In this study, five homoconjugated NLOphore candidates decorated with indole donor groups were synthesized in 55-85% yields via click-type formal [2 + 2] cycloaddition reactions. The obtained compounds were subsequently transformed into spirocyclic push-pull-type chromophores through thermal rearrangements, affording the corresponding spiro products in 54-80% yields. During the formation of the spiro derivatives, the commonly reported low-yield issue associated with aniline-containing substrates in the literature was successfully overcome through the incorporation of indole donor groups, enabling the efficient formation of the target structures. All target compounds were investigated by UV/vis spectroscopy, thermogravimetric analysis (TGA), theoretical calculations, and custom-made Z-scan experiments. The homoconjugated structures exhibit intramolecular charge-transfer (ICT) absorption bands between 496 and 619 nm, whereas the spiro derivatives display lambda max values in the range of 464-471 nm. TGA analysis revealed that the rigid spiro framework contributes to enhanced thermal stability compared to the homoconjugated chromophores. The ICT characteristics of the target molecules were examined in detail through frontier molecular orbital depictions, electrostatic potential maps, and timedependent density functional theory (TD-DFT) calculations. In addition, the calculated first hyperpolarizability values indicate that all chromophores possess significant potential as nonlinear optical (NLO) materials. In this context, the NLO properties were experimentally investigated using a custom-designed Z-scan system. The homoconjugated chromophore series exhibited nonlinear refractive index values (n2) ranging from -4.20 x 10- 7 to -22.30 x 10- 7 cm2 W- 1. A similar, yet even more pronounced trend was observed in the spirocyclic chromophore series, with n2 values ranging from -2.91 x 10- 7 cm2 W-1 to -46.21 x 10- 7 cm2 W-1. Overall, the theoretical and experimental results show good agreement, supporting the potential of these chromophores as promising NLOphore candidates.

A detailed investigation of structure, electronic and optical properties of two transition metal dichalcogenide (TMDC) structures is presented in this study. Sample 1 consists of epitaxially grown bilayer of PtSe2 (2 monolayers) on MoSe2 (1 monolayer) deposited on mica substrate - reported here for the first time. Sample 2 comprises a trilayer of WSe2 grown on mica. The photoconductivities of both samples were characterized using optical pump-terahertz probe spectroscopy under above- and near-bandgap excitations at 400 nm and 800 nm. Both structures exhibit rapid carrier generation and relaxation dynamics, with notable variations depending on excitation wavelength and structures. Complementary density functional theory (DFT) calculations are performed to evaluate the electronic and optical properties of free-standing single layers of MoSe2, PtSe2 and WSe2 and their combined structures corresponding to Sample 1 and Sample 2. The experimental results show strong agreement with calculated band structures. This consistency between experiment and theory underscores the potential of these TMDC structures for future applications in terahertz and high-frequency electronic devices.

In this study, combinations of phosphorous silicone methacrylate monomer (PSiMA) and CaB 4 O 7 nanoparticles (CBO NPs) were prepared for formation of halogen-free, flame-retardant, UV-curable polyurethane acrylate (PUA) films. The addition of either PSiMA or CBO NPs to PUA increased the flame-retardancy as expected, but the PSiMA-only addition, unfortunately, had adverse effects on the physical properties. However, the combined addition of PSiMA and CBO NPs not only resulted in the best performance on flame retardancy but also recovered the polymer’s thermal and physical properties. With additives high initial decomposition temperatures were observed in the range of 175–216°C. Among the combinations, PLU-60PSi-10NP (60 phr PSiMA + 10 phr CBO NPs) resulted in the best LOI performance of 27, which is 40% more than the PLU film (PUA-based film). In addition, the film had a remarkable char formation ability of 14.5% compared to PLU. The observed high LOI values could not be explained by the high percentages of P, Si, B, and N in the films, but the synergy among the additives was also considered. In this study, we have investigated the use of a promising technique, THz spectroscopy, on the characterization of these films as well. Very interestingly, the results showed a nice correlation between the dielectric responses measured by THz spectroscopy and the mechanical properties of the films. Observed great performances along with the simple preparation methods of these newly developed halogen-free , flame-retardant , PUA-based films are expected to significantly increase their potential use in many practical applications such as automobile, leather, printing, and coatings.

This study explores the synthesis, structural properties, and multifunctional potential of Yb3+/Tb3+ codoped alkaline earth tetraborates (CaB4O7, MgB4O7, and SrB4O7) synthesized via solid-state (SS), solution combustion (SC), and combustion (C) methods. The multifunctional potential of the synthesized materials arises from their unique combination of properties in one material. The first property is related to their high boron content and thus to their high neutron capture cross section, providing effective functionality for boron neutron capture therapy (BNCT) and shielding. This enables the particles to be selective tumor cell destruction agents under neutron irradiation. The second property is their strong upconversion luminescence that allows for near-infrared light-triggered photodynamic therapy. This offers deep-tissue treatment capability along with BCNT. The third property is their excellent photochemical stability and low biotoxicity. This combination of therapeutic modalities within a single platform holds promise for synergistic and minimally invasive cancer treatment strategies, along with imaging capabilities and drug delivery. X-ray diffraction analysis confirmed the phase purity and crystal structures of CaB4O7 (CBO), MgB4O7 (MBO), and SrB4O7 (SBO). CBO crystallizes in a monoclinic structure with a P21/n(14) space group, while both MBO and SBO adopt orthorhombic structures with Pcba and Pnm21 space groups, respectively. Scanning electron microscopy revealed particle sizes ranging from 100 to 200 nm, with more uniform and smaller particles achieved by SC. Strong upconversion luminescence, driven by cooperative energy transfer between Yb3+ and Tb3+ ions, was observed in all materials, particularly in CBO and MBO codoped with 5% Yb3+ and 5% Tb3+. The quantum yields (QY) for CBO and MBO reached approximately 0.35. Furthermore, neutron sensitivity was significantly enhanced with 10B isotope enrichment, making these materials promising candidates for BNCT and neutron shielding applications. Cytotoxicity tests confirmed the biocompatibility of the materials, especially for CBO and MBO, which have maintained high cell viability.

Push-pull chromophores, with strong intramolecular charge transfer (ICT), exhibit high ground-state polarization, driving strong NLO responses. The donor and acceptor abilities of the groups in the investigated compounds influence ICT, so the nonlinear response of these compounds was analyzed in relation to their strength. Two different families of NLOphores were synthesized through [2 + 2] cycloaddition-retroelectrocyclizations of heterocycle-based electron-rich alkynes with tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ). The lambda(max) values of push-pull chromophores, particularly for charge transfer bands, fall within the range of 424-758 nm. The linear and nonlinear optical properties of these NLOphores were subsequently examined through a combination of experimental and theoretical methods. NLO measurements were conducted using a validated custom-made Z-scan device. The nonlinear absorption coefficients range from -1.44 x 10(-4) cm.W-1 to -9.90 x 10(-4) cm.W-1, while nonlinear refractive indices range from -1.59 x 10(-7) cm(2). W-1 to -2.26 x 10(-6) cm(2). W-1. As expected from their molecular structures, the TCNQ products displayed stronger nonlinear responses than the TCNE products.

Few-layer Transition Metal Dichalchogenide (TMDC) heterostructures coated on mica by CVD technique were analysed for their dynamic properties by Optical Pump Terahertz Probe spectroscopy. The observed fast dynamics imply that the samples suit well for THz device applications and high-frequency requiring optoelectronic structures.

A sensor region in a single-mode optical fiber loop was created and utilized in order to study the coating effect on sensor durability and system sensitivity by the Fiber Loop Ringdown Spectroscopy (FLRDS) technique. The sensor system was simply designed without any additional optical components. The bending loss theory in the single-mode fiber (SMF) was taken into account in data calculation. After stretching was performed on 10.0 cm long coated and noncoated sensorheads from the mid-points, the strain detection limits were determined as 5.3345 mu epsilon and 6.7497 mu epsilon with bare and coated sensorheads, respectively. The purpose of this study is to analyze the effect of N,N-Diethyl-p-phenylenediamine (NDPD) coating of the sensorhead on the sensor durability and sensitivity. The baseline stability of the system was obtained as 1.18% by considering a hundred consecutive data. Regarding to obtained results, the difference between calculated total optical losses of FLRDS systems with noncoated and NDPD coated sensorheads shows that coating sensorhead enhanced the sensor durability and the system sensitivity. An FLRDS system with high sensitivity, simple design and easy setup offers real-time measurement with continuous monitoring and provides advantages on durability by modification the sensorhead such as NDPD coating. Due to its attractive features such as low cost, simplicity, easy setup, high sensitivity, increased durability and continuous monitoring, an FLRDS system has a wide range of application areas in structural health monitoring, transportation, early detection, biomedical, chemical trace elements, rail and asphalt applications for continuous monitoring in a real-time merit.

A novel fiber optic biosensor was purposed for a new approach to monitor amyloid beta protein fragment 1-42 (A beta 42) for Alzheimer's Disease (AD) early detection. The sensor was fabricated by etching a part of fiber from single mode fiber loop in pure hydrofluoric acid solution and utilized as a Local Optical Refractometer (LOR) to monitor the change A beta 42 concentration in Artificial Cerebrospinal Fluid (ACSF). The Fiber Loop Ringdown Spectroscopy (FLRDS) technique is an ultra-sensitive measurement technique with low-cost, high sensitivity, real-time measurement, continuous measurement and portability features that was utilized with a fiber optic sensor for the first time for the detection of a biological signature in an ACSF environment. Here, the measurement is based on the total optical loss detection when specially fabricated sensor heads were immersed into ACSF solutions with and without different concentrations of A beta 42 biomarkers since the bulk refractive index change was performed. Baseline stability and the reference ring down times of the sensor head were measured in the air as 0.87% and 441.6 mu s +/- 3.9 mu s, respectively. Afterward, the total optical loss of the system was measured when the sensor head was immersed in deionized water, ACSF solution, and ACSF solutions with A beta 42 in different concentrations. The lowest A beta 42 concentration of 2 ppm was detected by LOR. Results showed that LOR fabricated by single-mode fibers for FLRDS system design are promising candidates to be utilized as fiber optic biosensors after sensor head modification and have a high potential for early detection applications of not only AD but possibly also several fatal diseases such as diabetes and cancer.

The increasing contamination of water with antibiotics presents significant environmental and health hazards, leading to a rise in antibiotic-resistant microorganisms. This work focused on the removal of one common pharmaceutical contaminant, Amoxicillin (AMX) from water. The approach involved enhancing a microfluidic chip by integrating a poly vinylidene fluoride (PVDF) membrane, aiming the highest and most precise adsorption capacity. The designed microfluidic chip included optical pH and dissolved oxygen sensors. The sensors enabled real-time monitoring of the solution to guarantee efficient removal of AMX. To increase the efficiency of a PVDF membrane for AMX elimination, MnFe2O4 nanoparticles with particle size around 25 nm were utilized as modifier adsorbent. The chemical, morphological, and elemental content of the modified porous membrane was determined using FTIR, XRD, FESEM, and EDS characterizations and confirmed the loading of MnFe2O4 nanoparticles on the PVDF membrane. The BET analysis revealed that the structural alteration obtained using the electrospray approach greatly increased the membrane's surface area after adding the nanoparticles approximately from 11.09 to 80.87 m2g-1. The hydrophilicity and thermal stability of the membranes were assessed, showing their applicability for efficient filtering operations. The optical sensors enabled real-time monitoring of pH in the range of 6-8 and dissolved oxygen in the range of 80-120 %, ensuring optimal conditions for amoxicillin adsorption in high flow rates of 100 mu l/min, approximately 99 %. The comprehensive design of this system significantly improved the efficiency of removing the AMX by follows the Langmuir's model, and demonstrated the adaptability and effectiveness of microfluidic technology in decreasing pharmaceutical pollution in the water sources. Moreover, it offers a simple and quick approach for users in the membrane industry to assess the manufactured membrane, making the technology accessible and feasible for broad use.

Highly versatile co-doped borate particles with notable small sizes, up-conversion emission intensities, and high neutron sensitivities were successfully synthesized using three synthesis techniques: solution combustion, combustion, and solid-state. Structures and morphology of products were determined with X-ray diffraction and scanning electron microscopy. Impact of the synthesis method on the morphology was examined and discussed. The effect of doping on the structure was also investigated by monitoring the lattice parameters and cell volumes of the crystals. The incorporation of a substantial percentage of 10B isotopes within the unit cells of these compounds rendered them highly sensitive to neutrons and made them candidate materials for boron neutron capturing therapy or for neutron shielding. Up-conversion properties of Yb3+/Tb3+ co-doped CaB4O7, SrB4O7, and MgB4O7 crystals were also investigated as candidates for imaging, sensing, or energy conversion. The synthesized borates showed intense emission signals of Tb3+ ions with support of energy transfer from Yb3+ ions under 980 nm near-infrared laser excitation. The combined properties of the synthesized co-doped borates as discussed give them multifunctionality in many application areas.

UV-curable polymeric adsorbent was prepared using a diacrylate-functionalized hydrazone-oxime monomer (DAFHOM), trimethylolpropane triacrylate (TMPTA), and trimethylolpropane tris(3-mercaptopropionate) (TMPTP) through UV-initiated thiol-ene click reaction. Initially, a novel hydrazone-oxime-based Schiff base ligand was synthesized and modified with diacrylate functionality to prepare the UV-curable polymeric adsorbent. The structures of DAFHOM and the resulting polymeric adsorbent were confirmed using Fourier Transform Infrared Spectroscopy (FTIR) analysis. Additionally, the thermal behavior of the UV-cured adsorbent was investigated through thermal gravimetric analysis (TGA), which revealed that the adsorbent exhibited good stability and did not degrade at room temperature. The adsorption performance of the UV-curable polymeric adsorbent for Au(III) from aqueous solutions was studied under various experimental conditions, including pH, contact time, and initial metal concentration. The UV-curable polymeric adsorbent demonstrated effective and selective Au(III) adsorption from aqueous solutions. The findings indicated that removing Au(III) from water solutions positively correlated with pH, particularly within the pH range of 0.5-2.5. However, the efficiency declined when the pH exceeded 1.5. Among the various adsorption isotherm models investigated, the Langmuir model was found to be the most suitable for describing the behavior of the adsorbent. The maximum adsorption capacity of the adsorbent for Au(III) was determined to be 30.06 mg/g. In batch experiments, the UV-curable adsorbent displayed promising selectivity towards Au(III), even in the presence of competitive ions such as Cu (II), Pb(II), and Cd(II).

Explosive detection is crucial for public safety and confidence. Among various solutions for this purpose, hyperspectral imaging differs from its alternatives with its detection capability from standoff distances. However, the state-of-the-art for such a technology is still significantly missing a complete technical and experimental framework for surveillance applications. In this article, an end-to-end technical framework, which involves capturing, preprocessing, reflectance conversion, target detection, and performance evaluation stages, is proposed to reveal the potential of a ground-based hyperspectral image (HSI) surveillance system for the detection of explosive traces. The proposed framework utilizes a short-wave infrared region (0.9–1.7 μ m), which covers the distinctive absorption characteristics of different explosives. Three classes of detection methods, namely index, signature, and learning-based methods are adapted to the proposed surveillance system. Their performances are compared over various experiments, which are specifically designed for granular and sprayed residues, fingerprint residues, and explosive traces on vehicles. The experiments reveal that the best method in terms of precision and recall performances is hybrid structure detector, which effectively combines signature-based detection with unmixing. While deep-learning-based methods have also achieved satisfactory precision values, their low recall values for the moment have comparatively limited their usage for the high-risk cases. Although one of the main reasons for the current performances of deep-learning methods is less data for learning, these performances for HSIs can be increased with more data in the future as in other image applications.

In this study, capability of Terahertz (THz) spectroscopy for determination of thermal properties of phase change materials (PCM) in an acrylated polyurethane coating investigated. Spherical shaped mesoporous silica materials (MPSs) are prepared as a template for stearic acid (SA). SA was impregnated into MPSs for investigate its PCM properties. Surface of MPSs was modified with 3-(Trimethoxysilyl)propyl methacrylate (MEMO) to add acrylate functionality to form covalently bond to polyurethane (PU)-based composite UV matrix to avert leakage problem. Finally, this resin was photopolymerized and its change in thermal properties was determined by both conventional Differential Scanning Calorimetry (DSC) and THz. DSC results show that the heating process phase change enthalpy is measured between 20.83 J/g and 136.80 J/g, and the freezing process phase change enthalpy is found between 13.55 J/g and 181.13 J/g by DSC. The thermal properties of phase changing behavior of the sample were also analyzed by Terahertz Time Domain Spectroscopy (THz-TDS). Besides the phase changes THz spectroscopy has shown the temperature dependent variation in the host matrix, also final PCM sample. Comparison of the data suggest that THz Spectroscopy is a fairly strong technique for characterization of phase changing materials even in very complex resin environment and it is a strong complementary technique especially following the temperature dependent properties close to room temperature.

The potential for wide-range THz imaging applications can be significantly enhanced with the implementation of cost-effective IR microbolometer technologies. For real-time broadband THz imaging purposes, thin films based on a titanium alloy, TiAlV, is investigated as the potential THz absorber layer in a microbolometer structure. Fabricated TiAlV thin films are evaluated in terms of their thickness, sheet resistance, and THz absorbance to assess their use in the microfabrication of a single pixel detector. Owing to its much lower conductivity compared to other metals and compatibility to microfabrication methods, by tailoring the sheet resistance with control in layer thickness, significant enhancement in THz absorbance is observed over a wide frequency range.

Printed electronics are emerging technology products that we use in every moment of our daily lives. It is used in many fields from health, textile, electronics to communication. Inks with nanometal or organic content can be used in printed electronics. The ability of printed electronics to withstand temperature makes its use widespread in the electronics industry. Main aim of the study is to combine surface modified graphene oxide-based conductive inks with flame retardant materials. In this study, an effective and simple approach for the preparation of polyurethane acrylate (PUA) screen printing ink containing surface modified reduced graphene oxide (rGO) which has flame retardant activity. A new and effective flame-retardant additive; 9,10-dihydro-9,10-oxa-10-phosphaphenanthrene-10-oxide (DOPO), silane coupling agent and reduced graphene oxide was synthesized. In this synthesis, first reduced graphene oxide was modified with (methacryloyloxy)propyltrimethoxysilane, and then reacted with DOPO to obtain a flame-retardant monomer containing P and Si. Based on the successful modification reactions, screen-printing ink containing polyurethane acrylate and different amounts of modified graphene oxide content (0, 5 and 10 wt%) were prepared and screen printed on the paper surface. In addition, coatings were made on the paper surface to determine some the properties. LOI values, thermal properties, contact angle values, conductivity and surface properties of the obtained prints and coatings films were investigated. As a result, conductive screen-printing ink resistant to high temperatures was successfully produced and printed coatings and free films were formed.

Vanadium oxide plays a crucial role as the temperature-sensitive layer of microbolometers. This layer should possess a high temperature coefficient of resistance (TCR) along with a desirable resistivity suitable for readout electronics. Mixed phase vanadium oxide thin films (VxOy) consist of different ratios of pure phases, which affect the resultant resistivity and TCR. It is thus important to be able to control individual phase concentrations to obtain the desired resistivity and TCR. In this study, we show that W-doping does not only introduce a new W-phase but also supports the formation of new V-phases in addition to the change in relative ratios of the original phases. The new V-phase, V2O5, dominates the overall electrical properties. Here, we first present the formation of new phases with W-doping and the structural and electrical characterization with classical tools, and then we show that Terahertz Time-Domain Spectroscopy (THz-TDS) is a strong nondestructive characterization technique that can monitor these effects of doping especially on the electrical behavior of VxOy films. Exploration of the control of this behavior is essential for the fabrication of a high TCR film with a desirable resistivity. (C) 2022 Elsevier B.V. All rights reserved.

The microbolometer technology has proved its potential in the Infrared (IR) region due to its low fabrication costs, and room temperature operation, making this technology desirable to be used in various applications, and this interest has recently expanded into the Terahertz (THz) region as well. The detection in microbolometers is achieved through the absorption of THz radiation which subsequently heats up and is sensed by the temperature sensitive material at the core of the device. This temperature sensitive material is typically based on VOx, which exhibits a sufficient change in resistance with temperature. While this temperature sensitive material is useful in the IR, the low energy of the THz wave compared to the background radiation makes it a challenge to operate the device at room temperature and show a large change in resistance with respect to the slight change in temperature. Metal doped VOx films can show a better performance however these effects are not well understood in the THz region. In this study, Tungsten (W) doped and undoped VOx films are fabricated and then analyzed using Time Domain THz Spectroscopy. The DC electrical properties of the films as well as their optical behaviors in the region of 0.2-2.0 THz are analyzed as a function of temperature. The metal doping is seen to affect the overall electrical and optical response of the film. Understanding this dependence is key to achieving a better film for applications in the THz region.

Imaging in the Terahertz (THz) region has drawn attention in recent years, but the nature of the THz frequency regime causes some drawbacks in imaging such as long wavelength, high cost, and low emission levels at room temperature. Because of the high atmospheric absorption of THz waves, fabrication of a microbolometer pixel that works in the sub-1 THz frequency regime is necessary. Large pixel pitches due to longer wavelengths and the resulting higher thermal mass pose a difficult challenge. Due to those limitations, a unique design of an absorber is essential for THz microbolometers. This study investigates the use of absorbers based on novel materials and alloys with the goal of developing efficient absorbers in small pixel pitches. First, thin layer metal absorbers typically used in commercial IR microbolometers are characterized in terms of absorption performance in the sub-1 THz region. Thin films based on metal alloys such as TiAlV show a markedly lower absorption in this region than in the IR. To improve the performance of these absorbing layers and reduce pixel pitches. Use of effective media based on the mixture of dielectric materials and metals with patterned thin films are investigated to develop unique absorbing thin layers. It is seen that with the use of an effective medium whose complex dielectric constant is tailored appropriately, efficient absorption of sub-1 THz radiation can be achieved.

A sensitive fiber loop ringdown (FLRD) spectrometer without any additional optical component was utilized to obtain strain measurement on a single mode fiber optic sensor. The strain data were obtained by employing the theory of bending loss in single mode fibers. The best sensitivity of the sensors was obtained as 5.99 mu epsilon with an 80.0 cm long sensor head when the sensor heads were stretched at the midpoint. The spectrometer system had a baseline-stability of 0.22%. Stretching the sensor head from off-midpoint positions resulted faster decays with higher optical losses. Comparison of the slopes relative to the stress positions showed that it may be utilized to obtain strain location without using any high-cost equipment. This portable, basic, and simpler FLRD spectrometer system offers high sensitivity with great baseline stability without utilization of any additional optical components and/or creating air-gap/air-cavity and encapsulation on the sensor head region. With its very attractive features of such as easy setup, low cost, and simple design, sensitive FLRD sensors may have a high potential for early detection in several applications such as structural health monitoring, biomedical sensing, mining, transportation and rail applications for continuous monitoring in real-time.

Fiber optic pressure sensors utilizing ultra-high sensitive fiber loop ringdown (FLRD) spectroscopy were fabricated using a bare single mode fiber. The fiber optic pressure sensors were applied to monitor pressure change on a plastic pipe embedded into a sea sand filled container in laboratory conditions to simulate a tower. As the pressure applied to the sensor head was changed from 66.4 kPa to 331.6 kPa, changes in the ringdown time (RDT) were recorded. The lowest baseline stability of 0.20% was obtained in these simple FLRD pressure sensors. The minimum detectable optical loss was 992 mu dB. The results showed that FLRD pressure sensors tested by applying to a pipe embedded into sea sand simulating a tower are highly sensitive and have high potential to be applicable for monitoring wind turbine components such as blades and towers in the sea or on land to determine the pressure on structures due to damage, excessive waves, or strong winds. The study also suggests that this type of FLRD pressure sensor can be utilized for the purpose of early detection in other important structures such as dams, buildings, and bridges.