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We show that oxy-fluoride glass ceramics, with typical composition, 32(SiO2):9(AlO1.5):31.5(CdF2):18.5(PbF2):5.5(ZnF2): 3.5(ErF3) mol % have potential applications in telecommunications. Upon heat treatment, Er3+ nucleates the growth of the nanocrystalline β-PbF2, which acts as its host. Heat treatment at 440 °C for 5 h and at 390 °C for 3 h gave rise to ∼12 and ∼2.5 nm diameter crystals, respectively. The emission band of Er3+ in the 1.54 μm telecommunications window (4I13/2→4I15/2 transition, at the half-height width) was 75 nm in the former and 90 nm in the latter case, while I13/24↔I15/24 absorption and emission bands became wavelength divergent in both cases. Also in the latter case, the spectrum was flat from 1.53 to 1.56 μm. The evolution of spectral behavior is explained by changes in average site geometry of the Er3+ dopant, related to the α→β phase transition of PbF2, which is stimulated by heat treatment.

The progress, and current challenges, in fabricating rare-earth-doped chalcogenide-glass fibers for developing mid-infrared (IR) fiber lasers are reviewed. For the first time a coherent explanation is forwarded for the failure to date to develop a gallium-lanthanum-sulfide glass mid-IR fiber laser. For the more covalent chalcogenide glasses, the importance of optimizing the glass host and glass processing routes in order to minimize non-radiative decay and to avoid rare earth ion clustering and glass devitrification is discussed. For the first time a new idea is explored to explain an additional method of non-radiative depopulation of the excited state in the mid-IR that has not been properly recognized before: that of impurity multiphonon relaxation. Practical characterization of candidate selenide glasses is presented. Potential applications of mid-infrared fiber lasers are suggested.

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