The bandgap energy of semiconductor lead mixed halide perovskite can be flexibly tuned by changing the bromide to iodide ratio, which is beneficial for the fabrication of tandem solar cells to efficiently capture light power across the visible spectral range. Unfortunately, the phase segregation effect would be induced in mixed halide perovskite upon continuous light illumination, with the bandgap energy deviating from the desired value due to unexpected formations of bromide- and iodide-rich domains. Here we have induced phase segregation in a solid film of mixed halide perovskite CsPbBr1.2I1.8 nanocrystals (NCs) by laser excitation and demonstrated that the original mixed phase can be partially recovered right after the application or removal of an external electric field. We propose that the iodide ions created after phase segregation can be instantly enriched at the opposite direction of the external electric field, thus enhancing the entropic driving force for them to reoccupy the internal vacancies of some segregated CsPbBr1.2I1.8 NCs. This electric-field-induced partial phase remixing can also be applied to segregated CsPbBr1.5I1.5 and CsPbBr1.2I1.8 NCs, signifying the universal role played by the spatial distribution of iodide ions in the deep understanding and effective control of phase segregation in mixed halide perovskite NCs.

The transfer of single-crystalline gold flakes is crucial for device integration, yet its impact on optical performance remains unclear. Here, we develop a concentrated sulfuric acid-assisted post-treatment method that effectively removes transfer-induced micro/nano-bubbles on gold flakes, restoring the flake surface to a pre-transfer roughness level of similar to 0.26 nm. A scattering-type scanning near-field optical microscope reveals that this treatment significantly improves signal-to-noise ratio and propagation length of propagating surface plasmon polaritons in gold flakes. Moreover, nanoparticle-on-mirror nanocavities constructed on treated flakes exhibit a rise in quality factor from 9.7 (for nanocavities on untreated flakes) to 16.5, owing to suppressed bubble scattering. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

ABSTRACT Exciton polaritons (EPs), hybrid light‐matter quasiparticles, enable deep subwavelength field confinement and strong intrinsic nonlinearities, making them highly promising for integrated nanophotonic devices. Realizing such applications, however, requires a thorough understanding of EPs properties, particularly their transport and loss mechanisms. Here, we employ scattering‐type scanning near‐field optical microscopy (s‐SNOM) to probe MoTe 2 flakes on Si/SiO 2 substrates, where the characteristic back‐bending EPs dispersion around 1.05 eV (1.2 µm) is clearly resolved. By combining excitation‐energy‐ and thickness‐dependent s‐SNOM measurements with rigorous simulations, two dominant loss channels are identified: excitonic absorption and radiation leakage into the underlying silicon. Furthermore, both loss pathways are substantially suppressed by replacing the Si/SiO 2 substrate with LiNbO 3 , enhancing the EPs propagation length from 2.7 to 7.6 µm for 120‐nm‐thick MoTe 2 . Beyond eliminating silicon‐related radiation channels, the higher refractive index of LiNbO 3 draws a larger portion of the EPs field into the substrate, thereby reducing exciton‐absorption‐induced losses. These findings not only provide crucial insights into EPs dispersion and propagation loss mechanisms in the technologically important near‐infrared communication band, but also demonstrate substrate engineering as an effective route toward low‐loss, tunable polaritonic devices.

Full-Stokes polarization emitters and detectors are critically required for the implementation of various functional schemes in 3D display, high-resolution radar, optical imaging, and quantum key distribution. In this report, we have synthesized the 2D chiral perovskites of individual (S- and R-MBA)2PbI4 microplates and characterized their polarization-related optical properties mainly at the cryogenic temperature of ∼4 K. On the one hand, these 2D chiral microplates demonstrate a photoluminescence spectrum with both linearly and circularly polarized components, which originate from the directional dipole moment and the helical crystal structure imparted by the Pb-I-Pb bonds and the chiral molecules, respectively. On the other hand, the second harmonic signals are generated from these 2D chiral microplates under both linearly and circularly polarized excitations, owing to the coexistence of electric and magnetic dipole moments in the underlying crystal lattice. The above findings reveal the capability of 2D chiral perovskites to emit and detect both linearly and circularly polarized lights, with their compactness in the microplate form being beneficial to the further development of on-chip full-Stokes polarization devices.

Owing to the possession of naturally formed quantum wells with strong spatial and dielectric confinements, 2D lead-halide perovskites are attracting intensive research interest in the context of potential applications in classical optoelectronic devices. Here we have synthesized a 2D (PEA)2PbI4 perovskite microplate and observed at ∼3 K that it can emit single photons from the abundant ultranarrow peaks appearing in the photoluminescence spectrum. This signifies the formation of 0D quantum emitters within the otherwise homogeneous 2D energy landscape, which can be attributed to the thickness fluctuations induced by octahedral tiltings across an inorganic sheet. These findings mark the emergence of a hybrid type of quantum emitters with both 0D and 2D confinements, thus extending the fundamental and practical studies of 2D perovskites to the prospective regime of quantum information technologies.

ABSTRACT The core/shell structures have been widely adopted in traditional semiconductor nanocrystals (NCs) to suppress nonradiative Auger recombination of the biexcitons; however, the functionality of this strategy is still elusive in the emerging perovskite NCs owing to the difficulty of screening out the proper shell materials. Here we have coated the perovskite FAPbI 3 core with the NdF 3 shell to form a quasi‐type‐II energy level alignment, so that the spatial electron‐hole separation can be effectively increased with the further assistance of a built‐in electric field across the core/shell interface. As such, the exciton‐exciton repulsion is significantly enhanced to yield a negative binding energy for the biexcitons, whose suppressed Auger recombination is reflected in the high photoluminescence quantum yield of ∼22% and the long photoluminescence lifetime of ∼2.8 ns. The long biexciton optical‐gain time enables amplified spontaneous emission from the core/shell FAPbI 3 /NdF 3 NCs with a femtosecond‐pumped fluence threshold of ∼5.2 µJ/cm 2 , which is among the lowest values ever reported for the organic‐inorganic perovskite materials. The above findings demonstrate that the biexciton Auger recombination can be effectively controlled in the perovskite NCs with a suitable core/shell structure, thus paving the way toward their prospective applications in both classical optoelectronic devices and quantum information technologies.

Plasmons in few-nanometer-thick metals have attracted great research interest due to their strong optical confinement and electro-optic tunability. However, further optical confinement by reducing the metal thickness to subnanometer scale is difficult, and the dramatic momentum mismatch makes the excitation extremely challenging. Here, we overcome these challenges by integrating ultrathin gold with a silicon nanoribbon array (separated by a few-nanometer-thick silica) to form a hybrid plasmonic structure. The coupling between the ultrathin gold and high-refractive-index silicon not only increases the in-plane wavelength compression ratio up to ∼8 around 1410 nm wavelength but also squeezes the optical fields strongly into the silica spacer in the out-of-plane direction. Using a plasmon conversion approach, we efficiently excite ultraconfined plasmons in a 3.5 nm-thick gold-based hybrid structure with ∼45% absorption. By replacing the intrinsic silicon with highly doped silicon, we further create a compact plasmonic tunnel junction array, enabling direct electrical excitation of ultraconfined plasmons.

The core/shell structures have been widely adopted in traditional semiconductor nanocrystals (NCs) to suppress nonradiative Auger recombination of the biexcitons; however, the functionality of this strategy is still elusive in the emerging perovskite NCs owing to the difficulty of screening out the proper shell materials. Here we have coated the perovskite FAPbI(3) core with the NdF3 shell to form a quasi-type-II energy level alignment, so that the spatial electron-hole separation can be effectively increased with the further assistance of a built-in electric field across the core/shell interface. As such, the exciton-exciton repulsion is significantly enhanced to yield a negative binding energy for the biexcitons, whose suppressed Auger recombination is reflected in the high photoluminescence quantum yield of similar to 22% and the long photoluminescence lifetime of similar to 2.8 ns. The long biexciton optical-gain time enables amplified spontaneous emission from the core/shell FAPbI(3)/NdF3 NCs with a femtosecond-pumped fluence threshold of similar to 5.2 & micro;J/cm(2), which is among the lowest values ever reported for the organic-inorganic perovskite materials. The above findings demonstrate that the biexciton Auger recombination can be effectively controlled in the perovskite NCs with a suitable core/shell structure, thus paving the way toward their prospective applications in both classical optoelectronic devices and quantum information technologies.

The bandgap energy of semiconductor lead mixed halide perovskite can be flexibly tuned by changing the bromide to iodide ratio, which is beneficial for the fabrication of tandem solar cells to efficiently capture light power across the visible spectral range. Unfortunately, the phase segregation effect would be induced in mixed halide perovskite upon continuous light illumination, with the bandgap energy deviating from the desired value due to unexpected formations of bromide- and iodide-rich domains. Here we have induced phase segregation in a solid film of mixed halide perovskite CsPbBr1.2I1.8 nanocrystals (NCs) by laser excitation and demonstrated that the original mixed phase can be partially recovered right after the application or removal of an external electric field. We propose that the iodide ions created after phase segregation can be instantly enriched at the opposite direction of the external electric field, thus enhancing the entropic driving force for them to reoccupy the internal vacancies of some segregated CsPbBr1.2I1.8 NCs. This electric-field-induced partial phase remixing can also be applied to segregated CsPbBr1.5I1.5 and CsPbBr1.2I1.8 NCs, signifying the universal role played by the spatial distribution of iodide ions in the deep understanding and effective control of phase segregation in mixed halide perovskite NCs.

Abstract Plasmonics enables the miniaturization of photonic devices beyond the optical diffraction limit, yet its potential is hindered by inherently large ohmic losses. Hence, it is prudent to explore low-loss alternatives to the current mainstay of plasmonics—the noble metals. In this work, we demonstrate the potential of potassium as a plasmonic material with intrinsically low losses in the optical region. The ultra-flat, high-quality potassium film, fabricated via a rapid slipping-assisted oxide-free crystallization process, achieves measured optical damping rate down to 2.27 meV, with a measured imaginary permittivity of ~0.1 across the entire visible to near-infrared range (400–2000 nm). Near-field optical spectroscopic measurements further confirmed the reduced losses by revealing deeply subwavelength confinement of optical modes. This result overcomes the loss-confinement tradeoff existing in state-of-the-art plasmonic materials and devices, establishing a new platform for exploring extreme light–matter interactions in a variety of plasmonic systems.

Carrier multiplication (CM) describes a strong charge-carrier interaction process in semiconductor colloidal nanocrystals (NCs), wherein two band-edge excitons are simultaneously created by an absorbed photon with at least twice the bandgap energy (2 Eg). While being fundamentally intriguing, it has been exclusively utilized to enhance the light-to-electricity conversion efficiencies in the photodetector and solar-cell devices. In this report, we have synthesized the core/shell perovskite FAPbI3/NdF3 NCs with a biexciton recombination lifetime of 3.9 ns, and demonstrated that a CM efficiency of 25.7

Exciton polaritons (EPs), hybrid light-matter quasiparticles, enable deep subwavelength field confinement and strong intrinsic nonlinearities, making them highly promising for integrated nanophotonic devices. Realizing such applications, however, requires a thorough understanding of EPs properties, particularly their transport and loss mechanisms. Here, we employ scattering-type scanning near-field optical microscopy (s-SNOM) to probe MoTe2 flakes on Si/SiO2 substrates, where the characteristic back-bending EPs dispersion around 1.05 eV (1.2 & micro;m) is clearly resolved. By combining excitation-energy- and thickness-dependent s-SNOM measurements with rigorous simulations, two dominant loss channels are identified: excitonic absorption and radiation leakage into the underlying silicon. Furthermore, both loss pathways are substantially suppressed by replacing the Si/SiO2 substrate with LiNbO3, enhancing the EPs propagation length from 2.7 to 7.6 & micro;m for 120-nm-thick MoTe2. Beyond eliminating silicon-related radiation channels, the higher refractive index of LiNbO3 draws a larger portion of the EPs field into the substrate, thereby reducing exciton-absorption-induced losses. These findings not only provide crucial insights into EPs dispersion and propagation loss mechanisms in the technologically important near-infrared communication band, but also demonstrate substrate engineering as an effective route toward low-loss, tunable polaritonic devices.

Benefiting from the versatile energy band structure design of 2D materials and effective modulation of dopant concentration in Si, 2D/Si hybrid heterostructures demonstrate desirable device performances. Bismuth oxychalcogenide material Bi 2 O 2 Se, exhibits high carrier mobility and ultrafast optoelectrical dynamics, when interfaced with Si, the device efficiencies will be improved in the aspects of photo‐induced carrier separation and collection. However, due to the indirect bandgap features of Bi 2 O 2 Se and Si, the light absorption of the heterostructure is unsatisfactory, deteriorating the external quantum efficiency. To address this, additional light absorption enhancing materials (LAEMs) are incorporated, and boosted with the photo‐gating effects generated from the residual carriers within the LAEMs, and photoconductive gain and photoresponsivity are improved at the cost of response speed. In this study, the CsPbI 3 quantum dot layer is adopted to provide excess carriers, which are injected into Bi 2 O 2 Se/p‐Si heterojunction in the form of excitonic energy transfer. The carrier multiplication effect is thus circumvented, leading to an improved photoresponsivity as high as 2078 A W −1 , while specific time constants of the rising and falling edges of photocurrent are accelerated to 267 and 391 µs.

The band gap energy of lead mixed bromide-iodide perovskite can be simply tuned by adjusting the ratio between the composing halide anions, which would be segregated again upon continuous light illumination to form the iodide-rich domains. Here, we have employed transient absorption microscopy to investigate the carrier diffusion dynamics in an individual CsPbBr1.5I1.5 microplate under the influence of such iodide-rich domains. As expected in the phase-segregated microplate, the lifetime of charge carriers is shortened owing to their migration into the iodide-rich domains with a low band gap energy. Surprisingly, the diffusion coefficient of charge carriers is significantly increased in the phase-segregated microplate, signifying their effective acceleration by the iodide-rich domains according to our Green's function simulations. The above findings have advanced the understanding of the carrier diffusion dynamics in mixed-halide perovskites, which would facilitate their potential applications in various optoelectronic devices such as solar cells and photodetectors.

For optoelectronic devices based on lead-halide perovskites and other semiconductors, a comprehensive understanding of the electric field influences on the carrier transport characteristics is critical to the optimization of their practical performances. To fulfill this challenging goal, here we have employed photoluminescence spatial image and transient absorption microscopy measurements on an individual CsPbBr3 microplate biased at external voltages in an Au/CsPbBr3/Au device. At the subpicosecond time scale, some photogenerated excitons are dissociated into free electrons and holes that drift toward the electrodes to leave behind unfilled defect sites, which are capable of scattering the residual excitons to yield a reduced diffusion coefficient. While the free electrons drift smoothly across the Au/CsPbBr3 interface with a p-type Schottky barrier, the free holes are accumulated therein and recombine radiatively with the injected electrons. These electro-optical studies have visualized how the carrier transport characteristics of an individual CsPbBr3 microplate are connected with the intrinsic defect sites and extrinsic electrode interfaces, which can be naturally extended to other lead-halide perovskites and semiconductors under realistic device operations.

Semiconductor lead-halide perovskite nanocrystals (NCs) are associated with a soft ionic lattice interacting strongly with the photogenerated charge carriers, which can bring about very novel photophysical properties in these quantum-confined materials with a large surface-to-volume ratio. Here we have performed high-resolution optical measurements on single perovskite CsPbI3 NCs at the cryogenic temperature of ∼4 K, with a specific focus on how an extra charge trapped on the surface influences the recombination energies of their neutral and charged excitons. As expected, the surface-trapped charge can impart a local electric field on the charged exciton inside a single CsPbI3 NC, leading to the shift of its recombination energy mainly by the quantum-confined Stark effect. Interestingly, the neutral-exciton recombination energy is also shifted even after the surface-trapped charge has disappeared for a time period longer than ∼2 μs, signifying that the lattice distortion induced by the previous local electric field is not fully relaxed at this time scale. The above findings have established very unique charge-property relationships in lead-halide perovskite NCs, the understanding and manipulation of which are critical to their practical performance in various classical and quantum optical applications.

Chiral ligand-functionalized perovskite nanocrystals (NCs) are promising sources of circularly polarized light, yet their intrinsic emissive behavior is often blurred by ensemble averaging, limiting mechanistic insights into chirality transfer. Here, by resolving individual emitters, single-NC spectroscopy unveils heterogeneity that complements ensemble measurements. Only a minority (∼22.2%) of NCs exhibit detectable chiroptical response, whereas rare emitters display circular polarization degrees approaching ∼48.0% while maintaining excellent single-photon purity of ∼95.0%. By disentangling fluorescence blinking and inhomogeneous broadening, we reveal that ligand chirality imprints distinct fingerprints on excitonic emission, including static energy splitting and dynamic asymmetry in radiative decay rates. These results provide direct evidence of the coupling between molecular chirality and NC band-edge emission states. Our findings underscore single-particle spectroscopy as an effective probe to identify emitter-specific behavior and offer fundamental insights for advancing chiral perovskite NCs toward efficient chiral quantum light sources.

Background: Alzheimer’s disease (AD) is a neurodegenerative disease which significantly and negatively affects families and society. Aerobic exercise serves as a non-pharmacological strategy, potentially safeguarding against cognitive decline and lowering the risk of AD. However, how aerobic exercise ameliorates AD remains unknown. This study investigated the effects of two types of aerobic exercise, including aerobic interval training (AIT) and aerobic continuous training (ACT), on cognitive and exploratory function, brain histopathology, and hepatic amyloid beta (Aβ) clearance in amyloid precursor protein/presenilin-1 double transgenic (APP/PS1) transgenic mice. Methods: Twenty-four six-month-old male APP/PS1 transgenic mice (body weight: 20–22 g) were used to establish the AD model. APP/PS1 transgenic mice were randomly assigned to one of the three groups: rest (AD group, n = 8), aerobic interval training (AIT group, n = 8), and aerobic continuous training (ACT group, n = 8). The exploration ability and anxiety of AD mice were measured using the open-field test. Learning and memory of AD mice were detected using the novel object recognition test, Y-maze test, and Morris water maze test. Neuronal damage was analyzed using hematoxylin and eosin staining and Nissl staining. Aβ deposition in the brain was detected using a thioflavin-S fluorescence assay and immunofluorescence. The mechanisms underlying hepatic Aβ clearance were investigated using an immunofluorescence assay and western blotting. Data were analyzed using one-way ANOVA with Tukey’s post hoc test, and p < 0.05 was deemed statistically significant. Results: The results revealed that both AIT and ACT improved the recognition memory and exploration ability of mice after 8 weeks of intervention. Additionally, both forms of aerobic exercise significantly mitigated neuronal damage and Aβ deposition in the brain and improved the hepatic clearance of Aβ. Conclusions: Our findings indicated that AIT and ACT can improve cognitive deficits in APP/PS1 mice, potentially by increasing the hepatic phagocytic capacity of Aβ. Hepatic clearance of Aβ may serve as a supplementary mechanism by which aerobic exercise can improve AD.

The perovskite nanocrystals (NCs) are featured with a strong two-photon absorption (TPA) due to the quantum-confinement effect, but suffer from a short transport distance of the photogenerated charge carriers isolated within the 0D spatial volumes. On the other hand, the 2D semiconductors of transition metal dichalcogenide (TMDC) possess a large carrier transport mobility across the homogeneous monolayer, whose atomic-scale thickness results in too poor an absorption capability to accommodate plentiful charge carriers upon light illumination. Here a solid film of the perovskite CsPbBr3 NCs is deposited on top of a TMDC WSe2 monolayer to form a mixed-dimensional 0D/2D heterostructure, whose charge-transfer interaction is facilitated by the type-II band alignment between the two composing materials. According to the ultrafast transient reflection measurements, the photogenerated holes in the CsPbBr3 NCs can migrate into the WSe2 monolayer within approximate to 800 fs to yield the current flow in a photodetector fabricated out of this 0D/2D heterostructure. When the CsPbBr3 NCs are excited at the TPA wavelength of approximate to 1015 nm corresponding to the resonant bandgap transition, a responsivity of approximate to 7.5 x 10(-5) A W-1 is achieved that is the highest among all the currently-available values from the various photodetectors operated under the TPA conditions.

Despite recent progress,it remains challenging to fabricate stable deep blue-emitting perovskites.Here,we propose a molecular etching strategy to obtain ultra-small CsPbBr3 perovskite quantum dots(QDs)with robust deep-blue emission.The diphenylalanine(FF)with high polarity is used to break ionic bonds of CsPbBr3 to strip off atomic layers from the QDs.Simultaneously,perfluoroglutaric acid(PFGA)ligands are employed to passivate the QDs surface,effectively overcoming the surface defects induced by ligand detachment.By adjusting the volume ratio of QD:FF solutions,the emission wavelength can be continuously tuned from 506 to 458 nm,yielding deep-blue emission with high color purity.Comprehensive analyses using transient absorption,time-resolved photoluminescence(PL),and temperature-dependent PL measurements indicate that the emission blueshift is primarily attributed to the enhanced quantum confinement effects resulting from the reduced size.Furthermore,a dual-level optical encryption strategy is proposed by leveraging the intrinsically higher photostability of ultra-small CsPbBr3 than that of mixed halide CsPb(Cl/Br)3 QDs.This work provides a viable pathway for fabricating high-efficiency,ultra-stable deep-blue emitting perovskite QDs,showing significant potential for advanced applications in high-resolution displays and optoelectronic encryption.