Luminescent Glass Ceramics for White LED Applications

• Applicant: Professor Dr. Stefan Schweizer
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics
• Term: from 2016 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 323730539

White LEDs mostly consist of blue emitting LED chips combined with a yellow-emitting phosphor. Due to the lack of red spectral component, the color impression of such LEDs is often shifted slightly to the cold blue spectral range. The limitation of the phosphor is its degradation when exposed to the high temperatures of the LED chips. The use of luminescent glasses and glass ceramics as a combination of phosphor and encapsulant are more resistant to high temperatures than conventional polymer-based encapsulation. Through selective doping with elements from the group of rare-earth metals, the emission and subsequently the color impression can be adjusted. Owing to their high mechanical, chemical and thermal stability, borate glasses are to be used as matrix material.Within the framework of this project, new luminescent glass ceramics are developed and optimized in terms of their optical properties. Crystallites were obtained through the thermal treatment of pre-synthesized luminescent glasses. By scattering and multiple reflections on the crystallites, the optical path length in these systems can be significantly increased, so that the light output at the same optical excitation power increases. The glass ceramics under examination consist of lithium, sodium or barium borate glasses with different levels of doping of different rare-earth metal ions. The rare-earths are used as optical activators. Upon excitation in the ultraviolet or blue spectral range, they show a strong emission in the visible spectrum.

• DFG Programme: Research Grants