Phosphorescent materials for the watch industry

A piece of Empa on your wrist

May 24, 2023 | ANNA ETTLIN
Empa research helps Swiss watches to glow in the dark: The luminescent material Swiss Super-LumiNova, which was refined at Empa, now adorns the hands and dials of a number of wristwatches, including the MoonSwatch collection from Swatch and Omega.
A MoonSwatch glows brightly in the dark, thanks in part to Empa research. Image: Beat Geyer, Empa

Hardly any other watch has traveled as far as the Omega Speedmaster Professional, also known as the Moonwatch. NASA astronaut Buzz Aldrin wore it on his wrist when he became the second man to walk on the surface of the moon on 20 July 1969. More than 50 years later, the MoonSwatch collection from Swatch and Omega makes the iconic design more affordable.

Although the MoonSwatch is not approved for use in space, it does contain a piece of Empa research: Both the hands and hour markers are coated with the luminescent material Swiss Super-LumiNova. From 2013 to 2015, it was jointly improved by the Appenzell-based company RC Tritec AG, Empa and the University of Geneva as part of a CTI-funded project (Commission for Technology and Innovation, now Innosuisse).

The luminescent material is based on strontium aluminate. This crystalline inorganic compound was developed in the 1990s to replace luminous paints based on the radioactive elements radium and tritium. Individual atoms of the rare earths europium and dysprosium are embedded in the crystal structure of strontium aluminate. Through a complex mechanism, the material stores incoming light and emits it at a later time. This phenomenon is known as phosphorescence. The use of such luminescent materials extends beyond wristwatches: Many emergency signs, as well as the floor markings on passenger aircraft, contain phosphorescent compounds.
Light without radioactivity: The luminescent material Swiss Super-LumiNova is based on strontium aluminate and was developed to replace the radioactive phosphors radium and tritium. Image: RC Tritec AG

How bright and for how long a material luminesces depends on numerous variables during manufacturing, from the exact composition of the starting mixture to the temperature and atmosphere in the kiln. By varying these parameters and precisely analyzing the resulting material samples, the research team had succeeded in developing a very bright and very long-lasting luminescent material for the Swiss watch industry.

The luminescent material is not only used in the MoonSwatch, but also in numerous other watch brands and models. So if you check the time at night, you may see Empa know-how shining through.

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Anna Ettlin
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