrared regions, corresponding to the transitions of 5F4/5S2 -> 5I8, 5F5 -> 5I8, and 5F4/5S2 -> 5I7 of Ho3+, respectively. According to the emission spectra, the sample with a Yb3+ doping concentration of 6 % exhibited the strongest luminescence intensity, with a quantum yield reaching 4.01 %. To further explore its temperature sensing properties, the fluorescence intensity ratios (FIR) of both thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) of Ho3+ were systematically analyzed. Notably, temperature sensing materials based on NTCLs exhibit significantly enhanced sensitivity while maintaining a broad temperature measurement range. Specifically, the absolute sensitivity (SA) increased from 0.011 % to 0.498 %, representing an approximately 45-fold improvement. These findings indicate that Y2O2S: Ho3+/Yb3+ UCL materials possess excellent potential for applications in optical temperature sensing.