Gecombineerde theoretische-experimentele studie van luminescente materialen

  1. Gecombineerde theoretische-experimentele studie van luminescente materialen

    MM_14_SPEC_06 / Spectroscopy
    Promotor(en): K. Hemelsoet, P. Smet / Begeleider(s): A. Ghysels, J. Joos, K. Lejaeghere

    Luminescent materials, also known as phosphors, form an interesting group of materials with a variety of applications. Traditional application domains are LED lighting and imaging. In these applications, the phosphors convert blue light into green, yellow or red light in order to achieve a white emission spectrum from one (blue) pumping LED. To date, many questions remain on the precise physical processes responsible for their particular luminescent behavior, and a combination of theory and experiment is often needed to gain a deeper understanding. Herein, we will combine theory and experiment to investigate an interesting class of phosphors, based on the luminescence of transition metal ions (such as Mn2+, Cr3+, Cu+, …) inside inorganic host crystals.

    Ab initio modeling has evolved to the level at which it can be used to rationalize and elucidate the structure-activity relationship of complex materials. In this view, Density Functional Theory (DFT) is one of the most interesting electronic structure methods due to its excellent accuracy/computational cost ratio. It is in principle exact, although an approximated exchange-correlation functional has to be used. Here, we want to treat excited-state properties and therefore we will use the time-dependent form of DFT (TD-DFT).[1] Modeling of luminescent solid state materials is based on accurate structure optimizations involving periodic codes. Computation of the luminescent behavior itself requires optimization of the excited state and is no routine activity yet. Currently, there are many developments in this field and new implementations are written in existing software packages.

    Optical spectroscopy allows distilling information on the electronic structure of the metal ion inside the host crystal directly from experiment. Furthermore, measurements of the decay dynamics of the luminescent material yield information on the lifetime of the excited electronic state. Temperature dependent measurements allow probing the impurity levels of the dopant inside the band gap of the host crystal.

    Goal and objectives The goal of this master thesis is to unravel the luminescent behavior of metal-doped solid state materials using a combined theoretical-experimental approach. Theoretical spectra will be computed using periodic unit cells. A first step will be the geometry optimization of the parent and metal-doped material. The band structure and density of states can then be examined. Optimization of the excited state is more challenging, however TD-DFT will be tested; both on the periodic structure as on extracted clusters. Overall, the theoretical information will be compared with experimental data obtained by optical and luminescence spectroscopy.

    The main challenge of this master thesis is the combination of theory and experiment. This combined approach ensures that the interested student gains a profound insight in the luminescent materials and the precise physical processes responsible for it. Due to the variety of aspects available in this master topic, the focus can be shifted to particular items depending on the interest of the student.

    [1] C. Adamo and D. Jacquemin, Chem. Soc. Rev. 2013, 42, 845.

  1. Study programme
    Master of Science in Engineering Physics [EMPHYS], Master of Science in Physics and Astronomy [CMFYST]
    Luminescence, Molecular modeling, Optical spectroscopy
    Recommended courses
    Simulations and modeling for the nanoscale, Luminescence


Prof. Dr. ir. Karen Hemelsoet