Ag-sensitized Tb3+/Yb3+ codoped silica-zirconia glasses and glass-ceramics: Systematic and detailed investigation of the broadband energy-transfer and downconversion processes

Abstract Various studies report that Tb3+/Yb3+ co-doped materials can split one UV or 488 nm (visible) photon in two near infrared (NIR) photons at 980 nm by an energy-transfer process involving one Tb3+ and two Yb3+ ions. Additionally, it was demonstrated that Ag multimers can provide an efficient optical sensitizing effect for rare earth ions (RE3+ ions), resulting in a broadband enhanced excitation, which could have a significant technological impact, overcoming their limited spectral absorptions and small excitation cross sections. However, a systematic and detailed investigation of the down-conversion process enhanced by Ag nanoaggregates is still lacking, which is the focus of this paper. Specifically, a step by step analysis of the energy-transfer quantum-cutting chain in Ag-exchanged Tb3+/Yb3+ co-doped glasses and glass-ceramics is presented. Moreover, the direct Ag-Yb3+ energy-transfer is also considered. Results of structural, compositional, and optical characterizations are given, providing quantitative data for the efficient broadband Ag-sensitization of Tb3+/Yb3+ quantum cutting. A deeper understanding of the physical processes beneath the optical properties of the developed materials will allow a wiser realization of more efficient energy-related devices, such as spectral converters for silicon solar cells and light-emitting devices (LEDs) in the visible and NIR spectral regions

HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands

We present the complete photometric database and the color-magnitude diagrams for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the F439W and F555W bands. A detailed discussion of the various reduction steps is also presented, and of the procedures to transform instrumental magnitudes into both the HST F439W and F555W flight system and the standard Johnson B and V systems. We also describe the artificial star experiments which have been performed to derive the star count completeness in all the relevant branches of the color magnitude diagram. The entire photometric database and the completeness function will be made available on the Web immediately after the publication of the present paper.Comment: 21 pages, 77 figures. High resolution version of this paper can be retrived at http://dipastro.pd.astro.it/globular

Photometric metallicity for 694233 Galactic giant stars from Gaia DR3 synthetic Stromgren photometry. Metallicity distribution functions of halo sub-structures

We use the calibrations by Calamida et al. and by Hilker et al., and the standardised synthetic photometry in the v, b, and y Stromgren passbands from Gaia DR3 BP/RP spectra, to obtain photometric metallicities for a selected sample of 694233 old Galactic giant stars having |b|>20.0 and parallax uncertainties lower than 10%. The zero point of both sets of photometric metallicities has been shifted to to ensure optimal match with the spectroscopic [Fe/H] values for 44785 stars in common with APOGEE DR17, focusing on the metallicity range where they provide the highest accuracy. The metallicities derived in this way from the Calamida et al. calibration display a typical accuracy of ~0.1 dex and 1 sigma precision ~0.2 dex in the range -2.2 <=[Fe/H]<= -0.4, while they show a systematic trend with [Fe/H] at higher metallicity, beyond the applicability range of the relation. Those derived from the Hilker et al. calibration display, in general, worse precision, and lower accuracy in the metal-poor regime, but have a median accuracy < 0.05 dex for [Fe/H]>= -0.8. These results are confirmed and, consequently, the metallicities validated, by comparison with large sets of spectroscopic metallicities from various surveys. The newly obtained metallicities are used to derive metallicity distributions for several previously identified sub-structures in the Galactic halo with an unprecedented number of stars. The catalogue including both sets of metallicities and the associated uncertainties is made publicly available.Comment: Accepted for publication by Astronomy & Astrophysics. Latex. 20 pages, 21 color figures. The catalogue will be publicly available at CDS. In the meanwhile it is available upon request to the first autho

Wustite as a new precursor of industrial ammonia synthesis catalysts

Contradictory results about the best oxidic precursor of Fe ammonia synthesis catalyst prompted the present comparative investigation on wustite- and magnetite-based catalysts. Many physical (density, porous texture, crystalline phases, reduction rate, metal surface, abrasion loss) and catalytic (kinetic constants, thermoresistancy) properties have been determined on both catalysts. The wustite-based catalyst proved to be much more active, especially at lower temperatures, approaching the performances of Ru/C catalyst, except at high conversion. Possible reasons for such a behavior of the wustite-based catalyst are discussed, suggesting that a reconsideration of the present consolidated knowledge on Fe ammonia synthesis catalyst might be convenien

The Red Giant Branch in Near-Infrared Colour-Magnitude Diagrams. II: The luminosity of the Bump and the Tip

We present new empirical calibrations of the Red Giant Branch (RGB) Bump and Tip based on a homogeneous near-Infrared database of 24 Galactic Globular Clusters. The luminosities of the RGB Bump and Tip in the J, H and K bands and their dependence on the cluster metallicity have been studied, yielding empirical relationships. By using recent transformations between the observational and theoretical planes, we also derived similar calibrations in terms of bolometric luminosity. Direct comparison between updated theoretical models and observations show an excellent agreement. The empirical calibration of the RGB Tip luminosity in the near-Infrared passbands presented here is a fundamental tool to derive distances to far galaxies beyond the Local Group, in view of using the new ground-based adaptive optics facilities and, in the next future, the James Webb Space Telescope.Comment: 7 pages, 7 figures, accepted for publication in MNRA

An Intermediate Redshift Supernova Search at ESO: Reduction Tools and Efficiency Tests

We present the reduction and archiving tools developed for our search for supernovae at intermediate redshifts at ESO as well as the efficiency tests performed. The data reduction recipes developed for the SN candidates selection are described. All the variable sources detected are stored using a MySQL database which enables the identification of previously detected variable sources during past observational runs. Finally, experiments performed with artificial stars have shown that seeing plays a crucial role for the limiting magnitude of detection. Crucial is also the detection threshold used by Sextractor.Comment: Poster presented at the ESO/MPA/MPE Workshop "From Twilight to Highlight, The Physics of Supernovae", Garching, Jul 29-31, 2002, to be published in the Conference Proceeding

Internal calibration of Gaia BP/RP low-resolution spectra

The full third Gaia data release will provide the calibrated spectra obtained with the blue and red Gaia slit-less spectrophotometers. The main challenge when facing Gaia spectral calibration is that no lamp spectra or flat fields are available during the mission. Also, the significant size of the line spread function with respect to the dispersion of the prisms produces alien photons contaminating neighbouring positions of the spectra. This makes the calibration special and different from standard approaches. This work gives a detailed description of the internal calibration model to obtain the spectrophotometric data in the Gaia catalogue. The main purpose of the internal calibration is to bring all the epoch spectra onto a common flux and pixel (pseudo-wavelength) scale, taking into account variations over the focal plane and with time, producing a mean spectrum from all the observations of the same source. In order to describe all observations in a common mean flux and pseudo-wavelength scale, we construct a suitable representation of the internally calibrated mean spectra via basis functions and we describe the transformation between non calibrated epoch spectra and calibrated mean spectra via a discrete convolution, parametrising the convolution kernel to recover the relevant coefficients. The model proposed here is able to combine all observations into a mean instrument to allow the comparison of different sources and observations obtained with different instrumental conditions along the mission and the generation of mean spectra from a number of observations of the same source. The output of this model provides the internal mean spectra, not as a sampled function (flux and wavelength), but as a linear combination of basis functions, although sampled spectra can easily be derived from them.Comment: 20 pages, 22 figure

Microwave driven synthesis of narrow bandgap alpha-tin nanoparticles on silicon

This work proposes a microwave-based synthetic route for the preparation of tin nanospheres with a diamond-like a-phase structure on silicon. The main characteristics of the synthesized material are an extraordinarily narrow (around 50 meV) direct bandgap and an improved thermal stability (up to 200° C). Structural and compositional characterizations showed a core–shell structure comprised of an outer amorphous oxide shell and inner core containing a-phase tin domains. Microwaves turned out to be instrumental in achieving the specific nanostructures reported, due to their peculiar heating characteristics. Low pressure, low temperature and compatibility with integrated circuits manufacturing represent the most innovative features of the present synthetic process

Grape berry responses to sequential flooding and heatwave events: a physiological, transcriptional, and metabolic overview

Grapevine cultivation, such as the whole horticulture, is currently challenged by several factors, among which the extreme weather events occurring under the climate change scenario are the most relevant. Within this context, the present study aims at characterizing at the berry level the physiological response of Vitis vinifera cv. Sauvignon Blanc to sequential stresses simulated under a semi-controlled environment: flooding at bud-break followed by multiple summer stress (drought plus heatwave) occurring at pre-vèraison. Transcriptomic and metabolomic assessments were performed through RNASeq and NMR, respectively. A comprehensive hormone profiling was also carried out. Results pointed out a different response to the heatwave in the two situations. Flooding caused a developmental advance, determining a different physiological background in the berry, thus affecting its response to the summer stress at both transcriptional levels, with the upregulation of genes involved in oxidative stress responses, and metabolic level, with the increase in osmoprotectants, such as proline and other amino acids. In conclusion, sequential stress, including a flooding event at bud-break followed by a summer heatwave, may impact phenological development and berry ripening, with possible consequences on berry and wine quality. A berry physiological model is presented that may support the development of sustainable vineyard management solutions to improve the water use efficiency and adaptation capacity of actual viticultural systems to future scenario

Extinction Correction for Type Ia Supernova Rates. I. The Model

In this paper we present and discuss a new Monte Carlo approach aimed at correcting the observed Supernova (SN) rates for the effects of host galaxy dust extinction. The problem is addressed in a general way and the model includes SN position distributions, SN light curve and spectral library, dust properties and distribution as input ingredients. Even though the recipe we propose is in principle applicable to all SN types, in this paper we illustrate the use of our model only for Type Ia. These represent in fact the simplest test case, basically due to their spectroscopic homogeneity which, to a first approximation, allows one to treat them all in the same way. This test case shows that the final results do not depend critically on the spiral arm dust geometry, while the total amount of dust, its properties and the size of the galactic bulge do have a strong effect. With the availability of more complete spectral libraries and a more accurate knowledge of SN spatial distribution, the method we propose here can be easily extended to Core Collapses events.Comment: Accepted for publication on MNRA