Photoinduced transformations in (As_1–xBi_x)₂S₃ glass observed by Raman spectroscopy

Abstract

Raman spectra of (As1–xBix)2S3 glass samples with x ≤ 0.2 measured at the excitation with above‐bandgap (532 nm) laser light at a relatively low power density (Pexc = 4 kW/cm2) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As1–xBix)2S3 glass previously known (x ≤ 0.06). Spectra measured at an increased Pexc (40 kW/cm2) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage‐type As4S4 units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm−1, which emerge in the Raman spectra of the (As1–xBix)2S3 glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As1–xBix)2S3 glass surface with formation of units containing arsenate AsO43− and sulphate SO42− ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.

Raman evidence for the oxidation of amorphous As2(SexS1–x)3 film surfaces under visible light

“…Formation of arsenates can be strongly assisted by the presence of dopants in the arsenic chalcogenide, for instance, Pb [52]. Our recent Raman study of (As 1-x Bi x ) 2 S 3 glasses [53] confirmed that AsO 4 3ions are formed under visible-light illumination only at a noticeable amount of bismuth (x 0.14) while for the glasses with lower Bi content no signs of oxidation were observed. On the other hand, it is known that doping amorphous As 2 Se 3 with metals prevents (in case of Cu dopant) or inhibits (doping with Ag) the photooxidation reactions on the surface [21].…”