Narrow-band UV Research Articles

Cerium-based halide perovskite derivatives: A promising alternative for lead-free narrowband UV photodetection

Cerium-based halide perovskite derivatives: A promising alternative for lead-free narrowband UV photodetection

Laser spectroscopy of highly charged ions at the storage ring CSRe: Schottky-based spectroscopic investigation and XUV fluorescence detector development

Laser spectroscopy stands out as a powerful tool to investigate atomic and nuclear properties and also test fundamental theories by precisely measuring the energy levels in highly charged ions. In this work, the fine-structure splitting 1s22s2S1/2−1s22p2P1/2 transition in lithium-like 16O5+ has been investigated in a laser spectroscopy experiment at the heavy-ion storage ring CSRe. The excitation resonance of the tunable narrowband UV laser and the ions was observed using a Schottky resonator with very high sensitivity. The experimental uncertainties including the ion beam velocity determination, the space charge effects, laser wavelength calibration, and angular misalignment between the laser and ion beam were analyzed, and the 2S1/2−2P1/2 transition wavelength was determined to be λ0= 103.45(38) nm. The primary source of experimental uncertainty arises from the inaccurate measurement of the high voltage applied on the electron cooler and therewith the ion beam velocity at the CSRe. In order to solve this problem, a high-precision divider to precisely measure the high-voltage of the electron cooler is under construction, which is expected to improve the present experimental accuracy by three orders of magnitude. In addition, an XUV optical detector equipped with an off-axis parabolic mirror has been developed and installed at the CSRe for the investigation of slow dipole-forbidden transitions in highly charged ions, such as hyperfine splitting and M1 transitions. The experimental studies presented here pave the way for future laser spectroscopy experiments at the CSRe as well as at the future larger-scale scientific facility HIAF in China.

The expected characteristics of the Cherenkov telescope TAIGA-IACT equipped with SiPM detectors

Monte-Carlo modeling of effective area and count rate of the TAIGA-IACT Cherenkov gamma-ray telescope unit with an upgraded camera based on SiPM OnSemi MicroFJ-60035 detectors and optical filters SL 290-590 and SL 290-590 has been carried out. It has been shown that with the SL 290-590 filter the threshold detection energy of the telescope would be improved compared with its current PMT-based configuration and would reach about 0.4 TeV. With the narrow band UV filter SL 290-590 the estimated threshold would reach about 0.7 TeV, which is a reasonable value for a 10 m2 class IACT, especially because with a SiPM-based telescope it will be possible to carry out observations during moonlit nights and at twilight without a substantial increase of the threshold. One may conclude that an upgraded TAIGA-IACT unit will be an efficient instrument for studies of TeV-band gamma-ray emission of various cosmic objects.

COMPARATIVE CHARACTERISTICS OF SKIN RECOVERY IN RATS AFTER ULTRAVIOLET IRRADIATION WITH AND WITHOUT ERBIUM LASER

Introduction. Ultraviolet radiation, which has a significant biological impact among the spectrum of sunlight, can cause skin aging and tumors, but in controlled use it also has therapeutic effects on the skin. Ultraviolet radiation with a wavelength of 311 nm is used for phototherapy of skin diseases. Melanin, contained in melanosomes (MS), is produced in melanocytes (MC) during melanogenesis. Phototherapy can cause clinical hyperpigmentation by provoking an increase in the number of MCs. Ablative lasers, such as Er:YAG, are used to manage hyperpigmentation, but at the same time have the risk of causing hyperpigmentation. The frequency of such side effects varies from 10 to 46%. The aim of the study was to determine changes in the number of MCs in the epidermis relative to the length of the basement membrane and the density of MSs in the epidermis in two groups of animals: after UV irradiation without and with an ablative laser. Materials and methods. The study began with an imitation of phototherapy of dermatoses with narrow-band UV radiation. The animals were divided into 2 experimental groups: free readaptation, using laser and a separate control group (intact rats). Skin samples were taken from 54 rats: 12 animals per checkpoint (6 for each group) on days 31, 45, 61, and 121, and 6 animals in the control group. The melanocytic and melanosomal components of the epidermis were evaluated, and comparisons were made between groups and with intact animals. Results. In the group of free readaptation on day 45, the density of MCs reached 0.78±0.16 cells per 100 mkm of basal membrane (units), which exceeded the normal value, but did not show statistical significance (p=0.37). On days 61 and 121, the density was 0.72±0.13 units and 0.70±0.17 units, respectively, which indicated a correlation with the elapsed time, r = -0.732, but at once was not significantly different from the control group. In the laser hypopigmentation group, the density of MCs on the basement membrane was 0.68±0.26, 0.70±0.26 and 0.69±0.23 units on days 45, 61 and 121, respectively, demonstrating stability. The correlation between MCs density and time after UV irradiation was not taken into account (r = ‑0.485). As for the analysis of MSs, in the control group, the area of MSs was 0.77±0.24% of the epidermis square. On day 31, the density of MSs reached a peak and amounted to 1.21±0.32%, statistically different from the control group (p=0.04). Subsequently, in the group of free readaptation, the area of MSs decreased to 1.03±0.16% on day 45, 0.91±0.13% on day 61, and 0.91±0.25% on day 121. An inverse correlation was observed between the density of MSs and the elapsed time, r = -0.735. Similar patterns were observed in the laser ablation group. On days 45, 61, and 121, the area of MSs was 1.07±0.28%, 0.92±0.22%, and 0.84±0.19%, respectively. The correlation between MSs density and time after UV irradiation was significant, r = -0.881. Comparison of the density of MSs in the epidermis between the experimental groups did not reveal statistical differences at any stage of the experiment. Conclusions. The described ultraviolet impact on the skin did not lead to a statistically significant increase in the number of MCs on the basal membrane (p=0.37), but significantly increased the area of MSs in the epidermis (p=0.04). Comparison of the density of MCs in the groups of laser hypopigmentation and free readaptation did not reveal statistically significant differences between each other and the control group. Laser ablation did not lead to either an increase or decrease in the average concentration of MSs in the epidermis compared to the free readaptation group.

Robust Bi-anchoring carbon dot/BiOCl sheet heterojunction photocatalysts toward superior photocatalytic activity.

BiOCl has attracted much attention due to its robust layered structure, excellent photocatalytic activity and nontoxicity. However, its practical application is hindered by its narrowband UV photoresponse and rapid recombination of photocarriers. Herein, zero-dimensional Bi-anchoring carbon quantum dot (Bi-CD)/two-dimensional BiOCl heterojunction (Bi-CD/BiOCl) photocatalysts are designed and synthesized by a facile hydrothermal method. Under 190-1100 nm broadband light irradiation, the optimized Bi-CD/BiOCl sample exhibits a superb rhodamine B (RhB) degradation rate of nearly 100%, which is 2.3 (1.7) times that of pristine BiOCl (CD/BiOCl). Additionally, the optimized sample exhibits an RhB degradation rate of up to 88.1% even under direct outdoor light and robust durability in water solution. Experimental results combined with DFT calculations reveal that the superior photocatalytic activity arises from the synergetic effects of broader light absorption due to the incorporation of CD, extra hot electron excitation by the localized surface plasmon resonance (LSPR) effect of metallic Bi, and enhanced electron transfer across the heterojunction interface as well as the existence of more oxygen vacancy traps in BiOCl. This work gives insights into the structure and photocatalytic properties of Bi-CD/BiOCl and provides a new strategy for the design and fabrication of robust high-performance photocatalysts under wide spectrum light irradiation.

Clinical effect of platelet-rich fibrin in combination with narrow-band ultraviolet B treatment in patients with small area deep burn wounds

Purpose: To investigate the influence of the combined use of platelet-rich fibrin and narrow-band UV B (NB-UVB) treatment on small-area deep burn wounds in patients.Methods: A total of 86 patients with small area deep burn wounds were assigned to control and study groups (n = 43/group). The control patients received routine drugs in combination with NB-UVB, while the study group was administered a combination of platelet-rich fibrin and NB-UVB therapy. Clinical efficacy indices were.Results: In the study group, the pre and post-treatment serum levels of TNF-α were 222.75 ± 4.86 and 65.42 ± 5.33 ng/L, while those in control group were 221.45 ± 6.84 and 114.68 ± 2.53 ng/L, respectively. The study group serum concentrations of IL-8 at pre- and post-treatment were 120.75 ± 4.53 ng/L and 45.39 ± 8.26 ng/L, while the control group values were 122.38 ± 2.65 and 79.52 ± 2.34 ng/L, respectively. After treatment, the serum levels of TNF-α and IL-8 were significantly down-regulated in both groups, relative to pre-treatment values, with lower levels in the study group (p < 0.001). Wound healing time and frequency of dressing change in the study group were 20.6 ± 3.6 days and 7.1 ± 2.5 times, respectively, which were significantly lower than the corresponding control group values of 40.3 ± 10.7 days and 20.5 ± 5.6 times (p < 0.001). There was a significantly higher incidence of scars in the control group than in study group (p < 0.05).Conclusion: Combined use of platelet-rich fibrin and NB-UVB in the treatment of small area deep burn wounds lowers the serum levels of inflammatory factors. However, the combined therapy should be subjected to further clinical trials prior to application in clinical practice.

Dual Photochemistry of Benzimidazole.

Monomers of benzimidazole trapped in an argon matrix at 15 K were characterized by vibrational spectroscopy and identified as 1H-tautomers exclusively. The photochemistry of matrix-isolated 1H-benzimidazole was induced by excitations with a frequency-tunable narrowband UV light and followed spectroscopically. Hitherto unobserved photoproducts were identified as 4H- and 6H-tautomers. Simultaneously, a family of photoproducts bearing the isocyano moiety was identified. Thereby, the photochemistry of benzimidazole was hypothesized to follow two reaction pathways: the fixed-ring and the ring-opening isomerizations. The former reaction channel results in the cleavage of the NH bond and formation of a benzimidazolyl radical and an H-atom. The latter reaction channel involves the cleavage of the five-membered ring and concomitant shift of the H-atom from the CH bond of the imidazole moiety to the neighboring NH group, leading to 2-isocyanoaniline and subsequently to the isocyanoanilinyl radical. The mechanistic analysis of the observed photochemistry suggests that detached H-atoms, in both cases, recombine with the benzimidazolyl or isocyanoanilinyl radicals, predominantly at the positions with the largest spin density (revealed using the natural bond analysis computations). The photochemistry of benzimidazole therefore occupies an intermediate position between the earlier studied prototype cases of indole and benzoxazole, which exhibit exclusively the fixed-ring and the ring-opening photochemistries, respectively.

Hydrothermal zinc oxide nanostructures: geometry control and narrow band UV emission

In this work we study zinc oxide nanostructures of various geometries synthesized via the hydrothermal technique on Si (111) substrate. We demonstrate capabilities of the growth protocol for control over the morphology of nanostructures varying from nanowires to hexapods. The obtained samples were studied by photoluminescence spectroscopy to demonstrate a very narrow spontaneous emission near 370 nm. Despite cheap and feasible fabrication, the obtained nanostructures possess high crystallinity confirmed by the absence of typical for ZnO wide emission band in the visible region, related with the structure imperfections. This property together with the capabilities of the geometrical control over the nanostructures unveil perspectives of the reported approach for future UV photonic applications.

Fractional carbon dioxide laser, platelet –rich plasma and narrow band ultraviolet B in the treatment of Vitiligo (A prospective randomized comparative trial)

Abstract Vitiligo is a disease that causes the loss of skin color in patches due to loss of melanin pigmentation of specific areas of the skin. Although several hypotheses have been proposed, the leading theory is still the auto-immune etiology linked to specific genetic mutations. Vitiligo can also be associated with several autoimmune diseases. There is no curative treatment for vitiligo but, several treatment modalities are considered. Topical therapies like steroids and Calcineurin inhibitors are of popular use in clinical settings also, steroids can be administered systemically in vitiligo patients. Physical therapies as fractionated CO2 (Fr: CO2) laser and Narrowband-UV (NBUV) phototherapy represent a gold standard in treatment in clinical practice. Moreover, intralesional therapies are emerging, one of which is autologous platelet-rich plasma injection. Aim of the study This study aimed to evaluate and compare the efficacy and safety of Fr: CO2 laser, PRP, combined Fr: CO2 laser and PRP, combined Fr: CO2 laser and NB-UVB, combined Fr: CO2 laser, PRP and NB-UVB in the treatment of vitiligo as well as reporting the side effects. Patients and methods This study included 20 vitiligo patients with at least 6 patches of stable vitiligo (120 patches), the patches were divided into six groups according to the treatment modality. Assessment of treatment response was done through patient satisfaction score and Vitiligo analysis by computer-assisted grid (VACAG). Results Regarding surface area reduction in included patients, fractional CO2 laser achieved the best results followed by triple combination therapy (CO2 with PRP and NB-UVB), the least response was with CO2 with PRP treatment. Patient satisfaction in the current study had a different outcome, PRP treated patients exhibited the highest satisfaction scores while triple combination treated group showed the least satisfaction scores.

High‐Performance Ultraviolet Organic Light‐Emitting Diode Enabled by High‐Lying Reverse Intersystem Crossing

AbstractUltraviolet (UV) organic emitters that can open up applications for future organic light‐emitting diodes (OLEDs) are of great value but rarely developed. Here, we report a high‐quality UV emitter with hybridized local and charge‐transfer (HLCT) excited state and its application in UV OLEDs. The UV emitter, 2BuCz‐CNCz, shows the features of low‐lying locally excited (LE) emissive state and high‐lying reverse intersystem crossing (hRISC) process, which helps to balance the color purity and exciton utilization of UV OLED. Consequently, the OLED based on 2BuCz‐CNCz exhibits not only a desired narrowband UV electroluminescent (EL) at 396 nm with satisfactory color purity (CIEx, y=0.161, 0.031), but also a record‐high maximum external quantum efficiency (EQE) of 10.79 % with small efficiency roll‐off. The state‐of‐the‐art device performance can inspire the design of UV emitters, and pave a way for the further development of high‐performance UV OLEDs.

Accurate surface ultraviolet radiation forecasting for clinical applications with deep neural network

Exposure to appropriate doses of UV radiation provides enormously health and medical treatment benefits including psoriasis. Typical hospital-based phototherapy cabinets contain a bunch of artificial lamps, either broad-band (main emission spectrum 280–360 nm, maximum 320 nm), or narrow-band UV B irradiation (main emission spectrum 310–315 nm, maximum 311 nm). For patients who cannot access phototherapy centers, sunbathing, or heliotherapy, can be a safe and effective treatment alternative. However, as sunlight contains the full range of UV radiation (290–400 nm), careful sunbathing supervised by photodermatologist based on accurate UV radiation forecast is vital to minimize potential adverse effects. Here, using 10-year UV radiation data collected at Nakhon Pathom, Thailand, we developed a deep learning model for UV radiation prediction which achieves around 10% error for 24-h forecast and 13–16% error for 7-day up to 4-week forecast. Our approach can be extended to UV data from different geographical regions as well as various biological action spectra. This will become one of the key tools for developing national heliotherapy protocol in Thailand. Our model has been made available at https://github.com/cmb-chula/SurfUVNet.

Visible-blind ultraviolet narrowband photomultiplication-type organic photodetector with an ultrahigh external quantum efficiency of over 1 000 000.

A visible-blind ultraviolet (UV) photodetector can detect UV signals and is not interfered with by visible light or infrared light in the environment. In order to realize high-performance visible-blind UV organic photodetectors (OPDs), we design photomultiplication-type (PM-type) OPDs by using a novel strategy. Firstly, wide bandgap organic semiconductor materials, which do not absorb visible light, are selected as donors to absorb UV light. Secondly, a very small amount of C60 is used as an acceptor to trap photogenerated electrons. These accumulating electrons near the Al electrode form a potential, which leads to band bending and narrowing of the interface barrier, thereby assisting hole-tunneling injection to form a multiplication. The fabricated visible-blind UV PM-type OPDs with donor/acceptor doping ratio of 50 : 1 exhibit a narrowband response with full-width at half-maximum (FWHM) of approximately 36 nm, an ultrahigh external quantum efficiency of 1.08 × 106% and a remarkable specific detectivity of 1.28 × 1014 jones at 335 nm wavelength under -14 V bias. The UV-to-visible rejection ratio exceeds 103 by adjusting the donor/acceptor mixing ratios. The devices made with other wide bandgap organic materials also showed similar performance, indicating that this device structure provides an effective method for the preparation of high-performance visible-blind UV PM-type OPDs. In addition, we prepared a flexible visible-blind UV PM-type OPD based on a PET substrate and integrated it with a flexible OLED to fabricate a wearable UV monitor, which can visually detect the intensity of UV light.

Conformational Analysis, Spectroscopy and Photochemistry of Matrix-Isolated 1H- and 2H- Tautomeric Forms of Ethyl Tetrazole-5- Carboxylate

The preferred conformations, infrared spectra and photochemistry of matrix-isolated 1H- and 2H- tautomers of ethyl tetrazole-5-carboxylate (ET5C) were investigated. Experimentally, isolated monomeric forms of the two tautomers were trapped in cryogenic argon matrices (15 K), and studied by infrared spectroscopy. Identification of the conformational species trapped in the matrices was undertaken by combining the experimental spectroscopic data with results of quantum chemical calculations performed at the DFT(B3LYP)/6-311++G(d,p) level of theory. For each tautomer, two conformers were observed in the matrices, all forms exhibiting the ester group in the anti configuration (C–O–C–C dihedral equal to 180º). In turn, the conformers having a gauche ester group that are predicted by the calculations to be significantly populated in the gas phase equilibrium (room temperature), were found to convert into the anti forms during matrix deposition (conformational cooling). Very interestingly, and contrarily to what is in general found for tetrazoles, the 1H- tautomer is the most stable tautomer of ET5C, and strongly predominates in the studied matrices. Narrowband UV irradiation (λ = 250 nm) was found to lead to tetrazole fragmentation, with release of molecular nitrogen and production of four isomeric photoproducts (diazirine, cyanamide, carbodiimide and nitrile imine), all of them being successfully identified through comparison of the experimental spectroscopic spectra of the irradiated matrices with the DFT(B3LYP)/6-311++G(d,p) predicted infrared spectra of these species. This study also stresses the structural relevance of the N–H//O = C intramolecular interaction between the ring hydrogen atom and the carbonyl group of the substituent in the 1H-tautomer of ET5C.

Trivalent gadolinium doped SrZrO3 perovskite ceramic: Sol-gel synthesis, paramagnetic centres, and luminescence studies

Trivalent gadolinium (Gd3+) doped SrZrO3 perovskite ceramic has been prepared and their X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), and photoluminescence (PL) spectra are recorded. The existence of divalent and tetravalent cations in SrZrO3 along with a trivalent dopant ion provides an opportunity to study the effect of charge compensators on the system properties. The cubic phase is evident from XRD diffraction patterns of the product. The SEM analysis suggests the formation of voids and pores in the ceramics caused by gases those liberated during the process of sintering. The EPR technique has been used to investigate the un-doped and Gd3+-doped SrZrO3 ceramics. The un-doped SrZrO3 shows an axially symmetric EPR line with g∥ = 1.94 and g⊥ = 1.99, which is attributed to the Zr3+ ion. The Gd3+-doped SrZrO3 shows dominant EPR lines with effective g-values at 1.93, 2.04, and 2.35. Weak lines are observed at 2.72, 3.64, 6.08, and 15.5. At higher dopant concentrations, a broad line with geff ~2.1 is seen, together with low field lines. In the low field region of the EPR spectrum, lines appear because of immediate environment distortions. Under the excitation of 273 nm, the emission spectrum shows band 6P7/2 → 8S7/2 (313 nm). The emission at 313 nm suggests that the prepared sample can be used as a narrow band UV radiation source. Emission and EPR analysis of the sample confirm that Gd3+ is distributed in both Sr2+ and Zr4+ sites in the SrZrO3 matrix.

Highly Efficient Microcavity Organic Light-Emitting Devices with Narrow-Band Pure UV Emission.

Ultraviolet organic light-emitting devices (UVOLEDs) may combine the tunability properties of organic materials through modifying the molecular structure and the advantages such as large-area, low-cost, and facile to realize high-performance UV sources. In the state-of-the-art UVOLEDs, the external quantum efficiencies (EQE) are more than 3%, but only a few have achieved pure UV emission and could not compromise the durability and irradiance at the same time. Portable compact UV sources with a narrow band made significant achievements in biomedical science and forensic appraisal. The microcavity effect is useful for achieving the desired narrow peak emission. In this study, asymmetric structural design with a specific distributed Bragg reflector (DBR) structure was employed to achieve narrow-band pure UV emission microcavity UVOLEDs (μC UVOLEDs). These μC UVOLEDs can realize tunable wavelength from 366 to 400 nm, with a full width at half maximum (FWHM) of 9.95-15.2 nm and a maximum irradiance of 2.79-5.63 mW/cm2. Also, the durability of the μC UVOLED has been considered, which presents a lifetime of 63.2 h under an irradiance of 0.016 mW/cm2. Moreover, the ability to identify 100 RMB with an efficient μC UVOLED has also been demonstrated. This investigation not only demonstrates the encouraging potential of narrow-band pure UVOLEDs but also provides a feasible strategy for the optimal design of μC UVOLEDs by utilizing the asymmetric structure.

Inorganic vacancy-ordered perovskite Cs2SnCl6:Bi/GaN heterojunction photodiode for narrowband, visible-blind UV detection

A heterojunction photodiode was fabricated from Bi doped Cs2SnCl6 nanoparticles (Cs2SnCl6:Bi NPs) spin-coated on an epitaxially grown GaN substrate. With the back illumination configuration, the heterojunction photodiode demonstrated excellent narrow-band UV sensing capability with a full wavelength of half maximum of 18 nm and a maximum detectivity of 1.2 × 1012 jones, which is promising for biomedical applications. In addition to the excellent narrow band UV sensitivity, the device also demonstrated a large linear dynamic range of 71 decibels (dB) and a fast photoresponse speed (a rise time of 0.75 μs and a fall time of 0.91 μs). The excellent performance is attributed to excellent carrier separation efficiency at the heterojunction interface and improved carrier collection efficiency through the multi-walled carbon nanotube (MWCNT) network. All the above advantages are of great importance for commercial deployment of perovskite-based photodetectors.

Quantification of histopathological changes in patients with psoriasis before and after phototherapy.

One of the most used resources for the treatment of psoriasis is ultraviolet radiation (UV) with psoralens (PUVA) and narrow-band UV (UVB-NB 311-312nm). Although many researchers have assessed the histopathological effects of this therapy modality, none used a morphological classification system specific to psoriasis. To assess the clinical and histopathological response in the phototherapy treatment of plaque psoriasis with PUVA and UVB-NB with use of PASI and TROZAK. Histopathological changes of plaque psoriasis were quantified with help of the grading system for psoriasis-Trozak in 20 patients of both sexes, before and after 32 PUVA phototherapy sessions (10 patients-GPUVA) and UVB-NB (10 patients-GUVB-NB). The severity and extension of psoriasis was evaluated through PASI. The slides stained with hematoxylin and eosin were scanned in an Aperio CS2 scanner (Leica Biosystems) and evaluated through the software ImageScopeTM (Aperio Technologies). Statistical analysis was performed with the use of the program SPSS 22.0, with application of the Wilcoxon and Mann-Whitney tests. All patients presented improvement in psoriatic plaques with decrease in PASI after treatment (P<0.01) and significant reduction in histopathological changes in psoriasis from 15.4±1.7 to 3.7±3.2 (P<0.01) in group GPUVA and from 13.2±1.7 to 4.9±5.2 (P<0,01) in group GUVB-NB. Phototherapy, regardless of type, is an effective treatment for moderate and severe psoriasis, with possibility of being quantified clinically by PASI and histopathologically by Trozak.

Aging degradation of asphalt binder by narrow-band UV radiations with a range of dominant wavelengths

To investigate the aging degradations of dominant wavelength of UV radiation on asphalt binder, five narrow-band UV radiations with different dominant wavelengths, namely 300, 320, 340, 360 and 380 nm, were used to age asphalt. After the UV aging, the aging degradations of the UV radiations on the chemical compositions, physical properties, rheological properties and complex viscosities of asphalt binder were tested by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), physical property test, and dynamic shear rheometer (DSR) respectively. The results show that all UV radiations, with the dominant wavelengths from 300 nm to 380 nm, can cause the aging degradations on the neat asphalt, UV aging can change the chemical compositions of asphalt, as well as the macro-performance of asphalt, such as physical and rheological performance. While, the molecules of asphalt have different susceptibilities to different wavelengths of UV radiations, different dominant wavelengths of UV radiations have different aging degradations on asphalt, it is not that a UV radiation with shorter wavelength (higher photon energy) definitely produces more serious aging effect on asphalt. Making into comparison, under the same aging condition, the asphalt binder aged by the UV – 360 has the highest aging degree, followed with the asphalt binders aged by UV – 340, UV – 320, UV – 300 and UV – 380, respectively.

The role of dispersion and anharmonic corrections in conformational analysis of flexible molecules: the allyl group rotamerization of matrix isolated safrole.

Conformational changes of the monomeric safrole (5-(2-propenyl)-1,3-benzodioxole) isolated in low temperature xenon matrices were induced thermally or using narrow-band UV radiation. The rotation of the allyl group taking place in the studied matrices was followed by FTIR spectroscopy. Safrole represents a challenging example of a flexible molecule highlighting the importance of dispersion interactions and anharmonic effects in the structural, spectroscopic and energetic analysis. Structures of the safrole conformers, their energetics and infrared spectra have been calculated using various computational methods ranging from density functional theory (DFT) to coupled cluster (CC). The best theoretical results were obtained by integrating CCSD(T) energies including complete basis set extrapolation and core-valence corrections with B2PLYP-D3 equilibrium structures and hybrid B2PLYP-D3/B3LYP-D3 anharmonic computations for IR spectra and thermodynamics.

Framework for predicting the photodegradation of adhesion of silicone encapsulants

We developed a framework to predict and model the photodegradation of adhesion and cohesion of a silicone encapsulant for concentrator photovoltaic applications. Silicone encapsulant specimens were artificially weathered under narrow band UV filters to determine the effects of individual wavelengths within the UV spectrum on the photodegradation of the cohesion of encapsulant material and its adhesion with adjacent interfaces. The threshold wavelength, signifying the upper bound of the damaging action spectrum for the silicone, was identified from the results. In addition, specimens were artificially weathered with different relative humidities to understand the effects of moisture on the rate of photodegradation. The adhesion energy was measured using a fracture mechanics approach. The complementary delaminated surfaces were characterized to determine the failure pathway and chemistry changes resulting from photodegradation. A previously developed model was modified to account for the effects of damaging wavelengths in the terrestrial solar spectrum and reciprocity law failure due to varying UV intensity during weathering. With these modifications, the model showed good agreement with the behavior of the silicone encapsulant exposed in an outdoor solar concentrator simulating concentrator photovoltaics operating conditions. Similar studies can be adopted to develop models that can have high predictive accuracies based on accelerated aging studies.