TY  - JOUR
A1  - Klier, Dennis Tobias
A1  - Kumke, Michael Uwe
T1  - Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale
JF  - RSC Advances
N2  - In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure beta 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.
Y1  - 2015
U6  - https://doi.org/10.1039/c5ra11502g
SN  - 2046-2069
VL  - 5
IS  - 82
SP  - 67149
EP  - 67156
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - GEN
A1  - Hesse, Julia
A1  - Klier, Dennis Tobias
A1  - Sgarzi, Massimo
A1  - Nsubuga, Anne
A1  - Bauer, Christoph
A1  - Grenzer, Jörg
A1  - Hübner, René
A1  - Wislicenus, Marcus
A1  - Joshi, Tanmaya
A1  - Kumke, Michael Uwe
A1  - Stephan, Holger
T1  - Rapid synthesis of sub-10 nm hexagonal NaYF4-based upconverting nanoparticles using Therminol® 66
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - 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.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 613 
KW  - core-shell materials
KW  - lanthanides
KW  - nanostructures
KW  - photoluminescence
KW  - upconversion
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-423515
SN  - 1866-8372
IS  - 613
ER  - 
TY  - JOUR
A1  - Schimka, Selina
A1  - Klier, Dennis Tobias
A1  - de Guerenu, Anna Lopez
A1  - Bastian, Philipp
A1  - Lomadze, Nino
A1  - Kumke, Michael Uwe
A1  - Santer, Svetlana
T1  - Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles as mediator
JF  - Journal of physics : Condensed matter
N2  - Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm-3(+) or Er-3(+) as activator ions, the UCNPs provide emissions in the spectral range of 450 nm < lambda(em) < 480 nm (for Tm-3(+), three and four photon induced emission) or 525 nm < lambda(em) < 545 nm (for Er-3(+), two photon induced emission), respectively. Especially for UCNPs containing Tm-3(+) a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (lambda(ex) = 976 nm) in the presence of the Tm-3(+)-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl3) in contrast to water, which shows a distinct absorption in the NIR.
KW  - upconversion nanoparticles
KW  - azobenzene containing surfactants
KW  - kinetic of cis-trans isomerization
Y1  - 2019
U6  - https://doi.org/10.1088/1361-648X/aafcfa
SN  - 0953-8984
SN  - 1361-648X
VL  - 31
IS  - 12
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -