Regensburg 2016 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 15: Ceramics and Applications (DF with KR)
DF 15.1: Vortrag
Donnerstag, 10. März 2016, 15:00–15:20, H26
Crystallization in luminescent borate glass for use in white LEDs — •A. Charlotte Rimbach1, Franziska Steudel2, and Stefan Schweizer1,2 — 1South Westphalia University of Applied Sciences, Luebecker Ring~2, 59494 Soest — 2Fraunhofer Application Center for Inorganic Phosphors, Branch Lab of Fraunhofer Institute for Microstructure of Materials and Systems IMWS, Luebecker Ring~2, 59494 Soest
The majority of white LEDs is comprised of a blue light emitting diode and a yellow phosphor. The phosphor powder, which converts a part of the blue light to yellow light, is embedded in an organic polymer and directly coated onto the LED chip. Heat-induced degradation of the polymer-based encapsulate, however, results in an efficiency decrease and color temperature change. Luminescent glasses and glass ceramics might represent an interesting alternative due to their higher thermal and chemical stability. For optical activation, the glasses are doped with rare-earth ions such as europium and terbium. Due to the relatively low absorption coefficient of the rare-earths the blue LED light is only absorbed by a small amount resulting in a too high color temperature. To increase the optical absorption by multiple scattering and reflection the glasses are subsequently processed to glass ceramics. This work focuses on the crystallization process in europium-doped lithium-aluminium-borate glass upon annealing at different temperatures for different periods of time. Differential scanning calorimetry and X-ray diffraction are the methods chosen to monitor the crystal growth and to identify the crystal phases.