Verônica C. Teixeira

Effect of lithium excess on the LiAl 5 O 8 :Eu luminescent properties under VUV excitation

The influence of lithium excess and calcination temperature on the luminescence properties of the LiAl5O8:Eu under VUV excitation was investigated. The presence of both broad bands and sharp peaks in the VUV and X-ray emission spectra suggests the presence of Eu2+, even in absence of reducing atmosphere in the synthesis. The VUV excitation spectra indicated a band gap of 8.5 eV while the UV excited one showed the Eu3+ charge transfer transition starting at 3.9 eV. These values indicate that Eu2+ is stable in this host since its ground state is below the Fermi level of the host (ca. 4.1 eV). The relation between the intensity of Eu2+ and Eu3+ emissions showed that the reduction is favored at higher temperatures and lower Li content, leading to the proposition of a reduction mechanism based on the incorporation of charge compensation defects formed in the aliovalent doping of Eu3+ in Li+ sites.

ARAPUCA light trap for large liquid argon time projection chambers

ARAPUCA is a totally innovative device for liquid argon scintillation light detection. It is composed of a passive light collector and of active devices. The active devices are standard SiPMs that operate at liquid argon temperature, while the passive collector is a photon trap that allows the collection of light with extremely high efficiency. The total detection efficiency of the device can be tuned by modifying the ratio between the area of the active components (SiPM) and that of the optical window. Few arrays of ARAPUCAs will be installed inside the prototype of the Deep Underground Neutrino Experiment - protoDUNE - and their performances will be compared with those of more standard solutions based on guiding bars. The results of the most recent tests of ARAPUCAs in a liquid argon environment, which led to the actual design for the protoDUNE, will be reported together with the proposal of a photon detection system for the Deep Underground Neutrino Experiment based on ARAPUCAs combined with dielectric mirror foils coated by wavelength-shifter.

The Coherent X-ray Sub-micro and Nanoprobe Stations for the CARNAUBA Beamline at the Sirius-LNLS Storage Ring.

CARNAÚBA (Coherent X-Ray Nanoprobe Beamline) is the tender-to-hard X-ray nanoprobe under construction at the new Brazilian synchrotron light source SIRIUS [1]. The beamline provides two separated experimental stations, one with sub-micrometer resolution and another with nanometer resolution, to cover various analysis techniques, including XRD, XAS, XRF, XEOL, CDI and ptychography with 2D and 3D imaging capabilities exploring the coherent properties of the light. The innovative modified-Delta undulator, with four independent jaws, able to deliver any polarization, is optimized to provide photons with vertical polarization allowing for scattering in the horizontal plane from the source up to the endstations, with unitary polarization factor. The all achromatic CARNAÚBA optics, based on state-of-theart KB mirrors, covers continuously the energy range from 2.05 to 15 keV with a resolution of E/E=10 , using an in-house developed four-bounce crystal monochromator. An unprecedent coherent flux @Si(111)BW close to 10 – 10 ph/s/100mA will be delivered [2].