Middle Ultraviolet Research Articles

A UV-Reflective Organic-Inorganic Tandem Structure for Efficient and Durable Daytime Radiative Cooling in Harsh Climates.

Radiative cooling shows great promise in eco-friendly space cooling due to its zero-energy consumption. For subambient cooling in hot humid subtropical/tropical climates, achieving ultrahigh solar reflectance (≥96%), durable ultraviolet (UV) resistance, and surface superhydrophobicity simultaneously is critical, which, however, is challenging for most state-of-the-art scalable polymer-based coolers. Here an organic-inorganic tandem structure is reported to address this challenge, which comprises a bottom high-refractive-index polyethersulfone (PES) cooling layer with bimodal honeycomb pores, an alumina (Al2 O3 ) nanoparticle UV reflecting layer with superhydrophobicity, and a middle UV absorption layer of titanium dioxide (TiO2 ) nanoparticles, thus providing thorough protection from UV and self-cleaning capability together with outstanding cooling performance. The PES-TiO2 -Al2 O3 cooler demonstrates a record-high solar reflectance of over 0.97 and high mid-infrared emissivity of 0.92, which can maintain their optical properties intact even after equivalent 280-day UV exposure despite the UV-sensitivity of PES. This cooler achieves a subambient cooling temperature up to 3 °C at summer noontime and 5 °C at autumn noontime without solar shading or convection cover in a subtropical coastal city, Hong Kong. This tandem structure can be extended to other polymer-based designs, offering a UV-resist but reliable radiative cooling solution in hot humid climates.

Investigating homeopathic preparations with light spectroscopy

Background
 
 Several series of experiments from our research group have shown ultraviolet (UV) light transmission of homeopathic preparations to slightly but significantly differ from controls. We now investigated whether visible and near infrared spectroscopy were also useful for exploring properties of homeopathic preparations.
 
 Materials and methods
 
 Homeopathic preparations of copper sulfate (CuSO4), hypericum and sulfur (S8) were produced in 30 sequential steps of 1:100 dilutions (c-preparations). As controls, succussed potentization medium was used. Transmission of the samples from 190-1100nm was measured 4 times on 5 days with a double beam Shimadzu UV PC 1601 spectrophotometer. To correct for the daily variations of the spectrophotometer, transmission of the samples at each nm was divided by the average transmission of the controls. Median transmissions of the samples were calculated for the ranges of 190-340nm (near and middle UV), 340-640nm (visible light without red), and 640-1100nm (red and near infrared). Differences in the median transmission between potency levels from 6c to 30c were determined using Kruskal-Wallis and Jonckheere-Terpstra tests.
 
 Results
 
 Differences in transmissions of the various potency levels were more pronounced in the UV range than in the visible or red/near infrared range. The Kruskal-Wallis test revealed significant differences for homeopathic preparations of CuSO4, hypericum and S8 in the UV range (p=0.032, 0.008, 0.009, respectively) and of S8 in the visible range (p=0.026).
 
 Jonckheere's test showed a tendency towards ascending medians with ascending potency levels for CuSO4 in the UV range (p=0.080). Significant trends were revealed for hypericum in the visible range (p=0.042, descending medians) and S8 in the UV range (p=0.015, ascending medians).
 
 Conclusion
 
 UV spectroscopy seemed to be more suitable for investigating homeopathic preparations than visible or near infrared spectroscopy, since differences in transmission were more pronounced in the UV range.

Laboratory Study of the Cameron Bands, the First Negative Bands, and Fourth Positive Bands in the Middle Ultraviolet 180–280 nm by Electron Impact Upon CO

AbstractWe have analyzed medium‐resolution (full width at half maximum, FWHM = 1.2 nm), Middle UltraViolet (MUV; 180–280 nm) laboratory emission spectra of carbon monoxide (CO) excited by electron impact at 15, 20, 40, 50, and 100 eV under single‐scattering conditions at 300 K. The MUV emission spectra at 100 eV contain the Cameron Bands (CB) CO(a 3Π → X 1Σ+), the fourth positive group (4PG) CO(A 1Π → X 1Σ+), and the first negative group (1NG) CO+(B 2Σ+ → X 2Σ) from direct excitation and cascading‐induced emission of an optically thin CO gas. We have determined vibrational intensities and emission cross sections for these systems, important for modeling UV observations of the atmospheres of Mars and Venus. We have also measured the CB “glow” profile about the electron beam of the long‐lived CO (a 3Π) state and determined its average metastable lifetime of 3 ± 1 ms. Optically allowed cascading from a host of triplet states has been found to be the dominant excitation process contributing to the CB emission cross section at 15 eV, most strongly by the d 3Δ and a' 3Σ+ electronic states. We normalized the CB emission cross section at 15 eV electron impact energy by multilinear regression (MLR) analysis to the blended 15 eV MUV spectrum over the spectral range of 180–280 nm, based on the 4PG emission cross section at 15 eV that we have previously measured (Ajello et al., 2019, https://doi.org/10.1029/2018ja026308). We find the CB total emission cross section at 15 eV to be 7.7 × 10−17 cm2.

NLO response as a function of structural water presence: A comparative experimental (UV-vis) and DFT (structural, NPA, MEP) study on Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2

A comparative experimental (UV–vis) and theoretical (DFT) study on the nonlinear optical (NLO) response of the double salts Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2 is presented in the current paper. For that purpose, a detailed analysis on the electronic absorption behavior of the compounds under investigation in the range from 200 to 1100 nm is conducted. The position of the experimentally registered electronic transitions is compared with that of the corresponding theoretical ones (calculated by means of DFT at B3LYP/6–311+G(d,p) level of theory). A time-dependent variant of DFT is applied to calculate the oscillator strengths and absorption maxima. Moreover, structural parameters, net atomic charges and molecular electrostatic potential surface are accomplished at B3LYP/6–311+G(d,p) level of theory as well.Results showed that the NLO response depends strongly on the structural water presence. Hence, the ionic salt Cs2Ni(SeO4)2•4H2O is a good NLO material in the middle ultraviolet (MUV), near ultraviolet (NUV) and near infrared (NIR) regions, while MUV and NUV areas characterize Cs2Ni(SeO4)2. However, it was revealed that Cs2Ni(SeO4)2 possesses considerably better NLO properties within 200–400 nm than Cs2Ni(SeO4)2•4H2O. These findings were related to a different electron density rearrangement in the Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2, a consequence of the metal-oxygen interactions strength.

<inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3 NEMS Oscillator for Real-Time Middle Ultraviolet (MUV) Light Detection

We report on the first beta gallium oxide (\beta-Ga2O3) crystal feedback oscillator built by employing a vibrating \beta-Ga2O3 nanoresonator as the frequency reference for real-time middle ultraviolet (MUV) light detection. We fabricate suspended \beta-Ga2O3 nanodevices through synthesis of \beta-Ga2O3 nanoflakes using low-pressure chemical vapor deposition (LPCVD), and dry transfer of nanoflakes on microtrenches. Open-loop tests reveal a resonance of the \beta-Ga2O3 device at ~30 MHz. A closed-loop oscillator is then realized by using a combined optical-electrical feedback circuitry, to perform real-time resonant sensing of MUV irradiation. The oscillator exposed to cyclic MUV irradiation exhibits resonant frequency downshifts, with a measured responsivity of $\mathscr{R}$ = -3.1 Hz/pW and a minimum detectable power of \delta Pmin = 0.53 nW for MUV detection.

Insight into the structural, electronic, elastic and optical properties of the alkali hydride compounds, XH (X = Rb and Cs)

The equilibrium structural parameters, electronic and optical properties of the alkali hydrides RbH and CsH compounds in rock-salt (RS) and cesium chloride (CsCl) structures have been studied using the full-potential linearized augmented plane-wave (FP-LAPW) method. Wu and Cohen generalized gradient approximation (WC-GGA) was used for the exchange-correlation potential to compute the equilibrium structural parameters, such as the lattice constant (a0), the bulk modulus (B) and bulk modulus first order pressure derivative (B'). In addition to the WC-GGA, the modified Becke Johnson (mBJ) scheme has been also used to overcome the underestimation of the band gap energies. RbH and CsH compounds are found to be semiconductors (wide energy-band gap) using the WC-GGA method, while they are insulators using the mBJ-GGA method. Elastic constants, mechanical and thermodynamic properties were obtained by using the IRelast package. RbH and CsH compounds at ambient pressure are mechanically stable in RS and CsCl structures; they satisfy the Born mechanical stability criteria. Elastic constants (Cij), bulk modulus (B), shear modulus (S) and Debye temperatures (θD) of RbH and CsH compounds decrease as the alkali radius increases. The RS structure of these compounds at ambient conditions is mechanically stronger than CsCl structure. RbH and CsH in RS and CsCl structures are suitable as dielectric compounds. The wide direct energy band gap for these compounds make them promising compounds for optoelectronic UV device applications. Both RbH and CsH have a wide absorption region, on the other hand RbH absorption is very huge compared to the CsH absorption, RbH is an excellent absorbent material, maximum absorption regions are located in the middle ultraviolet (MUV) region and far ultraviolet (FUV) region. The absorption coefficient α (w), imaginary part of the dielectric constant ε2(w) and the extinction coefficient k(w) vary in the same way. The present calculated results are in good agreement with the experimental data, indicating the high accuracy of the performed calculations and reliability of the obtained results.

Intrinsic luminescence centers in γ- and θ-alumina nanoparticles

In this study, we investigate the photoluminescence (PL) properties of γ and θ-alumina nanoparticles synthesized by the chemical wet method followed by annealing. The obtained experimental results indicate the presence of some favorable near ultraviolet (NUV)-orange luminescent centers for usage in various luminescence applications, such as oxygen vacancies (F, , , and F2 centers), OH related defects, cation interstitial centers, and some new luminescence bands attributed to trapped-hole centers or donor–acceptor centers. The energy states of each defect are discussed in detail. The defects mentioned could alter the electronic structure by producing some energy states in the band gap that result in the optical absorption in the middle ultraviolet (MUV) region. Spectra show that photoionazation of F and F2 centers plays a crucial role in providing either free electrons for the conduction band, or the photoconversions of aggregated oxygen vacancies into each other, or mobile electrons for electrons-holes recombination process by the Shockley–Read–Hall (SRH) mechanism.

High resolution ultraviolet imaging spectrometer for latent image analysis.

In this work, we present a close-range ultraviolet imaging spectrometer with high spatial resolution, and reasonably high spectral resolution. As the transmissive optical components cause chromatic aberration in the ultraviolet (UV) spectral range, an all-reflective imaging scheme is introduced to promote the image quality. The proposed instrument consists of an oscillating mirror, a Cassegrain objective, a Michelson structure, an Offner relay, and a UV enhanced CCD. The finished spectrometer has a spatial resolution of 29.30μm on the target plane; the spectral scope covers both near and middle UV band; and can obtain approximately 100 wavelength samples over the range of 240~370nm. The control computer coordinates all the components of the instrument and enables capturing a series of images, which can be reconstructed into an interferogram datacube. The datacube can be converted into a spectrum datacube, which contains spectral information of each pixel with many wavelength samples. A spectral calibration is carried out by using a high pressure mercury discharge lamp. A test run demonstrated that this interferometric configuration can obtain high resolution spectrum datacube. The pattern recognition algorithm is introduced to analyze the datacube and distinguish the latent traces from the base materials. This design is particularly good at identifying the latent traces in the application field of forensic imaging.

Intrinsic and extrinsic absorption of chemical vapor deposition single-crystal diamond from the middle ultraviolet to the far infrared

Optical absorption is reported in high-quality single-crystal Type IIa diamonds grown by microwave-assisted chemical vapor deposition. Laser calorimetry and spectrophotometry were used at wavelengths from the ultraviolet to the infrared. There is minimal evidence of extrinsic absorption on or near the short wavelength side of the middle-ultraviolet (MUV) region (200–300 nm) or in the infrared absorption bands. At the long wavelength side of the MUV and extending into the visible, extrinsic absorption dominates, which is related to the amount of nitrogen and nitrogen-related lattice defects in diamond. In the samples studied nitrogen concentrations were between 10 and 40 ppb. At 10.6 μm, the measured absorption coefficient of a representative sample is comparable with, or less than, those of the highest quality samples previously reported. Evidence is presented showing that our measurements serve as upper bounds on the absorption coefficients and call into question previous calorimetric reports of intrinsic absorption in the visible, near infrared, and at 10.6 μm.

Picard SODISM, a Space Telescope to Study the Sun from the Middle Ultraviolet to the Near Infrared

The Solar Diameter Imager and Surface Mapper (SODISM) onboard the Picard space mission provides wide-field images of the photosphere and chromosphere of the Sun in five narrow bandpasses centered at 215.0, 393.37, 535.7, 607.1, and 782.2 nm. The Picard spacecraft was successfully launched on 15 June 2010 into a Sun-synchronous dawn–dusk orbit. The Picard space mission represents a European asset in collecting solar observations useful to improve Earth climatic models. The scientific payload consists of the SODISM imager and of two radiometers, SOlar VAriability Picard (SOVAP) and PREcision MOnitor Sensor (PREMOS), which measure the Total Solar Irradiance (TSI) and part of the Solar Spectral Irradiance (SSI).The SODISM telescope continuously monitors solar activity from the middle ultraviolet to the near infrared spectral ranges and produces solar images that feed SSI reconstruction models. Further, SODISM probes the solar interior via a helioseismic analysis of the solar disc and limb images at 535.7 nm, and via astrometric investigations at the limb. The latter allows us to deduce the spectral dependence of the solar limb profile, and the asphericity of the Sun. Furthermore, SODISM data taken during the transit of Venus allow a determination of the absolute value of the solar diameter. This paper provides a detailed description of the SODISM instrument, including thermo-optical analysis, its different modes of observation, and its first performance in space.

Self-consistent performance modeling for dual band MIS UV photodetectors based on Si/SiO2multilayer structure

In this paper, we present a self-consistent theoretical model for a metal-insulator semiconductor (MIS) dual band ultraviolet (UV) photodetector with a modified structure implying an arbitrarily defined insulating potential barrier as its active region. Utilizing our proposed model, the dark and photocurrent density-voltage (J-V) characteristics of MIS UV photodetectors with multi-quantum wells of silicon (MQWs) are calculated. We demonstrate that dark current is reduced in the suggested structure, because the electron-tunneling probability becomes unity at energies coincident with the peak detection wavelength. This is due to the resonant tunneling and decreases at energies that are significantly smaller than this optimum value. In consequence, the number of carriers contributing to the dark current, which have a broad energy distribution at high temperatures, will decrease. It is also shown that the designed structure could detect two individual UV wavelengths, simultaneously. The width of each Si quantum well has been considered at around 1.2 nm, in order to observe these two absorption peaks in the middle and near UV regions of photon spectrum (about 365 nm, 175 nm).

Middle-ultraviolet-enhanced photodetectors based on Mg0.4Zn0.6O/ZnO homojunction with a high selectivity for 300 nm around light

High-quality Mg0.4Zn0.6O film with a ZnO buffer layer was prepared on glass by the reactive magnetron cosputtering method, and the MgZnO/ZnO homojunctions were fabricated into metal–semiconductor–metal middle ultraviolet (UV) photodetectors (PDs). The MgZnO-based PD with a ZnO buffer layer showed a high selectivity for 300 nm around middle UV light and its responsivity was larger than that of the PD without a buffer layer. Its peak responsivity was 0.45 A W−1 at 300 nm under −5 V bias, which was comparable to the highest value ever reported in MgZnO-based PDs. Also, we observed that the PDs with a smaller spacing of the finger electrodes showed a larger responsivity, indicating that the PD with a small spacing shows a large internal gain. The results may provide a simple route to gain low-cost and high-performance middle UV PDs.

Quenching rate coefficients for O+(2P) derived from middle ultraviolet airglow

O+(2P) is produced in the sunlit thermosphere primarily by photoionization of atomic oxygen. Thermospheric atomic oxygen concentrations can be inferred from measurements of airglow produced near 732.0 nm by the transition of this excited state to the 2D state and at 247.0 nm by the transition to the 4S ground state. The accuracy of these concentrations depends on the accuracy of the important chemical reaction rates used in the airglow model, including quenching of O+(2P). We obtain coefficients for the quenching of O+(2P) by O and N2 by modeling rocket and satellite limb measurements of thermospheric middle ultraviolet (MUV) airglow at 247.0 nm. We derive a reaction rate for N2 of 1.8 × 10−10 cm3 s−1, which is lower than the value obtained by other airglow studies but in agreement with laboratory measurements. We obtain a best fit value for the O reaction rate of 5.0 × 10−11 cm3 s−1, with an upper limit of 8.4 × 10−11 cm3 s−1. The value of the O reaction rate determined by fits to 172 altitude profiles of the 247.0 nm emission shows a strong correlation with the magnitude of the excitation g factor. However, the airglow profile above 260 km favors the upper limit we have identified.

The middle ultraviolet‐visible spectrum of H2 excited by electron impact

The electron‐impact‐induced emission spectrum of H2 has been measured in the extended wavelength region 175–530 nm at a spectral resolution of 1.7 nm (full width at half maximum). The laboratory spectra observed in the middle ultraviolet (MUV) and visible spectral region are characterized by underlying H2 ( ) continuum emission, together with many strong lines assigned to the radiative decay of the gerade singlet states of H2, and to members of the H Balmer series resulting from dissociative excitation of H2. Our calibrated MUV spectral data, obtained at 14, 19, and 100 eV electron‐impact energies, provide absolute emission cross sections of these H2 lines and will assist in the interpretation of planned Galileo ultraviolet spectrometer observations of Jupiter's aurora in this wavelength region.

Electron Excitation Function of the N 2 Second Positive System

view Abstract Citations (36) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Electron Excitation Function of the N 2 Second Positive System Shemansky, D. E. ; Ajello, J. M. ; Kanik, I. Abstract The band strengths of the electron excited N2 (C 3Πu-B 3Πg) second positive system (2PG) have been measured in the middle ultraviolet (MUV) range (280-444 nm). The energy dependence of the (0,0) and (1,0) band cross sections is reported with analytic shape functions for use in model calculations. The excitation functions were measured at low pressure to avoid effects of collisional cascade from higher lying states. At low electron energies (11-15 eV), the resolution and energy spacing of the excitation function measurements were sufficient to reveal the importance of threshold effects from resonance processes. The absolute cross section of the 337.14 nm band has a peak value of 1.11±0.15 × 10-17 cm2 at 14.1 eV. Above 30 eV the cross section decreases with an asymptotic E-2 dependence. A spectral analysis of the 2PG band system at 14 and 20 eV has provided relative excited state vibrational level cross sections. The variation of the electronic transition moment over the wavelength range indicated above, has been derived, and an improved transition probability matrix has been obtained. The rate coefficient for solar photoelectron excitation of the (0,0) band is 9.1 × 10-10 cm-3 s-1 for photoelectrons above 11.0 eV, a factor of ∼1.3 smaller than the previous recommended value. Publication: The Astrophysical Journal Pub Date: October 1995 DOI: 10.1086/176319 Bibcode: 1995ApJ...452..472S Keywords: ATMOSPHERIC EFFECTS; EARTH; MOLECULAR DATA; ULTRAVIOLET: GENERAL full text sources ADS |

The complete UV spectrum of SO2 by electron impact, 2, The middle ultraviolet spectrum

We have measured the middle ultraviolet (MUV) electron impact induced fluorescence spectrum of SO2 from 200 to 430 nm in a crossed beam experiment. The spectrum is dominated by two features at the experimental resolution of 0.5 nm. These two features are referred to as MUV1 and MUV2. MUV1 is the SO(A3∏ → X3 ∑‐) band system extending from 240 to 265 nm produced by dissociative excitation. MUV2 is a blend of the molecular band systems in the range 264‐430 nm. In addition, the excitation function measurements of MUV2 indicate that low‐energy electrons effectively prepare SO2 in one or more electronically excited triplet states that involve the SO2 (ā(3B1)) state by direct excitation and/or cascading. A candidate triplet band system for this emission process is the electronic transition. This emission process is the largest contributor to the MUV2 emission cross section at low electron impact energy. The peak cross section for MUV1 occurs at 20 eV with a value of 25.0 ± 5.5 × 10‐19 cm2. The peak cross section for MUV2 arises at 9 eV with a value of 368 ± 81 × 10‐19 cm2. The laboratory measurements of the excitation functions of both MUV features were made from 0 to 1 keV. The emission cross sections are an important part of the total inelastic cross section of SO2 needed in modeling the Io atmosphere. The laboratory results give a plausible explanation of the Io auroral hot spots observed by Voyager 2.

A study of electron impact excitation of NO: The middle ultraviolet from 170 to 270 nm

The electron impact induced fluorescence spectrum of NO at 200 eV has been studied from 170 to 270 nm in a crossed beam experiment. By modeling the laboratory spectrum, including the effects of spin‐orbit splitting of the ground state, we determined the emission cross sections of the γ (A²Σ+ → X²Πr) and ε (D²Σ+ → X²Πr) band systems. The emission cross section of the γ bands includes a large cascade cross‐section contribution from high lying Rydberg states that predominantly populate the υ′ = 0 level of the A²Σ+ state. The ε bands are modeled by excitation rates proportional to Franck‐Condon factors for direct excitation. One feature is tentatively identified as the (1, 0) δ band and permits an estimate of the (C²Πr, υ′ = 1 → X²Πr, υ′ = 0) emission cross section. Previous low‐resolution emission studies of electron impact excitation of the γ bands have not taken into account the heavy spectral blending by the δ, υ, and β′ bands. A major result of this study indicates great care has to be used if NO is taken as a target for relative calibration in the middle ultraviolet (MUV) using the molecular branching ratio technique. The identification of all features in the MUV spectrum allows aeronomers to identify emission features that may arise from electron impact excitation and other chemical processes occurring in the upper atmospheres of the inner planets where NO is a constituent.

Stratospheric Ozone, Middle Ultraviolet Radiation, and Carbon-14 Measurements of Marine Productivity

The effects of increased ultraviolet radiation, due to decreased stratospheric ozone, on marine phytoplankton have been investigated with the use of static bottle in situ carbon-14 productivity measurements. The relative biological efficiency for photoinhibition may be used to calculate biologically effective doses and resultant amplification factors. The carbon-14 technique (short-term incubations) is inadequate for assessment of possible large amplification factor photoprocesses that may be ecologically significant.

Influence of Clouds, Haze, and Smog on the Middle Ultraviolet Reaching the Ground

We extend the multiple scattering formalism of Shettle and Green using a turbid atmosphere of uniform horizontal layers with vertical nonhomogeneities by introducing uniform cloud, haze, and smog layers. Our solution follows the rigorous equations of Chandrasekhar. The fact that it is capable of handling a cloud layer of large optical thickness with minimal subdivision of that layer permits a fast computer solution. A formalism for treating a fractional cloud layer is presented, and this allows the interesting possibility of an increase in the global flux over the clear-sky case that was not allowed by the uniform layers. The uv spectral and dose results are then compared with existing experimental data, and averaged effects are presented and parameterized.

Multiple Scattering Calculation of the Middle Ultraviolet Reaching the Ground

We use a multiple channel solution to the radiative transfer equation, a computationally fast method which achieves reasonable accuracy. The method is applied to the problem of light scattering in a turbid atmosphere in the 280-340 nm wavelength region to calculate the direct, downward diffuse and global flux reaching the ground. This spectral region is of particular interest in studies of the biological effects of possible depletion of the ozone layer by a future fleet of supersonic transport planes. We input atmospheric conditions in terms of analytic models chosen to encompass standard ozone and aerosol distributions.We examine the changes in the results with respect to the variations of the solar zenith angle, wavelength ozone thickness, aerosol thickness, ground albedo, and ground height level. The results are fairly well represented by a semiempirical analytic formula which may be used for the purposes of interpolation and communication.