| dc.description.abstract | The unique luminescence of lanthanide-doped nanocrystals has led to numerous scientific and
technological applications. Over the last decades, synthesis methods have been developed to
produce core/shell nanostructures, which enable spatial separation of dopant ions and thereby
create new functionalities. Ionic diffusion is unwanted in these specific structures as it eliminates
this spatial separation. On the other hand, the temperature dependence of ionic diffusion could
also be useful, for instance to study migration of lanthanide ions under different conditions
or to use in applications such as thermal history sensing. However, we currently lack the
necessary practical, qualitative methods for measuring ion distribution. In this thesis, we
study ion diffusion through simulations and experimental measurements. We calculated model
decay curves from simulated concentration profiles to fit experimental decay curves from heated
core/shell nanocrystals with different lanthanide dopants and shell lattices to study the effect of
materials and temperature on diffusion speed. We found an increase by two orders of magnitude
in the diffusion coefficient of NaYF4:Ho3+/NaYF4 from 1.31·10−24 to 1.11·10−22 m2/s when
the temperature increased from 350 to 400 ◦C. Similar diffusion coefficients were found for
NaYF4:Ho3+/NaGdF4. Thus, we have successfully developed a modelling technique to enable
facile and quantitative tracking of ion diffusion. This technique can help to gain insight to
improve core/shell structures and develop thermal history sensors for independently measuring
the temperature and duration of a heating event. | |
