Optical Lens

Germanium dioxide is well-known as a glass-forming material; it has the ability to form tetrahedral units (similar to those formed by silicon dioxide). Since the cation-to-anion ratio of GeO₂ is in the right range, many GeO₂ based compositions form glasses on melting and cooling.

The different forms of GeO₂ (vitreous, hexagonal, tetragonal) lead to different corresponding infra-red spectra, but all are optically transparent over a wide spectral range between 280 nm and 5000 nm.

In addition, GeO₂ based glasses have a higher coefficient of thermal expansion than silica- or boron-based glasses, and thus provide for a much better performance when vacuum seals (to brass or copper) are required.

Pure germanium is used for lenses and windows in IR systems that operate at even higher wavelengths (from 2 to 12 microns).

Gallium and gallium oxide can be used to increase the refractive index of glass and are used in the manufacture of lenses and optical mirrors. Optical mirrors made from gallium have high reflectivity and are stable at high temperatures.