Ab-initio and experimental study of the optical properties of alkaline-earth chalcogenides
(2012) Ph.D. Students’ Day — Location: Louvain-la-Neuve – Belgium (1.June.2012)
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- Abstract
- Alkaline-earth chalcogenides have a bright future as photoluminescence materials and opto-electronic devices. Despite the strong current interest for red emitting phosphors, which can be obtained upon doping with europium, some of these compounds have not been heavily studied and relatively little is known about the details of the physical mechanisms behind luminescence and thermal quenching behavior. In this work we report a systematic study by means of low temperature excitation and emission spectra, thermal quenching, as well as decay behavior for europium doped CaS and CaO. In the literature different models exists to explain the thermal quenching behavior (e.g. a cross-over in the configuration diagram or interactions with the conduction band) and in order to sort these out we decide to used ab initio calculations. A systematic study of the electronic band structure, lattice parameter, phonon band structure and dielectric constant is proposed for the undoped chalcogenides comparing different effective potentials as well as using many body theories to describe the excited states. For CaS we report a value of 5.619 Å for the lattice parameter, 242 and 352 cm-1 for phonon LO-TO splitting at the Г zone center. The calculated indirect Г-X gap is 4.031 eV using one-shot G0W0. We also report a calculated value of respectively 4.39 and 9.18 for optical and static dielectric constant. The associated refractive index of 2.095 is close to the 2.135 experimental value. Going in the direction of a full ab initio calculation of europium doped chalcogenides we designed norm-conserving as well as effective potential based on projector augmented wave method that were tested on experimental data available for europium oxides.
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Poncé, S., Bertrand, B., Smet, P., Poelman, D., Mikami, M., & Gonze, X. (2012). Ab-initio and experimental study of the optical properties of alkaline-earth chalcogenides. Ph.D. Students’ Day, Louvain-la-Neuve – Belgium. https://hdl.handle.net/2078.5/191888