Search Results (418)

Vanadium dioxide (VO₂) is a prominent active material for reconfigurable nanophotonics because its reversible metal-insulator transition produces large changes in complex refractive index and electrical conductivity. The usable phase contrast, however, is not an intrinsic constant: it is governed by defect type and location, vanadium valence, oxygen stoichiometry, strain, crystallographic orientation, dimensionality, and the chemical, electrical, optical, and thermal boundary conditions imposed by interfaces. This focused narrative review develops a defect- and interface-centred framework linking VO₂ phase physics to device-level optical modulation. Bulk, surface, grain-boundary, and heterointerface defects are distinguished, together with their effects on carriers, V-V bonding, phase stability, optical loss, and cycling reliability. Epitaxial and polycrystalline films, ultrathin layers, and nanostructures are compared across the visible, near-infrared, mid-infrared, and terahertz ranges. Thermal, optical, electrical, electrostatic, electrochemical, ionic, strain, and ferroelectric activation pathways are then compared according to volatility, speed, retention, reversibility, and endurance. Representative free-space metasurfaces, guided-wave modulators, adaptive emitters, and photonic memories are benchmarked separately to avoid mixing incomparable performance definitions. The resulting analysis shows that optical modulation, insertion loss, thermal overhead, ambient stability, and endurance are coupled through the same defect and interface landscape. Progress, therefore, requires coordinated control of phase purity, local chemistry, interface energetics, thermal transport, and architecture-specific performance reporting. Full article

Antimony (Sb) nanopowder was synthesized using fine Sn powder as a reducing agent. The Sn powder was first produced by the chemical reduction of SnCl₂·2H₂O using commercial Al foil in acidic medium, yielding approximately 89% of the theoretical Sn yield. The resulting Sn powder exhibited a mean particle size of approximately 93 nm and a mean crystallite size of 57 nm, which promoted rapid reduction during Sb synthesis. Prior to synthesis, the composition of the Al foil was examined using SEM/EDS, confirming an Al-rich matrix containing minor Fe and Si impurities. High-purity Sb nanopowder was synthesized by reducing SbCl₃ in acetone at 50 °C under magnetic stirring and ultrasonic agitation, using the produced fine Sn powder as a reducing agent, achieving approximately 97% of the theoretical yield. SEM analysis revealed nearly spherical particles of black Sb nanoscale powder with the most frequent size falling within the 20–40 nm range and a mean particle size of approximately 32 nm. XRD analysis confirmed a trigonal Sb structure with a mean crystallite size of around 23 nm. For comparison, pellets prepared from synthesized Sb nanopowder and commercial Sb powder were compacted and sintered under identical conditions. Vickers microhardness measurements showed that the hardness of the sintered Sb nanopowder pellet was approximately 62% higher than that of the commercial Sb pellet. In addition, UV-Vis-NIR reflectance measurements (240–840 nm) demonstrated that the reflectance of the Sb nanopowder pellet was approximately three times higher than that of the commercial Sb pellet. These results demonstrate that fine Sn powder can serve as an efficient reducing agent for the synthesis of high-purity Sb nanopowder with enhanced mechanical and optical properties. Full article

High-purity quartz (HPQ) is an essential material for photovoltaic, semiconductor, optical fiber, and advanced glass industries. However, natural quartz commonly contains gangue minerals, inclusions, and lattice impurities, and therefore requires deep purification. Owing to its ability to dissolve impurity-bearing components, acid leaching is widely adopted for quartz purification. This review critically summarizes recent advances in the mechanisms and enhancement strategies of acid purification of quartz sand. The partitioning characteristics of impurities in quartz are discussed; fundamental mechanisms of acid leaching are then reviewed. Particular attention is given to the differences between non-HF acid systems and HF-containing systems. Process enhancement strategies, including mechanical activation, thermal pretreatment, pressure leaching, and ultrasound-assisted leaching, are critically discussed. These strategies improve impurity accessibility, accelerate mass transfer, and improve reaction kinetics. This review provides guidance for the design of efficient, selective, and sustainable acid purification for HPQ production. Full article

Replacing synthetic colorants with natural alternatives requires source-specific extraction strategies because pigment classes differ in polarity, pH response and thermal stability. This first-pass screening focused on six plant and agro-food matrices: red cabbage, Iris germanica petals, dragon fruit, orange peel, spent coffee grounds and pine bark. Each matrix was subjected to twelve extraction treatments combining water, ethanol, acetone 30%, acid/base modifiers, boiling water, freezing and ultrasound assistance. Extracts were evaluated by visible transmittance spectroscopy from 360 to 740 nm, operationally transformed to apparent optical attenuation according to Aapp (λ) = −log10 [%T (λ)/100] only where measured %T exceeded 0.01; this signal may include both absorption and light scattering, and converted to CIELAB coordinates under D65/10° conditions. The combined spectral and colorimetric approach separated the extracts into red-purple and yellow-brown groups. Red cabbage and Iris showed anthocyanin-like behaviour, dragon fruit showed a betalain-compatible magenta response, orange peel showed carotenoid-compatible short-wavelength attenuation, and coffee grounds and pine bark generated broad brown-yellow profiles. Pigment-family assignments remain putative because chromatographic identification was not performed. This study is explicitly intended as a proof-of-concept descriptive mapping step rather than as a statistically validated extraction optimisation. Because every matrix–treatment combination was prepared once, all comparisons in this article describe the observed screening preparations only; they do not estimate reproducible treatment effects, confidence intervals or statistical significance. The previous equal-weight low-L*/high-C*ab intensity score has been removed from the revised analysis. No extraction yield, recovery percentage, mass balance, purity, pigment concentration or application performance was measured; accordingly, this study describes the optical appearance of the obtained extracts and does not quantify colorant recovery. Visible transmittance, apparent optical attenuation and CIELAB coordinates support only literature-informed class-level hypotheses and cannot identify a pigment family or individual compound. Full article

High-purity quartz processing currently faces three critical factors: depleting reserves of high-grade natural ore, inadequate impurity removal efficiency, and heavy environmental pollution driven by traditional refining methods. Therefore, this article first introduces the reasons for the formation of different types of impurities in quartz, as well as the methods and difficulties in removing different types of impurities. Then, a comprehensive summary was made of the current research progress and purification mechanism of quartz purification technology. The study of acid leaching kinetics in quartz purification can accurately determine the optimal operating parameters and support process scaling up. Calcination treatment has been verified to achieve efficient impurity removal. Specifically, the phase transformation and vacuum calcination behaviors during thermal treatment dominate the impurity elimination mechanism. Correspondingly, targeted and efficient purification strategies are proposed to remove different categories of impurities. The future quartz purification holds strong potential in several key areas. These include optical sorting, microwave-assisted calcination furnaces, biological surfactants, and fluoride-free acid leaching. Additional high-potential directions involve rapid macroscopic identification methods for quartz ore and the extraction of quartz from solid waste. Full article

Flexible transparent conductive films with symmetric and asymmetric multilayered structures are studied using the ZnS–TiO₂–Ag material system, in order to capitalize on the divergent properties of the two dielectric layers for improved performance. The dielectric/metal/dielectric-structured films were deposited by magnetron sputtering sequentially, with high-purity targets. Multilayered films with various dielectric combinations and metallic layer thicknesses were prepared and analyzed. The surface morphology and phase structure were characterized by atomic force microscopy and scanning electronic microscopy. The optical properties were tested by spectrophotometry and analyzed by numerical simulation approach. The sheet resistance was measured via a four-point probe tester. Among the series of multilayers, asymmetric ZnS/Ag/TiO₂ film with 35 nm thickness of dielectric layers and 8.5 nm of metallic layer possesses the optimum comprehensive optoelectronic performance. The average light transmittance reaches 90.72% in the visible spectrum, and the sheet resistance is 7.69 Ω/sq. The good result is ascribed primarily to the combined advantages of superior percolation effect of bottom ZnS layer on ultrathin Ag layer, beneficial impingement effect of top layer deposition on the metallic layer, and excellent surface smoothness of the top dielectric layer. Full article

Environmental pollution, particularly water contamination, requires the continuous development of robust, effective monitoring technologies. While chemical optical sensors offer significant advantages for environmental monitoring, many traditional devices rely on complex combinations of chemical dyes with specific acid dissociation constants. To overcome these limitations, this study presents a dye-free approach centered on a fiber-optic pH sensor based on a TiO₂ thin film. The protective coating of multimode optical fibers was successfully removed using a controlled hydrofluoric acid (HF) treatment, enabling deposition of TiO₂ films via a low-cost sol–gel dip-coating method. Structural characterizations through X-ray diffraction (XRD) and Raman spectroscopy confirmed the preferential growth and high purity of the anatase phase. Furthermore, energy-dispersive X-ray spectroscopy (EDS) confirmed the presence and relatively uniform distribution of Ti on the fiber surface. The optical performance of the sensor was evaluated using a 940 nm light source over a broad pH range (4–14), where the device exhibited distinguishable stepped optical-power responses at four pH conditions spanning pH 4–14. A preliminary analysis yielded an apparent average slope of 0.40 µW/pH. These results support the feasibility of using sol–gel derived TiO₂ coatings in the preliminary development of dye-free optical devices for aqueous pH monitoring. Full article

This study investigated the development of biopolymer films from bitter cassava starch (Manihot esculenta) and coconut mesocarp cellulose as a promising alternative for biodegradable packaging. The biopolymer film was prepared using the casting method, with glycerol as a plasticiser and Tween 80 as an emulsifier. Different formulations were developed by varying the cellulose concentration to 6%, 8% and 10% to determine how this influences their physical and optical properties. FTIR analysis confirmed the presence of characteristic –OH, C–H, C=O, C–O–C and OH groups in the structure of the cellulose and starch, demonstrating their purity and chemical structure. It was found that the variation in cellulose within the starch polymer matrix significantly influences the microstructural organisation of the material, yielding film thicknesses of between 0.49 and 0.56 mm, with a moisture content ranging from 6.46% to 8.01% and a water absorption percentage between 67.7% and 109.5%; highlighting that the cellulose concentration of 0.4 g (8%) yielded the best results. This research contributes to bridging the existing gap in the utilisation of agricultural waste from bitter cassava and coconut mesocarp, integrating them to form biodegradable composites with potential use in biodegradable packaging, thereby strengthening environmental sustainability through the circular economy. Full article

Germanium is a strategically critical metal with indispensable applications in infrared optics, fiber-optic communications, and semiconductor devices. Although previous reviews have extensively addressed the hydrometallurgical recovery of germanium from specific enriched materials and the associated extraction efficiencies, a systematic and integrated understanding of its migration behavior, occurrence states, and phase transformations across the entire zinc smelting process is still lacking. This review fills this gap by investigating the migration and enrichment characteristics of germanium in zinc smelting residues and by constructing a comprehensive framework encompassing occurrence, roasting, leaching, separation, and purification, covering the entire route from zinc concentrate to high-purity germanium production. By establishing this integrated analytical framework that traces the migration and enrichment pathways throughout the whole process chain, this review provides a valuable technical reference for elucidating the migration patterns of germanium in complex smelting systems, devising efficient recovery strategies, and advancing the sustainable utilization of germanium resources. Full article

High-temperature chlorination roasting is a critical technique for achieving ultra-high-purity quartz required in semiconductor, photovoltaic, and fiber-optic applications. However, the removal mechanisms of lattice-bound impurities remain poorly understood due to a lack of integrated thermodynamic and kinetic analysis. This study systematically investigates the removal behavior of seven key lattice impurities, namely Ti, Al, B, Fe, Li, Na, and K, during chlorination roasting using combined thermodynamic modeling and diffusion kinetics. Thermodynamic calculations reveal that carbonaceous reductants are indispensable for enabling spontaneous chlorination of substitutional impurities such as Ti, Al, and B, while alkali metals including Na, K, and Li can be effectively removed under HCl atmosphere at moderate temperatures. Kinetic analysis identifies solid-state diffusion through the SiO₂ lattice as the likely rate-determining step based on the modeling framework, with activation energies ranging from approximately 90 kJ/mol for Na⁺ to 400 kJ/mol for Ti⁴⁺. A significant diffusion crossover effect is observed, where high-activation-energy impurities exhibit exponential mobility gains above 1200 °C. An alkali-first, Al-follows coupled diffusion mechanism is elucidated for aluminum removal. Based on these findings, a temperature-staged, atmosphere-segmented roasting strategy is proposed. This work provides a quantitative mechanistic framework for deep impurity removal and offers practical guidance for overcoming the 4N8 purity bottleneck in high-purity quartz production. Full article

Quartz purity is essential for reliable optically stimulated luminescence (OSL) dating, yet the mineralogical evolution of sediment samples during extraction is rarely documented at each preparation stage. This study uses scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) to characterise two loess samples from the Urluia section, Dobrogea, Romania, across sixteen successive stages of a standard OSL quartz extraction protocol. Four compositional indices—the Quartz Purity Index (QPI), Feldspar Contamination Index (FCI), Heavy Mineral Index (HMI), and Carbonate Index (CI)—are introduced to quantify purification efficiency. Each preparation stage played a different role: HCl treatment primarily removed carbonates, grain-size separation and density fractionation reduced heavy minerals by ~99%, and feldspar removal resulted from the combined effects of density separation and HF etching. Despite identical protocols, two samples collected from stratigraphically adjacent positions showed markedly different HF etching efficiencies, reaching ~94% and ~66% quartz purity, respectively. However, luminescence measurements showed similarly weak feldspar signals in both samples, with intensities substantially lower than the quartz OSL signal. These results demonstrate that purification efficiency cannot be assumed to be uniform across loess samples in Romania and highlight SEM-EDS as a practical quality-control tool for OSL sample preparation. Full article

All inorganic CsPbBr₃ perovskite nanocrystals (NCs) exhibit outstanding luminescence for optoelectronics, yet poor environmental stability severely restricts their practical deployment. As a stable derivative phase, Cs₄PbBr₆ can effectively improve structural stability. Nevertheless, the rational fabrication of high-quality Cs₄PbBr₆/CsPbBr₃ hybrid NCs remains challenging owing to the lack of straightforward and scalable synthetic strategies. To overcome these hurdles, we synthesize well-defined Cs₄PbBr₆/CsPbBr₃ hybrid NCs via a temperature-controllable continuous-flow microfluidic route. This platform precisely modulates phase composition via systematic temperature tuning across a range of 110–170 °C, producing distinct compositions from Cs₄PbBr₆-dominant to high-purity CsPbBr₃. A direct correlation was elucidated between temperature-induced phase transformation and optical properties. The NCs synthesized at 130 °C exhibited a high photoluminescence quantum yield of 96.24% and bright 521 nm green emission. These NCs were successfully integrated into white light-emitting diodes incorporating a 478 nm blue excitation chip and K₂SiF₆:Mn⁴⁺ red phosphor, which demonstrated excellent color performance with a luminous efficiency of 86.3 lm W⁻¹ and Commission Internationale de l’Éclairage coordinates of (0.2991, 0.3784). This work highlights the potential of continuous-flow microfluidics for precise phase modulation and scalable production of high-quality perovskite NCs, offering a viable route for advanced optoelectronic applications. Full article

Composite vortex beams (CVBs) with multiple spatial singularities and orbital angular momentum (OAM) are widely used in various applications including multiple optical traps and optical communication. Here, based on the equal-angle segmentation and radial displacement modulation approach, we propose an innovative scheme for generating CVBs with controllable OAM spectrum by proposing a simple and compact optical element termed as single-helicity annulus-sector spiral zone plates (SASZPs). Theoretical analysis reveals that by modulating the structural parameters of the SASZPs, such as the topological charge, the radial misalignment parameter and the number of annulus-sector primitives, an attractive intensity pattern consisting of petal-like structures can not only be produced but also the mode purity of CVBs can also be flexibly controlled. In addition, by adopting the high-quality and low-defect diamond substrate we have synthesized, based on the electron beam lithography technology and dry etching technology, the SASZP samples with different parameters have been fabricated and the focusing properties of such optics in the visible light region have been carried out and verified. These findings direct a new avenue for improving the performance of ultra-compact solar-blind UV imaging, optical communication and integrated optics. Full article

White LEDs are widely used in fields such as lighting and display. However, existing white light devices suffer from excessively broad emission spectra full width at half maximum (FWHM) and severe leakage of pump blue light. Hence, this study proposes a theoretical design for an ultra-narrow-band white LEDs based on an asymmetric Fabry-Pérot (F-P) microcavity. The microcavity employs a dual-DBR configuration with asymmetric optical responses: the bottom DBRs utilize a ZnS/MgF₂ ($d_L$/2-$d_H$-$d_L$/2)⁵ stack, providing a low reflectance of ~20% at 457 nm for efficient blue light transmission and quantum dot excitation; conversely, the final device incorporating top DBRs with a TiO₂/MgF₂ ($d_H$/2-$d_L$-$d_H$/2)⁴-stacked structure achieved a high reflectivity of approximately 89% at 457 nm, effectively decreasing the excessive blue light in the output spectrum. The intermediate emissive layer uses polymethyl methacrylate (PMMA) as the quantum dot host. By precisely tuning the cavity thickness, the resonant modes of the F-P microcavity—specifically the fourth-order (626 nm) and fifth-order (534 nm)—are aligned with the emission peaks of the red and green quantum dots, respectively. Simulation results demonstrate that the structure leverages the cavity filtering effect to compress the FWHM of the red and green emissions from initial values of 36.5 nm and 29.8 nm down to 2.2 nm and 1.9 nm, respectively, representing an order-of-magnitude improvement in color purity. Through the co-optimization of the top-DBR’s central wavelength, cavity optical thickness, and the doping ratio of red/green quantum dots, standard white light emission with CIE coordinates of (0.32, 0.33) was achieved, accompanied by emission efficiencies of 6.3% (green) and 22.3% (red) for the QDs. However, strict manufacturing tolerances and narrow observation angles limit the applicability of the device. This work provides theoretical research for developing white light sources. Full article

Silicon carbide (SiC) is the leading wide-bandgap semiconductor material, providing mature doping and device fabrication. Additionally, SiC hosts a multitude of optically active point defects (color centers) and is relevant for many applications in quantum technologies. A crucial step towards harnessing the full potential of the SiC platform includes technologies to create color centers with defined localization and density, e.g., to facilitate their coupling to nano-photonic structures and to observe cooperative effects. Here, silicon vacancy centers and divacancies stand out, as no impurity atom is needed, and high-thermal budget annealing steps can be avoided. We characterize the effect of localized, femtosecond laser irradiation of SiC, investigating surface modifications and photoluminescence, including Raman spectroscopy and optical lifetime measurements. We employ commercial, high-purity, semi-insulating substrates and an industrial-grade laser system to explore broader applicability of the method. As a novel approach, we apply femtosecond laser irradiation to SiC substrates with an epitaxial graphene layer and find that the threshold for photoluminescence due to laser treatment is lowered. Full article