Photodarkening effect in glassy As2S3 and As2O3

Abstract Photodarkening, or the shift of the optical absorption edge to smaller energies after excitation with light whose energy is near that of the optical band edge, has been studied in the chalcogenide glasses for many years. Recently we have conducted high field nuclear magnetic resonance (NMR) studies at 17 T and nuclear quadrupole resonance (NQR) studies of 75 As in glassy As 2 S 3 . We have compared the 75 As NMR and NQR lineshapes in glassy As 2 S 3 and As 2 O 3 before and after irradiation. An increase in the asymmetry parameter would have implied an increase in the departure from cylindrical symmetry in the bonding at the arsenic pyramidal sites. The null result reported here is inconsistent with microscopic models of photodarkening that involve switching of large numbers of As–Chalcogen bonds.