Abstract
Null ellipsometry has been used to determine the index of refraction of amorphous Ge1−xSnxSe2 in the composition range 0 ≤ x ≤ 0·6 at the wavelength 632·8 nm. The index n increases from 2·61 to 2·84 as x increases in the range 0 ≤ x ≤ 0·30. For higher values of x, n is essentially constant at 2·88. Optical absorption has been used to measure the optical band gap, which decreases from 2·11 eV to 1·62 eV as x increases from 0 to 0·60. An anomaly at x ∼ 0·30 is associated with a change in the glass structure. These results are interpreted in a virtual-crystal picture, in which the band edges shift rigidly.