Structural analysis of Tm3+ doped As–S–Ga glasses by Raman and EXAFS spectroscopy

Abstract Structural properties of Tm3 + doped As–S–Ga glasses were investigated using Raman spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy at As K-edge, Ga K-edge and Tm L3-edge. The Raman spectra are interpreted on the basis of comparison with the well-known Raman spectra of As2S3 glasses the structure of which mainly consists of pyramidal [AsS3/2] units interconnected by S–S chains. Incorporation of Ga2S3 in As2S3 glass matrix induced the dissociation of S–S chains in behalf of the formation of tetrahedra [GaS4]. Moreover, introduction of Tm into As–S–Ga glasses forms Tm–S bonds through the further dissociation of [AsS3/2] pyramidal units. The deficiency of S in the glasses is compensated with the formation of As4S4 structural units. The EXAFS results indicate that Ga–S bond distance in the tetrahedra [GaS4] decreases from 2.29 A to 2.26 A with the increase of Tm concentration in the glass. Meanwhile, Tm–S bond distance increases from 2.66 A to 2.71 A approaching to that of crystalline Tm2S3 and simultaneously, the coordination number of Tm gradually decreases from 7 to 4.