Mid-infrared emissions from Er3+ in Ga2S3−GeS2−Sb2S3 glasses

Emission properties of Er3+ in Ga2S3–GeS2–Sb2S3 glasses at the mid-infrared region were investigated from the viewpoint of their dependence on the concentration of the active ion and the glass composition. In the Judd–Ofelt analysis, no variation in omega parameters were observed when GeS2 was replaced by Ga2S3, while Ω2 increased as Sb2S3 was replaced by Ga2S3. This is due to the structural similarity and difference between the glass network units, GaS4 and GeS4 tetrahedra, and SbS3 pyramid. Clear mid-infrared emissions were observed at 2750 and 4300 nm assigned to the 4I11/2 → 4I13/2 and 4I9/2 → 4I11/2 transitions, respectively. The lifetime of the initial level of the 4.3 μm emission, 4I9/2, rapidly decreased with the Er3+ concentration because of the cross relaxation of this level, which can take place even at considerably low Er3+ concentration. The cross-relaxation processes were suppressed by the increase in the content of Ga2S3 because the solubility of Er3+ ions in the glasses increases with the Ga2S3 content.