Blue Layer Research Articles

Chronopotentiometric method for assessing antioxidant activity: A reagentless measuring technique

A simple chronopotentiometric method designed for the estimation of the antioxidant activity of liquid samples was investigated. A carbon electrode with a thin immobilized redox mediator layer on its surface was used for detection. A two-step measuring protocol was used. Firstly, in a short potential-controlled step, the mediator was set to its oxidized state; then, in the second step, the electrode potential–time curve was recorded in open circuit mode. The initial slope of this curve served as the analytical signal. It is clear that a higher antioxidant concentration produced a higher slope. The performance of adsorbed and electropolymerized Meldola Blue redox mediator layers formed on glassy carbon electrodes was investigated and compared. L-ascorbic acid was used as a sample antioxidant in this study.

Resistive Switching in Electrodeposited Prussian Blue Layers.

Prussian blue (PB) layers were electrodeposited for the fabrication of Au/PB/Ag stacks to study the resistive switching effect. The PB layers were characterized by different techniques to prove the homogeneity, composition, and structure. Electrical measurements confirmed the bipolar switching behavior with at least 3 orders of magnitude in current and the effect persisting for the 200 cycles tested. The low resistance state follows the ohmic conduction with an activation energy of 0.2 eV.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

Engineering Novel Blue Emissive Thiazolidinedione (TD) Poly Lactic Acid (PLA) Composite Thin Films for Bioplastic Scintillation

In this article, we demonstrate luminescent properties of PLA blended with new 3-[2-(4-methylphenyl)-2-oxoethyl]-5-(thiophen-2-ylmethylidene)-1, 3-thiazolidine-2, 4-dione and 3-[2-(4-chlorophenyl)-2-oxoethyl]-5-(thiophen-2-ylmethylidene)-1, 3-thiazolidine-2, 4-dione (TD). This paper mainly aims at the preparation of intercalated thin films of PLA and TD. The formation of matrix-dopant composite films was confirmed by FTIR, SEM, TGA, DSC and XRD characterizations. This work really stands out from our previous work as TD has been better recognized as drug material in the medical field and less known as an organic fluorophore in luminescent materials. Pure PLA exhibits absorption maximum at 300nm whereas absorption of TD doped composite films resulted in Stoke’s shift to 350nm. These films turned into blue emissive layers showing emission band at 440nm on being shined at 350nm. The quantitative increase in the absolute quantum yield of 0.18-0.42 and 0.16-0.52 for the aforesaid materials was demonstrated which was in accordance with the concentration of the dopant in the film. Thus, the material obtained by PLA-TD combination was found to absorb UVA radiations and emit blue light, which not only might emerge as prospective material for bioplastic scintillation but also as ecofriendly blue emissive layers.

Modelling and assessment of earthquake ground response in areas characterised by a thick buried low-velocity layer

It is known that local geology can alter the ground motion characteristics at a particular site. Whereas some sites are characterised by outcropping low-velocity layers, others might have buried ones of considerable thickness which might still be a cause of ground motion amplification. The Maltese islands (Central Mediterranean) provide a good case study for profiles with a buried low-velocity layer. Parts of the islands are characterised by Upper Coralline Limestone covering a soft Blue Clay layer of considerable thickness (up to 75 m). This gives rise to a velocity inversion and makes the travel-time average shear-wave velocity (VS) in the upper 30 m not suitable for seismic microzonation purposes. This study presents a comprehensive site response analysis for such areas. Previously obtained shear-wave velocity (VS) profiles were used as an input to the equivalent linear programme SHAKE2000. Maps of amplification factors and 5% damped elastic response spectra confirm that the clay, even when buried under a hard outcropping layer, can still produce significant amplifications at frequencies which are of engineering interest when considering the recent urbanisation patterns. Moreover, the suitability of the VS30 and the travel-time average shear-wave velocity till bedrock parameters as proxies for site response was investigated, with the results highlighting the inadequacy of these parameters for sites characterised by buried low-velocity layers and the necessity for site-specific response studies.

Double functionalization strategy toward Co-Fe-P hollow nanocubes for highly efficient overall water splitting with ultra-low cell voltage

Due to their inherent structural and functional defects, most bifunctional catalysts usually delivered excellent electrocatalytic activities for one half-reaction at expense of the performances for another one, thus exhibiting inconspicuous electrocatalytic abilities for overall-water-splitting. In the present work, a novel strategy of controllable assembly and synergistic catalysis based on hydrogen evolution reaction (HER) active and oxygen evolution reaction (OER) active single functional sites, was ingeniously assembled to high-performance catalysts for overall-water-splitting. Monodispersed zeolitic imidazolate framework cubes were adopted as the reaction precursors to construct bi-functional electrocatalysts through conformal Prussian blue analogue layer coating and the subsequent thermal phosphorization process. HER active Co-P and OER active Co-Fe-P hetero-components were simultaneously anchored on the shell layers of the resulted Co-Fe-P hollow nanoboxes. Benefiting from the unique structural design and functional integration, the product catalyst afforded small overpotentials of 174 and 53 mV at 10 mA/cm2 for the OER and HER in alkaline media, respectively and a ultra-low operating cell voltage of 1.46 V for overall-water-splitting, superior to most recently reported striking bi-functional electrocatalysts. Moreover, its ultrastable catalytic activity was also impressive, delivering only negligible performance loss after a 24 h durability testing. More broadly, this combined double functionalization concept and nanoscale hollowing design is unique and advantageous, especially suitable for developing highly active and durable electrocatalysts of energy conversion reactions.

Photosynthesis Z-Scheme biomimicry: Photosystem I/BiVO4 photo-bioelectrochemical cell for donor-free bias-free electrical power generation

Photo-bioelectrochemical cells that are based on photosynthetic proteins are drawing increased attention for both fundamental and applied research. While novel photosynthetic based systems have been introduced, further optimization in terms of stability and efficiency is required. Photosystem I has been utilized extensively in bioelectronic devices, often in conjugation with viologen moieties which act as electron acceptors. It has been shown previously that a partial reduction of oxygen to H2O2 can facilitate damage to proteins hence, limits their long-term activation. Here, we show a newly developed bias-free, donor-free photo-bioelectrochemical system that mimics the natural photosynthetic Z-scheme. Polymethylene blue and polybutyl-viologen were tailored to fit the photosystem I donor and acceptor sides, respectively. Furthermore, we show that by coupling the developed biocathode with a BiVO4/CoP photoanode, a power output of 25 μW/cm2 can be achieved. We further show that our configuration can minimize the damaging effect of H2O2 by two different pathways, oxidation at the photoanode or reduction by the polymethylene blue layer at the biocathode.

Thermally Assisted Fluorescent Polymers: Polycyclic Aromatic Materials for High Color Purity and White-Light Emission.

Thermally activated delayed fluorescence (TADF) sensitization of fluorescence is a promising strategy to improve the color purity and operational lifetime of conventional TADF organic light-emitting diodes (OLEDs). Here, we propose a new design strategy for TADF-sensitized fluorescence based on acrylic polymers with a pendant energy-harvesting host, a TADF sensitizer, and fluorescent emitter monomers. Fluorescent emitters were rationally designed from a series of homologous polycyclic aromatic amines, resulting in efficient and color-pure polymeric fluorophores capable of harvesting both singlet and triplet excitons. Macromolecular analogues of blue, green, and yellow fourth-generation OLED emissive layers were prepared in a facile manner by Cu(0) reversible deactivation radical polymerization, with emission quantum yields up to 0.83 in air and narrow emission bands with full width at half-maximum as low as 57 nm. White-light emission can easily be achieved by enforcing incomplete energy transfer between a deep blue TADF sensitizer and yellow fluorophore to yield a single white-emissive polymer with CIE coordinates (0.33, 0.39) and quantum yield 0.77. Energy transfer to the fluorescent emitters occurs at rates of 1-4 × 108 s-1, significantly faster than deactivation caused by internal conversion or intersystem crossing. Rapid energy transfer facilitates high triplet exciton utilization and efficient sensitized emission, even when TADF emitters with a low quantum yield are used as photosensitizers. Our results indicate that a broad library of untapped polymers exhibiting efficient TADF-sensitized fluorescence should be readily accessible from known TADF materials, including many monomers previously thought unsuitable for use in OLEDs.

Axial strength of short concrete-filled plastic tubes

The axial compressive behavior of concrete-filled plastic tube (CFPT) with five different cement–admixture combinations were examined. A commercially available modified polycarboxylate superplasticizer used at five different concentrations. The plastic tube was an un-plasticized polyvinyl chloride (uPVC) made up of three layers: a blue layer sandwiched between two white layers to achieve solid wall construction. Test results showed that the strength of the CFPT specimens influenced by the increase in superplasticizer dosage up to an optimum dosage. Further increase in the admixture-cement ratio had an adverse effect on strength enhancement. To assess the performances of CFPT specimens under monotonic axial compression, an extensive database comprising the test results of the 157 CFPT column established. The database supplemented by the sum of eighteen test results from the current experimental study used to assess the applicability of ten existing FRP-confined concrete, two steel-confined concrete, and one CFPT strength model to predict the strength of CFPT specimens. By considering the light confinement mechanisms of the tube and general regression analysis, four simple ultimate strength models were proposed based on the database assembled in the present study. Three different statistical indices, the coefficient of determination (R2), the Root Mean Square Error (RMSE), and Average Absolute Error (AAE), were used to assess the performance of the strength models. The proposed four strength models yielded the best fitting results compared with the predictions from the existing ten FRP-confined concrete, two steel-confined concrete, and one CFPT strength model.

Tunable band alignment in boron carbon nitride and blue phosphorene van der Waals heterostructure

The hybrid monolayer of boron nitride and graphene, namely the BCxN monolayer, has been recently revealed as a direct bandgap semiconductor with exceptional thermal, mechanical and optical properties. The integration of such monolayer with other 2D materials into a van der Waals heterostructure (VDWH), however, remains largely unexplored thus far. In this work, we investigate the electronic and structural properties of a new class of VDWH obtained via the vertical stacking of BCxN (x = 2, 6) and blue phosphorene monolayers. By using first-principle density functional theory (DFT) simulation, we show that BCxN couples to the blue phosphorene layer via weak van der Waals interactions and exhibits a type-II band alignment which is beneficial for electron-hole pair separation in photodetection and solar cell applications. Intriguingly, changing the interlayer separation induces a indirect-to-direct band gap transition which changes the band alignment types of the VDWH. The interlayer separation, which can be readily tuned via a vertical strain, thus provides a useful tuning knob for switching the heterostructures between type-I and type-II VDWHs. Our findings reveals the BCxN-based VDWH as a versatile material platform with tunable band alignments, thus opening a route towards novel VDWH-based optoelectronic devices.

Simulating re-impacts from craters at the deepest location of Phobos to generate its blue spectral units

The spatial distribution pattern of ejecta from an impact crater on the surface of a body in space holds clues to understanding the ejecta launch conditions, the crater excavation process, and the dynamical environment. In particular, focusing on re-impact sites from larger or deeper craters on the surface is important, as they tend to preserve much of the original information. The surface of the Martian satellite Phobos is spectrally divided into red and blue units. The former are globally distributed, while the blue units have been observed inside and outside the Stickney crater—the largest and deepest crater on Phobos. Outside the crater, the blue units are concentrated in the region from the south to the west (south-west blue units) and in the region east of the crater (east blue units). Several models can explain the concentration of east blue units. However, the mode of formation of south-west blue units is still unknown, despite its vast area. We proposed that the combination of ejecta from Stickney and Limtoc (a crater located on the floor of Stickney) contributed to the formation of the blue units. We tested the model using ballistic simulations incorporating, an updated shape model with randomly generated ejecta velocities, different values of orbital radii to Mars, and various launching velocities, to track the emplacement of the ejecta particles. The results showed that the distribution of the two blue units is recreated when the combined re-impact sites of ejecta from Stickney and Limtoc have orbital radius (XPh) values of XPh > 3.34 Mars radii (RM) and XPh < 3.04 RM, respectively. The observations and the results suggest that Phobos comprises an inner blue layer covered by red materials globally and locally excavated blue materials. Using the squared term of the orbital evolution, we calculate the approximate age of Stickney to > 23 Myr, which may be sufficiently old to be estimated from the crater densities. We restrict the age of Limtoc to < 109 Myr, which indicates that this crater is one of the youngest features on Phobos.

Spatially indirect excitons in black and blue phosphorene double layers

Monolayer black and blue phosphorenes possess electronic and optical properties that result in unique features when the two materials are stacked. We devise a low-strain van-der-Waals double layer and investigate its properties with ab initio many-body perturbation theory techniques. A type-II band alignment and optical absorption in the visible range are found. The study demonstrates that spatially indirect excitons with full charge separation can be obtained between two layers with the same elemental composition but different crystalline structure, proving the system interesting for further studies where dipolar excitons are important and for future opto-electronic applications.

Understanding the degradation of the blue colour in the wall paintings of Ariadne's house (Pompeii, Italy) by non‐destructive techniques

AbstractAriadne's house is in the Regio VII of the Archaeological Park of Pompeii (Italy). As it is exposed to external alteration agents (rainfall, water infiltration and atmospheric pollution), the mural paintings located in this important residence clearly show the effects of ongoing degradation processes. This is especially the case of Room 22 (also called the blue room), where the original blue decorations varied towards greyish green hues. In situ and laboratory spectroscopic analyses by means of non‐destructive X‐ray fluorescence, infrared and Raman spectroscopies identified the original pigments and the materials used in the conservation works. Looking in detail at the stratigraphic distribution of the original pigments, using Raman spectroscopy, an inner layer of Egyptian blue mixed with celadonite was detected under a layer of pure Egyptian blue. This discovery proves the presence of a more ancient painting below the one that can be observed today. Considering that celadonite was an inexpensive pigment (thus, probably used to reduce the costs of the paintings), this information strengthens the hypothesis that based on archaeological evidences, there is evidence of an evolution of the socio‐economic status of the ancient owners of the residence. In addition to that, Raman data also proved the occurrence of salt efflorescences; they provided insights about the compromised conservation state of the wall paintings, and they highlighted the action of atmospheric acid gases as an important factor.

Small molecule gas adsorption onto blue phosphorene oxide layers

We report a first-principles study of the electronic and optical properties of BPO (Blue phosphorene oxide) and BPO-V (Blue phosphorene oxide with vacancy) with the adsorption of low molecular weight gases (CH4, CO2, CO, SO2, and O2). Blue phosphorene oxide -with and without vacancies- shows different optoelectronic compared to blue phosphorene. The BPO has proven to be more energetically, and structurally stable than blue phosphorene under ambient conditions. Our calculations show that: Blue phosphorene oxide -with and without vacancies- exhibits different optoelectronic compared to blue phosphorene. Physical adsorption occurs for all gas molecules. Highest values of adsorption energy are found when the monolayers interact with O2 and SO2. This is associated with a modification of conducting nature, which is changed from semiconductor to conductor character, depending on the orientation of adsorbed molecules. By contrast, the coupling with CO and CO2 molecules leads to the lowest values of the energy of adsorption. The observed features of the electronic properties and optical response of BPO + adsorbed-gas complexes allow to suggest that this phosphorene-based structures could be promising candidates for gas sensing applications.

Iris biometric recognition of latin american eyes in a white light controlled environment

Iris biometric recognition has taken a great interest in the last decade. Many private and public facilities need to improve their security access due to the increasing terrorist attacks, the growing number of fraud and identity theft among other felonies. The regular technologies are almost all based on infrared light illumination due to the ease of using this for texture approach recognition. Even Though this technique is suitable in most cases, the highest price of these cameras on the market demands the research of either daylight or a white light solution. There are some known iris databases such as CASIA and UBIRIS, but they are not from Latin-American eyes that have different occlusion and color issues. A white light controlled environment was used to take the set of pictures 500 that let us have a new color database to carry out the experiments based on the EigenIris technique. The best iris and pupil segmentations were obtained either on the red or green color layers of the RGB images at 100% of correct localization. In this research, a sensitivity of 0,82 and specificity of 0,85 was achieved with a modified version of the EigenIris method using the blue color layer.&#x0D;

High efficiency and color quality undoped phosphorescent white organic light-emitting diodes based on simple ultrathin structure in exciplex

Abstract White organic light-emitting diodes (WOLEDs) with ultra-thin emitting layers have shown considerable potential in solid-state lighting fields due to the simplified structures. However, such WOLEDs with high efficiency, high color rendering index (CRI) and stable spectral emission are still facing challenges. In this paper, we demonstrated a high efficiency and high CRI phosphorescent WOLED by strategically adjusting the positions of red, green and blue phosphorescent ultra-thin layers in exciplex emitter. By investigating the processes of energy transfer and utilization of triplet excitons, a high efficiency, high CRI and stable spectrum emission warm WOLED was successfully fabricated. The maximum external quantum efficiency (EQE), power efficiency (PE) and current efficiency (CE) reached 26.1%, 50 lm W−1,and 40 cd A−1, respectively, and the CRI was as high as 80 in the luminance range from 1000 cd m−2 to 30000 cd m−2 with stable emission spectra, exhibiting superior comprehensive EL performances. This work also indicates the potential of undoped ultra-thin layer structures to fabricate high performance WOLEDs for lighting applications.

Evidence for the catalytic properties of ultramarine pigment

Abstract Ultramarine blue paint layers in oil paintings can be affected by ultramarine ‘disease’ or ‘sickness’: a phenomenon described by a grey appearance and a loss of detail in the artwork. An explanation for this phenomenon is an interaction between the organic binder network and ultramarine pigment, with the pigment acting as a catalyst for the breakdown of the network. This breakdown results in micro-cracks in the paint film, which influences the appearance of the artwork. To investigate the possible catalytic property of ultramarine pigment, a test reaction – the dehydration of methanol to dimethyl ether – was carried out, with and without ultramarine pigment present in a micro-reactor with in-line gas chromatography mass spectrometry. It was observed that a higher yield of dimethyl ether was obtained in the presence of ultramarine pigment, confirming that ultramarine pigment possesses catalytic properties similar to commercial zeolitic silica-alumina catalysts.

Chemical-technological research and radiocarbon AMS dating of wall painting fragments from the ruins of the XIIth-XIIIth centuries AD church from archaeological excavations in the city of Smolensk, Russia

In 2012, the ruins of a temple of the old Russian period were found during archaeological research in the medieval historical territory of Smolensk. The archaeological complex consists of the ruins of an ancient temple, built in the middle of the XIIth century AD, and adjacent to it from the South-West of the territory, which housed the remains of the market XI-turn XIII-XIV centuries AD and necropolis XIII–XVI centuries AD. Chronologically diverse use of the investigated territory up to the XVIth century AD was determined by the nearby Church. Approximately 1000 fragments of wall paintings, 5 fragments window glass and 4 glazed floor tiles were found near the ruins of the Church building. For the first time fragments of wall paintings medieval of Old Russian temple were dated by the AMS radiocarbon dating and went through chemical-technological research (analysis of the plaster foundation, the definition of used pigments) by X-RAY diffractometry (XRD) and scanning electron microscopy (SEM/EDS). Optical microscopy also was used for visual observations of the samples of the wall painting. According to the results of the radiocarbon analysis, the fragments of the wall paintings were divided into two chronological groups. The earlier belongs to the last quarter of the XIIth–the first quarter of the XIIIth century AD. Samples of the wall paintings from the second group are dated back to the third quarter of the XIIIth century AD. A narrow range of Accelerator Mass Spectrometry (AMS) radiocarbon dating of fragments of the murals, obtained from carbonates due to the presence of high content of C14 isotope in carbon of the plaster, is simultaneous in age to the moment of creation of the plaster base. As a result of chemical and technological researches of the fragments of the wall paintings it was established that the plaster basis of the fragments of the wall painting consists of two layers. The plaster base contains organic binders. Chemical and technological analysis of pigments presents the following results: (1) the basis of the blue paint layer is ultramarine (mineral) and anatase (mineral); (2) the basis of the green paint layer is celadonite (mineral); (3) the basis of the brown paint layer is ochre (clay); (4) black particles in the colorful mixture of brown is an organic wood coal pigment.

The influence of the Rubrene thickness on the performance of white organic light-emitting devices

A group of white OLEDs (organic light-emitting devices), were fabricated using the blue yellow complementary principle. Among them, MCP(1,3-Bis(carbazol-9-yl)benzene) was used as the main material for the blue light layer, FIrPic(Bis(3,5-difluoro)-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(III)) as the phosphorescent object material, and Rubrene(5,6,11,12-Tetraphenylnaphthacene) as the fluorescent material for the yellow light layer. The device structure is NPB(N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine) (20 nm)/Rubrene (0.5 nm)/MCP (3 nm)/MCP: FIrPic (30 nm, 10%)/Rubrene (z nm)/TPBi(1,3,5-Tris(1-phenyl-1Hbenzimidazol-2-yl) benzene)(10 nm)/Alq3(20 nm/LiF (0.6 nm)/Al (100 nm). By adjusting the thickness of Rubrene, the structure of the device was optimized and the performance of the device was improved. When the thickness of Rubrene was 0.5 nm, the performance of the device was the best, the maximum efficiency was 6.41 cd/A, the maximum luminance was 8344 cd/m2. When the driving voltage changed from 5 V to 14 V, the device changed from warm white light to cold white light.

All‐Fluorescence White Organic Light‐Emitting Diodes Exceeding 20% EQEs by Rational Manipulation of Singlet and Triplet Excitons

AbstractWhite organic light‐emitting diodes (WOLEDs) composed of conventional fluorophores possess color purity, low efficiency roll‐off, and rare metal absence, but suffer from theoretical limits due to the lack of triplet utilization. Due to the different diffusion distance for singlets and triplets, multiple Förster resonance energy transfer (FRET) channels can be adequately built up. Herein, besides the complementary component, a blue fluorescence layer, hosted by pure hydrocarbon material SF4‐TPE, is put forward as the spatial exciton manipulating layer to rationally allocate singlets and triplets to the corresponding channels. Hence, singlets are captured by the blue fluorophore, diffused triplets subsequently undergo energy resonance between the blue fluorophore and green assistant, and up‐conversion effect for eventual emission from the yellow fluorophore. Owing to the utilization of singlets and triplets, all‐fluorescence WOLEDs exhibit high efficiency exceeding 20%, with slight efficiency roll‐off even under high luminance of 5000 cd cm−2. Moreover, CIE coordinates can be surrounding and precisely inside the American National Standard Institute (ANSI) quadrangles, as well as outstanding color stability (ΔCIE‐(x, y) within (0.001, 0.012)) from 300 to 13000 cd cm−2.