Composition dependence of optical band gap of the Se–Ge–Te far infrared transmitting glasses

Abstract

A systematic series of Se x Ge 25 −x Te 75 ( x=0, 5, 10, 15, 20 at%) far infrared transmitting glasses were prepared by traditional melt-quenching method. Physical, thermal and optical properties of the glass system were analyzed. The allowed indirect transition of samples was calculated according to the classical Tauc equation. The results show the density increases with the substitution of Ge by Se and a maximum Τ g value of 175 °C was obtained for the Se 15Ge 10Te 75 glass. The energy band gap of Se 15Ge 10Te 75 glass is 1.25 eV, possessing the largest metallization criterion value (0.25) and the lowest refractive index (3.16). When the dissolved amount of Se increased from 0 to 15 at%, the values of indirect optical band gap were in the range from 0.573 to 0.679 eV. A wide optical transparent window with a cut-off wavelength beyond 18 μm was shown.