@phdthesis{Haubitz2021,
  author    = {Haubitz, Toni},
  title     = {Transient absorption spectroscopy},
  doi       = {10.25932/publishup-53509},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-535092},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 176},
  year      = {2021},
  abstract  = {The optical properties of chromophores, especially organic dyes and optically active inorganic molecules, are determined by their chemical structures, surrounding media, and excited state behaviors. The classical optical go-to techniques for spectroscopic investigations are absorption and luminescence spectroscopy. While both techniques are powerful and easy to apply spectroscopic methods, the limited time resolution of luminescence spectroscopy and its reliance on luminescent properties can make its application, in certain cases, complex, or even impossible. This can be the case when the investigated molecules do not luminesce anymore due to quenching effects, or when they were never luminescent in the first place. In those cases, transient absorption spectroscopy is an excellent and much more sophisticated technique to investigate such systems. This pump-probe laser-spectroscopic method is excellent for mechanistic investigations of luminescence quenching phenomena and photoreactions. This is due to its extremely high time resolution in the femto- and picosecond ranges, where many intermediate or transient species of a reaction can be identified and their kinetic evolution can be observed. Furthermore, it does not rely on the samples being luminescent, due to the active sample probing after excitation. In this work it is shown, that with transient absorption spectroscopy it was possible to identify the luminescence quenching mechanisms and thus luminescence quantum yield losses of the organic dye classes O4-DBD, S4-DBD, and pyridylanthracenes. Hence, the population of their triplet states could be identified as the competitive mechanism to their luminescence. While the good luminophores O4-DBD showed minor losses, the S4-DBD dye luminescence was almost entirely quenched by this process. However, for pyridylanthracenes, this phenomenon is present in both the protonated and unprotonated forms and moderately effects the luminescence quantum yield. Also, the majority of the quenching losses in the protonated forms are caused by additional non-radiative processes introduced by the protonation of the pyridyl rings. Furthermore, transient absorption spectroscopy can be applied to investigate the quenching mechanisms of uranyl(VI) luminescence by chloride and bromide. The reduction of the halides by excited uranyl(VI) leads to the formation of dihalide radicals X^(·-2). This excited state redox process is thus identified as the quenching mechanism for both halides, and this process, being diffusion-limited, can be suppressed by cryogenically freezing the samples or by observing these interactions in media with a lower dielectric constant, such as ACN and acetone.},
  language  = {en}
}
@misc{BeckHildebrandtLoehmannsroeben2006,
  author    = {Beck, Michael and Hildebrandt, Niko and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Quantum dots as acceptors in FRET-assays containing serum},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-9504},
  year      = {2006},
  abstract  = {Quantum dots (QDs) are common as luminescing markers for imaging in biological applications because their optical properties seem to be inert against their surrounding solvent. This, together with broad and strong absorption bands and intense, sharp tuneable luminescence bands, makes them interesting candidates for methods utilizing F{\"o}rster Resonance Energy Transfer (FRET), e. g. for sensitive homogeneous fluoroimmunoassays (FIA). In this work we demonstrate energy transfer from Eu<SUP>3+</SUP>-trisbipyridin (Eu-TBP) donors to CdSe-ZnS-QD acceptors in solutions with and without serum. The QDs are commercially available CdSe-ZnS core-shell particles emitting at 655 nm (QD655). The FRET system was achieved by the binding of the streptavidin conjugated donors with the biotin conjugated acceptors. After excitation of Eu-TBP and as result of the energy transfer, the luminescence of the QD655 acceptors also showed lengthened decay times like the donors. The energy transfer efficiency, as calculated from the decay times of the bound and the unbound components, amounted to 37\%. The F{\"o}rster-radius, estimated from the absorption and emission bands, was ca. 77 {\AA}. The effective binding ratio, which not only depends on the ratio of binding pairs but also on unspecific binding, was obtained from the donor emission dependent on the concentration. As serum promotes unspecific binding, the overall FRET efficiency of the assay was reduced. We conclude that QDs are good substitutes for acceptors in FRET if combined with slow decay donors like Europium. The investigation of the influence of the serum provides guidance towards improving binding properties of QD assays.},
  subject      = {Quantenpunkt},
  language  = {en}
}
@phdthesis{Chemura2023,
  author    = {Chemura, Sitshengisiwe},
  title     = {Optical spectroscopy on lanthanide-modified nanomaterials for performance monitoring},
  doi       = {10.25932/publishup-61944},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-619443},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 116},
  year      = {2023},
  abstract  = {Lanthanide based ceria nanomaterials are important practical materials due to their redox properties that are useful in technology and life sciences. This PhD thesis examined various properties and potential for catalytic and bio-applications of Ln3+-doped ceria nanomaterials. Ce1-xGdxO2-y: Eu3+, gadolinium doped ceria (GDC) (0 ≤ x ≤ 0.4) nanoparticles were synthesized by flame spray pyrolysis (FSP) and studied, followed by 15 \% CexZr1-xO2-y: Eu3+|YSZ (0 ≤ x ≤ 1) nanocomposites. Furthermore, Ce1-xYb xO2-y (0.004 ≤ x ≤ 0.22) nanoparticles were synthesized by thermal decomposition and characterized. Finally, CeO2-y: Eu3+ nanoparticles were synthesized by a microemulsion method, biofunctionalized and characterized. The studies undertaken presents a novel approach to structurally elucidate ceria-based nanomaterials by way of Eu3+ and Yb3+ spectroscopy and processing the spectroscopic data with the multi-way decomposition method PARAFAC. Data sets of the three variables: excitation wavelength, emission wavelength and time were used to perform the deconvolution of spectra. GDC nanoparticles from FSP are nano-sized and of roughly cubic shape and crystal structure (Fm3̅m). Raman data revealed four vibrational modes exhibited by Gd3+ containing samples whereas CeO2-y: Eu3+ displays only two. The room temperature, time-resolved emission spectra recorded at λexcitation = 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 two species; a high-symmetry species and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded at 4 K after probing the 5D0-7F0 transition revealed additional variation in the low symmetry Eu3+ sites in pure ceria and GDC. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is inversely related to Gd3+ and oxygen vacancy concentration. The particle crystallites of the 773 K and 1273 K annealed Yb3+ -ceria nanostructure materials are nano-sized and have a cubic fluorite structure with four Raman vibrational modes. Elemental maps clearly show that cluster formation occurs for 773 K annealed with high Yb3+ ion concentration from 15 mol \% in the ceria lattice. These clusters are destroyed with annealing to 1273 K. The emission spectra observed from room temperature and 4 K measurements for the Ce1-xYb xO2-y samples have a manifold that corresponds to the 2F5/2-2F7/2 transition of Yb3+ ions. Some small shifts are observed in the Stark splitting pattern and are induced by the variations of the crystal field influenced by where the Yb3+ ions are located in the crystal lattices in the samples. Upon mixing ceria with high Yb3+ concentrations, the 2F5/2-2F7/2 transition is also observed in the Stark splitting pattern, but the spectra consist of two broad high background dominated peaks. Annealing the nanomaterials at 1273 K for 2 h changes the spectral signature as new peaks emerge. The deconvolution yielded luminescence decay kinetics as well as the accompanying luminescence spectra of three species for each of the low Yb3+ doped ceria samples annealed at 773 K and one species for the 1273 K annealed samples. However, the ceria samples with high Yb3+ concentration annealed at the two temperatures yielded one species with lower decay times as compared to the Yb3+ doped ceria samples after PARAFAC analysis. Through the calcination of the nanocomposites at two high temperatures, the evolution of the emission patterns from specific Eu3+ lattice sites to indicate structural changes for the nanocomposites was followed. The spectroscopy results effectively complemented the data obtained from the conventional techniques. Annealing the samples at 773 K, resulted in amorphous, unordered domains whereas the TLS of the 1273 K nanocomposites reveal two distinct sites, with most red shifted Eu3+ species coming from pure Eu3+ doped ZrO2 on the YSZ support. Finally, for Eu3+ doped ceria, successful transfer from hydrophobic to water phase and subsequent biocompatibility was achieved using ssDNA. PARAFAC analysis for the Eu3+ in nanoparticles dispersed in toluene and water revealed one Eu3+ species, with slightly differing surface properties for the nanoparticles as far as the luminescence kinetics and solvent environments were concerned. Several functionalized nanoparticles conjugated onto origami triangles after hybridization were visualized by atomic force microscopy (AFM). Putting all into consideration, Eu3+ and Yb3+ spectroscopy was used to monitor the structural changes and determining the feasibility of the nanoparticle transfer into water. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials and in solutions, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different emission contributions to any given spectrum.},
  language  = {en}
}
@misc{LoehmannsroebenKantorKumkeetal.2005,
  author    = {L{\"o}hmannsr{\"o}ben, Hans-Gerd and Kantor, Zoltan and Kumke, Michael Uwe and Schm{\"a}lzlin, Elmar and Reich, Oliver},
  title     = {OPQS - optische Prozess- und Qualit{\"a}ts-Sensorik},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-13205},
  year      = {2005},
  abstract  = {Im vorliegenden Beitrag wird an Hand dreier Beispiele der Einsatz von optischer Sensorik zur Produktcharakterisierung dargestellt, n{\"a}mlich Untersuchungen zum O2-Gehalt in Fruchts{\"a}ften, zur Isotopiesignatur von CO2 in Mineralw{\"a}ssern und zu Lichtstreueigenschaften eines Sonnenschutzmittels. Inhalt: Bestimmung von O2 mit Lumineszenzsonden Isotopenselektive Bestimmung von CO2 mit TDLAS Optische Charakterisierung stark streuender Materialien mit Photonendichtewellen},
  language  = {de}
}
@misc{LoehmannsroebenBeckHildebrandtetal.2006,
  author    = {L{\"o}hmannsr{\"o}ben, Hans-Gerd and Beck, Michael and Hildebrandt, Niko and Schm{\"a}lzlin, Elmar and van Dongen, Joost T.},
  title     = {New challenges in biophotonics : laser-based fluoroimmuno analysis and in-vivo optical oxygen monitoring},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10120},
  year      = {2006},
  abstract  = {Two examples of our biophotonic research utilizing nanoparticles are presented, namely laser-based fluoroimmuno analysis and in-vivo optical oxygen monitoring. Results of the work include significantly enhanced sensitivity of a homogeneous fluorescence immunoassay and markedly improved spatial resolution of oxygen gradients in root nodules of a legume species.},
  subject      = {Sauerstoff},
  language  = {en}
}
@phdthesis{Gessner2011,
  author    = {Geßner, Andr{\´e}},
  title     = {Neuartige Lanthanoid-dotierte mikro- und mesopor{\"o}se Feststoffe : Charakterisierung von Ion-Wirt-Wechselwirkungen, Speziesverteilung und Lumineszenzeigenschaften mittels zeitaufgel{\"o}ster Lumineszenzspektroskopie},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52371},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Por{\"o}se Sol-Gel-Materialien finden in vielen Bereichen Anwendung bzw. sind Gegenstand der aktuellen Forschung. Zu diesen Bereichen z{\"a}hlen sowohl klassische Anwendungen, wie z. B. die Verwendung als Katalysator, Molekularsieb oder Trockenmittel, als auch nichtklassische Anwendungen, wie z. B. der Einsatz als Kontrastmittel in der Magnet-Resonanz-Tomographie oder in Form von d{\"u}nnen Zeolithfilmen als Isolatoren in Mikrochips. Auch f{\"u}r den Einsatz in der Photonik werden por{\"o}se Materialien in Betracht gezogen, wie die Entwicklung des Zeolith-Farbstoff-Lasers zeigt. Mikropor{\"o}se Zeolithe k{\"o}nnen generell {\"u}ber einfache Ionenaustauschreaktionen mit Lanthanoidionen in lumineszente Materialien umgewandelt werden. Neben der Erzeugung eines lumineszenten Materials, dessen Lumineszenzeigenschaften charakterisiert werden m{\"u}ssen, bietet die Nutzung von Lanthanoidionen die M{\"o}glichkeit diese Ionen als Sonde zur Charakterisierung der Ion-Wirt-Wechselwirkungen zu funktionalisieren, was z. B. in Bezug auf die Anwendung als Katalysator von großer Bedeutung ist. Dabei werden die einzigartigen Lumineszenzeigenschaften der Lanthanoidionen, in diesem Fall von Europium(III) und Terbium(III), genutzt. In dieser Arbeit wurden Lanthanoid-dotierte mikropor{\"o}se Zeolithe, mikropor{\"o}s-mesopor{\"o}se Hybridmaterialien und mesopor{\"o}se Silikate hinsichtlich ihrer Lumineszenzeigenschaften und ihrer Wechselwirkung des Wirtsmaterials mit den Lanthanoidionen mittels zeitaufgel{\"o}ster Lumineszenzspektroskopie untersucht. Zeitaufgel{\"o}ste Emissionsspektren (TRES) liefern dabei sowohl Informationen in der Wellenl{\"a}ngen- als auch in der Zeitdom{\"a}ne. Erstmalig wurden die TRES mittels einer umfangreichen Auswertemethodik behandelt. Neben der Anpassung des Abklingverhaltens mit einer diskreten Zahl von Exponentialfunktionen, wurden unterst{\"u}tzend auch Abklingzeitverteilungsanalysen durchgef{\"u}hrt. Zeitaufgel{\"o}ste fl{\"a}chennormierte Emissionsspektren (TRANES), eine Erweiterung der normalen TRES, konnten erstmals zur Bestimmung der Zahl der emittierenden Lanthanoidspezies in por{\"o}sen Materialien genutzt werden. Durch die Berechnung der Decayassoziierten Spektren (DAS) konnten den Lanthanoidspezies die entsprechenden Lumineszenzspektren zugeordnet werden. Zus{\"a}tzlich konnte, speziell im Fall der Europium-Lumineszenz, durch Kombination von zeitlicher und spektraler Information das zeitabh{\"a}ngige Asymmetrieverh{\"a}ltnis R und die spektrale Evolution des 5D0-7F0-{\"U}bergangs mit der Zeit t untersucht und somit wesentliche Informationen {\"u}ber die Verteilung der Europiumionen im Wirtsmaterial erhalten werden. {\"U}ber die Abklingzeit und das Asymmetrieverh{\"a}ltnis R konnten R{\"u}ckschl{\"u}sse auf die Zahl der OH-Oszillatoren in der ersten Koordinationssph{\"a}re und die Symmetrie der Koordinationsumgebung gezogen werden. F{\"u}r die mikropor{\"o}sen und mikropor{\"o}s-mesopor{\"o}sen Materialien wurden verschiedene Lanthanoidspezies, im Regelfall zwei, gefunden, welche entsprechend der beschriebenen Methoden charakterisiert wurden. Diese Lanthanoidspezies konnten Positionen in den Materialien zugeordnet werden, die sich im tief Inneren des Porensystems oder auf bzw. nahe der {\"a}ußeren Oberfl{\"a}che oder in den Mesoporen befinden. Erstere Spezies ist aufgrund ihrer Position im Material gut vor Feuchtigkeitseinfl{\"u}ssen gesch{\"u}tzt, was sich deutlich in entsprechend langen Lumineszenzabklingzeiten {\"a}ußert. Zus{\"a}tzlich ist diese Europiumspezies durch unsymmetrische Koordinationsumgebung charakterisiert, was auf einen signifikanten Anteil an Koordination der Lanthanoidionen durch die Sauerstoffatome im Wirtsgitter zur{\"u}ckzuf{\"u}hren ist. Ionen, die sich nahe oder auf der {\"a}ußeren Oberfl{\"a}che befinden, sind dagegen f{\"u}r Feuchtigkeit zug{\"a}nglicher, was in k{\"u}rzeren Lumineszenzabklingzeiten und einer symmetrischeren Koordinationsumgebung resultiert. Der Anteil von Wassermolek{\"u}len in der ersten Koordinationssph{\"a}re ist hier deutlich gr{\"o}ßer, als bei den Ionen, die sich tiefer im Porensystem befinden und entspricht in vielen F{\"a}llen der Koordinationszahl eines vollst{\"a}ndig hydratisierten Lanthanoidions. Auch der Einfluss von Oberfl{\"a}chenmodifikationen auf die Speziesverteilung und das Verhalten der Materialien gegen{\"u}ber Feuchtigkeit wurde untersucht. Dabei gelang es den Einfluss der Feuchtigkeit auf die Lumineszenzeigenschaften und die Speziesverteilung durch die Oberfl{\"a}chenmodifikation zu verringern und die Lumineszenzeigenschaften teilweise zu konservieren. Im Fall der mesopor{\"o}sen Silikamonolithe wurde auch eine heterogene Verteilung der Lanthanoidionen im Porensystem gefunden. Hier wechselwirkt ein Teil der Ionen mit der Porenwand, w{\"a}hrend sich die restlichen Ionen in der w{\"a}ßrigen Phase innerhalb des Porensystems aufhalten. Das Aufbringen von Oberfl{\"a}chenmodifikationen f{\"u}hrte zu einer Wechselwirkung der Ionen mit diesen Oberfl{\"a}chenmodifikationen, was sich in Abh{\"a}ngigkeit von der Oberfl{\"a}chenbeladung in den enstprechenden Lumineszenzeigenschaften niederschlug.},
  language  = {de}
}
@misc{Reger2018,
  type      = {Master Thesis},
  author    = {Reger, Carolin},
  title     = {Dating of alluvial fans from NW Argentina using cosmogenic nuclides and optically stimulated luminescence technique},
  doi       = {10.25932/publishup-47147},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-471470},
  school      = {Universit{\"a}t Potsdam},
  pages     = {4, IV},
  year      = {2018},
  abstract  = {Alluvial fans are important geomorphic markers and sedimentary archives of tectonic and climatic changes. Hence, basins providing perfect studying conditions can often be found in arid regions due to the low weathering impact and thus well preservation of sedimentary features. Twelve samples for optically/infrared stimulated luminescence (OSL/IRSL) dating and one depth profile for cosmogenic radionuclide dating (10Be) were collected in the Santa Maria Valley in NW Argentina, where the exceptional preservation of several generations of alluvial fans allow exploring the external forcing conditions that led to repeated cycles of incision and aggradation. The results of the OSL/IRSL dating yielded ages ranging between 0.4 ± 0.1 ka and 271.8 ± 24.5 ka. Previous studies next to the study area indicate a depositional age of 1.5-2 Mio years for the oldest generation of alluvial fans, which might still be supported by our ongoing 10Be dating. Due to field observations, sediment provenance, stratigraphic characteristics and the geomorphic pattern of erosion, seven (/eight) generations of alluvial fan deposits were recognized. Comparing my ages with global glaciation cycles as well as linking them to temperature proxies retrieved from a lake on the Altiplano Plateau, a good fit between alluvial fan accumulation phases and global glacial periods (corresponding to cold/wet phases within the central Andes) is observed. This suggests that aggradation occurs during the early stages of glacial periods, while incision is expected at the end of glacial phases. This pattern might be linked to variations in the vegetational cover (controlled by water availability), which will decrease/increase during hot and dry/cold and wet interglacial/glacial phases favoring/limiting sediment production and will increase/decrease during cold and wet/hot and dry glacial/interglacial phases. Even though the eastern Andean margin is showing neotectonic activities and is assumed to be active up to recent times, deformation and seismicity might most probably have played only a minor role in relation to the rather short timescale reflected by the data.},
  language  = {en}
}