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Growth and Optical Characterization of Europium and Cerium Doped KCl Single Crystals by Czochralski Method for Dosimetric Applications
摘要： Rare-earth-doped alkali halide single crystals KCl:Eu, KCl:Ce, and KCl:Eu,Ce were grown from melt using the Czochralski technique, and optical characterization was carried out with the prime focus on dosimetric applications. The grown crystals were investigated using XRD analysis, PL analysis, TSL measurements, and OSL measurements. The XRD of the crystals matched well with ICDD patterns (00-041-1476), and diffraction peaks can be assigned to the KCl structure, indicating that all the crystals have the same structure as KCl. The enhanced intensity of TSL and OSL was observed for co-doping of (Eu, Ce) in KCl crystals as compared to single doping. The appearance of a single glow peak in KCl:Eu,Ce at 230°C compared to single-doped KCl:Ce crystals suggested the use of the material in TL dosimetry. The intensity of OSL also showed a two-fold increase compared to single-doped crystals, suggesting its use in OSL dosimetry. PL studies showed a very high enhancement of intensity in Eu2+ emissions, reaching a maximum of about 421 nm in the (Eu2+, Ce3+) co-doped crystal compared to single-doped crystals. This justifies the occurrence of energy transfer from Ce3+ to Eu2+ in the KCl host lattice. These results showed that KCl:Eu,Ce acts as a potential TL and OSL dosimeter due to its high sensitivity to ionizing radiation.
关键词： crystal growth,Single crystal,potassium chloride,optical characterization,Czochralski method
更新于2025-09-23 15:23:52
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Fabrication, Modelling and Assessment of Hybrid 1-D Elastic Fabry Perot Microcavity for Mechanical Sensing Applications
摘要： 1-D multilayer dielectric films consisting of seven pairs of SiO2 and TiO2 alternating layers are deposited on a SiO2 substrate using the radio frequency sputtering technique. The thicknesses of the film layers are chosen to reflect the visible radiation around 650 nm. An elastic microcavity layer made of Polydimethylsiloxane was sandwiched between two Bragg reflectors. A fabrication process was then developed for elastic microcavity in order to tailor the thickness, establish the surface planarity and to increase reproducibility of the samples. Optical transmittance of the single Bragg reflector and the microcavity were both simulated and measured. A comparison between measurement data and Transfer Matrix Method calculations shows a favourable correlation. Furthermore, in order to assess the suitability of the microcavity as a force sensor, transmittance measurements were carried out as a function of the applied forces. The change in the elastic microcavity thickness due to applied forces resulted in cavity resonance peak shifts proportional to the applied forces.
关键词： Optical Characterization and Modelling,Silica and Titania,1D Elastic Photonic Crystal,Mechanical Sensor,RF sputtering,PDMS
更新于2025-09-23 15:22:29
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Ultrasonic spray pyrolyzed copper oxide and copper-aluminum oxide thin films: optical, structural and electronic properties
摘要： A study of the structural, electrical and optical properties of copper oxide and copper-aluminum oxide thin films deposited by ultrasonic spray pyrolysis is presented in this work. On one hand copper oxide films were deposited at working temperatures in the range from 300 °C to 500 °C. These films present a mixture of Cu2O and CuO phases, CuO phase being more abundant at higher temperatures; all samples present p-type conductivity. On the other hand, copper-aluminum oxide samples were deposited at 350 °C but with different copper-aluminum ratios in the start solution (0, 12.5, 25, 50, 100, and 200 at.%). The films present a mixture of Cu2O and Al2O3 phases, being the Cu2O the most abundant and becoming amorphous as aluminum concentration rises. Electrical characterization indicates that electronic conductivity depends on the amount of Cu2O, while ionic conductivity increases with aluminum concentration. Aluminum concentration also provokes a shift in the valence band towards lower binding energies, as well as an increase in the optical band gap (from 2.6 to 3.7 eV). Upon a thermal annealing at 800 °C the samples turned to CuAl2O4 spinel structure.
关键词： Optical characterization,Electrical characterization,Semiconducting copper-aluminum compounds,Spray pyrolysis
更新于2025-09-23 15:21:01
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Facilitating Tip-Enhanced Raman Scattering on Dielectric Substrates via Electrical Cutting of Silver Nanowire Probes
摘要： TERS is a powerful tool for nanoscale optical characterization of surfaces. However, even after 20 years of development, the parameters for optimal TERS tips are still up for debate. As a result, routine measurements on bulk or dielectric substrates remain exceptionally challenging. Herein we help to alleviate this by using electrical cutting to strategically modify silver nanowire TERS probes. Following cutting, the tips present a large, spherical apex and are often nanostructured with numerous nanoparticles, which we argue improve light collection and optical coupling. This doubles TERS signals on a highly-enhancing, gap-mode substrate compared to our standard nanowire tips, whilst maintaining a high reproducibility and resolution. More interestingly, on a dielectric substrate (graphene on SiO2) the tips give ~7x higher signals than our standard tips. Further investigations point to the non-local nature of the enhancement using standard, smooth, TERS probes without gap-mode, making such nanostructuring highly beneficial in these cases.
关键词： electrical cutting,silver nanowire,TERS,Tip-Enhanced Raman Scattering,nanoscale optical characterization,dielectric substrates
更新于2025-09-23 15:21:01
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Accelerated aging of absorber coatings for CSP receivers under real high solar flux – Evolution of their optical properties
摘要： The use of durable high solar absorptance receivers is a key element in a CSP plant project. In this article, different receiver materials are studied: four alloy substrates (T91, T22, VM12, Inconel 617) combined with four new absorber coatings, operable in solar towers with molten salts or steam as heat transfer fluids, and a classic Pyromark? paint considered as a reference. In order to test the durability of the coatings, 200 solar accelerated aging cycles were applied on the samples, using a concentrated solar facility (named SAAF). The cycles were defined so as to apply realistic high solar flux and temperature on the front side of the samples, and with high cooling and heating rates reproducing the fast variation of solar irradiation due to cloudy weather and subsequent thermal shocks. The optical characteristics of the coatings were measured at the beginning and at regular intervals during the aging procedure. Different behaviors of the coatings were observed depending on the substrate, before any aging cycle. After this first aging campaign, some evolutions were observed on the solar absorptance or thermal emittance, depending on the substrate and the coating. Nevertheless, the degradations noticed are not significant enough to conclude about the durability of the coatings.
关键词： Optical characterization,CSP receiver absorber coatings,Solar furnace,Accelerated aging
更新于2025-09-19 17:15:36
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Sub-400 nm film thickness determination from transmission spectra in organic distributed feedback lasers fabrication
摘要： The design and fabrication of thin-film based organic optoelectronic devices require knowledge of the film optical properties. A low-cost and non-destructive method often used for optical characterization of films is the well-established spectrophotometric envelope method. However, this method is typically limited to thickness above 400 nm, a value often higher than that of the films involved in these devices. This paper studies a procedure to obtain the thickness of sub-400 nm active films from their spectrophotometric trace when the refractive index is previously known. The proposed procedure is based on comparing the experimental transmission spectrum in the transparent spectral window with that obtained by simulation. The capabilities of the proposed method are demonstrated here by its application in the fabrication of organic distributed-feedback lasers where a fine control of film thickness is important to obtain an optimized and reproducible response. Results were verified with other techniques, such as ellipsometry and profilometry. Thus, with the proposed method, film thickness can be easily determined down to 40 nm maintaining an accuracy of about 5 nm even for films with low refractive index (1.5-1.7). Different methods to determine refractive index of these films are also discussed.
关键词： Optical characterization,Thin film thickness,Transmission spectra,Distributed feedback lasers
更新于2025-09-19 17:13:59
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Synthesis, Crystal Structure, and Optical Characterization of the Sulfide Chloride Oxide CsBa <sub/>6</sub> V <sub/>4</sub> S <sub/>12</sub> ClO <sub/>4</sub> with a Near-Infrared Fluorescence
摘要： When CsCl, BaS, BaO, V, and S are reacted in a solid-state reaction under inert conditions, pure powders and single crystals of senary CsBa6V4S12ClO4 can be obtained. Its unique crystal structure has the symmetry R3?H (no. 148) and unit cell parameters a = 9.0575(2) and c = 28.339(1) ?. The crystal structure contains polar units [VS3O]3? and a complex BaS7ClO2 coordination. The compound gets its deep-red color from a low-energy charge transfer, which can be explained by an electron transfer from S2? to V5+. In the near-infrared range, down-converted ?uorescence occurs at 1.06 and 0.90 eV, and both emissions appear <450 ps after excitation at about 1.27 eV.
关键词： optical characterization,crystal structure,near-infrared fluorescence,synthesis,sulfide chloride oxide
更新于2025-09-19 17:13:59
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Origin of Band-Tail and Deep-Donor States in Cu <sub/>2</sub> ZnSnS <sub/>4</sub> Solar Cells and Their Suppression through Sn-Poor Composition
摘要： By comparing optical spectral results of both Sn-rich and Sn-poor Cu2ZnSnS4 (CZTS) with the previously calculated defect levels, we confirm that the band-tail states in CZTS originate from the high concentration of 2CuZn+SnZn defect clusters, whereas the deep-donor states originate from the high concentration of SnZn. In Sn-rich CZTS, the absorption, reflectance and photocurrent (PC) spectra show band-tail states that shrink the bandgap to only ~1.34 eV, while, photoluminescence (PL) and PC spectra consistently show that abundant CuZn+SnZn donor states produce a PL peak at ~1.17 eV and abundant SnZn deep donor states produce a PL peak near 0.85 eV. In contrast, Sn-poor CZTS shows neither bandgap shrinking nor any deep-donor-defect induced PL and PC signals. These results highlight that a Sn-poor composition is critical for the reduction of band-tailing effects and deep-donor defects and thus the overcoming of the severe open-circuit voltage (Voc) deficiency problem in CZTS solar cells.
关键词： Band-tail states,Deep defects,Cu2ZnSnS4 (CZTS),Optical characterization
更新于2025-09-12 10:27:22
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A 4H-SiC UV Phototransistor With Excellent Optical Gain Based on Controlled Potential Barrier
摘要： In this article, we report the experimental results of a visible-light-blind 4H-polytype silicon carbide phototransistor able to detect ultraviolet (UV) radiations for wavelengths lower than 380 nm with a significative improvement in the optical gain compared with the state-of-the-art of 4H-SiC UV phototransistors. From the electro-optical measurements, the device shows a dark current of 0.62 pA, an ON-/OFF-current ratio of seven orders of magnitude up to bias voltage of ?0.5 V, and an excellent optical gain of 1.14·105 at 300 nm, whereas it is only 2.6·10?3 at 400 nm demonstrating a good rejection of visible radiations. Besides having high optical gain, the phototransistor is also more sensitive than the conventional 4H-SiC UV detectors for wavelengths with low penetration depths, because its structure is designed to have the electric field up to the radiated surface where the photogenerated electron–hole pairs are efficiently swept up before recombination occurs. The operating principle of the detector is also investigated, and we experimentally proved that differently from the conventional 4H-SiC bipolar junction transistor phototransistor, it is based on the change in the potential barrier height, which controls the current flow, due to the variation in the Fermi levels when the electron–hole pairs are photogenerated. A comparison with the state-of-the-art of 4H-SiC UV phototransistors is reported.
关键词： 4H-SiC semiconductor device,phototransistor,potential barrier,ultraviolet (UV) detector,electro-optical characterization
更新于2025-09-12 10:27:22
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Electrical and optical analysis of a spray coated transparent conductive adhesive for two-terminal silicon based tandem solar cells
摘要： This work presents the results of the electrical and optical characterization of a new transparent conductive adhesive (TCA) that combines the techniques of spray pyrolysis and a sol-gel like process. This approach is of particular interest since the adhesive itself forms both the electrical and the mechanical interconnection of the bonded sub-cells. The electrical and optical characterization of the developed TCA shows a minimum connecting resistivity of 17 ?cm2 and a simulated reflection at the Si-TCA interface of ≈ 20%. By coating both substrate surfaces with a TiO2 anti reflection coating (ARC), the reflectance at the Si-TCA interface was successfully reduced down to <5%. The efficiency potential of a glued dual junction device was simulated in dependence of the electrical and optical properties of the TCA. The reported values of 17 ?cm2 connecting resistivity and 20% reflection limit the device efficiency to 22.3% (71% of the maximum achievable efficiency). Reducing the reflection to below 5%, as practically demonstrated in this paper, allows to increase this value to 25.3% (>80% of maximum), while additionally reducing the connecting resistivity to 10 ?cm2 or 1 ?cm2 allows for a further increase to 27.3% and 30.0%, respectively.
关键词： reflection losses,sol-gel process,tandem solar cells,connecting resistivity,TiO2 anti reflection coating,electrical characterization,transparent conductive adhesive,optical characterization,spray pyrolysis
更新于2025-09-11 14:15:04