Ultraviolet Emission Research Articles

Identifying Key Physical Properties of Simple Organic Drop Cast Films that give Visible to Ultraviolet Light Up‐Conversion.

We demonstrate UV‐emitting films of 2,5‐diphenyloxazole (PPO) sensitised by 3,3′‐carbonylbis(7‐diethylaminocoumarin) (CBDAC), prepared by simple drop casting with rapid solvent evaporation, giving up‐converted emission even at low excitation intensities. The mechanisms of up‐conversion and triplet quenching in these films has been studied through time‐resolved and steady‐state spectroscopy. The CBDAC sensitizer aggregates strongly even at low concentrations, with CBDAC phosphorescence being observed in all films, indicating that many triplet excitons do not transfer to the surrounding PPO annihilator. Nonetheless, at very low sensitiser concentrations (1:40000 CBDAC:PPO), up‐converted PPO UV emission is observed at room temperature which is critically dependent on the film formation conditions. Only in films cast onto substrates held at 60o C is dominant TTA‐UC observed. Comparing to similar sensitised films of TIPS‐naphthalene, which are TTA‐inactive, we deduce that π‐stacking of the PPO, prevented by the TIPS side groups in the TIPS‐naphthalene films is crucial for efficient triplet diffusion and up‐conversion.

Pure Exciton UV Emission of Colloidal ZnO Nanocrystals and Evidence of Surface Origin of Green Luminescence

A semiconductor–molecule interface acts as a quasi‐two dimensional system with fruitful physics. Up to date, how the surface or interface affects the photophysical properties of the ZnO nanocrystals (NCs) is still under debate. Here, we fabricate the ideally surface‐passivated colloidal ZnO NCs, which exhibit nearly pure exciton‐stemmed UV emission. The nitrogen atoms of amino‐moiety of the long‐chain oleylamine groups passivate the ZnO NC surfaces and cause complete vanishing of the green emission exhibited in the un‐passivated ZnO NCs and usually observed in various kinds of ZnO nanostructures. It is found that the arising and disappearance of the green emission are reversible by breaking and recovering the optimal surface passivation. The green emission of these ZnO NCs originates from the electronic transition from the conduction‐band delocalized state to surface‐localized state.

The S4G-WISE View of Global Star Formation in the Nearby Universe

In this work, we present source-tailored Wide-field Infrared Survey Explorer (WISE) mid-infrared photometry (at 3.4, 4.6, 12, and 23 μm) of 2812 galaxies in the extended Spitzer Survey of Stellar Structure in Galaxies sample, and characterize the mid-infrared colors and dust properties of this legacy nearby galaxy data set. Informed by the relative emission between W3 (12 μm) and W4 (23 μm), we rederive star formation rate (SFR) scaling relations calibrated to L TIR, which results in improved agreement between the two tracers. By inverse–variance weighting the W3 and W4-derived SFRs, we generate a combined mid-infrared SFR that is a broadly robust measure of star formation activity in dusty, star-forming galaxies in the nearby Universe. In addition, we investigate the use of a W3-derived dust density metric, Σ12 μm (L ⊙/kpc2), to estimate the SFR deficit of low mass, low dust galaxies. This is achieved by combining WISE with existing Galaxy Evolution Explorer ultraviolet (UV) photometry, which we further use to explore the relationship between dust and UV emission as a function of morphology. Finally, we use our derived SFR prescriptions to examine the location of galaxies in the log SFR–log M stellar plane, as a function of morphological type, which underscores the complexity of dust-derived properties seen in galaxies of progressively earlier type.

Facile control of giant green-emission in multifunctional ZnO quantum dots produced in a single-step process: femtosecond pulse ablation.

Controlling both UV and visible emissions in ZnO quantum dots (QDs) poses a significant challenge due to the inherent introduction of defects during the growth process. We have refined the photoluminescence (PL) emission characteristics of ZnO QDs through a single-step, reagent-free femtosecond pulsed laser ablation in liquid (fs-PLAL) technique. The ratio of the near band edge (NBE) to deep-level emission (DLE), which determines the shape of the QDs' optical emission spectrum, is precisely controlled by the ablation laser pulse parameters-namely, pulse energy and temporal duration. Having established our ability to control the optical properties, we have investigated the mechanisms and physics involved in controlling optical emission. The key highlight of the work is that ablation with a fs-pulse induces substantial defect states without altering the particle size, with the extent of the effect being dependent on the pulse energy and pulse duration. The spectroscopic techniques inducing Raman spectroscopy, excitation power dependent PL and transient PL study provided deep insight into the PL emission properties of these similarly sized QDs. The improved DLE in these laser-ablated QDs is explained by a surface-recombination-layer approximation process employing steady-state and transient PL. Moreover, we have demonstrated the applicability of green emission for pH sensing within a linear range of 7-10 and highlight the inherent antibacterial properties of these QDs.

Prospects of UV and blue laser emission from the 5D3 level in Tb3+:LiYF4

Prospects of UV and blue laser emission from the 5D3 level in Tb3+:LiYF4

On the Photoluminescence of Pr(III) Activated Ca2P2O7 Polymorphs

In this work the optical properties of two distinct, praseodymium activated, UV-C emitting pyrophosphate polymorphs are presented. The materials were obtained as single-phase samples using a facile solid state method with annealing at target phase-dependent temperatures. The activator concentration dependent luminescence quenching was investigated revealing significant differences between the [Xe]4f2→ [Xe]4f2 and the [Xe]4f15d1→ [Xe]4f2 transitions. The highest emission intensities were observed at Pr3+ concentration of 0.5 and 2.0% for the [Xe]4f2→ [Xe]4f2 line and the [Xe]4f15d1→ [Xe]4f2 band emission, respectively. Furthermore, temperature dependent fluorescence spectroscopy and VUV spectroscopy were employed to investigate the thermal quenching behaviour as well as the excitation and emission properties in the deep UV range. Fitting of the temperature dependent emission integrals showed thermal quenching temperatures exceeding 700 K. It was revealed that the samples show two types of emission that can be traced back to the inter- and intraconfigurational transition of trivalent praseodymium. Praseodymium emission bands around 235 and 265 nm correspond to the various [Xe]4f15d1 → [Xe]4f2 interconfigurational transitions. Meanwhile, narrow emission lines throughout the visible and NIR range are caused by the [Xe]4f2 → [Xe]4f2 intraconfigurational transitions of Pr3+. Qualitative and quantitative comparisons between the emission properties of the two polymorphs revealed significant differences arising from the different coordination environments. α-Ca2P2O7:Pr phosphors exhibited around 60% of the emission intensities of the β-Ca2P2O7 materials in the red spectral range while a reversed trend was observed for the UV emission caused by [Xe]4f15d1→ [Xe]4f2 transitions.

The ALPINE-ALMA [CII] Survey: Modelling ALMA and JWST lines to constrain the interstellar medium of z∼ 5 galaxies

Aims. We have devised a model for estimating the ultraviolet (UV) and optical line emission (i.e. CIII] 1909 Å, Hβ, [OIII] 5007 Å, Hα, and [NII] 6583 Å) that traces HII regions in the interstellar medium (ISM) of a subset of galaxies at z ~ 4-6 from the ALMA large programme ALPINE. The aim is to investigate the combined impact of binary stars in the stellar population and an abrupt quenching in the star formation history (SFH) on the line emission. This is crucial for understanding the ISM’s physical properties in the Universe’s earliest galaxies and identifying new star formation tracers in high-z galaxies. Methods. The model simulates HII plus PhotoDissociation Region (PDR) complexes by performing radiative transfer through 1D slabs characterised by gas density (n), ionisation parameter (U), and metallicity (Z). The model also takes into account (a) the heating from star formation, whose spectrum has been simulated with Starburst99 and Binary Population and Spectral Synthesis (BPASS) to quantify the impact of binary stars; and (b) a constant, exponentially declining, and quenched SFH. For each galaxy, we selected from our CLOUDY models the theoretical ratios between the [CII] line emission that trace PDRs and nebular lines from HII regions. These ratios were then used to derive the expected optical/UV lines from the observed [CII]. Results. We find that binary stars have a strong impact on the line emission after quenching, by keeping the UV photon flux higher for a longer time. This is relevant in maintaining the free electron temperature and ionised column density in HII regions unaltered up to 5 Myr after quenching. Furthermore, we constrained the ISM properties of our subsample, finding a low ionisation parameter of log U≈ − 3.8 ± 0.2 and high densities of log(n/cm−3)≈2.9 ± 0.6. Finally, we derive UV/optical line luminosity-star formation rate relations (log(Lline/erg s−1) = α log(SFR/M⊙ yr−1) + β) for different burstiness parameter (ks) values. We find that in the fiducial BPASS model, the relations have a negligible SFH dependence but depend strongly on the ks value, while in the SB99 case, the dominant dependence is on the SFH. We propose their potential use for characterising the burstiness of galaxies at high z.

Manipulating Oxygen Vacancies in γ-Ga2O3 Nanocrystals: Correlation between Defect Location, Charge State, and Photophysical Properties.

Recent advancements in colloidal synthesis have enabled precise control of extrinsic dopants in semiconductor nanocrystals (NCs), enriching our understanding of dopant-exciton interactions and opening new avenues for controlling NC properties. However, the manipulation of intrinsic defects in colloidal NCs remains challenging. Here, we demonstrate regulation of oxygen vacancy concentration and location in γ-Ga2O3 NCs, significantly altering their photoluminescent properties. Spectroscopic analysis and density functional theory calculations reveal that bulk oxygen vacancies are mostly neutral and lead to the formation of a deep donor band that contributes to the UV emission. Conversely, surface-proximate oxygen vacancies, influenced by the band bending effect, exhibit a tendency toward double ionization, giving rise to the characteristic donor-acceptor pair emission. This work highlights the correlation between the oxygen vacancy location and charge states, leading to diverse defective states and distinct photophysical processes. Precise defect manipulation offers new insights into structure-property relationships and the design of functional nanomaterials.

Multispectral Schwarzschild imaging system for the extreme ultraviolet emission measurement of tokamak plasma

Multispectral Schwarzschild imaging system for the extreme ultraviolet emission measurement of tokamak plasma

Preparation and the Photoelectric Properties of ZnO-SiO2 Films with a Sol-Gel Method Combined with Spin-Coating.

This study explores the fabrication of ZnO-SiO2 composite films on silicon substrates via a sol-gel method combined with spin-coating, followed by annealing at various temperatures. The research aims to enhance the UV emission and photoelectric properties of the films. XRD showed that the prepared ZnO sample has a hexagonal structure. SEM images revealed the formation of ZnO nanorods within a dense SiO2 substrate, ranging from 10 μm to 30 μm in length. Photoluminescent analysis showed that the film exhibited strong UV emission centered at 360 nm. The response time measurements indicated that the optimal photoresponse time was approximately 2.9 s. These results suggest the potential of ZnO-SiO2 films as efficient UV-emitting materials with high photoconductivity and a stably reproducible response under visible light, thereby laying the foundation for their application in advanced optoelectronic devices.

Luminescent and Scintillation Properties of LiLu(PO3)4:Pr3+Nanophosphor

Background: Recent advancements in luminescent materials have drawn significant interest due to their wide-ranging applications in radiation detection, lighting, and display technologies. Praseodymium-doped phosphates, in particular, have shown promise because of their unique luminescent and scintillation properties. Objective: This study aims to synthesize, characterize, and evaluate the luminescent and scintillation properties of praseodymium-doped polyphosphate LiLu(PO3)4, focusing on the potential applications of these materials. Methods: LiLu(PO3)4:Pr3+ microcrystals were synthesized using the flux method, while nanocrystals were produced via the coprecipitation technique. The synthesized polyphosphates were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. Results: LiLu(PO3)4:Pr3+ crystals were found to crystallize in the monoclinic C2/c space group with specific lattice parameters. The structural analysis revealed that the basic units are helical ribbons of (PO3)n formed by corner-sharing PO4 tetrahedra, with LuO8 dodecahedra and LiO4 tetrahedra forming linear chains. The incorporation of praseodymium ions resulted in the observation of both ultraviolet and visible luminescence under X-ray and laser excitations. UV emission, originating from 4f-5d → 4f2 transitions, exhibited a very fast lifetime (τ4f-5d = 3 ns), while visible emission from transitions within the Pr3+ 4f2 ground configuration showed a short decay time of approximately 100 ns. Conclusion: The scintillation properties of LiLu(PO3)4:Pr3+ demonstrated promising results, indicating their potential for various high-performance applications, including solid-state lighting, bioimaging, and radiation detection.

Multispectral Schwarzschild imaging system for the extreme ultraviolet emission measurement of tokamak plasma：erratum

Multispectral Schwarzschild imaging system for the extreme ultraviolet emission measurement of tokamak plasma：erratum

Analyzing Electron Beam-Induced Coronal Extreme Ultraviolet Emissions and Solar Radio Bursts Type III During M-Class Flares: A Preliminary Study

Abstract Solar flare events are triggered by the process of magnetic reconnection, which leads to a sudden release of stored magnetic energy and intensifies the electromagnetic emissions across the entire spectrum. In this preliminary study, we investigate the role of accelerated electron beams from acceleration site in enhancing Extreme Ultraviolet (EUV) emissions in the solar corona and generating metric solar radio bursts type III (SRBT III) during M-class flare events. By focusing on six flare events associated with SRBT III, which occurred between June 15, 2024, and June 25, 2024, we utilize data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and the Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) network to conduct our analysis. Our analysis involves examining the temporal and spatial patterns of coronal 171 Å EUV emissions and Type III radio bursts during these M-class flare events. Additionally, we conducted a visual inspection of 171 A EUV image in the active region to observe changes in the coronal loops and structural modifications throughout the flare. Our findings reveal a significant temporal correlation between the EUV and Type III radio emissions, along with noticeable structural modifications in the EUV images. These observations suggest that accelerated electron beams originating from the acceleration site play a crucial role in driving both phenomena.

NEOWISE-R Caught the Luminous SN 2023ixf in Messier 101

During routine survey imaging, the reactivated Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE-R) serendipitously caught the Type II supernova SN 2023ixf in Messier 101 on the rise, starting day 3.6 through day 10.9, and again on the decline at late times from days 211 through 213 and days 370 through 372. We have considered these mid-IR data together with observations from the ultraviolet (UV) through the near-IR, when possible. At day 3.6 we approximated the optical emission with a hot, ∼26,630 K blackbody, with a notable UV excess inferred to result from strong supernova (SN) shock interaction with circumstellar matter (CSM). In the IR, however, a clear excess is also obvious, and we fit it with a cooler, ∼1620 K blackbody with a radius of ∼2.6 × 1015 cm, consistent with dust in the progenitor’s circumstellar shell likely heated by the UV emission from the CSM interaction. On day 10.8, the light detected was consistent with SN ejecta-dominated emission. At late times we also observed a clear NEOWISE-R excess, which could arise either from newly formed dust in the inner ejecta or in the contact discontinuity between the forward and reverse shocks, or from more distant pre-existing dust grains in the SN environment. Furthermore, the large 4.6 μm excess at late times can also be explained by the emergence of the carbon monoxide 1–0 vibrational band. SN 2023ixf is the best-observed SN II in the mid-IR during the first several days after the explosion and one of the most luminous such SNe ever seen.

Open quantum systems theory of ultraweak ultraviolet photon emissions: Revisiting Gurwitsch's onion experiment as a prototype for quantum biology

A century ago it was discovered that metabolic processes in living cells emit a spectrum of very low intensity radiation. This was based on observations that radiant energy from proliferating cells can amplify the rate of cell division in other nearby cellular life. Although metabolic radiation is now thoroughly documented in research on ultraweak photon emissions (UPE), the original finding that UPE can enhance mitogenesis remains controversial. This controversy is addressed by establishing a physical basis for phenomenological observations that biological UPE can amplify mitogenesis in living cells. Enhanced mitosis is rationalized as a resonance effect based on open quantum systems theory using Fano and Feshbach's methods. This application of quantum theory to biology has important consequences for understanding health, medicine, and principles of living matter.

Spider-Webb: JWST Near Infrared Camera resolved galaxy star formation and nuclear activities in the Spiderweb protocluster at z = 2.16

ABSTRACT Near-infrared (NIR) emission is less affected by dust than ultraviolet and optical emission and is therefore useful for studying the properties of dust-obscured galaxies. Although rest-frame NIR observations of high-redshift galaxies have long been made using space telescopes, their structures were unresolved due to the lack of angular resolution. This letter reports the early results from the analysis of high-resolution Pa$\beta$ imaging of the Spiderweb protocluster at $z=2.16$ with the JWST Near Infrared Camera. We investigate radial profiles of Pa$\beta$ lines and rest-frame NIR continua from luminous H $\alpha$-emitting galaxies (HAEs) in the protocluster. Particularly, we compare those of 11 HAEs (N-HAEs) on the star-forming main sequence with those of 8 HAEs (X-HAEs) with X-ray active galactic nuclei (AGNs). Resultant composite Pa$\beta$ line images of N-HAEs indicate significant star formation in galactic discs. In contrast, X-HAEs are dominated by point source components rather than outer star formation, as inferred from our earlier work based on multiwavelength spectral energy distribution fitting. Given their higher stellar potentials suggested from their rest-frame NIR images, the different characteristics may be driven by the impact of AGN feedback.

A Ferroelastic Salt Cocrystal with Ultraviolet Emission.

The coexistence and coupling of photoluminescence and ferroelasticity in a single matter are vitally important for developing multifunctional materials and devices. However, the effective construction of ferroelastics with efficient photoluminescence, especially in the ultraviolet range, is a great challenge. In this work, a salt cocrystal, (DPA)(DPAH)PF6 (DPA = diphenylamine, DPAH = diphenylamine cation), with ultraviolet emission and ferroelasticity was reported by introducing the anion group PF6- in the parent DPA crystal. Besides, the thermally triggered order-disorder transition of PF6- groups leads to a ferroelastic phase transition at ∼340 K with the Aizu notation of 2/mF1̅. In addition, (DPA)(DPAH)PF6 displays a bright ultraviolet emission at 392 nm with a photoluminescence quantum yield of 49.4%. This work presents a strategy to achieve ultraviolet (UV)-emissive ferroelastic based on the luminescent organic crystal, which not only extends the luminescence of ferroelastic to the UV region but also paves a new way for the development of multifunctional ferroelastic materials and devices.

Study of late-time ultraviolet emission in core collapse supernovae and its implications for the peculiar transient AT2018cow

Over time, core-collapse supernova (CCSN) spectra become redder due to dust formation and cooling of the SN ejecta. An ultraviolet (UV) detection of a CCSN at late times will thus indicate an additional physical process, such as an interaction between the SN ejecta and the circumstellar material, or viewing down to the central engine of the explosion. Both of these models have been proposed to explain the peculiar transient AT2018cow, a luminous fast blue optical transient detected in the UV two to four years after the event, with only marginal fading over this time period. To identify whether the late-time UV detection of AT2018cow could indicate that it is a CCSN, we investigate whether CCSNe are detectable in the UV between two and five years after the explosion. We determine how common late-time UV emission in CCSNe is and compare those CCSNe detected in the UV to the peculiar transient AT2018cow. We used a sample of 51 nearby (z<0.065) CCSNe observed with the Hubble Space Telescope within two to five years of discovery. We measured their brightness or determined an upper limit on the emission through an artificial star experiment in cases of no detection. For two CCSNe, we detected a point source within the uncertainty region of the SN position. Both have a low chance alignment probability with bright objects within their host galaxies. Therefore, they are likely to be related to their SNe, which are both known to be interacting SNe. Comparing the absolute UV magnitude of AT2018cow at late times to the absolute UV magnitudes of the two potential SN detections, there is no evidence that a late-time UV detection of AT2018cow is atypical for interacting SNe. However, when limiting the sample to CCSNe closer than AT2018cow, we see that it is brighter than the upper limits on most CCSN non-detections. Combined with a very small late time photospheric radius of this leads us to conclude that the late-time UV detection of AT2018cow was not driven by interaction. Instead, it suggests that we are possibly viewing the inner region of the explosion that is perhaps due to the long-lived presence of an accretion disc. Such properties are naturally expected in tidal disruption models and are less straightforward (though not impossible) in SN scenarios.

Decisive role of organic fluorophore and surface defect state in the photoluminescence of carbon quantum dots

Carbon quantum dots (CQDs) hold significant promise for applications in biological imaging, sensing, and optoelectronic devices owing to their superior photostability and low toxicity. Nevertheless, the elucidation of their photoluminescence mechanism remains an open question, necessitating further comprehensive investigation. In this Letter, CQDs exhibiting ultraviolet (UV) and white fluorescence were isolated through silica gel column chromatography separation of the crude product obtained from a one-step solvothermal synthesis. CQDs with different luminescent properties exhibit the same crystal structure and similar particle size distributions. Both CQDs exhibit orthorhombic structure where C60/C70 molecules are located at lattice points, having average particle sizes of 2.71 and 2.98 nm, respectively. Consequently, the luminescent properties of the synthesized CQDs are predominantly governed by their surface structure. The results of microstructure characterization and spectroscopic analysis demonstrate that the UV emission originates from the C(=O)OH and C–O–C related luminescent moieties within organic fluorophores, and the blue emission band is attributed to defect states related to surface group C–O–C, while the green/yellow emission arises from C(=O)O related surface defect levels. These observations have gained a profound understanding of the luminescent genesis of CQDs, broadened the luminescence coverage wavelength range of CQDs, and enriched the family of CQDs materials.

A CIGALE module tailored (not only) for low-luminosity active galactic nuclei

The spectral energy distribution (SED) of low-luminosity active galactic nuclei (LLAGN) presents unique challenges as the emission from these objects is comparable to the radiation from their host galaxy and the accretion physics involved is particularly complex. This study introduces a novel CIGALE module specifically designed to address these challenges. The module combines the empirical $L_ X $--$L_ m $ relationship with physically motivated accretion models, such as advection-dominated accretion flows (ADAFs) and truncated accretion disks, providing a more accurate depiction of LLAGN central engine emission. A mock analysis of the module revealed good recovery of true parameters, with only a slight bias toward higher input values, further validating its reliability. We tested the module on a sample of 50 X-ray-detected local galaxies, including low-ionization nuclear emission-line regions (LINERs) and Seyferts, and demonstrated its capacity to accurately estimate bolometric luminosities, even in the presence of significant galaxy contamination. Notably, the previous X-ray module failed to provide AGN solutions for this sample, stressing the need for a novel approach. Comparisons with mid-luminosity AGN datasets confirm the module’s robustness and applicability up to $L_ X $ erg/s. We also expanded the X-ray-to-bolometric correction formula, making it applicable to AGN spanning ten orders of magnitude in luminosity, and revealing lower $k_ X $ values for LLAGN than typically assumed. Additionally, our analysis of the $ ox $ index, which represents the slope between UV and X-ray emissions, uncovered trends that differ from those observed in high-luminosity AGN. Unlike quasars, where $ ox $ correlates with $ Edd $, LLAGN exhibit nearly constant or weakly correlated $ ox $ values, suggesting a shift in accretion physics and photon production mechanisms in low-luminosity regimes. These results underscore the importance of a multiwavelength approach in AGN studies and reveal distinct behaviors in LLAGN compared to quasars. Our findings significantly advance our understanding of LLAGN and offer a comprehensive framework for future research to complete the AGN population census.