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Lossy Mode Resonance Generation by Graphene Oxide Coatings onto Cladding-Removed Multimode Optical Fiber
摘要： In this work, we have studied the suitability of graphene oxide-based thin films to be not only excellent sensitive coatings but also lossy mode resonance (LMR)-generating materials. Thin films of graphene oxide (GO) and polyethylenimine (PEI) fabricated by means of layer-by-layer assembly were selected in this study. Two optical fiber devices with 8 and 20 bilayers of the LMR-generating coating were fabricated and characterized as refractometers. Both devices show no hysteresis and high sensitivity, improving previously reported values. This research opens very promising and exciting possibilities in the field of optical fiber sensors based on LMR, strategically including specific recognition groups to the device surface to exploit this high sensitivity for monitoring a range of target analytes. The carboxylate functional groups at the edges of the GO sheets should provide excellent attachment sites for the required coupling chemistry to realize such devices.
关键词： optical fiber sensor,thin films,Dip-assisted layer by layer,lossy mode resonance,refractometer,graphene oxide
更新于2025-11-14 15:19:41
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Dependence of Mechanical Stresses in Silicon Nitride Films on the Mode of Plasma-Enhanced Chemical Vapor Deposition
摘要： Films of silicon nitride SiNx, obtained by plasma-enhanced chemical vapor deposition from the monosilane SiH4 and ammonia NH3 gases, are widely used in microelectronics and micro- and nanoelectromechanical systems. Residual mechanical stresses and film composition are important characteristics for many applications. The properties of SiNx films, particularly mechanical stresses and composition, depend largely on the conditions of production, e.g., the ratio of the reacting gas flow rates, the composition of the gas mixture, the power and frequency of the plasma generator, and the temperature and pressure during deposition. Despite the great volume of works on the subject, data regarding the dependence of the properties and composition of SiNx films on the conditions of production remain sparse. This work considers the effect the ratio of the reacting gas flow rates has on the mechanical stresses and composition of silicon nitride films SiNx obtained by plasma-enhanced chemical vapor deposition from gaseous mixtures of SiH4 monosilane and NH3 ammonia using low-frequency plasma. It is found that when the ratio of the gas flow rates of SiH4 and NH3 is raised from 0.016 to 0.25, the compressive mechanical stresses are reduced by 31%, the stoichiometric coefficient falls from 1.40 to 1.20, the refractive index rises from 1.91 to 2.08, the concentration of N–H bonds is reduced by a factor of 7.4, the concentration of Si–H bonds grows by a factor of 8.7, and the concentration of hydrogen atoms is reduced by a factor of 1.5. These results can be used for the controlled production of SiNx films with such specified characteristics as residual mechanical stresses, refractive index, stoichiometric coefficient, and the concentration of hydrogen-containing bonds.
关键词： mechanical stresses,optical profilometry,films of PECVD silicon nitride SiNx,IR Fourier spectroscopy
更新于2025-11-14 15:18:02
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Green and red emitting YBO3:Ln3+ (Ln=Eu, Tb) phosphors for detection of latent fingerprint
摘要： In this paper, we report the synthesis of green and red emitting YBO3:Ln3+ (Ln = Eu, Tb) phosphors through a solvothermal method. The crystal structure of YBO3:Ln3+ (Ln = Eu, Tb) phosphors is well crystallized. The photoluminescence spectra of YBO3:Ln3+ (Ln = Eu, Tb) phosphors exhibit the strong green and red emission. The photoluminescence intensity is increased with increasing Ln3+ ion concentration from 0.01 to 0.07 mol. The latent fingerprints developed on various substrates using YBO3:Ln3+ (Ln = Eu, Tb) phosphors exhibited the highly clear ridge patterns of fingerprints regardless of background interference. Also, the detailed minutiae of fingerprint with different levels can be clearly observed. Therefore, YBO3:Ln3+ (Ln = Eu, Tb) phosphors can be applied to luminescent materials for detection of latent fingerprint.
关键词： Solvothermal,Fingerprint,Phosphor,Optical materials
更新于2025-11-14 15:15:56
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Optical and luminescence studies on Tm3+-doped KCl single crystals
摘要： Thulium-doped KCl crystals have been successfully grown using Bridgman–Stockbarger technique. The crystals were characterized by optical absorption, photoluminescence (PL), thermoluminescence glow, TL emission, powder X-ray diffraction, scanning electron microscopy (SEM), laser Raman spectroscopy and electron paramagnetic resonance spectroscopy (EPR). PL spectra exhibit broadband blue emission at 468 nm for the application of light-emitting diodes. The trap parameters of the TL glow curve are calculated using Chen’s peak shape method. XRD analysis carried out on the grown crystals and lattice parameters predicted that it crystallized in cubic structure. SEM studies revealed the presence of microcrystalline structure. EPR measurements were made at X-band frequencies with 9–10 GHz ?eld modulation at room temperature, and the g-factor value of 2.4 was calculated by using Lande formula.
关键词： Optical absorption,TL emission,PL,TL glow,EPR
更新于2025-11-14 14:48:53
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Structural and optical properties of a revived Pb0.5Ba1.5BiVO <sub/>6</sub> perovskite oxide
摘要： The polycrystalline ceramic Pb0:5Ba1:5BiVO6 manifesting the complex double perovskite structure was tailored by the conventional solid state route at a moderate temperature. Qualitative phase analysis and formation of the ceramic were affirmed by XRD analysis. The X-ray powder diffraction pattern of the compound explored at room temperature affirms the single phase formation with double perovskite structure exhibiting rhombohedral phase. Microstructural analysis of the studied compound procured from the Scanning Electron Microscope (SEM) validates the formation of dense microstructures and nonuniformly distributed grains with minimal voids. Compositional analysis was shaped through the Electron Diffraction Spectroscopy (EDS) confirming the absence of contamination of any other metals apart from the mentioned ones. Dielectric (Cr and tan δ) parameters of the compound were studied using the LCR analyzer at different temperatures and wide range of frequencies. The polarization and dielectric study affirms the presence of ferroelectricity in the material with transition temperature much above the room temperature. The tangent dielectric loss of this sample being almost minimal at room temperature attributes it to find applications in different grounds of electronics. Optical equities of the ceramic were further analyzed by the RAMAN, FTIR, UV–Vis and Photoluminescence spectroscopy.
关键词： EDS,Ceramic,X-Ray diffraction,LCR,optical properties
更新于2025-11-14 14:48:53
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Illumination conditions in microsphere-assisted microscopy
摘要： White-light microsphere-assisted microscopy is a full-field and label-free imaging promising technique making it possible to achieve a sub-diffraction lateral resolution. However, performance of this technique depends not only on the geometrical parameters but also on the illumination conditions of the optical system. In the present work, experimental measurements and computer simulations have been performed in air in order to determine the influence of the two diaphragm apertures of the K?hler arrangement and the spectral width of the light source on both the depth-of-focus of the microsphere and the optimisation of the imaging contrast. Furthermore, the super-resolution phenomenon is demonstrated and the cumulated optical aberrations are shown through the measurement of the optical transfer function for the different arrangements of the illumination part.
关键词： Super-resolution microscopy,Illumination,Microsphere,Optical transfer function,Imaging depth
更新于2025-10-24 16:39:32
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An optical test to unveil twisting of birefringent crystals in spherulites
摘要： Helical conformations and structures are frequently observed in materials. The presence of helices at points of the unit cell of a crystal, on a larger size scale in the crystalline lattice or even in the microscopic structure of crystals, affects the chemico-physical properties of a solid and, hence, also interactions with light. Here, attention has been drawn to the geometrical properties of helices produced by a hypothetical torque of a transparent crystal, and optical properties of twisted crystals easily observed by a polarizing microscope have been discussed. Radially grown spherulites are obtained by most substances crystallized from melt. The circular optical arrangement of behaviour of larger dimensions of spherulites, allows investigations otherwise hardly feasible on separate crystals. According to the torsional analysis of elongated bodies and the birefringence theory, information on the existence of helically shaped crystals can be deduced, as hereinafter explained, from the microscopic appearance and birefringence pattern of spherulites. Indeed, twisting decreases the birefringence throughout an elongated crystal and, therefore, also the birefringence of spherulites formed by twisted radial crystals is reduced.
关键词： optical microscopy,microstructure,helical deformation,birefringence,crystals,banding
更新于2025-10-24 16:38:51
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Twins in YAl3(BO3)4 and K2Al2B2O7 Crystals as Revealed by Changes in Optical Activity
摘要： Many borate crystals feature nonlinear optical properties that allow for efficient frequency conversion of common lasers down into the ultraviolet spectrum. Twinning may degrade crystal quality and affect nonlinear optical properties, in particular if crystals are composed of twin domains with opposing polarities. Here, we use measurements of optical activity to demonstrate the existence of inversion twins within single crystals of YAl3(BO3)4 (YAB) and K2Al2B2O7 (KABO). We determine the optical rotatory dispersion of YAB and KABO throughout the visible spectrum using a spectrophotometer with rotatable polarizers. Space-resolved measurements of the optical rotation can be related to the twin structure and give estimates on the extent of twinning. The reported dispersion relations for the rotatory power of YAB and KABO may be used to assess crystal quality and to select twin-free specimens.
关键词： optical activity,inversion twin,YAB,optical rotatory dispersion,KABO,second harmonic generation,frequency conversion,K2Al2B2O7,NLO crystals,YAl3(BO3)4
更新于2025-10-22 19:40:53
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Tannic acid-derivatized graphitic carbon nitride quantum dots as an “on-off-on” fluorescent nanoprobe for ascorbic acid via copper(II) mediation
摘要： A microwave-assisted hydrothermal route was employed to prepare fluorescent tannic acid (TA)-derivatized graphitic carbon nitride quantum dots. The resulting dots display blue fluorescence (best measured at excitation/emission wavelengths of 350/452 nm) with a quantum yield as high as ~44%. The incorporated TA imparts a fluorescence switching behavior in that very low concentrations of Cu(II) can quench the fluorescence, while (AA) can restore it. It is presumed that AA causes Cu(II) to be transformed to Cu(I). Based on these findings, a fluorometric method was designed for AA detection. The probe allows AA to be detected with a 50 pM limit of detection and a linear analytical range that extends from 0.1 to 200 nM of AA. Real and spiked samples were successfully assayed by the probe to demonstrate its analytical applicability.
关键词： Fluorescence recovery,Metal ions,Graphitic nanosheets,Biomolecules,Polyphenolic compounds,Optical probe,Quantum dots
更新于2025-10-22 19:40:53
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AIP Conference Proceedings [Author(s) SILICONPV 2018, THE 8TH INTERNATIONAL CONFERENCE ON CRYSTALLINE SILICON PHOTOVOLTAICS - Lausanne, Switzerland (19–21 March 2018)] - Understanding the optics of industrial black silicon
摘要： Industrial scale black silicon texturing has become a topic of increasing importance as a method for enabling lower cost multicrystalline silicon wafers through diamond wire sawing, as well as for its potential to provide improved efficiencies through enhanced optical characteristics. Two different texturing processes have emerged as candidates for mainstream industrial uptake, metal catalyzed chemical etching (MCCE) and reactive ion etching (RIE). However, these techniques can produce substantially different textures and both provide a wide parameter space allowing for various feature shapes and sizes to be produced. The surface texture not only determines the total reflectance of a solar cell, but also impacts the light trapping and subsequent absorption through scattering. Here, we carry out a detailed analysis on a representative range of both MCCE and RIE textures on multiple substrate types in order to further develop the fundamental understanding of how these specific surface morphologies impact the optical characteristics. This will better enable integration with other process conditions as well as optimization between optical and electrical requirements.
关键词： black silicon,surface morphology,RIE,MCCE,optical characteristics
更新于2025-10-22 19:40:53