Energy-saving solid state chemistry - New materials light up the world

(f.l.t.r.) Dr. rer. nat. Peter J. Schmidt, Prof. Dr. rer. nat. Wolfgang Schnick

Prof. Dr. rer. nat. Wolfgang Schnick (Spokesperson)
Dr. rer. nat. Peter J. Schmidt

Ludwig-Maximilians-Universität, München
Philips Technologie GmbH, Aachen

Conventional incandescent lamps waste energy; ordinary "energy-saving lamps" are unpopular due to other disadvantages. How can a lighting technology be developed that is energy efficient, environmentally-friendly and can be used for a variety of applications while creating entirely new ways of using light?

Prof. Dr. Wolfgang Schnick, Dr. Peter J. Schmidt and their teams found the answer to this question: they synthesized innovative fluorescent materials with which, for example, warm-white LEDs (light emitting diodes) can be manufactured for a variety of different applications with an unprecedented level of quality. The impacts are vast: if all conventional lamps were replaced by these novel light sources, total power consumption worldwide could be reduced up to 10%. Wolfgang Schnick holds the chair for Inorganic Solid State Chemistry at Ludwig-Maximilians-Universität, LMU, the University of Munich. Peter J. Schmidt is group leader for Material Research at the Lumileds Development Center of Philips Technologie GmbH in Aachen.

Incandescent bulbs are extremely inefficient. They only convert a negligible percentage of electricity into visible light - the rest is lost as heat. Consequently, the EU has banned the manufacture and sale of most incandescent bulbs. Electric discharge lamps, so-called energy-saving lamps, do not waste as much power, but have other disadvantages: they contain toxic mercury and the color rendering is often not optimal. For this reason, they are considered merely an interim solution. The future, experts agree, belongs to LEDs (light emitting diodes) that provide illumination from the excitation of electrons in solid-state semiconductor diodes. But: every single LED is only capable of emitting light of a certain color. In the past, producing high-quality white light with blended spectral primary colors was very difficult and expensive due to a lack of suitable materials.

While conducting fundamental research, the group of LMU scientists headed by Wolfgang Schnick stumbled upon a class of substances that solve this problem. They replaced the oxygen atoms in naturally occurring silicates with nitrogen. This produced silicon nitrides: chemical compounds made of silicon and nitrogen, ecologically safe substances that are found in nearly inexhaustible quantities on earth. The scientists succeeded in endowing the substances with special properties: they are very robust and can be customized for use in light emitting diodes by adding foreign atoms and are capable for converting the light of blue LEDs into white light.

Philips Lumileds transferred the academic findings to an industrial application. The research scientists led by Peter J. Schmidt continued the development of the materials and technology and readied them for mass production. In the meantime, LEDs and LED lamps from Philips are already on the market. They are highly efficient, extremely long-lasting, affordable, and offer excellent color rendering. Silicon nitride luminous materials are also being developed in Aachen for what have been the most energy-efficient light emitting diodes, green and amber LEDs, which are used in turn signals for cars or traffic lights. The experts at Philips anticipate that LEDs based on silicon nitrides will revolutionize the lighting market - particularly since they are ideally suited to innovative illumination concepts: for example, the development of lamps whose light color can individually be set by the user.

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