Dresden 2011 – scientific programme
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O: Fachverband Oberflächenphysik
O 74: Focussed session: Theory and computation of electronic structure: new frontiers VI (jointly with HL, DS)
O 74.3: Talk
Thursday, March 17, 2011, 15:30–15:45, TRE Phy
First-principles study (GW+PAW) on new phosphors for white LED — •Bruno Bertrand1,2, Masayoshi Mikami3, Martin Stankovski1, and Xavier Gonze1 — 1European theoretical spectroscopy facility (ETSF), Université Catholique de Louvain, Louvain-la-Neuve, Belgium — 2CERDECAM, Institut Supérieur Industriel ECAM, Bruxelles, Belgium — 3Mitsubishi Chemical Group Science and Technology (S&T) Research Center, Inc., Yokohama, Japan
White-LEDs will be one of the major actor involved in the future generations of eco-friendly light sources. For novel types of white LEDs, an optimal combination of two green- and red-emitting phosphors absorbing partly the blue light from the InGaN LED is mandatory to obtain a white light source by post recombination of the light.
We have theoretically studied two oxynitride phosphors, one is an efficient green phosphor Ba3Si6O12N2:Eu developed at the Mitsubishi Chemical Group (S&T) Research Center, and the other is a bluish-green phosphor Ba3Si6O9N4:Eu that exhibits little luminescence at room temperature. Our results rely on many body perturbation approach (GW+PAW) applied to the two hosts : Ba3Si6O12N2 and Ba3Si6O9N4. The calculation shows a slightly narrower energy gap for Ba3Si6O9N4, that is 0.33 eV. Yet such a result provides keys to understand the thermal quenching mechanism, by comparing materials with a similar chemical composition, but different thermal behaviour. Then a deeper analysis with Eu-doped models sheds new light onto the relationship between emission/excitation colors from the Europium luminescent centers, and the properties of their complex ligands.