Advanced methods for preparing especially pure glasses based on germanium and gallium chalcogenides. Part 1. Synthesis via volatile and low-melting compounds. Review

Glasses based on germanium and gallium chalcogenides are promising optical materials for the near and mid-infrared (IR) regions. They are used to develop fiber-optic sensors, sources of supercontinuum, luminescent and laser radiation, glassceramic materials with improved mechanical properties, memory cells, and other optical and optoelectronic devices. The most important characteristic of chalcogenide glasses is the content of limiting impurities that have the most negative effect on their optical properties. Conventional methods for producing these materials include melting simple substances with getters in evacuated silica-glass ampoules and then distilling the melt. These methods do not allow achieving extremely low concentrations of impurities that do not affect optical transparency of glasses. Therefore, new approaches need to be developed. The purpose of the review is to systematize the scientific information related to the methods for preparing especially pure chalcogenide glasses which have been developed over the past 15 years at the Institute of Chemistry of High Purity Substances of the Russian Academy of Sciences. The methods discussed in the first part of the paper include: 1) synthesis of p-element chalcogenides via volatile iodides; 2) preparing a batch by thermal decomposition of germanium sulfide and selenide iodides; 3) synthesis and deep purification of germanium monochalcogenides. The developed methods made it possible to reduce the content of hydrogen, oxygen, and carbon impurities and heterogeneous inclusions in chalcogenide glasses by1–2 orders of magnitude as compared to conventional methods. In conclusion, the article discusses the possibilities for further reduction of the content of impurities in glasses based on germanium and gallium chalcogenides to achieve extremely low optical losses