@article{LopezdeGuerenuKurganovaKlierHaubitzetal.2022,
  author    = {L{\´o}pez de Guere{\~n}u Kurganova, Anna and Klier, Dennis Tobias and Haubitz, Toni and Kumke, Michael Uwe},
  title     = {Influence of Gd3+ doping concentration on the properties of Na(Y,Gd)F-4},
  series = {Photochemical \& photobiological sciences / European Society for Photobiology},
  volume    = {21},
  journal   = {Photochemical \& photobiological sciences / European Society for Photobiology},
  number    = {2},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1474-905X},
  doi       = {10.1007/s43630-021-00161-4},
  pages     = {235 -- 245},
  year      = {2022},
  abstract  = {We present a systematic study on the properties of Na(Y,Gd)F-4-based upconverting nanoparticles (UCNP) doped with 18\% Yb3+, 2\% Tm3+, and the influence of Gd3+ (10-50 mol\% Gd3+). UCNP were synthesized via the solvothermal method and had a range of diameters within 13 and 50 nm. Structural and photophysical changes were monitored for the UCNP samples after a 24-month incubation period in dry phase and further redispersion. Structural characterization was performed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) as well as dynamic light scattering (DLS), and the upconversion luminescence (UCL) studies were executed at various temperatures (from 4 to 295 K) using time-resolved and steady-state spectroscopy. An increase in the hexagonal lattice phase with the increase of Gd3+ content was found, although the cubic phase was prevalent in most samples. The Tm3+-luminescence intensity as well as the Tm3+-luminescence decay times peaked at the Gd3+ concentration of 30 mol\%. Although the general upconverting luminescence properties of the nanoparticles were preserved, the 24-month incubation period lead to irreversible agglomeration of the UCNP and changes in luminescence band ratios and lifetimes.},
  language  = {en}
}
@article{BastianYudeGuerenuKurganovaetal.2020,
  author    = {Bastian, Philipp U. and Yu, Leixiao and de Guere{\~n}u Kurganova, Anna Lopez and Haag, Rainer and Kumke, Michael Uwe},
  title     = {Bioinspired confinement of upconversion nanoparticles for improved performance in aqueous solution},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {124},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {52},
  publisher = {American Chemical Society},
  address   = {Washington, DC},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.0c09798},
  pages     = {28623 -- 28635},
  year      = {2020},
  abstract  = {The resonance energy transfer (RET) from NaYF4:Yb,Er upconverting nanoparticles (UNCPs) to a dye (5-carboxytetramethylrhodamine (TAMRA)) was investigated by photoluminescence experiments and microscale thermophoresis (MST). The dye was excited via RET from the UCNPs which was excited in the near-infrared (NIR). The change of the dye diffusion speed (free vs coupled) was investigated by MST. RET shows significant changes in the decay times of the dye as well as of the UCNPs. MST reveals significant changes in the diffusion speed. A unique amphiphilic coating polymer (customized mussel protein (CMP) polymer) for UCNP surface coating was used, which mimics blood protein adsorption and mussel food protein adhesion to transfer the UCNP into the aqueous phase and to allow surface functionalization. The CMP provides very good water dispersibility to the UCNPs and minimizes ligand exchange and subsequent UCNP aging reactions because of the interlinkage of the CMP on the UCNP surface. Moreover, CMP provides N-3-functional groups for dick chemistry-based functionalization demonstrated with the dye 5-carboxytetramethylrhodamine (TAMRA). This establishes the principle coupling scheme for suitable biomarkers such as antibodies. The CMP provides very stable aqueous UCNP dispersions that are storable up to 3 years in a fridge at 5 degrees C without dissolution or coagulation. The outstanding properties of CMP in shielding the UCNP from unwanted solvent effects is reflected in the distinct increase of the photoluminescence decay times after UCNP functionalization. The UCNP-to-TAMRA energy transfer is also spectroscopically investigated at low temperatures (4-200 K), revealing that one of the two green Er(III) emission bands contributes the major part to the energy transfer. The TAMRA fluorescence decay time increases by a factor of 9500 from 2.28 ns up to 22 mu s due to radiationless energy transfer from the UCNP after NIR excitation of the latter. This underlines the unique properties of CMP as a versatile capping ligand for distinctly improving the UCNPs' performance in aqueous solutions, for coupling of biomolecules, and for applications for in vitro and in vivo experiments using UCNPs as optical probes in life science applications.},
  language  = {en}
}