Near-ultraviolet Range Research Articles

Recording Radiation in the Near-Ultraviolet Range to Determine the Initial Ignition Voltage of Surface Discharge in Air

The method of radiation recording in the near-ultraviolet range arising at the surface electric discharge. In the experiment, a double-electrode cell is used in the mode of a power supply by a single rectangular pulse of positive polarity. Using a photoelectric multiplier, a coincidence between the moment of appearance of the discharge current and moment of appearance of the radiation arising at it is specified, which is important for determination of the initial voltage of appearance of the discharge.

A novel highly efficient single-composition tunable white-light-emitting LiCa3MgV3O12:Eu3+ phosphor

In this paper, self-activated LiCa3MgV3O12 (LCMV) and Eu3+-activated LCMV phosphors were prepared by a traditional solid-state synthesis method. The LCMV host exhibited a broadband excitation spectrum in the near-ultraviolet (NUV) wavelength range of 250–400 nm and gave rise to a strong broadband bluish-green emission in the 400–700 nm visible region. Due to the energy transfer from [VO4]3− groups to Eu3+ ions, Eu3+-activated LCMV phosphors showed tunable bluish-green-to-white-to-red photoluminescence by increasing the Eu3+ concentrations under NUV excitation at 336 nm. Particularly, the LCMV:0.005Eu3+ sample emitted bright white light with high internal quantum efficiency as great as 53%. These tunable white-light-emitting LCMV:Eu3+ phosphors are promising for applications in white light-emitting diodes and optoelectronic displays.

Enhancement of signal intensity for inverse photoelectron spectroscopy by surface plasmon resonance in the near-ultraviolet range

Enhancement of signal intensity for inverse photoelectron spectroscopy by surface plasmon resonance in the near-ultraviolet range

Improved light harvest in diffraction grating-embedded TiO2 nanoparticle film

We show that a high-efficiency diffraction grating can be embedded into nanoparticulate TiO2 film via imprinting combined with TiCl4 treatment. The grating-embedded film consists of two layers in intimate contact. A thin TiO2 layer was first patterned on a glass substrate by imprinting. The patterned layer was TiCl4-treated with a higher concentration than the over-coated thicker layer, so that it diffracts incident light as a refractive-index grating. Gratings with a period scaled down to 1 µm could be embedded into the film. Diffraction efficiency increased with an increasing grating height and an efficiency over 80% was achieved in the near-ultraviolet and visible range. Dye-sensitized solar cells fabricated using a grating-embedded TiO2 photoanode exhibited much better photovoltaic performance than those without a grating. It was also found that the incorporation of a diffraction grating greatly enhances the photocatalytic activity of nanoparticulate TiO2 film. All these are attributed to improved light harvest.

Joint measurements of PM<sub>2. 5</sub> and light-absorptive PM in woodsmoke-dominated ambient and plume environments

Abstract. DC, also referred to as Delta-C, measures enhanced light absorption of particulate matter (PM) samples at the near-ultraviolet (UV) range relative to the near-infrared range, which has been proposed previously as a woodsmoke marker due to the presence of enhanced UV light-absorbing materials from wood combustion. In this paper, we further evaluated the applications and limitations of using DC as both a qualitative and semi-quantitative woodsmoke marker via joint continuous measurements of PM2. 5 (by nephelometer pDR-1500) and light-absorptive PM (by 2-wavelength and 7-wavelength Aethalometer®) in three northeastern US cities/towns including Rutland, VT; Saranac Lake, NY and Ithaca, NY. Residential wood combustion has shown to be the predominant source of wintertime primary PM2. 5 emissions in both Rutland and Saranac Lake, where we conducted ambient measurements. In Ithaca, we performed woodsmoke plume measurements. We compared the pDR-1500 against a FEM PM2. 5 sampler (BAM 1020), and identified a close agreement between the two instruments in a woodsmoke-dominated ambient environment. The analysis of seasonal and diurnal trends of DC, black carbon (BC, 880 nm) and PM2. 5 concentrations supports the use of DC as an adequate qualitative marker. The strong linear relationships between PM2. 5 and DC in both woodsmoke-dominated ambient and plume environments suggest that DC can reasonably serve as a semi-quantitative woodsmoke marker. We propose a DC-based indicator for woodsmoke emission, which has shown to exhibit a relatively strong linear relationship with heating demand. While we observed reproducible PM2. 5–DC relationships in similar woodsmoke-dominated ambient environments, those relationships differ significantly with different environments, and among individual woodsmoke sources. Our analysis also indicates the potential for PM2. 5–DC relationships to be utilized to distinguish different combustion and operating conditions of woodsmoke sources, and that DC–heating-demand relationships could be adopted to estimate woodsmoke emissions. However, future studies are needed to elucidate those relationships.

The Solar Ultraviolet Imaging Telescope On-Board Aditya-L1

The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 mission of ISRO that will measure and monitor the solar radiation emitted in the near-ultraviolet wavelength range (200-400 nm). SUIT will simultaneously map the photosphere and the chromosphere of the Sun using 11 filters sensitive to different wavelengths and covering different heights in the solar atmosphere and help us understand the processes involved in the transfer of mass and energy from one layer to the other. SUIT will also allow us to measure and monitor spatially resolved solar spectral irradiance that governs the chemistry of oxygen and ozone in the stratosphere of Earth's atmosphere. This is central to our understanding of the Sun climate relationship.

Intense supercontinuum generation in the near-ultraviolet range from a 400-nm femtosecond laser filament array in fused silica**Project supported by the National Basic Research Program of China (Grant No. 2013CB922404), the National Natural Science Foundation of China (Grant Nos. 11274053, 11474039, 11474040, and 11004240), the Science and Technology Department of Jilin Province, China (Grant No. 20170519018JH), and the Innovation Fund of

An intense supercontinuum (SC) in the near-ultraviolet range is generated from filamentation by focusing a 400-nm laser into fused silica with a microlens array (MLA). The spectrum of the SC is shown to be sensitive to the distance between the MLA and fused silica. In our optimal conditions, the near-ultraviolet SC can cover a range of 350–600 nm, where a bandwidth of approximately 55 nm above the 1μ J/nm spectral energy density and 20 nm bandwidth with tens of μJ/nm are achieved. In addition, the energy conversion efficiency of the 400 nm laser for SC generation is further analyzed. A maximum conversion efficiency of 66% is obtained when the entrance face of fused silica is set around the focus of the MLA.

Nanomanipulating and Tuning Ultraviolet ZnO-Nanowire-Induced Photonic Crystal Nanocavities

We report on the fabrication, nanomanipulation, and optical properties of ZnO-nanowire-induced nanocavities in grooved SiN photonic crystals. We show that subwavelength ZnO nanowires supporting intrinsically no Fabry–Perot mode in the violet and near-ultraviolet range can induce optical confinement when introduced in a grooved two-dimensional photonic crystal waveguide. Despite fabrication challenges arising at such short wavelengths, this hybrid approach leads to fundamental nanocavity modes with resolution-limited quality factors larger than Qexp = 2.1 × 103 at λ = 403 nm for a mode volume Vm = 5.9(λ/nrNW)3 = 3.4(λ/nrSiN)3, as deduced from three-dimensional finite-difference time-domain calculations. The investigation of optical losses in our system shows that at wavelengths shorter than λ = 390 nm Qexp is limited by self-absorption, indicating a good nanowire to cavity coupling. These results validate our hybrid approach as an efficient way to circumvent the processing issues that were so far preventin...

Asphaltenes: Absorbers and Scatterers at Near-Ultraviolet–Visible–Near-Infrared Wavelengths

This study examined the dominant mechanisms of near-ultraviolet–visible–near-infrared (NUV–vis–NIR) light attenuation in toluene solutions with asphaltene concentrations (CA) in the wide range of 0.20–1880 mg/L. The analysis of experimental results indicates that in the near-ultraviolet range (270–430 nm) the main mechanism at all CA is electronic absorption by 1–4 ring aromatic chromophores and by vanadyl porphyrins. In the visible range (430–730 nm), no distinct peaks of electronic absorption by larger aromatic chromophores were found and all light attenuation spectra followed a λ–4 dependence, consistent with the dominance of Rayleigh scattering mechanisms. In the near-infrared range (730–1100 nm), a significant mechanism of light attenuation by more dilute solutions (CA 120–130 mg/L), the most important light attenuation mechanism in the NIR range also...

Scroll-like Alloyed CdSxSe1–x Nanoplatelets: Facile Synthesis and Detailed Analysis of Tunable Optical Properties

Scroll-like colloidal quasi-two-dimensional CdSxSe1–x nanoplatelets (NPLs) with a thickness of five monolayers and average lateral dimensions of 100 nm over the whole composition range (0 ≤ x ≤ 1) were synthesized by using a mixture of chalcogenide precursors. According to X-ray diffraction and X-ray energy dispersive spectroscopy mapping in a scanning transmission electron microscope, as-synthesized NPLs are solid solutions with a uniform elemental distribution in each individual nanoplatelet. A change in composition leads to the continuous shift and gradual broadening of exciton absorption and photoluminescence (PL) lines in the visible blue and near-ultraviolet light range. Detailed analysis of optical properties, including temperature-dependent PL spectroscopy, revealed the nonmonotonic behavior of several optical parameters (average phonon temperature, electron–phonon interaction coefficient, and Stokes shift) starting from a sulfur content of ∼40% in alloyed NPLs. This behavior may be attributed to ...

Ultrafast Optical Modulation of Rationally Engineered Photonic–Plasmonic Coupling in Self-Assembled Nanocrystalline Cellulose/Silver Hybrid Material

Controlling light–matter interactions in optoplasmonic structures has recently attracted considerable attention due to their potential applications in metamaterials and metasurfaces. Here we present a bottom-up self-assembly method for large-scale organization of plasmonic silver nanorods (SNRs) into photonic liquid-crystalline cellulose nanocrystal matrices, exhibiting rationally engineered photonic–plasmonic coupling across the near-ultraviolet spectra range. In these metamaterials, we show that the resonant coupling of the photonic–plasmonic mode has a strong effect not only on the stationary optical response of guest SNRs but also on controlling light in ultrashort time scales. By using the time-resolved femtosecond pump–probe technique, we experimentally investigate the relaxation dynamics of SNRs embedded in hybrid photonic–plasmonic systems as the photonic band gap of the host matrix provides a varying local density of optical states to manipulate the radiative lifetimes of SNRs. The close correlat...

The spectral signature of cloud spatial structure in shortwave irradiance.

In this paper, we used cloud imagery from a NASA field experiment in conjunction with three-dimensional radiative transfer calculations to show that cloud spatial structure manifests itself as a spectral signature in shortwave irradiance fields – specifically in transmittance and net horizontal photon transport in the visible and near-ultraviolet wavelength range. We found a robust correlation between the magnitude of net horizontal photon transport (H) and its spectral dependence (slope), which is scale-invariant and holds for the entire pixel population of a domain. This was surprising at first given the large degree of spatial inhomogeneity. We prove that the underlying physical mechanism for this phenomenon is molecular scattering in conjunction with cloud spatial structure. On this basis, we developed a simple parameterization through a single parameter ε, which quantifies the characteristic spectral signature of spatial inhomogeneities. In the case we studied, neglecting net horizontal photon transport leads to a local transmittance bias of ±12–19 %, even at the relatively coarse spatial resolution of 20 km. Since three-dimensional effects depend on the spatial context of a given pixel in a nontrivial way, the spectral dimension of this problem may emerge as the starting point for future bias corrections.

Theoretical investigation of the electronic structure and optical properties of zinc-doped magnesium oxide

In this work, the electronic structure and optical properties of $$\hbox {Mg}_{1-x}\hbox {Zn}_{x}\hbox {O}$$Mg1-xZnxO ($$0\le x \le 0.5$$0≤x≤0.5) are investigated within the framework of the density functional theory (DFT), the GW method, and the Bethe---Salpeter equation (BSE). We find that zinc doping can lower the band gap of pure MgO via the Zn 4s states near the Fermi level and reduce the lattice symmetry, both of which will affect the optical properties. The energy of the first absorption peak decreases as the concentration of zinc increases, so are the exciton energy and binding energy of the lowest excited state. The results nicely fit to published experimental results and are compared to those of the simple hydrogen-like atom model for excitons. As the lowest excited state is closely related to light emission at that energy according to Kasha's rule, zinc doping will lower the light emission energy of pure MgO, while still exhibiting an exciton binding energy much higher than that of $${k}_{\mathrm{B}}{T}$$kBT at room temperature. This means that $$\hbox {Mg}_{1-x}\hbox {Zn}_{x}\hbox {O}$$Mg1-xZnxO materials are perfectly suited for optoelectronic devices operating in the deep blue and near-ultraviolet (UV) range.

Optical absorption and transmission in a molybdenum disulfide monolayer

Our recently proposed theoretical formulation [presented in D. Novko et al., Phys. Rev. B 93, 125413 (2016)] is used to study optical absorption and transmission in molybdenum disulfide $({\mathrm{MoS}}_{2})$ monolayer as a function of incident photon energy and angle. The investigation is not focused on exploration of well-documented spin-orbit split excitons around optical absorption onset, but rather on the most intensive features in absorption spectrum in the visible and near-ultraviolet photon energy range $(1.7--4\phantom{\rule{0.28em}{0ex}}\mathrm{eV})$. It is shown that three most intensive peaks, at 2.7, 3.1, and 3.7 eV, result from transitions between $\text{Mo}(d)$ and $\text{S}(p)$ valence and conduction bands and that the character of their charge/current density fluctuations is intrinsically in plane, located in the molybdenum plane. This also implies that ${\mathrm{MoS}}_{2}$ monolayer is completely transparent when illuminated by grazing incidence $p$-polarized light. The validity of the presented results is supported by our effective two-band tight-binding model and finally by good agreement with some recent experimental results.

VUV and X-ray free-electron lasers: The technology and its scientific promise

Currently available, fully coherent (laser) light sources emit radiation only in a limited range of wavelengths in the infrared, visible and near-ultraviolet range, excluding their use in all the measurements needing tunable photons of energy higher than a few eV. Consequentially, the strong scientific need for tunable, coherent radiation sources from the vacuum ultraviolet (VUV) to the X-ray in the femtosecond and picosecond time domain has spurred international research efforts to develop a new generation of research facilities. Laser-driven light sources that use non-linear processes to create very high harmonics and the interaction between an ultra-short laser pulse and an electron bunch in a storage ring are both able to produce radiation pulses in the femtosecond time domain and in the soft EUV and X-ray region, but with a relatively low useful photon flux on the sample. In contrast Free-Electron Lasers (FELs) can produce light pulses with peak brilliance as much as ten orders of magnitude higher than the pulses generated in present third-generation synchrotron light sources and with photon energies ranging from the VUV to the hard X-rays, i.e. from about 10eV (120nm) to 10keV (0.12nm). This manuscript reviews the scientific fields that can be opened or extended by the new techniques along with the progress of FEL physics and the supporting accelerator physics and technology.

Advanced collinear LiNbO3acousto-optical filter for astrophysical spectroscopy in the near-ultraviolet: exploring high-spectral resolution

We explore the potentiality of using an advanced collinear LiNbO3 acousto-optical filter as a dispersive element for a high-resolution optical spectrograph. Our analysis is focused on weak optical signals in the blue to near-ultraviolet range accessible to ground-based facilities. We examine the phenomenon affecting the filter transmission efficiency and its spectral resolution, namely, the light-induced absorption and photorefraction. A new nonlinear approach is used to determine the performance of this collinear LiNbO3 filter governed by acoustic waves of finite amplitude. The highest available spectral resolution attains δλ=0.15 Å at λ=370 nm (the resolving power R∼25,000), with an efficiency of 11%, or δλ=0.18 Å at λ=532 nm (R∼30,000), with an efficiency of 33%. A slight decrease in the spectral resolution would imply a significant increase in transmission efficiency. Then, we carried out proof of principle experiments with the collinear filter based on the congruent LiNbO3 crystal of 6.3-cm length at λ=405 and 440 nm to verify our analysis and estimations. Potential applications are tackling many issues in astronomy, from detailed abundance analysis in a variety of targets to precise radial velocity measurement.

HUBBLE SPACE TELESCOPENEAR-ULTRAVIOLET SPECTROSCOPY OF BRIGHT CEMP-sSTARS

We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the bright carbon-enhanced metal-poor (CEMP) stars HD196944 (V = 8.40, [Fe/H] = -2.41) and HD201626 (V = 8.16, [Fe/H] = -1.51), based on data acquired with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. Both of these stars belong to the sub-class CEMP-s, and exhibit clear over-abundances of heavy elements associated with production by the slow neutron-capture process. HD196944 has been well-studied in the optical region, but we are able to add abundance results for six species (Ge, Nb, Mo, Lu, Pt, and Au) that are only accessible in the NUV. In addition, we provide the first determination of its orbital period, P=1325 days. HD201626 has only a limited number of abundance results based on previous optical work -- here we add five new species from the NUV, including Pb. We compare these results with models of binary-system evolution and s-process element production in stars on the asymptotic giant branch, aiming to explain their origin and evolution. Our best-fitting models for HD 196944 (M1,i = 0.9Mo, M2,i = 0.86Mo, for [Fe/H]=-2.2), and HD 201626 (M1,i = 0.9Mo , M2,i = 0.76Mo , for [Fe/H]=-2.2; M1,i = 1.6Mo , M2,i = 0.59Mo, for [Fe/H]=-1.5) are consistent with the current accepted scenario for the formation of CEMP-s stars.

Principle and application of low energy inverse photoemission spectroscopy: A new method for measuring unoccupied states of organic semiconductors

Information about the unoccupied states is crucial to both fundamental and applied physics of organic semiconductors. However, there were no available experimental methods that meet the requirement of such research. In this review, we describe a new experimental method to examine the unoccupied states, called low-energy inverse photoemission spectroscopy (LEIPS). An electron having the kinetic energy lower than the damage threshold of organic molecules is introduced to a sample film, and an emitted photon in the near-ultraviolet range is detected with high resolution and sensitivity. Unlike the previous inverse photoemission spectroscopy, the sample damage is negligible and the overall resolution is a factor of two improved to 0.25eV. Using LEIPS, electron affinity of organic semiconductor can be determined with the same precision as photoemission spectroscopy for ionization energy. The instruments including an electron source and photon detectors as well as application to organic semiconductors are presented.

Luminescent properties of Ca3SiO4Cl2 co-doped with Ce(3+) and Eu(2+) for near-ultraviolet light-emitting diodes.

Ca3SiO4Cl2 co-doped with Ce(3+),Eu(2+) was prepared by high temperature reaction. The structure, luminescent properties and the energy transfer process of Ca3SiO4Cl2:Ce(3+),Eu(2+) were investigated. Eu(2+) ions can give enhanced green emission through Ce(3+) → Eu(2+) energy transfer in these phosphors. The green phosphor Ca2.9775SiO4Cl2:0.0045Ce(3+),0.018Eu(2+) showed intense green emission with broader excitation in the near-ultraviolet light range. A green light-emitting diode (LED) based on this phosphor was made, and bright green light from this green LED could be observed by the naked eye under 20 mA current excitation. Hence it is considered to be a good candidate for the green component of a three-band white LED.

Graphene/Si-quantum-dot heterojunction diodes showing high photosensitivity compatible with quantum confinement effect.

Graphene/Si quantum dot (QD) heterojunction diodes are reported for the first time. The photoresponse, very sensitive to variations in the size of the QDs as well as in the doping concentration of graphene and consistent with the quantum-confinement effect, is remarkably enhanced in the near-ultraviolet range compared to commercially available bulk-Si photodetectors. The photoresponse proves to be dominated by the carriertunneling mechanism.