@misc{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+,Er3+-co-doped NaYF4 nanomaterials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-89630},
  pages     = {11228 -- 11238},
  year      = {2015},
  abstract  = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.},
  language  = {en}
}
@misc{WessigBaderKlieretal.2016,
  author    = {Wessig, Pablo and Bader, Denise and Klier, Dennis Tobias and Hettrich, Cornelia and Bier, Frank Fabian},
  title     = {Detecting carbohydrate-lectin interactions using a fluorescent probe based on DBD dyes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394382},
  pages     = {1235 -- 1238},
  year      = {2016},
  abstract  = {Herein we present an efficient synthesis of a biomimetic probe with modular construction that can be specifically bound by the mannose binding FimH protein - a surface adhesion protein of E. coli bacteria. The synthesis combines the new and interesting DBD dye with the carbohydrate ligand mannose via a Click reaction. We demonstrate the binding to E. coli bacteria over a large concentration range and also present some special characteristics of those molecules that are of particular interest for the application as a biosensor. In particular, the mix-and-measure ability and the very good photo-stability should be highlighted here.},
  language  = {en}
}
@misc{HesseKlierSgarzietal.2018,
  author    = {Hesse, Julia and Klier, Dennis Tobias and Sgarzi, Massimo and Nsubuga, Anne and Bauer, Christoph and Grenzer, J{\"o}rg and H{\"u}bner, Ren{\´e} and Wislicenus, Marcus and Joshi, Tanmaya and Kumke, Michael Uwe and Stephan, Holger},
  title     = {Rapid synthesis of sub-10 nm hexagonal NaYF4-based upconverting nanoparticles using Therminol® 66},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {613},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-42351},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423515},
  pages     = {10},
  year      = {2018},
  abstract  = {We report a simple one-pot method for the rapid preparation of sub-10nm pure hexagonal (-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol((R))66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.},
  language  = {en}
}
@phdthesis{Klier2016,
  author    = {Klier, Dennis Tobias},
  title     = {Upconversion luminescence in Er-codoped NaYF4 nanoparticles},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98486},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 89},
  year      = {2016},
  abstract  = {In the context of an increasing population of aging people and a shift of medical paradigm towards an individualized medicine in health care, nanostructured lanthanides doped sodium yttrium fluoride (NaYF4) represents an exciting class of upconversion nanomaterials (UCNM) which are suitable to bring forward developments in biomedicine and -biodetection. Despite the fact that among various fluoride based upconversion (UC) phosphors lanthanide doped NaYF4 is one of the most studied upconversion nanomaterial, many open questions are still remaining concerning the interplay of the population routes of sensitizer and activator electronic states involved in different luminescence upconversion photophysics as well as the role of phonon coupling. The collective work aims to explore a detailed understanding of the upconversion mechanism in nanoscaled NaYF4 based materials co-doped with several lanthanides, e.g. Yb3+ and Er3+ as the "standard" type upconversion nanoparticles (UCNP) up to advanced UCNP with Gd3+ and Nd3+. Especially the impact of the crystal lattice structure as well as the resulting lattice phonons on the upconversion luminescence was investigated in detail based on different mixtures of cubic and hexagonal NaYF4 nanoscaled crystals. Three synthesis methods, depending on the attempt of the respective central spectroscopic questions, could be accomplished in the following work. NaYF4 based upconversion nanoparticles doped with several combination of lanthanides (Yb3+, Er3+, Gd3+ and Nd3+) were synthesized successfully using a hydrothermal synthesis method under mild conditions as well as a co-precipitation and a high temperature co-precipitation technique. Structural information were gathered by means of X-ray diffraction (XRD), electron microscopy (TEM), dynamic light scattering (DLS), Raman spectroscopy and inductively coupled plasma atomic emission spectrometry (ICP-OES). The results were discussed in detail with relation to the spectroscopic results. A variable spectroscopic setup was developed for multi parameter upconversion luminescence studies at various temperature 4 K to 328 K. Especially, the study of the thermal behavior of upconversion luminescence as well as time resolved area normalized emission spectra were a prerequisite for the detailed understanding of intramolecular deactivation processes, structural changes upon annealing or Gd3+ concentration, and the role of phonon coupling for the upconversion efficiency. Subsequently it became possible to synthesize UCNP with tailored upconversion luminescence properties. In the end, the potential of UCNP for life science application should be enunciated in context of current needs and improvements of a nanomaterial based optical sensors, whereas the "standard" UCNP design was attuned according to the special conditions in the biological matrix. In terms of a better biocompatibility due to a lower impact on biological tissue and higher penetrability for the excitation light. The first step into this direction was to use Nd3+ ions as a new sensitizer in tridoped NaYF4 based UCNP, whereas the achieved absolute and relative temperature sensitivity is comparable to other types of local temperature sensors in the literature.},
  language  = {en}
}
@misc{KumkeKlier2015,
  author    = {Kumke, Michael Uwe and Klier, Dennis Tobias},
  title     = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-102677},
  pages     = {67149 -- 67156},
  year      = {2015},
  abstract  = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.},
  language  = {en}
}
@misc{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-89618},
  pages     = {67149 -- 67156},
  year      = {2015},
  abstract  = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.},
  language  = {en}
}