UV Pumping Research Articles

Rapid Response Mode observations of GRB 160203A: Looking for fine-structure line variability at z = 3.52

Context. Gamma-ray bursts are the most energetic known explosions. Although they fade rapidly, they give us the opportunity to measure redshift and important properties of their host galaxies. We report the photometric and spectroscopic study of the Swift GRB 160203A at z = 3.518, and its host galaxy. Fine-structure absorption lines, detected in the afterglow at different epochs, allow us to investigate variability due to the strong fading background source. Aims. We obtained two optical to near-infrared spectra of the GRB afterglow with X-shooter on ESO/VLT, 18 minutes and 5.7 hours after the burst, allowing us to investigate temporal changes of fine-structure absorption lines. Methods. We measured H I column density log N(HI/cm–2) = 21.75 ± 0.10, and several heavy-element ions along the GRB sightline in the host galaxy, among which Si II, Al II, Al III, C II, Ni II, Si IV, C IV, Zn II and Fe II, and Fe II∗ and Si II∗ fine-structure transitions from energetic levels excited by the afterglow, at the common redshift z = 3.518. We measured [M/H]TOT = –0.78 ± 0.13 and a [Zn/Fe]FIT = 0.69 ± 0.15, representing the total (dust corrected) metallicity and dust depletion, respectively. We detected additional intervening systems along the line of sight at ɀ = 1.03, ɀ = 1.26, ɀ = 1.98, ɀ = 1.99, ɀ = 2.20, and ɀ = 2.83. We could not measure significant variability in the strength of the fine-structure lines throughout all the observations and determined an upper limit for the GRB distance from the absorber of d < 300 pc, adopting the canonical UV pumping scenario. However, we note that the quality of our data is not sufficient to conclusively rule out collisions as an alternative mechanism. Results. GRB 160203A belongs to a growing sample of GRBs with medium resolution spectroscopy, provided by the Swift/X-shooter legacy programme, which enables a detailed investigation of the interstellar medium in high-redshift GRB host galaxies. In particular, this host galaxy shows relatively high metal enrichment and dust depletion already in place when the universe was only 1.8 Gyr old.

PDRs4All

Context. Mid-infrared emission features are important probes of the properties of ionized gas and hot or warm molecular gas, which are difficult to probe at other wavelengths. The Orion Bar photodissociation region (PDR) is a bright, nearby, and frequently studied target containing large amounts of gas under these conditions. Under the “PDRs4All” Early Release Science Program for JWST, a part of the Orion Bar was observed with MIRI integral field unit (IFU) spectroscopy, and these high-sensitivity IR spectroscopic images of very high angular resolution (0.2″) provide a rich observational inventory of the mid-infrared (MIR) emission lines, while resolving the H II region, the ionization front, and multiple dissociation fronts. Aims. We list, identify, and measure the most prominent gas emission lines in the Orion Bar using the new MIRI IFU data. An initial analysis summarizes the physical conditions of the gas and demonstrates the potential of these new data and future IFU observations with JWST. Methods. The MIRI IFU mosaic spatially resolves the substructure of the PDR, its footprint cutting perpendicularly across the ionization front and three dissociation fronts. We performed an up-to-date data reduction, and extracted five spectra that represent the ionized, atomic, and molecular gas layers. We identified the observed lines through a comparison with theoretical line lists derived from atomic data and simulated PDR models. The identified species and transitions are summarized in the main table of this work, with measurements of the line intensities and central wavelengths. Results. We identified around 100 lines and report an additional 18 lines that remain unidentified. The majority consists of H I recombination lines arising from the ionized gas layer bordering the PDR. The H I line ratios are well matched by emissivity coefficients from H recombination theory, but deviate by up to 10% because of contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni. We show how the Ne III/Ne II, S IV/S III, and Ar III/Ar II ratios trace the conditions in the ionized layer bordering the PDR, while Fe III/Fe II and Ni III/Ni II exhibit a different behavior, as there are significant contributions to Fe II and Ni II from the neutral PDR gas. We observe the pure-rotational H2 lines in the vibrational ground state from 0–0 S(1) to 0–0 S (8), and in the first vibrationally excited state from 1–1 S (5) to 1–1 S(9). We derive H2 excitation diagrams, and for the three observed dissociation fronts, the rotational excitation can be approximated with one thermal (~700 K) component representative of an average gas temperature, and one nonthermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model of the Orion Bar PDR, and find that the predicted excitation matches the data qualitatively, while adjustments to the parameters of the PDR model are required to reproduce the intensity of the 0–0 S (6) to S (8) lines.

EPR and optical study of erbium-doped CeO2 and CeO2 / CeF3 nanoparticles

Here, the facile dry synthesis of composite CeO2/CeF3 nanoparticles doped with Er3+ probe ions using ammonium bifluoride (NH4HF2) is reported. This method allows synthesizing composite nanoparticles with different ratio of СеО2 and CeF3. The structural properties of the composite nanoparticles were studied using XRD, SEM, and TEM techniques, which confirmed the formation of composite CeO2/CeF3 nanoparticles. The luminescence spectra show that the intensity of the Ce3+ peak increases after fluorination procedure, revealing the fact that the amount of Ce3+ is increased. In particular, the total 4f-4f luminescence intensity of CeO2/CeF3:Er3+(0.1 at.%) nanoparticles is 3.5 time higher compared to CeO2:Er3+(0.1 at.%) ones under both UV or resonant pumping. Probably it can be associated with the increased concentration of trivalent rare-earth ions in a cubic-distorted environment. The same tendency is observed for the excitation spectra. EPR measurements showed that fluorination of CeO2 nanoparticles doped with different concentration of Er3+ ions leads to the formation of trigonal sites in ceria nanoparticles.

Neutral carbon in diffuse interstellar medium: abundance matching with H2 for damped Lyman alpha systems at high redshifts

ABSTRACT We present a study of C i/H2 relative abundance in the diffuse cold neutral medium (CNM). Using the chemical and thermal balance model, we calculate the dependence of C i/H2 on the main parameters of the medium: hydrogen number density, metallicity, strength of the UV field, and cosmic ray ionization rate (CRIR). We show that the observed relative C i and H2 column densities in damped Lyman alpha systems (DLAs) at high redshifts can be reproduced within our model assuming the typically expected conditions in the diffuse CNM. Using additional observed information on metallicity, H i column density, and excitation of C i fine-structure levels, as well as temperature, we estimated for a wide range metallicities in the CNM at high redshifts that CRIRs are in the range from ∼10−16 to a $\rm few \times 10^{-15}\, \rm s^{-1}$, hydrogen number densities are in the range ∼10−103 cm−3, and the UV field is in the range from 10−2 to a $\rm few \times 10^2$ of the Mathis field. We argue that because the observed quantities used in this work are quite homogeneous and much less affected by radiative transfer effects (in comparison with, for example, the dissociation of HD and UV pumping of H2 rotational levels), our estimates are quite robust against the assumption of the exact geometrical model of the cloud and local sources of the UV field.

Oxygen vacancies in the Spotlight: On the engineering of intrinsic defects in highly defective TiO2 photocatalysts

Nanostructured oxide semiconductors are widely used in energy conversion, catalysis, sensing and environmental applications, due to their high stability, commercial availability, efficiency and low cost. Despite its crucial importance for the design of more efficient materials, the interplay between intrinsic and extrinsic defects is yet to be clarified. For example, oxygen vacancies (VO’s) can be either beneficial or detrimental to the desired performances, depending on a variety of factors. Here, we synthesize TiO2-x samples by the addition of three different N chemical sources (NH3, triethylamine, urea). X-ray absorption spectroscopy, confocal microscopy, UV–vis absorbance and fluorescence, are employed to explore the occurrence and location of VO’s both in real and energy spaces. High–grade bulk DFT simulations complement the experimental picture. Synergy between theory and experiment, on the one hand, estimates the relative VO’s content in the different samples from local structural information. On the other hand, a sharp optical transition at ≈2.7 eV serves an unequivocal spectral signature of bulk VO’s, allowing a semi-quantitative analysis by confocal microscopy. Surface oxygen vacancies do not display fluorescence features under UV pumping, possibly due to the reaction of surface defects with atmospheric O2. Thus, the comparison between local structure and confocal microscopy can discriminate surface-localized and bulk VO’s. Concurrently, UV-induced photochromism and visible light photodegradation shed light on the most effective reactive defects. Eventually, surface-localized oxygen vacancies are predominant where actual N substitutional doping occurs, leading to materials exhibiting visible-light activity and characteristic photochromic behaviour. Implications on strategies for concomitant VO engineering and extrinsic doping are discussed.

(INVITED)Broadband emission of Lu2SrAl4SiO12:Eu2+ phosphor for full-spectrum lighting

Single-component broadband white-emitting phosphor is essential in next-generation white light-emitting diodes (WLEDs) devices for full-spectrum lighting applications. Herein, we report an ultra-broadband emitting Lu2SrAl4SiO12:Eu2+ phosphor with the full width at half maximum (FWHM) of ∼245–260 nm. Detailed analysis of the broadband emission mechanism reveals that it consists of two emission bands originating from Eu2+: one is the normal 4f65d1 →4f7(8S7/2) transition, and another is related with Eu2+-Eu3+ intervalence charge transfer (IVCT) emission with bandwidth of 210 nm. Moreover, the broad IVCT emission can be also suppressed by Be2+ doping, forming a narrow-band emission with FWHM = ∼75 nm. A warm WLED with a low correlated color temperature (CCT) of 3373 K and high CIR (Ra) of 85.7 is obtained by coating the broadband Lu2SrAl4SiO12:Eu2+ phosphor on an UV pumping LED, implying its application in full-spectrum warm white lighting.

The measurements of the CMB temperature in diffuse interstellar medium of the Milky-Way and high redshift galaxies based on excitation of CI fine-structure and H2 rotational levels

Evolution of the cosmic microwave background (CMB) temperature with redshift is predicted by the standard ΛCDM cosmological model and has been confirmed by measurements of the Sunyaev-Zel’dovich effect in Plank data (at z ≤ 1) and excitation of CO rotational levels in quasar spectra (at 1.7 ≤ z ≤ 2.7). Excitation of the fine-structure levels of neutral carbon (CI) is also sensitive to the temperature of the CMB radiation. However collisions and UV pumping lead to a significant degeneracy of the fitting parameters, since poor data on physical conditions. We found that a joint fit to excitation of low H2 rotational and CI fine-structure levels can break this degeneracy and provide a tighter constraints on the T CMB. We present estimates of the T CMB derived from excitation of CI fine-structure levels in the Milky Way clouds and high redshift absorption systems.

UV-pumped visible Tb3+-lasers.

We report on continuous-wave laser operation of Tb3+:LiLuF4 under UV pumping. More than five times higher absorption cross sections in the UV allow for shorter gain media, which are required for future high-power diode pumping. The cross-relaxation process is found to efficiently populate the upper laser level 5D4 at doping concentrations typically used in Tb3+-doped gain media. Pumping with a frequency doubled Ti:sapphire laser at 359 nm enables laser operation in the green and yellow spectral range with slope efficiencies of 41% and 20%, respectively, at optical-to-optical efficiencies a factor of two higher than under cyan-blue pumping.

Structural and excitation dependent emission properties of octahedral CeO2:Er3+ nanocrystal

Octahedral CeO2:Er3+ nanocrystals were successfully prepared using a simple hydrothermal method, and the structural and excitation dependent emission properties were investigated in detail. Green (2H11/2, 4S3/2 → 4I15/2), red (4F9/2 → 4I15/2) and NIR (4I11/2 → 4I15/2 and 4I13/2 → 4I15/2) emission were observed under 980 nm laser diode excitation. The optimal Er3+ doping concentration was 3 mol%, and the effect of Li+ co-dopants with concentration up to 10 mol% on microstructure and emission was investigated. However, for the samples excited under 352 nm down-conversion excitation, the Vis-NIR spectral distribution induced distinct changes related to the excitation mode. Remarkably high enhancement of 1532 nm NIR emission about 12 times was achieved by codoping with Li+ ions, which make CeO2:Er3+,Li+ nanocrystal a promising candidate for optical amplifier using broadband UV pumping. The possible mechanism of above up-and down-conversion emission and energy transfer process has also been discussed.

Dy^3+ doped borate glasses for laser illumination

Intense multi-peak warm yellowish-white fluorescence emissions of Dy3+ are exhibited in alkaline-earth borate glasses under the excitation of a blue laser. The net emission power and net emission photon number are identified to be 498.23μW and 14.28 × 1014cps, respectively, and the quantum yield is as high as 23.10% in 2.0wt% Dy2O3 doped alkaline-earth borate glass under the excitation of a 453nm blue laser with 14.13mW power. Anticipation of fluorescence color reveals that white luminescence can be achieved when the intensity ratio between residual laser light and Dy3+ emission reaches the appropriate range. By the introduction of Ce3+, the excitation wavelength range and the emission intensity of Dy3+ in alkaline-earth borate glasses are expanded to UVB region and improved by a maximum sensitization factor of 38.2, respectively, demonstrating the utilizability of a UV pumping laser for Ce3+−Dy3+ codoped alkaline-earth borate glasses. Efficient fluorescence emission and realizable white lighting in Dy3+ doped alkaline-earth borate glasses under the laser excitation will promote the development of laser illumination devices.

Energy transfer and enhanced near-infrared emission in Er3+ ions doped composite containing In2O3 QDs

Er3+ ions doped transparent composite containing In2O3 QDs was successfully prepared by a melt-quenching route. Intense Er3+-related near-infrared (NIR) emission around 1534nm, important for optic telecommunication systems, was observed in the obtained composite. Impressively, the Er3+-related NIR emission was enhanced by 9 times with respect to the one without In2O3 content by optimal QDs size. Quantitative studies of steady-state and transient emission spectral data demonstrated that In2O3 QDs acted as sensitizers for the Er3+ emission. Furthermore, the influence of QDs size and Er3+ concentration on the sensitization efficiency was investigated in detailed. These results indicated that the obtained Er3+ ions doped composite containing In2O3 QDs could be a promising material for high-performance fiber amplifiers using broadband UV pumping.

AN EMPIRICAL SEQUENCE OF DISK GAP OPENING REVEALED BY ROVIBRATIONAL CO

The fundamental rovibrational band of CO near 4.7 $\mu$m is a sensitive tracer of the presence and location of molecular gas in the planet-forming region of protoplanetary disks at 0.01--10 AU. We present a new analysis of a high-resolution spectral survey (R$\,\sim\,$96,000, or $\sim3.2\,\rm km\,s^{-1}$) of CO rovibrational lines from protoplanetary disks spanning a wide range of stellar masses and of evolutionary properties. We find that the CO emission originates in two distinct velocity components. Line widths of both components correlate strongly with disk inclination, as expected for gas in Keplerian rotation. By measuring the line flux ratios between vibrational transitions $F_{v=2-1}/F_{v=1-0}$, we find that the two velocity components are clearly distinct in excitation. The broad component ($\rm FWHM=50-200\,km\,s^{-1}$) probes the disk region near the magnetospheric accretion radius at $\approx0.05$ AU, where the gas is hot ($800-1500$ K). The narrow component ($\rm FWHM=10-50 km\,s^{-1}$) probes the disk at larger radii of 0.1--10\,AU, where the gas is typically colder (200--700 K). CO excitation temperatures and orbital radii define an empirical temperature-radius relation as a power law with index $-0.3\pm0.1$ between 0.05--3 AU. The broad CO component, co-spatial with the observed orbital distribution of hot Jupiters, is rarely detected in transitional and Herbig Ae disks, providing evidence for an early dissipation of the innermost disk. An inversion in the temperature profile beyond 3 AU is interpreted as a tracer of a regime dominated by UV pumping in largely devoid inner disks, and may be a signature of the last stage before the disk enters the gas-poor debris phase.

Improved sensitization efficiency in Er(3+) ions and SnO2 nanocrystals co-doped silica thin films.

Er(3+) ions and SnO2 nanocrystals co-doped silica thin films are prepared by an improved sol-gel spin-coating method. With increase in annealing temperature, the related 1.54 μm characteristic emission intensity from Er(3+) ions is obviously enhanced by more than two orders of magnitude via SnO2 nanocrystals size control to boost the sensitization efficiency. Quantitative studies of steady-state spectroscopic data and fluorescence decay curves demonstrate that the related sensitization efficiency via size-tunable nanocrystals is increased from 0.14% to 1.3%. This improved sensitization efficiency is achieved by doping some of the Er(3+) ions into the SnO2 inner sites at a high annealing temperature, as revealed by high-resolution TEM, X-ray diffraction patterns and elemental mapping technique. Different sensitization mechanisms are also discussed separately according to the selective photoluminescence excitation measurements. All these results have not only explained the greatly improved sensitization efficiency resulting from SnO2 nanocrystals but also indicated that the development of Er(3+) ions and SnO2 nanocrystals co-doped silica thin films could result in promising high-performance near-infrared luminous materials using broadband UV pumping.

Evaluating the use of blue phosphors in white LEDs: the case of Sr0.25Ba0.75Si2O2N2:Eu2+

Abstract The luminescence properties of the blue emitting phosphor Sr0.25Ba0.75Si2O2N2:Eu2+ are extensively investigated. This oxonitridosilicate phosphor features strong 4f65d1 - 4f7 luminescence originating from the Eu2+ ion, with a narrow emission band peaking at 467 nm and a full width at half maximum of only 41 nm. Thermal quenching of the blue luminescence only sets in above 450 K, making this material an interesting candidate as LED conversion phosphor. The fast decay of the luminescence prevents the phosphor to be susceptible to saturation effects at high excitation fluxes. Furthermore it is proven to be chemically stable against moisture. The only drawback is the relatively low quantum efficiency of the synthesized powder, provisionally preventing this material to be used in applications. In addition, the phosphor features a weak yellow emission band, originating from small domains featuring a different crystal structure. It is shown that the majority of the powder grains only exhibit blue emission. Finally, the spectrum of a white LED, based on a UV pumping LED and three (oxy)nitride phosphors is simulated in order to assess the usefulness of blue phosphors in LEDs for lighting. Only a marginal improvement in terms of color quality can be achieved with a narrow banded phosphor, at the expense of a decrease in luminous efficacy and overall electrical to optical power efficiency. PACS 70 – Condensed Matter: Electronic structure, Electrical, Magnetic, and Optical Properties PACS 42.70.-a Optical materials

Radiation thermo-chemical models of protoplanetary discs

The carbon monoxide rovibrational emission from discs around Herbig Ae stars and T Tauri stars with strong ultraviolet emissions suggests that fluorescence pumping from the ground X1 Sigma+ to the electronic A1 Pi state of CO should be taken into account in disc models. We implemented a CO model molecule that includes up to 50 rotational levels within nine vibrational levels for the ground and A excited states in the radiative photochemical code ProDiMo. We took CO collisions with hydrogen molecules, hydrogen atoms, helium, and electrons into account. We estimated the missing collision rates using standard scaling laws and discussed their limitations. UV fluorescence and IR pumping impact on the population of ro-vibrational v > 1 levels. The v = 1 rotational levels are populated at rotational temperatures between the radiation temperature around 4.6 micron and the gas kinetic temperature. The UV pumping efficiency increases with decreasing disc mass. The consequence is that the vibrational temperatures, which measure the relative populations between the vibrational levels, are higher than the disc gas kinetic temperatures (suprathermal population). Rotational temperatures from fundamental transitions derived using optically thick 12CO lines do not reflect the gas kinetic temperature. CO pure rotational levels with energies lower than 1000 K are populated in LTE but are sensitive to a number of vibrational levels included in the model. The 12CO pure rotational lines are highly optically thick for transition from levels up to Eupper=2000 K. (abridged)

Silicon nanoparticle-ZnS nanophosphors for ultraviolet-based white light emitting diode

Present red phosphor converters provide spectra dominated by sharp lines and suffer from availability and stability issues which are not ideal for color mixing in display or solid state lighting applications. We examine the use of mono dispersed 3 nm silicon nanoparticles, with inhomogeneously broadened red luminescence as an effective substitute for red phosphors. We tested a 3-phase hybrid nanophosphor consisting of ZnS:Ag, ZnS:Cu,Au,Al, and nanoparticles. Correlated color temperature is examined under UV and LED pumping in the range 254, 365–400 nm. The temperature is found reasonably flat for the longer wavelengths and drops for the shorter wavelengths while the color rendering index increases. The photo stability of the phosphors relative to the silicon nanoparticles is recorded. The variation in the temperature is analyzed in terms of the strength of inter-band–gap transition and continuum band to band transitions.

Rotationally Excited H2 in the Magellanic Clouds

AbstractWe have performed a survey study of rotational excited-state H2 Lyman-Werner absorption lines in the entire FUSE Magellanic Clouds Legacy archive. These lines reflect the UV pumping and formation conditions of H2, enabling a more comprehensive study of H2 gas properties, e.g. J-level populations N(J) and b-values (generally indicating the velocity dispersion). Combining with our previous measurements of N(Hi) and N(H2), we derived H2 excitation temperatures, gas volume density n(H), and local UV radiation field strength IUV for each sight line. The results indicate a weaker correlation between n(H) and IUV in Magellanic Clouds than the Galactic sight lines. We also obtained N(H)/E(B − V) ratios from the Spitzer-SAGE and previous CO J = 1 − 0 / Hi 21 cm surveys at sight line locations, using dust modeling and standard line brightness-column density conversion factors. They show a roughly linear correlation with absorption-based N(H)/E(B − V) values, and have a similar scatter (∼0.7 dex) across the LMC and SMC.

Efficient Energy Transfer and Enhanced Infrared Emission in Er-Doped ZnO-SiO2 Composites

Intense near-infrared (NIR) emission around 1534 nm has been obtained from ZnO-SiO2:Er3+ composites upon broadband ultraviolet light excitation. Remarkably, enhancement of the NIR emission as much as 20 times was achieved by optimal codoping with Li+ ions. To elucidate the relevant mechanisms, comprehensive spectroscopic measurements have been performed on ZnO-SiO2 composites with and without Er3+ ions doping. Photoluminescence spectroscopy and fluorescence decay dynamics clearly verify the efficient energy transfer from ZnO quantum dots (QDs) to Er3+ ions. Our results have not only demonstrated an efficient approach of color down-conversion but also indicated that ZnO-SiO2:Er3+ composites could be a promising material for optical amplifier using broadband UV pumping.

Unprecedented solid-state laser action from BODIPY dyes under UV-pumping radiation

Highly efficient and stable laser emission is demonstrated under drastic UV pumping conditions from recently synthesized BODIPY dye incorporated into polymer host. Under transversal pumping at 355 nm, lasing efficiencies of up to 29%, similar to those obtained in liquid phase, were obtained, with useful lifetimes (drop of the emission by 50%) of 70,000 pulses at 5 Hz repetition rate. The obtained efficiency and photostability are much higher than those obtained with usual commercial dyes emitting in the same spectral region, such as Coumarin 540A, under the same experimental conditions.

Formation of molecular hydrogen from protonated 9,10-dihydroanthracene: Is the ejected H 2 rotationally and vibrationally excited?

The infrared multiple-photon dissociation (IRMPD) spectrum of protonated 9,10-dihydroanthracene ([DHA+H] +, m/ z 181) has been recorded using an infrared free electron laser. Protonation was accomplished by electrospray ionization with subsequent mass-selection and trapping in a Fourier transform ion cyclotron mass spectrometer. IR-induced fragment ions were observed at m/ z 179, 166, and 165. Density functional calculations (B3LYP/6-311++G(d,p)) of the infrared spectra of the two possible protonated isomers of DHA showed that the observed IRMPD spectrum is best fit to a mixture of the two isomers. Potential energy surfaces for the loss of atomic and molecular hydrogen from the aliphatic carbons of [DHA+H] + have been calculated. The lowest energy barriers are for loss of H 2. After H 2 ejection, stabilization of the remaining fragment occurs by hydrogen migration from one of the aliphatic carbons to the bare ejection site. In all cases the stabilized fragment is computed to be 9-hydroanthracene. The IRMPD spectrum of the m/ z 179 fragment has been recorded and is shown to correspond closely both to the calculated and previously recorded IRMPD spectrum of ionic 9-hydroanthracene. The highly asymmetric transition state conformation of the to-be-formed H 2 and the remaining fragment is highly suggestive of rotational, vibrational, and, possibly, translational excitation of the ejected H 2. Evidence for such excitation from astronomical observations that show the close proximity of PAHs and H 2 in certain interstellar objects and that show H 2 rotational excitation, which has been difficult to explain via either collisional activation or UV pumping, is reviewed.