Tellurium is a rare, brittle metalloid with a silvery-white, metallic luster. Its most significant applications leverage its semiconductor properties. It is a critical component in the production of thin-film solar cells, specifically cadmium telluride (CdTe) cells, which are highly efficient at converting sunlight to electricity. Tellurium is also a vital element in thermoelectric devices, which can convert a temperature difference directly into electrical energy, used in everything from power generation to cooling systems. Furthermore, it's used as an alloying agent to improve the machinability of steel and copper.

Tellurium dioxide is a white, solid oxide of tellurium that can also appear in a yellow form. This versatile compound is used in a range of advanced technological applications. A key use is in fiber optics, where it's used to make specialized tellurite glass with a high refractive index, which improves data transmission rates. It's also utilized in the manufacturing of acousto-optic devices and for producing pigments in ceramics and glass. Beyond optics, it serves as a catalyst in various chemical processes.