Rare earths—what should photonics experts know about them?

Seltene Erden

Photonics question of the month

Lasers and rare earths: Doping with rare earths influences the wavelengths in which laser crystals, fiber lasers, LEDs, lamps, and displays emit light. Rare earths are also used in optical filters, absorbers, and as activators in lamps.

The “hieroglyphs” used in the solid-state and fiber laser fields, such as Nd:YAG, Yb:KGW, Yb:KYW, and Er,Cr:YSGG contain the whole range of rare earths. Erbium (Er), ytterbium (Yb), europium (Eu), gadolinium (Gd), yttrium (Y), terbium (Tb), and thulium (Tm) as well as neo-dymium (Nd), cerium (Ce), and scandium (Sc) are used frequently. Because of its high price, scandium is still a niche material in photonics.

Competition among users: According to the German Mineral Resources Agency, three quarters of rare earths are used in the production of magnets, alloys, catalysts, and polishing products; the latter mainly in the glass industry. Another seven percent are used in lamps, six per-cent each in the production of special glass and ceramics and the remainder for various niche applications. A study (unfortunately only available in German), contains a breakdown of how technological trends will change demand for rare earths. Findings: The amount of yttrium and neodymium required by the laser industry is negligible in the overall market. With ytterbium and erbium, the industry’s share is higher – however, there will be no problems in the supply situation in the foreseeable future.

Interesting secondary aspect: Scandium demand will rise at least by a factor of seven by 2035. The drivers are solid oxide fuel cells (SOFC) for homes and hybrid power plants and growing demand for stable lightweight metal alloys from the aviation industry. For example, Airbus, together with partners, has developed the aluminum-magnesium-scandium alloy Scalmalloy, which is especially suitable for selective laser melting processes.