Gallium lanthanum sulfide glass

Gallium-lanthanum-sulfide glasses have a wide range of vitreous formation centered around a 70% Ga2S3 : 30% La2S3 mixture, and readily accept other modifier materials into their structure.

[1] This means that Ga-La-S composition can be adjusted to give a wide variety of optical and physical properties.

[2] Optically, Ga-La-S has a high refractive index, a transmission window covering most of the visible wavelengths and extending to about 10 μm and a low maximum phonon energy, approx.

A clear advantage over other chalcogenides is its high lanthanum content which allows excellent rare-earth solubility and dispersion of the ions in the glass matrix for active devices.

The effect of adding an ionic sulfide modifier such as a La2S3 molecule to the crystal is to break one of the Ga-S dative bonds and replace it with a S2− anion.

These impurities contribute to the optical loss through absorption and scattering as well as serving as nucleation sites for crystallization.

Although these may have been synthesized from high purity elements, the conversion process itself can readily introduce oxide, water or organic impurities.

The conventional method for producing chalcogenide glasses is through the use of sealed ampoule melting.

The requirement for the sealed atmosphere is dictated by the volatile nature of many of the precursors which if melted in open atmosphere can result in large compositional changes or complete removal of components with low vapour pressures.

Batches of the compounds are prepared in a nitrogen-purged glovebox, placed in a vitreous carbon crucible and transferred to a silica tube furnace in a sealed vessel.

The melt is normally quenched to glass by pushing it into a water cooled jacket.