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Organic semiconducting materials that are optically transparent in the near-ultraviolet (NUV) region from 300 to 400 nm are needed for advanced perovskite devices such as bifacial semitransparent a...

The exploration of narrow-emitting phosphors in the red, green, and blue spectral region is of great significance for improving the color gamut of liquid-crystal displays (LCD). In this work, a nar...

Near ultraviolet (NUV) light-emitting materials and devices are significant due to unique applications in anti-counterfeit, manufacturing industries, and hygienic treatments. However, the development of high-efficiency NUV electroluminescent devices encounters great challenges and is far behind their RGB emitter counterparts. Besides the photoluminescence quantum yields (PLQYs) of NUV materials being higher than 40%, charge injection and lopsided carrier transport also determine the device performance, leading to great efforts in optimizing the frontier molecular orbitals to fit the adjacent function layer. In the exploration of NUV materials, organic molecules are one of the primary candidates, given their preparative facility and structural variability. Recently, all-inorganic quantum-dot light-emitting diodes (QLEDs) of Cd-based, ZnSe, graphene and inorganic perovskite emitters and organic-inorganic hybrid lead halide perovskite nanocrystals (NCs) were demonstrated for achieving NUV electroluminescence. Owing to the great efforts devoted to NUV material engineering and device configuration, NUV materials and devices have achieved great advances over the last two decades. In this review, we retrospect the development of NUV materials and devices covering all promising systems, which may inspire the enthusiasm of researchers to explore the huge potential in the NUV region.

A near-ultraviolet (NUV) blue-emitting phosphor Ba9 Al2 Si6 O24 :Ce3+ (BAS:Ce3+ ) was synthesized using a high-temperature solid-state reaction. BAS:Ce3+ had an excitation band peak at about 328 nm and showed a blue emission band. The NUV-blue emission band had a peak at about 386 nm with a band width of about 60 nm, attributed to the 5d-4f transition of Ce3+ . Fluorescent decay showed an exponential model with a lifetime of 27.2 nsec. At 150°C, the luminescence intensity decreased to 68.7% compared with the intensity at room temperature.

The optical output of near-ultraviolet (NUV) light-emitting diodes (LEDs) was improved by including a monolayer of hexagonal close-packed polystyrene (PS) nanospheres. PS nanospheres with different sizes were deposited on the indium tin oxide layer of the NUV LEDs. The electroluminescence results showed that the light extraction efficiency of the NUV LEDs was increased by the inclusion of PS nanospheres, and the maximum optical output enhancement was obtained when the size of the nanospheres was close to the light wavelength. The largest enhancement of the optical output of 1.27-fold was obtained at an injection current of 100 mA. The enhanced optical output was attributed to part of the incident light beyond the critical angle being extracted when the exit surface of the NUV LEDs had a PS nanosphere monolayer. This method may serve as a low-cost and effective approach to raise the efficiency of NUV LEDs.

The purpose of the present study was to determine the age dependence of the ultraviolet (UV) absorption of the different parts of the human crystalline lens. Cryostat sections of human cadaveric lenses (60 μm) were cut. The UV absorbance of nine samples, derived from different parts of the lens, was determined using a Shimadzu scanning spectrophotometer. The absorbance of the anterior and posterior lens capsules was measured separately. The absorption coefficients were calculated from the measured absorbance and values taken at 280 as well as at 360 nm were compared statistically. ANCOVA analysis of the values taken at 280 and at 360 nm wavelengths shows that correlation between the absorption coefficients and age can be found only in the case of the posterior layers. These results suggest a differential age-dependent increase of the UV absorption of the posterior layers compared to the anterior ones and can be related to the differential protein expression in the anterior and posterior parts. Posterior crystalline lens capsules have higher absorption coefficients than the anterior ones regardless of age.

Pulsating and non-pulsating asymptotic giant branch (AGB) stars exhibit a variable near-ultraviolet (near-UV) spectrum, which suggest that mechanisms other than pulsation may affect their near-UV spectrum. In this work, we analyse the near-UV spectra of two groups of AGB stars: (1) regularly pulsating and (2) irregular, small-amplitude stars. Near-UV and blue spectra were obtained for 27 stars distributed into these two groups with the Isaac Newton Telescope (La Palma, Spain). Additional near-UV spectra were taken from the IUE library. The occurrence of Fe II lines depends mainly on the intensity of the stellar continuum: as it increases, Fe II lines are gradually hampered. Balmer emission lines are pulsation driven, as they appear only among the large-amplitude pulsating stars of our sample, between −0.10 < φ < 0.50. Among the regularly pulsating stars, the intensity of the Mg II λ2800 doublet is driven by pulsation, with its maximum between 0.20 < φ < 0.35. On the other hand, this feature is also highly variable among small-amplitude, irregularly pulsating stars. This suggests that, besides pulsation, other mechanisms may participate in the formation of this line. The spectral slope between 3000 < λ(Å), MAG acknowledges support of the grant AYA 2014-57280-P and PGC2018-102184-B-I00, co-funded by European Funds for Regions in Development (FEDER). We acknowledge the ING staff and particularly Lara Monteagudo for the acquisition in service mode of the INT observations presented in this work.

In the present work, a remarkable combination of non-thermal plasma and photocatalyst was developed to widen the operating temperature window of selective catalytic reduction(SCR) of NOx with CH4, especially to improve the low-temperature removal efficiency of NOx. It was shown that the operating temperature window was significantly widened. Among all the catalysts prepared, 1%Ag2O/TiO2 showed the highest catalytic activity for NOx removal due to the utilization of near ultraviolet light. The conversion of NOx to N2 over the in-plasma 1%Ag2O/TiO2 photocatalyst at 60 and 300 °C could achieve 31.8% and 53.0%, respectively. The combination mode of plasma and catalyst affected NOx removal efficiency greatly, the in-plasma catalysis outperformed the post-plasma catalytic mode remarkably, signifying the contribution of photocatalytic processes on the catalysts. Meanwhile, the characterizations of the catalyst demonstrated that the morphology and structure of the Ag2O/TiO2 catalyst were unchanged throughout the non-thermal plasma and photocatalytic processes, implying the superior stability of the catalyst.

The effect of low-intensity near ultraviolet irradiation and subsequent thermal annealing on the surface morphology of gold and silver granular films was investigated. It was found that exposure to light does not lead to immediate changes in the extinction spectra and the microstructure of the films. However, after annealing at a temperature of about 200°C, the difference between irradiated and non-irradiated areas becomes clearly visible both visually and in the extinction spectra of the island films. For the irradiated gold film, changes in the annealing process occur much more slowly than for the non-irradiated one. For silver films, the changes after annealing vary significantly depending on whether the film is irradiated in a vacuum or in air. From the optical extinction spectra and SEM images, it can be concluded that the conditions for the annealing-induced surface diffusion of metal atoms in the irradiated area change significantly, and these changes depend on the irradiation conditions.

The present study examined the electronic dynamics of 4,5-dimethoxy-2-nitrobenzyl acetate after π-π* excitation. Pump-probe measurement using a near-ultraviolet sub-10 fs pulse laser revealed that the lifetime of the S*(π-π*) state is 500 fs after photoexcitation to produce the S*(n-π*) state and that the lifetime of the S*(n-π*) state is 1000 fs. By studying different alpha substituents, the lifetimes of the S*(π-π*) state and the S*(n-π*) were found to be independent on the alpha substituents.

(MgO)60 and (ZnO)60 are predicted to be magic-number clusters in the shapes of cuboid (CB) and double-layer cage (DC), respectively. The composite ZnxMg60–xO60 nanoclusters that are isovalent to (MgO)60 and (ZnO)60 are studied using a basin hopping method with our newly developed combinatorial-ion-exchange (CIE) sampling technique and molecular dynamics in conjunction with density functional theory. The most stable ZnxMg60–xO60 is found to be either a CB (at low x) or a DC (at high x) nanocluster depending on the value of x with the crossover point at x = 42 or at Zn/Mg ≈ 2:1. CIE basin hopping calculations reveal that Zn prefers sites with the lowest Zn–O coordination, whereas Mg prefers sites with the highest Mg–O coordination. Aggregation of two small nanoclusters to form a large magic-number ZnO–MgO composite nanocluster is thermodynamically favorable. Born–Oppenheimer molecular dynamics simulations show that the aggregation is dependent on the structural motifs of the small (MgO)n and (ZnO)n reactant...

A series of near-ultraviolet-excitable emission-tunable phosphors K3YB6O12:Ce3+,Tb3+ have been successfully prepared via a conventional high-temperature solid-state reaction technique. Their phase structures and luminescence properties were investigated. The green emission of Tb3+ can be largely sensitized by Ce3+ in K3YB6O12 host due to efficient Ce3+ → Tb3+ energy transfer process, which leads to broad and strong excitation band in near-ultraviolet region for K3YB6O12:Ce3+,Tb3+ phosphors. The critical distance, efficiency, and mechanism of Ce3+ → Tb3+ energy transfer are also calculated and determined in term of theoretical formulas. Upon excitation with near-ultraviolet (∼365 nm), the tunable emission-color from blue to green can be realized in the as-prepared phosphors. These results indicate that the K3YB6O12:Ce3+,Tb3+ phosphors might have potential application in near-ultraviolet pumped white light-emitting diodes.

Circular dichroism (CD) spectroscopy is an important technique to investigate the structural information about chiral molecules. The intrinsically weak chirality of molecules often requires long op...

The color-tunable GdCaAl3O7: RE3+ (RE=Eu, Tb, Eu@Tb) phosphors were synthesized via an ultrafast sol-gel auto-combustion synthesis method. The XRD (X-ray diffraction) patterns confirmed the forming of GdCaAl3O7 tetragonal phase, and the SEM (Scanning electron microscopy) images indicated that the obtained products presented honeycomb-like structure due to the gas releasing during the auto-combustion process. The EDS (Energy dispersion spectra) results suggest that Eu3+ and Tb3+ were well incorporated into the host matrices of GdCaAl3O7. The luminescent properties, concentration quenching mechanism, energy transfer mechanism, luminescent dynamics, thermal stability and product practicability of GdCaAl3O7: R3+ (RE=Eu, Tb, Eu@Tb) phosphors were investigated systematically. All the GdCaAl3O7: RE3+ (RE=Eu, Tb, Eu@Tb) products presented the characteristic emission of doped RE3+. Using GdCaAl3O7: 50% Tb3+@3.0% Eu3+ as yellow-emitting phosphors in combination with commercial BAM: Eu2+ blue-emitting phosphors and a NUV chip can successfully package a warm white LED device with high color rendering index (CRI, 86.3) and low correlated color temperature (CCT, 3348 K) that was very suitable for near-ultraviolet light-triggered indoor illumination.

There is growing interest in the use of algorithms to objectively compare near-UV spectra of protein biopharmaceuticals in a regulated environment. Such use will require that the methods be validated, with International Conference on the Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q2(R1) currently being the key document. A key aspect of such validation is to understand how robust the method is to experimental variation. Noise-free simulated spectra, obtained by fitting multiple Gaussian peaks to experimental data obtained from a pharmaceutical protein, were used to assess the robustness of several algorithms in response to spectral data “imperfections”. Sources and magnitudes of these imperfections were derived from published inter-laboratory studies. Spectral noise, wavelength calibration errors, intensity variation, and spectral offset errors were “titrated” into the noise-free simulated spectrum and imperfect data sets were compared with the simulated data using a variety of published algorithms, including Pearson, Prestrelski, and derivative correlation algorithms, and spectral overlap, spectral difference and weighted spectral difference methods, to understand how robust outputs are to imperfect data. Algorithm was assessed by comparing their sensitivity to imperfect data against the pairwise statistical variation between 20 replicate spectra.

Nanoparticulate double-heterojunction photocatalysts comprising TiO2(Anatase)/WO3/TiO2(Rutile) were produced by a sol–gel method. The resulting photocatalysts exhibit clear synergistic effects when tested toward the degradation of methyl orange under both UV and visible light. Kinetic studies indicate that the degradation rate on the best double-heterojunction photocatalyst (10 wt % WO3-TiO2) depends mainly on the amount of dye concentration, contrary to pure oxides in which the degradation rate is limited by diffusion-controlled processes. The synergistic effects were confirmed through systematic and careful studies including holes and OH radical formation, X-ray diffraction, electron microscopy, elemental analysis, UV–vis diffuse reflectance spectroscopy, and surface area analysis. Our results indicate that the successful formation of a double heterojunction in the TiO2(Anatase)/WO3/TiO2(Rutile) system leads to enhanced photoactivity when compared to individual oxides and commercial TiO2 P25.

International audience; Among the geological features revealed by the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) mission on the surface of Mercury, hollows are the most surprising and least understood. Possibly related to volatile components, hollows are small depressions, surrounded by bright halos and are not observed on any other surfaces in our solar system. Previous analysis of multispectral data obtained by Mercury Dual Imaging System (MDIS) has shown that some hollows have weak spectral absorption features centered at around 600 nm. In this work, we analyzed four hollows with observations acquired by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on board MESSENGER with more than 230 spectral channels from the near‐ultraviolet to the near‐infrared. Unlike previous MDIS multispectral data, the MASCS reflectance spectra exhibit no absorption features in the MDIS wavelength range. However, we found that hollows have unique spectral properties in the near‐ultraviolet, with a spectral curvature between 300 and 600 nm that is distinctly different from other geological units. Moreover, we used MASCS observations with the best available spatial resolution (

Ricotta cheese is a potential growth medium for a wide range of microorganisms. The aim of the current study was to investigate the efficacy of ultraviolet (UV-C) and near-ultraviolet&ndash, visible light (NUV&ndash, vis) in microbial decontamination of ricotta artificially inoculated with Pseudomonas fluorescens. Cheese samples were stored at 4 &deg, C, and microbiological and sensory analyses were performed for 9 days. From the microbiological point of view, control samples became unacceptable after less than 5 days, whereas ricotta treated by both UV-C and NUV&ndash, vis light remained acceptable for more than 6 days. Similar effects of UV-C and NUV&ndash, vis light were also recorded in terms of sensory quality. The shelf life of the samples subjected to the treatments was thus extended by 50%, suggesting the potential application of UV-C and NUV&ndash, vis light for cheese decontamination.

The competition between plasmonic resonances and noble-metal interband transitions at near-ultraviolet (NUV) frequencies complicates nonlinear conversion processes at nanoscales. Here, we experimentally design a highly enhanced and reproducible plasmon-enhanced second-harmonic generation (PESHG) platform suitable for NUV frequencies by constructing three-dimensional silver mushroom arrays. The SHG emission from proposed platforms involved in geometrical asymmetry greatly outperforms that from unpatterned metallic films. Studies among mushroom arrays with various geometric parameters and weight ratios of component materials enable us to distinguish characteristics exhibited by plasmon-driven enhancement and interband-transition suppression, such that competitive effects on PESHG can be readily observed and quantitatively measured. Our work may provide insights for understanding the physical mechanism governing plasmon-enhanced nonlinear optical processes and may help attain efficient nonlinear wavelength conversions for quantum-optical and nonlinear metamaterial applications.

We investigate near-ultraviolet (NUV) variability in the Galactic globular cluster (GC) 47 Tucanae (47 Tuc). This work was undertaken within the GC sub-project of the Transient UV Objects project, a programme which aims to find and study transient and strongly variable UV sources. Globular clusters are ideal targets for transient searches because of their high stellar densities and large populations of variable systems. Using all archival observations of 47 Tuc obtained with the UV/optical telescope (UVOT) aboard the Neil Gehrels Swift observatory with the uvm2 filter, we searched for UV variability using a specialised pipeline which utilises difference image analysis. We found four clear transients, hereafter SW1-4, with positions consistent with those of known cataclysmic variables (CVs) or CV candidates identified previously using Hubble Space Telescope observations. All four sources exhibit significant outbursts. Based on the inferred outburst properties and the association with known CVs, we tentatively identify the UV transients as CV-dwarf novae (DNe). Two DNe have been previously observed in 47 Tuc: V2, which has a position consistent with that of SW4; and AKO 9, which was not in outburst during any of the UVOT observations. We thus increase the known number of DNe in 47 Tuc to 5 and the total number of detected DNe in all Galactic GCs combined from 14 to 17. We discuss our results in the context of the apparent scarcity of DNe in GCs. We suggest that the likely cause is observational biases, such as limited sensitivity due to the high background from unresolved stars in the GC and limited angular resolution of the telescopes used. We additionally detected one strongly variable source in 47 Tuc, which could be identified as the known RR Lyrae star HV 810. We found its period to have significantly increased with respect to that measured from data taken in 1988., Comment: 12 pages, 6 figures. Accepted to A&A on 15/12/2019

The thermal stability of phosphor is a crucial factor for practical white-LED application since phosphor would suffer from emission loss due to non-radiative transition with increasing operational temperature. In this work, a single-host phosphor Sr3La(AlO)3(BO3)4: Dy3+ has been synthesized via high-temperature solid-state reaction method. Interestingly, the phosphor performs prominent zero-thermal-quenching property from 298K to 573K, during which the emission intensity rises to 157% at 498K and remains 138% even at 573K in comparison that at room temperature instead of decrease. This particular phenomenon could be attributed to the energy transfer and trap mechanism arising from the high temperature. Moreover, under near ultraviolet excitation (352 nm), two main emission peaks located at 488 nm and 580 nm are observed, ascribed to transitions of Dy3+ ion from 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 respectively. Meanwhile, the effect of different Dy3+ content on the luminescence properties is investigated. Among these, 30 mol% of Dy3+ ions is found as the optimum concentration and the phosphor emits white light situated at (0.3298, 0.3786) in CIE coordinates. Based on the zero-thermal-quenching property and near ultraviolet excitation, the as-prepared Sr3La(AlO)3(BO3)4: Dy3+ phosphor can be potential candidates in white-LEDs.

Brown carbon (BrC) can affect atmospheric radiation due to its strong absorption ability from the near ultraviolet to the visible range, thereby influencing global climate. However, given the complexity of BrC's chemical composition, its optical properties are still poorly understood, especially in mountainous areas. In this study, the black carbon (BC) tracer method is used to explore the light-absorbing properties of primary and secondary BrC at Mount Hua, China during the 2018 summer period. The primary BrC absorption contributes to 10–15% of the total BrC absorption at a wavelength of 370 nm. From the positive matrix factorization analysis, traffic emissions are found to be a major source of primary BrC absorption (44%), followed by industry and biomass-burning emissions (29%). The secondary BrC accounts for 87% of the total BrC absorption at a wavelength of 370 nm, indicating that BrC is dominated by secondary formation. The observation of a higher secondary BrC absorption diurnal pattern at Mount Hua can be affected by secondary BrC in the residual layer after sunrise and the formation of light-absorbing chromophores by photochemical oxidation in the afternoon. The estimated average mass absorption efficiencies of primary and secondary BrC (MAE_pri and MAE_sec, respectively) are 0.4 m2/g and 2.1 m2/g at wavelengths of 370 nm, respectively, indicating a stronger light-absorbing ability for secondary BrC than for primary BrC. There is no significant difference in MAE_pri within a daily variation, but the daytime MAE_sec value is higher than that during the night. Our study shows that secondary BrC is important to light absorption in mountainous areas.

We have investigated Tamm plasmon structure and periodic metal-dielectric structures with active organic CBP (N,N-dicarbazolyl-4,4-biphenyl) layer. Tamm structure is based on SiO2/TiO2 5 pairs DBR, with 26 nm CBP and 50 nm silver layer on the top of it. Two periodic silver-organic structures using thermal evaporation technique with different CBP layer thickness (15 and 30 nm) was fabricated. The rate of fluorescence intensity decay of Tamm plasmon and periodic structures was experimentally measured in near ultraviolet region. We demonstrate, that decay time of CBP fluorescence intensity in Tamm plasmon structure and periodic metal-organic structures decreases several times.

In this paper, near-ultraviolet AlGaN/GaN distributed Bragg reflectors (DBRs) are designed by the optimization of refractive index contrast (△n/n) and prepared by metalorganic vapor phase epitaxy. The relationship between refractive index contrast and Bragg wavelength for Al0.2Ga0.8N/GaN DBRs are analyzed theoretically. Through the calculation, it is found that the refractive index contrast, the reflectivity and the stopband of DBRs are the function of Bragg wavelength. According to the calculation results, Al0.2Ga0.8N/GaN DBRs with Bragg wavelength ranging from 375 nm to 387 nm show a high reflectivity and a wide stopband. To confirm the results above, crack-free Al0.2Ga0.8N/GaN DBRs with different Bragg wavelength and different pairs are prepared. The relationship between the reflectivity and the Bragg wavelength for the prepared DBRs is agreed with the calculation results. Especially, a high peak reflectivity of 95% and wide stopband of about 15 nm are achieved for the 50-pair crack-free Al0.2Ga0.8N/GaN DBRs with Bragg wavelength at 385 nm. It is reasonable believe the that the AlGaN/GaN structured DBRs in this paper can be applied to improve luminous efficieny of near ultraviolet light emitting diodes.