ABSTRACT Precise neural modulation is an important tool in neuroscience research for intervening in specific neural pathways. Photoacoustic is an emerging photonics technology enabling high precision non‐genetic neural stimulation in vitro and in vivo. Fiber‐based and film‐based optoacoustic emitters have demonstrated their capability in fundamental studies of how neurons respond to mechanical stimuli at the single‐cell level, as well as in brain stimulation in vivo. Here, we report a new and general method to fabricate optoacoustic emitters through an in situ photothermal curing process of PDMS (Polydimethylsiloxane) on different platforms, including the tip of tapered fibers with high precision, and flat substrates with programmed patterns. Candle soot‐based tapered fiber optoacoustic emitter (CS‐TFOE) prepared through this new method generated a highly localized ultrasound field and enabled efficient and precise neuromodulation. We designed an integrated and compact photoacoustic neuromodulation system incorporating the FOE, a nanosecond pulsed laser for photoacoustic generation, and a function generator for synchronization. We have shown that the system can be easily integrated with standard neuroscience recording methods, such as Ca 2+ imaging, and achieves effective neuromodulation in vitro.

ABSTRACT Persistent luminescence (PersL) attracts growing attention due to its potential for energy‐efficient optical storage, sensing, and imaging technologies. Although extensively investigated in bulk and powder forms, its translation into transparent and functional thin films or glassy systems remains a major challenge. This review discusses the state of the art in the development of persistent luminescent thin films and glasses, emphasizing processing strategies, structure‐property correlations, and emerging device‐level applications. The mechanisms governing PersL are briefly described. This is followed by an analysis of thin‐film growth techniques, including chemical, physical, and hybrid routes, and highlighting their influence on defect engineering, dopant distribution, and luminescence performance. The discussion integrates advances on polymeric and glass matrices, where control over morphology and interfaces is essential to achieve optical transparency and environmental stability. This review also aims to present opportunities for studying and developing new materials through thin‐film fabrication techniques that contribute to the creation of devices beneficial to society, the environment, and energy. Current limitations and future directions are discussed focusing on trap modulation, compositional design, and scalable fabrication toward next‐generation photonic and optoelectronic devices.

ABSTRACT Single‐nanoparticle and single‐molecule fluorescence detection delivers unparalleled capabilities for quantifying concentrations, hydrodynamic sizes, and molecular dynamics for biosensing assays or environmental monitoring. Metalenses offer a promising route to miniaturizing high‐NA objective lenses, but their use in fiber‐integrated probes for quantitative single‐particle analysis remains largely unexplored. In this work, we introduce an achromatic metalens integrated with a solid‐core optical fiber (AMOF) as a compact sensing head that enables remote epi‐fluorescence correlation spectroscopy (FCS) in aqueous solutions. We achieve remote epi‐fluorescence monitoring of polystyrene nanoparticles of sizes from 110 nm to 4 µm and streptavidin biomolecules in the far‐red spectral range within a defined focal volume. By systematically varying the optical fiber core diameters, we reveal and quantify a design trade‐off between single‐nanoparticle sensitivity and detection volume, enabling accurate determination of particle concentration and size down to low picomolar‐femtomolar regimes through remote FCS. The robust operation of the AMOF head over meter‐scale fiber lengths without complicated alignment demonstrates that high numerical aperture (NA) achromatic metalenses can be effectively combined with optical fibers for remote single‐particle fluorescence analysis. This approach opens promising opportunities for in situ diagnostics, environmental nanoparticle monitoring, and remote emitter characterization.

ABSTRACT Highly sensitive cryogenic temperature probing is important for many frontier fields such as quantum computing and deep‐space exploration. However, it has remained a huge challenge to achieve high‐sensitivity thermometry at cryogenic temperatures for luminescent materials. Here, we propose an effective strategy to tune and enhance thermo‐responsive upconversion of Er sublattice at ultralow temperatures through Ho 3+ ‐mediated energy looping. We show that the design of energy looping between Er 3+ and Ho 3+ ions makes the populations of Er 3+ at its intermediate states much more sensitive on temperature, resulting in a better enhanced upconverted green emission at low temperatures. This further amplifies the spectral contrast between the non‐thermally coupled green and red emissions, and contributes to a high relative sensitivity of 7.97%·K −1 at 20 K, much higher than that of the pure Er sublattice (1.98%·K −1 ). Moreover, the sample also exhibits emission color changes from red to yellowish green with decreasing temperatures, allowing for the low‐temperature visual. These results demonstrate the great potential of Ho 3+ ‐modulated NaErF 4 :Ho@NaErF 4 nanoparticles for applications such as ultralow‐temperature sensing and information security.

ABSTRACT Multiple resonance (MR) emitters with excellent color purity hold promise for high‐performance organic light‐emitting diodes (OLEDs), yet their practical applications face severe efficiency roll‐off at high luminance due to inefficient triplet exciton utilization inherent in themselves. Herein, an energy‐level ladder engineering strategy is presented to address this challenge. By introducing an electron‐rich fragment into the MR framework, a locally excited (LE) intermediate energy level (T 2 ) is constructed that facilitates rapid spin‐flipping with reduced thermal activation energies. The synthesized emitter, tCzBNNOp, with pure green emission at 520 nm (CIE: (0.20, 0.72)), exhibits a remarkably high reverse intersystem crossing rate ( k RISC = 1.45 × 10 6 s −1 ). Theoretical calculations and experimental data jointly reveal that the LE T 2 state with large spin orbital coupling and a small energy difference between S 1 , creating an extra RISC channel. In the corresponding non‐sensitized OLED devices, tCzBNNOp achieves a maximum external quantum efficiency (EQE max ) of 30.3% with an efficiency roll‐off of only 12.5% at 1000 cd m −2 , outperforming its structural analog in roll‐off suppression. Moreover, the device retains an EQE of 16.6% at 5000 cd m −2 and demonstrated better operational stability. This work establishes energy‐level ladder engineering as a powerful approach for developing high‐efficiency MR‐based OLEDs with suppressed efficiency roll‐off.

ABSTRACT Polarization‐based visual detection overcomes the limitations of conventional vision systems by providing additional optical polarization information for accurate target recognition and environmental assessment in critical scenarios. However, current neuromorphic vision systems lack adequate polarization sensitivity in the infrared band and cannot support integrated “broad‐spectrum polarization perception and brain‐inspired processing”. To address this, high‐performance polarization‐sensitive infrared neuromorphic synaptic devices are urgently needed. This study designs a 2D PdSe 2 /Ta 2 NiS 5 heterojunction, taking advantage of the pronounced in‐plane anisotropy and narrow bandgap inherent to PdSe 2 and Ta 2 NiS 5 . Through bias‐induced band bending, the electronic properties are modulated to achieve photoelectric synaptic functionality. The heterojunction demonstrates a broad spectral response from 808 to 2200 nm, with a high polarization ratio of 15.6 at 808 nm and 8.7 at 2200 nm. It successfully emulates key synaptic behaviors such as paired‐pulse facilitation (PPF = 56% at 808 nm), paired‐pulse depression (PPD), and the transition from short‐term to long‐term plasticity (STP to LTP), while consuming only 153.2 fJ per synaptic event. Synaptic weight can be dynamically modulated via light intensity, pulse width, and polarization angle. This heterojunction shows great potential for applications in autonomous driving, industrial infrared inspection, and bionic navigation.

ABSTRACT Polaritonic crystals for hyperbolic phonon‐polaritons (PhP) in van der Waals materials are burdened by the intermode scattering due to the inherently multimodal nature of PhP. So far, polaritonic crystals have been demonstrated within the Type‐II Reststrahlen band (RB‐II) where the in‐plane components of the dielectric permittivity tensor are negative, while the out‐of‐plane component is positive. By contrast, a Type‐I Reststrahlen band (RB‐I) is characterized by the negative out‐of‐plane and positive in‐plane permittivity, and consequently, the inversion of PhP field symmetry, negative phase velocity, and anomalous dispersion. Such an operation regime remains unexplored for periodic structures supporting collective polaritonic modes. Here, we employ a biaxial crystal α‐MoO 3 and near‐field imaging to study mid‐infrared polaritonic Bloch modes in a 1‐D Fourier crystal within the RB‐I. Surprisingly, we observe a manifestation of Bloch waves as a dispersionless near‐field pattern across the first Brillouin zone, in contrast to previous works exclusively focused on the RB‐II. Our results demonstrate the possibility to realize a quasi‐single‐mode operation regime of polaritonic crystal for the inherently multimode hyperbolic PhP, and reveal the importance of field symmetry for polaritonic crystals in general and for the emerging field of Fourier crystals in particular, promising new ways to manipulate the nanolight.

Abstract High‐precision optical diagnostics and therapy in deep tissues are hindered by light scattering and absorption. Engineered optical fibers, serving as minimally invasive optical fibers, provide a powerful platform to bypass these barriers. This review systematically deconstructs the design of these advanced fibers from the unified perspectives of materials science and structural engineering. First, key material systems are analyzed—from traditional silica to emerging polymers and hydrogels—evaluating how their intrinsic properties dictate the fiber's optical performance, mechanical compliance, and biocompatibility. Then, critical structural paradigms are examined, including propagation modes, refractive index profiles, and core geometries, elucidating how these designs control features such as signal fidelity, resolution, and functional integration. The review further considers how the fiber's potential is amplified by auxiliary front‐end physical modulation and back‐end computational reconstruction techniques. Building on this foundational framework, the application of these engineered fibers is comprehensively surveyed in state‐of‐the‐art biomedical diagnostics, such as endoscopic imaging and biosensing, and in targeted therapeutics, including optogenetics, phototherapies, and drug delivery. Ultimately, by systematically linking engineering principles to biomedical functions, this review establishes a foundational framework for designing next‐generation, clinically focused fiber‐optic systems, concluding with a critical assessment of prevailing challenges to illuminate future research directions in this burgeoning field .

ABSTRACT MAPbBr 3 single crystals (MPB SCs) are promising materials for X‐ray detection; however, their use in low‐dose imaging is limited by high dark current, low detectability, and noise that degrades image clarity. Under X‐ray irradiation, where electron–hole pair generation is inherently low, suppressing defects is critical to minimize losses and maximize charge collection. In this study, metastable zone engineering is employed by tuning the MABr:PbBr 2 ratio during inverse temperature crystallization (ITC) to produce defect‐suppressed MPB SCs. Excess MABr broadens and stabilizes the metastable zone, reducing nucleation events and enabling the growth of large, high‐crystallinity MPB SCs exceeding 10 mm within 11 h. These crystals exhibit electronic properties closer to intrinsic behavior, with prolonged carrier lifetimes of 371 ns and an enhanced mobility‐lifetime ( µτ ) product of 3.43 × 10 −3 cm 2 V −1 . Photoluminescence spectra reveal a distinct secondary peak from photon recycling, with intensity 1.25 times greater than the band‐edge peak, indicating efficient photon reabsorption due to reduced non‐radiative losses. Devices fabricated from excess MPB SCs achieve a record‐low detection limit of 0.47 nGy s −1 , high sensitivity (6.117 × 10 3 µC Gy air −1 cm −2 ), and high‐resolution X‐ray imaging, demonstrating strong potential for advanced medical and industrial applications.