Research on optical band gap of the novel GeSe2–In2Se3–KI chalcohalide glasses

The glass-forming region of the GeSe2–In2Se3–KI system was reported firstly. The dependence of physical, thermal and optical properties on compositions as formula of (1 − x)(0.8GeSe2–0.2In2Se3)–xKI (x = 0, 0.1, 0.2, 0.3) chalcohalide glasses was investigated. The allowed direct transition and indirect transition, and Urbach energy of samples were calculated according to the classical Tauc equation. The results show that the glass system has good thermal stability and that there is an obvious blue-shift at the visible absorbing cutting-off edge. When the dissolved amount of KI increased from 0 to 30 mol%, the direct optical band gap and the indirect optical band gap were in the range from 1.617 to 1.893 eV and 1.573 to 1.857 eV. With the decrease of the molar refraction the refractive index decreases, optical band gap and metallization criterion increase. The relationship between energy band gap and metallization criterion was analyzed and the optical properties of chalcohalide glasses were summarized.