Microscopic investigation of redox processes in luminescent materials

Groep: LumiLab

Promotoren: prof. dr. Philippe Smet en prof. dr. Dirk Poelman
Begeleiding: Lisa Martin en David Van der Heggen

Luminescent materials emit light that is not generated thermally, as in an incandescent lamp. These materials, also known as phosphors, are ubiquitous for modern lighting and display applications, such as LEDs. Most photo and electroluminescent materials, such as LED phosphors, also show light emission when they are exposed to ionizing radiation. In case of electrons, the process is called cathodoluminescence (CL). Inside a scanning electron microscope (SEM), high-resolution imaging can be combined with the analysis of the CL emission spectrum on a microscopic level, opening new possibilities to study luminescent materials on a nanometer scale. This in contrast to standard luminescence spectroscopy where macroscopic averages are measured. The underlying processes are then blurred and difficult to model.

In this master thesis, you will be trained to work independently with an electron microscope, equipped with elemental analysis (EDX, energy-dispersive X-ray spectroscopy), temperature stage and luminescence spectrometer (CL detection). By combining these techniques, it is possible to correlate local variations in luminescent properties to variations in chemical composition and particle morphology. You will apply these techniques to gain improved understanding of the energy transfer phenomena between lanthanide dopants. The goal is to look at a specific and emerging class of luminescent materials, with metastable charge transfer states. They enable energy storage or can induce new emission bands, but the details of these mechanisms are far from clear. As impurities or local variations in dopant concentrations are expected to play an important role, it is a good strategy to investigate these materials on unexplored spatial dimensions in order to gain more insight in the emission mechanism.

(Figure: mapping of CL emission intensity of a phosphor particle at different temperatures. For each pixel, the influence of temperature can be investigated, and used to model the thermal quenching behaviour)
(Figure: mapping of CL emission intensity of a phosphor particle at different temperatures. For each pixel, the influence of temperature can be investigated, and used to model the thermal quenching behaviour)

Opmerkingen:

  • Dit thesisonderwerp kan ook opgenomen worden in het kader van de Educatieve Master Fysica en Sterrenkunde.
  • Aan dit onderwerp is geen mobiliteitsaspect verbonden. Er kan met de promotoren wel overlegd worden over gerelateerde stage-activiteiten en/of vakken aan andere universiteiten.