Ultraviolet Region Research Articles

The electronic and optical properties of Al interstitial defects in KH2PO4 crystal: First principles study

KH2PO4 (KDP) crystals are widely used as frequency multipliers in inertial confinement controlled fusion ignition devices. The electronic and optical properties of KDP crystals with Al interstitial defects based on first principles are investigated. The results show that neutral and +3 charged Al interstitial can exist stably in the crystal. The +3 charged defect produces a larger lattice distortion. Bond length varies from −18.78 % to 43.71 % in the paraelectric phase(P-KDP) and from −25.57 % to 66.09 % in the ferroelectric phase (F-KDP). At the same time, +3 charged Al interstitial may also cause HO bond to break, resulting in the generation of H interstitials, which may compensate for the H vacancies in as-grown KDP. This may make the laser damage threshold slightly increase when KDP crystal is doped with +3 charged Al ion at low concentration. The optical spectra of Al interstitial are calculated, and the results show that in the paraelectric and ferroelectric phases, the optical transition of Al ions generally produces a large lattice relaxation energy, such as the lattice relaxation energy of up to 4.00 eV in the +2 to +3 charged defect transition in the paraelectric phase. This shows that the optical transition of Al interstitial will cause serious damage to the crystal. In the paraelectric phase, the absorption peaks of optical transitions found in the ultraviolet and visible regions are consistent with experiments. The absorption peak of the +1 to +2 charged defect transition is at 260 nm, which is very close to the absorption peak at 270 nm measured by experiments. The analysis of the Huang-Rys factors and transition displacement further confirms the conclusion that the optical transition of the defect charged state will cause serious crystal damage.

Formula process and coloring mechanism of bluish‐white porcelains from the Lanxi kiln in Fujian, China

AbstractBluish‐white porcelain was a prominent type of porcelain in ancient China, renowned for its distinctive artistic style and unique characteristics. The Lanxi kiln in Jianning County, Fujian Province, has unearthed a multitude of bluish‐white porcelain products from the Southern Song dynasty that exhibit vibrant glaze color and exceptional craftsmanship. The quality of these porcelains surpasses that of contemporaneous Jingdezhen and Baishe kiln products in Jiangxi Province, representing the pinnacle of bluish‐white porcelain excavated across various regions of China during the Southern Song dynasty. In this study, samples of bluish‐white porcelain from the Lanxi kiln and Baishe kiln, dating back to the Southern Song dynasty, were selected and analyzed via energy dispersive X‐ray fluorescence, ultraviolet–visible–near infrared (UV–Vis–NIR) spectrophotometer, metallographic microscopy, and scanning electron microscopy with EDS to investigate their glaze formula process and coloring mechanism. Moreover, these findings were subsequently compared with those of Jingdezhen bluish‐white porcelain from the same period. The results demonstrate that the raw materials of porcelain stones used in the glaze of the Lanxi and Jingdezhen kiln are similar in composition yet differ significantly from that employed in the Baishe kiln. Potassium feldspar was added to the glazes of the Baishe and Lanxi kiln, potentially existing exchanges of process of the two kilns due to their geographic proximity. The firing atmosphere of bluish‐white porcelain with different glaze colors in the same kiln exhibits significant variations. In particular, the lake blue sample undergoes firing under a strong reducing atmosphere, resulting in an excess content of Fe2+ in octahedral hexagon coordination within the glaze, thereby intensifying its blue hue. The colors of various glazes are determined by both chemical color and physical color. The former is a result of the absorption of Fe3+ in the ultraviolet region and the d‐d electron orbital transition of Fe2+ in the infrared region. However, the latter is not the scattering physical color but the diffuse reflection physical color produced by bubbles and anorthite crystallization layers.

Exploring optoelectronic and thermal characteristics of Janus MoSeTe and WSeTe monolayers under mechanical strain

This paper reveals the effect of external strain on the electronic, thermal and optical properties of Janus MSeTe (M=Mo, W) using first principles. Phonon spectrum calculations confirm the dynamic stability of the system. Biaxial stretching can effectively modulate its thermal properties. Uniaxial, biaxial and shear strains modulate the band structure, structural parameters, averaged differential charge density and optical properties of the MSeTe system to different degrees. The increase of compressive and shear strains leads to a gradual decrease of the band gap and triggers a semiconductor-metal phase transition at the critical point. The intrinsic system exhibits strong light absorption in the visible and ultraviolet regions, while strain induces a redshift of the light-absorbing edge, which enhances the response to the infrared and visible wavelength bands. These findings provide a theoretical basis and application potential for the design of optoelectronic devices and thermoelectric materials.

A novel fluorescent material K3NbOF6: Mn4+ for light-emitting diode devices

A series of K3Nb1-xOF6:xMn4+ fluorescent materials were prepared by the cation exchange method. Phase structure, morphology, emission, excitation spectrum and LED packaging of fluorescent materials were tested. The fluorescent material particles are micron-sized (5 μm–20 μm) and have a micro-rod morphology. It has two absorption bands, with the blue light region (∼468 nm) being stronger than the ultraviolet region (∼370 nm). Under the excitation of 468 nm, it shows good narrowband emission in the red light region, mainly with anti-stokes v6 (∼627 nm), which is caused by the double barrier of the 2Eg→4A2g transition broken by the coupling effect of electron and phonon. The optimum doping concentration was 9.1 %, and as the concentration increased again, the dipole–dipole interaction between Mn4+ resulted in concentration quenching. When the fluorescent material operates at high temperature (150 ℃), the emission intensity drops to 50.2 % of which at room temperature. At high temperature, the electrons absorb a large amount of heat energy, and the non-radiation transition to 4A2g energy level causes the thermal quenching effect. In addition, the sample also showed good water stability, after 1 h of hydrolysis, the luminescence intensity decreased to 85.6 % of the initial value. The use of LED packaging with fluorescent materials and InGaN-YAG:Ce3+ can effectively reduce the color temperature of LED from 6856 K to 3745 K, and enhance the Color index from 61.5 % to 76.8 %. Which has great potential for development in the fields of plant growth and backlight display technology.

Polyphosphazene Microparticles with High Free Radical Scavenging Activity for Skin Photoprotection.

Ultraviolet (UV) filters are the core ingredients in sunscreens and protect against UV-induced skin damage. Nevertheless, their safety and effectiveness have been questioned in terms of their poor photostability, skin penetration, and UV-induced generation of deleterious reactive oxygen species (ROS). Herein, an organic UV filter self-framed microparticle sunblock was exploited, in which quercetin (QC) and hexachlorocyclotriphosphazene (HCCP) were self-constructed into microparticles (HCCP-QC MPs) by facile precipitation polymerization without any carriers. HCCP-QC MPs could not only significantly extend the UV shielding range to the whole UV region but also remarkably reduce UV-induced ROS while avoiding direct skin contact and the resulting epidermal penetration of small-molecule QC. Meanwhile, HCCP-QC MPs possess a high QC-loading ability (697 mg g-1) by QC itself as the microparticles' building blocks. In addition, there is no leakage issue with small molecules due to its covalently cross-linked structure. In vitro and vivo experiments also demonstrated that the HCCP-QC MPs have excellent UV protection properties and effective ROS scavenging ability without toxicity. In summary, effective UV-shielding and ROS scavenging ability coupled with excellent biocompatibility and nonpenetration of small molecules make it a broad prospect in skin protection.

Bicone nanoflower evolution and multi-peak emission of polymer caped Cu doped ZnO.

A low-temperature polymer-assisted wet chemical method was used to synthesise Cu-doped ZnO bicone nanoflowers at three different PEG concentrations.The effects of PEG concentration on the structural, morphological and optical properties of Cu doped ZnO nanostructures were studied. X-ray diffraction studies revealed that the as-synthesized ZnO nanostructures are highly crystalline with a hexagonal wurtzite phase. The scanning electron microscopy (SEM) analysis showed that the prepared nanostructures have bicone-nanoflower morphology and PEG concentration has strongly influenced the size as well the shape of nanoflowers. The surface passivation effect of PEG on the band gap energies was studied by analysing UV -visible spectra of all the samples. The room-temperature fluorescent spectra of all the nanoflowers showed multiple peak emissions, both in the ultra-violet and visible regions, with varying intensities.These recasted multiple peaks are attributed to the morphological modification caused by the PEG addition.&#xD.

Expanding Color Control of Anodically Coloring Electrochromes Based on Electron-Rich 1,4-Dihydropyrrolo[3,2-b]pyrroles.

Anodically coloring electrochromes have received attention in recent years as high-contrast alternatives to cathodically coloring electrochromes due to their superior optical contrast during electrochemical switching. While current systems represent significant progress for organic electrochromics, it is necessary to expand the structural diversity of these materials while simultaneously reducing the hazards associated with synthetic protocols. With these considerations in mind, a family of 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) chromophores with varying functionalities along the 2,5-axis was envisioned to accomplish these goals. After predicting different absorbance traits as oxidized molecules with time-dependent density functional theory, DHPP chromophores with varying peripheral functionalities were synthesized in a single aerobic synthetic step via an iron-catalyzed multicomponent reaction and characterized as high-contrast chromophores. In solution, the DHPP chromophores absorb in the ultraviolet region of the electromagnetic spectrum, resulting in color-neutral L*a*b* color coordinates of ∼100, 0, 0. Upon chemical oxidation, each molecule transitions to absorb at various points across the visible spectrum based on the extent of electron-donating ability and can display five distinct colors. Importantly, the chromophores are redox-active and display switching capabilities with an applied electrochemical potential. In conjunction with building fundamental insights into molecular design of DHPP chromophores, the results and synthetic simplicity of DHPPs make them compelling materials for color-controlled high-contrast electrochromes.

Polarization independent highly insensitive ultra-wideband absorber for infrared, visible light and ultraviolet region

This work proposes a nickel-dielectric-nickel-based superwideband absorber for the infrared, visible, and ultraviolet spectrums. A square ring is loaded with a corner-truncated square patch to form the resonating structure. The absorber measures 25 × 25 × 10.6 nm3 in total. Absorption (A) is above 90 % throughout a frequency spectrum of 136.3564–5407.291 THz (55.48–2200.12 nm), with an average absorption of 96.49 %. Absorption is ≥95 % within the frequency range of 713.12–4684.15 THz (64.04–420.68 nm). The absorber has A ≥ 80 % for incident angle (θ) ≤ 50°. In the operational band, absorption averages 92.39 % at θ = 50° and 86.65 % at θ = 60°. This absorber has volume reduction upto 99.99 % (in terms of λL3, λL is wavelength at cutoff frequency for A ≥ 90 %), A ≥ 90 % ultrawide bandwidth of ∼190 % (for A ≥ 90 %), average A = 96.49 %, polarization insensitiveness, stable A ≥ 80 % for θ ≤ 50°, almost stable absorption performance for ±0.2 nm dimensions variations due to fabrication tolerances.

A theoretical study on deep ultraviolet supercontinuum generation in subwavelength optical fiber

In order to obtain supercontinuum (SC) spectra in the deep ultraviolet (UV) region, a generation method of UV SC is proposed based on subwavelength fiber (SWF) composed of background material MgF2. The nonlinear Schrödinger equation is solved by the split-step Fourier method, the optical fiber transmission characteristics are analyzed by the full-vector finite element, and the evolution of the pumping light into SC is numerically simulated in detail. The results of the numerical analysis show that the SC spectra have a spectral width extending from 229.11 nm to 2366.68 nm when 350 fs input pulses of 6 kW peak power, centered about λ0 = 400 nm, are launched into a 4 cm long MgF2 SWF. Such a deep UV SC spectrum has many applications, especially in telecommunication and military fields.

Theoretical analysis of magnetic, optoelectronic, and thermoelectric properties of Cs2CuCrX6 (X = Cl and Br) double perovskites for spintronic and data storage devices

Spintronics is an emerging field that has the potential to replace conventional electronics due to their comparatively high speed, low power consumption, and infinite endurance. The phenomena of ferromagnetism with high spin polarization in double perovskites make them the desired materials for spintronics. In the present work, the structure of Cs2CuCrX6 (X = Cl and Br) and their magnetic and optoelectronic properties were studied by utilizing density functional theory (DFT). For the calculations of exchange-correlation potential, PBE-sol approximation was utilized while for the accurate measurement of electronic band structure and density of states (DOS), we employed mBJ potential. Both materials exhibit cubic structure and are thermodynamically stable as confirmed by volume optimization and negative formation energy respectively. Spin-based energy-volume optimization and values of exchange constants reveal the ferromagnetic nature of materials. It has been observed that 3-d states of Cr are responsible for ferromagnetism and have the major contribution to the net magnetic moment caused by exchange splitting. Furthermore, investigations of band structure and electronic density of states showed that both Cs2CuCrCl6 and Cs2CuCrBr6 were indirect bandgap (Eg) semiconductors with the Eg values of 1.2 eV and 0.33 eV respectively. The optical spectra of materials showed strong absorption in the ultraviolet region. Lastly, the transport and thermoelectric properties (TE) of materials were investigated in the range of temperature 300 K–800 K by using the BoltzTrap code. The transport parameter which included the electrical conductivity (σ/τ) and thermal conductivity (κe/τ) of the materials showed a decreasing trend with temperature whereas the Seebeck coefficient (S) and Power factor (P.F) showed an increasing trend for Cs2CuCrCl6 while decreases in case of Cs2CuCrBr6. Furthermore, a high figure of merit (ZT) with values of 0.75 and 0.64 was obtained for Cs2CuCrCl6 and Cs2CuCrBr6 respectively. The results of this work are encouraging and show the capabilities of the discussed materials in the fields of spintronics, thermoelectric, and optoelectronics.

Tailoring of structural and optical properties of GeOx thin films using 100 MeV Si ions

In the present work, the effects of 100 MeV Si ions on the structural and optical properties of GeOx thin films have been investigated. Thin films of Germanium oxide (GeOx) were deposited onto silicon substrates using electron beam evaporation technique. Subsequently, 100 MeV Si7+ ions were used to irradiate as-deposited films at different fluences ranging from 5 × 1012 to 2 × 1013 ions/cm2. As-deposited films are amorphous as evident from XRD and Raman results. After irradiation with a fluence of 5 × 1012 ions/cm2 the films show partial crystallization. The strong photoluminescence (PL) exhibited from as-deposited and irradiated films is in ultraviolet (UV) and blue region. The blue shift was observed in PL bands after ion beam irradiation. PL band intensity was found to vary with irradiation fluence. The possible mechanism of variation in the PL emission from GeOx thin films with Si ion irradiation has been studied.

Effect of Bi doping on the electrochemical behaviour of Mg2SiO4 nanoparticle for energy storage applications

Silicate-based compounds are promising nanomaterials due to their high specific surface area, thermal stability, chemical stability, and fast kinetics. In this study, we synthesised pure, 2% Bi-doped, and 4% Bi-doped Mg2SiO4 nanoparticles using a simple and cost-effective sol-gel method. Various techniques such as XRD, FESEM, EDAX, FTIR, Raman, UV-Vis-NIR, cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) were employed to investigate the prepared samples. XRD patterns confirmed the crystalline phases through phase matching; and the crystallite size, dislocation density, and residual strain were derived. FESEM images showed that pure and Bi-doped Mg2SiO4 have regular spherical shapes and uniform sizes with minimal agglomeration. Particle sizes determined from FESEM images were 49 nm for the pure sample, 42 nm for the 2% Bi-doped sample, and 40 nm for the 4% Bi-doped sample. FTIR and Raman spectra verified the presence of various vibrational modes characteristic of the Mg2SiO4 structure. The UV-Vis-NIR spectra indicated strong absorption in the ultraviolet region upon doping with bismuth. The impact of Bi doping on the electrochemical behaviour of Mg2SiO4 was studied using CV and GCD techniques in a three-electrode system, where the sample-coated Mg foil (active material/activated carbon/polypyrrole) served as the working electrode. GCD curves showed that the 4% Bi-doped Mg2SiO4 electrode exhibited a maximum specific capacitance of 1043 F/g, outperforming the pure and 2% Bi-doped samples. Additionally, the 4% Bi-doped electrode maintained a capacity retention of 80% over 400 cycles. These results suggest that 4% Bi-doped Mg2SiO4 nanoparticles are excellent candidates for electrode material in energy storage applications.

Remarkable improvement in photocatalytic activity of NiO nanoparticles through Ag doping: A kinetics-mechanism & recyclability

Metal oxides are recognized as exemplary materials for photocatalytic dye degradation attributed to their unique characteristics such as tunable electronic structure, prolonged stability, and cost-effectiveness. However, the wide band gap inherent to most of these materials often limits their light absorption to the ultraviolet (UV) region. Consequently, the doping of noble metal nanoparticles into the metal oxide nanostructures has been proposed to significantly improve their light-harvesting ability. This enhancement is primarily ascribed to the localized surface plasmon resonance (LSPR) effect associated with noble metal nanoparticles, which facilitates more effective utilization of light. Thus, in this study, we synthesized silver-doped nickel oxide (Ag:NiO) with varying Ag concentrations (0, 1, 2, 4, 6 wt%) to evaluate their photocatalytic performance. The X-ray diffraction (XRD) spectra revealed that NiO possesses a cubic crystalline structure, and a peak shift to a higher angle was noted for Ag doping, indicative of compressive strain. Further analyses of morphological, vibrational, and absorption properties were conducted through the acquisition of scanning electron microscopy (SEM) images, Raman spectra and UV–Vis absorption spectra, respectively. The photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB) dyes was assessed, revealing that NiO with 4.wt.% Ag doping exhibited enhanced photocatalytic activity, achieving 99% degradation of MB and 90% degradation of RhB. Notably, Ag doping significantly enhances the light absorption capabilities and modifies the electronic structure of the NiO, thereby improving its performance in photocatalytic dye degradation.

Optoelectronic properties of β-Cyclodextrin compound and doped with Na: Comparative study by experimental and DFT approaches

The chemical and physical properties of β-Cyclodextrin (β-CD) and doped with Na can be useful in drug delivery, organic solar cells and photoprotective applications. Physicochemical properties of pure β-CD and doped with Na were investigated by both density functional theory (DFT) and experimental methods. Theoretical calculations and the experimental measurements revealed that β-CD has a direct band gap of 3.44 and 4.14 eV, respectively. The optical absorption measurements indicate that band gap value decreases by Na doping to 3.09 eV. DOS spectra confirmed the stabilization of β-CD by the strong covalent bonds between C and O atoms. Obtained small effective mass of charge carriers with the high carrier mobility in β-CD show that it is a good candidate for using in the organic electronic applications. The significant isotropic behavior was observed in all optical spectra. The positive values of the real part of dielectric function confirm the dielectric nature of β-CD. Maximum dielectric polarization is observed at the ultraviolet region with the static dielectric constant of 2.03. High reflectivity at the ultraviolet region and beyond that confirm the photoprotective properties of β-CD compound against harmful solar radiations. There is a good agreement between the obtained experimental and DFT spectra. Our findings may be useful in design of new organic optoelectronic devices.

In-water lidar simulations: the ALADIN ADM-Aeolus backscattered signal at 355 nm

The Lidar Ocean Color (LiOC) Monte Carlo code has been developed to simulate the in-water propagation of the lidar beam emitted by the ALADIN ADM-Aeolus instrument in the ultraviolet (UV) spectral region (∼ 355 nm). To this end, LiOC accounts for reflection/transmission processes at the sea surface, absorption and multiple scattering in the water volume, and reflection from the sea bottom. The water volume components included in the model are pure seawater, Chlorophyll-a concentration (Chl-a), Colored Dissolved Organic Matter (CDOM), and/or a generic absorbing species. By considering the transmission/reception measurement geometry of ALADIN ADM-Aeolus, the study documents the variability of the normalized backscattered signal in different bio-optical conditions. The potential for data product retrieval based on information at 355 nm is considered by developing a demonstrative lookup table to estimate the absorption budget exceeding that explained by Chl-a. Results acknowledge the interest of space programs in exploiting UV bands for ocean color remote sensing, as, for instance, addressed by the PACE mission of NASA.

Radiative emissions from charge exchange processes in collisions of 0.7–10.0 keV He[formula omitted] with N[formula omitted] and O2 molecules

We present an experimental study of the dissociative excitation in the collision of helium ions with nitrogen and oxygen molecules for collision energy of 0.7–10.0 keV. Absolute emission cross sections are measured and reported for the most pronounced nitrogen and oxygen atomic and ionic lines in vacuum ultraviolet (80–130nm) and visible (380–670nm) spectral regions. Remarkable similarities of the processes realized in He++N2 and He++O2 collision systems are observed. We present polarization measurements for He++N2 collision system.The emission of excited dissociative products was detected using an improved high-resolution optical spectroscopy method. This method incorporates the retarding potential method and a high resolution electrostatic energy analyzer to precisely measure the energy of incident particles and the energy of dispersion. The improvement in the optical sensitivity allows us to measure the cross section on the order of 10−19 cm2 or lower.

Sputter deposition of ZnO–AlN pseudo-binary amorphous alloys with tunable band gaps in the deep ultraviolet region

ZnO–AlN pseudo-binary amorphous alloys (a-ZAON hereinafter) with tunable band gaps in the deep ultraviolet (DUV) region have been synthesized using magnetron sputtering. The miscibility gap between ZnO and AlN has been overcome using room-temperature sputtering deposition, leveraging the rapid quenching abilities of sputtered particles to fabricate metastable but single-phase alloys. X-ray diffraction patterns and optical transmittance spectra revealed that the synthesized films with chemical composition ratios of [Zn]/([Zn] + [Al]) = 0.24–0.79 likely manifested as single-phase of a-ZAON films. Despite their amorphous structures, these films presented direct band gaps of 3.4–5.8 eV and thus high optical absorption coefficients (105 cm−1). Notably, the observed values adhered to Vegard’s law for crystalline ZnO–AlN systems, implying that the a-ZAON films were solid solution alloys with atomic-level mixing. Furthermore, atomic force microscopy analyses revealed smooth film surfaces with root-mean-square roughness of 0.8–0.9 nm. Overall, the wide-ranging band gap tunability, high absorption coefficients, amorphous structures, surface smoothness, and low synthesis temperatures of a-ZAON films position them as promising materials for use in DUV optoelectronic devices and power devices fabricated using large-scale glass and flexible substrates.

A theoretical study of the photochemistry of 1,3-cyclopentadiene and its cyano derivatives bound to a water dimer: Assessing reactivity of ionized clusters and possible photoproducts

We theoretically investigate the photoionization scenarios of molecular complexes involving cyclopentadiene and cyanocyclopentadiene bound to water dimers. Using electronic structure calculations within density-functional theory (DFT) and time dependent DFT (TD-DFT), we explore the potential photochemical pathways following ionization, and determine the charge transfer excitations related to the possible subsequent reactions. Our findings suggest that the investigated photochemical pathways of the hydrated complexes take place in two well-defined ultraviolet regions: (i) 8.2–9.5 eV for the cyclic compounds and (ii) 11.2–11.4 eV for the bound water dimer. We quantify how H-bonding effects can influence the photoionization channels. Before forming possible photoproducts, we also examine the regiospecificity of OH addition to 1,3-cyclopentadiene and its cyano derivatives We analyze our results in light of photoionization studies of jet-cooled molecular complexes and possible implications in astrochemical environments.

Validation of the VUV-reflective coating for next-generation liquid xenon detectors

Coating detector materials with films highly reflective in the vacuum ultraviolet region improves sensitivity of the next-generation rare-event detectors that use liquid xenon. In this work, we investigate the MgF2-Al-MgF2 coating designed to achieve high reflectance at 175 nm, the mean wavelength of liquid xenon (LXe) scintillation. The coating was applied to an unpolished, passivated copper substrate mimicking a realistic detector component of the proposed nEXO experiment, as well as to two unpassivated substrates with “high” and “average” levels of polishing. After confirming the composition and morphology of the thin-film coating using TEM and EDS, the samples underwent reflectance measurements in LXe and gaseous nitrogen (GN2). Measurements in LXe exposed the coated samples to -100°C for several hours. No peeling of the coatings was observed after several thermal cycles. Polishing is found to strongly correlate with the measured specular reflectance (R spec). In particular, 5.8(5)% specular spike reflectance in LXe was measured for the realistic sample at 20° of incidence, while the values for similar angles of incidence on the high and average polish samples are 62.3(1.3)% and 27.4(7)%, respectively. At large angles (66°–75°), the R spec in LXe for the three samples increases to 23(5)%, 80(8)%, and 84(18)%, respectively. The R spec at around 45° was measured in both GN2 and LXe for average polish sample and shows a reasonable agreement. Importantly, the total reflectance of the samples is comparable and estimated to be 92(8)%, 85(8)%, and 83(8)% in GN2 for the realistic, average, and high polish samples, respectively. This is considered satisfactory for the next-generation LXe experiments that could benefit from using reflective films, such as nEXO and DARWIN, thus validating the design of the coating.

Asteroid reflectance spectra from Gaia DR3: Near-UV in primitive asteroids

Context. In the context of charge-coupled devices (CCDs), the ultraviolet (UV) region has mostly remained unexplored after the 1990s. Gaia DR3 offers the community a unique opportunity to explore tens of thousands of asteroids in the near-UV as a proxy of the UV absorption. This absorption has been proposed in previous works as a diagnostic of hydration, organics, and space weathering. Aims. In this work, we aim to explore the potential of the NUV as a diagnostic region for primitive asteroids using Gaia DR3. Methods. We used a corrective factor over the blue part of Gaia spectra to erase the solar analog selection effect. We identified an artificial relation between the band noise and slope and applied a signal-to-noise ratio (S/N) threshold for Gaia bands. Meeting the quality standards, we employed a Markov chain Monte Carlo (MCMC) algorithm to compute the albedo threshold, maximizing primitive asteroid inclusion. Utilizing one- and two-dimensional (1D and 2D) projections, along with dimensionality-reduction methods (such as PCA and UMAP), we identified primitive asteroid populations. Results. We uncovered: (a) the first observational evidence linking UV absorption to the 0.7 µm band, tied to hydrated iron-rich phyllosilicates; and (b) a 2D space revealing a split in C-type asteroids based on spectral features, including UV absorption. The computed average depth (3.5 ± 1.0 %) and center (0.70 ± 0.03 µm) of the 0.7 µm absorption band for primitive asteroids observed with Gaia is in agreement with the literature values. Conclusions. In this paper, we shed light on the importance of the UV absorption feature to discriminate among different mineralogies (i.e., iron-rich phyllosilicates vs. iron-poor) or to identify taxonomies that are conflated in the visible (i.e., F-types vs. B-types). We have shown that this is a promising region for diagnostic studies of the composition of primitive asteroids.