@article{ChemuraHaubitzPrimusetal.2020,
  author    = {Chemura, Sitshengisiwe and Haubitz, Toni and Primus, Philipp A. and Underberg, Martin and H{\"u}lser, Tim and Kumke, Michael Uwe},
  title     = {Europium-doped Ceria-Gadolinium mixed oxides},
  series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {124},
  journal   = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {24},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/acs.jpca.0c03188},
  pages     = {4972 -- 4983},
  year      = {2020},
  abstract  = {Gadolinium-doped ceria or gadolinium-stabilized ceria (GDC) is an important technical material due to its ability to conduct O2- ions, e.g., used in solid oxide fuel cells operated at intermediate temperature as an electrolyte, diffusion barrier, and electrode component. We have synthesized Ce1-xGdxO2-y:Eu3+ (0 <= x <= 0.4) nanoparticles (11-15 nm) using a scalable spray pyrolysis method, which allows the continuous large-scale technical production of such materials. Introducing Eu3+ ions in small amounts into ceria and GDC as spectroscopic probes can provide detailed information about the atomic structure and local environments and allows us to monitor small structural changes. This study presents a novel approach to structurally elucidate europium-doped Ce1-xGdxO2-y:Eu3+ nanoparticles by way of Eu3+ spectroscopy, processing the spectroscopic data with the multiway decomposition method parallel factor (PARAFAC) analysis. In order to perform the deconvolution of spectra, data sets of excitation wavelength, emission wavelength, and time are required. Room temperature, time-resolved emission spectra recorded at lambda(ex) = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals a high-symmetry species (which can also be probed directly via the CeO2 charge transfer band) and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded under cryogenic conditions after probing the D-5(0)-F-7(0) transition at lambda(ex) = 575-583 nm revealed additional variation in the low-symmetry Eu3+ sites in pure ceria and GDC. The total luminescence spectra of CeO2-y:Eu3+ showed Eu3+ ions located in at least three slightly different coordination environments with the same fundamental symmetry, whereas the overall hypsochromic shift and increased broadening of the D-5(0)-F-7(0) excitation in the GDC samples, as well as the broadened spectra after deconvolution point to less homogeneous environments. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is decreased with increasing Gd3+ and oxygen vacancy concentration. For reference, the Judd-Ofelt parameters of all spectra were calculated. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different contributions to any given spectrum.},
  language  = {en}
}
@article{MondalBehrensMatthesetal.2015,
  author    = {Mondal, Suvendu Sekhar and Behrens, Karsten and Matthes, Philipp R. and Sch{\"o}nfeld, Fabian and Nitsch, J{\"o}rn and Steffen, Andreas and Primus, Philipp-Alexander and Kumke, Michael Uwe and M{\"u}ller-Buschbaum, Klaus and Holdt, Hans-J{\"u}rgen},
  title     = {White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+},
  series = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  volume    = {18},
  journal   = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  number    = {3},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7534},
  doi       = {10.1039/C4TC02919D},
  pages     = {4623 -- 4631},
  year      = {2015},
  abstract  = {Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a-d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+.},
  language  = {en}
}
@article{MondalBehrensMatthesetal.2015,
  author    = {Mondal, Suvendu Sekhar and Behrens, Karsten and Matthes, Philipp R. and Sch{\"o}nfeld, Fabian and Nitsch, J{\"o}rn and Steffen, Andreas and Primus, Philipp-Alexander and Kumke, Michael Uwe and M{\"u}ller-Buschbaum, Klaus and Holdt, Hans-J{\"u}rgen},
  title     = {White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+},
  series = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  volume    = {3},
  journal   = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  number    = {18},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7526},
  doi       = {10.1039/c4tc02919d},
  pages     = {4623 -- 4631},
  year      = {2015},
  language  = {en}
}