SCHOTT solutions no. 1/2013 > Research and Technology

Photo: SCHOTT/C. Costard

Ceramic Inspirations for Optics and Lighting

Transparent and translucent ceramics are on the verge of being used industrially as new optical materials that offer great potential. SCHOTT developers have set important foundations on manufacturing them in a reproducible manner.

Thilo Horvatitsch

At first glance, they remind us of glass lenses or color filters. And yet, immense potential lies in these transparent or milky-yellowish platelets made of ceramic. “We have now ­succeeded in meeting long-standing requests from the optical ­industry for a new transparent material that can be used in ­photography and other imaging devices. And we are paving the way for highly-efficient LED systems,” Dr. Yvonne Menke says in describing two of the main fields of application.

The Materials Development Manager in the Research and ­Development Department of SCHOTT AG learned how to prepare this promising material class in the laboratory of Dr. Akio Ikesue. The Japanese scientist and winner of the Otto Schott Research Award achieved a breakthrough in the 1990s on the development of transparent ceramics that actually produce laser light. Passive transparent ceramics not only offer superior thermal and mechanical qualities, they also provide high optical refractive indexes of 2 and more, as well as exceptional dispersion values. This, in turn, has opened up new areas in the Abbe diagram, which systematically depicts the properties of optical materials, that glass had previously not been able to address. This development has expanded the toolbox for optic designers. Thus, they are able to realize more compact camera lenses and minimize color defects and aberrations
The transparent ceramics placed on the feeder on their way into the high-temperature furnace have already been sintered and are completely finished. Photo: SCHOTT/C. Costard
The advantages that this unique material offers are particularly important in the infrared spectral range because the toolbox is not nearly as full here as it is with glasses for the visible spectral range. Unlike various types of glass, some transparent ceramics have an extremely broad light transmission window that ranges from the ultraviolet (UV) all the way to the infrared (IR) wavelength range of 6 micrometers. In view of this, the new material that is extremely insensitive to environmental influences is also of interest in technical measurement applications or geo-observations of raw material deposits using special cameras.

These ceramics are also of great benefit as translucent or semi-transparent materials for color conversion. Color conversion is the foundation of all white LED light sources, which are actually blue LEDs coated by a luminescent material. This material is usually bound inside silicone, and therefore not nearly as heat resistant as a fluorescent ceramic manufactured at temperatures in excess of 1600°C. ”In combination with high-intensity LEDs or laser diodes, the outstanding temperature stability and thermal conductivity of these ceramic converters allow for new light sources to be developed,” explains Dr. Volker Hagemann, Senior Scientist at SCHOTT. Their luminance is two to three times higher than that of a typical xenon burner. Areas of application include LCD projectors, next-generation digital projectors or headlights.
A special device is used to place the translucent ceramic in the measurement station for optical measurement at the SCHOTT laser laboratory. Photo: SCHOTT/C. Costard
The versatile properties and color coordinates of the ceramics can be custom designed or optimized using a multistep manufacturing process that has been implemented in the SCHOTT laboratories (see details).
Partly due to funding from the joint research project OptoKeramat supported by Germany’s Federal Ministry of Research (BMBF), efforts aimed at manufacturing preformed ceramic ­sintered parts quite easily in a reproducible manner for optical and fluorescent applications have proven to be successful. “Our expertise lies mainly in the area of materials design as well as in special powder and sintering technology,” Dr. Menke notes.
This has made it possible to manufacture transparent ceramics nearly 30 millimeters in diameter. ”We are even able to manufacture translucent ceramics close to 50 millimeters in diameter,” Dr. Volker Hagemann emphasizes. Initial sampling is already underway. <

From a nanopowder to a ceramic

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