Long lifetime of Er3+: 4I11/2 in low phonon-energy fluoro-chloride glasses for mid-infrared optical applications

A new kind of fluoro-chloride glass was successfully prepared based on fluoroaluminate glass modified by various Cl−. The reductions of phonon density and OH− content revealed by the measured Raman and FTIR spectra show that structural changes caused by the Cl− ions have an effect on the optical properties. With increasing chloride content, the thermal stability factor ΔT showed an increase trend, indicating a better thermal stability of the host. Meanwhile, according to Judd-Ofelt calculation, the intensity parameter Ω2 increased, which indicates a stronger covalency and local asymmetry of the coordination bonds around the Er3+ ions after introduction of Cl−. Noticeably, the lifetime (3.48 ms) of Er3+: 2.7 μm obtained in the chloride-rich glass (AYF-8Cl) is the longest in reported glass systems, along with obvious enhanced fluorescence intensity. All the results suggested that the fluoro-chloride glasses hint its potential applications in laser materials, especially in 3 μm wavelength.