Er3+ as glass structure modifier of Ga–Ge–S chalcogenide system

Abstract

Er3+ clustering phenomenon in Ga–Ge–S chalcogenide system is studied using Raman spectroscopy. The Raman spectra from 10 to 500 cm−1 for glasses (100−y)[15Ga2S3–85GeS2]–yEr2S3 (y=0.08−5.00 mol. %) have been analyzed. To reveal the influence of the chemical composition on the glass structure the intensity of the peak corresponding to Ge–Ge (Ga–Ga) homopolar bonds has been examined. The peak intensity increase with Er2S3 concentration change in the region 0<C(Er2S3)<2 mol. % has been interpreted in terms of the sulphur deficiency in the glass resulting in the formation of S3Ge–GeS3 (S3Ga-GaS3) structural units. The further increase in concentration beyond 2 mol. % reduces the sulphur deficiency, which can be attributed to the formation of the ternary compound Er3GaS6. The structural units Er3GaS6 contain a large mol. fraction of Er3+ or, in other words, Er3+ clusters. The data obtained from the low-frequency Raman spectra (boson band) indicate strong variations of the medium-range order (MRO) in the glasses induced by Er3+. The observed behavior of the MRO size (the correlation length) with increasing of Er2S3 concentration provides for additional evidence of the Er3+ clustering.