EFFECT OF HALOGEN CONTENT ON THE POSITION OF THE SPECTRAL WINDOW OF CHALCOGENIDE-HALIDE GLASSES IN THE GE-S-I SYSTEM

[Ge0.3S0.7]I-100-x(x) system chalcogenide-halide glasses with x = 0, 5 , 10, 20 and 30, have been examined via spectroscopic absorption in th e range 0.2 to 20 mu m. The Urbach edge tends to occur at longer wavel engths with increasing iodine content of the glasses but the infrared edge seems to be unaffected. Glasses which had been stored at room tem perature for more than a year inside polyethylene bags appeared to hav e suffered some surface attack and a mechanism for this is suggested.