Advanced Optical Materials最新文献

Improving light absorption is essential for the development of solar thermoelectric generators. Most efficient light absorbers require a back mirror (a thick metal film) to reduce the reflectivity by promoting the interference between the incident and the reflected light. However, the presence of thick a continuous metal film supposes a limitation for thermoelectric applications, as it behaves like a shortcut of the Seebeck voltage. In this work, a back mirror-free selective light absorber is presented, designed for the fabrication of thermoelectric devices. The combination of a high and a low refractive index material covered by a semi-transparent electrode is optimized. As a difference to the back mirror, the semi-transparent electrode can be patterned to prevent the quenching of the Seebeck voltage. Thanks to this, the low refractive index material can be replaced by a transparent thermoelectric, enabling efficient heat-to-energy conversion with negligible loss of absorption performance.

In the current scientific landscape, the understanding of optical properties in the mid-infrared (mid-IR) range (3–30 µm) is crucial in simulations and models to explore the potential of materials for various applications. However, due to the challenges associated with mid-IR characterization, accurate refractive index (n) and extinction coefficient (κ) data are often lacking in the literature. This study addresses this gap by investigating the mid-IR n and κ spectra of anodic aluminum oxide (AAO) nanostructures anodized under different conditions, using two distinct approaches: IR ellipsometry and a theoretical model based on multilayer reflection and effective medium. The results demonstrate a strong agreement: the anodizing conditions have a significant influence on the optical properties of the AAO nanostructures. These differences enable accurate simulations of the emissivity spectra of AAO nanostructures on Al foils, which align closely with experimental measurements. This theoretical approximation is versatile and extensible to a broad range of materials. Different materials are tested, namely, a sapphire, a polycarbonate film, and a polyethylene terephthalate (PET) film achieving a useful qualitative description. This study paves the way for a novel approach in the engineering of new micro and nano-optical materials, facilitating their evaluation for suitability in mid-IR applications.

Achieving high-performance spectral imaging over large fields of view (FOV) has remained challenging, particularly with conventional bulky optical systems. Here, a compact transversely dispersive metasurface array is introduced, designed for wide FOV spectral imaging. The system achieves efficient aperture encoding via distinct phase gradients tailored to different incident angles. A genetic algorithm optimizes the spectral reconstruction process, allowing for high-accuracy imaging with a single snapshot. The system demonstrates 120° FOV spectral imaging across 11 channels in the 400–700 nm visible range, using a 91 × 91 metasurface array with 81.5% efficiency in light focusing and first-order diffraction. This approach represents an advancement over traditional methods, offering broad potential in material classification, chemical analysis, remote sensing, and defect detection.

Cr³⁺-doped near-infrared (NIR) phosphors have attracted significant attention in recent years. Despite this, achieving high-performance NIR phosphors with broadband emission and excellent thermal stability remains a considerable challenge. This study presents Lu₃Ga₅O₁₂:Cr³⁺, which demonstrates a tunable emission peak ranging from 705 to 759 nm and an increased full-width at half-peak maximum (FWHM) from 46 to 139 nm by substituting the [Mg²⁺-Ge⁴⁺] chemical unit for the [Ga³⁺-Ga³⁺] unit. Additionally, in Lu₃MgGa₃GeO₁₂:Cr³⁺, Yb³⁺, an energy transfer channel (Cr³⁺-Yb³⁺) is constructed. Under blue light excitation, the characteristic emission peaks of Cr³⁺ (600–900 nm) and Yb³⁺ (900–1100 nm) are observed simultaneously. However, the emission band between 850 and 900 nm is relatively weak, resulting in a discontinuous emission spectrum. To address this, Lu₃MgGa₃GeO₁₂:Cr³⁺, Yb³⁺, Nd³⁺ phosphors are proposed, which exhibit a continuous broadband NIR emission with a FWHM of 253 nm and internal quantum efficiency of 47.3%. The luminescence intensity retains 81% of its room temperature value even at 423 K. Combining this new phosphor with a blue LED chip results in a portable NIR light source with potential applications in non-destructive detection, information encryption, bio-imaging, and NIR remote control. This work offers a novel perspective for developing high-performance NIR phosphors.

Salts and co-crystals composed of planar π-conjugated functional units represent a fascinating class of materials, featuring both enlarged birefringence and a strong SHG effect. Herein, the optical properties of π-conjugated (C₄H₇N₃)²⁺ functional unit within 2-aminopyrimidine (2-AP) family are investigated for the first time. Furthermore, twelve novel compounds are successfully synthesized by applying four different strategies. In these strategies, (C₄H₇N₃)²⁺, (C₄H₆N₃)⁺, and (C₄H₅N₃) functional units are introduced into the crystal structure, both solely and in combination, to analyze the alteration in birefringence. Remarkably, a birefringence rule with (C₄H₇N₃)²⁺ < (C₄H₆N₃)⁺ < (C₄H₅N₃), stating that an increase in net charge over π-conjugated functional unit leads to a reduced birefringence, is discovered. Consequently, the inclusion of a charge-neutral (C₄H₅N₃) functional unit within the crystal structure along with coplanar arrangement is a promising approach to enhance birefringence. Furthermore, D-2 [(C₄H₅N₃)(H₃C₃N₃O₃)] realizes Δn_calc = 0.412 maximum in the (2-AP) family. Notably, both A-1 [(C₄H₇N₃)(CF₃SO₃)₂] and B-1 [(C₄H₆N₃)₂(IO₃)₂(H₂O)] crystalize in the non-centrosymmetric space groups, with B-1 exhibiting SHG efficiency of ≈1.4 × KDP @ 1064 nm, with the shortest λ_PM at 384 nm. This work provides new insight into discovering novel birefringent and non-linear optical materials with high performances in the wide chemical space.

A switchable conformal-skin cloak for multi-polarization cloaking-illusion is presented. Multi-polarization electromagnetic cloaking-illusion of the Poincaré sphere is analyzed and realized based on generalized Snell's law and Pancharatnam–Berry (PB) phase theory. The cloak achieves adaptive cloaking-illusion with linearly polarized in X-band (7.5–9.5 GHz) and circularly polarized in K-band(16–20 GHz), respectively. To achieve a reconfigurable carpet cloak, structured water acting as a phase-change material is introduced into the cell structure design, enabling reconfigurable reflection phases during circularly polarized excitation. This is the first time that a water structure is used instead of a phase-change material to create a phase-shifting invisibility cloak. Conformal integration samples are fabricated and tested by combining 3D-printing technology and PCB fabrication technology, and the simulation results are in agreement with the experimental results. This method realizes switchable cloaking-illusion. The impact of surface fabrication on electromagnetic properties are reduced using 3D printing. The approach is adaptable to terahertz and optical bands, providing crucial guidance for the integrated creation of cloaking-illusion on arbitrary shapes.

Lead halide perovskite nanocrystals (NCs) rapidly emerge as promising materials for photovoltaics. However, to fully harness their potential, efficient charge extraction is crucial. Despite rapid advancements, the specific active sites where acceptor molecules interact remain inadequately understood. Surface chemistry and interfacial properties are pivotal, as they directly impact charge transfer efficiency and overall device performance. This study identifies and maps binding sites for hole transporters, examining their influence on charge transfer dynamics through ligand engineering with 2,3-dimercaptopropanol (DMP), a compound with a strong affinity for lead (Pb). DMP effectively passivates Pb sites in CsPbBr₃ (CPB) NCs, enhancing photoluminescence (PL) by forming stable chelating bonds. DMP-modified CPB nearly completely suppresses hole transfer to ─COOH-functionalized ferrocene (FcA) and partially suppresses transfer to ─NMe₂-functionalized ferrocene (FcAm), suggesting an alternative hole extraction pathway for FcAm. This is further supported by enhanced hole transfer in bromine-excess CPB (CPB-Br(XS)) synthesized via SOBr₂ treatment. The distinct binding interactions and charge transfer dynamics are validated through steady-state and time-resolved PL, along with transient absorption spectroscopy. These findings underscore the role of strategic ligand engineering in enhancing perovskite NC-charge acceptor interactions, enabling better charge extraction, higher solar cell efficiency, and reduced lead toxicity through strong Pb binding.

Thiahelicenes, an important subclass of helicenes, are renowned for their pronounced chiroptical properties, particularly circular dichroism. However, the exploration of their circularly polarized luminescence (CPL) has been hindered due to their inherently weak fluorescence, leaving a critical gap in the development of thiahelicenes as efficient CPL emitters. To address this limitation, a novel strategy for enhancing the luminescence of thiahelicenes by integrating thiophene-containing units with a highly emissive hexabenzoperylene (HBP) core is presented. Two isomeric HBP-cored double thiahelicenes are synthesized, which serve as proof of concept. These molecules exhibit exceptionally high fluorescence quantum yields (Φ_F = 83% and 91%), surpassing all previously reported thiahelicenes. Furthermore, their luminescence dissymmetry factors show a four-fold enhancement compared to the parent HBP, resulting in a remarkable CPL brightness of up to 84.9 M⁻¹ cm⁻¹. These findings not only address the fluorescence limitation of thiahelicenes but also establish a new pathway for developing high-performance CPL materials.

The recent discovery that linearly polarized light with a helical wavefront can exhibit vortex dichroism (also referred to as helical dichroism) has opened up new horizons in chiroptical spectroscopy with structured chiral light. Recent experiments have now pushed optical activity with vortex beams into the regime of nonlinear optics. Here the theory of two-photon absorption (TPA) of focused optical vortices by chiral molecules: nonlinear vortex dichroism (NVD) is presented. It is discovered that highly distinct features arise in the case of TPA with focused vortex beams, including the ability to probe chiral molecular structure not accessible to current methods and that the differential rate of TPA is significantly influenced by the orientation of the state of linear polarization. This study provides strong evidence that combining nonlinear optical activity with structured light provides new and improved routes to studying molecular chirality.

The impact of magnetic coupling effects on the luminescence of 0D (zero-dimensional) perovskite materials doped with TM (transition metal) ions remains underexplored. This study synthesizes Mn²⁺-doped 0D Rb₄CdCl₆ halide structures using a solvent-based method, with Rb⁺ ions systematically arranged around isolated [CdCl₆]⁴⁻ octahedra. The resulting Rb₄Cd_1-xMn_xCl₆ powder exhibits stable orange-red luminescence under UV (ultraviolet) excitation, achieving a PLQY (photoluminescence quantum yield) of 88.96%. The parent Rb₄CdCl₆ is non-luminescent, but doping with Mn²⁺ induces strong luminescence due to combined emissions from d-d transitions of Mn²⁺, weakly ferromagnetically coupled Mn²⁺ pairs, and STEs (self-trapped excitons). Characterization via XRD (X-ray diffraction) and DFT (density functional theory) reveals that Mn²⁺ doping occurs through both substitutional and interstitial processes, facilitating magnetic coupling. Raman spectroscopy identifies strong electron-phonon coupling at a phonon mode of 112 cm⁻¹, supporting STEs generation. Magnetic property analysis shows significant ferromagnetic coupling between Mn²⁺ pairs and paramagnetic single Mn²⁺ ions, enhancing luminescence. The material demonstrates remarkable structural and thermal stability, positioning Rb₄Cd_1-xMn_xCl₆ as a promising candidate for optoelectronic applications.