Glass is a versatile material used in a variety of everyday objects and technology we rely upon, such as cameras or film projectors, and fiber-optic communication for high-speed internet. In space exploration, glass is an essential component of telescopes used in satellites, which provide images of the Earth and deep space. Traditional oxide glasses transmit light in the visible range, but developing lenses and other optical materials with combined thermal and visible imaging capability allows for an even wider variety of applications. By substituting oxygen for another heavier chalcogen element, glass can transmit light into the infrared region. For example, gallium lanthanum sulfide (GLS) glass is widely used in IR optics and photonics.

In a communication in Advanced Materials, Andrea Ravagli and co-workers from the Optoelectronics Research Centre at the University of Southampton, substitute sulfur for selenium in GLS glass.

The authors prepared Ga₂S₃-doped GLS glasses by a melt–quench method. In a tube furnace under argon gas, the batched precursor mixtures were first melted in a carbon crucible at 1150 °C for 24 hours. After annealing for 24 hours at 490 °C, the glasses were cut, polished, and characterized. Thermal analysis revealed that the glass transition temperature was reduced for the Se-doped samples compared to GLS glass, where the greatest reduction occurred when sulfide was completely substituted by selenide.

By varying the composition of the quaternary system (La₂S₃-Ga₂Se₃-Ga₂S₃), the authors found that samples containing a combined total of 70 mol% sulfide and selenide formed a homogenous glass, while other compositions resulted in crystallization or phase separation. The infrared absorption edge of the glassy samples occurs at much longer wavelengths and ranges from about 13 μm for 20 mol%, to 14 μm for 40 mol%, and reaching up to 15 μm for 60 mol% Se-doping. This is a significant improvement over GLS glass, which has an IR cutoff at 9 μm.

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