Dresden 2011 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 83: Joint Focussed Session: Theory and Computation of Electronic Structure: New Frontiers VI

HL 83.3: Talk

Thursday, March 17, 2011, 15:30–15:45, TRE Phy

First-principles study (GW+PAW) on new phosphors for white LED — •Bruno Bertrand^1,2, 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.