@article{BurekEidnerKukeetal.2018,
  author    = {Burek, Katja and Eidner, Sascha and Kuke, Stefanie and Kumke, Michael Uwe},
  title     = {Intramolecular deactivation processes of electronically excited Lanthanide(III) complexes with organic acids of low molecular weight},
  series = {Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy},
  volume    = {191},
  journal   = {Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {1386-1425},
  doi       = {10.1016/j.saa.2017.09.012},
  pages     = {36 -- 49},
  year      = {2018},
  abstract  = {The luminescence of Lanthanide(Ill) complexes with different model ligands was studied under direct as well as sensitized excitation conditions. The research was performed in the context of studies dealing with deep-underground storages for high-level nuclear waste. Here, Lanthanide(III) ions served as natural analogues for Actinide(III) ions and the low-molecular weight organic ligands are present in clay minerals and furthermore, they were employed as proxies for building blocks of humic substances, which are important complexing molecules in the natural environment, e.g., in the far field of a repository site. Time-resolved luminescence spectroscopy was applied for a detailed characterization of Eu(III), Tb(III), Sm(III) and.Dy(III) complexes in aqueous solutions. Based on the observed luminescence the ligands were tentatively divided into two groups (A, B). The luminescence of Lanthanide(III) complexes of group A was mainly influenced by an energy transfer to OH-vibrations. Lanthanide(Ill) complexes of group B showed ligand-related luminescence quenching, which was further investigated. To gain more information on the underlying quenching processes of group A and B ligands, measurements at different temperatures (77 K <= T <= 353 K) were performed and activation energies were determined based on an Arrhenius analysis. Moreover, the influence of the ionic strength between 0 M <= 1 <= 4 M on the Lanthanide(III) luminescence was monitored for different complexes, in order to evaluate the influence of specific conditions encountered in host rocks foreseen as potential repository sites.},
  language  = {en}
}
@article{BurekKrauseSchwotzeretal.2018,
  author    = {Burek, Katja and Krause, Felix and Schwotzer, Matthias and Nefedov, Alexei and S{\"u}ssmuth, Julia and Haubitz, Toni and Kumke, Michael Uwe and Thissen, Peter},
  title     = {Hydrophobic Properties of Calcium-Silicate Hydrates Doped with Rare-Earth Elements},
  series = {ACS sustainable chemistry \& engineering},
  volume    = {6},
  journal   = {ACS sustainable chemistry \& engineering},
  number    = {11},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2168-0485},
  doi       = {10.1021/acssuschemeng.8b03244},
  pages     = {14669 -- 14678},
  year      = {2018},
  abstract  = {In this study, the apparent relationship between the transport process and the surface chemistry of the Calcium-Silicate Hydrate (CSH) phases was investigated. For this purpose, a method was developed to synthesize ultrathin CSH phases to be used as a model substrate with the specific modification of their structure by introducing europium (Eu(III)). The structural and chemical changes during this Eu(III)-doping were observed by means of infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and time-resolved laser fluorescence spectroscopy (TRLFS). These alterations of the CSH phases led to significant changes in the surface chemistry and consequently to considerable variations in the interaction with water, as evidenced by measurements of the contact angles on the modified model substrates. Our results provide the basis for a more profound molecular understanding of reactive transport processes in cement-based systems. Furthermore, these results broaden the perspective of improving the stability of cement-based materials, which are subjected to the impact of aggressive aqueous environments through targeted modifications of the CSH phases.},
  language  = {en}
}
@article{BurekDenglerEmmerlingetal.2019,
  author    = {Burek, Katja and Dengler, Joachim and Emmerling, Franziska and Feldmann, Ines and Kumke, Michael Uwe and Stroh, Julia},
  title     = {Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems},
  series = {ChemistryOpen},
  volume    = {8},
  journal   = {ChemistryOpen},
  number    = {12},
  publisher = {Wiley-VCH-Verl.},
  address   = {Weinheim},
  issn      = {2191-1363},
  doi       = {10.1002/open.201900249},
  pages     = {1441 -- 1452},
  year      = {2019},
  abstract  = {The hydration process of Portland cement in a cementitious system is crucial for development of the high-quality cement-based construction material. Complementary experiments of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time-resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time-dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium-silicate-hydrates (C-S-H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C-S-H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.},
  language  = {en}
}
@misc{BurekDenglerEmmerlingetal.2019,
  author    = {Burek, Katja and Dengler, Joachim and Emmerling, Franziska and Feldmann, Ines and Kumke, Michael Uwe and Stroh, Julia},
  title     = {Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {808},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-44243},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-442433},
  pages     = {14},
  year      = {2019},
  abstract  = {The hydration process of Portland cement in a cementitious system is crucial for development of the high-quality cement-based construction material. Complementary experiments of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time-resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time-dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium-silicate-hydrates (C-S-H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C-S-H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.},
  language  = {en}
}