Phase separation and photoinduced migration of silver in Agx (As2S3) 1-x glasses

Ag x (As 2 S 3 ) 1-x glasses with x from 0 to 0.4 were prepared from pre-synthesized amorphous As 2 S 3 and colloidal silver. X-ray diffraction data confirm the amorphous structure of the samples with x ≤ 0.3 while the sample with x = 0.4 contains crystalline inclusions of alacranite As 4 S 4 with the average size of 50 nm. For the glasses with x > 0.2 the data of energy-dispersive Xray spectroscopy show the presence of two co-existing amorphous phases (Ag-rich and Ag-poor). At below-bandgap excitation ( exc =671 nm and  exc =785 nm), in the Raman spectra of Ag x (As 2 S 3 ) 1-x glasses a feature near 360 cm -1 is revealed, corresponding to the vibrations of As-S bonds in AsS 3 pyramids linked by S-Ag-S bridges. Meanwhile, at above-bandgap excitation ( exc =532 nm), this feature is missing in the spectra of samples with x ≤ 0.2, independent of the laser power density. This is explained by photoinduced migration of Ag atoms away from the laser spot under the abovebandgap illumination. A similar behaviour is observed for the Ag-poor regions of Ag x (As 2 S 3 ) 1-x glasses with x > 0.2 while for the Ag-rich areas the features typical for amorphous Ag-As-S are clearly observed.